Tokyo Electric Power Co. said Monday that one of two radioactive water filters will be shut until at least September at its stricken Fukushima No. 1 nuclear plant, even as it searches for the cause of a leak that prompted the biggest escalation in the crisis since it started in March 2011.
The loss of the advanced liquid processing system, taken offline Aug. 8 due to corrosion, compounds concerns that the utility is losing its battle, now raging for two years, to manage the buildup of radioactive water. The lost layer of filtration adds to the contamination levels of water in the plant’s storage tanks, hundreds of which may be susceptible to leaks.
Tepco said Monday it will set up a special unit to deal with the storage of highly radioactive water, most of which had been used to keep its three melted reactors cool and is increasing at a rate of 400 metric tons a day. The step comes a week after a storage tank leaked 300 tons of highly radioactive water, an event the Nuclear Regulation Authority labeled a “severe incident” in its worst assessment of the problems at Fukushima since the earthquake and tsunami of 2011 led to the three meltdowns.
“We are inspecting all the parts now,” Tepco spokeswoman Mayumi Yoshida said of the idled ALPS unit, which was made by Toshiba Corp. “We are aiming for September,” she said regarding the ALPS restart.
ALPS, which began operating in March, was taken offline after the radioactive water it was designed to filter was found corroding its pipes and basins, Yoshida said. It’s being treated with a protective coating.
ALPS is used to filter strontium and other radioactive elements from water after it’s used to cool the melted reactor fuel. Water is pumped through the system after being first treated via a separate filtration unit for removing cesium. That system remains in operation.
After the two layers of filtration, only tritium should remain in the water when it is added to the hundreds of thousands of tons already in storage at the site.
The tank that leaked had levels of beta radiation of 80 million becquerels per liter, including strontium, Tepco said Aug. 20. That’s 8 million times the safety limit for drinking water under health ministry guidelines. Strontium has been linked to bone cancers.
There are about 300 tanks with designs similar to the leaky unit. Two others have had radioactive hot spots detected on their seams. The NRA said the chance of other tanks leaking is the biggest concern at Fukushima No. 1.
An inspection of the leaky tank, which can hold 1,000 metric tons of radioactive water, was inconclusive, Tepco official Noriyuki Imaizumi said Saturday. He said the tank had been built in a different location before earth subsidence forced it to be disassembled and moved to its current site. He said it isn’t known if this contributed to the leak.
The tanks were installed by a joint venture of Shimizu Corp., Taisei Corp. and Hazama Ando Corp., Yoshida said.
The NRA rated the leak as a 3 on the 7-stage International Nuclear and Radiological Event Scale, or INES, denoting a “serious incident.” That was the highest-level accident since the March 2011 start of the crisis, which received a level 7, the same as Chernobyl.
If the first round of decontamination work fails to sufficiently reduce radiation levels in evacuation areas near the crippled nuclear power plant in Fukushima Prefecture, a second round will be considered, a senior government official indicated Monday.
Once the first round is finished the central government will monitor radiation levels in those areas, Senior Vice Environment Minister Shinji Inoue told reporters at the Fukushima Prefectural Government office.
Municipalities in the prefecture are seeking further decontamination since radiation levels have not declined to an annual dose of 1 millisievert.