The operator of the disaster-hit Fukushima Daiichi nuclear complex said Saturday an underwater robot captured images of what is likely to be melted nuclear fuel at the bottom of one of its damaged reactors as it wrapped up the latest surveys.
Tokyo Electric Power Company Holdings Inc. already succeeded in taking images of material deemed "highly likely" to be melted fuel for the first time in a survey conducted at the No. 3 reactor a day before. The robot was sent closer to the bottom of the reactor on Saturday and found possible fuel debris scattered in a wide area.
The latest findings are likely to provide important clues toward the ultimate goal to remove the fuel and scrap the crippled reactors, but the fact that it took some six years to just capture images of the fuel debris indicate Tepco still has a long way to go.
The images taken by the robot showed possible fuel debris in the form of rocks and sand. One image showed some blackish rocky material existing just below the reactor pressure vessel, a container that is supposed to hold the fuel.
"It's natural to think that melted material flowed (out from the reactor pressure vessel)," a Tepco official said at a press conference.
Deposits likely to contain fuel debris were accumulating from the bottom of the primary containment vessel at a height of least 1 meter, according to Tepco.
The plant operator has been trying to confirm the internal conditions of the Nos. 1 to 3 reactors that suffered fuel meltdowns following the earthquake and tsunami disaster that hit the Fukushima Daiichi plant on March 11, 2011.
The investigation into the No. 3 reactor was seen to be falling behind those for the Nos. 1 and 2 reactors, but the outcome turned out to be more successful because the reactor container has been filled with enough water to send in an underwater robot, which can move freely without easily being blocked.
Water is injected into each reactor to keep the fuel inside cool, but the water level differs depending on the damage the reactor containers suffered during the disaster. The water level at the No. 3 reactor container has been about 6.4 meters deep.
The survey on Saturday began at around 5 a.m. following two previous ones earlier this week and ended around noon, according to Tepco. The robot -- a cylinder-shaped underwater robot with a diameter of 13 centimeters and dubbed "little sunfish" -- has been retrieved from inside the reactor's container.
From January to March, Tepco conducted surveys into the Nos. 1 and 2 reactors, using robots that run on the ground, but they failed to ascertain the condition of fuel debris due to obstacles that blocked their way and the high radiation levels.
© Kyodo News International, Inc., source Newswire