After only a month on the job, the Nuclear Regulation Authority has been forced to apologize after a utility spotted errors in its forecast maps showing the likely spread of radioactive substances from a serious accident at each of the nation's 16 nuclear power plants.
The errors on the maps, released by the government's new nuclear regulatory agency on Oct. 24, involved the spread of radiation in both direction and distance from six nuclear plants.
Hokuriku Electric Power Co. officials contacted the Japan Nuclear Energy Safety Organization (JNES), which did the calculations, on Oct. 26 after looking at the maps. Hokuriku Electric had provided weather data it monitored at its Shika nuclear plant in Ishikawa Prefecture.
"We are to blame for the very fact that an external body pointed out (the errors)," Hideka Morimoto, NRA deputy secretary-general, told a news conference on Oct. 29.
"The objective of the Nuclear Regulation Authority is to set up a system to supervise nuclear plant operators, but regretfully, we are not living up to that goal. We will learn from the experience for what we do in the future."
Local government officials, who are responsible for reviewing their nuclear contingency response plans or drawing up new ones on the basis of the NRA's radiation forecast maps, expressed frustration at the errors.
"I want them to convey accurate information, because we have to draw up an evacuation plan by March," said Mito Deputy Mayor Mitsuru Tajiri.
NRA officials attributed the errors to data input mistakes and released corrected forecast maps for the corresponding sites on Oct. 29.
The revised maps provided a forecast where radioactive substances would spread toward central Mito if an accident similar to the March 2011 disaster at the Fukushima No. 1 nuclear plant were to hit the Tokai No. 2 plant in Ibaraki Prefecture.
The city hall of Hitachinaka in the same prefecture was included in the zone that would be subject to weekly doses of 100 millisieverts in the revised forecast map.
"The authorities didn't tell us anything about the corrigenda," said one official at the city government's living safety division. "That was also the case when the maps were released initially on Oct. 24."
The errors were found in the forecast maps for the Kashiwazaki-Kariwa nuclear plant in Niigata Prefecture; the Tokai No. 2 plant in Ibaraki Prefecture; the Shika plant in Ishikawa Prefecture; the Tsuruga plant in Fukui Prefecture; the Genkai plant in Saga Prefecture; and the Sendai plant in Kagoshima Prefecture.
NRA officials said the maps utilize wind directions, rainfall and other meteorological data monitored by nuclear plant operators at the respective sites. But different operators use different coding systems for the 16 wind directions, with one company labeling north as number 1 and another labeling north as number 16, the officials said.
Workers committed mistakes while converting wind directions to code number input, which resulted in rotations, either clockwise or counterclockwise, by one dial notch for the six nuclear plants. They also miscalculated distances where the weekly radiation doses would likely reach 100 millisieverts.
While the JNES, an external body, made the mistakes, Morimoto admitted at the Oct. 29 news conference that the nuclear watchdog is to blame for insufficient checking.
"We should have verified the data on the premise that they could contain errors," Morimoto said. "We did lack that consideration."
Further errors were discovered in the materials distributed during the news conference to apologize for the data errors.
Reporters pointed out inconsistencies in the NRA's table of municipalities that include the farthest locations where radiation levels are likely to force evacuations, prompting NRA officials to quickly correct the municipality names.
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