The Japanese government rates the accident at the Fukushima Number One nuclear power plant at level 4 on an international scale of 0 to 7.
Two radioactive substances, cesium and radioactive iodine, were detected near the Number One reactor at the plant on Saturday. Their presence indicates nuclear fission of uranium.
The Nuclear and Industrial Safety Agency said that fuel in the reactor partially melted. It’s the first such accident in Japan.
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