|The latest findings renew doubt about the Fukushima Daiichi plant's stability [Reuters]
One of Japan's crippled nuclear reactors still has fatally high radiation levels and much less water to cool it than officials had estimated, according to an internal examination that renews doubts about the plant's stability.
A tool equipped with a tiny video camera, a thermometer, a dosimeter and a water gauge was used to assess damage inside the containment chamber of Fukushima Daiichi plant's number 2 reactor for the second time since the tsunami swept into the complex more than a year ago.
The data collected on Tuesday showed the damage from the disaster is so severe that the plant operator will have to develop special equipment and technology to tolerate the harsh environment and decommission the plant. The process is expected to last decades.
The other two reactors that had meltdowns could be in even worse shape. The number 2 reactor is the only one officials have been able to closely examine so far.
'Dangerously high' radiation
Tuesday's examination with an industrial endoscope detected radiation levels up to 10 times the fatal dose inside the chamber. Plant officials previously said more than half of the melted fuel had breached the core and dropped to the floor of the primary containment vessel, some of it splashing against the wall or the floor.
Particles from melted fuel have likely been responsible for sending radiation levels up to a dangerously high 70 sieverts per hour inside the container, said Junichi Matsumoto, spokesman for Tokyo Electric Power Company.
The figure far exceeds the highest level previously detected, 10 sieverts per hour, which was detected around an exhaust duct shared by number 1 and 2 units last year.
"It's extremely high," he said, adding that an endoscope would last only 14 hours in those conditions. "We have to develop equipment that can tolerate high radiation" when locating and removing melted fuel during the decommissioning.
The probe also found that the containment vessel, a beaker-shaped container enclosing the core, had cooling water up to only 60 centimeters from the bottom, far below the 10 metres estimated when the government declared the plant stable in December. The plant is continuing to pump water into the reactor.
Video footage taken by the probe showed the water inside was clear but contained dark yellow sediments, believed to be fragments of rust, paint that had been peeled off or dust.
Three Daiichi reactors had meltdowns, but the number 2 reactor is the only one that has been examined because radiation levels inside the reactor building are relatively low and its container is designed with a convenient slot to send in the endoscope.
The exact conditions of the other two reactors, where hydrogen explosions damaged their buildings, are still unknown.
'Vulnerable to aftershocks'
Simulations have indicated that more fuel inside number 1 has breached the core than the other two, but radiation at number 3 remains the highest.
The high radiation levels inside the number 2 reactor's chamber mean it is inaccessible to the workers, but parts of the reactor building are accessible for a few minutes at a time, with the workers wearing full protection.
Last year's massive earthquake and a tsunami set off the worst nuclear accident since Chernobyl, causing three reactor cores to melt and massive radiation leaks.
The government said in December that the reactors were safely cooled and the plant had stabilised, while experts have questioned its vulnerability.
During a recent visit by a group of journalists, the head of the plant said it remained vulnerable to strong aftershocks and tsunami, and that containing contaminated water and radiation was a challenge.
Radioactive water had leaked into the ocean several times already.