A Nuclear Regulation Authority (NRA) working group approved a plan on May 26 for an ice wall at the Fukushima No. 1 Nuclear Power Plant that is aimed at reducing the inflow of groundwater that becomes contaminated with radiation.
The wall is part of a three-pronged strategy to lower the inflow of groundwater. Currently the amount of radiation-contaminated water at the plant increases by around 400 tons per day due to groundwater flowing into the crippled plant's reactor buildings.
The Ministry of Economy, Trade and Industry and Tokyo Electric Power Co. (TEPCO) want to start construction of the wall in June. The wall will be made by inserting 26.4 meter-long freezing tubes into the ground at one-meter intervals and circulating minus 30 degree Celsius cooling liquid through the tubes to freeze the nearby groundwater. The process should create an ice wall around two meters thick, 30 meters deep and 1.5 kilometers long that will surround the No. 1 through 4 reactors at the plant and block much of the water flow.
However, the NRA raised around 30 points of concern about the ice wall, such as over its safety and effectiveness at blocking water. It sent these concerns to the main authorities behind the plan, which include the Agency for Natural Resources and Energy and TEPCO. In particular, the NRA sought the release of evidence that the creation of the ice wall will not interfere with the cooling system of the melted nuclear fuel in the No. 1 through 4 reactors by lowering the ground level and causing the reactor buildings to tilt.
In response, at an NRA meeting on May 26 to discuss and evaluate the Fukushima plant, TEPCO released an estimate that an ice wall would cause at most a ground level fall of 1.4 to 1.6 meters, and "the reactor buildings will hardly move." No major concerns were raised from the NRA side, and the ice wall plan received an overall green light to proceed. The wall is planned to be finished sometime during fiscal 2015.