Workers at the Fukushima Daiichi nuclear plant appear to have stemmed the flow of highly radioactive water into the ocean, although water with a lower level of contamination continues to enter the environment as engineers work to drain flooded reactor buildings.
On Tuesday, Kyodo and other news agencies reported that Tokyo Electric Power Co. had injected 1,500 liters of sodium silicate into a pit near unit 2. That effort appeared to seal a crack sighted in the pit and stop the outflow of water that’s given off dose readings topping 1,000 millisieverts per hour. Draining water from the pit, an interconnected network of tunnels and the basement of buildings at the Japanese plant has taken priority so that radiation readings will fall to levels that will allow workers to resume work on damaged core cooling systems.
Nikkei news, quoting an estimate by Japan’s trade minister, reported that the turbine buildings of units 1 through 3 and their associated tunnels each contain about 20,000 tons of seawater. Unit 2, which may have suffered a containment breach in an earlier hydrogen explosion, contains the most highly radioactive water, which will be moved to a waste processing facility on site. To make room, slightly contaminated seawater from that building, mostly from the tsunami that blacked out the plant March 11, is being pumped into the ocean.
Several tests – taken before the leak was sealed and the intentional discharge began – showed elevated levels of radioactive elements in the ocean near the plant. Kyodo, quoting government sources, reported Tuesday that testing of a fish caught Friday in Ibaraki Prefecture revealed concentrations of radioactive iodine at 4,080 bequerels per kilogram. A different fish from the same area showed levels of cesium at 526 bequerels per kilo, slightly over the legal limit. In response, the Ministry of Health, Labor and Welfare has set a new limit for radioactive iodine in seafood at 2,000 bequerels per kilo, the same level on the books for vegetables.
Containing radiation from the damaged reactors and their spent fuel tanks has proved challenging. Kyodo also quoted government sources as saying a proposal to surround the damaged units in sheeting designed to absorb radioactive materials could not be implemented until at least September because of high dose levels at the plant.