Tokyo Electric Power Co. will implement a "difficult" proposal to use walls of frozen soil to reduce the amount of groundwater flowing into reactor buildings at its crippled Fukushima No. 1 nuclear power plant.
A government committee working on measures to deal with water contaminated with radioactive materials submitted the proposal to industry minister Toshimitsu Motegi on May 30. Motegi then instructed TEPCO President Naomi Hirose to carry it out.
"From a technical viewpoint, it will be difficult to do so," a TEPCO official said, "but we will implement the proposal along with other measures."
According to the industry ministry's Agency for Natural Resources and Energy, the proposal to create frozen soil walls to block the flow of groundwater into the reactor buildings was made by Kajima Corp., a leading construction company.
The proposal will also be incorporated into the government's "middle- and long-term road map" to decommission reactors at the plant.
According to the proposal, ducts will be inserted into the ground around reactor buildings at intervals of 1 meter to a depth of up to about 30 meters. Then, coolants of about minus 50 degrees will be circulated in those ducts to freeze the soil. The frozen soil will then serve as a wall against groundwater.
The wall will be able to block more groundwater than other walls that are made of clays or crushed stones and can be constructed more quickly.
However, the cost of creating the system is expected to reach several tens of billions of yen, and maintenance of the system will also entail considerable outlays. There are no instances of the system being used for extended periods.
The government, TEPCO and construction companies will set up a joint working group in June at the earliest to design the system, with the goal of putting it into practical use in the first half of fiscal 2015.
Contaminated water at the plant is being produced and accumulated in reactor buildings when water is used to cool melted nuclear fuel. Now, groundwater flowing into those buildings through cracks made by earthquakes and other impacts is increasing the amount of contaminated water by 400 tons every day.
The government estimates that the frozen soil walls will reduce the amount of groundwater flowing into the reactor buildings to 100 tons a day.
TEPCO is also considering a "groundwater bypass" plan in which it digs wells around reactor buildings, pumps up groundwater before it flows into the buildings, confirms its safety and then dumps it in the sea.
However, local fishermen are opposed to the plan on grounds it may fan groundless rumors that fish caught in local waters are contaminated with radioactive materials. TEPCO and the government are now trying to dispel that fear by offering detailed explanations to the fishermen.
(This article was written by Shunsuke Kimura and Keisuke Katori.)
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