Additional errors were found on the Nuclear Regulation Authority’s maps forecasting the spread of radioactive substances from a serious nuclear accident, but the industry watchdog said these mistakes would not affect evacuation plans.
Tohoku Electric Power Co. on Nov. 22 said it discovered errors in data used to forecast the extent of radioactive substances released into the air if an accident were to occur at its Onagawa nuclear power plant in Miyagi Prefecture and Higashidori nuclear power plant in Aomori Prefecture.
The utility classified “atmosphere stability” above the plants into 10 levels depending on wind speed and the amount of insolation, or radiation received from the sun. That information was submitted to the Japan Nuclear Energy Safety Organization (JNES), an institution that carried out computer simulations to make the forecast maps.
Of all the 17,520 weather entries for a full year at the two plants, 177 of them--108 for Onagawa and 69 for Higashidori--contained errors in classification.
Tohoku Electric officials said an affiliate entered the incorrect data when it developed a computer program to classify atmosphere stability.
The utility informed the NRA and the JNES of the mistakes on Nov. 22, and apologized at a news conference the same day.
Tohoku Electric checked its own data for potential mistakes after the NRA’s series of announcements of errors on the radiation forecast maps.
The NRA first released the maps on Oct. 24, showing where radioactive substances would spread in the event of an accident similar to the one at the Fukushima No. 1 nuclear power plant. These forecasts obliged municipalities in the danger zones to start drawing up evacuation procedures.
However, the NRA believes the impact of the latest errors will be minimal because they were only a small part of all the data used for the two areas.
On the day the maps were first released, the NRA was forced to correct data about the governments located farthest from the nuclear plants where radiation doses were likely to reach 100 millisieverts in the first week after the accident.
On Oct. 29, the NRA acknowledged additional errors on the distances and directions of the spread of radioactive substances from Tokyo Electric Power Co.’s Kashiwazaki-Kariwa nuclear plant in Niigata Prefecture and five other nuclear plants.
On Nov. 6 and 8, the NRA announced mistakes in the radiation forecasts for Kyushu Electric’s Genkai plant in Saga Prefecture and the Sendai plant in Kagoshima Prefecture.
The NRA says it plans to release the corrected maps later this month after again checking for possible errors.
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