Showing posts with label Three Mile Island. Show all posts
Showing posts with label Three Mile Island. Show all posts

Tuesday, May 17, 2011

10/05福島第1原発:柳田邦男さん 政府対応の遅れ批判

 菅直人首相は10日、東京電力福島第1原発事故の原因などを究明する事故調査委員会を近く発足させることを表明した。一方、ノンフィクション作家の柳田邦男さんは首相会見に先立って同日開かれた参院経済産業委員会に参考人として出席し、「発生から2カ月が経過するのに、いまだに事故調査体制ができていないことは日本の特異な側面だ」と対応の遅れを批判した。

 さらに「米国のスリーマイル島原発事故では、大統領がすぐに特別調査委員会を作り、利害関係者を一切排除して調査した。それに対し、過去の日本の事故調査体制は企業や行政幹部ら利害関係者がメンバーになり、『被告が裁判官席についている』との批判も出た」と述べ、調査委の構成にも注文を付けた。【関東晋慈、中西拓司】

毎日新聞 2011年5月10日 22時07分(最終更新 5月10日 22時09分)

Tuesday, April 19, 2011

19/04 原発作業の恐怖「まるで宇宙空間」 スリーマイル経験者

写真:「ストレスは大変なものだった」。スリーマイル島原発の同僚作業員たちと記念につくったTシャツや当時の識別票を前に語るリチャード・レッシュさん=米ペンシルベニア州、田中写す拡大「ストレスは大変なものだった」。スリーマイル島原発の同僚作業員たちと記念につくったTシャツや当時の識別票を前に語るリチャード・レッシュさん=米ペンシルベニア州、田中写す

写真:スリーマイル島原発の放射能除去作業の際、リチャード・レッシュさんは防護服に身を包み、バルブ室に入った。インスタントカメラで撮った写真の日付は1980年6月13日とあった=本人提供拡大スリーマイル島原発の放射能除去作業の際、リチャード・レッシュさんは防護服に身を包み、バルブ室に入った。インスタントカメラで撮った写真の日付は1980年6月13日とあった=本人提供

写真:スリーマイル島原発は現在も稼働中だ。対岸には、32年前に事故があったことを伝える看板が立つ=米ペンシルベニア州ミドルタウン、田中写す拡大スリーマイル島原発は現在も稼働中だ。対岸には、32年前に事故があったことを伝える看板が立つ=米ペンシルベニア州ミドルタウン、田中写す

 収束の兆しが見えない福島第一原発事故。米国で最悪といわれる1979年のスリーマイル島原発事故をくぐり抜けた電力会社の作業員や住民にとっては、決してひとごとではない。32年前を振り返りながら、懸命に作業を続ける福島の人たちにエールを送る。

 「福島の作業員は、現代のサムライだ。彼らは、自らの寿命が縮まる恐怖を抱きながら、作業をしているはずだ」。米東部ペンシルベニア州のサスケハナ川の中州にあるスリーマイル島原発から車で2時間の自宅で、リチャード・レッシュさん(73)は「サムライ」という言葉を繰り返した。

 レッシュさんは当時、原発を運営していた電力会社の送電部門の作業員だった。原発の知識は全くなかったが、1週間の研修を受け、事故から約2カ月後の5月から原発施設の放射性物質の除去作業に入った。志願に基づいていたため、「給料は全然、変わらなかった」。年齢制限や家族構成などの条件もなかったという。

 放射能から身を守る防護服での作業は、困難を極めた。あらゆるつなぎ目をテープで保護するため、装着するのに40分ぐらいかかる。20キロ近い氷を入れたベストを付けたこともある。特殊なマスクでは、普通の8割ぐらいしか息ができない。視野も狭く、同僚作業員との会話もできない。

 そして、薄い防護服の外は見えない放射能で充満しているという恐怖が常につきまとい、自分の心臓の音が聞こえたように感じた。「まるで宇宙空間での作業だった」。嘔吐(おうと)して窒息しそうになったり、閉所恐怖症でパニックになったりした同僚もいた。「なんで俺はこんなことをしてるんだ」と何度も思った。

 被曝(ひばく)量を抑えるため、1回当たりの作業は最長でも30分程度に制限された。ただ、4週間作業して4週間休むというシフトが約2年間、続いたものの、どれだけ被曝したのか、会社から聞いたこともないし、その後の健康被害の調査も受けたことがない。「今さら、考えても仕方がない」

 幸い、いまのところ体に異変はないという。しかし、「我々の場合は、放射能で汚染された場所が限られていたが、福島は範囲が広いように見える。彼らの方が恐怖心は大きいはずだし、身体に影響が出るのではないか」と心配する。

 スリーマイル近くの住民も「福島」の行く末が心配でならない。25キロ離れた州都ハリスバーグで、市民団体のエリック・エプスタインさん(51)は、毎日、原発周辺の放射能を監視する。「スリーマイル、チェルノブイリ、そして福島に共通するのは、政府や電力会社からの情報は頼りにできないということだ。ここで再び事故があるとは思いたくないが、自ら、情報を入手する手段は持っておきたい」と話していた。

 スリーマイルはいまも稼働する。近くの対岸を訪れると、蒸気をはき出す二つの巨大な冷却塔の隣に、下部の鉄骨がむき出しになったままの冷却塔が二つ並んでいるのが見える。(米ペンシルベニア州ミドルタウン=田中光)

     ◇

 〈スリーマイル島原発事故〉1979年、ポンプ故障などで冷却水が失われ、炉心が溶融。8キロ以内の幼児と妊婦に避難、16キロ以内に屋内退避が勧告され、1週間余り後に解除された。放射性ヨウ素の放出は限定的で、住民の推定被曝量は健康影響が無視できる程度とされたが、炉心に相当の損傷があったため「レベル5」(施設外へのリスクを伴う事故)と認定された。

Thursday, April 14, 2011

14/04 Nuclear accident's rating of 7 demands calm response

The Yomiuri Shimbun

The Nuclear and Industrial Safety Agency on Tuesday raised the provisional severity level of the nuclear accident at the Fukushima No. 1 nuclear power plant to the worst rating of seven on the International Nuclear Event Scale (INES), up from the previous level of 5.

The only other nuclear crisis to have been rated level 7 was the 1986 Chernobyl accident in the former Soviet Union. The latest rating reflects the seriousness of the Fukushima plant accident that was caused by the March 11 Great East Japan Earthquake and subsequent tsunami.

The government and Tokyo Electric Power Co., the operator of the nuclear plant, must work harder to bring the situation under control.

