TOKYO (Kyodo) -- Water inside the troubled No. 1 reactor of the Fukushima Daiichi nuclear power plant was at an unexpectedly low level, not enough to cover the nuclear fuel, hinting that a large part of the fuel melted after being fully exposed, Tokyo Electric Power Co. said Thursday based on data obtained by adjusted gauges.
But the plant operator said the water at the bottom of the reactor pressure vessel holding the fuel is keeping the melted fuel cool, assuring that the company is succeeding in preventing the reactor's fuel from overheating by injecting water from outside.
Based on the latest data after workers adjusted gauges for measuring the water level at the reactor, water could not be confirmed inside the pressure vessel at a point 5 meters below where the top of the 4-meter-long fuel rods normally are, according to the utility also known as TEPCO.
The water level is far lower than earlier thought. Measurements taken before the gauge adjustment indicated that about 1.5 to 1.7 meters of the fuel rods were exposed and not submerged in water.
Still, the surface temperature of the pressure vessel was relatively low, measuring between 100 C and 120 C.
The utility had earlier estimated that 55 percent of the reactor core at the No. 1 unit has been damaged. It is unknown how much fuel melted and dropped to the bottom, but the fuel is unlikely to be at its original position.
TEPCO has been trying to check the levels of water inside the No. 1 reactor's pressure vessel and the outer primary container so that it can move ahead with a plan to flood the container with water up to the level above the fuel and create a system to stably keep the fuel cool.
But the latest finding on the situation inside the unit -- one of the six at the plant crippled by the March 11 massive quake and tsunami -- suggests that a significant amount of the water injected into the reactor core to keep the fuel cool as an emergency measure was leaking out to the primary container.
A TEPCO official said the company will review its plan to flood the primary container up to the level above the fuel.
Hidehiko Nishiyama, a spokesman for the government's Nuclear and Industrial Safety Agency, said even if the container is not flooded with water, creating a system that would enable coolant to circulate around the reactor is possible by using the water that now exists inside the vessel and primary container.
(Mainichi Japan) May 12, 2011