Power failure hits Fukushima spent fuel ponds

A power failure at Japan's tsunami-hit Fukushima nuclear plant has affected cooling systems for spent fuel ponds.

A statement from operator Tepco said the cause of the power failure, which began at 18:57 on Monday (09:57 GMT), was still being assessed.

The outage had hit ponds at reactors 1, 3 and 4, it said, but cooling to the reactors themselves was not affected.

There was no immediate danger as it would take four days for the hottest pool to hit safety limits, Tepco said.

"We are trying to restore power by then," Tokyo Electric Power Company (Tepco) spokesman Kenichi Tanabe said.

The temperature in the hottest fuel pond, at Unit 4, was 30.5 degrees Celsius on Tuesday morning, Tepco said, well below the safety limit of 65 degrees.

The two ponds in Units 1 and 3 had lower temperatures and would take even longer to reach the safety limit, the spokesman said.

Another common storage pool was also affected, Japan's NHK reported.

'Back-up system'

The ponds store spent fuel from the nuclear reactors. They cool the fuel - which generates intense heat - and provide shielding from radiation. The spent fuel remains in the ponds for a year or more.

There is no immediate threat of a radiation release. But if fresh cooling water is not restored within the deadlines, it is possible that the water in the ponds could start to boil.

That would lead to a loss of water and eventually to the exposure of the spent fuel rods to air. If that were to happen, reports the BBC's Rupert Wingfield-Hayes in Tokyo, it would be a very serious situation and could lead to a release of radiation.

Tepco said it was trying to repair a broken switchboard that could have caused the problem, AP news agency reports.

"In the worst case scenario, we have a system in place to put water into the pools, so we have a double strategy: we have time to find a solution before the temperature gets out of hand and then also the ability to inject water into the pools if needed," Tepco official Masayuki Ono said.

The government said Tepco was tackling the problem.

"As they are planning to take all possible substitute measures for cooling, we do not need to worry at all," government spokesman Yoshihide Suga said.

The Fukushima nuclear plant was crippled by the 11 March 2011 earthquake and tsunami. Waves knocked out cooling systems to the reactors, leading to meltdowns at three of them.

Engineers have since stabilised the plant but years of work lie ahead to fully contain the disaster and tackle its effects.

Tens of thousands of evacuees remain unable to return home.

BBC