Tokyo Electric Power Company (Tepco) says it has completed construction of a 780-metre impermeable underground wall on a section of a pier close to the Fukushima-Daiichi NPP to prevent groundwater from entering the Pacific Ocean after flowing through the four damaged reactor buildings. Construction of the wall, which is made of 594 steel sheet piles, began in April 2012. It is expected to "significantly reduce" the risk of contaminated groundwater flowing into the ocean and is also intended to prevent contaminated rainwater overflow from entering the shipping port. Tepco said around 300t of groundwater a day enter the reactor buildings through cracks, and become radioactively contaminated after mixing with the water injected into the reactor to maintain cold shutdown. An additional 100t of rainwater a day, on average, fall onto the reactor area.
Difficulty in controlling groundwater, as well as strong opposition from local fishermen, have delayed the project. Local fishermen were anxious about the releasing of once-contaminated water into the sea and also expressed little confidence in Tepco's water clean-up measures.
After long negotiations, the fishermen agreed to the plan in August this year, allowing the wall to approach completion.
In early October, Tepco said it had released more than 4,000 cubic metres of groundwater into the sea at Fukushima since the operation to treat it at a purification facility began on 3 September. The treated groundwater is only released when it is confirmed that concentrations of radioactive material have been reduced to between 0.001 and 0.0001% of their original levels and are below operational targets. Those targets are about one-tenth below targets set by the World Health Organisation for acceptable drinking water.
Tepco says the wall will reduce the amount of caesium and strontium in the groundwater flowing into the sea by one-fortieth, and tritium by one-fifteenth. The levels of caesium 137 inside the plant's port are currently around 10 becquerels at the highest, and several becquerels at the sea outside it. Tepco will monitor the levels of the substances in the sea water to confirm the effectiveness of the wall. Immediately after the 2011 accident, levels of caesium 137 rose to several million becquerels per litre in the sea adjacent to the plant. They dropped significantly after a year.
Along with the seaside wall, Tepco is reinforcing the drainage system that collects surface water from various parts of the facility with a new covered channel. Work on the new configuration, which began in May, is expected to be completed by March.The company also hopes to start freezing a soil barrier around the wrecked reactor buildings by the end of the year.