Original title: Fukushima nuclear power plant No. 1 unit found suspected nuclear fuel debris for the first time, TEPCO: there are results
From February 8 to 10, Japan’s Tokyo Electric Power Company conducted an internal investigation of the reactor containment of Unit 1 of the Fukushima Daiichi nuclear power plant and found a large amount of accumulation. On February 13, TEPCO said that these deposits may be nuclear fuel debris. This is the first time that Unit 1 has discovered or is fuel debris.
Deposits that may be fuel debris were discovered during an investigation inside the reactor containment of Unit 1 of the Fukushima Daiichi nuclear power plant.
According to Kyodo News on February 13, the person in charge of Tepco commented that “considerable results have been achieved”. However, the report pointed out that even if the fuel debris is found so far, it is only a small part, and it is still very far from the goal of taking out all of it. This is the first time material that may be nuclear fuel debris has been found in Unit 1 of the Fukushima Daiichi Nuclear Power Plant. The deposits found were rock-like lumps with a rough, blackened surface near the opening in the base that supports the reactor pressure vessel containing nuclear fuel from below. Some analysts believe that almost all the nuclear fuel in Unit 1 melted after penetrating the pressure vessel, and the fuel debris flowed to the outside from the opening of the base and spread. If the lumps found this time are nuclear fuel fragments, this analysis may be confirmed.
At the bottom of the reactor containment vessel of Unit 1 under investigation, there is about 1.8 meters of accumulated water, and the lumps were photographed by a remote-operated underwater robot. The size and hardness of the lumps are not yet known. However, the original task of the robot was to install metal rings called “guide rings” on the side 4 of the containment to avoid the subsequent robot cables actually responsible for the investigation from hanging on the objects in the reactor. During the investigation in March 2017, TEPCO found flat deposits at the bottom of the containment vessel, but TEPCO judged that it was not fuel debris at that time based on the amount of radiation around it. According to the plan, TEPCO will invest 5 robots in succession in the future to investigate the thickness, distribution and radiation amount of the deposits in detail.
Kyodo News previously reported that Tepco began investigating the inside of the reactor containment of Fukushima No. 1 nuclear unit 1 from February 8. During the investigation, TEPCO used underwater robots to collect information on the deposits at the bottom of the containment and the molten nuclear fuel (ie, nuclear fuel debris) below it. This is the first such survey since March 2017. According to the images captured by the camera mounted on the robot at that time, the bottom of the containment shell was uneven, and a large amount of debris was suspected to have accumulated. TEPCO said that among Units 1 to 3, only Unit 1 detected the substance.
On March 11, 2011, an earthquake with a magnitude of 9.0 occurred in the waters off northeastern Japan and triggered a huge tsunami. Affected by both the earthquake and the tsunami, a large amount of radioactive material leaked from the Fukushima Daiichi Nuclear Power Plant, resulting in a serious nuclear accident.