Fukushima nuclear disaster

Underwater robot probe continues inside Fukushima plant's reactor

The condition of fuel debris inside the reactors remains unknown even though six years have passed since the earthquake and tsunami

PUBLISHED : Friday, 21 July, 2017, 4:06pm
UPDATED : Friday, 21 July, 2017, 4:06pm

The operator of the crippled Fukushima Daiichi nuclear power plant on Friday conducted its second probe in the space of a week on one of three damaged reactors using an underwater robot.

The probe to examine the condition of melted fuel inside unit three follows the first on Wednesday inside the reactor’s containment vessel, which houses 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.

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Decommissioning work has progressed slowly while radiation levels inside the reactors remain extremely high.

Operator Tokyo Electric Power Company (Tepco) meanwhile aims to commence work to remove fuel debris at the plant in 2021, one of the most difficult stages of the decommissioning project, which is expected to take at least 30 to 40 years to complete.

Wednesday’s probe showed a metallic scaffold, which was placed inside the containment vessel before the disaster, had gone missing. Meanwhile, Friday’s investigation focused searching the area in detail before examining fuel debris inside the vessel.

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About 6.4 metres of water – injected into the reactor to cool fuel debris – has accumulated at the bottom of the containment vessel, according to the operator.

Tepco has decided to carry out another search on Saturday, sending the 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 10 meters above sea level, and flooded power supply facilities.

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Reactor cooling systems were crippled while units one to three all suffered fuel meltdowns in the world’s worst nuclear catastrophe since the 1986 Chernobyl crisis.

From January to March, Tepco conducted multiple surveys, including sending a self-propelled robot into reactors of units one and two, where water levels are lower than in the unit three reactor. That search, however, failed to ascertain the condition of fuel debris.

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