2011/04/03
Most signs in Tokyo's Ginza shopping district have been switched off. (Keiko Nannichi)
The Kan administration is close to finalizing a decree to impose limits on peak electricity use this summer in Tokyo and other parts of the Kanto region, sources said.
The crisis at the Fukushima No. 1 nuclear power plant and damage to non-nuclear thermal plants caused by the March 11 earthquake and tsunami have cut Tokyo Electric Power Co.'s generating capacity to about 75 percent of expected peak demand this summer.
The decree is aimed at averting large-scale blackouts, the sources said.
Businesses that use 500 kilowatts or more will likely be asked to cut up to 25 percent from their usage last year during the summer peak, according to the sources.
The decree, to be issued under the electricity business law, would be the first of its kind from the central government since 1974, when a 15-percent cut was imposed during the oil shock.
The government is also considering proposing energy saving measures for households and small- and medium-size businesses, which collectively account for about 40 percent of total demand.
A comprehensive package to deal with the projected electricity crisis is expected to be produced by the end of the month, the sources said.
Firms violating the decree would be ordered to pay up to a 1 million yen ($12,000).
According to a projection by the industry ministry based on last year's figures, peak demand this summer in the Kanto region is likely to be about 60 gigawatts. TEPCO, which services the region, is expected to have a maximum capacity of about 45 gigawatts.
The 25-percent cut by large electricity consumers being considered by the administration would cover the expected shortfall. The government has been talking to business leaders to try to minimize damage to industry.
Nippon Keidanren (Japan Business Federation), the nation's most influential business lobby, is already formulating voluntary power saving plans.
Automakers have been discussing rolling production stoppages, which would require companies to take turns in suspending operations to avoid unplanned power outages in the middle of production.
The government is looking at certifying small- and midsize businesses that are pushing energy saving efforts and will call on households to do their bit to conserve power, the sources said.
Showing posts with label Tokyo Electric Power. Show all posts
Showing posts with label Tokyo Electric Power. Show all posts
Sunday, April 3, 2011
Wednesday, March 23, 2011
23/03 Work resumes after fire scare
The Yomiuri Shimbun
Work to restore electricity to power cooling systems of the troubled reactors at the Fukushima No. 1 nuclear power plant resumed Tuesday morning, 16 hours after all workers were evacuated because gray smoke--raising fears of a fire--was seen rising from the No. 3 nuclear reactor.
Though occasional thin white smoke was still observed at the Nos. 2 and 3 reactors in the morning, Tokyo Electric Power Co., operator of the quake-hit nuclear plant, judged it safe to resume restoration work because it believed the white smoke was not caused by fire and that radiation levels had decreased.
However, since the cause of the smoke was unknown, the situation at the plant remained unpredictable, added the utility.
TEPCO and the Nuclear and Industrial Safety Agency said operations to restore power resumed at the Nos. 1 to 4 reactors at about 8 a.m.
At the No. 4 reactor, workers confirmed at 10:35 a.m. that electricity reached the switchboard-cum-transformer at its turbine building.
At the Nos. 1 and 2 reactors, which already had been connected to external power, workers checked instruments and electrical systems in preparation for distributing electricity. They prioritized restoring power to the No. 2 reactor, whose pressure suppression chamber under its containment vessel has apparently been damaged. Lighting and functions of meters and gauges in the reactor's central control room would be restored by the end of Wednesday, TEPCO added.
Workers were expected to restore instrument functions at the Nos. 3 and 4 reactors central control rooms by Thursday.
TEPCO added it would switch the No. 6 reactor power source from an emergency generator to an outside power source Tuesday afternoon.
Work to restore power at those reactors was suspended after gray smoke was observed at the No. 3 reactor at 3:55 p.m. Monday. White smoke also rose from the No. 2 reactor shortly after 6 p.m. that day.
"Smoke at the No. 2 reactor is believed to be steam from sprayed water," Defense Minister Toshimi Kitazawa said Tuesday. "However, smoke at the No. 3 reactor is likely due to residual materials such as oil inside [the facility], which burned briefly as temperatures there rose."
Meanwhile, a special squad of the Tokyo Fire Department postponed spraying water into the No. 3 reactor's fuel storage pool from Tuesday morning to the afternoon because smoke was observed there Monday.
On Tuesday afternoon, TEPCO began a water dousing operation at the No. 4 reactor with a German-made squeeze pump that can spray water over a long distance using a 58-meter-long arm. The Self-Defense Forces said they would decide whether to blast the No. 4 reactor with water after studying the progress of TEPCO's restoration work.
Meanwhile, TEPCO said the radiation level at the plant's front gate, which is one kilometer west of the Nos. 2 and 3 reactors, decreased to 257.5 microsieverts per hour at 11 a.m. Tuesday, from 1,932 microsieverts at 6:30 p.m. Monday after the gray smoke was emitted from the No. 3 reactor.
(Mar. 23, 2011)
Work to restore electricity to power cooling systems of the troubled reactors at the Fukushima No. 1 nuclear power plant resumed Tuesday morning, 16 hours after all workers were evacuated because gray smoke--raising fears of a fire--was seen rising from the No. 3 nuclear reactor.
Though occasional thin white smoke was still observed at the Nos. 2 and 3 reactors in the morning, Tokyo Electric Power Co., operator of the quake-hit nuclear plant, judged it safe to resume restoration work because it believed the white smoke was not caused by fire and that radiation levels had decreased.
However, since the cause of the smoke was unknown, the situation at the plant remained unpredictable, added the utility.
TEPCO and the Nuclear and Industrial Safety Agency said operations to restore power resumed at the Nos. 1 to 4 reactors at about 8 a.m.
At the No. 4 reactor, workers confirmed at 10:35 a.m. that electricity reached the switchboard-cum-transformer at its turbine building.
At the Nos. 1 and 2 reactors, which already had been connected to external power, workers checked instruments and electrical systems in preparation for distributing electricity. They prioritized restoring power to the No. 2 reactor, whose pressure suppression chamber under its containment vessel has apparently been damaged. Lighting and functions of meters and gauges in the reactor's central control room would be restored by the end of Wednesday, TEPCO added.
Workers were expected to restore instrument functions at the Nos. 3 and 4 reactors central control rooms by Thursday.
TEPCO added it would switch the No. 6 reactor power source from an emergency generator to an outside power source Tuesday afternoon.
Work to restore power at those reactors was suspended after gray smoke was observed at the No. 3 reactor at 3:55 p.m. Monday. White smoke also rose from the No. 2 reactor shortly after 6 p.m. that day.
"Smoke at the No. 2 reactor is believed to be steam from sprayed water," Defense Minister Toshimi Kitazawa said Tuesday. "However, smoke at the No. 3 reactor is likely due to residual materials such as oil inside [the facility], which burned briefly as temperatures there rose."
Meanwhile, a special squad of the Tokyo Fire Department postponed spraying water into the No. 3 reactor's fuel storage pool from Tuesday morning to the afternoon because smoke was observed there Monday.
On Tuesday afternoon, TEPCO began a water dousing operation at the No. 4 reactor with a German-made squeeze pump that can spray water over a long distance using a 58-meter-long arm. The Self-Defense Forces said they would decide whether to blast the No. 4 reactor with water after studying the progress of TEPCO's restoration work.
Meanwhile, TEPCO said the radiation level at the plant's front gate, which is one kilometer west of the Nos. 2 and 3 reactors, decreased to 257.5 microsieverts per hour at 11 a.m. Tuesday, from 1,932 microsieverts at 6:30 p.m. Monday after the gray smoke was emitted from the No. 3 reactor.
(Mar. 23, 2011)
Tuesday, March 22, 2011
22/03 福島県知事、東電の「おわび訪問」断る
2011年3月22日11時2分
福島県の佐藤雄平知事は２２日午前の災害対策本部会議で、東京電力側から社長のおわび訪問を打診されたが断った、と明らかにした。
佐藤知事は理由について「県民の不安と憤りを察するに、おわびを受ける状況じゃない。東京電力は死力を尽くして事態の収拾にあたるべきだ」と話した。
.
福島県の佐藤雄平知事は２２日午前の災害対策本部会議で、東京電力側から社長のおわび訪問を打診されたが断った、と明らかにした。
佐藤知事は理由について「県民の不安と憤りを察するに、おわびを受ける状況じゃない。東京電力は死力を尽くして事態の収拾にあたるべきだ」と話した。
.
Monday, March 21, 2011
20/03 580 on front line in battle at Fukushima nuclear plant
2011/03/20
In a second-floor room of Tokyo Electric Power Co.'s main office in Tokyo's Chiyoda Ward, about 100 people watch the events unfold on a large screen.
What they are witnessing is every operation at the Fukushima No. 1 nuclear power plant to cool reactor cores, keep spent fuel rods submerged and bring much needed power to the crippled facility.
"I feel like crying as I see the harsh conditions facing my colleagues at the site," said a TEPCO employee in the room.
Of the 800 workers at the plant when the Great East Japan Earthquake struck on March 11, 750 left on Tuesday after a fire broke out at the No. 4 reactor.
The remaining 50 members stayed amid the ever-present danger of high radiation levels to try to bring the situation under control and prevent a meltdown.
They were dubbed the "Fukushima 50" by U.S. and European media.
"They are the faceless 50, unnamed operators who stayed behind," The New York Times said.
But they have been increasingly receiving help.
The workers on the front line of the battle include employees of TEPCO and subsidiaries Toden Kogyo Co. and Tokyo Electric Power Environmental Engineering Co., as well as employees from Toshiba Corp. and Hitachi Ltd., which constructed the power plant.
Workers from the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture and other places have joined them in the operation.
By Friday morning, about 580 workers were at the site, including those installing cables to bring electricity to the site.
The workers wear full-body protective suits and masks. Everyone wears a dosimeter around the clock to measure radiation levels. The device sets off an alarm if radiation doses reach 80 percent of the maximum allowable daily limit.
The workers take turns performing such laborious tasks as injecting water into the reactors and storage pools and opening valves to relieve pressure in the container.
Scattered debris from the explosion of a building covering one of the reactors has hampered their work.
And dangerous radiation levels have on occasion forced the workers to retreat from the reactors.
Some of the workers have now been reassigned to deal with potential problems at the No. 5 and No. 6 reactors.
The efforts have taken their toll.
More than 20 workers at the site have been injured since the quake and tsunami struck on March 11. One worker was seriously injured when he opened a valve to release steam from the containment vessel.
The local task force for TEPCO's nuclear plants in Fukushima Prefecture is stationed at a earthquake-resistant building in the mountainside.
The task force is in constant contact with TEPCO's emergency headquarters in Tokyo. The Nuclear and Industrial Safety Agency has its office in a separate room of the same building.
In the headquarters, TEPCO President Masataka Shimizu sits at a round table in the center of the room. Workers in charge of restoration and measuring operations sit at desks surrounding the round table.
They have noticed that some pressure meters and water-level gauges in the pressure and containment vessels are no longer functioning.
"I am thinking what we should do, recalling what happened at Three Mile Island (in 1979) and the (1986) Chernobyl nuclear disaster," a TEPCO senior official said.
In a second-floor room of Tokyo Electric Power Co.'s main office in Tokyo's Chiyoda Ward, about 100 people watch the events unfold on a large screen.
What they are witnessing is every operation at the Fukushima No. 1 nuclear power plant to cool reactor cores, keep spent fuel rods submerged and bring much needed power to the crippled facility.
"I feel like crying as I see the harsh conditions facing my colleagues at the site," said a TEPCO employee in the room.
Of the 800 workers at the plant when the Great East Japan Earthquake struck on March 11, 750 left on Tuesday after a fire broke out at the No. 4 reactor.
The remaining 50 members stayed amid the ever-present danger of high radiation levels to try to bring the situation under control and prevent a meltdown.
They were dubbed the "Fukushima 50" by U.S. and European media.
"They are the faceless 50, unnamed operators who stayed behind," The New York Times said.
But they have been increasingly receiving help.
The workers on the front line of the battle include employees of TEPCO and subsidiaries Toden Kogyo Co. and Tokyo Electric Power Environmental Engineering Co., as well as employees from Toshiba Corp. and Hitachi Ltd., which constructed the power plant.
Workers from the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture and other places have joined them in the operation.
By Friday morning, about 580 workers were at the site, including those installing cables to bring electricity to the site.
The workers wear full-body protective suits and masks. Everyone wears a dosimeter around the clock to measure radiation levels. The device sets off an alarm if radiation doses reach 80 percent of the maximum allowable daily limit.
The workers take turns performing such laborious tasks as injecting water into the reactors and storage pools and opening valves to relieve pressure in the container.
Scattered debris from the explosion of a building covering one of the reactors has hampered their work.
And dangerous radiation levels have on occasion forced the workers to retreat from the reactors.
Some of the workers have now been reassigned to deal with potential problems at the No. 5 and No. 6 reactors.
The efforts have taken their toll.
More than 20 workers at the site have been injured since the quake and tsunami struck on March 11. One worker was seriously injured when he opened a valve to release steam from the containment vessel.
The local task force for TEPCO's nuclear plants in Fukushima Prefecture is stationed at a earthquake-resistant building in the mountainside.
The task force is in constant contact with TEPCO's emergency headquarters in Tokyo. The Nuclear and Industrial Safety Agency has its office in a separate room of the same building.
In the headquarters, TEPCO President Masataka Shimizu sits at a round table in the center of the room. Workers in charge of restoration and measuring operations sit at desks surrounding the round table.
They have noticed that some pressure meters and water-level gauges in the pressure and containment vessels are no longer functioning.
"I am thinking what we should do, recalling what happened at Three Mile Island (in 1979) and the (1986) Chernobyl nuclear disaster," a TEPCO senior official said.
20/03 消防放水「命中を確信」 涙の隊長、家族に陳謝（1/2ページ）
2011年3月20日5時6分
消防庁の放水オペレーション
「非常に難しく危険な任務だった。国民の期待をある程度達成でき、充実感でほっとしている」――。東京電力福島第一原発の冷却作戦で、１０時間以上の「連続放水」を成功させた東京消防庁の派遣隊員の一部が１９日夜、帰京した。佐藤康雄総隊長（５８）ら３人が東京都内で記者会見し、心境を語った。
会見したのは、災害救助のスペシャリストである「ハイパーレスキュー」の冨岡豊彦隊長（４７）と高山幸夫隊長（５４）。
冨岡隊長は「大変だったことは」と問われると、「隊員です」と言って１０秒ほど沈黙。涙を浮かべ、声を震わせながら、「隊員は非常に士気が高く、みんな一生懸命やってくれた。残された家族ですね。本当に申し訳ない。この場を借りておわびとお礼を申し上げたい」と言った。
高山隊長は１８日、職場から直接現地に向かった。妻に「安心して待っていて」とメールで伝えると、「信じて待っています」と返信があったという。
佐藤総隊長も妻にメールで出動を伝えた。「日本の救世主になってください」が返事だった。
高山隊長は今回の任務を「目に見えない敵との闘い」と振り返った。注意したのは放射線量。「隊員たちが常に測定しながら安全を確認し、アピールしてくれた。仲間のバックアップがあったから任務を達成できた」と話した。
会見では、作戦の具体的な中身も明かされた。
佐藤総隊長によると、派遣隊は本人が承諾した隊員から選抜された。
原発に入ったのは１８日午後５時５分。作戦は当初、車から出ずに車両でホースを延ばす予定だった。８分で設置できる計算だった。だが、海岸付近はがれきだらけ。車が走れそうなルートだと２．６キロあり、ホースが足りない。
20/03 Progress at Japan Reactors; New Signs of Food Radiation
Asahi Shimbun, via ReutersSumi Abe, 80, was helped by emergency workers after being rescued along with her 16-year-old grandson in Ishinomaki City, Miyagi Prefecture on Sunday, nine days after the earthquake. More Photos »
March 20, 2011
By HIROKO TABUCHI and NORIMITSU ONISHI
TOKYO — Japan appeared to make moderate progress in stabilizing some of the nuclear reactors at the stricken Fukushima Daiichi power plant on Sunday, but at the same time it disclosed new signs of radioactive contamination in agricultural produce and livestock.
The government said it was barring all shipments of milk from Fukushima Prefecture and shipments of spinach from Ibaraki Prefecture, after finding new cases of above-normal levels of radioactive elements in milk and several vegetables.
Relatively high levels were also found in spinach from Tochigi and Gunma Prefectures to the west, canola from Gunma Prefecture and chrysanthemum greens from Chiba Prefecture, south of Ibaraki.
The emergency efforts to mitigate damage at the Fukushima Daiichi Nuclear Power Station, meanwhile, brought some notes of relief in the face of persistently dire conditions. The authorities said they had restored water pumps to two damaged reactors, Nos. 5 and 6, that were not of central concern, putting them under control in a state known as “cold shutdown.”
But another reactor that has proved more worrisome, No. 3, continued to bedevil engineers.
The Tokyo Electric Power Company, which runs the plant, appeared to have experienced a serious setback as officials said that pressure buildup at the ravaged No. 3 reactor would require the venting of more radioactive gases.
But at a news conference a few hours later, officials from the power company said that the pressure had stabilized and that they had decided they did not need to release the gases immediately, which would have heightened worries about wider contamination among the population. They said they were unsure what had caused the pressure to rise, highlighting the uncertainty engineers must still grapple with at Fukushima.
The power company also said that on Sunday workers injected 40 tons of water into the storage pool containing spent fuel rods at Unit No. 2, and that firefighters began spraying water into the pool at Unit No. 4. On Saturday, firefighters sprayed water at the storage pool of Unit No. 3 for more than 13 hours.
The reactors placed in cold shutdown were already shut down before the earthquake and the tsunami struck on March 11, posing less of a risk than the other reactors at the plant. But their cooling systems were knocked out, and the fuel rods left inside the reactors started to heat up, together with spent fuel rods in a separate storage pool.
“We are getting closer to bringing the situation under control,” Tetsuro Fukuyama, the deputy chief cabinet secretary of the Japanese government, said of the entire plant late Sunday.
After connecting a mile-long electrical transmission line on Saturday, workers made progress in starting to restore power to the plant, which may allow the operator to restart its cooling systems. The government said that power was returned to Reactor No. 2 at 3:46 p.m. Sunday, and that other reactors were also expected to gain power early in the week.
Even with electrical power extended to the reactors, there was no immediate indication from officials that the damaged pumping systems could be quickly restored.
“In general, our utmost efforts are producing definite results in preventing a worsening of the situation,” said Yukio Edano, the government’s chief cabinet secretary, who confirmed for the first time that the nuclear complex — with heavy damage to reactors and buildings and with radioactive contamination throughout — would be closed once the crisis was over.
Steven Chu, the United States secretary of energy, also conveyed optimism in an interview on “Fox News Sunday,” saying that “with each passing hour, each passing day, things are more under control.”
Japanese technicians who are trying to limit the spread of radiation “are making very good progress,” he said.
Despite the positive tone from officials, steep challenges persist. Workers were trying to avoid further damage to fuel rods in the reactor cores of Nos. 1, 2, and 3, and to prevent rods in the storage pools of Nos. 2, 3 and 4 from overheating.
Some experts project that the longer it takes to resolve the crisis fully, the greater the chances that one or more reactors or fuel storage pools will have to be abandoned, increasing the risk of a catastrophic release of radiation.
The plant remains a hazardous place for the emergency crews trying to stave off further damage. At least 25 workers and five members of the Japanese Self-Defense Force have been exposed to unsafe amounts of radiation, according to the power company. At least 20 workers and four self-defense soldiers have been injured, and two workers remain missing.
