Photograph from Jiji Press/AFP/Getty Images
Published August 19, 2013
As contaminated groundwater continues to flow from Japan's crippled Fukushima Daiichi plant into the Pacific Ocean, the Japanese government has come up with a last-ditch solution that sounds like something out of the HBO fantasy series Game of Thrones: An underground wall of ice that would stop the radioactive leakage.
Multiple efforts by plant operator Tokyo Electric Power Company to halt the daily flow of 300 tons—nearly 72,000 gallons—of radioactive water from the plant into the ocean have failed. (See related story: "Fukushima Radioactive Water Leak: What You Should Know.") At a Tokyo press conference, Japanese Chief Cabinet Secretary Yoshihide Suga made the frozen containment, whose cost could reach 50 billion yen (about $410 million), sound like an edgy, exotic final resort for stopping the leakage from the plant's stricken reactor buildings, which were severely damaged by a March 2011 earthquake and tsunami that knocked out their cooling systems. "There is no precedent in the world to create a water-shielding wall with frozen soil on such a large scale," Suga told reporters. "To build that, I think the state has to move a step further to support its realization." (See related Pictures: The Nuclear Cleanup Struggle at Fukushima.")
To many people, the concept of an ice wall might sound almost too bizarre to be believable. The plan, initially proposed by Japanese construction company Kajima Corporation. and approved by a government panel in late May, reportedly calls for engineers to sink an array of vertical pipes into the ground around the buildings housing reactors 1 through 4. According to experts in ground-freezing technology, several large refrigerator units—the sort used to cool hockey arenas—would chill coolant that would circulate through the pipes, gradually lowering the temperature of the wet soil around them to subzero temperatures. In about two months, the soil would solidify and form a frozen barrier that would block water from flowing into the plant, and prevent already contaminated water inside it from reaching the ocean. (See related photos: "A Rare Look Inside Fukushima Daiichi.")
But fantastic as the ice wall seems, experts say the technology has been used extensively in the mining and construction industries for many years, and that it has been proven to be both durable and effective in stopping underground water movement. And while it hasn't been used previously at a nuclear power plant, they're confident that it will work—provided the project is designed and built properly. (See related photos: "Japan's Reactors Before And After.")
Photograph courtesy Joseph Sopko, Moretrench
"If you want to create a barrier to water flow, this is an excellent technique to use," explained Ed Yarmak, president of Arctic Foundations, an Anchorage, Alaska-based company that has been designing and building frozen soil containments since the early 1970s. If the bottom of the reactor buildings is sealed as well, "You're pretty much making the plant into an island. The groundwater coming down from the mountains will just go around it."
Dan Mageau, vice president and design engineer for SoilFreeze, a Seattle, Washington-based construction firm that specializes in creating ice walls, said that such barriers are far less permeable than clay containments or soil injected with chemical hardeners—other technologies that have been tried at Fukushima without success. He said that while a frozen soil barrier won't completely stop the massive flow of groundwater into the plant, which has been estimated at 400 tons (nearly 96,000 gallons) per day, it will reduce it to a negligible amount that can be easily managed with other measures.
"Structurally, [ice walls] are very stable," Mageau added. In mining and construction, he explained, frozen soil barriers have been used for many years to shore up mine shafts or foundations of structures while they are being erected.
But while ice walls are often designed to be used for only a few months or years, such frozen barriers also can be built to last a long time. Joe Sopko, director of ground freezing for Rockaway, New Jersey-based construction and engineering firm Moretrench, said that underground propane storage pits encased by ice walls have lasted for 30 to 40 years.
Diagram by Reuters
Detailed plans for Fukushima's ice wall haven't yet been unveiled, but Yarmak estimates that it would probably be a little less than a mile in length and extend about 65 feet beneath the surface. While that would make it one of the biggest ice walls ever constructed, there is some precedent. In the 1990s, Sopko helped design and build a 2.5-mile-long frozen barrier around the Aquarius gold mine in Ontario, Canada. That system was completed, but after gold prices unexpectedly plummeted during construction, it was never deployed, Sopko said. (See related, "One Year After Fukushima, Japan Faces Shortages of Energy, Trust.")
