One of Japan’s crippled nuclear reactors still has fatally high radiation levels and much less water to cool it than officials 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 number two reactor’s containment chamber for the second time since the tsunami swept into the Fukushima Daiichi plant, a year ago.
The data shows the damage from the disaster is so severe 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 two reactor is the only one officials have been able to closely examine so far.
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 probably sent radiation levels up to a dangerously high 70 an hour inside the container, said Junichi Matsumoto, spokesman for the plant operator, Tepco. The figure far exceeds the highest level previously detected, of 10 sieverts an hour, which was detected around an exhaust duct shared by the number one and two units last year.
“It’s extremely high,” he said, adding that an endoscope would last only 14 hours in those conditions. When locating and removing melted fuel during the decommissioning process, he said, “we have to develop equipment that can tolerate high radiation”.
The probe also found that the containment vessel – a beaker-shaped container enclosing the core – had cooling water up to only 60cms (24ins) 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.