Wednesday, April 27, 2011

27/04 High levels of radiation in areas near nuclear plant foreseen for a year


In this Friday, March 18, 2011 satellite image released by DigitalGlobe, the Fukushima Dai-ichi is shown. (AP Photo/DigitalGlobe)
In this Friday, March 18, 2011 satellite image released by DigitalGlobe, the Fukushima Dai-ichi is shown. (AP Photo/DigitalGlobe)

The Japanese government unveiled a map of radioactive contamination on April 26, predicting residents in areas near the troubled nuclear power plant could be exposed to radiation far greater than permissible levels.

According to the contamination map unveiled by the Ministry of Education, Culture, Sports, Science and Technology, a cumulative dose of radiation for the year to March 11, 2012 is expected to reach 235.4 millisieverts in Akogi Kunugidaira in Namie, Fukushima Prefecture, 24 kilometers northwest of the Fukushima No. 1 Nuclear Power Plant.

The cities of Fukushima and Minami-Soma are also predicted to receive more than 10 millisieverts of radiation, 10 times the dose of artificial radiation an ordinary person is allowed to be exposed to a year.

Based on data collected from 2,138 monitoring points, the ministry calculated total cumulative doses of radiation between March 12 and April 21 and added them up to expected cumulative doses of radiation for the period thereafter to March 11, 2012. Expected radiation exposure was based on the assumption that the nuclear power plant continues to spew the same level of radiation as that detected on April 22. The ministry assumed that people in each monitoring point spend eight hours outdoors and 16 hours inside wooden houses a day. The ministry assumes the level of exposure to radiation in wooden houses is 40 percent lower than outdoors.

As a result, higher levels of radiation were predicted in areas northwest of the nuclear power plant. On April 11, the government designated areas outside a 20-kilometer radius of the nuclear plant that were expected to receive 20 millisievers per year as "planned evacuation zones." Ten locations in the zones including Namie, Iitate and Kawamata were predicted to receive more than 20 millisieverts of radiation. Ryozen in Date, 48 kilometers northwest of the nuclear plant, was predicted to receive 21.2 millisieverts per year.

The ministry had unveiled a similar map on April 11, but the map released this time predicted radiation levels in wider areas based on larger quantities of data. The ministry plans to update the map regularly and release it twice a month. The Cabinet Office's Nuclear Safety Commission says, "We should continue to monitor radiation levels."

In this photo from a footage of a live camera released by Tokyo Electric Power Co. (TEPCO), black smoke billows from the crippled Fukushima No. 1 Nuclear Power Plant in Okumamachi, northeastern Japan, on March 22, 2011. (AP)
In this photo from a footage of a live camera released by Tokyo Electric Power Co. (TEPCO), black smoke billows from the crippled Fukushima No. 1 Nuclear Power Plant in Okumamachi, northeastern Japan, on March 22, 2011. (AP)

The ministry also unveiled a map of radiation distribution based on data of radiation levels monitored in the atmosphere as of April 24. The ministry also plans to later release a map of soil contamination.

(Mainichi Japan) April 27, 2011


東日本大震災:累積放射線、福島・浪江町で235ミリシーベルト--1年後予測

 ◇福島市も10ミリシーベルト超

 文部科学省は26日、東京電力福島第1原発から放出される放射性物質による周辺の汚染状況を予測した地図を公表した。現在の水準で放出が続いた場合、来年3月11日までの1年間の予想累積線量は、福島県浪江町赤宇木椚平(あこうぎくぬぎだいら)(原発の北西24キロ、計画的避難区域)で235・4ミリシーベルトに上った。福島市や福島県南相馬市でも、一般人の人工被ばくの年間限度量(1ミリシーベルト)の10倍に当たる10ミリシーベルトを超えると推定している。

 作製には、文科省が日常的なモニタリングを実施している測定地点(2138カ所)のデータを使った。地震翌日の3月12日から4月21日までの実測値を足し合わせた累積線量に加え、4月22日時点の線量がこれからも続くと仮定して来年3月11日までの累積線量を算出。各地点では、1日のうち8時間を屋外、16時間は木造家屋の中で過ごすとした。木造家屋は屋外に比べて被ばく量が4割低いという前提だ。

 その結果、原発の北西方向を中心に高い累積線量が予想された。政府は今月11日、原発の半径20キロ圏外で年間累積被ばく線量が20ミリシーベルトに達すると見込まれる地域を「計画的避難区域」に指定したが、同区域内では浪江町、飯舘村、川俣町などの10地点で20ミリシーベルトを超えると推測された。一方、現在は指定されていない同県伊達市霊山町(原発の北西48キロ)で年間21・2ミリシーベルトと予測された。

 同省は今月11日にも同様の手法で予測した地図を公表しているが、今回は20キロ圏内も含め、より多くのデータを基に広域で予想した。今後、データや気象条件を更新しながら、月2回の頻度で公表する。内閣府原子力安全委員会は「引き続き線量の推移を監視していく必要がある」としている。

 また同省は、今月24日時点の空間線量の実測データに基づいた放射線量分布地図も公表した。今後、土壌の汚染に関する地図も公表する予定だ。【関東晋慈】

毎日新聞 2011年4月27日 東京朝刊


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