Radiation contamination, meanwhile, appears to be spreading rapidly. The substances detected in the food products were iodine 131 and cesium 137, two of the more dangerous byproducts of reactor operations that are feared to have been released from the plants in Fukushima. If absorbed through milk and milk products, iodine 131 can accumulate in the thyroid and cause cancer. Cesium 137 can damage cells and lead to an increased risk of cancer.
Mr. Fukuyama, the deputy chief cabinet secretary, stressed that although the readings were above levels deemed normal, they posed no immediate health risks.
“At current levels, I would let my children eat the spinach and drink the water” from Fukushima, he said. His children did not drink much milk, he added.
None of the produce found to be contaminated has been shipped to market, he said, while acknowledging that contaminated produce that had not been tested could have slipped through.
Spinach from a farm in Hitachi, about 45 miles from the plant, contained 27 times the amount of iodine that is generally considered safe, while cesium levels were about four times higher than is deemed safe by Japan. Meanwhile, raw milk from a dairy farm in Iitate, about 18 miles from the plant, contained iodine levels that were 17 times higher than those considered safe, and milk had cesium levels that were slightly above amounts considered safe.
While challenges with the nuclear facility and radiation contamination persist, stories of individual dramas continued to emerge in the wake of the earthquake and the tsunami that slammed into the country’s northeastern coast on March 11.
On Sunday, two people were reported to have been found alive, nine days after the disaster. An 80-year-old woman and her 16-year-old grandson were found under the debris of their home in Ishinomaki, about 30 miles northeast of the city of Sendai, according to Miyagi Prefecture police officials and the public broadcaster NHK.
The boy, identified as Jin Abe, crawled out of the debris of the family home and was found by local police officers, who called rescuers to free his grandmother, Sumi Abe, NHK reported. Both were hospitalized, but details of their condition were not immediately available.
Meanwhile, the National Police Agency on Sunday raised the official death toll to more than 8,100 from the 9.0-magnitude earthquake and ensuing tsunami. The final toll is now expected to reach nearly 20,000. At a news conference, police officials in Miyagi, the prefecture hit hardest by the tsunami, said they expected the toll there alone to exceed 15,000.
Kantaro Suzuki contributed reporting from Tokyo.
Sunday, March 20, 2011
19/03 Sự cố tại Fukushima I qua cái nhìn chuyên gia
Thứ bảy, 19/3/2011, 10:09 GMT+7
'Khủng hoảng hạt nhân tại nhà máy Fukushima I vẫn tiếp diễn, nhưng thời gian đang đứng về phía con người, sự căng thẳng vẫn còn nhưng tôi tin mọi việc sẽ ổn thoả', tiến sĩ Hà Ngọc Tuấn viết tiếp.
> Phần I: Thảm hoạ qua cái nhìn người trong cuộc
Trong phần này tôi xin giải thích diễn biến, cơ chế khủng hoảng hạt nhân tại nhà máy Fukushima I và lý do vì sao tôi có niềm tin như vậy.
Trực thăng vận tại CH47 của quân đội Nhật đưa túi nước thả xuống lò phản ứng tại Fukushima I. Ảnh: AFP
Khủng hoảng sẽ đi đến đâu
Có thể nói câu hỏi cho thì tương lai này không ai có thể trả lời chắc chắn được trong một tình huống như thế này. Rất nhiều người trên khắp thế giới lo lắng và cầu nguyện cho nước Nhật. Nhưng từ trong lòng nước Nhật với những thông tin cập nhật liên tục từng phút tôi có thể tin tưởng mà nói với độc giả rằng khủng hoảng sẽ đi đến kết thúc và Fukushima I sẽ nằm trong vòng kiểm soát hoàn toàn của con người.
Với các bể chứa nhiên liệu qua sử dụng, phương pháp làm lạnh ít nhất đã có giải pháp. Các xe máy bơm áp lực cao đang tiến sát về nhà máy theo tính toán những xe này sẽ bơm nước vào các bể chứa từ khoảng cách 50 mét với góc 30 độ như tính toán để đạt hiệu quả nhất cho việc cấp nước cho các bể chứa. Chỉ cần bể có nước các thanh nhiên liệu nguội đi phóng xạ sẽ chấm dứt.
Cả nước Nhật vẫn bình tĩnh, không thấy hoảng loạn, kêu khóc, trộm cắp, hôi của. Người Nhật chia nhau cơm nắm để vượt khó, các cửa hàng giảm giá để khách hàng có đồ ăn thức uống. Công ty truyền thông cấp miễn phí các điện thoại vệ tinh cho công tác cứu trợ và tìm người thân. Viện trợ nhanh chóng tới các điểm lánh nạn trong vùng bị thiên tai.
Quốc tế cũng đã có mặt để giúp nước Nhật đáng kể nhất là sự hiện diện của người Mỹ với tàu hàng không mẫu hạm Ronald Regan. Thủ tướng Naoto Kan lệnh cho quân đội tăng quân số tham gia cứu hộ từ 20.000 người lên 100.000 người. Như vậy trung bình sẽ có 10 người lính giúp đỡ khoảng 5 người bị nạn nếu như thống kê 15.000 có thể chết và mất tích và 35.000 người đang trong hoàn cảnh tị nạn là chính xác.
Điện dù vẫn đang bị cắt luôn phiên nhưng trung tâm đầu não Tokyo đã dần dần quay lại hoạt động. Ngân hàng Nhật đã đưa ra một lượng tiền lớn để ổn định thị trường. Các nhà băng đã hồi phục lại hệ thống dịch vụ. Tàu cao tốc đã chạy...
Hà Ngọc Tuấn
(từ Fukuoka, Nhật Bản)
'Khủng hoảng hạt nhân tại nhà máy Fukushima I vẫn tiếp diễn, nhưng thời gian đang đứng về phía con người, sự căng thẳng vẫn còn nhưng tôi tin mọi việc sẽ ổn thoả', tiến sĩ Hà Ngọc Tuấn viết tiếp.
> Phần I: Thảm hoạ qua cái nhìn người trong cuộc
Trong phần này tôi xin giải thích diễn biến, cơ chế khủng hoảng hạt nhân tại nhà máy Fukushima I và lý do vì sao tôi có niềm tin như vậy.
Hình ảnh hư hại lớp vỏ ngoài của lò phản ứng số 1, nhà máy Fukushima I sau vụ nổ. Ảnh: AFP
Sơ lược về nhà máy điện nguyên tử Fukushima
Nhà máy Fukushima 1 thuộc thế hệ đầu tiên của ngành năng lượng hạt nhân của Nhật. Nó được xây dựng và đưa tổ máy số 1 vào vận hành vào tháng 3/1971, chỉ hơn tôi có vài tháng tuổi và với tuổi đời này người ta vẫn nghĩ có thể mọi thứ đã hết hạn sử dụng. Thực tế thì không phải như vậy!
40 đến 50 năm là tuổi đời thiết kế của nhà máy điện nguyên tử. Nhà máy như thế này qua rất nhiều lần bảo dưỡng kiểm tra định kỳ theo qui định nghiêm ngặt của Nhật. Có lẽ chỉ các kết cấu bê tông cốt thép và phần lò phản ứng là không thay đổi, tất cả các hệ thống khác liên quan đến vận hành và an toàn nhà máy đã được thay bởi thế hệ thiết bị mới chế tạo trong 40 năm qua.
Loại lò sử dụng trong nhà máy này là Boiling Water Reactor (BWR) hay có thể tạm gọi là lò phản ứng nước sôi. Các nhà máy của điện lực Tokyo (TEPCO) sử dụng loại lò này. Một loại lò khác cũng được sử dụng ở Nhật là Pressurized water reactors (PWR) hay gọi là Lò áp lực nước.
Fukushima 1 có 6 tổ máy với tổng công suất lên đến 4696MW, gấp gần 3 lần công suất nhà máy thủy điện Hòa Bình của chúng ta. Tổ máy đầu tiên do General Electric (GE) của Mỹ sản xuất, nhưng sau đó người Nhật đã tự chế tạo được lò cho mình. Toshiba là hãng có lịch sử gắn bó lâu dài với điện lực Tokyo và họ cung cấp lò cho hãng này.
Diễn biến khủng hoảng Fukushima
Khủng hoảng tại Fukushima 1 có thể nói là duy nhất, vì cùng một lúc người ta gặp vấn đề với hai nhà máy với nhiều lò phản ứng, nhiều hiện tượng sự cố cùng lúc và ngay cả trong lúc xử lý sự cố vẫn phải hứng chịu dư chấn liên tục. Có thể nói sự cố điện nguyên tử này dù không gây ra thảm họa nhiễm xạ trên diện rộng thì cũng sẽ viết một trang mới cho các bài học về hệ thống an toàn điện nguyên tử, cũng như xử lý trong tình trạng khẩn cấp mà trong đó tên tuổi các kỹ sư và nhân viên vận hành nhà máy Fukushima sẽ được ghi tên vào lịch sử.
Cuộc chạy đua với khủng hoảng chưa kết thúc nhưng theo dõi những gì diễn ra, một lần nữa tôi thêm tự tin rằng thời gian đang ủng hộ con người. Ít nhất nhiệt trong các lò phản ứng đang trong tầm kiểm soát. 50 con người dũng cảm vẫn tại vị trí làm việc.Vị giám đốc nhà máy Fukushima I vẫn trong tư thế lãnh đạo toàn bộ cuộc chạy đua với áp suất, nhiệt độ mà công cụ là nước biển.
Đoàn cán bộ chính phủ từ bộ Kinh Tế Công Thương Nhật bản (METI) có mặt thường trực tại trung tâm đầu não của TEPCO ở Tokyo để cùng họ ra những quyết định quan trọng. Nội các của thủ tướng Kan đoàn kết và bình tĩnh. Toàn thể người dân Nhật cũng vậy họ kiên nhẫn tuân thủ lệnh chính phủ không hốt hoảng hay kêu ca một lời nào.
Nhiên liệu hạt nhân và lò phản ứng
Câu trả lời tất nhiên là do động đất và sóng thần. Dù được thiết kế từ hơn 40 năm trước, nhà máy Fukushima I có khả năng chống động đất ở mức cao nhưng không phải cho một trận 9.0 độ Richter như thế này. Để trả lời được phần nào những câu hỏi liên quan đến tai nạn, tôi thấy cần phải nói qua về cấu tạo và nguyên lý vận hành của lò phản ứng nhà máy Fukushima này.
Nhiên liệu và lò phản ứng
Nhiên liệu của lò phản ứng hạt nhân là chất uranium. Khoáng uranium thiên nhiên sẽ được tinh chế để làm ra thỏi nhiên liệu (pelet) như thấy ở hình trên. Kích thước thỏi hình trụ này là 10x10mm nặng khoảng 10gram với thành phần gồm uranium 235 và 238 trộn với tỷ lệ thích hợp. 350 thỏi nhiên liệu này được nhồi vào một thanh nhiên liệu (fuel rod). Các thanh nhiên liệu lại được bó thành bó nhiên liệu (fuel assembly). Rồi các bó nhiên liệu được đưa vào lò phản ứng (reactor). Chẳng hạn ở tổ máy số 1 của Fukushima 1 có 400 bó nhiên liệu như vậy.
Ngoài các bó nhiên liệu người ta còn đưa vào lõi lò các thanh điều khiển (control rod). Những thanh này làm bằng chất Boron có tính chất có thể "bắt" được các neutron là tác nhân gây ra phản ứng hạt nhân dây truyền (chain reactor). Dùng thanh này người ta có thể kiểm soát được mức độ phản ứng cũng như dừng hoàn toàn phản ứng trong lò.
Các bó nhiên liệu được đưa vào lò để khởi động phát điện khi đó người ta sẽ cho quá trình phản ứng dây chuyền có kiểm soát (giảm tốc độ và khống chế lượng neutron) diễn ra trong lò. Phản ứng dây chuyền xảy ra khi các hạt neutron bắn phá vào các nguyên tử uranium 235. Mỗi hạt neutron bắn vào một nguyên tử U235 sẽ khiến nó phân hạch tức là vỡ ra thành các nguyên tử nhẹ hơn và là sản phẩm của phản ứng dây chuyền (fission products).
Quá trình trên phát sinh ra nhiệt và sinh ra 2 neutron. Người ta sẽ dùng thanh điều khiển nói trên để "bắt" một neutron vừa phát sinh như vậy lượng neutron trong lò sẽ không đổi. Đây là điểm khác biệt căn bản giữa một quả bom nguyên tử và lò phản ứng nguyên tử. Ở vụ nổ nguyên tử sự phát sinh theo cấp số nhân của neutron trong phản ứng sẽ nhanh chóng sinh ra một phản ứng dây truyền không kiểm soát và lượng nhiệt khổng lồ trong giây lát. Một phản ứng có kiểm soát sẽ sinh lượng nhiệt như ý muốn của con người.
Khi "đốt" lò như thế nhiệt sẽ giải phóng xung quanh các thanh nhiên liệu. Người ta bơm nước vào lò để "đun". Nước có nhiệt độ và áp suất cao sẽ được chuyển thành hơi đẫn theo ống để "thổi" tuốc bin phát điện. Sau đó nước này được ngưng tụ bằng một hệ thống làm lạnh dùng nước biển và lại quay lại tâm lò trong một vòng tuần hoàn kín để không cho phóng xạ lọt ra ngoài.
Về nguyên tắc một nhà máy nhiệt điện thông thường và một nhà máy điện nguyên tử có nguyên lý vận hành như nhau chỉ khác ở chỗ là đun bằng "bếp" than hay "bếp" nguyên tử mà thôi.
Xin nhắc lại là quá trình phản ứng sinh ra các sản phẩm là các chất phóng xạ. Đây là điểm căn bản giải thích vì sao sau khi "tắt" lò vẫn nóng. Khi tắt lò thông thường hoặc do sự cố người ta sẽ đưa tất cả các thanh kiểm soát vào tâm lò khi đó phản ứng sẽ ngừng và không có nhiệt sinh ra từ phản ứng dây truyền nữa. Tuy nhiên các sản phẩm phản ứng là các chất phóng xạ (cesium và iodine là ví dụ) sinh ra do "đốt" lò vẫn tiếp tục quá trình phân rã phóng xạ (Radioactive decay). Như vậy hai bước quan trọng khi dừng lò là "tắt" lò và làm nguội.
Nguyên lý an toàn của lò phản ứng
Bài học mang tính giáo khoa cho thiết kế nhà máy nguyên tử là bảo vệ 5 lớp gồm:
Lớp 1: Thỏi nhiên liệu (pellet) được chế tạo nén cứng để các chất phóng xạ phát sinh luôn bị "nhốt" trong các thỏi này.
Lớp 2: Thanh nhiên liệu (fuel rod) có chức năng như vỏ kín "nhốt" các chất phóng xạ và khí phát sinh khi nó thoát ra khỏi các thỏi nhiên liệu.
Lớp 3: Lò phản ứng (reactor). Là một cái "nồi" thép có vỏ dày 16 cm bằng kim loại. Lò này ngăn các chất phóng xạ thoát ra ngoài khi phóng xạ thoát ra từ các thanh nhiên liệu.
Lớp 4: Thùng lò (pressure vessel) làm bằng kim loại có vỏ dày 3 cm. Trong trường hợp xấu nhất khi lò phản ứng "vỡ" thùng lò sẽ ngăn phóng xạ ra ngoài.
Lớp 5: Vỏ bê tông cốt thép. Đây là kết cấu bê tông cốt thép có bề dày 1,5 mét, được thiết kế với một mục đích duy nhất là khi tất cả thành phần kim loại nằm trong nó chảy ra trong một sự cố nóng chảy lò giống như ở nhà máy Three Mile Island của Mỹ vào tháng 3/1979 thì phóng xạ vẫn bị "nhốt" trong vỏ này.
Trên thực tế ở nhà máy Fukushima 1 còn có một lớp "áo" ngoài cùng là nhà lò. Kết cấu này chỉ có mục đích che các kết cấu bên trong khỏi tác động của thời tiết. Nhưng cũng cần nhấn mạnh rằng nó là kết cấu "kín bưng". Hai vụ nổ ở lò phản ứng số 1 và số 3 ở nhà máy Fukushima I đều xảy ra ở lớp ngoài cùng này. Các vụ nổ đó chưa làm ảnh hưởng đến lớp phòng vệ bên trong.
Nếu xem xét như trên thì chúng ta thấy vấn đề ở Fukushima 1 chưa đến mức nghiêm trọng và qui mô của vấn đề khó có thể lớn hơn được nữa. Theo thang đo INES (International Nuclear and Radiological Event Scale) của cơ quan năng lượng nguyên tử Quốc tế sự cố này có cấp 4 trong thang 7 cấp, tức là sự cố có tính chất cục bộ. Cần nhắc đến là Chernobyl là sự cố có mức rất nghiêm trọng lớn nhất từ trước tới nay và xếp vào cấp 7. Cấp 6 là sự cố nghiêm trọng. Cấp 5 là sự cố có diện rộng trong thang đo này.
Vỏ ngoài lò phản ứng số 3 nhà máy Fukushima I sau vụ nổ. Ảnh: AFP
Trục trặc ở hệ thống làm mát lò
Một nhà máy điện nguyên tử như Fukushima I được thiết kế chống động đất và tính toán đến ảnh hưởng của sóng thần rất tốt. Nó cũng được trang bị không phải một mà là nhiều hệ thống làm mát với nguyên lý làm việc khác nhau độc lập với nhau cùng với các nguồn điện độc lập. Nhiều kịch bản về sự cố được xây dựng để có các thủ tục đối phó.
Kịch bản ở Fukushima chính vì thế không mới. Điều bất ngờ là sóng thần quá lớn đã phá hỏng các máy phát điện dự phòng diezen nguồn năng lượng huyết mạch cho công tác làm lạnh. Trên thực tế các máy diezen ở nhà máy Fukushima I đều làm việc ngay những phút đầu tiên khi nhà máy mất điện lưới do động đất gây ra. Chúng hoạt động tốt cho đến khi sóng thần ập đến.
Dù thế không có nghĩa là mất hết nguồn điện. Mọi chuyện không đơn giản như thế! Các nhà thiết kế cũng đã tính cả đến khả năng này và họ đặt một nguồn điện khác trong vỏ lò nơi sóng thần không thể đến được. Nguồn này là pin có khả năng duy trì năng lượng cho các máy bơm của hệ thống làm mát lò trong 8 giờ với tính toán rằng với từng đó thời gian các nguồn cấp điện di động đã được vận chuyển đến nhà máy qua đường bộ. Và tính toán này diễn ra đúng kịch bản các pin này đã làm việc như thiết kế.
Tuy nhiên kịch bản bị vỡ ở một điểm là các xe phát điện di động của TEPCO không thể đến hiện trường sớm như dự tính. Bạn biết vì sao rồi đó. Làm gì còn đường xá cầu cống qua cơn sóng thần vừa rồi đó là cái không tính được! Nhưng họ vẫn đã đến chỉ có điều đến muộn. Và giống như bất kỳ vụ đến muộn nào khác sẽ có ai đó tức giận đến đỏ mặt. Nhiên liệu trong các lò không được làm mát do mất nguồn điện đã làm nước trong lò sôi lên bốc hơi và áp suất trong các lò đã tăng lên hơn nhiều so với thiết kế.
Nổ do phản ứng hóa học
Do không kịp bơm nước vào tâm lò để làm lạnh do mất nguồn điện cho hệ thống bơm nhiệt trong lò làm nước bốc hơi trong lò. Mực nước trong lò hạ xuống làm các thanh nhiên liệu không còn ngập hết trong nước nữa. Bên ngoài khu vực nhà máy lúc này đã phát hiện ra sự có mặt của sản phẩm phản ứng trong lò bao gồm các chất cesium (Cs) và iodine (I).
