Tepco has begun pumping groundwater so that it bypasses the Fukushima Daiichi plant, reducing the volume of contaminated water that it must deal with. The water will be stored and tested before being released into the sea.
|Tanks for temporarily storing the groundwater prior to discharge to sea (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. Some water also leaves the buildings in similar ways, causing high levels of contamination to be found in test wells near the sea.
Tepco has sunk a line of 12 wells inland from the reactor buildings and today began pumping water out of the ground before it has a chance to become contaminated. The water will be temporarily stored in tanks where it will be tested for contamination. Unless above permissible levels, this water will then be discharged to sea.
Test operation of the groundwater bypass system was started by Tepco in April 2013 and it has since been carrying out water quality tests. The company says that, so far, the level of radioactive materials contained in the pumped-up groundwater is well below the permissible amount for release into the sea.
Last month, local fishermen granted permission for the bypass procedure on certain conditions. These included that the water Tepco releases must be below an agreed limit of 10 becquerels per litre of either caesium-134 or -137. This is highly conservative at only one tenth the level deemed acceptable by the World Health Organisation for drinking water. In addition, a third party must monitor the water and ensure the agreed standard is maintained.
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.
Researched and written
by World Nuclear News