Updated June 3, 2014: from Straight.com
” 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. ”
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Published May 28, 2014:
” The Nuclear Regulation Authority has decided to allow Tokyo Electric Power Co. to begin building an underground ice wall at the wrecked Fukushima No. 1 nuclear power plant in June as planned, despite safety concerns about the move.
The frozen wall, to be set up around the buildings housing reactors 1 through 4, is viewed as an important step in addressing the buildup of radioactive water at the complex. The project is being funded by the government and is expected to cost ¥32 billion.
The NRA has been wary that building the ice wall could cause the ground to sink around the reactor and adjacent turbine buildings. But on Monday the agency accepted Tepco’s explanation that any sinking would not be significant enough to put safety at risk.
A Tepco official told NRA members and experts that the ground may sink up to 16 mm in some spots, but that the utility believes it won’t pose a problem to the stability of the ground.
“I think we have been able to confirm today the scale of ground sinking, which is what we have most feared as side effects of building the wall,” NRA Commissioner Toyoshi Fuketa said after hearing Tepco’s explanation:
But he noted that other issues concerning the project must still be discussed, including ways to accurately measure the level of radioactive water accumulating inside the reactor buildings.
The 1.5-km frozen wall will be built by inserting a line of pipes into the ground that circulates a liquid cold enough to cause the earth around it to freeze.
The wall is expected to help prevent a large volume of groundwater from flowing into the basements of the reactor buildings and mixing with highly radioactive water already accumulating there.
Impermeable walls of this nature are used in civil engineering projects such as subway construction but have never been created on such a large scale for a prolonged period.
Also as part of addressing the toxic water buildup, Tepco has been discharging groundwater that has accumulated at the site into the sea.
The release uses the so-called groundwater bypass system, in which water is pumped out through wells before it flows into the reactor buildings. ”