Điều này là cơ sở để phán đoán rằng nhiệt độ nhiên liệu đang rất cao vì các chất trên trong nhiên liệu đã bốc hơi và giải phóng ra ngoài khi nhóm vận hành buộc phải xả khí ra ngoài để bào vệ lò. Nếu như vậy nhiệt độ có thể cao hơn 2000 độ C vì nhiên liệu chỉ nóng chảy khi nhiệt độ đạt mức này. Điều này đồng nghĩa là vỏ của thanh nhiên liệu đã nóng chảy. Zircaloy nóng chảy dưới xúc tác của môi trường nước nhiệt độ cao trong lò đã gây ra phản ứng sinh ra hydro.
Việc Hydro sinh ra không nằm ngoài dự đoán chỉ có điều do độ tin cậy của các thiết bị đo mực không được khẳng định, tổng lượng hydro phát sinh là bao nhiêu không nắm được. Hơn thế nữa việc xả khí trong lò ra là bất khả kháng vì rủi ro nổ lò là không thể chấp nhận được bởi khi đó phóng xạ sẽ ồ ạt tràn ra môi trường. Khí được xả ra không gian nhà lò, nơi như nói trên là không gian được thiết kế kín với mục đích chống rò rỉ bất kỳ khí nào từ trong lò xả ra. Hydro nhẹ sẽ bốc lên trần nhà lò tích tụ ở đấy tới khi nồng độ của nó đạt mức tới hạn. Khi đó hydro sẽ phản ứng với ô-xi trong không khí phát nổ.
Hai cú nổ do phản ứng này đã thổi tung mái nhà lò số 1 và số 3 của nhà máy Fukushima I có cơ chế như vừa giải thích trên đây. Cũng cần nói thêm rằng trong lò phản ứng không có ô-xi cho nên không thể có phản ứng nổ như vậy và như đã nhắc đến ở trên vụ nổ không làm hư hại đến thùng lò như đã khẳng định bởi TEPCO.
Cháy do các thanh nhiên liệu đã qua sử dụng
Diễn biến thảm họa ở Fukushima I đã trở nên quá kịch tính khi ngay cả tổ máy đang dừng hoạt động từ trước động đất cũng bốc cháy. Sau đó người ta phát hiện ra nguyên nhân của việc này là do nhiệt từ các thanh nhiên liệu đã qua sử dụng đang được ngâm trong các bể làm mát ở tầng 4 nhà lò. Mỗi một bể làm mát này có sức chứa khoảng 2000 mét khối nước ngâm trong đó là các bó nhiên liệu có chiều cao 4 mét. Những bó này để dưới sâu đáy bể với mức nước ngập cao hơn nó chừng 20 mét.
So với sự kiện trong tâm lò thì sự kiện ở các bể làm nguội vật liệu này phức tạp hơn ở khía cạnh ngăn ngừa phóng xạ. Kịch bản xảy ra như ở các bể này có lẽ chưa bao giờ được đặt ra. Các thanh nhiên liệu qua sử dụng có các chất phóng xạ, sản phẩm của phản ứng dây chuyền chúng phân rã sinh nhiệt và các tia phóng xạ, trong khi đó chúng không nằm trong vỏ lò mà hoàn toàn bị lộ ra khí quyển lúc này do mái các tòa nhà lò đã bị phá hủy.
Lý do gì dẫn đến sự tăng nhiệt ở các thanh nhiên liệu đã sử dụng trong các bể chứa là điều tôi cũng đang muốn biết nhưng tôi phán đoán rằng vụ nổ ở lò thứ 3 đã làm mất một lượng lớn nước trong bể của nó cũng như bể chứa ở lò số 4. Sau vụ nổ lò số 3 người ta phát hiện tòa nhà lò số 4 cũng bị tổn thất nghiêm trọng.
Nguy cơ và mức độ rò rỉ phóng xạ
Mức độ ảnh hưởng của liều phóng xạ SV (Sievert) vào cơ thể người
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- Liều 1000 mSv gây nôn mửa tại chỗ và là nguyên nhân ung thư về lâu dài
- Liều 500 mSv sẽ gây ra hiện tượng giảm các tế bào limpho trong máu người
- Liều 6.9 mSv là lượng nhiễm xạ sau một lần cắt lát CT khi kiểm tra sức khỏe
- Liều 1.0 mSv là lượng nhiễm xạ tự nhiên từ phóng xạ mặt trời và đất đá thiên nhiên trong một năm
- Một lần chụp X-quang sẽ có một liều 0.5 mSv
Trong ngày đầu tiên trước khi lò số 1 phát nổ người ta đã đo được nồng độ phóng xạ trong khu vực nhà máy ở mức hoàn toàn chưa có ảnh hưởng lên con người, do đó lệnh di tản dân ra khỏi bán kính 3 km được đưa ra như biện pháp phòng ngừa sớm. Có thể thấy rằng nồng độ này là do việc phóng xạ phát tán do việc xả hơi và khí trong lò để bảo vệ lò phản ứng. Mặc dù bộ lọc phóng xạ khi một thao tác xả khí như thế được thiết kế tốt một liều nhất định phóng xạ ra môi trường là không thể tránh khỏi.
Tuy nhiên sau vụ nổ lò số 3 rồi sau đó vụ cháy phát hiện lò số 4 do các nhiên liệu đã qua sự dụng nồng độ phóng xạ đã tăng lên. Đặc biệt nồng độ này bị tăng vọt sau khi bể chứa nhiên liệu đã qua sử dụng với gần 2000 tấn nước ở tầng 4 của lò số 3 sôi ùng ục tỏa một lượng bơi nước lớn lên trời đến mức ống kính kênh NHK từ 30 km có thể quay rõ đám hơi nước này.
Từ việc sử dụng đơn vị microsievert ban tình trạng khẩn cấp đã thông báo với dân chúng Nhật nồng độ bằng millisiverts chứng tỏ liều phóng xạ đã tăng lên cả ngàn lần so với ban đầu. Nồng độ lớn nhất đo được giữa hai tổ máy 2 và 3 là 400mSv. Với liều này các tế bào lympho trong máu người sẽ bị giảm đột ngột ảnh hưởng đến sức khỏe, tình hình đưa đến quyết định rút toàn bộ cán bộ vận hành khỏi nhà máy nhất thời khi đó.
Vào lúc 12h30 ngày 17/3, nồng độ nhiễm xạ tại khu vực nhà máy khoảng 3500 $\mu$Sv (3.5 mSv). Với nồng độ này quân đội Nhật Bản đã quyết định dùng trực thăng quân sự CH47 đổ nước từ trên cao để làm nguội các bể chứa nhiên liệu đã qua sử dụng ở lò số 3 và 4. Phi công được trang bị bảo hộ an toàn phóng xạ đeo máy đo nồng độ xạ cá nhân để tiến hành công việc này.
Theo lãnh đạo của quân đội Nhật liều lượng qui định để chấm dứt nhiệm vụ này là 50 mSv, thực tế phi công đã đo được nồng độ khá cao ở một thời điểm là 80 mSv vì thế việc dội nước từ trên cao bằng trực thăng tạm dừng. Kiểm tra sức khỏe của phi công sau khi rời hiện trường cho thấy họ không bị nhiễm xạ sau nhiệm vụ vừa rồi. Sau phương pháp làm nguội bằng trực thăng, người ta đang cử các xe bơm áp lực cao đang đứng chờ cách nhà máy 20 km tiếp cận các lò này để bơm trực tiếp bằng cần bơm. Phương pháp sẽ có hiệu quả hơn vì nước dễ bơm đến các vị trí mong muốn hơn so với cách trực thăng CH47 vừa thực hiện.
Tới lúc này có thể thấy được nguy cơ nhiễm xạ phải đối diện hiện nay không phải từ trong lòng các lò phản ứng nơi mà áp suất nhiệt độ đã phần nào được kiểm soát. Tuy nhiên nhiệm vụ nặng nề phải thực hiện lại là cuộc chạy đua với nhiệt của các bể chứa nhiên liệu đã qua sử dụng. Nguy cơ nhiễm xạ ở mức độ nhất định là có nhưng con người vẫn đang nắm kiểm soát. Người Nhật đang chạy đua với thời gian sự tham gia của quân đội và cảnh sát sử dụng các phương tiện của họ đã giúp TEPCO một lần nữa thêm tự tin trong cuộc đấu cam go này.
Trực thăng vận tại CH47 của quân đội Nhật đưa túi nước thả xuống lò phản ứng tại Fukushima I. Ảnh: AFP
Khủng hoảng sẽ đi đến đâu
Có thể nói câu hỏi cho thì tương lai này không ai có thể trả lời chắc chắn được trong một tình huống như thế này. Rất nhiều người trên khắp thế giới lo lắng và cầu nguyện cho nước Nhật. Nhưng từ trong lòng nước Nhật với những thông tin cập nhật liên tục từng phút tôi có thể tin tưởng mà nói với độc giả rằng khủng hoảng sẽ đi đến kết thúc và Fukushima I sẽ nằm trong vòng kiểm soát hoàn toàn của con người.
Với các bể chứa nhiên liệu qua sử dụng, phương pháp làm lạnh ít nhất đã có giải pháp. Các xe máy bơm áp lực cao đang tiến sát về nhà máy theo tính toán những xe này sẽ bơm nước vào các bể chứa từ khoảng cách 50 mét với góc 30 độ như tính toán để đạt hiệu quả nhất cho việc cấp nước cho các bể chứa. Chỉ cần bể có nước các thanh nhiên liệu nguội đi phóng xạ sẽ chấm dứt.
Cả nước Nhật vẫn bình tĩnh, không thấy hoảng loạn, kêu khóc, trộm cắp, hôi của. Người Nhật chia nhau cơm nắm để vượt khó, các cửa hàng giảm giá để khách hàng có đồ ăn thức uống. Công ty truyền thông cấp miễn phí các điện thoại vệ tinh cho công tác cứu trợ và tìm người thân. Viện trợ nhanh chóng tới các điểm lánh nạn trong vùng bị thiên tai.
Quốc tế cũng đã có mặt để giúp nước Nhật đáng kể nhất là sự hiện diện của người Mỹ với tàu hàng không mẫu hạm Ronald Regan. Thủ tướng Naoto Kan lệnh cho quân đội tăng quân số tham gia cứu hộ từ 20.000 người lên 100.000 người. Như vậy trung bình sẽ có 10 người lính giúp đỡ khoảng 5 người bị nạn nếu như thống kê 15.000 có thể chết và mất tích và 35.000 người đang trong hoàn cảnh tị nạn là chính xác.
Điện dù vẫn đang bị cắt luôn phiên nhưng trung tâm đầu não Tokyo đã dần dần quay lại hoạt động. Ngân hàng Nhật đã đưa ra một lượng tiền lớn để ổn định thị trường. Các nhà băng đã hồi phục lại hệ thống dịch vụ. Tàu cao tốc đã chạy...
Hà Ngọc Tuấn
(từ Fukuoka, Nhật Bản)
16/03 Q. and A. on the Nuclear Crisis in Japan
March 16, 2011, 12:54 pm
By THE NEW YORK TIMES
Tokyo Electric Power Co., via Kyodo News, via Associated Press The Fukushima Daiichi plant on Tuesday. Reactors No. 3, left, and No. 4, center, are among those that have been damaged.
5:17 p.m. Updated New York Times reporters answered questions from readers about the continuing nuclear crisis in Japan. Readers asked about media coverage of the crisis, health risks from radiation exposure, problems with the reactors and nuclear waste, the workers at the plant, comparisons to Chernobyl and the danger of building nuclear power plants in earthquake-prone regions.
About the Reporters
Keith Bradsher is covering the crisis from Hong Kong, where he is the bureau chief.
Henry Fountain is a science reporter covering the science and engineering of nuclear reactors.
Denise Grady, a health reporter, is covering the impact of the crisis on public health.
David E. Sanger is chief Washington correspondent and a former Tokyo bureau chief.
Matthew L. Wald reports on national energy developments from Washington and is a regular contributor to the Green blog.
Media Hysteria?
Q.Why is the media giving such hysteric coverage to an issue which at its absolute worst might cause some people to relocate away from the immediate vicinity of the power station and leave an expensive cleanup mess… all while there are tens of thousands dead and dying from the effects of the tsunami and a vast swath of devastation to infrastructure which poses a far more immediate and ongoing hazard to both individuals and the greater economy?
— ddblack1, Austin, Tex.
A.From the moment that the earthquake and tsunami hit, The Times recognized this would be a multidimensional crisis, and we began deploying our reporters to cover all aspects of it. There is the heartbreaking human story, as the bodies of thousands are uncovered, as parents go searching for their children, as the residents of the northeast coast — an area many of us who covered Japan have often visited — try to rebuild their lives. Those stories have been told with great compassion through in articles by Martin Fackler, our Tokyo bureau chief, as well as Michael Wines and other reporters who made their way into the devastation zone. And then, of course, there are the broader issues — for Japan as it struggles its way out of two decades of economic stagnation, and for the world economic markets.
But we also quickly realized that the nuclear crisis unfolding at the Fukushima plant was unlike any we have seen in history: multiple failures, fires and radiation leaks from at least four separate reactors. While damage from the earthquake and tsunami was instantly visible, the nuclear impact, we suspected, would take days to unfold, and could affect far larger swaths of Japan and neighboring countries. Unfortunately, that is exactly what is happening. The challenge for us now is to cover both stories vigorously, with the depth, compassion, expertise and investigative zeal that Times readers expect.
— David E. Sanger
Health Risks
Q.I live in Oakland and can’t seem to get clear information about when and if radioactive materials will arrive here from the jet stream. And if so, what dosage or for how many days we should take potassium iodide to protect our thyroids?
— EastBay, Oakland, Calif.
A.This is frustrating for all, because the answer depends in part on the prevailing winds, which can change. However, experts I’ve interviewed strongly doubt that there will be any significant risk on the West Coast, and say there is no reason to take the potassium iodide unless high levels of radioactive iodine develop. But again, scientists consider high levels unlikely in the United States. In addition, about 98 percent of a person’s dose comes from drinking contaminated milk, and if fallout were to reach here (again, unlikely) most people could protect themselves by not drinking milk or eating dairy products. Children are much more vulnerable than adults.
— Denise Grady
Q.Is there a danger in interacting with people who have been exposed to radiation from this disaster? Particularly for young children? Would radiation be left behind in an apartment if someone from Tokyo were to come right now to stay as a guest?
— Concerned, New York City
A.The only risk I’m aware of would be if someone contaminated at the site came into your home wearing clothing full of radioactive fallout. Otherwise, you are O.K. If you are worried that someone who ingested radioactive material could be harmful, that seems unlikely.
— Denise Grady
Q.Like many expats here in Japan I get my news from both Japanese and overseas services. But genuine nuclear experts are so inconsistent in their reactions to this crisis, and so much panic is spreading in Tokyo and throughout Japan in relation to this. With us in mind and the practicalities of our daily living, could you please give some realistic feedback as to how/whether this crisis is going to irradiate us 260 kilometers away in Tokyo, poison our food supply and create long-term serious health risks beyond that 30-kilometer radius around the plant? People here really want solid information about how radioactivity works in layman’s terms, and what we need is solid information that is not laden with fear-mongering doomsday scenarios but real, practical advice.
— Greg, Tokyo
A.In an article in Wednesday’s paper, Denise Grady reported that the Japanese government has “taken precautions that should prevent the accident from becoming another Chernobyl, even if additional radiation is released.”
The Japanese government has evacuated people closest to the plant, told others to stay indoors and distributed the drug potassium iodide to protect the thyroid gland from radioactive iodine.
The great tragedy of Chernobyl was an epidemic of thyroid cancer among people exposed to the radiation as children — more than 6,000 cases so far, with more expected for many years to come. There is no reason for it to be repeated in Japan.
The epidemic in Chernobyl was preventable and would probably not have happened if people had been told to stop drinking locally produced milk, which was by far the most important source of radiation. Cows ate grass contaminated by fallout from the reactors and secreted radioactive iodine in their milk.
Read the full article, “Precautions Should Limit Health Problems From Nuclear Plant’s Radiation.”
— The Editors
Q.Folks in the vicinity of the power plant have been asked to stay indoors to protect themselves from the radiation. Is that really sufficient? How does this kind of radiation differ from an X-ray?
— Callie, East Lansing, Mich.
A.People near the plant have been evacuated. The ones being warned to stay inside are actually miles and miles away. Given that there is some dispersion of the cloud, levels at a distance should diminish, so the risk diminishes, too, and staying inside, though imperfect, seems like a reasonable precaution. The Environmental Protection Agency Web site offers good information about different types of radiation and the effects of various doses.
— Denise Grady
Crisis at the Reactors
Q.How is water currently being pumped into the reactors? Are fire hoses the sole method being used? Reports have indicated that backup diesel generators were brought to the site but were not able to be used to drive the pumps. There have also been reports of pump failures. Have detailed descriptions of the status of each reactor (including cooling methods and equipment failures) been made public? Given the contamination of site, it would seem that finding a way to supply coolant with minimal human presence is essential.
— Rob, Atlanta
A.The Japanese authorities have provided few details of how they are pumping sea water into the three stricken reactors. Nuclear engineers and executives with experience at other reactors say that the Japanese are most likely using several pumper engine firetrucks in a row, with each increasing the pressure of the water and pushing it through a hose to the next truck. This technique is sometimes used in high-rise firefighting and bomb disposal, when the goal is to maximize the flow and pressure of the water actually reaching the target. At the Fukushima Daiichi nuclear power plant, maximum pressure is needed to force water into overheated reactors in which a significant proportion of the water has turned into very hot steam at very high pressure.
The pumping process has been fraught with problems — at least one engine ran out of fuel at Reactor No. 2 on Monday night for several hours, interrupting the pumping of sea water during this time, because no tanker truck was immediately available to refuel it. Temperature and pressure climbed in the reactor as a result, and may have contributed to damage to the fuel rods and to an explosion at the base of the primary containment building.
Japanese officials have looked for alternatives. One idea under consideration has been to use helicopters to drop water. But helicopter crews who participated in the response to the Chernobyl accident received heavy doses of radiation from the smoke. The United States Navy has already reported that several helicopter crews involved in post-tsunami rescue work over the past several days have shown low-level exposure to radiation; decontamination under these circumstances mainly involves a lot of soap and water to remove radioactive particles.
— Keith Bradsher
Q.Where is the sea water that is being pumped in to cool the reactors going, and is this water contaminated?
— T. Lowen, Minneapolis
A.To the best of our understanding, the sea water is turning to steam. The reactor is still so hot that the sea water they are pumping in is just intended to replace the amount that boils off. In other words, in the best of situations, they are just managing to keep the reactor covered with water.
In the reactors that have had fuel rod exposure (at least three of them, apparently), the steam would be contaminated with radioactive elements from the fuel, which has been exposed because of cracking of the zirconium cladding around it. The contaminated steam leaves the reactor vessel and enters the containment structure. To avoid a pressure buildup, the containment structure must be vented intermittently, resulting in the release of radioactivity to the environment. (In at least one of the reactors, the containment structure is reported to be damaged; if that’s the case then the radiation release could be continuous.)
— Henry Fountain
Q.I keep seeing the phrase “shut down” in reference to the nuclear reactors at Fukushima, but clearly they are not shut down as they are still generating tremendous energy in the form of heat. How is a nuclear reactor “turned off”?
They can’t keep using firetrucks to pump seawater through the reactor cores indefinitely. Since it is apparently not possible to turn off the reactors, what is the long term plan for preventing a meltdown?
— A.J., San Francisco
A.The reactors at the Fukushima Daiichi plant are shut down, meaning that the nuclear chain reaction (which generated heat to turn water to steam for the turbines that make electricity) has been halted. That happened automatically when the earthquake struck — in such an emergency, the reactors are designed to insert special rods into the core that absorb neutrons and stop the chain reaction.
