With the permission of local fishermen Tepco will soon let groundwater bypass the Fukushima Daiichi plant, alleviating a large part of its water management problem.
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 ruined 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's proposal is to sink a line of 12 wells inland from the reactor buildings and pump water out of the ground before it has a chance to become contaminated. It would then be checked and discharged to sea.
This week the plan was approved by the Fukushima prefecture Fishermen's Union, after around eight months of negotiations. A number of union members had been concerned about the impact on the public image of their products from Tepco 'releasing water' from the site.
Fishermen granted permission for the bypass procedure, which was first drawn up in mid-2013, on certain conditions: 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; A third party will monitor the water and ensure the agreed standard is maintained; Tepco are also required to be transparent in their release of information; And the company must also continue to compensate fishermen for reputational damage.
The bypass 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. Tackling the water issues has been a very high priority for the Japanese government since coming to light in the middle of last year.
The ALPS decontamination system is currently capable of processing 750 tonnes per day, which outweighs the net balance of injected water, plus the influx of groundwater, minus some of this water which is recycled for cooling. Two further ALPS plants are being built, to take total daily processing capacity to 2000 tonnes by around October. As these come online, Tepco should rapidly cut into its 340,000 tonne stock of contaminated water.
Researched and written
by World Nuclear News