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24 January, 2018

TEPCO Peers into Primary Containment Vessel at Fukushima Daiichi-2, Confirming Likelihood That Sediment Is Fuel Debris

On January 22, the Tokyo Electric Power Co. (TEPCO) released images from its investigation made three days earlier of the interior of the primary containment vessel (PCV) at its Fukushima Daiichi-2 Nuclear Power Plant.

(c)TEPCO

The power company is carrying out investigations of the PCV interiors of the various Fukushima Daiichi reactors to remove the fuel debris therein. In January and February last year, TEPCO already conducted a series of investigations at Unit 2 using self-propelled devices, and determined that a portion of the grating inside the pedestal (below the reactor pressure vessel) had fallen out.

In the latest investigation to confirm the nature of the debris at the bottom of the pedestal, TEPCO investigators used a longer telescopic guide pipe—inserted through the X-6 penetration of the PCV—than any of the devices used previously, after which they used a cable to further lower the unit at the end (containing two cameras, a dosimeter and a thermometer) from the place where the grating had fallen. The entire assembly greatly resembled a fishing rod.

At a press conference on January 19, TEPCO representatives explained the findings. Citing the Three Mile Island (TMI) accident that had occurred in the United States in 1979, TEPCO said that it believed that some of the fuel assemblies had fallen to the bottom of the pedestal, and that the sediment found around them was probably fuel debris (see photo).

At a Q&A session during a press conference held late in the afternoon of January 22, General Manager Takahiro Kimoto of TEPCO’s nuclear division showed a model of a fuel assembly and an image from the investigation, saying, “It would be hard not to call it debris.”

Moving forward, the power company plans to analyze the obtained images and data and assess both the radiation dosage and temperature.

At the same press conference, it was also reported that TEPCO had started work on the same day to remove rubble from the reactor building of Unit 1 at Fukushima Daiichi.

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