TOKYO -- Melted fuel likely leaked out into a reactor's containment vessel at the Fukushima Daiichi nuclear power plant and is emitting deadly radiation inside, Tokyo Electric Power Co. Holdings reported on Thursday.
Tepco inspected the inside of the No. 2 reactor's containment vessel in late January by inserting a camera on a telescoping pole. The resulting images showed a 1-sq.-meter hole apparently melted into a steel-grating walkway directly beneath the reactor pressure vessel, all but confirming that there was a leak.
Based on the "noise" in the images, the utility estimated that one area of the containment vessel was emitting radiation at a level of 530 sieverts per hour -- enough to kill a human in under a minute. Only emissions up to 73 Sv/hour had been detected before at the reactor, which was crippled by a March 2011 tsunami.
Tepco previously believed that most of the reactor's nuclear fuel had been contained in the pressure vessel, based on last year's muon tomography inspection -- a technique similar to X-rays but more powerful. But "it's highly possible that melted fuel leaked through," said Yuichi Okamura, a company spokesman for nuclear power.
The power company had planned to deploy a robot into the containment vessel to inspect debris that is thought to be melted nuclear fuel. But the newly discovered hole lies on the robot's planned path, forcing the company to change its approach.