While Fukushima would be the first use of an ice wall around a nuclear plant, there is evidence that such a barrier would be effective in keeping radioactive contamination from spreading. In the early 1960s, the U.S. Atomic Energy Commission successfully used naturally occurring frozen soil in Alaska to contain thousands of pounds of radioactive waste. In the late 1990s, Yarmak helped build a demonstration project for the U.S. Department of Energy at Oak Ridge National Laboratory in Tennessee, in which a frozen barrier was used to contain a pond of soil contaminated with radiation. The DOE noted in a report that the method was effective in isolating the pond, and Yarmak said the agency opted to continue using it after the experimental trial was over. Tennessee environmental regulators found that the level of radioactive material in a nearby creek dropped significantly after the barrier was built. While that project was much smaller than Fukushima's would be—it was about 300 feet long and extended 75 feet into the ground—Yarmak is confident that the idea would work on a larger scale.
The ground freezing experts say that Fukushima probably doesn't present any unusual technical challenges. "I've had problems on jobs, usually related to groundwater velocity," Sopko said. "But the water is only moving 10 centimeters per day at Fukushima, which is easy to manage. If it was 100 centimeters per day, that would make things more complicated."
One potentially worrisome issue is the amount of electrical power that such a large ice wall would require to stay cold and solid. Bernd Braun, consultant on ground freezing projects in the Dallas-Fort Worth area, told Bloomberg Businessweek that Fukushima's ice wall probably would require about 9.8 megawatts of power to maintain. That's enough electricity to supply about 3,300 Japanese households, the publication calculated.
Experts offered another important caveat, one that will have special relevance in quake-prone Japan. While ice walls are a proven technology, they require careful design and construction. SoilFreeze's Mageau said it would be crucial to include plenty of backup capability in the design, including additional refrigeration units.
Cancer in our air, land, water, and food.
"All Of Us Guinea-Pigs Now?"
FOIA Proof That TEPCO Has Been Regularly Dumping Highly Radioactive Water Into The Pacific Ocean; via @AGreenRoad
I guess no one can say that nukes are automatically the greenest tech out there anymore. The amount of energy and money spent cleaning up after a single disaster probably drawfs even the dirtiest fossil fuels. And then there is the impact of 10,000 years of radioactive waste management.
I hear breeder reactors are a better solution except for the weapons grade plutonium waste. Frankly I'd rather see every rooftop covered in solar panels, and wind generators put everywhere it was reasonable (the wealthy beach front owners can just get over it, the rest of us have to see coal plants).
Now do a moonshot effort to improve stationary batteries and the super capacitors National Geographic just published a story on. Use these to store any excess power the solar or wind or hydro produces.
I hear that a nickel-iron battery can last beyond a century and is perfect for stationary energy storage.
All these improvements to our energy sources can be done but the owners of the existing cash cows technologies will be resistant of course. And then there are those people who line up in teams to shout back and forth about their favorite solutions - some even resorting to name calling and FUD to make their points. Unfortunate.
Do we have the political willpower to do this in America or will we put this off until the economical fossil fuels are gone or the extraction processes for fossil fuels have poisoned our oceans and our groundwater reserves?
I don't think an ice wall will help. Isn't the water they are trying to stop at the boiling point or higher due to the ongoing, never ending nuclear reaction. The water will simply melt right through the ice wall. Like a hot knife through butter.
It's only a beginning, more answers will come...I'm certain that this just can 't be left ALONE.They, ANSWERS, are out there and they need to surface....are surfacing...like planting lots of hemp...it takes radiation out of the air..and sunflowers clean up ground and water radiation..whatever fungus is growing at Chernobyl likes radiation too. Mother earth is giving us some answers we just need to listen.
Phil Blank's point is exactly on point. The question of whether the wall will work for the long term is almost irrelevant. The leak is going on EVERY DAY since the crisis started. At 61 million gallons [minimum, if you accept TEPCO's numbers as true, a dubious assumption] and climbing to date, does an ice wall in 2015 really get us anything?
I watched this news report this morning over the air here in Ohio from NHK Nuclear Watch and also found it this morning on the NHK web site and sent the link to my friends.
I say no it can't!
Two, won't the ice become radioactive and transfer the radiation to the water running around the ice wall?
@Joe AverageUS Offshore Wind Energy; 4 X The Energy Potential Of ALL Existing Power Plants In US Today; via @AGreenRoad
@Steven GottliebNot neccessarily. The water that is leaking that would come into contact with this wall is not directly in the fuel pool or in the reactor basements but rather has leeched into ground water or is standing in trenches and draining into the bay. By the time it would contact this wall, it would have cooled. I think the challenges of power to maintain the ice wall, and the physical expense and challenge and timing of building the darn thing in the first place obviates its utility.
