“We don’t know if it’s debris.” Bumpy deposits at the bottom of the reactor.

February 9, 2022
　On February 9, Tokyo Electric Power Company (TEPCO) released a video of the bottom of the containment vessel of the Unit 1 reactor at the Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba towns, Fukushima Prefecture) taken by an underwater robot during an internal investigation. From the images, it was confirmed that orangeish bumpy deposits were spreading and adhering to the structure inside the vessel. It is possible that it is nuclear fuel (debris) that melted down during the accident. We don’t know if it is debris at this stage,” said Kenichi Takahara, a spokesman, at a press conference.

A video of the bottom of the containment vessel of the Unit 1 reactor shows a bumpy deposit spreading from the bottom center to the right side of the vessel at TEPCO’s Fukushima Daiichi Nuclear Power Plant (Courtesy of TEPCO)

According to TEPCO, it is unclear how high the confirmed deposit is; a survey in March 2017 confirmed a deposit of 90 centimeters high near this location. According to TEPCO, the height of the debris is unknown.

A part of the piping that was cut off for the introduction of the robots has sunk to the bottom of the containment vessel of the Unit 1 reactor (Courtesy of TEPCO)

By around 1:50 p.m. on the 9th, the underwater robot that was deployed on the afternoon of the 8th had moved through the water inside the containment vessel and attached four guide rings with a diameter of 30 centimeters at intervals to the structure inside the vessel. The purpose of these rings was to prevent cables from getting tangled in the structure when the robot, which will be used in the future, moves around, and we were finally ready for a full-scale investigation.

In the containment vessel of the Unit 1 reactor, an underwater robot moves through the vessel while attaching rings to the structure (TEPCO)

Oil-like suspended matter was observed on the water surface inside the containment vessel of the Unit 1 reactor. The yellow glow in the center is a pipe illuminated by a light (TEPCO)

　The radiation level in the water was 1 to 2 sievert per hour. The radiation level in the water was 1 to 2 sievert per hour. The exposure limit for workers at the nuclear power plant is 50 millisieverts per year, and even if one were to enter the water, it would take only 1 to 3 minutes to reach the exposure limit, so people are not allowed to go near the water.

A worker opens a valve leading to the containment vessel of the Unit 1 reactor to insert a robot (Courtesy of TEPCO)

Workers insert an underwater robot outside the containment vessel of the Unit 1 reactor (Courtesy of TEPCO)

　Of the three reactors that suffered core meltdowns in the March 2011 accident, video footage shows deposits of what appears to be debris in Units 2 and 3, but no debris was found in Unit 1 during the 2005 survey.
　Removing the debris is the most difficult task, and it is estimated that a total of 880 tons has melted down in Units 1-3. TEPCO is aiming to collect a few grams of debris from the Unit 2 reactor by the end of this year. (Shinichi Ogawa, Kenta Onozawa)
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