The INES assessment is based on the amount of radioactive material emitted, the estimated damage to nuclear reactors and other factors.

The agency, which is under the Economy, Trade and Industry Ministry, calculated the amount of radioactive substances emitted after explosions at buildings of the Fukushima plant's Nos. 1 to 3 reactors and the other events based on radiation levels monitored around the plant. The agency estimated the amount of radiation released so far to be second only to that emitted during the Chernobyl accident.

The crippled Fukushima plant has released far more radiation than the 1979 accident at the Three Mile Island nuclear power plant in the United States.

===

Not the same as Chernobyl

However, the amount of radioactive material released so far is equal to only about 10 percent of that released in the Chernobyl accident.

Explosive nuclear reactions in Chernobyl destroyed the reactor and set off a fire. A huge amount of radioactive material spread over vast swathes of Europe and far beyond for about 10 days.

In the Fukushima accident, nuclear reactions were stopped immediately after the powerful earthquake. Most functions of the reactors have been maintained and nuclear fuel is being cooled by emergency injections of water into the reactors. The amount of radioactive substances being emitted into the atmosphere has fallen compared with just after the explosions.

The government should carefully explain the vital differences between the Chernobyl and Fukushima Prefecture accidents to prevent public anxiety from spreading and to control damage that could be whipped up by groundless rumors.

Work to restore cooling functions at the Fukushima plant's reactors, however, is proceeding with difficulty. This leaves the possibility that the reactors could sustain further serious damage and a massive amount of radioactive material could be released into the air.

However, temperatures at the reactors are now under control. It seems the worst is apparently over in this regard. The agency did not raise the provisional severity level of the accident because the situation is deteriorating.

===

Keep guard up against quakes

Meanwhile, aftershocks centered around the nuclear plant have been occurring with unnerving frequency. Tremors with a seismic intensity of 5 or more on the Japanese scale of 7 have often disrupted restoration work at the plant. It was frightening to hear that cooling systems of the reactors lost power for about 50 minutes following a strong aftershock Monday.

Aftershocks are expected to continue for a while yet. We urge the government and TEPCO to do everything they can to protect the reactors' cooling functions from being affected by these temblors.

A huge amount of radioactive substances has been released into the environment. It will become increasingly important to determine which areas have been contaminated with radiation and to minimize any negative health impacts on people living there. The government must take necessary countermeasures as soon as possible.

(From The Yomiuri Shimbun, April 13, 2011)

(Apr. 14, 2011)

Wednesday, April 13, 2011

13/04 IAEA「チェルノブイリと全く異なる」 福島第一事故

2011年4月13日10時24分

 国際原子力機関(IAEA)のフローリー事務次長は12日、日本政府が福島第一原発事故を国際評価尺度(INES)で最悪のレベル7に引き上げたことを受けてウィーン本部で記者会見し、1986年の旧ソ連・チェルノブイリ原発事故とレベルは同じでも、事故の構造や規模では「全く異なる」と述べた。

 フローリー氏は、チェルノブイリ事故では原子炉の試験運転中に大きな爆発が起きて放射性物質が広範囲に拡散したのに対し、福島第一原発事故は運転停止後に起き、原子炉の圧力容器の爆発もなかった点などを指摘した。

 日本側は、79年の米スリーマイル島原発事故と同等のレベル5とする暫定評価結果を先月18日に発表してから、今回レベル7に引き上げるまでに約1カ月を要した。このため、住民避難などの対応に遅れが出たとの指摘もあるが、フローリー氏は「INESは事故の深刻度の尺度であり、対応とは関係ない」と説明。仮にレベルを早く上げたとしても、日本政府の初期対応に違いはなかったとした。

 フローリー氏はまた、福島第一原発事故の状況を「依然とても深刻」とした上で、原子炉冷却に必要な電源の復旧作業などで「回復の兆しもある」とした。(ウィーン=玉川透)

Sunday, April 10, 2011

10/04 大局的視点で「国のあり方」再考必要…構想会議

 菅首相は東日本大震災から1か月にあたる11日、「復興構想会議」(議長・五百旗頭いおきべ真防衛大学校長)を発足させ、復興に向けた作業に着手する。


 政府の復興構想会議で復興の青写真を描くことになるのは、五百旗頭氏や御厨貴東大教授ら有識者と地元の岩手、宮城、福島3県の知事らだ。これは95年の阪神大震災時の手法にならったものだ。

 ただ、政府内からは「阪神のスタイルを踏襲するだけでは不十分だ」(総務省幹部)との意見が出ている。神戸を中心とした地域の局地的被害が大きかった阪神大震災と異なり、東日本大震災は東北から関東までの広範な地域で、数多くの自治体が地震と津波によって壊滅し、原発事故による放射能漏れ事故も招いた。

 さらに、日本経済への打撃も大きい。被害の甚大な東北地方は、農林水産業で日本の「食」の産地の役割を担ってきただけでなく、多くの部品メーカーが日本の基幹産業である自動車や電機産業界を支えてきた。部品の調達ができなくなったトヨタは、海外での生産停止も余儀なくされた。首都圏の電力供給源である福島第一原発の機能が停止したことで、全国各地での企業活動の停滞をも引き起こしている。

 復興を考えるにあたっては、大局的な視点で「国のあり方」を再構築すべきだとの意見は強い。日本のエネルギー政策や産業立地計画の再検討、企業の供給体制の見直し、国民の生活様式など、日本の国家としてのたたずまいを再考する必要があるというわけだ。

 林芳正、藤末健三両参院議員ら民主、自民両党の議員有志と小宮山宏・前東大学長ら有識者のグループは6日、産業構造や労働スタイルの見直しなど原発事故を教訓にしたエネルギー戦略の見直しも含めた復興プランを練り上げるよう求める提言を首相に提出した。また、石原信雄・元官房副長官と民主の樽床伸二衆院議員ら超党派の有志議員も独自の復興ビジョン策定に乗り出した。

(2011年4月10日12時24分 読売新聞)

08/04 (4)福島事故の汚染度は

基礎からわかる原子力発電

 東京電力・福島第一原子力発電所の事故では、大量の放射性物質が大気圏や海域に放出され、私たちの生活にも大きな影を落としている。政府や東電の発表では、「今のところ」「直ちに」影響はない――が繰り返されるが、実際のところ放射線の影響はどうなのか。放射性物質の総量、健康影響、生活の工夫など、暮らしの視点で放射性物質を考えよう。

