Japan radioactivity being released "directly" into atmosphere: IAEA

Japan has told the UN nuclear watchdog a spent fuel storage pond was on fire at a reactor damaged by the earthquake and radioactivity was being released "directly" into the atmosphere, the Vienna-based agency said on Tuesday.

The International Atomic Energy Agency (IAEA), citing information it had received from Japanese authorities, said dose rates of up to 400 millisievert per hour have been reported at the Fukushima power plant site.

It did not give details or comparisons on the radiation level but the yearly background radiation from natural sources is estimated at around 3 millisieverts, a unit the IAEA uses to measure doses of radiation received by people.

"The Japanese authorities are saying that there is a possibility that the fire was caused by a hydrogen explosion," the IAEA said in a statement.

In Japan, authorities warned radiation levels had become "significantly" higher around the nuclear power plant on Tuesday after explosions at two reactors, and the French embassy said a low-level radioactive wind could reach Tokyo within hours.

The IAEA said it had been informed "that the spent fuel storage pond at the Unit 4 reactor of the Fukushima Daiichi nuclear power plant is on fire and radioactivity is being released directly into the atmosphere".

It added: "Dose rates of up to 400 millisievert per hour have been reported at the site. The Japanese authorities are saying that there is a possibility that the fire was caused by a hydrogen explosion."