Robot Finds Melted Fukushima Nuclear Fuel.
A survey conducted by Tepco in October 2015 found that the Primary Containment Vessel (PCV) of unit 3 was flooded with coolant to a depth of about 6 meters. A photographic inspection of the reactor suggested that, during the March 2011 accident, fuel assemblies melted from the excess heat, dropping from their original position down to the pedestal area. In this process, it is believed the pedestal area may have experienced some damage. In February 2017, Tepco sent a “scorpion-shaped” robot – also developed jointly by Toshiba and IRID – into the PCV of Fukushima Daiichi unit 2. About 54cm long, 9cm high and 9cm wide, and weighing about 5kg, that robot was designed to enter the unit’s PCV along a pipe about 10cm in diameter. It too was remotely operated by a wired cable. Although the robot was unable to reach the area directly under the reactor pressure vessel, the company said the information it gathered would help it determine how to decommission the unit. The following month, Tepco carried out an investigation of the PCV of unit 1 at Fukushima Daiichi using the PMORPH robot developed by Hitachi-GE Nuclear Energy and IRID. Equipped with a dosimeter and waterproof camera, it took radiation readings and digital images at ten different measurement points within that unit’s PCV.
Tepco inserted a screw-driven submersible robot developed by Toshiba and the International Research Institute for Nuclear Decommissioning into the unit’s PCV on 19 July. The company said an initial exploration of the vessel revealed damage to multiple structures inside the pedestal and also that some of the support fittings for the control rod drive (CRD) housing have fallen. Tepco announced that a survey of the pedestal area by the robot had confirmed the presence of what could be molten fuel as well as other fallen debris, including parts of the CRD housing support fittings. The company plans to carry out an investigation of the lower part of the pedestal area.
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