New approaches to removing the contaminated water from trenches around units 2 and 3 at the damaged Fukushima Daiichi plant are being explored after attempts to freeze it failed.
The trenches contain highly-contaminated water that has flowed from the main power plant buildings - a mixture of injected cooling water and groundwater that has leaked into the basements.
In April, Tokyo Electric Power Company (Tepco) attempted to freeze the water in the trench outside of unit 2 before removing it. By freezing it, the company hoped to prevent more water flowing from the unit's basement and refilling the trench. This operation is separate to the one to construct a wall of frozen soil around all four Fukushima Daiichi units to prevent groundwater flowing through the buildings and then into the sea.
Tepco said that, despite the success of early experiments, "it has proved exceptionally difficult" to freeze the trench water. This, it said, is due to the constant flow of water into and out of the trench because of the pumping of water from the unit's basement.
The company said that it has now discussed various new strategies for dealing with the trench water with Japan's Nuclear Regulation Authority. These include upgrading the capacity of the freezing system; suppressing the flow of the water; and, exploring alternatives means of freezing the water.
Tepco said it has already increased the flow of coolant into the trench water and is considering adding ice or dry ice to the water to help freeze it. If these measures do not work, the company may install additional coolant pipes. Efforts may also be made to stem the flow of water from the reactor buildings by grouting holes, such as spaces around pipes passing through the building's walls.
Tepco plans to implement at least some of these new strategies by the end of this month.
Site superintendent Akira Ono said, "We are committed to these efforts and will continue to pursue these alternatives until we have successfully removed the water from the trenches."
Efforts to freeze the trench water at unit 3 have yet to begin, the company noted, but said that once it has successfully frozen the water it will take 3-4 months to remove it from each unit.
Researched and written
by World Nuclear News