Japanese Ice Wall to Help Prevent Spread of Radiation

Japan's Nuclear Regulatory Authority (NRA) has approved a plan to freeze the soil around the damaged Fukushima nuclear power plant to prevent radioactive groundwater from entering the general water supply.

The government in Tokyo agreed to the plan last September, but the NRA only approved it on May 26. Construction of coolant-bearing pipes to create the "ice wall" will begin in June and is expected to be finished by March, 2015. The cost of the project is estimated at ¥32 billion ($314 million).

Under the plan, contractors will freeze the soil around Fukushima Reactors 1 through 4, and around nearby buildings, to a depth of almost 100 feet. The lateral extent of the frozen area will be 1.5 kilometers, or nearly a mile in diameter. The target temperature for the frozen earth is 40 degrees below zero Fahrenheit (40 degrees below zero Celsius).

The "ice wall" is intended not only to keep more ground water from escaping from Fukushima, but also to keep water from nearby high ground from seeping into the accident scene, becoming radioactive, and eventually leaching into the nearby Pacific Ocean. The nuclear power plant was damaged by an earthquake and tsunami in March 2011.

Although the Japanese government and the NRA have approved the project, some parts of it still may require the endorsement of the Tokyo Electric Power Co. (TEPCO), which operates the Fukushima plant.

Even if approval becomes universal, questions remain about the strategy. Freezing earth previously has been used successfully in building tunnels, for example, but the technique has never been used to contain radioactive groundwater. And no one has ever tried to artificially freeze earth for so long – in this case, perhaps several decades until the Fukushima plant is eventually decommissioned.

Before the NRA gave its approval, other concerns had been raised, including whether freezing groundwater might prevent a spread of the contamination over several years, and what the technique's effect might be on the immediate area.

In fact, the NRA didn't give its approval until TEPCO could allay the agency's concerns that building the "ice wall" would cause the ground around Fukushima to sink hazardously. TEPCO said the surrounding ground is likely to sink no more than 16 millimeters (0.63 inches) in some areas, but that wouldn't be enough to compromise the ground's stability.

This evidently convinced the NRA. The agency's commissioner, Toyoshi Fuketa, concluded, "I think we have been able to confirm today the scale of ground sinking, which is what we have most feared as side effects of building the wall."

Still, Fuketa said other potential problems haven't yet been addressed, specifically how to accurately assess the level of contaminated water inside the reactors themselves.

The Fukushima accident has been an environmental nightmare. For example, just after the accident, TEPCO pumped water to the reactors in an effort to cool them and to prevent fires. That contaminated water was supposed to have been contained, but TEPCO has acknowledged that more than 440 tons (400,000 kilograms) of highly radioactive water had escaped.