The operator of the crippled Fukushima Daiichi nuclear complex on Friday found black objects resembling stalactites in one of the three damaged reactors at the plant during its latest probe using an underwater robot.
Sources close to the matter said the robot confirmed the existence of the black objects hanging from the bottom of the damaged pressure vessel of the No. 3 reactor, raising the possibility that they could have been formed by melted fuel.
Friday's probe to examine the condition of melted fuel inside the unit follows one on Wednesday inside the reactor's containment vessel housing the pressure vessel, which is partially filled with contaminated water.
The condition of fuel debris inside the damaged reactors remains unknown, even though six years have passed since a huge earthquake and tsunami triggered the nuclear disaster at the coastal plant.
Decommissioning work has progressed slowly while radiation levels inside the reactors remain extremely high.
Plant operator Tokyo Electric Power Company Holdings Inc. is aiming to begin work to remove fuel debris at the plant in 2021, one of the most difficult stages of the decommissioning project that is expected to take at least 30 to 40 years to complete.
As Wednesday's probe showed that a metallic scaffold, which was inside the containment vessel before the disaster, is missing, Friday's investigation will focus on looking in detail around the area before examining fuel debris inside the vessel.
Water around 6.4 meters deep, which was injected into the reactor to cool fuel debris inside, has accumulated at the bottom of the containment vessel, according to the utility known as Tepco.
Tepco initially planned to only conduct probes on Wednesday and Friday but has decided to carry out another round on Saturday to send the remote-controlled robot to the bottom of the containment vessel, where a chunk of melted fuel is believed to lie.
On March 11, 2011, a huge tsunami hit the six-reactor plant, located on ground 10 meters above sea level, and flooded power supply facilities.
Reactor cooling systems were crippled and the Nos. 1-3 units suffered fuel meltdowns in the world's worst nuclear disaster since the 1986 Chernobyl crisis.
From January to March, Tepco conducted robot surveys including sending a self-propelled robot into the Nos. 1 and 2 reactors, where water levels are lower than the No. 3 reactor, but they failed to ascertain the condition of fuel debris.
© Kyodo News International, Inc., source Newswire