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Japan releases 1st simulations of nuclear radiation spreading

Last Updated: Wednesday, October 24, 2012 - 16:25

Tokyo: Japan`s nuclear regulatory authorities on Wednesday released for the first time projections for the spread of radiation from nationwide reactors in the event of a severe accident like the one at the Fukushima Daiichi complex last year.

The amount of radiation released a week after an accident at Tokyo Electric Power Co.`s Kashiwazaki-Kariwa plant in Niigata Prefecture could reach the level where evacuation is recommended for an area as far as 40 kilometers from the plant, the Nuclear Regulation Authority said.

The regulatory body conducted the radiation simulations for 16 atomic plants in Japan to provide references for local governments to expand areas that should be subject to special preparations against nuclear disasters from the current radius of 10 km from a plant.

The authority plans to propose in its new nuclear disaster mitigation measure guidelines that emergency zones be set within a radius of around 30 km, but the latest estimates may make some local governments think about whether to include areas at a greater distance.

It found that doses could reach 100 millisieverts in the city of Uonuma in Niigata Prefecture, about 40.2 km away from the Kashiwazaki-Kariwa plant, based on the assumption of that all seven of its reactors suffer meltdowns.

Locations a little more than 30 km away from Chubu Electric Power Co.`s Hamaoka plant in Shizuoka Prefecture, Kansai Electric Power Co.`s Oi plant in Fukui Prefecture and Tokyo Electric`s Fukushima Daini plant in Fukushima Prefecture may also see radiation doses reach 100 millisieverts.

The regulatory body said the simulations are based on simple assumptions, such as past weather records, but do not take into account geological formations in areas around the plants.

The International Atomic Energy Agency calls for evacuations when effective doses exceed 100 millisieverts in the first seven days of an emergency exposure situation.

The authority plans to introduce the idea of "precautionary action zone" and "urgent protective action planning zone" in line with IAEA standards in the new guidelines, which will be created based on the lessons learned from the Fukushima disaster.

The former, where residents will be asked to evacuate immediately after an accident occurs, is expected to cover a 5-km radius, while the latter, where people will be asked to be prepared for evacuation depending on the situation, is expected to cover a 30-km radius.


First Published: Wednesday, October 24, 2012 - 16:24
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