The reactors were very hot, though (they operate at about 550 degrees Fahrenheit) and it takes a while to remove that heat. In addition — and this is the real problem — even though the chain reaction is stopped, heat is still generated in the fuel by the natural decay of the radioactive elements present. This heat is why they need to keep pumping water into the reactor core — it stays so hot that the water can boil off, exposing the fuel rods. And if the fuel rods are exposed, even for a short time (as happened at at least two of the reactors), they become damaged and radioactivity is released.
Tokyo Electric Power, the operator of the reactors, has not discussed its long-term plans, but it’s probably safe to say that their goal is to restore regular electric service to the plant so that normal pumping operations can resume (although at this point, given the explosions, pump and plumbing repairs will likely have to be made, too).
— Henry Fountain
Related: Interactive Feature: How a Reactor Shuts Down and What Happens in a Meltdown
Q.In the case of a full core meltdown, would the entry/exit ports in the primary containment vessel used for adding cooling water and for venting steam be the first location of release of radioactive materials? Or would a full core meltdown be an explosive event that would destroy the entire containment vessel?
— Dan Baker, San Diego
A.Experts differ on the impact of a full meltdown of the nuclear fuel at any of the reactors. Some say that the molten fuel would be unlikely to burn through the walls of the reactor vessel, which are thick steel. (At the Three Mile Island accident in 1979, molten fuel burned only partly through the steel.) Others say that a burn-through would happen, with the molten fuel then falling to the floor of the containment structure. What would happen next is a subject of debate as well. Some experts think the fuel would not progress very far before it started to cool. Others say that it could reach the walls of the containment structure, which are made of thick concrete with a thin steel liner, and damage it, perhaps through cracking. Some experts are worried that steam explosions might completely destroy the containment structure. (A steam explosion is really an oxygen-hydrogen explosion — the fuel is so hot that if it hits water, it splits the molecules into hydrogen and oxygen, a highly combustible mix.)
Even if molten fuel remains in the reactor vessel, radiation will escape through vents into the containment structure. And even without further damage, the containment structures in at least two of the reactor buildings appear to have been damaged, allowing uncontrolled release of radioactivity.
— Henry Fountain
Q.The Onagawa nuclear plant is much closer to the earthquake and tsunami zone than the Fukushima plant but appears to have shut down safely while Fukushima has not. Can you explain the differences in what happened and is happening at the two nuclear locations?
— R.J.W., Dunkirk, N.Y.
A.We’re still trying to figure it out completely, but the answer appears to lie in the backup cooling systems. At Fukushima, the plants appeared to survive the earthquake without major damage, but the backup cooling was wiped out by the tsunami. The question of why one plant survived so well and another did not will be the focus of many of our questions as we try to reconstruct events.
— David E. Sanger
Q.If the reactors are still so hot, why can’t they turn the turbines back on to generate electricity just for the plant and get the cooling pumps running?
— L. Littlefield, Brooklyn
A.The reactors are damaged to the point where there would be no way to control them enough to restore the steam supply to the turbines. And even if the operators could somehow get one of the turbines spinning, the electricity has to flow through transformers, switches and other equipment, some of which has no doubt been damaged or destroyed. It’s not as simple as just hooking up a few wires from a generator to a pump.
— Henry Fountain
Workers at the Plant
Q.How were the 50 people remaining at the plant chosen? Did they volunteer? What are their genders? Is a medical team included? How are they being supplied with food and other necessities?
— Alan, Hawaii
A.In an article in Wednesday’s paper, Keith Bradsher and Hiroko Tabuchi reported on the technicians who stayed behind at the Fukushima Daiichi nuclear power plant and were “perhaps Japan’s last chance of preventing a broader nuclear catastrophe.”
They crawl through labyrinths of equipment in utter darkness pierced only by their flashlights, listening for periodic explosions as hydrogen gas escaping from crippled reactors ignites on contact with air.
They breathe through uncomfortable respirators or carry heavy oxygen tanks on their backs. They wear white, full-body jumpsuits with snug-fitting hoods that provide scant protection from the invisible radiation sleeting through their bodies.
They are the faceless 50, the unnamed operators who stayed behind. They have volunteered, or been assigned, to pump seawater on dangerously exposed nuclear fuel, already thought to be partly melting and spewing radioactive material, to prevent full meltdowns that could throw thousands of tons of radioactive dust high into the air and imperil millions of their compatriots.
For more details, read the full article, “Last Defense at Troubled Reactors: 50 Japanese Workers.”
— The Editors
Q.Has human error contributed to the severity of the situation? I’ve seen reports of a critical generator running out of fuel, a valve that was improperly left closed, and I suspect that preventive actions could have avoided the hydrogen buildup that led to at least two explosions.
— Greg Ebert, Hillsboro, Oregon
A.When a fire pump ran out of fuel and shut down outside Reactor No. 2 on Monday night, that was human error. But it is not clear that the rest of the difficulties are related to human error.
I have not seen confirmation that a valve was improperly left closed, and the valves have been under a lot of strain on these overheated reactors. Similarly, some Western nuclear engineers have wondered if the Japanese waited too long to begin pumping in seawater and boric acid, which temporarily cool the reactors and slow the formation of hydrogen gas. But the Japanese technicians faced a tough dilemma in figuring out how much boric acid to use and how to move the seawater after the tsunami disrupted so many of their backup systems.
— Keith Bradsher
Chernobyl and Three Mile Island
Q.The apparent solution to containing the “mess” in Chernobyl was to build a giant concrete sarcophagus around the reactor. Hindsight has shown that to be an error. When all is said and done here, what is the best way to deal with the toxic remnants of the reactors and nuclear waste?
— Marklemagne, Ohio
A.The international consensus is that eventually, reactor wastes will have to be buried. The United States plans to do that with all spent reactor fuel, and that includes the rubble from the core at Three Mile Island, which suffered a partial melt-down in 1979. It is sitting in containers at the Idaho National Laboratory, near Idaho Falls.
In the shorter term, the cores from Fukushima are also likely to go into containers, steel cylinders filled with inert gas and then sealed and placed into concrete silos. Such “dry cask storage” can keep reactor wastes isolated for decades, with minimal requirements for inspection, and no moving parts.
The Japanese “recycle” some of their fuel, chopping it up, dissolving it in acid, and then using a chemical separation process to leach out the plutonium that was created by the reactor’s operation. The plutonium is then formed into new fuel. The remaining materials can be embedded in glass. That could also happen to the reactor core rubble from Fukushima. But those wastes, too, will probably eventually be buried.
— Matthew L. Wald
(Correction: An earlier version of this answer misstated the location of the Idaho National Laboratory. It is near Idaho Falls, Idaho — not Idaho Springs, which is in Colorado.)
Q.In the event that the damaged reactors in Japan cool sufficiently to “entomb” their contents, then what? We know they will not be used again, but how can they be managed; and how long can they sustain an entombing integrity, especially considering that there may be multiple structural breaches within various components of each of these reactors? What should we expect from them in the event of future natural disasters in the same area?
— Leha, Santa Rosa, Calif.
A.At Three Mile Island, the fuel was cleaned out and shipped off site (see answer above) and the reactor vessel, empty, was left to sit until a companion plant was ready for retirement. At that point, probably both will be torn down just as other old reactors have been “decommissioned.” The Fukushima accident is not over, but unless it gets a lot worse, defueling is more likely than entombment, because eventually, someone is likely to want to reuse the site.
— Matthew L. Wald
Q.The Chernobyl plant used a graphite moderator that burned and distributed radioactive fallout over a wide area. The Japanese plant doesn’t use graphite. What, if anything, is the mechanism by which radioactive materials could be distributed over a wide area?
— Matthew, Salem, Mass.
A.There are two potential mechanisms. One is that the only form of cooling now available is to pump in cold water and wait for it to boil off, and then release the steam. The steam propels wastes into the atmosphere. The other is that the spent fuel pools are heating up. If they boil dry, there is a theory that the fuel could get hot enough so that its metal cladding, made of an alloy of zirconium, could catch fire. (The clad in the fuel in the reactors has already produced hydrogen, causing explosions.) A fire would produce enough energy to lift radioactive contaminants into the air.
At Chernobyl, the graphite burned and provided enough energy to lift the radioactive material into the jet stream at high altitude. It is not clear whether a significant portion of the wastes from Fukushima could rise that high. With a little luck, much of the material could stay in the lower atmosphere and be washed out by rainstorms over the Pacific.
— Matthew L. Wald
Nuclear Policy
Q.I read that Japan has 55 nuclear reactors on an island country about the size of California. How did the Japanese government justify this when the region is a hotbed for earthquakes? Were these plants pitched as being earthquake safe? How is it that with the threat of tsunamis that nuclear plants were built right on the beach?
— K.T., Minneapolis
A.Reactors are attractive to Japan because the country has barely any fossil fuels, neither coal nor natural gas, which together make up 70 percent of American power generation, or any significant oil supply.
Almost all of Japan’s civil infrastructure is built with earthquakes and tsunamis in mind. That includes big buildings, bridges and power stations. The country is ringed with tsunami barriers. But this earthquake was the largest in recorded history, and the tsunami was higher than the planners assumed. And along with killing thousands of people, it swamped the reactors.
— Matthew L. Wald
Q.I understand that the Japanese government stated that all prefectures in Japan should start reporting twice a day on any signs of elevated radiation levels and that these reports should be made public. Will The New York Times be providing (translated) access to this information? Have you inquired of the U.S. government, e.g. NARAC, as to the size, direction and radiation intensity of the radioactive plume arising from the Fukushima plant? At what point should radiation monitoring reports in the U.S., particularly in counties on the Pacific Coast, be made publicly available? Have you looked into this?
— Lyndon Comstock, Bolinas, Calif.
A.So far the reporting on radiation levels available from Japanese authorities has been spotty, at best. We have been pursuing more comprehensive data, not only from the Japanese government, but from the United States Navy, whose ships have been offshore from the nuclear site, and more than 40 American experts from the Department of Energy who have now landed in Japan. They brought some sophisticated measuring gear with them, and we expect to soon see new measurements. My colleague Bill Broad wrote about the plume in Monday’s paper. N.O.A.A., the Air Force and others are also tracking the plume, and we will be reporting more of that information once we have vetted it.
— David E. Sanger
Q.It seems that too much is at stake to allow private companies to operate nuclear reactors. They can’t even insure themselves, so of course they will keep operating even if they shouldn’t. If we are to rely on nuclear power, why not have a federal agency analogous to NASA run them?
— R.J.M. Hudson, Champaign, Ill.
A.You raise an interesting policy question that came up, in different form, during last year’s oil spill as well. Nuclear power plants are subject to federal regulation, of course; the question you are raising is whether safety would be better if they were state-owned. The answer to that question is far from clear. And of course, NASA no longer has a monopoly on space flight: One key element of the Obama administration’s space strategy is to encourage more private firms to enter the fray.
— David E. Sanger
Copyright 2011 The New York Times CompanyPrivacy PolicyNYTimes.com 620 Eighth Avenue New York, NY 10018
By THE NEW YORK TIMES
Tokyo Electric Power Co., via Kyodo News, via Associated Press The Fukushima Daiichi plant on Tuesday. Reactors No. 3, left, and No. 4, center, are among those that have been damaged.
5:17 p.m. Updated New York Times reporters answered questions from readers about the continuing nuclear crisis in Japan. Readers asked about media coverage of the crisis, health risks from radiation exposure, problems with the reactors and nuclear waste, the workers at the plant, comparisons to Chernobyl and the danger of building nuclear power plants in earthquake-prone regions.
About the Reporters
Keith Bradsher is covering the crisis from Hong Kong, where he is the bureau chief.
Henry Fountain is a science reporter covering the science and engineering of nuclear reactors.
Denise Grady, a health reporter, is covering the impact of the crisis on public health.
David E. Sanger is chief Washington correspondent and a former Tokyo bureau chief.
Matthew L. Wald reports on national energy developments from Washington and is a regular contributor to the Green blog.
Media Hysteria?
Q.Why is the media giving such hysteric coverage to an issue which at its absolute worst might cause some people to relocate away from the immediate vicinity of the power station and leave an expensive cleanup mess… all while there are tens of thousands dead and dying from the effects of the tsunami and a vast swath of devastation to infrastructure which poses a far more immediate and ongoing hazard to both individuals and the greater economy?
— ddblack1, Austin, Tex.
A.From the moment that the earthquake and tsunami hit, The Times recognized this would be a multidimensional crisis, and we began deploying our reporters to cover all aspects of it. There is the heartbreaking human story, as the bodies of thousands are uncovered, as parents go searching for their children, as the residents of the northeast coast — an area many of us who covered Japan have often visited — try to rebuild their lives. Those stories have been told with great compassion through in articles by Martin Fackler, our Tokyo bureau chief, as well as Michael Wines and other reporters who made their way into the devastation zone. And then, of course, there are the broader issues — for Japan as it struggles its way out of two decades of economic stagnation, and for the world economic markets.
But we also quickly realized that the nuclear crisis unfolding at the Fukushima plant was unlike any we have seen in history: multiple failures, fires and radiation leaks from at least four separate reactors. While damage from the earthquake and tsunami was instantly visible, the nuclear impact, we suspected, would take days to unfold, and could affect far larger swaths of Japan and neighboring countries. Unfortunately, that is exactly what is happening. The challenge for us now is to cover both stories vigorously, with the depth, compassion, expertise and investigative zeal that Times readers expect.
— David E. Sanger
Health Risks
Q.I live in Oakland and can’t seem to get clear information about when and if radioactive materials will arrive here from the jet stream. And if so, what dosage or for how many days we should take potassium iodide to protect our thyroids?
— EastBay, Oakland, Calif.
A.This is frustrating for all, because the answer depends in part on the prevailing winds, which can change. However, experts I’ve interviewed strongly doubt that there will be any significant risk on the West Coast, and say there is no reason to take the potassium iodide unless high levels of radioactive iodine develop. But again, scientists consider high levels unlikely in the United States. In addition, about 98 percent of a person’s dose comes from drinking contaminated milk, and if fallout were to reach here (again, unlikely) most people could protect themselves by not drinking milk or eating dairy products. Children are much more vulnerable than adults.
— Denise Grady
Q.Is there a danger in interacting with people who have been exposed to radiation from this disaster? Particularly for young children? Would radiation be left behind in an apartment if someone from Tokyo were to come right now to stay as a guest?
— Concerned, New York City
A.The only risk I’m aware of would be if someone contaminated at the site came into your home wearing clothing full of radioactive fallout. Otherwise, you are O.K. If you are worried that someone who ingested radioactive material could be harmful, that seems unlikely.
— Denise Grady
Q.Like many expats here in Japan I get my news from both Japanese and overseas services. But genuine nuclear experts are so inconsistent in their reactions to this crisis, and so much panic is spreading in Tokyo and throughout Japan in relation to this. With us in mind and the practicalities of our daily living, could you please give some realistic feedback as to how/whether this crisis is going to irradiate us 260 kilometers away in Tokyo, poison our food supply and create long-term serious health risks beyond that 30-kilometer radius around the plant? People here really want solid information about how radioactivity works in layman’s terms, and what we need is solid information that is not laden with fear-mongering doomsday scenarios but real, practical advice.
— Greg, Tokyo
A.In an article in Wednesday’s paper, Denise Grady reported that the Japanese government has “taken precautions that should prevent the accident from becoming another Chernobyl, even if additional radiation is released.”
The Japanese government has evacuated people closest to the plant, told others to stay indoors and distributed the drug potassium iodide to protect the thyroid gland from radioactive iodine.
The great tragedy of Chernobyl was an epidemic of thyroid cancer among people exposed to the radiation as children — more than 6,000 cases so far, with more expected for many years to come. There is no reason for it to be repeated in Japan.
The epidemic in Chernobyl was preventable and would probably not have happened if people had been told to stop drinking locally produced milk, which was by far the most important source of radiation. Cows ate grass contaminated by fallout from the reactors and secreted radioactive iodine in their milk.
Read the full article, “Precautions Should Limit Health Problems From Nuclear Plant’s Radiation.”
— The Editors
Q.Folks in the vicinity of the power plant have been asked to stay indoors to protect themselves from the radiation. Is that really sufficient? How does this kind of radiation differ from an X-ray?
— Callie, East Lansing, Mich.
A.People near the plant have been evacuated. The ones being warned to stay inside are actually miles and miles away. Given that there is some dispersion of the cloud, levels at a distance should diminish, so the risk diminishes, too, and staying inside, though imperfect, seems like a reasonable precaution. The Environmental Protection Agency Web site offers good information about different types of radiation and the effects of various doses.
— Denise Grady
Crisis at the Reactors
Q.How is water currently being pumped into the reactors? Are fire hoses the sole method being used? Reports have indicated that backup diesel generators were brought to the site but were not able to be used to drive the pumps. There have also been reports of pump failures. Have detailed descriptions of the status of each reactor (including cooling methods and equipment failures) been made public? Given the contamination of site, it would seem that finding a way to supply coolant with minimal human presence is essential.
— Rob, Atlanta
A.The Japanese authorities have provided few details of how they are pumping sea water into the three stricken reactors. Nuclear engineers and executives with experience at other reactors say that the Japanese are most likely using several pumper engine firetrucks in a row, with each increasing the pressure of the water and pushing it through a hose to the next truck. This technique is sometimes used in high-rise firefighting and bomb disposal, when the goal is to maximize the flow and pressure of the water actually reaching the target. At the Fukushima Daiichi nuclear power plant, maximum pressure is needed to force water into overheated reactors in which a significant proportion of the water has turned into very hot steam at very high pressure.
The pumping process has been fraught with problems — at least one engine ran out of fuel at Reactor No. 2 on Monday night for several hours, interrupting the pumping of sea water during this time, because no tanker truck was immediately available to refuel it. Temperature and pressure climbed in the reactor as a result, and may have contributed to damage to the fuel rods and to an explosion at the base of the primary containment building.
Japanese officials have looked for alternatives. One idea under consideration has been to use helicopters to drop water. But helicopter crews who participated in the response to the Chernobyl accident received heavy doses of radiation from the smoke. The United States Navy has already reported that several helicopter crews involved in post-tsunami rescue work over the past several days have shown low-level exposure to radiation; decontamination under these circumstances mainly involves a lot of soap and water to remove radioactive particles.
— Keith Bradsher
Q.Where is the sea water that is being pumped in to cool the reactors going, and is this water contaminated?
— T. Lowen, Minneapolis
A.To the best of our understanding, the sea water is turning to steam. The reactor is still so hot that the sea water they are pumping in is just intended to replace the amount that boils off. In other words, in the best of situations, they are just managing to keep the reactor covered with water.
In the reactors that have had fuel rod exposure (at least three of them, apparently), the steam would be contaminated with radioactive elements from the fuel, which has been exposed because of cracking of the zirconium cladding around it. The contaminated steam leaves the reactor vessel and enters the containment structure. To avoid a pressure buildup, the containment structure must be vented intermittently, resulting in the release of radioactivity to the environment. (In at least one of the reactors, the containment structure is reported to be damaged; if that’s the case then the radiation release could be continuous.)
— Henry Fountain
Q.I keep seeing the phrase “shut down” in reference to the nuclear reactors at Fukushima, but clearly they are not shut down as they are still generating tremendous energy in the form of heat. How is a nuclear reactor “turned off”?
They can’t keep using firetrucks to pump seawater through the reactor cores indefinitely. Since it is apparently not possible to turn off the reactors, what is the long term plan for preventing a meltdown?
— A.J., San Francisco
A.The reactors at the Fukushima Daiichi plant are shut down, meaning that the nuclear chain reaction (which generated heat to turn water to steam for the turbines that make electricity) has been halted. That happened automatically when the earthquake struck — in such an emergency, the reactors are designed to insert special rods into the core that absorb neutrons and stop the chain reaction.
