nuclear-news

Rebar of the foundation supporting the pressure vessel is exposed, debris may have melted the concrete

May 23, 2022
　On May 23, TEPCO released new images taken by an underwater robot of the bottom of the containment vessel of the Unit 1 reactor at the Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba, Fukushima Prefecture). It was confirmed that rebar was exposed in a part of the 1.2 meter thick reinforced concrete base (1.2 meters thick) that supports the pressure vessel where the nuclear fuel was located. There is a strong possibility that the concrete melted due to the heat from the nuclear fuel (debris) that melted down from the pressure vessel during the accident.

According to TEPCO, several lumpy deposits were observed near the opening from the bottom of the containment vessel to just below the pressure vessel. The closer to the opening, the thicker the deposits were, and the rebar of the foundation was exposed. Concrete is said to melt when heated to over 1,100 degrees Celsius, and if the foundation is severely damaged, in the worst case, the pressure vessel may fall because it can no longer support itself.

A spokesperson for TEPCO told a press conference about the reason the rebar was exposed, “One possibility is that the temperature was too severe, but we don’t know the mechanism. We would like to evaluate the damage after confirming the data in future investigations.

　The survey was conducted from the 17th to the 21st. The “neutron flux measurement,” which captures the characteristics of radiation, is being used to determine if the deposits are debris, and if so, they are being analyzed. Another four types of robots will be deployed in the future to determine the distribution of the sediments.
(Shinichi Ogawa and Kenta Onozawa)
https://www.tokyo-np.co.jp/article/179098?fbclid=IwAR1yHmGOTQLnZgk5vk06xyo7PaHPM9vVQ_myj6xFV5svs2eGkGdADumaRRU

May 29, 2022 - Posted by dunrenard | Fuk 2022 | Concrete base, Fukushima Daiichi, Pressure vessel, Unit1