スリーマイルを超える

 福島第一原発事故で、これまで大気中に放出された放射性物質の量はどのくらいか。汚染の全体像を、これまでの事故などと比較してみよう。

 被災した福島、宮城両県を除く各都道府県の観測所では、3月18日から、放射性物質セシウム137の降下量を24時間ごとに観測し続けている。セシウム137は世界的な放射能汚染の指標だ。

 調査の結果、4月5日朝までの18日間の降下総量は、茨城県ひたちなか市で1平方メートル当たり2万6399ベクレルに達し、東京・新宿区でも6615ベクレルとなっている。事故後、初めての雨となった3月21日から22日には雨と共に大量に降下し、汚染は関東を中心に1都13県に広がっている。

 私たちは、放射能汚染とは無縁の暮らしを続けてきたと感じがちだが、「核の時代」と呼ばれた20世紀には、放射性物質を世界中にまき散らした歴史がある。

 日本で放射性物質の調査が始まったのは1957年に遡る。その3年前、米国の大気圏核実験で、マグロ漁船「第五福竜丸」が被曝ひばくし、半年後に船員が亡くなった問題がきっかけだった。当時は、冷戦の真っただ中。米国や旧ソ連などが核実験を繰り返し、62年には178回以上行われ、プルトニウムなど大量の放射性物質を大気圏に拡散した。大阪市では63年5月、688ベクレルのセシウム137を検出。全国的には今以上に切実な事態だった可能性もある。

 一方、最悪の放射能汚染を招いたのが、86年4月、旧ソ連・ウクライナで起きたチェルノブイリ原発事故だ。広島型原爆の約400倍という約7トンの放射性物質が北半球全域に飛散。金沢市で5月の降下量は計318ベクレルを記録した。

 原発の周囲30キロは148万ベクレル以上のすさまじい汚染で、住民は強制移住させられた。地域的には、ドイツなど7万ベクレル以上を検出した地点も散在している。旧ソ連のベラルーシやモルドバ、オーストリア、フィンランドなどでは、国土全体の平均降下量が1万ベクレルを超えた。今回のひたちなか市などの地域では、米・スリーマイル島原発事故(79年)を超え、チェルノブイリ事故後の欧州並みといえそうだ。

 4月以降、関東各地の降下量は低減しており、1日あたりの量では60年代初期と同レベルに落ち着いている。専門家は「健康には問題のないレベル」と指摘しているが、福島第一原発では高濃度汚染水が海に漏れ出し、海洋生物への被害拡大が危惧されている。

リスクは…平時:年1ミリ・シーベルト以下 非常時:基準変更も

 放射線の健康影響には、「平時」と「非常時」の二つの基準がある。私たち市民の目安は、極力安全サイドに立った「平時の基準」だ。

 各国の専門家でつくる国際放射線防護委員会(ICRP)では、一般住民が1年に浴びて良い人工の放射線量を1ミリ・シーベルト以下と設定している。原爆被爆者の健康調査などから、被曝量が100ミリ・シーベルト以上になるとがん発症が増える可能性があるとのデータに基づき、「80歳まで放射線を浴び続けたとしても、80ミリ・シーベルト以下に抑えられる」量と考えたのだ。

 一方、原子力発電所の事故などを想定した災害時の基準もある。日本の原子力安全委員会は、この10倍にあたる年10ミリ・シーベルト以上を「屋内退避が必要」な線量としている。

 さらにICRPは2007年、「非常時には、一般住民の限度の目安を年20~100ミリ・シーベルトまで引き上げてもよい」と勧告。チェルノブイリ原発事故などの経験を踏まえ、危機を回避するための作業が続く間の一時的措置として示したものだ。

 佐々木康人・日本アイソトープ協会常務理事は、「年20ミリ・シーベルトの放射線量を浴びても、吐き気や火傷などの身体的影響は出ない。発がんのリスクが上がるとされるが、避難しないですむなどのメリットがある場合、限度を引き上げる選択肢がある」という。

 年間線量限度の非常時に対応した値への移行は、原子力安全委員会が、汚染の規模や地域ごとの線量を基に判断し、政府に伝えて決定される。

 一方、日本では原子力従事者の被曝総量を5年間で100ミリ・シーベルト以下と設定していたが、政府は今回の事故後、これを250ミリ・シーベルトに引き上げている。さらにICRPでは、緊急時には救急隊員などの被曝総量は500~1000ミリ・シーベルト以内に抑えられればよいと勧告している。

ベクレルとシーベルト
 1ベクレルは放射性物質の原子核が毎秒1個崩壊して、放射線を出す能力。シーベルトは、放射線を受けた際に体が受ける影響の度合いを示す。ベクレルの数値を、核種や被曝形態などを考慮した一定の計算式に基づいてシーベルトに換算する。

お金に例えると…100円以下は被害小さく

 「平時」は年間1ミリ・シーベルトとされる被曝量だが、事故などの際には、本当に健康影響が心配される線量の判断が求められる。その理解を助ける放射線の“換算表”がある。

 原子力安全研究協会研究参与の岩崎民子さんが、主婦向けの勉強会用に考え出したもので、「お財布の中の1円玉を1ミリ・シーベルトと数えてください」という。10ミリ・シーベルトは10円玉、100ミリ・シーベルトなら100円玉に置きかえる。

 被曝総量が500円になると、一時的にリンパ球細胞が減少するなどの影響があり、千円札(1000ミリ・シーベルト)では、頭痛やめまいなどの症状も起きる。

 同じ線量でも被曝時間が短いほど影響が大きく、JCO臨界事故(1999年・茨城県)など、1万ミリ・シーベルトを一瞬に浴びると、死亡など深刻な事態になる。一方、100円玉(100ミリ・シーベルト)以下では、健康被害はないと見られている。

 岩崎さんは「1円(1ミリ・シーベルト)以下の世界(マイクロ・シーベルト)では、健康の心配は全くありません」と話している。

(2011年4月8日 読売新聞)

10/04 原発事故、スリーマイル上回るレベル6の可能性

福島原発
 東京電力福島第一原子力発電所の事故の深刻さは、国際原子力事故評価尺度(INES)で、チェルノブイリ原発事故に次ぐ「レベル6」(大事故)である可能性が出てきた。


 経済産業省原子力安全・保安院は先月18日、暫定評価として米スリーマイル島原発事故と同じレベル5(施設外へのリスクを伴う事故)としていた。

 INESの評価は、国際原子力機関(IAEA)の基準をもとに、各国の監督機関が行い、IAEAに報告する。チェルノブイリ原発事故は、最悪のレベル7(深刻な事故)で、レベル6と確定すれば、商業炉の事故では初めてとなる。

 レベル5以上の大きな事故は、放出した放射性物質の量で判断される。原子力安全委員会によると、先月12~24日に大気に放出されたヨウ素131の総量は、単純計算で約3万テラ・ベクレル(テラは1兆)。これは数千~数万テラ・ベクレルというレベル6の条件にあてはまる。

(2011年4月10日01時55分 読売新聞)

Saturday, April 9, 2011

09/04 Engineers scrutinize US NRC's Japan evacuation call

REUTERS

2011/04/09

ROCKVILLE, Md.--Nuclear engineers on Thursday aggressively questioned the data and decisions behind the call from the U.S. nuclear regulator for a 50-mile evacuation zone around a failed Japanese nuclear plant.

