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NRA approves plan to start freezing wall of soil on ocean side at Fukushima plant

The Nuclear Regulation Authority (NRA) approved a plan on Feb. 15 to gradually freeze a wall of soil around the crippled Fukushima No. 1 nuclear plant, starting with shields on the ocean side.

    The NRA had expressed concern that if all the soil walls were frozen and if the groundwater level were mismanaged, highly contaminated water could leak out from the reactor buildings. With the NRA's approval of the plan, measures to deal with contaminated water will move a step forward. But it remains to be seen how effective the plan will be, as groundwater will continue to seep into the reactor buildings from the mountains.

    Tokyo Electric Power Co., the operator of the damaged plant, presented an outlook for the project which stated that if the soil walls were frozen in stages, it would take about eight months to complete work to freeze all of the walls. The NRA is likely to allow TEPCO to start freezing the walls in or after March, making it impossible for the utility to meet its target of finishing work to freeze the walls by the end of March this year.

    The shields set to make use of frozen soil have been built around the No. 1 to 4 reactors at the Fukushima nuclear plant. The NRA had pointed out that if the groundwater level inside the walls were to become too low, the level of highly contaminated water in the reactor buildings would exceed that of the groundwater, threatening to flow out of the reactor buildings. At a review session held on Feb. 15, TEPCO explained that the risk of contaminated water leaking from the reactor buildings would be smaller if the soil walls on the ocean side were frozen first, rather than following its original plan to freeze the walls on the mountain side first.

    TEPCO explained that it would monitor future groundwater through a total of 69 water-level gauges, injecting water into the ground during an emergency and urgently transporting contaminated water from the reactor buildings in the event of operations of the frozen walls coming to a halt, among other measures.

    NRA Commissioner Toyoshi Fuketa expressed his understanding of TEPCO's plan, saying concerns of the leakage of contaminated water had basically been defused. At the same time, he deferred a decision on whether to allow TEPCO to freeze all of the walls including those on the mountain side of the reactor buildings, saying that the NRA would make a decision on whether to approve the utility's subsequent plans after having the utility submit a detailed step-by-step process.

    The project to install equipment to freeze walls of soil began in June 2014 and was completed on Feb. 9, 2016. The government has put more than 32 billion yen into the project. Altogether, 1,568 pipes are being used to create frozen soil walls stretching a total of about 1.5 kilometers around the reactor buildings, and walls reaching a depth of about 30 meters have been built underground to drastically reduce the flow of groundwater into the reactor buildings. Upon completion of construction, TEPCO has said it will be able to reduce the inflow of groundwater to several dozen metric tons per day from about 150 to 200 tons.

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