Japan’s Tokyo Electric Power Company (Tepco) on 30 March won approval from the Nuclear Regulation Authority (NRA) to start freezing soil around the damaged reactors at the Fukushima Daiichi NPP. Tepco hopes to create an ice wall that will reduce the amount of groundwater flowing into the four reactor buildings where it becomes contaminated. The volume of contaminated water at the plant is increasing daily. Once the freezing process is complete, together with other measures, the daily accumulation of underground water is expected to fall from 400t to about 50t. The wall is expected to start restricting the inflow of groundwater about 45 days after the freezing starts. Tepco completed construction of the wall in February, after two years of work.

NRA did not approve Tepco’s initial plans for the 1.5km-long wall, citing concerns that it could lower the groundwater level too much and cause radioactive water pooled in the reactor buildings to leak out. Tepco then submitted a revised plan to do the freezing work in stages. Under the new plan, it will first freeze soil at the ocean (downstream) side of the buildings to prevent water leaking there. NRA Chairman Shunichi Tanaka said the operation will be a major challenge. He said it is important to carefully monitor the freezing process with adequate data.

To build the frozen soil walls, coolant chilled to a temperature of minus 30 degrees Celsius is to circulate through 1,568 pipes that are driven into the ground to a depth of around 30 metres, to create a "wall of ice." If the project goes as planned, work to freeze the walls is expected to be completed in about eight months.

The frozen-soil wall project is considered to be a key measure to deal with contaminated water along with the "subdrain" project designed to reduce the amount of water being contaminated by removing clean underground water from wells around the reactor buildings. Some JPY34.5bn ($306.8m) in state funds has so far been used for the shield system.