The first groundwater diverted from the Fukushima Daiichi plant has been released into the sea after tests showed that contamination was well below permissible levels. The bypass system will significantly reduce the volume of contaminated water that Tepco must deal with.
|Workers watch on as an operator starts the groundwater discharge system (Image: Tepco)
Groundwater naturally seeps from land to sea, but at the Fukushima Daiichi site it must negotiate the basements of reactors buildings. It is thought that more than 400 tonnes of groundwater enters the basements each day through cable and pipe penetrations as well as small cracks, mixing with the heavily contaminated water previously used to cool the damaged reactor cores.
Tepco began pumping water out of the ground through wells sunk inland from the reactor buildings in early April. The groundwater pumped up during trial operation of the system has been held storage tanks on the site and tested for contamination. Measurements, verified by independent third parties, showed that the water contained less than 1 becquerels per litre of caesium-134 and -137. This limit is highly conservative at only one-tenth the level deemed acceptable by the World Health Organisation for drinking water.
A final agreement on the marine discharge was reached with the government, Fukushima prefecture officials and the Fukushima fishermen's union yesterday. The discharge of the diverted groundwater into the sea began today at 10.25am. In an operation lasting just over two hours, a total of 561 tonnes of stored groundwater was released.
In full operation, the groundwater bypass system could reduce the ingress of water to the basements by 100 tonnes per day and therefore reduce the total volume of water Tepco must decontaminate. As well as the bypass, an impermeable underground wall has been built between the reactors and the sea and plans are being made to freeze the ground around the buildings. Together, these measures should greatly reduce the movement of groundwater.
Head of the Fukushima Daiichi Decontamination and Decommissioning Engineering Company, Naohiro Masuda, said, "We would like to express our sincere appreciation to many parties, including Fukushima prefecture and members of the fishing industry, for their understanding in the operation of the groundwater bypass, which plays an important role among the countermeasures to suppress the increase of contaminated water."
Researched and written
by World Nuclear News