Company officials said that 24 out of 25 filters attached to the water treatment equipment had been found damaged last month, after an alarm went off as workers were moving sludge from the unit to a container, temporarily suspending the water treatment. The operation partially resumed last week after the filters were replaced.
TEPCO said it had detected similar damage in all of the filters two years ago, but never investigated the cause of the problem and did not take any preventive steps after replacing the filters.
Another regulatory commissioner, Satoru Tanaka, said at the meeting that the utility company should have responded to the problem more quickly to minimize the risk of possible radiation leakage into the environment.
TEPCO officials said dust monitors indicated no radiation leaks to the outside or exposure to plant workers inside the water treatment facility.
Akira Ono, head of TEPCO's decommissioning unit, said he regretted the utility's failure to address the problem earlier. He promised to improve safety management.
Japanese officials are working with the International Atomic Energy Agency to prepare to discharge into the ocean the wrecked plant's cooling water, treated so its radioactivity levels are below legal limits. Slated to start in spring 2023, the controversial plan is fiercely opposed by Fukushima’s fishing community, as well as local residents and nearby countries.
Fully decommissioning the nuclear plant is expected to take decades, experts say.