A Mistake?

The BBC says that TEPCO admits a mistake:

The operators of a stricken Japanese nuclear plant have apologised for a “mistake” in reporting a radiation spike 10 million times above normal.

Tokyo Electric Power Company, which has previously been criticised by officials for its handling of the crisis at the plant, said it got the readings wrong.

Despite the mistake, the radiation spike at reactor 2 was still very high and enough to evacuate workers.
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A spokesman for Japan’s nuclear watchdog, Hidehiko Nishiyama, said the level of radiation in puddles near reactor 2 was confirmed at 1,000 millisieverts an hour.

“It is an extremely high figure,” Mr Nishiyama said.

The radiation levels are so high, that emergency workers near the contaminated water would have received four times their maximum annual dose of radiation in just one hour.
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Earlier, Japan’s nuclear agency said that levels of radioactive iodine in the sea near the plant had risen to 1,850 times the usual level.
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However, the government in Tokyo has said that airborne radiation around the plant is decreasing, so there is no need to extend the evacuation zone.

Apparently someone panicked having seen the reading on the radiation detector and garbled the number. The revised number is still in the “fatal” range.

According to the US Nuclear Regulatory Commission Fact Sheet on Biological Effects of Radiation: “Above background levels of radiation exposure, the NRC requires that its licensees limit maximum radiation exposure to individual members of the public to 100 mrem (1mSv) per year, and limit occupational radiation exposure to adults working with radioactive material to 5,000 mrem (50 mSv) per year.”

The “50 mSv per year” US limit on nuclear workers is fifty millisieverts per year, while the first article indicates that 250 millisieverts per year is the Japanese limit.

CNN noted that TEPCO hikes radiation limits as workers’ exposure rises: “The owner of the stricken nuclear power complex in northeastern Japan said Saturday that it will hike the radiation exposure limit for its workers at the plant from 100 millisieverts per shift to 150 millisieverts, Japan’s public broadcaster NHK reported.”

The Japanese workers are getting three times the US maximum for a year on every shift, and exceeding the Japanese limit in less than two shifts.