Ground freeze urged to curb seepage into Fukushima No. 1 radioactive basements

by Kazuaki Nagata

Staff Writer

To reduce the flow of groundwater into the crippled reactor buildings at Tokyo Electric Power Co.’s Fukushima No. 1 atomic plant, the government told Tepco on Thursday to freeze the soil around them.

Walls of frozen soil can be created by inserting pipes into the soil and injecting them with coolant. Tokyo-based major general contractor Kajima Corp. came up with the idea.

A panel under the Ministry of Economy, Trade and Industry discussing ways to lessen the radioactive water at the Fukushima plant drew up a draft report the same day that suggests using frozen-soil walls to keep the groundwater at bay. METI Minister Toshimitsu Motegi told Tepco President Naomi Hirose to take measures based on the report.

The report recommended creating frozen-soil walls to encircle the buildings housing reactors 1 to 4, all of which are damaged and their basements are continuously accumulating groundwater seeping in that is becoming radioactive.

Kajima said frozen-soil walls have zero permeability and are relatively easy to construct quickly, although they are mainly a short-term fix.

Even if a blackout halts the power to cool the pipes, the soil would remain frozen for several months, according to Kajima.

These merits prompted the METI panel to favor frozen-soil walls over other options, including building clay walls.

But long-term operation of frozen-soil walls can be costly, because powere will be continuously needed to keep cooling the pipes, METI officials said, adding the cost to build and maintain the system is also an unknown. Pipes and coolant would need periodic replacement for long-term use, Kajima said.

The panel’s draft report said the government and Tepco hope to create the frozen-soil walls between April and September 2015.

About 400 tons of groundwater apparently flow into the basements of the buildings for reactors 1 to 4 every day. The buildings are located between the sea and nearby mountains, the source of the ocean-bound groundwater.

Reactors 1 to 3, which suffered meltdowns after the March 11, 2011, mega-quake and tsunami, are cracked, so the water pumped into them to cool their highly radioactive fuel leaks into the basements, combining with and contaminating the daily inflow of groundwater.

Tepco has been processing the radioactive water to a certain extent, including pumping it into tanks, but the massive amounts are preventing work to decommission the crippled reactors.

A rough estimate suggests that groundwater seepage into the basements would be reduced from 400 tons to 100 tons once the frozen-soil walls are built.