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2013年12月17日 (火)

福島汚染水対策 浄化後の海洋放出は不可避だ

The Yomiuri Shimbun December 16, 2013
Release of water into sea inevitable after purification at Fukushima plant
福島汚染水対策 浄化後の海洋放出は不可避だ(12月16日付・読売社説)

It is imperative to speed up efforts to contain contaminated water at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear power plant.
 東京電力福島第一原子力発電所の汚染水封じ込めへ、取り組みを加速する必要がある。

A government panel on measures to dispose of contaminated water at the crippled nuclear complex has compiled a set of additional steps aimed at reducing radioactive water collecting there and preventing the water from leaking into the environment.
 政府の汚染水処理対策委員会が、汚染水発生を減らし、漏出を防ぐための追加対策をまとめた。

The source of the contaminated water is groundwater entering the crippled reactor buildings.
 汚染水の元は、壊れた原発建屋に流れ込んだ地下水だ。

According to an analysis by the panel, the groundwater stems from the precipitation of rainwater in the compound of the nuclear plant that sinks into the ground.
対策委の分析によると、この地下水は、原発敷地内に降った雨水が地中に浸透したものとみられる。

To prevent this, the panel proposed paving the compound with asphalt. This would likely result in significantly reducing the volume of contaminated water, which is said to amount to an estimated 400 tons a day.
 浸透防止のため、敷地を舗装するのが追加対策の柱だ。1日約400トンに上る汚染水の発生が、大幅に減ることが期待される。

The government has been in lockstep with TEPCO in a project to create as early as possible “frozen-soil underground water shields” to surround the damaged reactor buildings to prevent groundwater from entering the buildings. Given that the project has never been attempted anywhere else, the risk of the project encountering difficulties cannot be ruled out. Besides the additional measures, it is essential to take many other steps to prepare for unforeseen eventualities.
 政府と東電は原発建屋への地下水流入を防ぐ「凍土遮水壁」設置も急いでいるが、前例のない工事だけに、トラブルも起き得る。追加対策と併せ、二重三重の手立てを講じるのは重要なことだ。

The government panel report has also recommended improving the safety of tanks storing contaminated water in the plant’s compound, such as by doubling the tanks’ walls.
 対策委は、汚染水を貯蔵している敷地内のタンクの壁を二重にするなど、安全強化も求めた。

The tanks’ major weakness is their bolted joints. In one incident, contaminated water leaked through the joints and there is possibility of the water having flowed to some extent into the sea along trenches in the basements of the reactor buildings.
 現在のタンクは接合部が緩いといった欠点がある。接合部から汚染水が漏れ出す事故もあった。漏れた汚染水が排水溝伝いに海へ流出した可能性もある。

Tritium no danger

Although little radioactivity has been detected in seawater in the vicinity of the Fukushima plant, the additional measures worked out by the panel must be steadily put into practice to help alleviate local residents’ uneasiness.
 原発周辺の海で放射能はほとんど検出されていないとはいえ、地元の不安軽減のため、追加対策を着実に実行すべきだ。

The problem, however, is that these measures, even if fully implemented, will not be able to reduce the generation of contaminated water to zero.
 問題は、対策を施しても汚染水の発生はゼロにならない点だ。

The volume of contaminated water currently stored already amounts to nearly 400,000 tons. There are about 1,000 tanks, and the Fukushima plant could run out of space for building new tanks in two or three years.
貯蔵中の汚染水は既に40万トン近い。タンクは約1000基に及び、2~3年で設置場所がなくなる。

Should the tanks be destroyed because of a calamity such as a strong earthquake, there is a danger that a large quantity of contaminated water could spill from them, like the collapse of a dam.
 地震などでタンクが連鎖的に壊れれば、ダムの決壊のように、大量の汚染水が流出しかねない。

Many experts at home and abroad have called for purifying contaminated water before it is released into the sea. The government panel, however, has described the release of water after purification as a “task to be addressed from now on,” stopping short of saying anything of substance, but it did suggest that the task should be discussed by a separate group of experts.
 国内外の専門家の多くは、汚染水を浄化して海に放出するよう提言している。しかし、対策委は放出を「今後の課題」とし、別の専門家チームを設けて検討するよう求めるにとどまった。

Postponement of this problem is the same as leaving it unaddressed.
 懸案の先送りでは、リスクを放置しているのと変わるまい。

The upgraded water treatment machine operated by TEPCO could remove most of the radioactive isotopes. Tritium, a hydrogen isotope, is the exception.
 東電が運転中の放射能除去装置を使えば、水素の一形態であるトリチウム以外の放射性物質は、ほぼ取り除くことができる。

Tritium is generated during nuclear reactor operations. Other Japanese nuclear plants, as well as those in other countries utilizing nuclear power, including South Korea, have released tritium into the sea.
 トリチウムは通常の原発運転でも発生する。国内の他の原発や、韓国など原発利用国は海に放出している。

This is because tritium, with a property similar to hydrogen, is diffused immediately after the release, with no fear of it accumulating in fish and other living things.
水素と同じ性質なので、放出後すぐに拡散し、魚など生物に蓄積する恐れもないからだ。

Since the risk of tritium is not high, the European Union has yet to set safety standards concerning tritium emissions.
 リスクが高くないため、欧州連合(EU)は排出基準すら設けていない。

As Japan has established a certain level of emission concentration standards, there seems to be no problem with releasing tritium based on these standards.
日本は一定の排出濃度基準を定めており、それに基づく放出であれば、問題ないのではないか。

There should be in-depth exchanges of views on resolving the contaminated water problem.
汚染水問題の抜本解決のため、前向きの議論を求めたい。

(From The Yomiuri Shimbun, Dec. 16, 2013)
(2013年12月16日01時22分  読売新聞)

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