Meltdown alert at Japan reactor
BBC
Sun March 13, 2011
Technicians are battling to stabilise a third reactor at a quake-stricken Japanese nuclear plant that has been rocked by a second blast in three days.
Sea water is being pumped into reactor 2 at the Fukushima Daiichi plant after its fuel rods were fully exposed twice.
International nuclear watchdogs said there was no sign of a meltdown but one minister said a melting of rods was "highly likely" to be happening.
The crisis was sparked by Friday's 9.0-magnitude quake and tsunami.
Thousands of people are believed to have died, and millions are spending a fourth night without water, food, electricity or gas. More than 500,000 people have been left homeless.
'All our effort'
On Monday a hydrogen blast at the Fukushima Daiichi's reactor 3 injured 11 people and destroyed the building surrounding it. The explosion was felt 40km (25 miles) away and sent a huge column of smoke into the air.
It followed a blast at reactor 1 on Saturday.
Chief Cabinet Secretary Yukio Edano said there were signs that the fuel rods were melting in all three reactors.
"Although we cannot directly check it, it's highly likely happening," he told reporters.
Both explosions at the plant were preceded by cooling system breakdowns but the Tokyo Electric Power Company (Tepco) said neither blast penetrated the thick containment walls shielding the reactor cores.
It said radiation levels outside were still within legal limits.
But shortly after Monday's blast, Tepco warned it had lost the ability to cool Fukushima Daiichi's reactor 2.
Officials battled all Monday and into the early hours of Tuesday to try to keep water levels up in order to cool the nuclear fuel rods, but on two occasions the rods have been fully exposed.
Exposure for too long a period of time can damage the rods and raise the risk of a meltdown.
Four of the five pumps used to administer cooling sea water were believed to have been damaged by the blast at reactor 3.
Nuclear and Industrial Safety Agency official Ryohei Shiomi said reactors 1 and 3 had "somewhat stabilised" but "unit 2 now requires all our effort".
A Tepco official later pointed to some improvement and said the company did "not feel that a critical event is imminent".
Pressure has been released from the containment vessel, reducing the risk of a catastrophic explosion, but if the vessel is cracked it could still release radioactive material.
Nearly 185,000 people have been evacuated from a 20km (12 mile) exclusion zone around the plant.
The US said it had moved one of its aircraft carriers from the area after detecting low-level radiation 160km offshore.
Earlier, Tepco said it had restored the cooling systems at two of the three reactors experiencing problems at the nearby Fukushima Daini power plant, 11.5km (7 miles) to the south.
The Japanese government has asked the International Atomic Energy Agency (IAEA) to send a team of experts to help.
"Nuclear plants have been shaken, flooded and cut off from power. Operators have suffered personal tragedies," IAEA director general Yukiya Amano told reporters in Vienna. "[But] the reactor vessels have held and radioactive release is limited."
Mr Amano said the crisis was very unlikely to turn into another Chernobyl, the nuclear power plant in Ukraine that blew up in 1986.
James Lyons, a senior IAEA nuclear safety official, also said: "I think at this time we don't have any indication of fuel... currently melting."
But the French Nuclear Safety Authority (ASN) cast doubt on Japan's classification of the crisis at Fukushima as level 4 of 7 on the International Nuclear Event Scale. Chernobyl was classified as level 7.
"Level four is a serious level," ASN chief Andre-Claude Lacoste said, but added: "We feel that we are at least at level five or even at level six."
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