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Nuclear Regulator Says Radiation Leak at Japan’s Lab at Level 1

Japan’s nuclear watchdog said it tentatively ranked a radiation leak at the Japan Atomic Energy Agency’s laboratory last week at the second lowest level of 1 on the international scale for nuclear accident severity.

The leak caused a “slight increase” in radiation levels outside the site, and there would be “no impact on the general public,” the Nuclear Regulation Authority said in a statement yesterday. Japan Atomic failed to properly manage the leak and used ventilation fans to emit radiation into the air even though it confirmed contamination inside the facility, the regulator said.

The nuclear physics laboratory in Ibaraki prefecture was shut after the leak on May 23, which caused at least 30 people in the building to be exposed to radiation, the NRA said. The highest dose among the people was 1.7 millisieverts, less than the annual regulatory limit of 50 millisieverts for nuclear workers in Japan, the regulator said.

Japan’s Nuclear and Industrial Safety Agency, the now-defunct nuclear watchdog, rated the Fukushima disaster at the highest level 7, the same as the 1986 Chernobyl accident, a month after the quake and tsunami in March 2011 caused meltdowns and radiation leaks at Tokyo Electric Power Co.’s atomic station. Initially, the Fukushima accident was given a rating of 5 on the international rating, the same as the 1979 partial meltdown at Three Mile Island in the U.S.

To contact the reporter on this story: Tsuyoshi Inajima in Tokyo at

To contact the editor responsible for this story: Jason Rogers at

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