Ground broken for frozen soil wall at Fukushima nuclear plant

June 03, 2014

THE ASAHI SHIMBUN

Work started June 2 on a 32-billion-yen ($314 million) project to build an underground frozen wall at the stricken Fukushima No. 1 nuclear plant to address a chronic problem plaguing work at the site.

The plan is for the wall of frozen soil to divert groundwater into the ocean and prevent it from seeping into reactor buildings and becoming contaminated by radiation.

But given the enormity of the project--unprecedented in terms of scale and period of use--numerous risks and potential hazards exist.

More than 1,500 pipes will be used to create the frozen soil wall, which will be about 30 meters deep underground and extend for about 1,500 meters around the buildings housing the No. 1 to No. 4 reactors.

Under the plan, the freezing process will start in March 2015 and take an estimated six months to complete. The wall will be kept frozen until fiscal 2020.

Tokyo Electric Power Co., the plant’s operator, has been forced to continually pump in huge amounts of water to cool the three nuclear reactors that melted down after the Great East Japan Earthquake and tsunami struck on March 11, 2011.

However, an estimated 400 tons of groundwater is entering the reactor buildings on a daily basis and mixing with the contaminated water used to cool the nuclear fuel. This has exacerbated TEPCO’s problems of storing and decontaminating accumulating radioactive water at the site.

Government officials estimate the wall will reduce the daily volume of groundwater entering the reactor buildings by 280 tons.

TEPCO submitted an application in March 2014 to begin work on the frozen soil wall. The Nuclear Regulation Authority approved the application on the condition that the work would not damage the network of underground pipes already in place under the Fukushima No. 1 nuclear plant.

Frozen soil walls have previously been used as a temporary measure for tunnel construction to prevent the flow of groundwater from causing the tunnel to collapse. There has never been a frozen wall project as large as the one envisioned for the Fukushima nuclear plant.

The work that started June 2 involved digging holes at 1-meter intervals for the eventual burial of 1,550 pipes. Liquids at temperatures of minus 30 degrees will be circulated through those pipes to freeze the surrounding soil.

The Nuclear Regulation Authority, TEPCO and the central government must carefully monitor construction work for possible cracks in the underground piping that could cause leaks of the freezing agent. They also must ensure that the frozen soil wall does not cause a dramatic change in the groundwater flow that could cause radiation-contaminated water in the basements of the reactor buildings to spill out.

The agent in the piping system will have to be continuously circulated to freeze the surrounding soil, meaning electricity equivalent to the amount used by about 13,000 households will be needed to operate the frozen soil wall system.

But there is no assurance that the frozen wall will reduce the volume of contaminated water by the levels forecast. Groundwater could still flow under the 30-meter wall and enter the reactor buildings.

Rain falling on the Fukushima No. 1 plant site could also become contaminated after mixing with the water used to cool the nuclear fuel.

Even if the frozen soil wall succeeds as planned, TEPCO would still have about 480,000 tons of contaminated water--including 360,000 tons containing high levels of radiation--on its hands.

As of May 27, about 900 tanks at the plant site were holding that volume of water. TEPCO plans to install more tanks at the plant site so that a total of 800,000 tons can be stored by the end of fiscal 2014.

If the tanks leak--a repeated problem at the site--the water would contaminate the surrounding environment and affect work to eventually decommission the four reactors.

TEPCO in May began another measure to divert groundwater away from the reactor buildings at the Fukushima No. 1 plant.

On June 2, about 830 tons of groundwater that had been pumped up before it flowed under the reactor buildings was released into the ocean, the third such release since the groundwater bypass system started.

TEPCO officials initially said the bypass system could reduce 100 tons of groundwater that reached the reactor buildings.

However, that estimate was later reduced to between 20 and 100 tons because several months are needed before the full effects of the system come into play, according to TEPCO officials.

THE ASAHI SHIMBUN
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The Asahi Shimbun

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  • Holes are dug June 2 for pipes that will freeze soil near the No. 1 reactor of the Fukushima No. 1 nuclear plant. (Provided by TEPCO)
  • The Fukushima No. 1 nuclear power plant on June 2 (Satoru Semba)

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