Tokyo Electric Power Co. plans to inject nitrogen into one of the reactors to prevent a hydrogen explosion at the Fukushima Daiichi nuclear power station.

Hidehiko Nishiyama, a spokesman for the Nuclear Industrial Safety Agency, told a news conference that there is no immediate danger of further explosions.

The outer walls and roof of the number 1 reactor (unit 1) was blown off on march 12 when hydrogen gas, which had built up in the area outside the reactor vessel as a result of reactions between the zirconium allow cladding on the fuel rods and water. Ordinarily the hydrogen would have been burned off but the systems to do that weren't operating. Within days hydrogen explosions had also occurred at reactor Nos. 2 and 3.

Nishiyama said the concern now is that inside unit 1's reactor vessel, hydrogen can accumulate there and leak into the containment vessel. Exposed to oxygen and any sparks, hydrogen can ignite, which is what happened on March 12. Nitrogen is an inert gas, so injecting it into the reactor should prevent any further explosions and fires.

A TEPCO official told a separate news conference that the company suspects the reactor vessel itself is damaged. The company released estimates that inside reactor units 1, 2, and 3, a large percentage of the fuel rods are damaged, and some may well have simply melted. The radiation - alpha particles, neutrons and beta particles - can dissociate water into hydrogen and oxygen, an explosive mix.

TEPCO managed to stop highly radioactive water from leaking into the ocean, but now faces the prospect of finding a place to store it. The leak was stopped when workers at the plant injected a substance called liquid glass into the gravel at the bottom of a shaft that houses piping and power cables. The shaft had a crack in it that was allowing contaminated water to escape into the sea.

There are still concerns over what to do with the water that gets drained from the reactor and turbine buildings, as it has to be stored somewhere. That amounts to thousands of tons of water, and the amount is increasing all the time as the closed-loop cooling systems are no longer functioning.

Japan quake Energy