A subterranean ice wall which Tokyo Electric Power Co (Tepco) has constructed surrounding the damaged nuclear reactors at the Fukushima Daiichi NPP to block groundwater from flowing into plant buildings is almost complete, The Mainichi reported on 17 August. However, while the government has already invested JPY34.5bn ($315m) in the project, doubts remain about its effectiveness, the paper said.
In a news conference at the end of July, Naohiro Masuda, president and chief decommissioning officer of Fukushima Daiichi Decontamination & Decommissioning Engineering Co., stated, "We feel that the ice wall is becoming quite effective." However, he had no articulate answer when pressed for concrete details, stating, "I can't say how effective."
The ice wall is created by circulating a coolant with a temperature of minus 30 degrees Celsius through 1,568 pipes that extend to a depth of 30 metres below the surface around the plant's reactors. The soil around the pipes freezes to form a wall, which is supposed to stop groundwater from flowing into the reactor buildings where it becomes contaminated. Tepco began freezing soil in March 2016 and to date at least 99% of the wall had been completed, leaving just a 7-metre section to be frozen.
TEPCO ordered construction of the ice wall in May 2013 as one of several plans proposed by major construction firms that was selected by the government's Committee on Countermeasures for Contaminated Water Treatment. After the 2011 accident, some 400 tonnes of contaminated water was being produced each day. That figure has now falled to around 130 tonnes, largely due to the introduction of a subdrain system in which water is drawn from about 40 wells around the reactor buildings. However, Tepco has provided no concrete information on the effectiveness of the ice wall, The Mainichi said. An official of the Secretariat of the Nuclear Regulation Authority (NRA) commented, "The subdrain performs the primary role, and the ice wall will probably be effective enough to supplement that."
An official connected with the Committee on Countermeasures for Contaminated Water Treatment commented, "It was accepted that public funds could be spent if those funds were for the ice wall, which was a challenging project that had not been undertaken before." Small-scale ice walls had been created in the past, but the scale of this one -- extending 1.5km and taking years to complete -- was unprecedented.
Initially, the government and Tepco explained that an ice wall could be constructed more quickly than other barriers, and could be melted, returning the soil to its original state, if there were any problems. However, fears emerged that if the level of groundwater around the reactor buildings fell as a result of the ice wall blocking the groundwater, then contaminated water inside the reactor buildings could end up at a higher level, causing it to leak outside the building. Officials decided to freeze the soil in stages to measure its effects, significantly delaying its completion, originally scheduled for 2015.
Maintaining the ice wall will cost over JPY1bn a year, and radiation exposure of workers involved in its maintenance is high. Meanwhile, there are no immediate prospects of being able to repair the basement damage in the reactor buildings.
Meanwhile, Tepco faces continued problems over what to do with treated water at the plant. Treatment removes all radiomuclides except tritium and NRA sees no problem with releasing treated water into the sea, despite strong resistance from local fishing workers. The water, now approaching 800,000 tonnes is currently held in tanks on the site.
The Ministry of Economy, Trade and Industry has been considering ways to handle the treated water, setting up a committee in November last year that includes experts on risk evaluation and sociology. As yet the experts have failed to agree on a solution. " It will probably take some time to reach a conclusion," a government official commented.