U.S. nuclear regulatory commission says Japanese government, which is scrambling to avert a meltdown at a stricken nuclear plant, has formally asked the U.S. for help with cooling nuclear reactors. The U.S. nuclear regulatory commission said it is considering possible replies to the request, which includes providing technical advice. Meanwhile, there was another explosion on Monday in the Fukushima Daiichi plant.
Technicians are battling to stabilise a third reactor at a quake-stricken Japanese nuclear plant, which has been rocked by a second blast in three days.
The fuel rods inside reactor 2 at the Fukushima Daiichi plant have been fully exposed on two separate occasions, raising fears of a meltdown.
Seawater is being pumped into reactor to try to stop the rods overheating.
A cooling system breakdown preceded explosions at the plant’s reactor 3 on Monday and reactor 1 on Saturday.
The latest hydrogen blast injured 11 people, one of them seriously. It was felt 40km (25 miles) away and sent a huge column of smoke into the air.
The outer building around the reactor was largely destroyed.
But as with the first explosion, Tokyo Electric Power Company (Tepco) said the thick containment walls shielding the reactor cores remained intact. It also said radiation levels outside were still within legal limits.
Shortly after the blast, Tepco warned that it had lost the ability to cool Fukushima Daiichi’s reactor 2.
Hours later, the company revealed that the fuel rods inside had been exposed fully at one point, reportedly for about two-and-a-half hours. It said a fire pump that had been used to pump seawater into the reactor had run out of fuel.
The company is now trying to inject sea water into the reactor to cover the fuel rods, cool them down and prevent another explosion.
Initially, water levels continued to fall despite the efforts, as only one of the five fire pumps was working, officials said. The other four were believed to have been damaged by the blast at reactor 3.
By Monday evening, the water level inside the reactor had risen to 2m. But later, Tepco officials said the fuel rods had again been fully exposed.
Air pressure inside reactor 2 rose suddenly when the air flow gauge was accidentally turned off. That blocked the flow of water into the reactor, leading to the water level dropping and the rods being exposed at about 2300 local time (1400 GMT).
“We are not optimistic but I think we can inject water once we can reopen the valve and lower the air pressure,” a Tepco official told reporters.
Exposure for too long a period of time can damage the fuel rods and raise the risk of overheating and possible meltdown.