The reactors were very hot, though (they operate at about 550 degrees Fahrenheit) and it takes a while to remove that heat. In addition — and this is the real problem — even though the chain reaction is stopped, heat is still generated in the fuel by the natural decay of the radioactive elements present. This heat is why they need to keep pumping water into the reactor core — it stays so hot that the water can boil off, exposing the fuel rods. And if the fuel rods are exposed, even for a short time (as happened at at least two of the reactors), they become damaged and radioactivity is released.
Tokyo Electric Power, the operator of the reactors, has not discussed its long-term plans, but it’s probably safe to say that their goal is to restore regular electric service to the plant so that normal pumping operations can resume (although at this point, given the explosions, pump and plumbing repairs will likely have to be made, too).
— Henry Fountain
Related: Interactive Feature: How a Reactor Shuts Down and What Happens in a Meltdown
Q.In the case of a full core meltdown, would the entry/exit ports in the primary containment vessel used for adding cooling water and for venting steam be the first location of release of radioactive materials? Or would a full core meltdown be an explosive event that would destroy the entire containment vessel?
— Dan Baker, San Diego
A.Experts differ on the impact of a full meltdown of the nuclear fuel at any of the reactors. Some say that the molten fuel would be unlikely to burn through the walls of the reactor vessel, which are thick steel. (At the Three Mile Island accident in 1979, molten fuel burned only partly through the steel.) Others say that a burn-through would happen, with the molten fuel then falling to the floor of the containment structure. What would happen next is a subject of debate as well. Some experts think the fuel would not progress very far before it started to cool. Others say that it could reach the walls of the containment structure, which are made of thick concrete with a thin steel liner, and damage it, perhaps through cracking. Some experts are worried that steam explosions might completely destroy the containment structure. (A steam explosion is really an oxygen-hydrogen explosion — the fuel is so hot that if it hits water, it splits the molecules into hydrogen and oxygen, a highly combustible mix.)
Even if molten fuel remains in the reactor vessel, radiation will escape through vents into the containment structure. And even without further damage, the containment structures in at least two of the reactor buildings appear to have been damaged, allowing uncontrolled release of radioactivity.
— Henry Fountain
Q.The Onagawa nuclear plant is much closer to the earthquake and tsunami zone than the Fukushima plant but appears to have shut down safely while Fukushima has not. Can you explain the differences in what happened and is happening at the two nuclear locations?
— R.J.W., Dunkirk, N.Y.
A.We’re still trying to figure it out completely, but the answer appears to lie in the backup cooling systems. At Fukushima, the plants appeared to survive the earthquake without major damage, but the backup cooling was wiped out by the tsunami. The question of why one plant survived so well and another did not will be the focus of many of our questions as we try to reconstruct events.
— David E. Sanger
Q.If the reactors are still so hot, why can’t they turn the turbines back on to generate electricity just for the plant and get the cooling pumps running?
— L. Littlefield, Brooklyn
A.The reactors are damaged to the point where there would be no way to control them enough to restore the steam supply to the turbines. And even if the operators could somehow get one of the turbines spinning, the electricity has to flow through transformers, switches and other equipment, some of which has no doubt been damaged or destroyed. It’s not as simple as just hooking up a few wires from a generator to a pump.
— Henry Fountain
Workers at the Plant
Q.How were the 50 people remaining at the plant chosen? Did they volunteer? What are their genders? Is a medical team included? How are they being supplied with food and other necessities?
— Alan, Hawaii
A.In an article in Wednesday’s paper, Keith Bradsher and Hiroko Tabuchi reported on the technicians who stayed behind at the Fukushima Daiichi nuclear power plant and were “perhaps Japan’s last chance of preventing a broader nuclear catastrophe.”
They crawl through labyrinths of equipment in utter darkness pierced only by their flashlights, listening for periodic explosions as hydrogen gas escaping from crippled reactors ignites on contact with air.
They breathe through uncomfortable respirators or carry heavy oxygen tanks on their backs. They wear white, full-body jumpsuits with snug-fitting hoods that provide scant protection from the invisible radiation sleeting through their bodies.
They are the faceless 50, the unnamed operators who stayed behind. They have volunteered, or been assigned, to pump seawater on dangerously exposed nuclear fuel, already thought to be partly melting and spewing radioactive material, to prevent full meltdowns that could throw thousands of tons of radioactive dust high into the air and imperil millions of their compatriots.
For more details, read the full article, “Last Defense at Troubled Reactors: 50 Japanese Workers.”
— The Editors
Q.Has human error contributed to the severity of the situation? I’ve seen reports of a critical generator running out of fuel, a valve that was improperly left closed, and I suspect that preventive actions could have avoided the hydrogen buildup that led to at least two explosions.
— Greg Ebert, Hillsboro, Oregon
A.When a fire pump ran out of fuel and shut down outside Reactor No. 2 on Monday night, that was human error. But it is not clear that the rest of the difficulties are related to human error.
I have not seen confirmation that a valve was improperly left closed, and the valves have been under a lot of strain on these overheated reactors. Similarly, some Western nuclear engineers have wondered if the Japanese waited too long to begin pumping in seawater and boric acid, which temporarily cool the reactors and slow the formation of hydrogen gas. But the Japanese technicians faced a tough dilemma in figuring out how much boric acid to use and how to move the seawater after the tsunami disrupted so many of their backup systems.
— Keith Bradsher
Chernobyl and Three Mile Island
Q.The apparent solution to containing the “mess” in Chernobyl was to build a giant concrete sarcophagus around the reactor. Hindsight has shown that to be an error. When all is said and done here, what is the best way to deal with the toxic remnants of the reactors and nuclear waste?
— Marklemagne, Ohio
A.The international consensus is that eventually, reactor wastes will have to be buried. The United States plans to do that with all spent reactor fuel, and that includes the rubble from the core at Three Mile Island, which suffered a partial melt-down in 1979. It is sitting in containers at the Idaho National Laboratory, near Idaho Falls.
In the shorter term, the cores from Fukushima are also likely to go into containers, steel cylinders filled with inert gas and then sealed and placed into concrete silos. Such “dry cask storage” can keep reactor wastes isolated for decades, with minimal requirements for inspection, and no moving parts.
The Japanese “recycle” some of their fuel, chopping it up, dissolving it in acid, and then using a chemical separation process to leach out the plutonium that was created by the reactor’s operation. The plutonium is then formed into new fuel. The remaining materials can be embedded in glass. That could also happen to the reactor core rubble from Fukushima. But those wastes, too, will probably eventually be buried.
— Matthew L. Wald
(Correction: An earlier version of this answer misstated the location of the Idaho National Laboratory. It is near Idaho Falls, Idaho — not Idaho Springs, which is in Colorado.)
Q.In the event that the damaged reactors in Japan cool sufficiently to “entomb” their contents, then what? We know they will not be used again, but how can they be managed; and how long can they sustain an entombing integrity, especially considering that there may be multiple structural breaches within various components of each of these reactors? What should we expect from them in the event of future natural disasters in the same area?
— Leha, Santa Rosa, Calif.
A.At Three Mile Island, the fuel was cleaned out and shipped off site (see answer above) and the reactor vessel, empty, was left to sit until a companion plant was ready for retirement. At that point, probably both will be torn down just as other old reactors have been “decommissioned.” The Fukushima accident is not over, but unless it gets a lot worse, defueling is more likely than entombment, because eventually, someone is likely to want to reuse the site.
— Matthew L. Wald
Q.The Chernobyl plant used a graphite moderator that burned and distributed radioactive fallout over a wide area. The Japanese plant doesn’t use graphite. What, if anything, is the mechanism by which radioactive materials could be distributed over a wide area?
— Matthew, Salem, Mass.
A.There are two potential mechanisms. One is that the only form of cooling now available is to pump in cold water and wait for it to boil off, and then release the steam. The steam propels wastes into the atmosphere. The other is that the spent fuel pools are heating up. If they boil dry, there is a theory that the fuel could get hot enough so that its metal cladding, made of an alloy of zirconium, could catch fire. (The clad in the fuel in the reactors has already produced hydrogen, causing explosions.) A fire would produce enough energy to lift radioactive contaminants into the air.
At Chernobyl, the graphite burned and provided enough energy to lift the radioactive material into the jet stream at high altitude. It is not clear whether a significant portion of the wastes from Fukushima could rise that high. With a little luck, much of the material could stay in the lower atmosphere and be washed out by rainstorms over the Pacific.
— Matthew L. Wald
Nuclear Policy
Q.I read that Japan has 55 nuclear reactors on an island country about the size of California. How did the Japanese government justify this when the region is a hotbed for earthquakes? Were these plants pitched as being earthquake safe? How is it that with the threat of tsunamis that nuclear plants were built right on the beach?
— K.T., Minneapolis
A.Reactors are attractive to Japan because the country has barely any fossil fuels, neither coal nor natural gas, which together make up 70 percent of American power generation, or any significant oil supply.
Almost all of Japan’s civil infrastructure is built with earthquakes and tsunamis in mind. That includes big buildings, bridges and power stations. The country is ringed with tsunami barriers. But this earthquake was the largest in recorded history, and the tsunami was higher than the planners assumed. And along with killing thousands of people, it swamped the reactors.
— Matthew L. Wald
Q.I understand that the Japanese government stated that all prefectures in Japan should start reporting twice a day on any signs of elevated radiation levels and that these reports should be made public. Will The New York Times be providing (translated) access to this information? Have you inquired of the U.S. government, e.g. NARAC, as to the size, direction and radiation intensity of the radioactive plume arising from the Fukushima plant? At what point should radiation monitoring reports in the U.S., particularly in counties on the Pacific Coast, be made publicly available? Have you looked into this?
— Lyndon Comstock, Bolinas, Calif.
A.So far the reporting on radiation levels available from Japanese authorities has been spotty, at best. We have been pursuing more comprehensive data, not only from the Japanese government, but from the United States Navy, whose ships have been offshore from the nuclear site, and more than 40 American experts from the Department of Energy who have now landed in Japan. They brought some sophisticated measuring gear with them, and we expect to soon see new measurements. My colleague Bill Broad wrote about the plume in Monday’s paper. N.O.A.A., the Air Force and others are also tracking the plume, and we will be reporting more of that information once we have vetted it.
— David E. Sanger
Q.It seems that too much is at stake to allow private companies to operate nuclear reactors. They can’t even insure themselves, so of course they will keep operating even if they shouldn’t. If we are to rely on nuclear power, why not have a federal agency analogous to NASA run them?
— R.J.M. Hudson, Champaign, Ill.
A.You raise an interesting policy question that came up, in different form, during last year’s oil spill as well. Nuclear power plants are subject to federal regulation, of course; the question you are raising is whether safety would be better if they were state-owned. The answer to that question is far from clear. And of course, NASA no longer has a monopoly on space flight: One key element of the Obama administration’s space strategy is to encourage more private firms to enter the fray.
— David E. Sanger
Copyright 2011 The New York Times CompanyPrivacy PolicyNYTimes.com 620 Eighth Avenue New York, NY 10018
19/03 Japan Finds Tainted Food Up to 90 Miles From Nuclear Sites
March 19, 2011
By KEN BELSON and HIROKO TABUCHI
TOKYO — As Japan edged forward in its battle to contain the damage at its ravaged nuclear power plants on Saturday, the government said it had found higher than normal levels of radioactivity in spinach and milk at farms up to 90 miles away from the plants, the first confirmation that the unfolding nuclear crisis has affected the nation’s food supply.
While officials played down the immediate risks to consumers, the findings further unsettled a nation worried about the long-term effects of the hobbled reactors.
The Tokyo Electric Power Company, with help from the Japan Self-Defense Force, police officers and firefighters, continued efforts to cool the damaged reactors on Saturday to try to stave off a full-scale fuel meltdown and contain the fallout. The latest plan involved running a mile-long electrical transmission line to Reactor No. 2 at the Fukushima Daiichi Nuclear Power Station to try to restore power to its cooling system.
About 500 workers from the utility connected the power line on Saturday. They were checking the cooling system, which has been disabled since the earthquake and tsunami hit more than a week ago, and hope to restart it on Sunday.
Restoring power at the plant could provide a glimmer of hope after days of increasingly dire news that now includes contaminated food.
Yukio Edano, the chief cabinet secretary, said that spinach and milk were the only products found to have abnormally high radiation levels. The level of radioactivity found in the spinach would, if consumed for a year, equal the radiation received in a single CAT scan, he said, while that detected in milk would amount to just a fraction of a CAT scan.
“These levels do not pose an immediate threat to your health,” Mr. Edano said, adding that the Health, Labor and Welfare Ministry would provide additional details. “Please stay calm.”
Still, Fukushima Prefecture asked all dairy farms within 18 miles of the nuclear plant on Saturday to halt all milk shipments. Officials also halted shipments of spinach from the entire prefecture.
The milk with the elevated radiation levels was found in Fukushima Prefecture on farms about 19 miles from the nuclear plants. The contaminated spinach was found one prefecture to the south, in Ibaraki Prefecture, on farms 60 to 90 miles south of the plants.
Food safety inspectors said the iodine-131 in the tested milk was up to five times the level the government deems safe, and the spinach had levels more than seven times the safe level. The spinach also contained slightly higher than allowable amounts of cesium-137.
Minuscule amounts of radioactive iodine were also detected in the water supply in Tokyo and its five surrounding prefectures. In Tokyo, about 170 miles from the Fukushima Daiichi plant, the level was less than 1 percent of that considered dangerous by the government. In Fukushima city, about 50 miles from the power plant, the levels were still below half of the legal limit.
Iodine-131 and cesium-137 are two of the more dangerous elements that are feared to have been released from the plants in Fukushima. Iodine-131 can be dangerous to human health, especially if absorbed through milk and milk products, because it can accumulate in the thyroid and cause cancer. Cesium-137 can damage cells and lead to an increased risk of cancer.
The iodine levels are well beyond what the Food and Drug Administration in the United States considers a cause for concern. But experts say Japan’s reassurances about food safety were probably accurate.
Dr. Harold M. Swartz, a professor of medicine at Dartmouth who studies radiation exposure in people, said that the contamination levels were low and that the government’s advice was “probably reasonable.” But, he added, because people are so afraid of radiation, they are likely to avoid these foods altogether.
“Seems unnecessary to eat these” foods, said another expert, Dr. David J. Brenner, director of the Center for Radiological Research at Columbia University. “I wouldn’t.”
That judgment was shared by Katsuko Sato, 76, who was shopping at a supermarket in central Tokyo on Saturday evening. She said she would stop buying spinach and, after watching Mr. Edano’s news conference, she called her family and friends to urge them not to, either.
“I’m not going to believe the government because I don’t think only spinach from Ibaraki will be affected,” she said.
A handful of vegetable-shop owners in Tokyo said they were concerned about the report, but continued to sell vegetables from Fukushima and Ibaraki because they had not been told to stop.
Dr. Swartz said people consuming milk and produce, particularly children and pregnant women, should be taking potassium iodide, which saturates the thyroid gland with nonradioactive iodine, and prevents it from taking in the radioactive form. Children and fetuses have the highest risk of thyroid cancer from exposure to radioactive iodine.
The Japanese authorities recommended Wednesday that people fleeing the 12-mile-radius evacuation zone start taking iodine pills.
Dr. Swartz said the radiation levels detected so far were still far lower than those at Chernobyl, the nuclear plant that exploded in Ukraine in 1986 and is still the world’s worst nuclear accident. He said that in the United States food with similar levels of radiation would probably be taken off the market, but more for political and public relations reasons than for scientific or medical ones.
The Japanese government is considering conducting more comprehensive tests of agricultural products from areas farther from the damaged reactors to address public anxiety about the food supply, Mr. Edano said.
Health inspectors are still trying to determine whether any spinach had been shipped from the six farms in Ibaraki Prefecture, where the contaminated produce was found, said Taku Ohara, an official in the food safety division of the Health, Labor and Welfare Ministry. The tests were conducted Saturday. No contaminated milk had been shipped from the farm where higher than normal radioactive levels were detected.
Mr. Ohara said Japan was particularly strict in determining what constituted safe radioactive levels. It is also fastidious in inspecting food imported from China and other countries. Leafy spinach is especially susceptible to absorbing radioactive material, he said.
Asparagus, cucumbers, radishes, tomatoes and other vegetables are also grown in Fukushima, but have not been found to be contaminated. But only a small number of farms have been tested because officials have been overwhelmed in the wake of the earthquake, tsunami and the nuclear crisis that followed, Mr. Ohara said.
Though land-poor Japan imports much of its fruit, grain and soybeans, 79 percent of the vegetables eaten here are grown domestically. Japan is the largest net importer of food in the world.
There have been no reports of contaminated fish or meat.
Many of the ports, fleets and processing facilities in Tohoku, the area most affected by the tsunami and nuclear crisis, were so badly damaged that no fish or seafood from there has reached Tsukiji market in central Tokyo, according to the market’s general manager, Tsutomo Kosaka. The market handles 90 percent of the seafood for about 40 million consumers in the greater Tokyo area.
Japan’s leading producers of premium beef, including the world-famous Kobe brand, said Saturday that they had not yet tested their cattle or feed. But they were nervous about the possible spread of radiation from Fukushima, and just as concerned that fear of radiation, even if it is unfounded, could damage the market for gourmet beef.
While only spinach and milk were found to have elevated radiation levels, some countries have been testing food imports from Japan since the day after the quake and tsunami. In Hong Kong, for instance, 216 Japanese products passed food quality screenings, including meat, fish, fruits and vegetables.
In Japan, consumers were also grappling with rolling blackouts ordered after damage to the reactors reduced the electricity supply in the greater Tokyo region.
At the Fukushima plant, temperatures outside the four damaged reactors were lower than expected, Defense Minister Toshimi Kitazawa said Saturday, raising hopes that the nuclear fuel could be kept cool by spraying the reactors with water, while technicians worked on restoring power to the cooling systems.
But Mr. Kitazawa was unable to confirm how hot it was inside the buildings, leaving open the possibility that nuclear fuel may still be overheating.
“Currently, we have a level of stabilization, but the situation remains volatile,” said Mr. Edano, the cabinet secretary.
The National Police Agency said Saturday that there were nearly 7,200 confirmed deaths so far because of the earthquake and tsunami on March 11, and nearly 11,000 people remained missing. The authorities have said they expect the death toll to exceed 10,000.
Mark McDonald and Ayasa Aizawa contributed reporting from Tokyo, and Denise Grady from New York.
By KEN BELSON and HIROKO TABUCHI
TOKYO — As Japan edged forward in its battle to contain the damage at its ravaged nuclear power plants on Saturday, the government said it had found higher than normal levels of radioactivity in spinach and milk at farms up to 90 miles away from the plants, the first confirmation that the unfolding nuclear crisis has affected the nation’s food supply.
While officials played down the immediate risks to consumers, the findings further unsettled a nation worried about the long-term effects of the hobbled reactors.
The Tokyo Electric Power Company, with help from the Japan Self-Defense Force, police officers and firefighters, continued efforts to cool the damaged reactors on Saturday to try to stave off a full-scale fuel meltdown and contain the fallout. The latest plan involved running a mile-long electrical transmission line to Reactor No. 2 at the Fukushima Daiichi Nuclear Power Station to try to restore power to its cooling system.
About 500 workers from the utility connected the power line on Saturday. They were checking the cooling system, which has been disabled since the earthquake and tsunami hit more than a week ago, and hope to restart it on Sunday.
Restoring power at the plant could provide a glimmer of hope after days of increasingly dire news that now includes contaminated food.
