Tokyo Electric Power Company started building something new and very cold at the ruined Fukushima nuclear power plant complex on Monday. It’s basically a big underground cooler meant to freeze the soil into a rectangular wall around TEPCO’s four nonfunctioning but still highly radioactive reactors. The frozen ground of the Fukushima ice wall should prevent the steady flow of clean groundwater from nearby hillsides mixing with irradiated cooling water under the reactors and turning a huge water contamination problem (400 tons per day) into an insurmountable one.
By “new,” we mean that no one has ever tried to install such a structure this big or this permanent. Not at Fukushima, in Japan, or anywhere else in the world. Buried ice walls have been used for sinking mine shafts, protecting Arctic permafrost, and tunnel building near water bodies, but never on such a large scale. TEPCO cites construction of a Tokyo metropolitan government subway line as having involved more than half the amount of soil to be frozen as at Fukushima. However, that freeze, like most others conducted to date, was only a temporary measure. MIT Technology Review magazine cites a six-year ice wall 20% the size of the Fukushima one built at a plutonium-containing US Department of Energy site near Oak Ridge, Tennessee.
TEPCO has installed more than a thousand large aboveground tanks over the past three years to contain contaminated water. The company is running out of space for more tanks and has had problems with both leaks and potential ground subsidence. These difficulties prompted TEPCO to look for other solutions. Japan’s Nuclear Regulation Authority approved the Fukushima ice wall plan last week.
Workers from Kajioma Corp., TEPCO’s subcontractor, have started installing 1,500 thin pipes one meter apart. They’re sinking the tubes up to 30 meters underground in a 1.5-kilometer rectangle enclosing the four reactors. The tubes will carry refrigerant at -30° C and are expected to create an impervious wall of frozen soil about two meters thick. The wall has a projected seven-year lifetime, which should allow TEPCO time to repair cracks in reactor and turbine buildings and block the structural influx of groundwater.
A water bypass system put in use last month can divert up to 80 tons per day of fresh, treated, and only slightly polluted water into the Pacific Ocean. Unfortunately, the Advanced Liquid Processing System, which removes dozens of radioactive contaminants from cooling water, has not been working up to expectations so far. This has slowed bypass use.
The Fukushima ice wall is expected to reduce the flow of groundwater under the plant to a third of its current volume, say most sources. Kajioma tested the method last October and built a working small scale model onsite two weeks ago. The Japan Daily Press reports that TEPCO anticipates finishing the wall in March 2015, about twice as quickly as originally estimated. It will take several months after that to complete the freezing process.
However, plenty of people have predicted that the $313 million project (construction costs only) may fail or not work well enough. They include former US Nuclear Regulatory Commission Chairman Dale Klein, who told Kyodo News early in May that “No one has built a freeze wall this long for this period of time. Typically, you build a freeze wall for a few months.”
At the same time, former British Atomic Energy Authority Chairwoman Barbara Judge also expressed doubts. Both experts are part of an oversight panel for TEPCO’s nuclear safety efforts. Klein urged TEPCO to seek advice from experts in the US and Britain who have managed water and decontamination efforts at former military sites.
The Japan News reports this comment from Masashi Kamon, a professor emeritus at Kyoto University who is familiar with the soil-freezing construction method:
“There is a mountain of challenges, such as possible corrosion of frozen pipes and costs of electricity. They should discuss measures that would combine other methods, such as one using clay.”
Other experts have also raised concerns that the wall “may damage existing pipes underground,” and whether the “necessary work can be carried out properly at a place where the amount of radiation remains high.” Finally, operating costs and electric power needed to keep the ice wall frozen are expected to be colossal.