Japan’s Nuclear Regulation Authority (NRA) has given the go-ahead to the operator of the crippled Fukushima nuclear power plant to build a so-called ice wall around four reactors to prevent incoming groundwater from becoming severely contaminated.
The NRA, Japan’s nuclear watchdog agency, had been considering the plan by Tokyo Electric Power Co. (TEPCO), which runs the Fukushima Daiichi plant, since last fall.
TEPCO, which announced the idea in May 2013, conducted limited tests of the relatively unproven technological fix in October 2013 and, most recently, two weeks ago.
According to Asahi Shimbun news on May 17, a spokesperson for Kajioma Corp., the construction company building the ice wall, declared the latest test a success.
The Japanese government has pledged $313 million to fund the project.
Project will take almost a year
TEPCO is expected to commence construction of the underground ice-wall—which, along with a recently implemented groundwater-bypass scheme, is part of TEPCO’s approach to reduce the amount of radioactive groundwater now being stored and treated in temporary tank farms on the site—in June and finish the project sometime in March 2015, according to the Japan Daily Press on May 27.
The wall is designed to operate for about seven years.
The ice-wall project involves sinking tubes carrying coolant, one metre apart, up to 30 metres underground and in a roughly 1.5-kilometre rectangular shape around four reactors. The piped refrigerant, at minus-30 ° C, would freeze groundwater and create an impervious two-metre-thick soil wall.
Up to 400 tons of water per day flows underground from nearby hillsides into the site, often mixing with contaminated water used to cool reactors that were severely damaged in the March 2011 earthquake and tsunami.
More than 1,000 storage tanks already built
The groundwater-bypass plan—which is expected to lessen this volume of water by piping up to 80 tons per day of diverted (as well as treated and moderately contaminated) water into the Pacific Ocean—was designed to reduce the need to build additional water storage tanks at the site. More than 1,000 tanks have been installed in the past three years.
TEPCO has said that if all goes according to plan, with both the bypass and the ice wall in operation, the outside-groundwater inflow will be reduced to 130 tons per day.
The ice-wall technique has been used previously in tunnel construction near watercourses, but not on such a large scale.
Contaminated-soil storage plan moves ahead
Meanwhile, the Japan Daily Press reported on May 28 that the Japanese government is putting the finishing touches on a plan to store the Fukushima Daiichi site’s contaminated soil prior to disposal outside of the prefecture.
The decontamination process is expected to take upwards of 30 years.