Yukio Edano, the chief cabinet secretary, said that spinach and milk were the only products found to have abnormally high radiation levels. The level of radioactivity found in the spinach would, if consumed for a year, equal the radiation received in a single CAT scan, he said, while that detected in milk would amount to just a fraction of a CAT scan.
“These levels do not pose an immediate threat to your health,” Mr. Edano said, adding that the Health, Labor and Welfare Ministry would provide additional details. “Please stay calm.”
Still, Fukushima Prefecture asked all dairy farms within 18 miles of the nuclear plant on Saturday to halt all milk shipments. Officials also halted shipments of spinach from the entire prefecture.
The milk with the elevated radiation levels was found in Fukushima Prefecture on farms about 19 miles from the nuclear plants. The contaminated spinach was found one prefecture to the south, in Ibaraki Prefecture, on farms 60 to 90 miles south of the plants.
Food safety inspectors said the iodine-131 in the tested milk was up to five times the level the government deems safe, and the spinach had levels more than seven times the safe level. The spinach also contained slightly higher than allowable amounts of cesium-137.
Minuscule amounts of radioactive iodine were also detected in the water supply in Tokyo and its five surrounding prefectures. In Tokyo, about 170 miles from the Fukushima Daiichi plant, the level was less than 1 percent of that considered dangerous by the government. In Fukushima city, about 50 miles from the power plant, the levels were still below half of the legal limit.
Iodine-131 and cesium-137 are two of the more dangerous elements that are feared to have been released from the plants in Fukushima. Iodine-131 can be dangerous to human health, especially if absorbed through milk and milk products, because it can accumulate in the thyroid and cause cancer. Cesium-137 can damage cells and lead to an increased risk of cancer.
The iodine levels are well beyond what the Food and Drug Administration in the United States considers a cause for concern. But experts say Japan’s reassurances about food safety were probably accurate.
Dr. Harold M. Swartz, a professor of medicine at Dartmouth who studies radiation exposure in people, said that the contamination levels were low and that the government’s advice was “probably reasonable.” But, he added, because people are so afraid of radiation, they are likely to avoid these foods altogether.
“Seems unnecessary to eat these” foods, said another expert, Dr. David J. Brenner, director of the Center for Radiological Research at Columbia University. “I wouldn’t.”
That judgment was shared by Katsuko Sato, 76, who was shopping at a supermarket in central Tokyo on Saturday evening. She said she would stop buying spinach and, after watching Mr. Edano’s news conference, she called her family and friends to urge them not to, either.
“I’m not going to believe the government because I don’t think only spinach from Ibaraki will be affected,” she said.
A handful of vegetable-shop owners in Tokyo said they were concerned about the report, but continued to sell vegetables from Fukushima and Ibaraki because they had not been told to stop.
Dr. Swartz said people consuming milk and produce, particularly children and pregnant women, should be taking potassium iodide, which saturates the thyroid gland with nonradioactive iodine, and prevents it from taking in the radioactive form. Children and fetuses have the highest risk of thyroid cancer from exposure to radioactive iodine.
The Japanese authorities recommended Wednesday that people fleeing the 12-mile-radius evacuation zone start taking iodine pills.
Dr. Swartz said the radiation levels detected so far were still far lower than those at Chernobyl, the nuclear plant that exploded in Ukraine in 1986 and is still the world’s worst nuclear accident. He said that in the United States food with similar levels of radiation would probably be taken off the market, but more for political and public relations reasons than for scientific or medical ones.
The Japanese government is considering conducting more comprehensive tests of agricultural products from areas farther from the damaged reactors to address public anxiety about the food supply, Mr. Edano said.
Health inspectors are still trying to determine whether any spinach had been shipped from the six farms in Ibaraki Prefecture, where the contaminated produce was found, said Taku Ohara, an official in the food safety division of the Health, Labor and Welfare Ministry. The tests were conducted Saturday. No contaminated milk had been shipped from the farm where higher than normal radioactive levels were detected.
Mr. Ohara said Japan was particularly strict in determining what constituted safe radioactive levels. It is also fastidious in inspecting food imported from China and other countries. Leafy spinach is especially susceptible to absorbing radioactive material, he said.
Asparagus, cucumbers, radishes, tomatoes and other vegetables are also grown in Fukushima, but have not been found to be contaminated. But only a small number of farms have been tested because officials have been overwhelmed in the wake of the earthquake, tsunami and the nuclear crisis that followed, Mr. Ohara said.
Though land-poor Japan imports much of its fruit, grain and soybeans, 79 percent of the vegetables eaten here are grown domestically. Japan is the largest net importer of food in the world.
There have been no reports of contaminated fish or meat.
Many of the ports, fleets and processing facilities in Tohoku, the area most affected by the tsunami and nuclear crisis, were so badly damaged that no fish or seafood from there has reached Tsukiji market in central Tokyo, according to the market’s general manager, Tsutomo Kosaka. The market handles 90 percent of the seafood for about 40 million consumers in the greater Tokyo area.
Japan’s leading producers of premium beef, including the world-famous Kobe brand, said Saturday that they had not yet tested their cattle or feed. But they were nervous about the possible spread of radiation from Fukushima, and just as concerned that fear of radiation, even if it is unfounded, could damage the market for gourmet beef.
While only spinach and milk were found to have elevated radiation levels, some countries have been testing food imports from Japan since the day after the quake and tsunami. In Hong Kong, for instance, 216 Japanese products passed food quality screenings, including meat, fish, fruits and vegetables.
In Japan, consumers were also grappling with rolling blackouts ordered after damage to the reactors reduced the electricity supply in the greater Tokyo region.
At the Fukushima plant, temperatures outside the four damaged reactors were lower than expected, Defense Minister Toshimi Kitazawa said Saturday, raising hopes that the nuclear fuel could be kept cool by spraying the reactors with water, while technicians worked on restoring power to the cooling systems.
But Mr. Kitazawa was unable to confirm how hot it was inside the buildings, leaving open the possibility that nuclear fuel may still be overheating.
“Currently, we have a level of stabilization, but the situation remains volatile,” said Mr. Edano, the cabinet secretary.
The National Police Agency said Saturday that there were nearly 7,200 confirmed deaths so far because of the earthquake and tsunami on March 11, and nearly 11,000 people remained missing. The authorities have said they expect the death toll to exceed 10,000.
Mark McDonald and Ayasa Aizawa contributed reporting from Tokyo, and Denise Grady from New York.
Saturday, March 19, 2011
18/03 Japan Races to Restart Reactors’ Cooling System
March 18, 2011
By KEN BELSON, HIROKO TABUCHI and KEITH BRADSHER
This article is by Ken Belson, Hiroko Tabuchi and Keith Bradsher.
TOKYO — Scrambling to corral a widening crisis, engineers linked a power cable to the crippled Fukushima Daiichi Nuclear Power Station early Saturday as they struggled to restart systems designed to prevent overheating and keep radiation from escaping.
The Tokyo Electric Power Company, which runs the plant, said it hoped to connect the electric cord to the cooling equipment inside the facility later Saturday in an attempt to stabilize the reactors that were damaged by the powerful earthquake and tsunami that struck Japan eight days ago.
In a brief statement on Japanese television Saturday morning, an official for Japan’s Nuclear and Industrial Safety Agency said that workers had managed to restart a diesel pump and restored cooling functions at two of the reactors, Nos. 5 and 6, early Saturday morning. He did not provide any details.
Those reactors were not in use when the disaster occurred, but they contained spent fuel rods, and engineers were concerned this week when temperatures in the reactors began to rise.
About 150 of its people were working on the electrical cable, the power company said, and they were planning to start with Reactor No. 2, which on Friday was seen spewing steam, perhaps containing radioactive particles.
Officials have cautioned, however, that restoring electricity to the reactor would prove fruitless if the pumps were not working. In that case, a new cooling system would be needed, leading to more delays in an emergency that has bedeviled the power company and the government and caused anxiety and frustration overseas.
The nuclear safety agency said that the crisis now had wider consequences, and raised its assessment of the accident’s severity to Level 5 on a seven-level scale established by the International Atomic Energy Agency. Hidehiko Nishiyama, a senior official at the agency, said the assessment was retroactive to Tuesday and based on the fact that officials now assumed that more than 3 percent of the nuclear fuel at the plant had experienced meltdown.
The adjustment was an admission by Japanese officials that the problem was worse than it had previously stated. “We could have moved more quickly in collecting information and assessing the situation,” said Yukio Edano, the chief cabinet secretary.
Outside experts have said for days that this disaster is worse than the one in 1979 at Three Mile Island — which the United States classified as a 5 on the international scale but which released far less radiation outside the plant than Fukushima Daiichi already has.
Engineers are starting the power cord effort with Reactor No. 2 because its outer building has not blown off, thus making it hard to spray in water the way they can with Nos. 1, 3 and 4, according to NHK, Japan’s national broadcaster, which cited power company officials.
The plan was to lay a 1.5-kilometer power cable between Reactor Nos. 1 and 3 to get to No. 2. If they can hook it up, it will theoretically be able to power all six reactors. The main hazard was the exposure of workers.
Unable to contain the catastrophe on its own, Tokyo Electric has received help from Japanese police and fire departments and the country’s Self-Defense Forces. Assistance has started to flood in as well, with nuclear experts arriving from the United States and international agencies. France and South Korea are also providing support.
Overnight in Japan, crews from the Tokyo Fire Department doused water on Reactor No. 3, which was doused earlier Friday by teams from the Self-Defense Forces and the United States military. Workers planned to continue the spraying on Saturday.
In a further sign of spreading alarm on Friday that uranium in the plant could begin to melt, Japan planned to import about 150 tons of boron from South Korea and France to mix with water to be sprayed onto damaged reactors, French and South Korean officials said Friday. Boron absorbs neutrons during a nuclear reaction and can be used in an effort to stop a meltdown if the zirconium cladding on uranium fuel rods is compromised.
Tokyo Electric Power said this week that there was a possibility of “recriticality,” in which fission would resume if fuel rods melted and the uranium pellets slumped into a jumble on the floor of a storage pool or reactor core. Spraying pure water on the uranium under these conditions can actually accelerate fission, said Robert Albrecht, a longtime nuclear engineer.
Nuclear reactions at the plant were halted immediately after last week’s 9.0-magnitude earthquake and before the tsunami arrived minutes later.
In the past two days, Japanese officials have focused on cooling spent fuel rods in a storage pool in Reactor No. 3, but on Friday steam was seen rising from Reactor No. 2. It was one of two hit by an explosion on Tuesday.
Additionally, a senior Western nuclear industry executive said Friday that there appeared to be damage to the floor or sides of the spent fuel pool at Reactor No. 4, and that this was making it hard to refill the pool with water. The problem was first reported by The Los Angeles Times.
Engineers said Thursday that a rip in the stainless steel lining of the pool at Reactor No. 4 and the concrete base underneath it was possible as a result of earthquake damage. The steel gates at either end of the storage pool are also vulnerable to damage during an earthquake and could leak water if they no longer close tightly.
The senior executive, who asked not to be identified because his comments could damage business relationships, said that a leak had not been located but that engineers had concluded that it must exist because water sprayed on the storage pool had been disappearing much more quickly than would be consistent with evaporation.
Technicians focused Friday on fixing electrical connections at Reactor No. 2 and spraying more water on No. 3 while studying the problem at No. 4.
“They have to figure out what to do, and certainly you can’t have No. 2 going haywire or No. 3 going haywire at the same time you’re trying to figure out what to do with No. 4,” said the executive, who said he had learned of the problem from industry contacts in Japan.
One concern at No. 4 has been a fire that was burning at its storage pool earlier in the week; American officials are not convinced the fire has gone out. American officials have also worried that the spent-fuel pool at that reactor has run dry, exposing the rods.
The new setbacks emerged as the first readings from American data collection flights over the plant in northeastern Japan showed that the worst contamination had not spread beyond the 19-mile range of highest concern established by the Japanese.
While the findings were reassuring in the short term, the United States declined to back away from its warning to Americans there to stay at least 50 miles from the plant, setting up a larger perimeter than the Japanese government had established. American officials did not release radiation readings.
Japanese officials, meanwhile, said Friday that despite their decision to elevate the level of severity, they were not expanding the evacuation zone.
The National Police Agency said Saturday that there were nearly 7,200 confirmed deaths so far, and nearly 11,000 people missing.
At the request of the Japanese military, a Massachusetts company, iRobot, said it put four robots on a plane for Japan on Friday. Colin Angle, the chief executive, said it had sent two small robots that could measure radiation levels close to the reactors and two larger ones that could pull hoses to spray water on the fuel rods.
He said Japanese soldiers could operate the robots from a protected vehicle.
Ken Belson and Hiroko Tabuchi reported from Tokyo, and Keith Bradsher from Hong Kong. Reporting was contributed by Mark McDonald and Kantaro Suzuki from Tokyo, David E. Sanger from Washington, William J. Broad and Christopher Drew from New York, Thom Shanker from Washington and Alan Cowell from Paris.
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By KEN BELSON, HIROKO TABUCHI and KEITH BRADSHER
This article is by Ken Belson, Hiroko Tabuchi and Keith Bradsher.
TOKYO — Scrambling to corral a widening crisis, engineers linked a power cable to the crippled Fukushima Daiichi Nuclear Power Station early Saturday as they struggled to restart systems designed to prevent overheating and keep radiation from escaping.
The Tokyo Electric Power Company, which runs the plant, said it hoped to connect the electric cord to the cooling equipment inside the facility later Saturday in an attempt to stabilize the reactors that were damaged by the powerful earthquake and tsunami that struck Japan eight days ago.
In a brief statement on Japanese television Saturday morning, an official for Japan’s Nuclear and Industrial Safety Agency said that workers had managed to restart a diesel pump and restored cooling functions at two of the reactors, Nos. 5 and 6, early Saturday morning. He did not provide any details.
Those reactors were not in use when the disaster occurred, but they contained spent fuel rods, and engineers were concerned this week when temperatures in the reactors began to rise.
About 150 of its people were working on the electrical cable, the power company said, and they were planning to start with Reactor No. 2, which on Friday was seen spewing steam, perhaps containing radioactive particles.
Officials have cautioned, however, that restoring electricity to the reactor would prove fruitless if the pumps were not working. In that case, a new cooling system would be needed, leading to more delays in an emergency that has bedeviled the power company and the government and caused anxiety and frustration overseas.
The nuclear safety agency said that the crisis now had wider consequences, and raised its assessment of the accident’s severity to Level 5 on a seven-level scale established by the International Atomic Energy Agency. Hidehiko Nishiyama, a senior official at the agency, said the assessment was retroactive to Tuesday and based on the fact that officials now assumed that more than 3 percent of the nuclear fuel at the plant had experienced meltdown.
The adjustment was an admission by Japanese officials that the problem was worse than it had previously stated. “We could have moved more quickly in collecting information and assessing the situation,” said Yukio Edano, the chief cabinet secretary.
Outside experts have said for days that this disaster is worse than the one in 1979 at Three Mile Island — which the United States classified as a 5 on the international scale but which released far less radiation outside the plant than Fukushima Daiichi already has.
Engineers are starting the power cord effort with Reactor No. 2 because its outer building has not blown off, thus making it hard to spray in water the way they can with Nos. 1, 3 and 4, according to NHK, Japan’s national broadcaster, which cited power company officials.
The plan was to lay a 1.5-kilometer power cable between Reactor Nos. 1 and 3 to get to No. 2. If they can hook it up, it will theoretically be able to power all six reactors. The main hazard was the exposure of workers.
Unable to contain the catastrophe on its own, Tokyo Electric has received help from Japanese police and fire departments and the country’s Self-Defense Forces. Assistance has started to flood in as well, with nuclear experts arriving from the United States and international agencies. France and South Korea are also providing support.
Overnight in Japan, crews from the Tokyo Fire Department doused water on Reactor No. 3, which was doused earlier Friday by teams from the Self-Defense Forces and the United States military. Workers planned to continue the spraying on Saturday.
In a further sign of spreading alarm on Friday that uranium in the plant could begin to melt, Japan planned to import about 150 tons of boron from South Korea and France to mix with water to be sprayed onto damaged reactors, French and South Korean officials said Friday. Boron absorbs neutrons during a nuclear reaction and can be used in an effort to stop a meltdown if the zirconium cladding on uranium fuel rods is compromised.
Tokyo Electric Power said this week that there was a possibility of “recriticality,” in which fission would resume if fuel rods melted and the uranium pellets slumped into a jumble on the floor of a storage pool or reactor core. Spraying pure water on the uranium under these conditions can actually accelerate fission, said Robert Albrecht, a longtime nuclear engineer.
Nuclear reactions at the plant were halted immediately after last week’s 9.0-magnitude earthquake and before the tsunami arrived minutes later.
In the past two days, Japanese officials have focused on cooling spent fuel rods in a storage pool in Reactor No. 3, but on Friday steam was seen rising from Reactor No. 2. It was one of two hit by an explosion on Tuesday.
Additionally, a senior Western nuclear industry executive said Friday that there appeared to be damage to the floor or sides of the spent fuel pool at Reactor No. 4, and that this was making it hard to refill the pool with water. The problem was first reported by The Los Angeles Times.
Engineers said Thursday that a rip in the stainless steel lining of the pool at Reactor No. 4 and the concrete base underneath it was possible as a result of earthquake damage. The steel gates at either end of the storage pool are also vulnerable to damage during an earthquake and could leak water if they no longer close tightly.
The senior executive, who asked not to be identified because his comments could damage business relationships, said that a leak had not been located but that engineers had concluded that it must exist because water sprayed on the storage pool had been disappearing much more quickly than would be consistent with evaporation.
Technicians focused Friday on fixing electrical connections at Reactor No. 2 and spraying more water on No. 3 while studying the problem at No. 4.
“They have to figure out what to do, and certainly you can’t have No. 2 going haywire or No. 3 going haywire at the same time you’re trying to figure out what to do with No. 4,” said the executive, who said he had learned of the problem from industry contacts in Japan.
One concern at No. 4 has been a fire that was burning at its storage pool earlier in the week; American officials are not convinced the fire has gone out. American officials have also worried that the spent-fuel pool at that reactor has run dry, exposing the rods.
The new setbacks emerged as the first readings from American data collection flights over the plant in northeastern Japan showed that the worst contamination had not spread beyond the 19-mile range of highest concern established by the Japanese.
While the findings were reassuring in the short term, the United States declined to back away from its warning to Americans there to stay at least 50 miles from the plant, setting up a larger perimeter than the Japanese government had established. American officials did not release radiation readings.
Japanese officials, meanwhile, said Friday that despite their decision to elevate the level of severity, they were not expanding the evacuation zone.
The National Police Agency said Saturday that there were nearly 7,200 confirmed deaths so far, and nearly 11,000 people missing.
At the request of the Japanese military, a Massachusetts company, iRobot, said it put four robots on a plane for Japan on Friday. Colin Angle, the chief executive, said it had sent two small robots that could measure radiation levels close to the reactors and two larger ones that could pull hoses to spray water on the fuel rods.
He said Japanese soldiers could operate the robots from a protected vehicle.
Ken Belson and Hiroko Tabuchi reported from Tokyo, and Keith Bradsher from Hong Kong. Reporting was contributed by Mark McDonald and Kantaro Suzuki from Tokyo, David E. Sanger from Washington, William J. Broad and Christopher Drew from New York, Thom Shanker from Washington and Alan Cowell from Paris.
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Friday, March 18, 2011
17/03 Greater Danger Lies in Spent Fuel Than in Reactors
March 17, 2011
By KEITH BRADSHER and HIROKO TABUCHI
Years of procrastination in deciding on long-term disposal of highly radioactive fuel rods from nuclear reactors are now coming back to haunt Japanese authorities as they try to control fires and explosions at the stricken Fukushima Daiichi Nuclear Power Station.
