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.
　東京電力福島第一原子力発電所の汚染水抑制を目指す「凍土遮水壁」の設置工事が始まった。

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.
　汚染水の増加を食い止めることは、事故収束作業の当面の重要課題だ。着実に前へ進めねばならない。

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.
　１～４号機建屋の周囲１・５キロに冷却材を通す管を埋め込み、地下３０メートルまで凍らせて土の壁を築く。政府と東電は、汚染水増加の原因となる建屋への地下水流入を防げると期待している。

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.
　建屋周辺の地下には、重要な配管や電気ケーブルが数多く埋設されている。これらを誤って傷つければ、原子炉を冷却する機能が損なわれかねない。

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.
　現場は放射線レベルが高く、作業員の被曝ひばくを最小限にとどめる必要もある。作業には細心の注意を払ってもらいたい。

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.
　凍土壁の設置には、３２０億円を要する。研究開発事業の名目で政府が費用を負担する。冷却のために消費する電力は、一般家庭の１万３０００世帯分、単純計算で年間１０億円以上かかる。

Such massive spending aside, the question is whether the ice walls will ensure that groundwater will not flow into the reactor buildings.
　問題は、これだけの巨費を投じた工事で、建屋への地下水流入を確実に抑えられるかだ。

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.
　凍土壁は、トンネル工事の際に地下水を封じ込める臨時の工法として用いられてきた。今回のような規模は国内で例がない。

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.
　均一に凍らないと、地盤沈下が起きる恐れがある。冷却機能の故障で凍土壁が解けてしまうと、汚染水が建屋から周囲に広がる危険性も指摘されている。

There is no reason to place overly high expectations on the ice walls.
　凍土壁への過度の期待は禁物ということだろう。

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.
　これまでの汚染水対策がトラブル続きだったことを踏まえると、複数の対策を同時並行で進めていくことが肝要である。

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.
　汚染水は、１日に３００～４００トンずつ増えている。敷地内の貯蔵タンクはすでに約９００基に上り、その保守、監視などに多数の人員を割かざるを得ない。

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.
　事故収束へ向けて最優先すべき原子炉の補修作業にも支障が生じている。深刻な状況だ。

Sooner or later, there will be no more sites available for the construction of storage tanks at the plant.
　タンクを設置する場所も早晩、なくなるだろう。

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.
　対策の一つとして、地下水の元になる雨水の土壌浸透を減らすことが重要だ。敷地を舗装することが決まっているが、整地に手間取り、ほとんど進んでいない。

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.
　汚染水を浄化してから海に放出する必要性も、専門家から指摘されている。だが、浄化装置「ＡＬＰＳ」は故障続きだ。安定稼働を急ぎ、地元の理解を得ながら海洋放出の検討を本格化させたい。

(From The Yomiuri Shimbun, June 6, 2014)