The recommendation for U.S. citizens to leave that zone -- far larger than the 12-mile evacuation area that Japanese authorities had in place -- sparked international concern about the extent of the crisis at the tsunami-stricken Fukushima plant earlier this month.

A committee of top engineers that advises the U.S. Nuclear Regulatory Commission and reviews all its studies and license applications said it wants access to all the modeling data for the evacuation call.

"This was a very, very important decision. I would have expected there would have been high-level conversations between our regulatory bodies and our government (with their Japanese counterparts)", said Sam Armijo, former head of GE's nuclear fuel business, who invented the fuel cladding used on boiling water reactors.

"I want to make sure we get the analysis and the numbers that were actually used," Armijo said.

Regulatory staff had few answers for the advisory committee, which will review the NRC's response to the Japan tragedy, but they promised to deliver the calculations.

NRC staff said that after the third explosion at the Fukushima complex, they spoke with a Japanese regulatory official.

"There was limited and uncertain data," said Randy Sullivan, a senior emergency preparedness specialist.

The NRC was worried about the condition of pools holding spent fuel, and assumed they would contain as much radioactive waste as similar pools at U.S. plants -- something that turned out not to be the case, Sullivan said.

Using a computer model and assuming 100 percent damage to the No. 2 reactor, the NRC staff produced an estimate of risks and recommended the larger evacuation area.

The recommendation was not based on actual data from the site, which was unavailable, Sullivan said.

"Maybe the Japanese had some of that, but we didn't, alright?" he told the committee during a heated, lengthy question period.

Some of the NRC's assumptions were based on press reports, said William Ruland, the NRC's acting deputy director of engineering and corporate support.

"In an emergency event, you go with the best available information you have at the time," Ruland said, noting Japanese counterparts were focused on containing the situation rather than providing U.S. officials with information.

Michael Corradini, head of the nuclear engineering department at the University of Wisconsin, said the NRC's evacuation recommendation left him "confused."

He questioned why the NRC did not correlate its modeling with data from radiation monitors in the country before publicizing its recommendation.

"Thirty-two years ago, if Japan would have done a what-if calculation on Three Mile Island and said all the Japanese within 50 miles of Harrisburg should get out, what would be our response, from a policy standpoint?" Corradini said, referring to the worst-ever U.S. nuclear disaster that happened at the Three Mile Island plant in Pennsylvania in 1979.

Thursday, April 7, 2011

07/04 Fukushima not as bad as Chernobyl

Fukushima not as bad as Chernobyl

This March 24, 2011 aerial photo taken by a small unmanned drone and released by AIR PHOTO SERVICE shows damaged Unit 4 of the crippled Fukushima Dai-ichi nuclear power plant in Okumamachi, Fukushima prefecture, northern Japan. (AP Photo/AIR PHOTO SERVICE)
This March 24, 2011 aerial photo taken by a small unmanned drone and released by AIR PHOTO SERVICE shows damaged Unit 4 of the crippled Fukushima Dai-ichi nuclear power plant in Okumamachi, Fukushima prefecture, northern Japan. (AP Photo/AIR PHOTO SERVICE)

VIENNA (AP) -- The Japanese nuclear accident that has sparked worldwide radiation fears ranks "in between" those that occurred at Chernobyl and Three Mile Island, a U.N. expert said Wednesday.

Wolfgang Weiss, chairman of the U.N. Scientific Committee on the Effects of Atomic Radiation, said it's far too early to even begin an assessment of the situation at the Fukushima Dai-ichi plant because the crisis there is ongoing.

But, he noted, while radioactivity from the 1979 Three Mile Island incident in the United States was largely contained, traces of fallout from Fukushima detected around the world are "much, much, much lower" than traces seen at similar distances after the 1986 Chernobyl disaster in Ukraine.

The six-reactor Japanese complex was crippled by an earthquake-triggered tsunami on March 11 and has been seeping radiation into the environment. Authorities are struggling to get the situation under control and have indicated that could take months.

When reporters asked Weiss how he compares the Japanese crisis to its two predecessors, he said: "It's in between. It's not as dramatic as Chernobyl, but it's certainly much more serious than" Three Mile Island.

Weiss, who also heads the radiation protection and health department at Germany's Federal Office for Radiation Protection, noted that Fukushima's proximity to the Pacific Ocean was beneficial in containing the contamination and exposure to people.

This March 30, 1979, file photo shows an aerial view of the Three Mile Island nuclear power plant near Harrisburg, Pa. The small dome at center is where the
This March 30, 1979, file photo shows an aerial view of the Three Mile Island nuclear power plant near Harrisburg, Pa. The small dome at center is where the "incident" occured. (AP Photo/Barry Thumma, File)

"The Pacific takes it all and there we have huge dilution," Weiss said.

Fred Mettler, a member of the U.N. committee, agreed, noting that in contrast to Fukushima Chernobyl was surrounded by land. During that disaster, hundreds of people were exposed to very high doses of radiation and 135 got acute radiation sickness, he added.

"We haven't seen any of that at Fukushima, so the early management by the Japanese here is very different from what happened at Chernobyl," Mettler said.