Some countries have tried to limit the number of spent fuel rods that accumulate at nuclear power plants: Germany stores them in costly casks, for example, while China sends them to a desert storage compound in the western province of Gansu. But Japan, like the United States, has kept ever-larger numbers of spent fuel rods in temporary storage pools at the power plants, where they can be guarded with the same security provided for the plants.
Figures provided by Tokyo Electric Power on Thursday show that most of the dangerous uranium at the power plant is actually in the spent fuel rods, not the reactor cores themselves.
The electric utility said that a total of 11,125 spent fuel rod assemblies were stored at the site. That is about four times as much radioactive material as in the reactor cores combined.
Now those temporary pools are proving the power plant’s Achilles’ heel, with the water in the pools either boiling away or leaking out of their containments, and efforts to add more water having gone awry. While spent fuel rods generate significantly less heat than newer ones do, there are strong indications that some fuel rods have begun to melt and release extremely high levels of radiation. Japanese workers struggled on Thursday to add more water to the storage pool at Reactor No. 3.
Helicopters dropped water, only to have it scattered by strong breezes. Water cannons mounted on police trucks — equipment designed to disperse rioters — were then deployed to spray water on the pools. It is unclear if that effort worked.
Richard T. Lahey Jr., a retired nuclear engineer who oversaw General Electric’s safety research in the early 1970s for the kind of nuclear reactors used in Fukushima, said that the zirconium cladding on the fuel rods could burst into flames if exposed to air for hours when a storage pool lost its water.
Zirconium, once ignited, burns extremely hot and is difficult to extinguish, added Mr. Lahey, who helped write a classified report for the United States government several years ago on the vulnerabilities of storage pools at American nuclear reactors.
Very high levels of radiation above the storage pools suggest that the water has drained in the 39-foot-deep pools to the point that the 13-foot-high fuel rod assemblies have been exposed to air for hours and are starting to melt, said Robert Albrecht, a longtime nuclear engineer who worked as a consultant to the Japanese nuclear reactor manufacturing industry in the 1980s. Under normal conditions, the rods are kept covered with 26 feet of water that is circulated to prevent it from growing too warm.
Gregory Jaczko, the chairman of the United States Nuclear Regulatory Commission, made the startling assertion on Wednesday that there was little or no water left in another storage pool, the one on top of Reactor No. 4, and expressed grave concern about the radiation that would be released as a result.
The 1,479 spent fuel rod assemblies there include 548 that were removed from the reactor only in November and December to prepare the reactor for maintenance, and these may be emitting more heat than the older assemblies in other storage pools.
Even without recirculating water, it should take many days for the water in a storage pool to evaporate, nuclear engineers said. So the rapid evaporation and even boiling of water in the storage pools now is a mystery, raising the question of whether the pools may also be leaking.
Michael Friedlander, a former senior nuclear power plant operator who worked 13 years at three American reactors, said that storage pools typically had a liner of stainless steel three-eighths of an inch thick, and that they rested on reinforced concrete bases. So even if the liner ruptured, “unless the concrete was torn apart, there’s no place for the water to go,” he said.
Mr. Lahey said that much of the water may have sloshed out during the earthquake. Much smaller earthquakes in California have produced heavy water losses from sloshing at storage pools there, partly because the pools are located high in reactor buildings.
“It’s like being at the top of a flagpole, and once you start ground motion, you can easily slosh it,” he said.
When the water in a storage pool disappears, the fuel rods’ uranium continues to heat the rods’ zirconium cladding. This causes the zirconium to oxidize, or rust, and even catch fire. The spent fuel rods have little radioactive iodine, which has a half-life of eight days and has mostly disappeared through radioactive decay once fission stopped when the rods left the reactor cores. But the spent fuel rods are still loaded with cesium and strontium that can start to escape if the fuel rods burn.
One factor that might determine how serious the situation becomes is whether the uranium oxide pellets in the rods stay vertical even if the cladding burns off. This is possible because pellets sometimes become fused together while in the reactor. If the pellets stay standing up, then even with the water and zirconium gone, nuclear fission will not take place, Mr. Albrecht said.
But Tokyo Electric said this week that there was a chance of “recriticality” in the storage pools — that is, the uranium in the fuel rods could resume the fission that previously took place inside the reactor, spewing out radioactive byproducts.
Mr. Albrecht said this was very unlikely, but could happen if the stacks of pellets slumped over and became jumbled together on the floor of the storage pool.
Plant workers would then need to add water with lots of boron because the boron absorbs neutrons and interrupts nuclear chain reactions.
If a lot of fission occurs, which may happen only in an extreme case, the uranium would melt through anything underneath it. If it encounters water as it descends, a steam explosion could then scatter the molten uranium.
At Daiichi, each assembly has either 64 large fuel rods or 81 slightly smaller fuel rods. A typical fuel rod assembly has roughly 380 pounds of uranium.
One big worry for Japanese officials is that Reactor No. 3, the main target of the helicopters and water cannons on Thursday, uses a new and different fuel. It uses mixed oxides, or mox, which contains a mixture of uranium and plutonium, and can produce a more dangerous radioactive plume if scattered by fire or explosions. According to Tokyo Electric, 32 of the 514 fuel rod assemblies in the storage pond at Reactor No. 3 contain mox.
Japan had hoped to solve the spent fuel buildup with a large-scale plan to recycle the rods into fuel that would go back into its nuclear program. But even before Friday’s quake, that plan had hit setbacks.
Central to Japan’s plans is a $28 billion reprocessing facility in Rokkasho village, north of the quake zone, which would extract uranium and plutonium from the rods for use in making mox fuel. After countless construction delays, test runs began in 2006, and the plant’s operator, Japan Nuclear Fuel, said operations would begin in 2010. But in late 2010, its opening was delayed by two years.
To close the nuclear fuel recycling process, Japan also built the Monju, a fast breeder reactor, which started running in full in 1994. But a year later, a fire caused by a sodium leak shut down the plant.
Despite revelations that the operator, the quasi-governmental Japan Atomic Energy Agency, had covered up the seriousness of the accident, Monju again started operating at a reduced capacity.
Another nuclear reprocessing facility in Tokaimura has been shut down since 1999, when an accident at an experimental fast breeder showered hundreds in the vicinity with radiation, and two workers were killed.
Many of these facilities were hit by Friday’s earthquake. A spent fuel pool at Rokkasho spilled over, and power at the plant was lost, triggering backup generators, Japan Nuclear Fuel said.
According to the Citizens Nuclear Information Center, an anti-nuclear group, about 3,000 tons of fuel are stored at Rokkasho. But the plant, about 180 feet above sea level, escaped the tsunami. Grid power was restored on Monday, the company said.
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Japan Offers Little Response to U.S. Assessment
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By KEITH BRADSHER and HIROKO TABUCHI
Years of procrastination in deciding on long-term disposal of highly radioactive fuel rods from nuclear reactors are now coming back to haunt Japanese authorities as they try to control fires and explosions at the stricken Fukushima Daiichi Nuclear Power Station.
Some countries have tried to limit the number of spent fuel rods that accumulate at nuclear power plants: Germany stores them in costly casks, for example, while China sends them to a desert storage compound in the western province of Gansu. But Japan, like the United States, has kept ever-larger numbers of spent fuel rods in temporary storage pools at the power plants, where they can be guarded with the same security provided for the plants.
Figures provided by Tokyo Electric Power on Thursday show that most of the dangerous uranium at the power plant is actually in the spent fuel rods, not the reactor cores themselves.
The electric utility said that a total of 11,125 spent fuel rod assemblies were stored at the site. That is about four times as much radioactive material as in the reactor cores combined.
Now those temporary pools are proving the power plant’s Achilles’ heel, with the water in the pools either boiling away or leaking out of their containments, and efforts to add more water having gone awry. While spent fuel rods generate significantly less heat than newer ones do, there are strong indications that some fuel rods have begun to melt and release extremely high levels of radiation. Japanese workers struggled on Thursday to add more water to the storage pool at Reactor No. 3.
Helicopters dropped water, only to have it scattered by strong breezes. Water cannons mounted on police trucks — equipment designed to disperse rioters — were then deployed to spray water on the pools. It is unclear if that effort worked.
Richard T. Lahey Jr., a retired nuclear engineer who oversaw General Electric’s safety research in the early 1970s for the kind of nuclear reactors used in Fukushima, said that the zirconium cladding on the fuel rods could burst into flames if exposed to air for hours when a storage pool lost its water.
Zirconium, once ignited, burns extremely hot and is difficult to extinguish, added Mr. Lahey, who helped write a classified report for the United States government several years ago on the vulnerabilities of storage pools at American nuclear reactors.
Very high levels of radiation above the storage pools suggest that the water has drained in the 39-foot-deep pools to the point that the 13-foot-high fuel rod assemblies have been exposed to air for hours and are starting to melt, said Robert Albrecht, a longtime nuclear engineer who worked as a consultant to the Japanese nuclear reactor manufacturing industry in the 1980s. Under normal conditions, the rods are kept covered with 26 feet of water that is circulated to prevent it from growing too warm.
Gregory Jaczko, the chairman of the United States Nuclear Regulatory Commission, made the startling assertion on Wednesday that there was little or no water left in another storage pool, the one on top of Reactor No. 4, and expressed grave concern about the radiation that would be released as a result.
The 1,479 spent fuel rod assemblies there include 548 that were removed from the reactor only in November and December to prepare the reactor for maintenance, and these may be emitting more heat than the older assemblies in other storage pools.
Even without recirculating water, it should take many days for the water in a storage pool to evaporate, nuclear engineers said. So the rapid evaporation and even boiling of water in the storage pools now is a mystery, raising the question of whether the pools may also be leaking.
Michael Friedlander, a former senior nuclear power plant operator who worked 13 years at three American reactors, said that storage pools typically had a liner of stainless steel three-eighths of an inch thick, and that they rested on reinforced concrete bases. So even if the liner ruptured, “unless the concrete was torn apart, there’s no place for the water to go,” he said.
Mr. Lahey said that much of the water may have sloshed out during the earthquake. Much smaller earthquakes in California have produced heavy water losses from sloshing at storage pools there, partly because the pools are located high in reactor buildings.
“It’s like being at the top of a flagpole, and once you start ground motion, you can easily slosh it,” he said.
When the water in a storage pool disappears, the fuel rods’ uranium continues to heat the rods’ zirconium cladding. This causes the zirconium to oxidize, or rust, and even catch fire. The spent fuel rods have little radioactive iodine, which has a half-life of eight days and has mostly disappeared through radioactive decay once fission stopped when the rods left the reactor cores. But the spent fuel rods are still loaded with cesium and strontium that can start to escape if the fuel rods burn.
One factor that might determine how serious the situation becomes is whether the uranium oxide pellets in the rods stay vertical even if the cladding burns off. This is possible because pellets sometimes become fused together while in the reactor. If the pellets stay standing up, then even with the water and zirconium gone, nuclear fission will not take place, Mr. Albrecht said.
But Tokyo Electric said this week that there was a chance of “recriticality” in the storage pools — that is, the uranium in the fuel rods could resume the fission that previously took place inside the reactor, spewing out radioactive byproducts.
Mr. Albrecht said this was very unlikely, but could happen if the stacks of pellets slumped over and became jumbled together on the floor of the storage pool.
Plant workers would then need to add water with lots of boron because the boron absorbs neutrons and interrupts nuclear chain reactions.
If a lot of fission occurs, which may happen only in an extreme case, the uranium would melt through anything underneath it. If it encounters water as it descends, a steam explosion could then scatter the molten uranium.
At Daiichi, each assembly has either 64 large fuel rods or 81 slightly smaller fuel rods. A typical fuel rod assembly has roughly 380 pounds of uranium.
One big worry for Japanese officials is that Reactor No. 3, the main target of the helicopters and water cannons on Thursday, uses a new and different fuel. It uses mixed oxides, or mox, which contains a mixture of uranium and plutonium, and can produce a more dangerous radioactive plume if scattered by fire or explosions. According to Tokyo Electric, 32 of the 514 fuel rod assemblies in the storage pond at Reactor No. 3 contain mox.
Japan had hoped to solve the spent fuel buildup with a large-scale plan to recycle the rods into fuel that would go back into its nuclear program. But even before Friday’s quake, that plan had hit setbacks.
Central to Japan’s plans is a $28 billion reprocessing facility in Rokkasho village, north of the quake zone, which would extract uranium and plutonium from the rods for use in making mox fuel. After countless construction delays, test runs began in 2006, and the plant’s operator, Japan Nuclear Fuel, said operations would begin in 2010. But in late 2010, its opening was delayed by two years.
To close the nuclear fuel recycling process, Japan also built the Monju, a fast breeder reactor, which started running in full in 1994. But a year later, a fire caused by a sodium leak shut down the plant.
Despite revelations that the operator, the quasi-governmental Japan Atomic Energy Agency, had covered up the seriousness of the accident, Monju again started operating at a reduced capacity.
Another nuclear reprocessing facility in Tokaimura has been shut down since 1999, when an accident at an experimental fast breeder showered hundreds in the vicinity with radiation, and two workers were killed.
Many of these facilities were hit by Friday’s earthquake. A spent fuel pool at Rokkasho spilled over, and power at the plant was lost, triggering backup generators, Japan Nuclear Fuel said.
According to the Citizens Nuclear Information Center, an anti-nuclear group, about 3,000 tons of fuel are stored at Rokkasho. But the plant, about 180 feet above sea level, escaped the tsunami. Grid power was restored on Monday, the company said.
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18/03 福島原発：綱渡りの放水作戦 被ばく基準、急きょ変更
白煙を上げて崩れ落ちている福島第１原発３号機原子炉建屋＝２０１１年３月１６日、東京電力提供 東京電力福島第１原発の冷却機能回復を目指し、沸騰がやまない使用済み核燃料プールへの官民を挙げた注水作戦が１７日、展開された。周囲の放射線量が依然高い数値を示す中、午前には陸上自衛隊がヘリで上空から３号機に海水を投下し、夜は警視庁や自衛隊が地上から放水車で水を注いだ。しかし、警視庁の試みは奏功せず、放射線量の許容基準を緩めてまで実施した自衛隊のオペレーションも効果は限られる。東電による外部電源回復作業も本格化したが、未知の冷却作業はノウハウも乏しく、綱渡りの作戦が続く。【犬飼直幸、坂口裕彦、念佛明奈、八田浩輔】
