Science Council of Japan: 250 Millisievert External Radiation Exposure in 30 Years Possible in #Fukushima Without Continued Decontamination

That seem like a lot, but come to think about it, 250 divided by 30 equals 8.33. At this point, average 8.33 millisieverts per year exposure in parts of Fukushima, particularly near Fukushima I Nuclear Power Plant, seems almost reasonable.

Anyway, here's Yomiuri reporting on one of several report issued on April 9, 2012 by the Science Council of Japan:

帰還後も除染続けないと、がん死亡リスク増加

Risk of dying from cancer will increase unless decontamination continues after residents return

高濃度の放射性物質で汚染された東京電力福島第一原子力発電所の周辺地域では、住民の帰還後も除染を一定期間続けないと、３０年間の累積被曝(ひばく)線量が１００ミリ・シーベルトを超える恐れのあることが９日、日本学術会議の試算で明らかになった。累積で１００ミリ・シーベルトになると、がんの死亡リスクが０・５％高まる。

The Science Council of Japan's estimate shows that unless decontamination is carried out for a certain period of time after the residents return to the areas surrounding Fukushima I Nuclear Power Plant, the cumulative radiation exposure in 30 years may exceed 100 millisieverts. The estimate was published on April 9. The area surrounding the plant is highly contaminated with radioactive materials. When the cumulative radiation exposure reaches 100 millisieverts, the risk of dying from cancer goes up by 0.5%.

　同会議では、避難前の被曝線量や帰還時の年間被曝線量、帰還後の除染の有無で、３０年間の被曝線量がどう変わるかを試算した。

The Council calculated different scenarios for cumulative radiation exposure levels for 30 years, taking into account the amount of radiation exposure before the evacuation, annual radiation exposure levels on return, and decontamination after the return of the residents.

　その結果、仮に年間２０ミリ・シーベルトに下がった段階で帰還し、その後に除染しないと、放射能の減衰を考慮しても、３０年間で２５０ミリ・シーベルト近く被曝する可能性があるという。

The result shows that if the residents return when the annual radiation exposure levels drop to 20 millisieverts and if no decontamination is done afterwards, the residents may be exposed to nearly 250 millisieverts in 30 years, even with the attenuation of radioactivity.

Oops. The Japanese national government's guideline to return the residents to the areas inside the no-entry zone and the planned evacuation zone is that the annual radiation exposure levels drop down to 20 millisieverts. Judging from the decontamination work that has been done inside the zones and outside, it doesn't look like there will be on-going decontamination.

The original 53-page report by the Science Council of Japan is titled (my translation) "To take a first new step toward dealing with radioactivity - take action based on the scientific probe of facts". The radiation exposure for the residents who return to their homes in the evacuation zones is discussed from page 15 to page 20 in the report.

The average background (natural) external radiation exposure in Japan before the Fukushima nuclear accident was about 0.6 millisievert per year. In 30 years, the cumulative external radiation would have been 18 millisieverts.

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Japanese Government Decides 20 Millisieverts Annual Radiation Exposure Poses Little Cancer Threat to General Public

While the entire nation and the entire world wait with bated breath for the declaration by the Japanese national government of a cold shutdown of Fukushima I Nuclear Power Plant (to be exact, as NY Times correctly reported on December 14, "state of a cold shutdown") later in the evening of December 16 Japan Standard Time, the working group of government radiation experts has declared that:

• Annual radiation exposure of more than 100 millisieverts is known to raise risks for developing cancers, but nothing is known about annual radiation exposure of less than 100 millisieverts;

• Annual cumulative radiation exposure (external only, it seems) of 20 millisieverts for the general public poses hardly any danger of developing cancer;

• There is no difference between internal and external radiation exposure;

• Low-dose radiation exposure over a long period of time is less risky than one-time episodic exposure to large-dose radiation;

• The relationship between low-dose internal radiation exposure and bladder cancer cannot be proven.

Above points are from the article in Mainichi Shinbun 12/15/2011, the only paper that had any critical thinking on this issue. All the other large-circulation newspapers and NHK simply parroted what was said by the experts and the government officials.

Speaking of government officials, Asahi Shinbun reports (12/15/2011) that Minister in charge of the nuclear accident and Minister of the Environment Goshi Hosono explained the government's thinking in the press conference after the group meeting, saying:

「２０ミリシーベルトで人が住めるようになるということだ」

"So, 20 millisieverts per year radiation means people can live there."

