Radiation projections

October 24, 2012

Draft guideline expands evacuation zone

http://www3.nhk.or.jp/daily/english/20121024_24.html

Japan's Nuclear Regulation Authority has proposed expanding the evacuation radius for nuclear accidents from the current 10 kilometers to 30 kilometers.

The new figure was included in a draft disaster response guideline submitted to the authority's meeting on Wednesday.

The authority looked into the fact that many elderly and hospitalized patients died in the course of evacuating the Fukushima accident in March last year.

The draft guideline calls for deciding evacuation shelters in advance and setting up temporary shelters for those who cannot move far away.

The authority plans to complete the guideline before the end of this month.

The guideline will form the basis of disaster plans to be created by the end of next March by 135 municipalities in 21 prefectures that lie within 30 kilometers of a nuclear plant.

Japan regulator projects nuclear radiation spread

http://www3.nhk.or.jp/daily/english/20121024_23.html

Japan's Nuclear Regulation Authority has unveiled projections for the spread of radiation from nuclear power plants across the country in the event of an accident like the one last year at the Fukushima Daiichi plant.

The regulatory body says severe accidents at 4 of the 16 nuclear power stations examined could result in widespread contamination beyond a 30-kilometer radius of the plants, and exceeding an international benchmark for evacuation.

The authority proposed increasing the current size of the evacuation zone around Japan's nuclear plants from a 10-kilometer radius to 30 kilometers.

The projections released on Wednesday simulate an event equivalent to the Fukushima accident, with a one-time massive release of radioactive substances from each plant. Assumptions include weather patterns recorded over the past year.

The projections show locations where effective doses of radiation in the first 7 days would reach 100 millisieverts the international benchmark for evacuation.

At 12 plants, including the Tomari plant in Hokkaido and the Ikata plant in Ehime Prefecture, these locations were all within the 30-kilometer radius.

Locations with 100 millisieverts of radiation showed up outside the 30-kilometer radius of 4 plants.

At the Kashiwazaki-Kariwa plant in Niigata Prefecture, which has 7 nuclear reactors, high-level radiation locations were projected in Uonuma City, about 40.2 kilometers from the plant.

The other 3 plants examined are the Fukushima Daini in Fukushima Prefecture, the Ohi plant in Fukui Prefecture, and the Hamaoka plant in Shizuoka Prefecture.

The projections are expected to serve as a reference for municipalities compiling evacuation plans for their residents by the end of next March.

The regulatory body says the projections don't take into account the geological features of areas surrounding the plants and should therefore be viewed as rough estimates only.

October 24, 2012

Post-disaster radiation predictions for nuclear plants released

http://mainichi.jp/english/english/newsselect/news/20121024p2a00m0na014000c.html

The Nuclear Regulation Authority (NRA) on Oct. 24 released predictions for the spread of radiation for all of Japan's nuclear plants besides the crippled Fukushima No. 1 Nuclear Power Plant in the event of future nuclear disasters.

They are the first such predictions to be released, and for four plants, the predictions extend past a 30-km evacuation radius proposed by the national government.

Two scenarios were calculated -- one where around the same amount of radiation that was released from the Fukushima No. 1 Nuclear Power Plant's first through third reactors is released, and one where all of a plant's reactors have melted down. For most of the plants, weather conditions used in calculations were those of last year.

For each plant, the farthest point where the International Atomic Energy Agency's evacuation standard of 100 millisieverts of combined external and internal exposure over one week would be reached following a nuclear disaster was mapped in 16 directions. To eliminate the influence of extreme weather, the top three percent of distances were omitted.

In the results, the Fukushima No. 2 Nuclear Power Plant in Fukushima Prefecture, the Kashiwazaki-Kariwa Nuclear Power Plant in Niigata Prefecture, the Hamaoka Nuclear Power Plant in Shizuoka Prefecture, and the Oi Nuclear Power Plant in Fukui Prefecture were all predicted to see radiation spread further than 30 kilometers.

At the Kashiwazaki-Kariwa plant, a site with a very high power output, the predicted spread went 40.2 kilometers east-southeast to the city of Uonuma. For the Hamaoka plant, the spread was over the ocean. The other 12 nuclear plants' spreads were within 30-km radiuses.

The office of the NRA, however, pointed out, "The calculations are based on hypotheticals and there are limits to their accuracy and reliability."

The maps were made by the NRA and the Japan Nuclear Energy Safety Organization for use as reference by municipal governments in putting together area disaster response plans by the end of March next year.