Japan’s Nuclear Regulation Authority (NRA) approved a plan on 16 February to gradually freeze a wall of soil around the damaged Fukushima Daiichi NPP, starting on the ocean side. NRA had expressed concern that if all the soil walls were frozen and if the groundwater level were mismanaged, highly contaminated water could leak from the reactor buildings. The wall is intended to deal with the problems of contaminated water at the site, but it is unclear how effective the plan will be, as groundwater will continue to seep into the reactor buildings from the mountains.

Plant operator Tokyo Electric Power Co (Tepco) had said 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 expected to allow freezing of the walls to begin in or after March, although this will make it impossible for Tepco to meet its original target of completing the project by the end of March.

The shields set to make use of frozen soil have been built around reactors 1-4 at the plant. The NRA had pointed out that if the groundwater level inside the walls became too low, the level of highly contaminated water inside the reactor buildings would be higher and could flow out of the buildings. At a review on 15 February, Tepco argued that the risk of contaminated water leaking from the buildings would be reduced if the soil walls on the ocean side were frozen first, rather than following its original plan to initially freeze the walls on the mountain side.

Tepco undertook to monitor future groundwater using 69 water-level gauges, injecting water into the ground during an emergency and urgently transporting contaminated water from the reactor buildings in the event the frozen walls failing, among other measures.

NRA Commissioner Toyoshi Fuketa accepted Tepco’s argument but deferred a decision on whether to allow freezing of all the walls including those on the mountain side of the reactor buildings. He said NRA would make a decision on whether to approve Tepco’s subsequent plans after the company had submitted a detailed step-by-step process.

The project to install equipment to freeze walls of soil began in June 2014 and was completed on 9 February. The government has invested more than JPY32bn ($284m) in the project. A total of 1,568 pipes are being used to create frozen soil walls stretching 1.5km around the reactor buildings, with the walls reaching a depth of about 30 metres to reduce the flow of groundwater into the buildings. Tepco has said it will be able to reduce the inflow of groundwater to several dozen tonnes a day from about 150-200t at present.