High radiation halts debris cleanup at Fukushima plant
Tokyo Electric Power expects no big delays in probe of No. 2 reactor
TOKYO -- Tokyo Electric Power Co. Holdings was forced to suspend the operation of a robot that was clearing debris inside a reactor at the Fukushima Daiichi nuclear power plant on Thursday, after its camera stopped functioning due to high radiation levels.
Tepco is still working to remove nuclear fuel from the plant, which was wrecked by a March 2011 tsunami. The utility said operations inside the No. 2 reactor were suspended after radiation levels as high as 650 sieverts per hour were detected. The company estimated the radiation level by analyzing images sent by the robot.
The day's maximum radiation level exceeded a Feb. 2 measurement of 530 sieverts per hour estimated based on images from a telescopic camera. Tepco believes the nuclear fuel melted through the bottom of the reactor vessel and onto the surrounding containment vessel. The high-level radiation is coming from that part of the reactor.
The camera used in the debris-clearing robot was designed to withstand 1,000 sieverts of radiation in total, according to Tepco.
Thursday's operation was aimed at clearing away debris, estimated to be up to 2cm thick, with jets of water to make a smooth passage. In the next phase of the cleanup, a second robot will crawl down this passage and examine the area carefully before the melted nuclear fuel is removed.
Tepco said there are no large obstacles blocking the planned path of the second robot, which has cameras mounted on its head and the tip of its tail, which can be pointed forward like a scorpion's. The utility does not expect a major delay in deploying the scorpion robot, which is scheduled for the end of February.
Thursday's operation started around 5 a.m. but was halted about four hours later, three hours earlier than planned, after images sent from the robot to operators grew dark due to high radiation levels.