March 18, 2022
The water level in the spent nuclear fuel pool in Unit 2 of TEPCO’s Fukushima Daiichi Nuclear Power Plant (Okuma and Futaba, Fukushima Prefecture) dropped on March 17 after an earthquake measuring 6 on the Japanese seismic scale struck off the coast of Fukushima Prefecture, causing TEPCO to temporarily halt cooling of the pool. The number of waste materials continues to increase, and there is a risk that these materials could interfere with the work in the event of an earthquake.
According to TEPCO, 615 pieces of nuclear fuel are stored in the Unit 2 pool.
In the Unit 5 pool, where 1,542 pieces of nuclear fuel are stored, cooling automatically stopped and was restored in four and a half hours. Fire alarms were activated at three locations on the second floor of the turbine building of the same unit, but no abnormalities were found.
In Unit 4, a steel frame (approximately 5.6 meters long and weighing approximately 200 kg), believed to be part of a beam, fell from a large cover placed over the top of the building to remove spent nuclear fuel. No one was injured, but a bolt securing the steel frame was broken.
Of the approximately 1,000 tanks that store treated water, 85 were found to have shifted sideways, and some of them contained water in the process of purification, which has a relatively high level of radioactivity. The tanks are not secured to the ground to prevent damage, and while the displacement is to be expected, there is a risk of leakage if the piping connecting the tanks is damaged. Many of the tanks shifted during the earthquake in February of last year, and leaks were found at several locations this time.
Containers containing radioactive waste stacked in the open on the site also toppled over one after another. At least six of them toppled over, exposing used protective clothing and scrap iron. There are approximately 85,000 containers, many of which were stacked without a plan. The workers were also exposed to radiation during inspections of these containers and the recovery of their contents.
In Unit 1, a remote-controlled robot has entered the containment vessel to inspect the condition of debris, including melted-down nuclear fuel. The concentration of radioactive materials in the reactor buildings temporarily increased after the earthquake. Although the level did not reach the level that would have set off an alarm, the investigation was suspended.
Work was also halted on removing highly contaminated pipes between Units 1 and 2. The site was the highest radiation level outdoors and inaccessible to humans. The crane that hoists the remote-controlled cutting device weighs 800 tons and reaches a height of more than 100 meters. There are a total of three such cranes in the vicinity. Although the effects of the earthquake have not been confirmed, heavy machinery and temporary structures are crammed into the harsh environment under high radiation doses, and if they were to collapse, they would cause extensive damage.
The earthquake also caused the cooling of the pool at the decommissioned Onagawa Unit 1 of Tohoku Electric Power Company’s Onagawa Nuclear Power Plant (Miyagi Prefecture) to stop, but it was restored around midnight on March 17. No abnormalities were found at Tohoku Electric’s Higashidori Nuclear Power Plant (Aomori Prefecture) and the Tokai No. 2 Nuclear Power Plant of the Japan Atomic Power Company (Ibaraki Prefecture), both of which are not in operation. (Kenta Onozawa)