Fukushima Daiichi drainage system enters operation

03 September 2015

The flow of groundwater into the reactor buildings and port area of the damaged Fukushima Daiichi nuclear power plant in Japan should be significantly reduced with the start of use of a new system to pump, treat, test and discharge the water.

Fukushima Daiichi subdrain system - 460 (Tepco)
A schematic of the subdrain and groundwater drain systems (Image: Tepco)

The subdrain system is a group of 41 wells installed in the vicinity of the reactor and turbine buildings. Pumped up by the subdrain, the amount of groundwater flowing into the buildings is expected to be significantly reduced. The groundwater flowing into the port area is held back by the coastal impermeable wall and pumped up by another group of wells, the groundwater drain system, installed in the bank protection area.

Tokyo Electric Power Company (Tepco) announced the first pumping up of groundwater by 20 of the wells in the subdrain system had begun at 10.00am today.

The collected groundwater will be temporarily stored to check its quality and then discharged into the port area, with thorough treatment processes.

Tepco said it expects the water pumped up by the subdrain and groundwater drain to be slightly more contaminated than water from the existing groundwater bypass (which intercepts water on the land side of the reactor buildings). However, it said the water will be treated to meet the more stringent quality standards for the subdrain and groundwater drain than for the groundwater bypass. The company noted the water would also be monitored more frequently to verify its quality for discharge.

Once the subdrain and groundwater drain systems are found to be operating stably, the opening that was left in the seaside impermeable wall will be closed to prevent groundwater flowing into the port area, Tepco said. The subdrain and groundwater drain will then work to keep groundwater from accumulating behind the impermeable wall.

Tepco estimates the subdrain will reduce the flow of groundwater into the reactor buildings to 150 cubic meters per day from the current 300 cubic meters. In the longer term, the company said the pumping systems and seaside wall are expected to be joined with the land side impermeable wall (frozen soil wall) currently under construction, "creating a wall around the reactor buildings and further reducing the intrusion of groundwater".

Tepco sought the approval of prefectural and national fishermen's associations for use of the system.

Tepco's chief decommissioning officer Naohiro Masuda said, "The activation of the subdrain system is a major milestone in redirecting fresh water from contaminated area. It also enables the seaside impermeable wall to be closed to further prevent any leakage of contaminated water."

Researched and written
by World Nuclear News