The detection near the plant, which is located about 250 km northeast of Tokyo, indicates a reactor meltdown is about to occur, officials at the Nuclear and Industrial Safety Agency said Saturday.
According to an earlier report, the operator of the nuclear plant opened the valves of the containers housing the reactors to reduce pressure, a move that led to the release of a small amount of radioactive steam.
A massive 8.9-magnitude earthquake followed by tsunami rocked the northeastern Japan Friday, killing about 1,000 people.
Published 12 March 2011, 06:02 IST