This working group of so-called experts met for about a month to discuss the risk of "low-level" radiation exposure (meaning less than 20 millisieverts per year) and make a decision. Now they have made the decision and submitted the report to the government, the government duly accepts the independent experts' opinion, declares 20 millisieverts radiation to be an acceptable guideline, and plan accordingly.

What's the plan, you ask?

The government is set to convene a cabinet meeting in the evening and declare a "cold shutdown state" and will soon declare certain municipalities within the 20-kilometer radius "no entry" zone to be now "safe" to return (see my previous post).

In that country, if the government declares "one plus one equals four", or "tomorrow the sun rises from the west", people are expected to say "of course", and the calculators would start showing one plus one equals 4 and the sun would rise from the west. Or at least they would try. The land of miracles.

20 millisieverts per year of radiation exposure for the general public. There is no mention of different standard for children, except for the "effort" that the government is supposed to exert to lower the radiation for children.

Radiation control zone is 1.3 millisieverts per 3 months (5.2 millisieverts per year).

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508 Millisievert Annual Cumulative Radiation at 3 Kilometers from Fukushima I Nuke Plant

How do you even begin to decontaminate the area like that, not to mention returning people even on a temporary basis?

The Ministry of Education and Science announced the annual cumulative radiation levels within the no-entry evacuation zone within the 20-kilometer radius from the Fukushima I Nuclear Power Plant, and at the highest place - 3 kilometers west by southwest of the plant - it would be 508 millisieverts in one year from March 11, 2011.

From Asahi Shinbun (8/20/2011):

文部科学省は東京電力福島第一原発から２０キロ圏内の警戒区域の積算放射線量を、１９日に公表した。原発事故発生から１年間の推計値の最高は、西南西３キロにある福島県大熊町小入野で５０８．１ミリシーベルトにのぼり、除染作業の困難さが改めて示された。最低は南相馬市小高区の３ミリシーベルト台で、数値にばらつきがあった。

On August 19 the Ministry of Education and Science announced the amount of cumulative radiation within the no-entry evacuation zone within the 20-kilometer radius from Fukushima I Nuclear Power Plant. The highest estimated cumulative radiation in one year from the day of the accident would be 508.1 millisieverts in Koirino in Okuma-machi in Fukushima Prefecture, located at 3 kilometers west by southwest of the plant. It reinforces the fear that decontamination effort would be difficult. The lowest was 3-plus millisieverts in Kodaka-ku in Minami Soma City. The numbers differ significantly within the 20-kilometer radius.

　立ち入りが禁止された警戒区域９市町村のうち、８市町村の５０地点を調査。事故から来年３月１１日までの１年間、毎日、屋外に８時間、木造家屋内に１６時間いたと仮定して積算量を推計した。

Of 9 municipalities within the no-entry zone, 50 locations in 8 municipalities were surveyed. The cumulative radiation levels were estimated by assuming people would spend 8 hours outdoors, and stay 16 hours indoors in wooden houses everyday for 1 year until March 11 of 2012.

　計画的避難区域指定などの際に目安とされた年２０ミリシーベルトを超えたのは、５０地点のうち３５地点。第一原発のある大熊町では全１２地点が２０ミリシーベルトを超え、うち７地点で１００ミリシーベルト以上となった。最も高い同町小入野の５０８．１ミリシーベルトは、一般の人が浴びる人工の放射線量の限度１ミリシーベルトの５００年分にあたる。

35 locations out of 50 would exceed 20 millisieverts per year, which was used to determine the planned evacuation zone. In Okuma-machi where Fukushima I Nuke Plant is located, all 12 locations surveyed would exceed 20 millisieverts, with 7 exceeding 100 millisieverts. The highest number in Koirino in Okuma-machi is 508.1 millisieverts, which is equal to 500 years worth of the annual radiation exposure limit for non-nuclear workers (1 millisievert).

　浪江町では最高が北西２０キロの川房で２２３．７ミリシーベルト、最低は北８キロ地点の４．１ミリシーベルト。

In Namie-machi, the highest would be 223.7 millisieverts per year at Kawafusa, 20 kilometers northwest of the plant. The lowest would be 4.1 millisieverts at a location 8 kilometers north of the plant.

　文科省によると、原発から３キロ圏内の避難住民の一時帰宅が検討されており、参考にするという。

The temporary return of residents within the 3-kilometer radius from the plant is being discussed, and this result will be consulted, according to the Ministry of Education and Science.

The national government is planning to allow the residents temporarily returning to their homes within the 20-kilometer radius to bring in their cars and load up whatever they can from their homes.

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