Robot also took digital images of the deposits on the path toward the pedestal area
TOKYO, Feb. 10-Based on the digital images that were obtained from the preparatory investigations, a robot was sent yesterday into the Unit 2 Primary Containment Vessel (PCV) at Fukushima Daiichi Nuclear Power Station to clear a path for the "Scorpion" robot to further explore the PCV.
The robot removed a part of potentially troublesome deposits (one fifth of the originally planned area) on the rail that will be used to insert the Scorpion robot and then was retrieved because it run on the deposits and also the camera became dark after about two hours of removal work due to the effect of high radiation.
The robot also took pictures of the deposits and help engineers determine whether they will pose obstacles to the Scorpion's insertion. The photos will also help engineers select the best route for Scorpion to take to the pedestal area, the bottom of the PCV where fuel melted during the March 2011 accident, fell to, and resolidified, together with earlier photographs that indicate parts of the metal grating, used as a floor inside the PCV when it was operating normally, may be missing.
Following a remote-controlled telescopic inspection last week that detected a high radiation level inside the PCV, the robot also detected a higher level of radiation (as high as 650 Sieverts per hour) during the cleaning work.
Safety Precautions Taken
Various safety precautions have been taken to ensure that the radiation remains inside the PCV and to protect the robot. Based on the previous radiation measurements, the robot and cameras are designed to withstand 100 Sieverts per hour for 10 hours and the time it spends inside the PCV will be adjusted as necessary.
Although the levels of radiation inside the PCV discovered from the previous telescopic inspection and the robot insertion this time were high, there is no reason to believe that the level itself has increased or "spiked," as some reports suggested. The levels reported from inside the PCV were estimates based on noise images on the camera screen, and have a margin of error of plus or minus 30 percent.
There has also been no change to radiation levels outside the PCV. Extra precautions have been taken to prevent leaks of radiation during the investigation. The penetration pipe through the PCV wall is tightly shielded, and the work area is pressurized so that air only moves from the outside into the PCV and not the reverse. TEPCO Holdings routinely discloses on its website sampling results of radiation on the premises of the power station, and that sampling shows no significant changes. Overall, ambient radiation at the Fukushima Daiichi facility has been greatly reduced over the last few years, enhancing both the environment and worker safety, and has allowed workers to work across a much greater area without full protective gear.
For more information on the findings from this past week's telescopic investigation of Unit 2 PCV, go to https://www4.tepco.co.jp/en/nu/fukushima-np/handouts/2017/images/handouts_170202_01-e.pdf
Photographs and a video of yesterday's robot activity are available together with a detailed document at http://photo.tepco.co.jp/en/date/2017/201702-e/170209-01e.html
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)
TEPCO Website: https://www7.tepco.co.jp/index-e.html
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