Japan's nuclear safety agency has raised the crisis level at the stricken Fukushima Daiichi nuclear power plant to 7, from the current 5.
The agency told reporters on Tuesday that large volumes of radioactive substances that could affect human health and the environment are being released in a wide area.
Level 7 is the highest rank on an international standard and equivalent to the severity recorded after the Chernobyl disaster in 1986.
But the agency said the volume of radiation from Fukushima is one-tenth that at Chernobyl.
The agency said its calculations show that 370-thousand terabecquerels of radioactive iodine 131 and cesium 137 have been released from the plant.
The nuclear safety commission, in a joint press conference with the agency, put the estimated leak at 630-thousand terabecquerels of both substances.
One terabecquerel is equivalent to one trillion becquerels. Both organizations say the leak constitutes a level-7 crisis.
Senior agency official Hidehiko Nishiyama said 29 people died of acute radiation exposure at Chernobyl but there are no fatal radiation casualties at Fukushima.
He added that at Chernobyl the nuclear reactor itself exploded in contrast to the Fukushima plant, which was damaged by hydrogen explosions. He said the reactors themselves retain their shape.
Nishiyama also said the upgrade does not affect the existing evacuation plan, which was made on the basis of the same radiation evaluation.
The agency is required to announce the severity of a crisis at a nuclear facility based on the international standard from zero up to 7 set by the International Nuclear Event Scale.
Tuesday, April 12, 2011 13:09 +0900 (JST)