Pressure vessel « nuclear-news

If a major earthquake were to occur… “Will it be safe?” concerns the chairman of the regulatory committee after the damage to the foundation of the pressure vessel at the Fukushima Daiichi Unit 1 reactor is discovered

The foundation supporting the pressure vessel has lost its concrete, leaving the rebar exposed inside the reactor of TEPCO’s Fukushima Daiichi Nuclear Power Plant Unit 1 (courtesy of the International Nuclear Decommissioning Research and Development Organization and Hitachi GE Nuclear Energy).

May 25, 2022
At a press conference on May 25, Chairman Toyoshi Sarada of the Nuclear Regulation Authority of Japan (NRAJ) said, in response to an investigation that found rebar exposed in part of the reinforced concrete foundation supporting the Unit 1 reactor pressure vessel at TEPCO’s Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba, Fukushima Prefecture), “I have concerns about whether it will be safe when a major earthquake occurs. I have concerns about whether it will be safe in the event of a major earthquake. If we could reinforce it, we would.
　Sarada pointed out that “it is possible to speculate” about the possibility that nuclear fuel (debris) melted down during the accidental meltdown (core meltdown) and broke through the pressure vessel, melting the concrete (1.2 meters thick) of the foundation. He expressed a sense of crisis, saying, “It is necessary to consider what would happen if the foundation collapsed.
　He also recognized that it would be difficult to reinforce the foundation in a nuclear reactor with extremely high radiation levels, and said, “We cannot take too long when considering earthquake resistance, and we should remove the debris as soon as possible, even if it is just an earpick, and analyze its condition.
　TEPCO placed an underwater robot into the containment vessel from March 17 to 21 to investigate its interior. Near the base of the bottom of the containment vessel, several lumpy deposits were found that appeared to be debris. Although the accident caused the meltdown of Units 1-3, this was the first time that the exposure of rebar inside the concrete was confirmed. (Kenta Onozawa)
https://www.tokyo-np.co.jp/article/179502?fbclid=IwAR1Oq1_rEddpUnUyTDUjJXd494WNQk3_XfAyPMVz3zFFWVqZGcsV3X10qSY

May 29, 2022 Posted by dunrenard | Fuk 2022 | Concrete base, Fukushima Daiichi, Pressure vessel, Unit 1 | Leave a comment

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

The foundation supporting the pressure vessel has lost its concrete and the rebar is exposed inside the reactor of TEPCO’s Fukushima Daiichi Nuclear Power Plant Unit 1 (courtesy of the International Nuclear Decommissioning Research and Development Organization and Hitachi GE Nuclear Energy).

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.

Multiple lumpy deposits were observed at the bottom of the Unit 1 containment vessel at TEPCO’s Fukushima Daiichi Nuclear Power Plant (courtesy of the International Nuclear Decommissioning Research and Development Organization and Hitachi GE Nuclear Energy).

　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 | Leave a comment