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2014年6月 7日 (土)

福島原発汚染水 「凍土壁」だけでは解決しない

The Yomiuri Shimbun
Radioactive water issue cannot be resolved by ice wall project alone
福島原発汚染水 「凍土壁」だけでは解決しない

Tokyo Electric Power Co. has launched the construction of ice walls, a project aimed at curbing the buildup of radioactive water at its crippled Fukushima No. 1 nuclear power plant.

Halting the increase of contaminated water is the major task for the moment to end the crisis at the plant. Therefore, the project must be steadily promoted.

Pipes to circulate liquid coolants will be buried over a 1.5-kilometer perimeter around the plant’s Nos. 1 to 4 reactor buildings, thereby freezing the soil to a depth of 30 meters below ground to construct ice walls. The government and TEPCO expect the envisaged ice walls to help prevent groundwater from flowing into the reactor buildings, which has caused an increase of contaminated water at the plant.

Many essential pipes and electrical cables are installed underground around the reactor buildings. If such equipment is accidentally damaged, it could impair the cooling functions of the reactors.

Given the high radiation levels at the construction site, it is necessary to minimize workers’ radiation exposure. Due care must be taken in carrying out the work.

Installation will cost ¥32 billion. The government will bear the cost as a research and development project. Power consumption equivalent to that of 13,000 ordinary households, running more than ¥1 billion annually in simple calculation, will be needed to keep the underground walls frozen.

Such massive spending aside, the question is whether the ice walls will ensure that groundwater will not flow into the reactor buildings.

Ice walls have been used as a temporary method of halting the flow of groundwater when tunnels are constructed. The installation of ice walls on the currently planned scale is unprecedented in Japan.

Fears of subsidence

There are fears that if the soil is not frozen evenly, it could cause subsidence. Experts have warned that if the ice walls melt due to problems with cooling functions, there could be a widespread danger of radioactive water flowing outside the reactor buildings.

There is no reason to place overly high expectations on the ice walls.

Considering the fact that there has been constant trouble with the countermeasures taken so far to deal with radioactive water, it is essential to carry out several measures in parallel.

The amount of contaminated water has increased by 300-400 tons a day. Storage tanks built on the plant’s premises already number about 900, leaving no choice but to assign many workers to maintenance and surveillance duties.

This hinders work to repair the crippled reactors, which must be given top priority to end the crisis at the plant. This must be taken seriously.

Sooner or later, there will be no more sites available for the construction of storage tanks at the plant.

It is vital to reduce the amount of rainwater infiltrating the soil as one of the countermeasures. The decision was made to pave the plant’s site, but little progress has been made due to a delay in land leveling.

Experts have also pointed out the need to purify contaminated water before discharging it into the ocean. But the Advanced Liquid Processing System (ALPS) introduced for that purpose has continued to malfunction. It is necessary to achieve stable operation of the ALPS as soon as possible and launch a full-scale study into measures for discharging decontaminated water into the ocean, while seeking to win the support of the local governments and residents concerned.

(From The Yomiuri Shimbun, June 6, 2014)


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