Tepco begins ice wall activation

Tokyo Electric Power Company announced that it has today started up the equipment to create a wall of frozen soil at the Fukushima Daiichi nuclear power plant to prevent groundwater entering the reactor buildings. Regulatory approval to partially activate the ice wall was received yesterday.

Tokyo Electric Power Company (Tepco) announced that it has today started up the equipment to create a wall of frozen soil at the Fukushima Daiichi nuclear power plant to prevent groundwater entering the reactor buildings. Regulatory approval to partially activate the ice wall was received yesterday.

The ice wall will surround Fukushima Daiichi units 1-4 (Image: 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 some 150 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.

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. Tepco announced in December that all the necessary equipment was in place for the creation of the ice wall.

Tepco announced yesterday that the Nuclear Regulation Authority (NRA) had it given approval to activate about 95% of the wall. Approval to activate the remaining 5% will be sought later, the company said. Activation of the ice wall will take place in stages over the coming months, it said.

The full perimeter of the wall is not being frozen immediately so that the effects of the frozen barrier can be studied on the relative water levels inside and outside of the reactor building, Tepco said. "It is important to ensure that relative water levels are not changed in a way that would enable contaminated water to escape from the basements of those buildings into the surrounding groundwater," the company said. "By leaving a gap in the wall, it is expected that groundwater within the perimeter will stay at a higher level than the water inside the basements, thus preventing the latter's escape."

This first stage is expected to reduce the underground water flow by some 50%. Once the results of this stage have been assessed - which is expected to take "a period of months" - approval will be sought to close the remaining 5% and establish a completely frozen perimeter.

Naohiro Masuda, Tepco's chief decommissioning officer, said: "We understand that the biggest concern is that the contaminated water might escape from the buildings. We must not let that happen."

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).

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. The strategy to prevent water becoming contaminated has reduced the daily inflow of groundwater into the buildings to 150 tonnes per day.

Researched and written
by World Nuclear News