When TEPCO workers repaired a pressure gauge in the Unit 1 reactor at the crippled Fukushima nuclear power plant, they received an unpleasant surprise, as Reuters reported today:
“(TEPCO officals) discovered that the water level in the pressure vessel that contains its uranium fuel rods had dropped about 5 metres (16 ft) below the targeted level to cover the fuel under normal operating conditions.”
A TEPCO official concluded:
“There must be a large leak,” Junichi Matsumoto, a general manager at … TEPCO, told a news conference. “The fuel pellets likely melted and fell, and in the process may have damaged … the pressure vessel itself and created a hole,” he added.
Reuters also reported:
“Based on the amount of water that is remaining around the partially melted and collapsed fuel, Matsumoto estimated that the pressure vessel had developed a hole of several centimetres in diameter.”
“The finding makes it likely that at one point in the immediate wake of the disaster the 4-metre-high stack of uranium-rich rods at the core of the reactor had been entirely exposed to the air, he said.”
Matsumoto thinks that it is possible that the same thing happend in the Units 2 & 3 reactors:
Matsumoto said it was likely that the pressure vessels in the other two reactors could be leaking as well if fuel rods had collapsed and melted after the earthquake and tsunami.