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Can frozen soil wall save crippled N-plant?

Motegi instructed Hirose to carry out countermeasures proposed by the committee. -Japan News/ANN
Takashi Ito and Takashi Maemura

Sat, Jun 01, 2013
The Japan News/Asia News Network

Technological and financial obstacles are mounting in front of a central government plan to erect an underground wall of frozen soil around Tokyo Electric Power Co.'s crippled Fukushima No. 1 nuclear power plant.

A government panel on the contaminated water issue decided Thursday to create the wall, about 1.4 kilometers long and extending as deep as 30 meters underground, around nuclear reactor buildings, along with four other measures.

The wall, comprising series of pipes with coolant running through them, would prevent groundwater from seeping into contaminated areas--believed to be the main reason for the increase in contaminated water.

However, it is uncertain whether the plan is technically feasible, and it will take an enormous amount of time and money to realise. The risk thus remains of a shortage of storage tanks for contaminated water.

"Considering how serious the contaminated water issue is, measures must be taken at multiple levels. We ask for the immediate preparation and operation of a frozen soil wall around the entire plant," said Economy, Trade and Industry Minister Toshimitsu Motegi when he met TEPCO President Naomi Hirose after government panel on the contaminated water issue met Thursday.

Motegi instructed Hirose to carry out countermeasures proposed by the committee.

Currently, there are 390,000 tons of contaminated water--enough to fill about 1,500 25-meter pools--at the nuclear plant. As groundwater continues to seep into the reactor buildings through gaps in the walls or other places, the total amount increases every day.

Although TEPCO continues to make efforts to pump groundwater up before it leaks into the buildings and becomes contaminated, the committee concluded that the measure is insufficient and requested a frozen wall be built.

Freezing soil to make an underground wall involves relatively new technology. It is used in civil engineering work to prevent landslides.

To make such a wall, a series of pipes are installed underground, and coolant materials at dozens of degrees below zero are circulated through them. This technology was used in the building of tunnels on the Tokyo Bay Aqualine highway.

TEPCO previously studied a plan to build an underground wall near the reactor buildings but abandoned it out of concern that the water could change course during construction, possibly leading to changes in water levels outside the building that would allow contaminated water inside to more easily flow out.

In contrast, a frozen soil wall could be completed in only one or two months, meaning a large change in the water level is less likely. As the wall would prevent water from flowing in or out, contaminated water could be pumped out of the building.

However, the wall TEPCO has been told to make would be 1.4 kilometers long and as much as 30 meters underground, which would make it the largest such wall in the world. One member of the government's committee objected to the plan, asking if it is even possible to build such a wall.

Motegi said the ministry would use part of research and development funds for reactor decommissioning to create an expert panel under the committee to determine by year-end whether the plan is feasible.

The construction of the wall would appear to cost several tens of billions of yen, meaning that if its operation is prolonged, the cost of running it could be enormous.

The committee proposed four new countermeasures aside from the frozen soil wall. One is to seal cracks or gaps in walls of reactor buildings with cement to prevent groundwater from flowing in. However, this requires very careful construction work, so as not to damage underground structures.

Another proposal is to pump out 20,000 tons of highly contaminated water in currently sealed pipe tunnels leading to the sea and transfer it to another location next fiscal year. However, the committee did not give details about how to transfer the water while protecting workers from the risk of radiation exposure.

It is also important to pump water up from wells to stop groundwater from leaking into reactor buildings or other nuclear facilities by 2021. However, as local fishermen have yet to agree to releasing the groundwater into sea, there is no prospect of starting the project.

Though there is a plan to increase the capacity of storage tanks for contaminated water to 700,000 tons by 2015, they could be full as early as 2016. Furthermore, the sealant used in joints of the tanks has a lifespan of five years. The committee therefore proposed expanding the capacity target to 800,000 tons-- but there is little space left on the grounds for tanks.

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