Online:

U.N. Scientific Committee on the Effects of Atomic Radiation: http://www.unscear.org/

(Mainichi Japan) April 7, 2011

Friday, April 1, 2011

01/04 スリーマイルは1か月後、安全な冷温停止状態に

 福島第一原発と似た過酷事故に見舞われた米スリーマイル島原発事故(1979年)では、どう対応したのか。

 同原発では、発電用タービン停止に伴う原子炉の緊急停止後、運転員が判断ミスで炉内を冷やす緊急炉心冷却装置(ECCS)の注水量を絞るなどした。その結果、炉内の水位が下がり、核燃料の一部が溶融する事態になった。

 しかし、この時は福島第一原発と違い、ポンプなどを動かす電源に異常はなかったため、試行錯誤を繰り返しながらも各種冷却系を総動員。事故発生から約16時間で、原子炉を安定的に冷却する機能が回復し、約1か月後には安全な冷温停止状態になった。

(2011年4月1日13時38分 読売新聞)

Tuesday, March 22, 2011

16/03 5 myths about nuclear energy

By Michael A. Levi, Wednesday, March 16, 12:05 PM

Explosions. Radiation. Evacuations. More than 30 years after Three Mile Island, the unfolding crisis in Japan has brought back some of the worst nightmares surrounding nuclear power — and restarted a major debate about the merits and the drawbacks of this energy source. Does nuclear energy offer a path away from carbon-based fuels? Or are nuclear power plants too big a threat? It’s time to separate myth from reality.


1. The biggest problem with nuclear energy is safety.

Safety is certainly a critical issue, as the tragedy in Japan is making clear. But for years, the the biggest challenge to sustainable nuclear energy hasn’t been safety, but cost.

In the United States, new nuclear construction was already slowing down even before the partial meltdown at Three Mile Island in 1979; the disaster merely sealed its fate. The last nuclear power plant to come online started delivering power in 1996 — but its construction began in 1972. Today, nuclear power remains considerably more expensive than coal- or gas-fired electricity, mainly because nuclear plants are so expensive to build. Estimates are slippery, but a plant can cost well north of $5 billion. A 2009 MIT study estimated that the cost of producing nuclear energy (including construction, maintenance and fuel) was about 30 percent higher than that of coal or gas.

Of course, cost and safety aren’t unrelated. Concerns about safety lead to extensive regulatory approval processes and add uncertainty to plant developers’ calculations — both of which boost the price of financing new nuclear plants. It’s not clear how much these construction costs would fall if safety fears subsided and the financing became cheaper — and after the Fukushima catastrophe, we’re unlikely to find out.


2. Nuclear power plants are sitting ducks for terrorists.

It’s easy to get scared about terrorist attacks on nuclear plants. After the Sept. 11 attacks, a cottage industry sprung up around the threat, with analysts imagining ever-more horrific and creative ways that terrorists could strike nuclear facilities and unleash massive consequences.

There are certainly real risks: Nuclear expert Matthew Bunn of Harvard University has pointed out that well-planned terrorist attacks probably would produce the sort of simultaneous failures in multiple backup systems that Japan’s reactors are experiencing. But it’s much harder to target a nuclear power plant than one might think, and terrorists would have great difficulty replicating the physical impact that the March 11 earthquake had on the Japanese plants. It also would be tough for them to breach the concrete domes and other barriers that surround U.S. reactors. And although attacks have been attempted in the past — most notoriously by Basque separatists in Spain in 1977 — none has resulted in widespread damage.

Certainly, the water pools in which reactors store used fuel, which reside outside the containment domes, are more vulnerable than the reactors and could cause real damage if attacked; there is a debate between analysts and industry about whether terrorists could effectively target them.

3. Democrats oppose nuclear energy; Republicans favor it.

Yes, the GOP base is enthusiastic about nuclear energy, while the Democratic base is skeptical. Moreover, many Republican politicians support assistance to the industry such as loan guarantees for nuclear developers, while many Democrats oppose them. But the politics of nuclear power have changed in recent years, mainly because of climate change.

Democrats, including many supporters in the environmental movement, have become more open to nuclear power as a large-scale zero-emissions energy option. Steven Chu, President Obama’s energy secretary, has been enthusiastic about the nuclear option. When asked to compare coal and nuclear energy in 2009, Chu responded: “I’d rather be living near a nuclear power plant.”

The biggest prospective boost for nuclear power in the past two years was an initiative championed by Democrats and scorned by Republicans: cap-and-trade legislation. Cap-and-trade would have penalized polluting power sources such as coal and gas emitters, thus tilting the playing field toward nuclear power. Department of Energy simulations of the ill-fated Waxman-Markey climate bill projected that it would have increased nuclear power generation by 74 percent in 2030.

Yet although Democrats may have become more accepting of nuclear power, few became fully enthusiastic. Japan’s tragedy may make many reconsider their stance.


4. Nuclear power is the key to energy independence.

When people talk about energy independence, they’re thinking about oil, which we mostly use in vehicles and industrial production. When they talk about nuclear, though, they’re thinking about electricity. More nuclear power means less coal, less natural gas, less hydroelectric power and less wind energy. But unless we start putting nuclear power plants in our cars and semis, more nuclear won’t mean less oil.

This wasn’t always the case: During the the heyday of nuclear power, the early 1970s (45 plants broke ground between 1970 and 1975), oil was a big electricity source, and boosting nuclear power was a real way to squeeze petroleum out of the economy. Alas, we’ve already replaced pretty much all the petroleum in the power sector; the opportunity to substitute oil with nuclear power is gone.


5. Better technology can make nuclear power safe.

Technology can increase safety, but there will always be risks with nuclear power. The Japanese reactors at the center of the current crisis use old technology that increased their vulnerability. Next-generation reactors will be “passively cooled,” which means that if backup power fails like it has in Japan, meltdowns will be avoided more easily. (Passive-cooling systems vary, but their common feature is a lack of dependence on external power.) Other lower-tech improvements, such as stronger containment structures, have also mitigated risk.

But what happened in Japan reminds us that unanticipated vulnerabilities are inevitable in any highly complex system. Careful engineering can minimize the chance of disasters, but it can’t eliminate them. Operators and authorities will need to make sure that they’re prepared to deal with unanticipated failures even as they work to prevent them.

Most energy sources entail risks. In the past year, we’ve seen an oil spill in the Gulf of Mexico, fatal explosions at the Upper Big Branch coal mine in West Virginia and now the crisis in Japan. The American public will need to decide whether the risks of nuclear power — compared with those of other energy sources — are too high.

Michael A. Levi , a senior fellow and director of the program on energy security and climate change at the Council on Foreign Relations, is the author of “On Nuclear Terrorism.”

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© 2011 The Washington Post Company

Sunday, March 20, 2011

18/03 Risks, Radiation and Regulation

March 18, 2011, 6:00 am
By NANCY FOLBRE

Nancy Folbre is an economics professor at the University of Massachusetts Amherst.

