An operation to remove a small amount of radioactive debris from Unit 2 at Japan’s Fukushima-Daiichi nuclear station has begun, after technical issues led to the cancellation of an earlier attempt.
Tokyo Electric Power Company (Tepco) said in a statement on Tuesday (10 September) that its “pilot extraction operation” had started. It will take about two weeks, according to the company.
Tepco is aiming to retrieve just three grams of fuel mixed with other debris as part of a demonstration programme for the unprecedented cleanup, which reports have said is expected to take decades and cost 23 trillion yen ($161bn, €145bn).
The tiny sample will be studied for clues about conditions inside the reactors – a crucial step towards decommissioning Fukushima-Daiichi.
Unit 2 was one of three of six plants at the facility that melted down after a magnitude 9.0 quake and tsunami in March 2011 destroyed the station’s power supply and cooling systems.
Removal of the fuel debris has proved challenging, requiring the development of a telescopic device equipped with a gripper tool. The device can extend up to 22 meters and access the debris through a penetration point into the primary containment vessel.
Tepco originally planned to start its first trial removal on 22 August, but had to stop the work at a preliminary stage after detecting a problem involving the installation of the necessary equipment.
About 880 tonnes of fuel debris remain in the three reactors that suffered meltdown, according to estimates by the International Research Institute for Nuclear Decommissioning.
Tepco said that in Units 1, 2 and 3, the fuel and the metal cladding that forms the outer jacket of the fuel rods melted, then re-solidified as fuel debris.
“Fuel debris” refers to this melted fuel and other substances after they cooled and re-solidified.
At the time of the accident, Units 1 to 3 were operating and had fuel rods loaded in the reactors.
After the accident, the loss of emergency power prevented further cooling of the cores, resulting in overheating and melting of the fuel.
Tepco has been surveying the inside of the Unit 2 containment vessel before retrieval of the fuel debris can begin.
In Unit 2, Tepco believes there is a large amount of fuel debris in the bottom of the reactor pressure vessel, but little in the surrounding containment vessel.