@Phil Blank See my reply to Gottlieb & Anderson above. While I do not have direct experience with ground freezing, the time scale for installing such a wall is unlikely to be very great, probably less than a year. It consists of a row of boreholes into which refrigerant is circulated and can be constructed and brought on-line in stages, with different portions of the wall being independent of each other. Once authorized and done on a high priority basis, I would expect parts of the system (the uphill side) could be operating within about six months and the entire system within about a year. The article mentions previous attempts at installing clay and cementation barriers, so the site conditions should already be characterized. Even having the uphill part of the barrier working will improve conditions.
The ice wall is actually a barrier composed of cold ground and interstitial ice. The radioactive water within the barrier will not be flowing, except probably toward a collection and containment well pumping within the barrier. Other than the volume of water actually frozen in place on the downhill side of the barrier, none of the frozen water will be radioactive. In the absence of a pumping well inside the barrier, the transport of radioactivity would be limited to molecular diffusion (a slow process) and that due to the slow remaining movement of the water itself (called advective movement, not convective as in my previous comment). With a pumping well creating a cone of depression capture zone, no movement of radioactive water outward from the site should occur. All flow would be inward toward this well. The function of the barrier would be to limit the amount of water that needs to be pumped to create such a capture zone.
The technique works by continuously removing heat from the ground along the ice wall. Most of the energy goes into cooling the soil and rock materials through which the water flows, as these are the greater percentage of the volume and have a higher specific heat (energy required to produce a drop in temperature for a unit mass of material). Most of the energy will be expended in forming the wall. Once the wall has formed, the circulation rate to maintain it could probably be decreased. A brief interruption of power would have little effect because of the thermal inertia of the mass of frozen ground.
The reason the initial water flow rate is important is the flowing water carries the loss of heat with it, so locations where flow is high will be hardest to chill. Heat movement through the frozen ground is limited to movement through a solid, which is slower than the transmission of energy due to flowing water (called convective movement). The cold is applied at specific locations through boreholes and has to spread from there to chill the ground between the boreholes. If groundwater flow is too high, the rate of transmission of heat toward the boreholes cannot overcome the rate at which new heat is brought in by migrating water. However, this is old technology. Specialty firms should know how to evaluate this.
The technique is unlikely to take until 2015 to be installed. If it is prioritized, it could surely be operating in less than a year. The most important part is to establish a barrier in the inland side (called upgradient side) of the nuclear plant to reduce the flow of incoming water from beyond the plant. A barrier there would cause this water to flow around it and create a "shadow" effect of nearly stagnant water behind it. The remainder of the barrier would still have to be constructed, but the greatest impact would be once the upgradient part of the barrier was constructed.
Some leakage of such a barrier, probably a combination of water going under the barrier and local spots where the water flow is too fast to freeze on the uphill side, will still greatly reduce the driving force (called the head gradient) that is promoting the movement of radioactive water to the sea. The flow on the downhill side, near the ocean, would be both slower and less in quantity. Inside such a ring barrier, a pumping system could be employed to completely contain the escape of such water. Such pumping should not be to extreme, however, as it could induce breakthroughs under or through the ice wall. The pumping system would mostly be used for limiting movement.
Once the escape is stopped by an ice wall, passive methods such as clay slurry walls or other impervious barriers might be emplaced that would allow turning off the ice wall and could then operate without ongoing power input.
The article indicates that clay walls were tried unsuccessfully before at this site. I have not been following this so I don't know what the problem was. Any sort of engineering approach to containing water escape has to address the complications of this specific site and will have to be tweaked as site experience is gained. However, I see no reason that the ice wall approach would not work unless there are zones of concentrated, higher velocity groundwater flow (preferential flow pathways) present or the wall does not go deep enough. Preferential flow pathways require particular geologic causes. Again, a specialty firm who does this for mining and construction would have to have a successful track record to stay in business. If they did not produce for their customers, they would not still be in business. This is not new technology. It also does not have to be a perfectly impervious barrier to make the problem of groundwater leaving the site manageable, especially when combined by active pumping within the barrier to produce a well capture zone.
And how long does this ice wall remain in place... Ten years? A hundred years? Indefinitely? In the event of another earthquake, how will this effect the wall? Will the problem then be compounded by the leaking of coolants in to the ground and on down to the ocean?
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