Early warnings about potential nuclear dangers in Japan and about Wall Street’s propensity for risk-taking without liability were both dismissed as paranoid anticipation of low-probability events. With both disasters, regulatory failures set the stage, and taxpayers will end up paying most of the social costs.

Effective risk management is central to economic efficiency. Yet major players in both crises have insisted that they should not be held accountable for risks they underestimated.

Goldman Sachs’s chief executive, Lloyd C. Blankfein, likened the financial crisis to a once-every-hundred-years storm or an earthquake.

But no natural disaster played a role there, just vast mismanagement (too bad we can’t measure that on the Richter scale). Many economists, including my fellow Economix blogger Simon Johnson, argue that deregulation weakened the very foundations of our financial system.

A major earthquake and resulting tsunami were the proximate causes of the nuclear disaster in Japan. But it was engineering failures and lax oversight that made a bad situation grotesquely worse.

The plant owners, operators and regulators who confidently insisted that the reactors were foolproof and fail-safe apparently miscalculated (as with previous accidents at Three Mile Island and Chernobyl).

In my view, many social engineers, including economists, deserve the larger blame. The widespread view that capitalism is an automatically self-regulating system has weakened the checks and balances — the feedback mechanisms and control rods — that are crucial to the long-run viability of our operating system.

The threat of social meltdown arises not from excessive growth of the state and its regulatory role but from its capture by groups able to translate market power into political power: socialism for big investors, capitalism for everyone else.

Critics of nuclear power, including the Union of Concerned Scientists, have long pointed out that the Price-Anderson Act reauthorized by Congress in August 2005 provides a huge subsidy to the industry by limiting its financial liability in the event of disaster, essentially promising the ultimate bailout at taxpayer expense.

A more detailed economic analysis is provided by Geoffrey Heal of the Columbia University School of Business and Howard Kunreuther of the Wharton School at the University of Pennsylvania in a paper, “Environment and Energy: Catastrophic Liabilities.”

Like the United States, Japan has limited the liability of its nuclear power industry, and its taxpayers are expected to bear the brunt of the long-term economic costs of the meltdown. The industry’s track record is hardly reassuring. The Tokyo Electric Power Company, owner of the Fukushima Daiichi plant, admitted in 2002 that it had falsified results of safety tests.

The national agency designed to regulate the industry has often seemed more eager to promote it, failing to inspire much confidence among environmentalists, or, more recently, from the United States Nuclear Regulatory Commission.

Effective regulation requires effective containment of disproportionately powerful economic interests that can potentially contaminate both public policy and public debate. Considerable evidence suggests that this containment has been breached.

In the last election cycle, the Nuclear Energy Institute, along with a dozen companies with significant investments in nuclear power, spent tens of millions of dollars on lobbying and campaign contributions.

In the somewhat panicky initial coverage of the Japanese crisis, the institute was not always identified in the press as a trade group, even when one of its representatives answered questions about public subsidies and public safety.

On March 15, as concerns about explosions at Fukushima Daiichi were growing, an online Wall Street Journal article cheerfully reported, “The Nuclear Energy Institute’s top nuclear scientist said Tuesday that U.S. nuclear plants are equipped to handle natural disasters and the crisis in Japan isn’t expected to affect new nuclear projects.”

This wasn’t news. It was just part of the radiation emanating from our own regulatory meltdown.

19/03 Japan, a Crisis That Markets Can’t Grasp

March 19, 2011
By JEFF SOMMER

THE risks are clear enough in hindsight.

The Tokyo Electric Power Company built its Fukushima Daiichi nuclear power plant, nearly 40 years ago, to withstand a powerful earthquake — but not one as big as the 9.0-magnitude quake that struck on March 11. Or the tsunami that followed. Now, the terrible “ifs” accumulate, as Japanese engineers work to bring the station’s reactors under control. The ultimate price, in human life, may not be known for years.

The details of this catastrophe were unforeseeable, leading some to conclude this was a black swan event — something so wildly unexpected, so enormous in its impact, that it seems to defy our understanding and expose the fragility of our knowledge of the world. How could anyone have predicted this?

And yet in 2007, Tokyo Electric Power, or Tepco, escaped a disaster at its huge Kashiwazaki-Kariwa nuclear power station, on the opposite side of Japan, when that plant was damaged by a 6.8-magnitude earthquake — three times as large as what the plant was designed to withstand. Tepco basically lucked out last time.

So perhaps a bigger question is whether the markets — in which we have come to place so much trust — can put a true price on outsize risks like this.

Many have compared the events unfolding in Japan with 9/11, Hurricane Katrina, the financial collapse of 2008 and 2009, the BP oil spill, and the uprisings in the Arab world — in that all have shown the limits of the collective wisdom of the marketplace. For a moment, all the swans seemed black. And those swans seemed blacker still when viewed through the lens of today’s hyperkinetic global markets.

“There are an amazing number of crosscurrents in the world economy right now, more than I’ve seen in 25 years,” said Shawn Reynolds, a co-portfolio manager at Van Eck Associates in New York.

Like everyone else, corporate executives, economists and financial analysts in Tokyo, New York, London and beyond struggled last week to wrap their heads around the scale of this disaster. But, as they so often do, the analysts quickly fell to work assessing the implications for companies, markets and economies. At times, it was almost surreal: On Tuesday, Laszlo Birinyi, a prominent stock market analyst based in Westport, Conn., e-mailed around a succinct report titled “Nuclear Meltdowns at a Glance.”

This is what happens on Wall Street. If you’re not immersed in the culture, it might be hard to understand the cool calculus that is applied to world events, however dire those events might be. After the quake hit on March 11, the CNBC anchor Larry Kudlow told viewers, “The human toll here looks to be much worse than the economic toll, and we can be grateful for that.” He later apologized.

As the week wore on, and prices were gyrating on everything from a share of I.B.M. to a ton of copper, everyone was making back-of-the-envelope calculations. There is still no clear consensus about how far the economic shocks will reverberate. Many analysts are guessing — and then second-guessing — how the disaster will play out in northeast Japan. The first, tentative analysis seemed painfully obvious: the Japanese economy, already weak, perhaps already in a recession before calamity struck, will become even weaker.

On Friday, the Group of 7 industrialized nations took the rare step of intervening on the world’s foreign exchange markets to stem a sudden rise in the value of the yen. The currency had soared all week against the dollar — the exact opposite of what you might expect. But Japanese companies and investors were bringing their money home, to pay for huge rebuilding costs.

