May 30, 2023 https://www.asahi.com/ajw/articles/14920197
Damage to a pedestal inside the No. 1 reactor at the crippled Fukushima No. 1 nuclear power plant is more critical than previously believed, triggering a more intricate assessment of its resistance to a major earthquake.
Plant operator Tokyo Electric Power Co. (TEPCO) has no time to waste in confronting the issue. It must swiftly assess the damage and take effective action to prevent an accident or leak of radioactive materials.
An underwater robotic probe detected the damage in late March. It found that the metal framework lies exposed along the inner side of the pedestal's wall for about 1 meter from its bottom and for the entire inner circumference as concrete in these areas has been lost.
There are fears the containment vessel that houses the pressure vessel could crack if the pedestal collapses in a severe earthquake. That could cause radioactive materials to leak.
Referring to the structure's current earthquake resistance, TEPCO stressed that the pedestal has managed to support the reactor vessel even though the plant "has experienced strong earthquakes." The utility cited one last year that registered lower 6 on the Japanese seismic intensity scale of 7.
Although the possibility of the pressure vessel tilting or sinking cannot be ruled out, the company asserts the impact will be limited with no risk of radioactive material leaking to the outside.
the Nuclear Regulation Authority (NRA) said last week it could not decide whether the assumptions underlying TEPCO's risk assessment are accurate as the extent of damage and condition of the structural materials are not yet fully understood. The nuclear safety watchdog also said it would be difficult to reinforce the pedestal because of high radiation levels inside the containment vessel.
For this reason, the NRA called on the utility to evaluate the impact of a possible release of radioactive material into the environment and consider steps to deal with such an emergency.
As one NRA official put it, "I should say (TEPCO's evaluation) is too optimistic, and it is difficult to say that is very reassuring."
NRA Chairman Shinsuke Yamanaka said at a news conference, "It is TEPCO's responsibility to swiftly assess what risks could impact the surrounding environment and its residents."
Conditions surrounding the reactors that suffered core meltdowns in the nuclear disaster 12 years ago are only now finally being clarified. This has led to the discovery of additional problems that are already difficult to deal with, making the outlook of progress toward decommissioning the reactors even more uncertain.
The degradation of plant parts and materials will continue in the coming years. There is always the risk of a major earthquake striking the plant. Each time it is hit by a strong quake, the damage accumulates and the danger increases. If a radioactive leak occurs, it will seriously compromise the safety of residents, the reconstruction of the local communities and the local fishing industry.
The NRA this month decided not to lift a ban on the movement of nuclear fuel within TEPCO's Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture, citing flawed measures to protect the facility against terrorist attacks. There are growing concerns about whether TEPCO is equipped to operate nuclear power plants.
There is absolutely no room for complacency when it comes to the consequences of the Fukushima nuclear disaster. TEPCO must always remain vigilant to a worst-case scenario in tackling related challenges.
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