ONE of the reactors at the crippled Fukushima Daiichi power plant did suffer a nuclear meltdown, Japanese officials admitted for the first time yesterday, describing a pool of molten fuel at the bottom of the reactor's containment vessel.
Engineers from the Tokyo Electric Power company (TEPCO) entered the No 1 reactor at the end of last week for the first time and saw that the top five feet or so of the core's 13ft fuel rods had been exposed to the air and melted down.
Previously, TEPCO believed that the core of the reactor was submerged in enough water to keep it stable and that only 55pc of the core had been damaged.
Now the company is worried that the molten pool of radioactive fuel may have burned a hole through the bottom of the containment vessel, causing water to leak.
"We will have to revise our plans," said Junichi Matsumoto, a spokesman for TEPCO. "We cannot deny the possibility that a hole in the pressure vessel caused water to leak."
TEPCO has not clarified what other barriers there are to stop radioactive fuel leaking if the steel containment vessel has been breached. Greenpeace said the situation could escalate rapidly if "the lava melts through the vessel".
However, an initial plan to flood the entire reactor core with water to keep its temperature from rising has now been abandoned because it might exacerbate the leak.
TEPCO said there was enough water at the bottom of the vessel to keep both the puddle of melted fuel and the remaining fuel rods cool. The company added that it had sealed a leak of radioactive water from the No 3 reactor after water was reportedly discovered to be flowing into the ocean. A similar leak had discharged radioactive water into the sea in April from the No 2 reactor.
Greenpeace said significant amounts of radioactive material had been released into the sea and that samples of seaweed taken from as far as 40 miles from the Fukushima plant had been found to contain radiation well above legal limits.
Of the 22 samples tested, 10 were contaminated, with five times the legal limit of iodine 131, and 20 times of caesium 137. Seaweed is a huge part of the Japanese diet and the average household eats almost 7lb a year.
Inland from the plant, there has been a huge cull of the livestock left inside the 18-mile mandatory exclusion zone, with thousands of cows, horses and pigs being destroyed.
The environment ministry has announced that it will attempt to rescue the thousands of pets that were left behind when residents were ordered to leave. At least 5,800 dogs were owned by the residents of the zone, although it is unclear how many remain alive two months after the earthquake and tsunami struck.
Nuclear Industrial and Safety Agency officials said the new data indicates that it is likely that partially melted fuel had fallen to the bottom of the pressurised vessel that holds the reactor core together and possibly leached down into the drywell soon after the March 11 quake and tsunami that struck Japan's north-eastern coast.
While officials said it was unlikely that the chunks of fuel were still dangerously hot or that they could melt through the concrete base of the containment vessel, they acknowledged that the level of damage could complicate plans detailed in April to bring the plant to a cold shutdown within nine months. (© Daily Telegraph, London)