After its most harrowing week since the 1987 market crash, the Tokyo Stock Exchange found its footing on Friday. But it was a week like few others on the exchange: the Nikkei 225 stock index, Japan’s equivalent of the Dow Jones industrial average, fell 6.2 percent on Monday, plunged 10.5 percent on Tuesday, rebounded 5.7 percent on Wednesday and sank 1.4 percent on Thursday. It closed up 2.7 percent on Friday, at 9,206.75.

The loss for the week totaled 1,048 points, or 10.2 percent.



IF you happen to visit a Wall Street trading floor, walk over to the nearest Bloomberg terminal, type “WRST” and hit the green key that says “go.”

WRST — that is short for “worst,” as in, “worst-case scenario.” The program enables Wall Street types to measure the level of risk in their investment portfolios under a variety of scary circumstances modeled on past crises, including the attacks of Sept. 11, 2001, the bankruptcy of WorldCom in 2002 and the devaluation of the Thailand’s currency, the baht, in 1997.

Such “what if” scripts are the stuff of modern Wall Street. Everyone runs them. Entire schools of financial analysis are devoted to examining historical market patterns in the belief that those patterns can predict the future.

Such analysis, of course, depends on — and perhaps even encourages — our belief that tomorrow will be much like today. And all that despite the fine-print caveat on your 401(k) statement that reads, “Past performance is no guarantee of future success.”

Nassim Taleb, the author and market theorist who popularized the phrase “black swan” in his 2007 best seller, argues that we have psychological biases that blind us to the enormous role played by rare events — like a 9.0-magnitude earthquake. And yet we rely on history for guidance. On Wednesday, Mr. Birinyi’s research firm sent out another report, this one titled “S.& P. 500 Enters Modest Correction.” His firm predicted a slight decline in the American stock market.

“If the averages hold,” the report said, “the S.& P. 500 will bottom at 1,232 on 3/31/11.” On Friday, the S.& P. 500 closed at 1,279.19, down 1.9 percent for the week.

Whatever else they may be, markets are immensely complex counting machines. They assign values to products, whether computer chips or potato chips, based on the canny appraisals and gut beliefs of people around the planet. From day to day, it is often hard, if not impossible, to know exactly why a certain price moved the way it did. Those daily movements are often just the white noise of global capitalism.

Then there are stretches of extreme volatility, periods when no one quite seems to agree about where anything is going. That may be part of what occurred last week: in the face of such a disaster, not even a short-term trend could congeal.

As yet, no one has reliable numbers about the scope of the destruction, said Al Tobin, who heads the property practice at Aon Risk Solutions, the risk management brokerage business of the Aon Corporation. The human toll, the economic toll — “no one knows the answer to that question,” he said.

Given such uncertainty, the markets could remain even more volatile than usual, said Mohamed A. El-Erian, chief executive of Pimco, the world’s largest bond manager. “The market right now is trying to wrap its arms around the enormity,” he said.

The verdict is not yet in.

Mr. El-Erian divided market strategists into two camps. The first, he says, views the events in Japan as “more than just a massive human tragedy; it also has significant implications for the global economy.” The second, he says, believes that the effects of this disaster, however heart-rending, will be transitory for most of us.

But he doesn’t yet know which camp is right. “I don’t understand it fully yet,” he said, “but I am worried about it.”

Big economic questions remain unanswered. How would a severe slowdown in Japan, the world’s third-largest economy, affect the rest of the globe? How will Japan, which is already deeply in debt, pay for the reconstruction? Some are already arguing that the enormous, high-cost task of rebuilding could, over time, snap Japan out of its long economic funk.



MARKET strategists pride themselves on being able to digest vast quantities of data quickly. They tend to be practical and versatile people, the kind who can put aside emotions and philosophical questions when business calls.

On Thursday, a sunny St. Patrick’s Day in Manhattan, Jonathan Golub, the chief equity strategist for the giant Swiss bank UBS, said he was trying to master some of the intricacies of nuclear technology. “Now I find myself talking about fuel rods and cooling pools,” he said. It was, he said, not an uncommon type of experience: Before the financial crisis, even many people on Wall Street didn’t quite know what a credit default swap was. Before long, everyone was throwing around terms like “swaps” and “C.D.S.”

Mr. Golub said he felt for the people of Japan. He then went on to say, at a news briefing, that once the current market volatility subsided, this crisis should have only a marginal impact on America’s economy and stock market, whose prospects were quite good. He predicted that the S.& P. 500 would reach 1,425 by the end of the year.

Still, because supply chains have gone global like so much else, the disaster has already had a very real impact in the United States. Last week, Subaru slowed operations of its auto plant in Indiana because it could not obtain key parts from Japan. General Motors said it would shut a truck plant in Louisiana because of a shortage of parts. The semiconductor industry has also slowed because Japan is a major supplier of silicon wafers and other components.

Despite its position as the world’s No. 3 economy, Japan actually accounts for a relatively small — and shrinking — amount of the world’s collective economic output. It contributes about 9 percent of global gross domestic product, down from about 18 percent in the 1990s. And because of the rapid acceleration of the so-called BRIC countries — Brazil, Russia, India and China — and of other emerging markets, Japan’s contribution to growth of global G.D.P. is marginal.

Lakshman Achuthan, the managing director of the Economic Cycle Research Institute, a private forecasting group with an excellent track record, says that Japan’s economy, which he believes is already in recession, won’t appreciably affect the direction of the economy in the United States. The disaster, however, “ensures that Japan is in a recession,” he said.

All of this, of course, assumes that the nuclear disaster, already the biggest since Chernobyl, doesn’t get too much worse.



THE financial markets have always had a difficult relationship with nuclear power, largely because the costs — and potential risks — associated with nuclear plants are so huge. Day to day, nuclear power is cheap. But it is unclear how to accurately assess the cost of disposing of nuclear waste over the long run — or, perhaps, the cost of disasters like the one in Japan.

Robert N. Stavins, a professor at the Kennedy School of Government at Harvard and director of the university’s environmental economics program, has studied this issue for years. In an article in the centennial edition of the American Economic View in February, Professor Stavins said that economists had not yet solved the “tragedy of the commons,” the quandaries that arise when many people, acting in their own self-interest, ultimately pose a threat to the common good. For instance, how should we allocate environmental costs to power producers? How should the environmental costs of various fuels — fossil or nuclear — be calculated?

