[3C01-05] Decommissioning Technology for Fukushima 3

[3C04] Investigation Results on Deposits Accumulating over the Pedestal Bottom of PCV of Fukushima Daiichi Nuclear Power Station Unit 2

*Tessai Sugiura¹, Chiari Shimizu², Naoya Sakamoto², Naoto Kume², Kiyoshi Haruna³ (1. TOSHIBA ESS, Isogo Nuclear Engineering Center, 2. TOSHIBA ESS, Energy Systems R&D Center, 3. TEPCO, Fukushima Daiichi D&D Engineering Company)

Keywords:Fukushima Daiichi Nuclear Power Station, Decommissioning, Fuel debris, PCV survey

In January 2018, the images confirmed that the pedestal bottom under the PCV at 1F Unit 2 was covered with pebble-like deposits and falling part of fuel assembly. It is assumed that such deposits were originally nuclear fuel, being melted at the accident, becoming fuel debris and felling off from the RPV. The results led to planning for further investigations to examine the deposit conditions, which could provide valuable information for reviewing the method for fuel debris retrieval. The survey unit, equipped with a two-finger drive mechanism, is capable of touching the deposits with its opening/closing movements. Using this device, investigations were conducted in February 2019 to examine the deposit physical states; finally, the images confirmed that some deposits were removable.