TOKYO, Oct. 23 (Kyodo) — Radiation doses in areas located over 30 kilometers from four nuclear power plants in Japan, including those in Niigata and Fukui prefectures, could reach 100 millisieverts in the first seven days following a severe accident like the one at the Fukushima Daiichi complex last year, estimates by the Nuclear Regulation Authority showed Monday.

The NRA is currently crafting new guidelines on nuclear disaster mitigation measures in the wake of the Fukushima disaster and has proposed a radius of 30 km from a nuclear plant as a rough standard for areas where special preparations should be made.

The latest simulation results, however, could lead local governments to set areas requiring preparations beyond the 30-km zone.

The four nuclear power stations are Tokyo Electric Power Co.'s Kashiwazaki-Kariwa plant in Niigata Prefecture and Fukushima Daini plant in Fukushima Prefecture, Kansai Electric Power Co.'s Oi plant in Fukui Prefecture, and Chubu Electric Power Co.'s Hamaoka plant in Shizuoka Prefecture.

In the simulation, the NRA assumed two cases -- one in which the amount of radioactive substances released by a plant is as high as in the Fukushima disaster and another in which severe accidents occur in all reactors at each plant -- to identify areas in which exposure could reach 100 millisieverts in the first seven days.

The simulation, however, did not take into account geological formations in areas around the plants.

As for the Kashiwazaki-Kariwa plant, areas located within a 40-km radius of the plant would also register 100 millisieverts.

Of the four power stations, only two reactors at the Oi plant are currently in operation.