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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.

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.

The source of the contaminated water is groundwater entering the crippled reactor buildings.

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.

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.

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.

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.

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.

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.

The problem, however, is that these measures, even if fully implemented, will not be able to reduce the generation of contaminated water to zero.

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.

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.

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.

Postponement of this problem is the same as leaving it unaddressed.

The upgraded water treatment machine operated by TEPCO could remove most of the radioactive isotopes. Tritium, a hydrogen isotope, is the exception.

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.

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.

Since the risk of tritium is not high, the European Union has yet to set safety standards concerning tritium emissions.

As Japan has established a certain level of emission concentration standards, there seems to be no problem with releasing tritium based on these standards.

There should be in-depth exchanges of views on resolving the contaminated water problem.

(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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