Water was only 60 centimeters deep in a reactor containment vessel at the crippled Fukushima No. 1 nuclear plant, a fraction of what was previously assumed, Tokyo Electric Power Co. said March 26.
Water was only 60 centimeters deep in a reactor containment vessel at the crippled Fukushima No. 1 nuclear plant, a fraction of what was previously assumed, Tokyo Electric Power Co. said March 26.
TEPCO officials said they believe the water is still covering the melted nuclear fuel at the No. 2 reactor based on the water temperatures ranging from 48.5 to 50.0 degrees. If the melted fuel was exposed, the temperatures would be much higher, they said.
However, the low water level indicates that water being pumped in to cool the fuel could be flowing into the suppression pool and leaking to other parts of the reactor building interior. The water depth is high enough for the water to overflow into the suppression pool, which is connected to the main part of the containment vessel, TEPCO officials said.
The water level and temperatures were determined by direct measurement on March 26 for the first time using an industrial endoscope. It was second time an endoscope had been used to inspect the interior of the No. 2 reactor containment vessel.
TEPCO assumed the water level was 3.5 to 4 meters in the containment vessel after the first inspection on Jan. 19 failed to detect the water surface 4.5 meters from the bottom of the vessel, which was the level that TEPCO had previously expected.
TEPCO officials said the gross overestimation was presumably caused by inaccurate pressure gauge readings that were used to evaluate the water level.
The air temperatures inside the containment vessel ranged between 40 and 45 degrees, roughly unchanged from the temperatures measured in January.
On March 26, the endoscope stretching 20 meters, or double the length of the device used in January, was inserted through an opening that penetrates into the containment vessel.
The endoscope, with a diameter of 8.5 millimeters, reached a space below a scaffold grating about 4 meters above the bottom of the vessel, which had been out of range in January.
Pictures released by TEPCO show an inner wall of the containment vessel. On the left side, coating was peeling off the surface. The right side showed a thermometer cable connected to the endoscope.
One image showing the water surface is rather blurry. But another picture that was shot in the water shows tiny particles. Those particles have not been identified, but TEPCO officials said they are likely dust, coating or rust that came off the surface.
They said the particles are unlikely to be fragments of nuclear fuel because melted fuel is thought to have fallen on the other side of a wall.