So far, the markets seem to have failed to provide an answer to all of those questions. A National Research Council study last year tallied up environmental costs for various fossil fuels but did not even try to do so for nuclear power because the “power-plant risk modeling and spent-fuel transportation modeling” required was beyond the scope of the council’s study.

In the United States and elsewhere, governments have capped the liability of nuclear power producers. As a result, Professor Stavins said, “You can argue that the markets have never really had a chance to price nuclear power.”

In the face of black swans — also known as fat-tail events, for the way their occurrences are distributed along a probability curve — market pricing may be impossible.

Martin Weitzman, another Harvard economist, wonders, for example, how Wall Street or anyone else could place an accurate price on the risk that an asteroid would crash into a major population center. In a controversial mathematical proof called, perhaps appropriately, the Dismal Theorem, he found that “it’s very hard to make reliable inferences about rare events on the tails of probability distributions.”

Is the nuclear disaster under way in Japan such a rare event, one that economists cannot accurately price? It is too early to say, Professor Weitzman said. “It might be.”



IT has been more than 30 years since Three Mile Island, and 25 since Chernobyl.

In the ensuing years, one nuclear plant was completed in the United States and shut down before ever going into commercial operation. That was the Shoreham plant, on Long Island, which cost roughly $6 billion. Its fate was decided in 1989, when state officials concluded that Long Island could never be evacuated in case of a disaster.

The Fukushima accident has already caused a temporary slowdown in the nuclear industry. Officials in India and China said last week that they would re-evaluate their plans for building plants. Germany announced that it would temporarily shut seven nuclear plants that went online before 1980. The European Union made plans to test all the other nuclear power plants within its member countries.

In the United States, President Obama, who has promoted building new nuclear power plants, asked the Nuclear Regulatory Commission last week to review the safety of all United States plants.

However imperfectly, the market will pass judgment.

Mr. El-Erian of Pimco says the outlook is unusually uncertain. Investors, like everyone else, should understand that the world is a risky place.

“You need to use a whole range of approaches to understand the market in a situation like this,” he says, “and you need to be humble.”

And, perhaps, accept a sober reality: the next black swan is out there somewhere.  

Wednesday, March 16, 2011

15/03 Wind and Rain Steer Radiation’s Reach

March 15, 2011
By HENRY FOUNTAIN

So, how bad could it get?

Experts say it is impossible to forecast how events at Japan’s stricken nuclear plant will unfold, whether there will be a meltdown or other crisis at one or more of the reactors that results in a large release of radioactivity into the environment. And even if such a release occurred, the impact in Japan and elsewhere would depend greatly on wind and rain and how long the release lasted.

“We’re in uncharted territory here,” said Robert Alvarez, a nuclear expert and adviser to the secretary of energy during the Clinton administration. “But in very general terms, the worst-case scenario would be a catastrophic release of radiation that will not necessarily happen all at once.”

That would make the event similar to, and perhaps worse than, the Chernobyl accident in 1986, in which large amounts of radioactivity were released and hundreds of square miles of land in Ukraine were left uninhabitable. But without such a catastrophic release, the events would likely be closer in scale to the partial meltdown in 1979 at Three Mile Island in Pennsylvania, where the plant’s containment structure held and a relatively small amount of radioactivity was released.

So far, the problems at the Fukushima Daiichi plant in Japan are more severe than at Three Mile Island but less so than in Chernobyl.

The Chernobyl reactor, which caught fire after electrical tests resulted in a series of explosions, was not surrounded by a containment structure, as the Japanese reactors are. So a key factor in Japan is whether, if one or more of the reactors has a full meltdown of its nuclear fuel, the containment barriers hold. Complicating matters is the presence of large amounts of spent fuel — which contain most of the same radioactive elements as the fuel in the reactor — in storage ponds that are outside any containment barrier.

Experts differ as to whether breaching of the containment is likely or not. “There’s quite a lot of redundancy and barriers built into the system,” said Mary Lou Dunzik-Gougar, an assistant professor of nuclear engineering at Idaho State University. “A full-fledged meltdown might result in a breach of the pressure vessel, with the fuel dropping into the lower part of the plant. But it’s not going to go very far.”

But a breach would most likely be catastrophic.

“If there’s a breach of containment and a significant release of radioactivity, I think it’s safe to draw parallels to Chernobyl,” said Kenneth L. Mossman, a professor of health physics at Arizona State University. But he described Chernobyl as an “upper bound” of what might happen in Japan.

Dr. Mossman said the impact of the radiation would be twofold. Workers would be at risk for illness or death because of high levels of gamma rays and other ionizing radiation. But the area around the plant would become a no-man’s land, contaminated with radioactive elements like cesium, plutonium and iodine.

Just how large this area would be would depend on whether the poisons were released slowly and stayed close to the ground or were spewed into higher altitudes by explosions or fire. Wind would push the radiation in one direction, and tend to disperse it over a larger area. Rain would bring much of it to the surface.

The size of the contaminated area would also depend on how much of the radiation escaped. At Chernobyl, where the reactor burned for about a week, no one knows for certain how much of the radiation in the fuel was released — one estimate is about 40 percent. At the Japanese plants, unless the containment vessels were totally destroyed by explosions — which some nuclear engineers said was unlikely — some percentage of the radiation in the roughly 150 tons of fuel in each reactor would still be kept safe.

However large, the contaminated area would be uninhabitable for decades.

The spent-fuel pools represent another risk. They are designed to keep the old fuel rods, which are removed from the reactor regularly, submerged to prevent overheating as the radioactive elements in the fuel decays.

“Any of the pools at units 1 through 4 are problems,” Mr. Alvarez said.

It is not clear how much spent fuel there is at each reactor. At the Vermont Yankee plant, a reactor in southern Vermont that is nearly identical to the crippled ones in Japan, close to 700 metric tons of spent fuel is stored. The Japanese plants probably do not have nearly as much — perhaps tens of tons at each reactor, Mr. Alvarez said.

If they overheat and the rods crack or, worse yet, the fuel burns — again, experts differ as to whether this is likely — radioactivity would be released. Because the fuel is older, iodine, an element with a relatively short half-life, would not be a problem. But cesium, plutonium and strontium would still be present in large quantities.

The plume might even be larger than that from a reactor meltdown, because of the lack of containment. But that is another of many unknowns, Mr. Alvarez said.

“The kinds of things that are happening have in very general terms been vaguely predicted,” he said. “The phenomenon of multiple hydrogen explosions, for example — will there be more explosions, will they damage or otherwise compromise the primary containment?

“There are things we don’t know but things we need to be concerned about.”



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