A giant wall that extends deep into the earth to block groundwater from flowing into the port area has been completed at the Fukushima Daiichi Nuclear Power Station. This marks a major milestone in the implementation of TEPCO’s multi-faceted strategy to manage and treat water during the decommissioning of the plant.
The wall, combined with the pumping operations that will remove the water that builds up behind it, will not only keep contaminated water from entering the port area but is also expected to decrease the amount of groundwater flowing into the reactor buildings. That, in turn, will reduce the amount of water on the site that becomes contaminated.
Fukushima Daiichi sits on a hillside between the mountains and the sea. As water flows downhill, it flows around and under Fukushima Daiichi. The seaside impermeable wall is designed to protect the ocean by blocking water from flowing into the port area. Starting from April 26, 2012, the wall was constructed by driving 594 steel pipe sheet-piles deep into the earth across a width of about 780 meters, between the reactor buildings and the largely enclosed port area as well as a part of the Pacific Ocean.
Although most of the wall has been in place for some time, it was impractical to close it completely until TEPCO received an understanding of pumping up, treating, and discharging of the water that would build up behind it. In September, TEPCO was able to begin pumping up water from wells called “subdrain” that are installed around the four reactor buildings, and additional wells called “groundwater drain” to pump up water closer to the seaside impermeable wall. Once it was determined that the pumping operation using the subdrain systems was effective in reducing the flow of water behind the wall, TEPCO was able to go ahead with closing the wall.
The water that is pumped up from behind the wall is expected to be much less severely contaminated than the water from inside the reactor buildings, which is being treated and held in on-site storage tanks. Similar to the water pumped up in the groundwater bypass operation, the water pumped from the subdrain systems will be treated to a more stringent standard than WHO standards for drinking water. The water will be kept until an independent third-party tests and confirms it has been treated to that standard, and only then will be discharged into the port area adjacent to the plant. TEPCO appreciates the understanding of all concerned parties including Fukushima prefecture and prefectural and national fishermen’s associations.
Intensive monitoring of the port area will continue and the analysis results that show seawater conditions will be collected and made available. The effects of stopping the groundwater flow to the seaside impermeable wall will be evaluated by measuring the change in water levels behind the wall.