Among the many problems plaguing the cleanup at Fukushima is the threat of radioactive water spilling from the site. The Japanese government is now ramping up its efforts to contain this problem, by flicking the switch on an underground ice wall that will enclose the failed nuclear facility to slow the spread of contaminated material.

An ice wall might sound like something out of science fiction, but is actually an engineering technique that has been used for tunnel boring and mining, albeit on a smaller scale. Refrigerated brine cooled to -30 degrees Celsius (-22 ° F) will be pumped through pipes plunging 30 m (98.5 ft) into the ground, freezing the soil and eventually sealing the four reactors damaged in the 2011 earthquake and tsunami inside a 1,500 m (5,000 ft) barrier.

Scientists have recently detected elevated levels of radiation in seawater samples collected near the reactors, and even as far away as the US west coast, confirming that there is an ongoing release of toxic materials from the plant. Workers at Fukushima have already filled purpose-built steel tanks with tons of toxic water from the reactors, but there are some areas that they simply can't access as radiation levels remain dangerously high, so high in fact that even robots sent in to investigate are having their wiring fried.

So, with 400 tons of groundwater flowing downhill into the reactor basements each day and some of that then spilling into the sea, there is a need for alternative solutions.

Construction on the frozen soil wall began in 2014 and is now complete. Japan's nuclear regulator gave the green light for the wall to be activated on Wednesday, setting in motion a plan to surround the four damaged reactors with an impenetrable barrier. The wall will be turned on in stages, but the first will see around 95 percent of the barrier activated. Plant operator Tepco says that initially leaving a gap in the wall will keep groundwater levels within the perimeter at a higher level than that of the basement water, therefore preventing the latter from spilling over.

Once it has assessed the success of this first stage, which it expects to cut the flow of groundwater into the buildings by 50 percent, it will seek approval to switch on the remaining portion to form a solid boundary around the four reactors. There is no set timeline, but the process is expected to take place over a period of months.

Source: Tepco

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