A Series of Investigations Inside of Primary Containment Vessel of Fukushima Daiichi Nuclear Power Station Unit2

Abstract

Abstract In January 2012, Toshiba Energy Systems & Solutions Corporation inserted a camera into the damaged Primary Containment Vessel (PCV) of Fukushima Daiichi Nuclear Power Station unit 2 for the first time since the Great East Japan Earthquake. Since then, we, as a member of International Research Institute for Nuclear Decommissioning (IRID), has developed several devices and has investigated inside of PCV. The investigation devices for unit 2 are roughly categorized into three types. For the investigations in early stages, just a camera and sensors with simple support tools were inserted through a small hole. Then small crawler type robots were developed to expand the investigation area to inside of Pedestal which exists the central part of PCV. Since the devices found that there were not enough areas to run around by the robots in the Pedestal, a long telescopic guiding pipe device was chosen to deliver cameras, sensors, and tools into the Pedestal. This type of device took movie of wide area of inside of the Pedestal. An image processing software was also developed to get a high quality and extensive picture from the movie taken by a low resolution camera and insufficient lighting. In February 2019, the other telescopic guiding pipe device finally delivered a camera and fingers like tong to grab deposits fallen on the bottom of pedestal for the first time after the earthquake, and found that some of deposits can be lift up. Some of projects were implemented as subsidized projects of “Decommissioning and Contaminated Water Management” founded by the Ministry of Economy, Trade and Industry.