In this image taken from Japan's NTV/NNN Japan television footage, smoke ascends from the Fukushima Dai-ichi nuclear plant's Unit 3 in Okumamachi, Fukushima Prefecture, northern Japan, Monday, 14 March 2011. The second hydrogen explosion in three days rocked Japan's stricken nuclear plant Monday, sending a massive column of smoke into the air and wounding 11 workers. NTV

TOKYO, April 12 (Kyodo) -- Japan on Tuesday raised the severity level of the accident at the crippled Fukushima Daiichi nuclear plant to the maximum 7 on an international scale, up from the current 5 and matching that of the 1986 Chernobyl catastrophe.

The previous evaluation of 5 on the International Nuclear Event Scale provisionally set by the Nuclear and Industrial Safety Agency, a body under the Ministry of Economy, Trade and Industry, was at the same level as the Three Mile Island accident in the United States in 1979.

While raising the level for the accident, the agency said, however, that the amount of radioactive materials released into the external environment from the nuke plant is estimated to be about 10 percent of the amount released in the Chernobyl catastrophe.

The decision comes after the release of a preliminary calculation Monday by the Nuclear Safety Commission of Japan, which said the crippled nuclear plant was releasing up to 10,000 terabecquerels of radioactive materials per hour at one point after a magnitude 9.0 earthquake and subsequent tsunami hit northeastern Japan on March 11.

Level 7 accidents on the INES correspond to the release into the external environment of radioactive materials equal to more than tens of thousands of terabecquerels of radioactive iodine 131. One terabecquerel equals 1 trillion becquerels.

The agency estimated that up to 370,000 terabecquerels of radioactive materials had been released in the air while the commission said it estimated 630,000 terabecquerels, both far exceeding the criteria for level 7.

Haruki Madarame, chairman of the commission, said earlier it estimates the release of 10,000 terabecquerels of radioactive materials per hour continued for several hours.

The commission says the release has since come down to under 1 terabecquerel per hour and that it is still examining the total amount of radioactive materials released.

It also released a preliminary calculation for the cumulative amount of external exposure to radiation, saying it exceeded the yearly limit of 1 millisievert in areas extending more than 60 kilometers northwest of the plant and about 40 km south-southwest of the plant. …

Japan raises nuke accident severity level to highest 7 from 5

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