Tokyo Electric Power Company (Tepco) on 13 February released photos of fuel debris within the primary containment vessel (PCV) of unit 2 at Japan’s damaged Fukushima Daiichi NPP. The photos were obtained using a remotely-operated probe developed by Toshiba Energy Systems & Solutions Corporation, which was inserted through a penetration hole that gives access to the PCV. Six locations within the vessel were surveyed – a key step toward retrieving the radioactive material as part of a JPY21.500 billion ($195 billion) cleanup programme. Tepco determined that the debris can be lifted, which will help in its removal. The probe - approximately 30cm in length and 10cm in width - features a camera, LED lighting, a pan-tilt mechanism, finger drive mechanism (tongs), radiation dosimeter and a thermometer.
Tepco said that during the survey it was able "to touch sediments at the bottom of pedestal in the PCV for the first time". It added, "With the closer approach to the sediment than in the previous survey, images, dose and temperature data were acquired. In the future, along with confirmation of the acquired images, an evaluation [will be made] of dose and temperature data.” The probe was able to pick up debris in five of six areas surveyed but could not manipulate the material in sixth area, which was in a large, clay-like mass. No samples were removed from the PCV.
The data gathered will help Tepco decide how to remove the melted fuel from the reactors prior to their decommissioning. Retrieval of fuel debris from the Fukushima Daiichi units is expected to begin in 2021, the Nuclear Damage Compensation and Decommissioning Facilitation Corporation said in June 2015. Decommissioning of the plant is estimated to take 30 to 40 years. Tepco has also carried out robotic surveys of the PCVs of Fukushima units 1 and 3 and is planning a survey inside the containment vessel of unit 1 sometime between April and September, which may include collecting a small portion of deposits.
