Fukushima Daiichi NPS Prompt Report 2017

After robot explores PCV basement, retained water will be extracted and examined to determine nature of floating deposits observed during previous investigation

TOKYO, March 9?TEPCO Holdings is about to insert a Hitachi-developed robot, "PMORPH," into reactor Unit 1 at Fukushima Daiichi Nuclear Power Station to explore the basement area around the pedestal as part of the preparatory work for eventual removal of the fuel debris.

The activity is separate from the effort last month to use a Toshiba-developed robot to explore the pedestal area of Unit 2. In that case, although the robot was obstructed from reaching all the way into the pedestal area, important information was obtained about conditions at the base area of the reactor. http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170215_01-e.pdf

Insertion of the "PMORPH" robot into Unit 1 follows the acquisition of digital images, radiation dose data, and other information in April 2015. http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2015/images/handouts_150430_04-e.pdf. Now, armed with that information, the robot will carry a dosimeter and waterproof camera to measure the distribution of radiation rates in the water that has been retained inside the reactor, specifically around the pedestal opening of the basement area of the Primary Containment Vessel (PCV) to estimate the location and spreading of fuel debris.

Relatively high levels of radiation more than several hundreds of Sievert per hour may be measured during the investigation due to the proximity to fuel debris expected to exist at the bottom of PCV. Even in this case, the radiation is shielded with thick concrete walls of PCV and separate steel walls. Airborne radiation and dust dispersion are constantly monitored along with the power station boundary and the real-time monitoring data are available at TEPCO Holdings website. http://www.tepco.co.jp/en/nu/fukushima-np/f1/index-e.html

Before the robot is sent in, preparations will include replacement of a guiding pipe and various steps to ensure radiation does not escape from the PCV, including tight air seals around the guiding pipe and continuous dust monitoring at the work site. Insertion of the robot is tentatively scheduled for March 14-17, and digital images and radiation data obtained from each day's investigation will be published on the following business day. Thorough analysis will be conducted later.

Although an effort will be made to locate fuel debris that fell to the bottom of the reactor during the March 2011 accident, engineers believe the floating deposits seen in the April 2015 investigation may pose an obstacle for future investigations and fuel debris removal. After the robot investigation is concluded, TEPCO Holdings plans to use a hose (not the robot) to extract retained water from the reactor and analyze the deposits with X-ray fluorescence. The analysis results will be used to identify the deposits and determine how to remove or treat them.

For more details of this Unit 1 PCV investigation, go to http://www.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170309_01-e.pdf

About TEPCO Group
Tokyo Electric Power Company Holdings, Inc. (TEPCO Holdings) is Japan's largest power company group, holding three independent business entities: TEPCO Fuel & Power, Inc., TEPCO Power Grid, Inc., and TEPCO Energy Partner, Inc. As a group, it generates, distributes, and sells electricity and other types of energy principally to the Kanto metropolitan area, which includes Japan's two most populous cities, Tokyo and Yokohama. Its 33,000 employees are committed to providing safe, reliable power to its 29 million customers as well as fulfilling its responsibilities to the communities of Fukushima. (As of April 1, 2016)
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