Japan Nuclear Regulation Authority Halts Fukushima Daiichi’s Ice Wall
Japanese Nuclear Regulation Authority, the NRA, has put the kibosh on plans by Tokyo Electric Power Co. to start freezing underground soil at the crippled Fukushima No. 1 nuclear power plant–a stunningly expensive project intended to solve the crisis of accumulating radioactive groundwater at the site.
The installation of the equipment required for forming a wall of frozen soil at the Fukushima Daiichi nuclear power plant to prevent groundwater entering the reactor buildings has been completed. Approval from the Japanese regulator must be sought before the creation of the wall itself can begin.
Ice wall technology is already widely used in civil engineering projects, such as the construction of tunnels near waterways. Small-scale tests using the technology have already been completed at the Fukushima Daiichi site. However, the full-scale use of the technology at Fukushima will see the largest ground freezing operation in the world.
Installation of the equipment for forming the ice wall began in June 2014 and a test that has circulated the chilling liquid to specific parts of the wall has been under way since April 2015. The north, south and west sides of the facility were completed last September, while the remaining pipes on the east side facing the sea were placed within the ground in November.
Tokyo Electric Power Company (Tepco) announced yesterday that all the necessary equipment is now in place for the creation of the ice wall. However, the company noted that it must get approval from the Nuclear Regulation Authority before the equipment can be put into operation. The regulator’s approval, Tepco said, would partly depend on the company “showing a method to ensure that the wall (and other groundwater pumping operations) do not invert the water level difference in any way that would cause contaminated water to flow out of the building’s basements”.
Kajima Corporation, the main contractor for the facility, has drilled holes some 30-35 metres into the ground and inserted pipes through which refrigerant will be then be pumped. This cooling will freeze the soil surrounding the pumps creating an impenetrable barrier around the reactor buildings. In total, some 1550 pipes have been placed in the ground to create a 1.5km-long ice wall around units 1 to 4. The wall is designed to remain effective for up to two months in the event of a loss of power. The Japanese government agreed to pay for construction of the ice wall, estimated to cost some JPY32 billion ($278 million).
Reducing the amount of contaminated water that it must deal with is a priority for Tepco. Groundwater naturally seeps from land to sea, but at the Fukushima Daiichi site it must negotiate the basements of reactors buildings. It is thought that more than 400 tonnes of groundwater enters the basements each day through cable and pipe penetrations as well as small cracks, mixing with the heavily contaminated water previously used to cool the damaged reactor cores.
The ice wall is only one part of a multi-layered strategy being employed to manage the flow of groundwater and rainwater at Fukushima Daiichi, Tepco said. Tepco is saying that its strategy to prevent water becoming contaminated has reduced the daily inflow of groundwater into the buildings to 150 tonnes per day. “Successful implementation of the frozen soil water is designed to reduce that inflow further, by keeping water out of the reactor buildings,” the company contends.
TEPCO has maintained that once the soil is frozen, it will form a circular barrier and reduce the flow of groundwater into the reactor buildings; and that, in turn, will prevent water contaminated with radioactive substances from accumulating.
But the Nuclear Regulation Authority contends that contaminated water accumulated in the reactor buildings could leak into the groundwater if the level inside the frozen soil wall drops too much.
TEPCO planned to construct a 1,500-meter-long frozen soil wall around the four reactor buildings by inserting 1,568 pipes to a depth of 30 meters at 1-meter intervals. Each pipe will freeze the soil around it once liquid of minus 30 degrees circulates inside the cylinder.
On Feb. 9, TEPCO completed the last part of the project to install temperature indicators, allowing it to start freezing the soil at a moment’s notice.
Groundwater is continuing to flow into basements of reactor buildings with melted nuclear fuel, adding to the amount of highly contaminated water being produced.
In May 2013, a committee of the Ministry of Economy, Trade and Industry drew up a report on the merits of constructing a frozen soil wall to reduce the volume of contaminated water.
Based on the report, TEPCO started the construction work in June 2014. The government has already spent about 34.5 billion yen ($300 million) on the project.
TEPCO maintained that once the frozen soil wall is completed, it should reduce the flow of groundwater into the reactor buildings from about 400 tons a day to 100 tons in tandem with other measures, including work to pump out groundwater from wells dug around the reactor buildings.
From the outset, the NRA cast doubt on the effectiveness of the frozen soil wall, saying that highly contaminated water accumulated in reactor buildings could leak into the ground if the groundwater level inside the wall drops too much.
The NRA repeatedly asked TEPCO whether the frozen soil wall would prove truly effective in reducing the amount of contaminated water.
“TEPCO is scattering a strange illusion that the problem of contaminated water can be solved completely if a frozen soil wall is constructed,” NRA chairman Shunichi Tanaka said in spring 2015.
In a test operation which started that spring, the reduction of groundwater levels was larger than expected in some places. The speed and direction of the groundwater flow could not be clarified in some locations.
Because it takes two months or so for the soil to thaw out, countermeasures cannot be taken immediately if problems crop up.
TEPCO acknowledges that there are limits to its crystal ball-gazing with regard to the problem of groundwater. However, it contends that it can prevent contaminated water from leaking into the ground by pouring water into the ground through wells if the level drops too much.
In December, the NRA took the rare move of proposing to TEPCO in a written document that the utility operate the frozen soil wall only in places where contaminated water is unlikely to leak into the ground.
However, TEPCO dug in its heels and said it intended to operate the frozen soil wall as a whole. But it also plans to consider the NRA’s proposal.
On Feb. 9, TEPCO President Naomi Hirose visited the NRA office and told Tanaka, “We will consider your proposal and get back to you in a most sincere manner.”
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