The operator of the crippled Fukushima Daiichi nuclear power plant on Friday conducted its second probe this week of one of three damaged reactors using an underwater robot.
The probe to examine the condition of melted fuel inside the No. 3 unit follows the first one conducted Wednesday inside the reactor's containment vessel housing a damaged pressure vessel and 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 subsequent tsunami triggered a nuclear disaster at the seaside plant.
Decommissioning work has progressed slowly while radiation levels inside the reactors remain extremely high.
The robot probe comes as 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 placed 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.
About 6.4 meters of water -- 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 conduct the probe on Wednesday and Friday but decided to carry out another round on Saturday to send the remote-controlled robot as far as the bottom of the containment vessel, where a chunk of melted fuel is believed to have accumulated.
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 catastrophe since the 1986 Chernobyl crisis.
From January to March, Tepco conducted robot surveys including sending a self-propelled robot into the Nos. 1-2 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