◇首相「自衛隊が最後のとりで」
１７日夕。首相官邸であった緊急災害対策本部の席上、菅直人首相は午前に決行された自衛隊ヘリによる注水を踏まえ「危険な中での作戦遂行で、隊員はじめ自衛隊の皆さんには心から感謝申し上げます」と、自衛隊の最高指揮官らしからぬ低姿勢で謝辞を述べた。
一方、北沢俊美防衛相は同日午後の省内の災害対策本部で、午後は地上から放水する方針を示したうえで、「何とか危険な状態を緩和していきたい。昼に官邸に行き、首相との緊密な連携について話をした」と、被ばくの危険を伴う「命がけの放水作戦」は首相の指示を直接受けて進めていることを強調した。
東日本大震災の発生後、東電が同原発の情報を十分伝えてこないなかで、自衛隊内には危険な作業を強いられることへの不信感が募っていた。１４日に３号機で起きた爆発で給水作業中の隊員４人が負傷した後、いったんは同原発から退避した。
しかし、１５日未明、政府と東電の統合連絡本部が東電本店に設置され、政府主導の形に仕切り直されたことで、「有事」対応で自衛隊が前面に出るようになった。首相は北沢氏に「自衛隊が最後のとりでだ」と覚悟を迫り、北沢氏は１６日の記者会見で「最後に国民の命を守らなければならないのは自衛隊の任務。ぎりぎりのところで任務を遂行する決意は固めている」と応じてみせた。
上空からの海水投下は１６日、任務にあたる自衛隊員個人の累積被ばく総量限度（５０ミリシーベルト）を大幅に上回る放射線が観測されたため、ヘリを飛ばした後に見送られた。それが１７日は限度値を一気に１００ミリシーベルトまで緩め、投下に踏み切った。
防衛省は国家公務員を対象に１００ミリシーベルトと定めた人事院規則を準用したと説明した。その規則も１７日付で、同原発に原子力緊急事態宣言が発令されている期間に限り、２５０ミリシーベルトへと緩和された。
駆け込みで引き上げられた限度値に、自衛隊内からは「周知されたことがない数値だ」と戸惑う声も漏れ、陸上自衛隊の火箱芳文幕僚長は「明確に方針として示されたわけでもない」と語るなど、混乱ぶりも露呈した。北沢氏は会見で「（１７日も）状況が変わっていないのにどうして投下したかと言えば、首相と私の重い決断を統幕長が判断していただいた」と述べ、「作戦実施ありき」の政治決断だったことを認めた。
自衛隊は隊員の被ばくリスクを軽減するため、３号機に海水を投下する大型輸送ヘリＣＨ４７Ｊの床には放射線をさえぎるタングステンを敷き詰め、乗員は防護服とガスマスクに身を包んだ。１７日午前の３号機を狙った４回の海水投下では結果的に周辺にも水が散り、警視庁の放水車や自衛隊の高圧消防車が現場に近づくための「除染」の役割も果たした。
地上からの放水には、航空自衛隊百里基地（茨城県小美玉市）に配備され、航空機火災を泡で包み込んで消火する機能を持つＡ－ＭＢ－３などの高圧消防車５台を投入、隊員約３０人は防護服を着て車内で作業した。
これだけ危険を冒しても、冷却効果が見通せないことへのいら立ちも募る。自衛隊幹部は１７日夜、「きちんと任務を終えて無事に戻ってきて本当に良かった。効果のほどは分からないが……」とつぶやいた。東電への不信感もなお強く、１７日午後の省内の会議では「放射線の情報が東電から十分提供されていない」として、統合連絡本部に改善を求めることになった。
◇電源復旧へ 東電職員３０人作業
一方、２号機の電源復旧作業は１７日午前から、東電職員ら３０人の手で始まった。被ばく人数を抑えるため、平時より少ない態勢だ。
非常用電源が失われた１～４号機のうち、唯一配電盤が水没しなかった２号機の電気系統回復が頼みの綱。作業では放射線量の比較的低い海側に変電盤を仮設し、建屋の各機器などと接続していった。担当者は「少ない工事量で復帰するよう計画している。（電源復旧の）実現性はかなり高い」と強調する。
ただし、電源復旧は原子炉冷却のための入り口に過ぎない。まずは海水を送り込むポンプの作動試験をする必要があるが、１６日夕には東京・内幸町の本店との連絡回線を切断するミスも起きた。７時間後の復旧までの間、水位計などのデータのやり取りは衛星携帯での通話でしのいだ。
東電は２号機との間の回線が生きている１号機も、近く電源復旧が可能とみる。しかし、３、４号機は新たな外部電源をひく必要があり、復旧には時間がかかる見通し。また、使用済み核燃料プールの水温が上昇している５、６号機では、５号機の非常用電源が機能していない。６号機の電源を５号機につないでいるものの、東電は「この状態が長く続けば１～４号機のように温度が上昇する」と焦燥感を募らせる。
◇電源復旧までつなぎ
東京電力福島第１原発３号機への放水は、低下しているとみられる使用済み核燃料プールの水位の回復は期待できず、むしろ外部電源復旧後の本格的な注水をにらんだ「つなぎ」の要素が濃い。
この日、陸上自衛隊のヘリから投下された海水は最大で約３０トン。地上からは、警視庁の高圧放水車と陸海空自衛隊の高圧消防車から計７０トンが放水され、最大で約１００トンになる。どの程度がプールに入ったかは不明だが、仮に全部入れば、１２００立方メートル（１２００トン）のプールの水位が１メートル高くなる計算だ。
３号機では１６日以降、プールの水位が下がって燃料棒の一部が露出しているとみられる。この状態が続くと、燃料棒の被覆管が劣化し、放射性物質が出やすくなる。空と陸からの放水は、政府と東電のひねり出した「窮余の策」だ。
放水でプールの水位が回復できなくても、水滴が燃料棒にかかるだけで熱を奪って蒸発するため、燃料棒を冷やす効果が期待できる。この仕組みは、真夏に水をまいて涼を取る「打ち水」と基本的に同じだ。プールから立ち上った水蒸気に含まれた水滴も、同様に燃料棒を冷やしていく。
効果について、経済産業省原子力安全・保安院は「今後の結果を見て判断したい」とし、東電はヘリによる水の投下後、水蒸気が上がり「冷却効果があった」としている。奈良林直（ただし）・北海道大教授（原子炉工学）は「ヘリを使って消防車のホースの先端をプール内に落とすなど、より効率的な方法を検討してほしい」と話した。【須田桃子】
【関連記事】
【動画でみる】東京電力が撮影した福島第１原発
【被爆を最小限に抑えるには】
【被災地サポート情報一覧】
【最新の地震関連ニュース一覧】
東日本大震災:福島原発事故、各国警戒 退避勧告も続々
毎日新聞 2011年3月17日 20時55分（最終更新 3月18日 0時47分）
◇首相「自衛隊が最後のとりで」
１７日夕。首相官邸であった緊急災害対策本部の席上、菅直人首相は午前に決行された自衛隊ヘリによる注水を踏まえ「危険な中での作戦遂行で、隊員はじめ自衛隊の皆さんには心から感謝申し上げます」と、自衛隊の最高指揮官らしからぬ低姿勢で謝辞を述べた。
一方、北沢俊美防衛相は同日午後の省内の災害対策本部で、午後は地上から放水する方針を示したうえで、「何とか危険な状態を緩和していきたい。昼に官邸に行き、首相との緊密な連携について話をした」と、被ばくの危険を伴う「命がけの放水作戦」は首相の指示を直接受けて進めていることを強調した。
東日本大震災の発生後、東電が同原発の情報を十分伝えてこないなかで、自衛隊内には危険な作業を強いられることへの不信感が募っていた。１４日に３号機で起きた爆発で給水作業中の隊員４人が負傷した後、いったんは同原発から退避した。
しかし、１５日未明、政府と東電の統合連絡本部が東電本店に設置され、政府主導の形に仕切り直されたことで、「有事」対応で自衛隊が前面に出るようになった。首相は北沢氏に「自衛隊が最後のとりでだ」と覚悟を迫り、北沢氏は１６日の記者会見で「最後に国民の命を守らなければならないのは自衛隊の任務。ぎりぎりのところで任務を遂行する決意は固めている」と応じてみせた。
上空からの海水投下は１６日、任務にあたる自衛隊員個人の累積被ばく総量限度（５０ミリシーベルト）を大幅に上回る放射線が観測されたため、ヘリを飛ばした後に見送られた。それが１７日は限度値を一気に１００ミリシーベルトまで緩め、投下に踏み切った。
防衛省は国家公務員を対象に１００ミリシーベルトと定めた人事院規則を準用したと説明した。その規則も１７日付で、同原発に原子力緊急事態宣言が発令されている期間に限り、２５０ミリシーベルトへと緩和された。
駆け込みで引き上げられた限度値に、自衛隊内からは「周知されたことがない数値だ」と戸惑う声も漏れ、陸上自衛隊の火箱芳文幕僚長は「明確に方針として示されたわけでもない」と語るなど、混乱ぶりも露呈した。北沢氏は会見で「（１７日も）状況が変わっていないのにどうして投下したかと言えば、首相と私の重い決断を統幕長が判断していただいた」と述べ、「作戦実施ありき」の政治決断だったことを認めた。
自衛隊は隊員の被ばくリスクを軽減するため、３号機に海水を投下する大型輸送ヘリＣＨ４７Ｊの床には放射線をさえぎるタングステンを敷き詰め、乗員は防護服とガスマスクに身を包んだ。１７日午前の３号機を狙った４回の海水投下では結果的に周辺にも水が散り、警視庁の放水車や自衛隊の高圧消防車が現場に近づくための「除染」の役割も果たした。
地上からの放水には、航空自衛隊百里基地（茨城県小美玉市）に配備され、航空機火災を泡で包み込んで消火する機能を持つＡ－ＭＢ－３などの高圧消防車５台を投入、隊員約３０人は防護服を着て車内で作業した。
これだけ危険を冒しても、冷却効果が見通せないことへのいら立ちも募る。自衛隊幹部は１７日夜、「きちんと任務を終えて無事に戻ってきて本当に良かった。効果のほどは分からないが……」とつぶやいた。東電への不信感もなお強く、１７日午後の省内の会議では「放射線の情報が東電から十分提供されていない」として、統合連絡本部に改善を求めることになった。
◇電源復旧へ 東電職員３０人作業
一方、２号機の電源復旧作業は１７日午前から、東電職員ら３０人の手で始まった。被ばく人数を抑えるため、平時より少ない態勢だ。
非常用電源が失われた１～４号機のうち、唯一配電盤が水没しなかった２号機の電気系統回復が頼みの綱。作業では放射線量の比較的低い海側に変電盤を仮設し、建屋の各機器などと接続していった。担当者は「少ない工事量で復帰するよう計画している。（電源復旧の）実現性はかなり高い」と強調する。
ただし、電源復旧は原子炉冷却のための入り口に過ぎない。まずは海水を送り込むポンプの作動試験をする必要があるが、１６日夕には東京・内幸町の本店との連絡回線を切断するミスも起きた。７時間後の復旧までの間、水位計などのデータのやり取りは衛星携帯での通話でしのいだ。
東電は２号機との間の回線が生きている１号機も、近く電源復旧が可能とみる。しかし、３、４号機は新たな外部電源をひく必要があり、復旧には時間がかかる見通し。また、使用済み核燃料プールの水温が上昇している５、６号機では、５号機の非常用電源が機能していない。６号機の電源を５号機につないでいるものの、東電は「この状態が長く続けば１～４号機のように温度が上昇する」と焦燥感を募らせる。
◇電源復旧までつなぎ
東京電力福島第１原発３号機への放水は、低下しているとみられる使用済み核燃料プールの水位の回復は期待できず、むしろ外部電源復旧後の本格的な注水をにらんだ「つなぎ」の要素が濃い。
この日、陸上自衛隊のヘリから投下された海水は最大で約３０トン。地上からは、警視庁の高圧放水車と陸海空自衛隊の高圧消防車から計７０トンが放水され、最大で約１００トンになる。どの程度がプールに入ったかは不明だが、仮に全部入れば、１２００立方メートル（１２００トン）のプールの水位が１メートル高くなる計算だ。
３号機では１６日以降、プールの水位が下がって燃料棒の一部が露出しているとみられる。この状態が続くと、燃料棒の被覆管が劣化し、放射性物質が出やすくなる。空と陸からの放水は、政府と東電のひねり出した「窮余の策」だ。
放水でプールの水位が回復できなくても、水滴が燃料棒にかかるだけで熱を奪って蒸発するため、燃料棒を冷やす効果が期待できる。この仕組みは、真夏に水をまいて涼を取る「打ち水」と基本的に同じだ。プールから立ち上った水蒸気に含まれた水滴も、同様に燃料棒を冷やしていく。
効果について、経済産業省原子力安全・保安院は「今後の結果を見て判断したい」とし、東電はヘリによる水の投下後、水蒸気が上がり「冷却効果があった」としている。奈良林直（ただし）・北海道大教授（原子炉工学）は「ヘリを使って消防車のホースの先端をプール内に落とすなど、より効率的な方法を検討してほしい」と話した。【須田桃子】
【関連記事】
【動画でみる】東京電力が撮影した福島第１原発
【被爆を最小限に抑えるには】
【被災地サポート情報一覧】
【最新の地震関連ニュース一覧】
東日本大震災:福島原発事故、各国警戒 退避勧告も続々
毎日新聞 2011年3月17日 20時55分（最終更新 3月18日 0時47分）
18/03 電力館（東京・渋谷）における空気中の放射線量の状況について
（３月18日 10時現在）
東京（渋谷）の電力館に設置しているモニタリングポストにおいて、空気中の放射線量を測定しております。下表にて、同モニタリングポストのデータを表示しています。引き続き、測定結果についてお知らせしてまいります。
○放射線の単位について
グレイ（Ｇｙ）は、放射線が物質に当たったとき、そのエネルギーが物質にどれだけ吸収されたかを表す単位で、シーベルト（Ｓｖ）は人体が放射線を受けたとき、その影響の度合いを表す単位です。人体への放射線の影響を評価する際はシーベルト（Ｓｖ）を用います。
※下記のとおり換算します。
１ｎＧｙ／ｈ（ナノグレイ／毎時）
≒１nＳｖ／ｈ（ナノシーベルト／毎時）
＝0.001μＳｖ／ｈ（マイクロシーベルト／毎時）
＝0.000001ｍＳｖ／ｈ（ミリシーベルト／毎時）
（PDF） 下表１ 「１時間毎の屋外線量率最大値(ｎＧｙ／ｈ)」
（PDF） 下表２ 「毎日の屋外線量率最大値および最小値(ｎＧｙ／ｈ)」
日常生活と放射線
東京（渋谷）の電力館に設置しているモニタリングポストにおいて、空気中の放射線量を測定しております。下表にて、同モニタリングポストのデータを表示しています。引き続き、測定結果についてお知らせしてまいります。
○放射線の単位について
グレイ（Ｇｙ）は、放射線が物質に当たったとき、そのエネルギーが物質にどれだけ吸収されたかを表す単位で、シーベルト（Ｓｖ）は人体が放射線を受けたとき、その影響の度合いを表す単位です。人体への放射線の影響を評価する際はシーベルト（Ｓｖ）を用います。
※下記のとおり換算します。
１ｎＧｙ／ｈ（ナノグレイ／毎時）
≒１nＳｖ／ｈ（ナノシーベルト／毎時）
＝0.001μＳｖ／ｈ（マイクロシーベルト／毎時）
＝0.000001ｍＳｖ／ｈ（ミリシーベルト／毎時）
（PDF） 下表１ 「１時間毎の屋外線量率最大値(ｎＧｙ／ｈ)」
（PDF） 下表２ 「毎日の屋外線量率最大値および最小値(ｎＧｙ／ｈ)」
日常生活と放射線
17/03 「夕から夜、予測不能の大規模停電の恐れ」 経産相
2011年3月17日14時16分
海江田万里経済産業相は１７日午後、計画停電中の電力使用について「これまで以上の精いっぱいの節電にご協力をお願いします」と、産業界や国民に呼びかける大臣談話を発表した。
東京電力が電力を送る関東とその周辺地域では、３３５０万キロワットの電力供給力に対し、午前８～９時に最大３２９２万キロワットの需要が発生。海江田氏は「１日のピークを迎える夕方から夜にかけて需要量が供給量を上回り、予測不能な大規模の停電が発生する恐れがある」と警戒を発した。１７日は気温が低く、暖房の使用が増加しているとみられる。
.
海江田万里経済産業相は１７日午後、計画停電中の電力使用について「これまで以上の精いっぱいの節電にご協力をお願いします」と、産業界や国民に呼びかける大臣談話を発表した。
東京電力が電力を送る関東とその周辺地域では、３３５０万キロワットの電力供給力に対し、午前８～９時に最大３２９２万キロワットの需要が発生。海江田氏は「１日のピークを迎える夕方から夜にかけて需要量が供給量を上回り、予測不能な大規模の停電が発生する恐れがある」と警戒を発した。１７日は気温が低く、暖房の使用が増加しているとみられる。
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Wednesday, March 16, 2011
15/03 Japan Says 2nd Reactor May Have Ruptured With Radioactive Release
DigitalGlobe, via ReutersWorkers are struggling at the Fukushima Daiichi plant, seen in a satellite photo at 9:35 a.m. Wednesday.
March 15, 2011
By HIROKO TABUCHI and KEITH BRADSHER
TOKYO — Japan’s nuclear crisis intensified again Wednesday, with Japanese authorities announcing that a containment vessel in a second reactor unit at the stricken Fukushima Daiichi plant in northeastern Japan may have ruptured and appeared to be releasing radioactive steam. That would be the second vessel to be compromised in two days.
The vessel had appeared to be the last fully intact line of defense against large-scale releases of radioactive materials from that reactor, but it was not clear how serious the possible breach might be.
The announcement came after Japanese broadcasters showed live footage of thick plumes of steam rising above the plant.
Yukio Edano, the chief cabinet secretary, said the government believed the steam was coming from the No. 3 reactor, where an explosion on Monday blew out part of the building surrounding the containment vessel.
The reactor has three layers of protection: that building; the containment vessel, and the metal cladding around fuel rods, which are inside the reactor. The government has said that those rods at the No. 3 reactor were likely already damaged.
A spike in radiation levels at the plant as the steam was rising forced some of the relatively few workers left at the plant to retreat indoors, suspending some critical efforts to pump water into several reactors to keep them cool.
Earlier in the morning, the company that runs the plant reported that a fire was burning at a different reactor, just hours after officials said flames that erupted Tuesday had been doused.
A government official at Japan’s nuclear regulatory agency soon after said that flames and smoke were no longer visible, but he cautioned that it was unclear if the fire, at the Reactor No. 4 building, had died out. He also was not clear if it was a new fire or if the fire Tuesday had never gone out.
There are a total of six reactors at the plant.
The developments are troubling reminders of the difficulties the company is having in bringing the plant, which has suffered multiple explosions since Saturday, under control. And the confusion is emblematic of days of often contradictory reports about what is happening at the plant.
The company, Tokyo Electric Power, says it cannot know for sure what is happening in many cases because it is too dangerous for workers to get close to some reactors.
The situation became especially dire on Tuesday, when releases of radiation led the company to pull most of its workers from the plant.
Among the authorities’ main concerns are pools for spent fuel rods at several reactors at the plant, including Reactor No. 4, where the pool has lost some of the water needed to keep the fuel rods stable. The rods are still radioactive and potentially as hot and dangerous as the fuel rods inside the reactors.
Minoru Ogoda, the official with Japan’s nuclear regulatory agency, said a proposed plan to use helicopters to put more cold water into the pool was looking unlikely.
The hole or holes in the roof caused by an earlier blast did not appear big enough to allow sufficient amounts of water in, he said.
He said Tokyo Electric would probably try to spray water into the reactor building through a gaping hole in the wall blasted open by the explosion.
That explosion on Tuesday was caused by hydrogen gas bubbling up from chemical reactions set off by the fuel rods in the pool, Japanese officials said. Inspectors from the United States Nuclear Regulatory Commission said they had been told by Japanese authorities that what was burning was lubricating oil from machinery near the pool.
Concern remained high about the storage pools at two other reactors, Nos. 5 and 6. None of those three reactors at the plant, 140 miles northeast of Tokyo, were operating on Friday afternoon when an offshore earthquake with a magnitude now estimated at 9.0 shook the site. A tsunami rolled into the northeast Japanese coastline minutes later, swamping the plant.
At least 750 workers were evacuated on Tuesday morning after a separate explosion ruptured the inner containment building at Reactor No. 2 at the Daiichi plant, which was crippled by Friday’s earthquake and tsunami. The closely spaced but apparently coincidental explosions at Reactors Nos. 2 and 4 together released a surge of radiation 800 times as intense as the recommended hourly exposure limit in Japan.
But 50 workers stayed behind, a crew no larger than would be stationed at the plant on a quiet spring day. Taking shelter when possible in the reactor’s control room, which is heavily shielded from radiation, they struggled through the morning and afternoon to keep hundreds of gallons of seawater a minute flowing through temporary fire pumps into the three stricken reactors, Nos. 1, 2 and 3, where overheated fuel rods continued to boil away the water at a brisk pace.
By early afternoon radiation levels had plunged, according to the International Atomic Energy Agency. Workers have released surges of radiation each time they bleed radioactive steam from the troubled reactors in an attempt to manage the pressure inside them, but the reactors are not yet releasing high levels of radiation on a sustained basis, Japanese officials said.
The United States military revised its plans as radiation from the plant worsened. Some American warships that had been expected to arrive at the tsunami-shattered northeast coast of Honshu Island were diverted to the west coast instead because of concerns about radiation, the Navy said.
The Navy also promised to continue relief missions even though several more helicopter crews were testing positive for low-level exposure to radiation, and even as American military personnel and their families at the Yokosuka and Atsugi bases were encouraged to take precautions against radiation exposure.
Late Tuesday morning, Prime Minister Naoto Kan warned in a nationally televised address of rising radiation.
Mr. Edano, the chief cabinet secretary, urged people who live within about 18 miles of the plant to take precautions. “Please do not go outside, please stay indoors, please close windows and make your homes airtight,” he said. Yukiya Amano, the director general of the International Atomic Energy Agency, said at the organization’s Vienna headquarters that there was a “possibility of core damage” at reactor No. 2, but that the damage “is estimated to be less than 5 percent of the fuel.”
The sudden turn of events, after an explosion on Monday at one reactor and then an early-morning explosion on Tuesday at yet another — the third in four days at the plant — had already made the crisis at the plant the worst nuclear accident since the Chernobyl reactor disaster a quarter-century ago. It had become impossible for workers to remain at many areas within the plant for extended periods, the agency said. In Tokyo, the metropolitan government said Tuesday that it had detected radiation levels 20 times above normal over the city, though it stressed that such levels posed no immediate health threat and that readings had dropped since then. The explosion in Reactor No. 2, a little after 6 a.m. on Tuesday, particularly alarmed Japanese officials and nuclear power experts around the world because it was the first detonation at the plant that appeared to occur inside one of the primary containment vessels.
Those buildings are fortresslike structures of steel and reinforced concrete, designed to absorb the impact of a plane crash and minimize radiation leaks. After a series of conflicting reports about how much damage the reactor had sustained after that blast, Mr. Edano said, “There is a very high probability that a portion of the containment vessel was damaged.”
Japanese officials subsequently said that the explosion had damaged a doughnut-shaped steel container of water, known as a torus, that surrounds the base of the reactor vessel inside the primary containment building.
Ruptures in the torus are serious, said Michael Friedlander, a senior nuclear power plant operator for 13 years at three plants in the United States, including three years at a General Electric boiling water reactor very similar to the ones in trouble in Japan. But the torus is not as important as the reactor vessel itself, which has 6.7-inch-thick steel walls and 8.4-inch-thick steel for its roof and floor. The vessel is designed to hold very high-pressure steam as well as the uranium fuel rods.
The reactor vessel has 20 safety valves that during a shutdown of the reactor inject steam into a million-gallon “suppression pool” of water in a steel torus immediately underneath it.
“Imagine if you had a big pressure cooker and you had a tube off the pressure cooker into a big tub of water — the suppression pool is the tub of water,” said Mr. Friedlander, a defender of nuclear power who is now a money manager in Hong Kong.
Steam vented into the suppression pool from the reactor vessel is not supposed to be radioactive. But it becomes radioactive, and potentially very radioactive, if the fuel rods in the reactor vessel above have begun to melt.
The atmosphere in the primary containment building, around the reactor vessel and above the suppression pool, is supposed to consist of inert nitrogen, with no oxygen at all. An inert atmosphere is used in the primary containment building to avoid the risk of oxygen explosions with hydrogen if the reactor starts producing much larger quantities of hydrogen gas than usual. Hydrogen gas is highly combustible with oxygen.
Hiroko Tabuchi reported from Tokyo, and Keith Bradsher from Hong Kong. David E. Sanger and Matthew L. Wald contributed reporting from Washington.
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