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Engineers at the Fukushima Daiichi Nuclear Power station have started to build a huge “ice wall” around the four stricken reactors in an effort to prevent groundwater from becoming contaminated.
The so-called ice wall is a system of 1550 pipes that are designed to freeze the ground below and around the four crippled reactor units at Fukushima, effectively creating a barrier 1.5km in circumference and 30m deep to block the flow of groundwater and prevent its mixing with contaminated water.
The company responsible for the Fukushima site, the Tokyo Electric Power Company (Tepco), said that engineers were unable to build a seamless physical wall underground because of obstacles such as pipes underground, but that tests carried out earlier this year have demonstrated the effectiveness of the ice wall design.
The Fukushima Daiichi plant suffered multiple meltdowns following Japan's massive earthquake and tsunami in March 2011. Tepco has struggled with containing the massive amounts of contaminated water at the plant. It has built hundreds of tanks around the plant to store the water coming from the three melted reactors, as well as underground water running into reactor and turbine basements.
Installation of the pipes for freezing the soil has started at the site's northwest corner. The start of construction follows approval from the Nuclear Regulatory Authority at the end of May. Construction is expected to be completed in early 2015.
Construction is being undertaken by the Kajima Corporation, which has previously used the technique in the construction of tunnels near watercourses to block water penetration. However critics have pointed out that the method has never been applied on this scale before. The refrigerant being used is chilled brine.
The barrier is being funded by the Japanese government and is designed to withstand long-term interruptions of electricity, so that its effectiveness can be maintained for approximately two months after the loss of power, said Tepco.
Naomi Hirose, president of Tepco, said: "Beginning construction of the ice wall represents another milestone in our overall effort to move forward in decontamination and decommissioning at Fukushima Daiichi.”