Crews fixing gauges inside Fukushima Daiichi unit 1 discovered water levels in the reactor were much lower than originally thought – likely 5 meters below the top of the 4-meter-long fuel rods.
Workers were not able to access the reactor for weeks following the March 11 earthquake and tsunami that triggered a series of serious accidents at the plant. Before workers could fix it, the gauge showed water levels at only 1.6 meters below the top of the fuel rods. But Tokyo Electric Power Co. officials said Thursday that they now believe the fuel is fully exposed to air, has likely melted and dropped to the bottom of the pressure vessel, the Daily Yomiuri newspaper reported.
The utility also revealed new concerns that water injected from external pumps is leaking from both the pressure vessel and its containment. Kyodo News quoted TEPCO as saying it has found multiple small holes in the pressure vessel's welded piping. The possibility of core-exposed coolant seeping into underground tunnels that might leak complicates TEPCO’s plan to circulate water inside the containment vessel to bring the fuel to cold-shutdown temperatures in six to nine months.
The volume of water pumped into the unit so far indicates significant leakage has already occurred: The containment can only hold 7,800 cubic meters of water. More than 10,000 cubic meters of water has been pumped into the 360-cubic-meter pressure vessel within it.