Turning soil into virtual permafrost with refrigerated coolant piped through the earth was first used in the 1860s to shore up coal mines. One hundred and fifty years on, it’s the newest idea for containing the Fukushima nuclear disaster.
At least 300 tons of water laced with radioactive particles of cesium, strontium linked to bone cancer, and tritium flow each day into the Pacific Ocean from the crippled atomic station in Japan. The plan to contain the health threat is to build an underground containment wall made of ice.
After repeated failures to hold back water contaminated by the 2011 disaster, plant operator Tokyo Electric Power Co. is running out of options to deal with what was called an “urgent problem” by Prime Minister Shinzo Abe last week for the first time. Dealing with the water leaks is an “emergency,” the Nuclear Regulation Authority said. Japanese taxpayers already face an 11 trillion yen ($112 billion) estimated clean-up cost.
Underground ice walls have been used to block radiation before, in an experiment at the former site of the Oak Ridge National Laboratory in Tennessee, which produced plutonium for atomic weapons, according to a report by Arctic Foundations Inc., an Alaska-based earth-freezing contractor.
“It’s just sometimes it’s the only scenario that will really work,” said Joseph Sopko, executive vice president of Moretrench, a Rockaway, New Jersey-based contractor specialized on frozen-earth projects. “When nothing else will work, it just jumps out at you and says ‘Wow, it’s a freeze job.’”
The plan at Fukushima has drawbacks: it won’t be completed until 2015, and there’s no cost estimate yet. The envisioned wall of ice would run 1.4 kilometers (0.9 mile) underground, the world’s longest continuous stretch of artificially frozen earth, according to Japan’s nuclear accident response office.
Kajima Corp., the construction company that was the principal builder of the Dai-Ichi nuclear plant, has been given until March 31, 2014, to complete a feasibility study of the project.
Highly contaminated water started to accumulate in basements of Fukushima buildings when crews began injecting tons of water into the reactors after the earthquake and tsunami on March 11, 2011, knocked out power to cooling systems.
Groundwater then started leaking into the basements, adding to the volume of contaminated water. In turn, radiated water seeped into groundwater, causing radiation at nearby monitoring wells to spike. At least 300 tons of contaminated groundwater are thought to be flowing into the ocean from the plant each day, according to the Ministry of Economy, Trade and Industry.
Kajima’s proposal calls for engineers to sink vertical pipes about a meter apart and between 20 and 40 meters deep into the ground around the structures. Coolant would be cycled from on-site refrigerator units into the pipes, where they would form a frozen wall to keep contaminated water in and keep out any fresh water flowing down from nearby mountains. The government anticipates keeping the ground frozen for six years starting in July 2015.
“We expect the walls will stem the flow of groundwater from the mountain side and also keep water inside the buildings from leaking,” Tatsuya Shinkawa, director of the nuclear accident response office in the Agency for Natural-Resources and Energy, said at an Aug. 7 press conference.
Government officials have not released a cost estimate for the project.
“The proposal to freeze the earth is nothing but a cash cow for the contractor,” said Richard McPherson, a California-based energy and defense consultant who has researched the nuclear accidents at Chernobyl and Fukushima. “The amount of energy alone required to maintain the coolant below freezing temperature is a waste.”
Kajima declined to comment on the cost of the project or any other details, saying in an e-mailed response that it has yet to start the feasibility study. Hirofumi Shibata, also at the nuclear accident response office, said the energy requirements were not yet known.
A project of the scale being discussed at the Fukushima plant would require about 9.8 megawatts of power to maintain, according to Bernd Braun, a geotechnical consultant in Texas who works on ground-freezing projects. That’s enough electricity to supply about 3,300 Japanese households, according to calculations by Bloomberg.
“This will require a hell of a refrigeration station and a huge power supply,” Braun said in an e-mail.
The technique of freezing the earth was devised in the late 19th century by German scientist F.H. Poetsch, who chilled a saline solution using Frenchman Ferdinand Carre’s recently invented machine that achieved frozen temperatures using a chemical reaction between water and ammonia.
It’s now commonly used for temporary reinforcement in tunnel building and other projects, such as the construction of the Second Avenue subway in New York and the Port of Miami tunnel, according to Sopko, who worked on the projects.
Officials decided to go with Kajima’s proposal as part of the government’s offer to contribute more funds to efforts to stem the flow of contaminated water into the ocean.
“This operation is unprecedented in scale, anywhere in the world,” Chief Cabinet Secretary Yoshihide Suga said at a press conference. “So we believe the government must step forward and support its realization.”