The Ice Wall Cometh in Fukushima Contamination Fight

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August 31, 2016

The ice wall is nearly all frozen.

The 100-foot-deep underground frozen wall at the Fukushima Dai-ichi Nuclear Power Plant is 99 percent complete, Japanese engineers have announced. The wall has as its official name the Land-Side Impermeable Wall. Operators of the Tokyo Electric Power Company (Tepco) are counting on the wall’s being impermeable to radioactive groundwater, which continues to seep into the damaged buildings at the reactor five years after the Sendai Earthquake and resulting tsunami crippled the reactor while also killing and displacing hundreds of thousands of people.

In constructing the buildings in the 1960s, Tepco removed a hillside so as to situate the nuclear power plant closer to the sea, to more easily allow seawater to be pumped in to the plant. In the process, however, the engineers also laid the foundations of the buildings next to a deep layer of rock that was filled with rainwater and snowmelt from the nearby Abukuma Mountains. When the earthquake hit,on March 11, 2011, the basements of the buildings cracked, and groundwater poured in. That flow of groundwater has not ceased.

Five years later, Tepco is continuously pumping that groundwater out of the basements and into more than 1,000 holding tanks, all of which together hold more than 800,000 tons of radioactive water. The tanks, which are 95 feet high, now nearly fill the available area inside the plant. Tepco workers are continually building more tanks.

A giant steel wall, which extends partly underground, has been in place since 2015 and has stopped the water from flowing into the Pacific Ocean.

The ice wall, however, is a bid to stop that proliferation of radioactive water. The wall extends a mile in length and 100 feet into the ground. Pipes of 100 feet in length contain a brine solution that has been frozen to -22 degrees Fahrenheit. The pipes are three feet apart, and the expected result is a series of ice columns with a one-and-one-half-foot radius, creating a rectangular barrier. It is, in effect, a manmade ring of permafrost, which would be in direct contrast to the heat level on the day of the disaster.

Engineers think that the uranium fuel heated up to such a high temperature after the earthquake that the uranium melted the reactor’s steel floors and seeped into the basements. The continual flooding has prevented inspections by all but five robots, and none of those returned from their expeditions. Engineers are hopeful that they can send in human inspectors soon to survey the damage.

The Japanese government has spent 35 billion yen ($320 million) on the Land-Side Impermeable Wall. Tepco threw the first switches in March, to coincide with the fifth anniversary of the disaster, and work has continued at a fever pitch since then. Japan’s Nuclear Regulation Authority mandated a phased powering up of different parts of the wall in order to avoid a sudden reversal of water flow, which could send the water into the surrounding ground instead.

With just a few parts of the wall left to freeze, engineers are hopeful that their wall will stem the radioactive tide. Once the water stops flowing, engineers can carry on with inspections, repairs, and removal of the radioactive water.

Employing ice walls to block groundwater is not an innovation. Engineers have used the technique in mines and tunnels in other countries, on a smaller scale.

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