社説:原発と火山災害 巨大噴火を侮るなかれ

September 08, 2014(Mainichi Japan)
Editorial: Volcanic threat no light matter for Japan's nuclear plant operators
社説:原発と火山災害 巨大噴火を侮るなかれ

The Nuclear Regulation Authority (NRA) has released a "basic concept" for dealing with major volcanic eruptions threatening the nation's nuclear power plants. If abnormal volcanic activity posing a threat is detected near a nuclear plant, the regulatory body will ask the power company in charge to halt the plant's reactors and remove nuclear fuel -- even if it might turn out to be a false alarm. The NRA is set to convene a meeting of experts to determine standards for taking such action.

Experts are aligned on the view that the No. 1 and 2 reactors at Kyushu Electric Power Co.'s Sendai Nuclear Power Plant in Kagoshima -- recently judged by the NRA to meet new safety standards -- together face the greatest risk of being damaged in a major volcanic eruption. This should have been considered before the plant underwent safety screenings. Japan is one of the most volcanic countries in the world, and neither the NRA nor the nations' power companies should make light of the threat of eruptions.

The landscape around the Sendai plant is marked by calderas -- cauldron-like geographical features that form when a large amount of magma spews out from under the ground, causing it to collapse. Mount Aso and Kagoshima Bay are two examples. In Japan, a major caldera-forming eruption is said to occur about once every 10,000 years.

Nuclear safety regulations established last year require power companies to conduct surveys on the possible effects of eruptions of volcanoes located within 160 kilometers of any nuclear power plant. Under the regulations, if there is a chance that an eruption could occur while the plant is in operation and produce a pyroclastic or lava flow that reaches the plant, then the land will be deemed unfit for nuclear power generation, and the plant will not be able to operate.

Kyushu Electric Power Co. has said the chance of such an eruption occurring while reactors at the Sendai plant are in operation is "sufficiently low." It says the plant could endure an eruption of the Sakurajima volcano that produced 15 centimeters of volcanic ash. Additionally, it says that even if a major eruption were to occur, then magma would build up several decades in advance, and if changes in the earth's crust were observed, then officials could perceive the danger.

In its safety evaluation, the NRA basically accepted Kyushu Electric Power Co.'s arguments.

However, during a subsequent meeting of experts, it was pointed out that it is difficult to predict the size and timing of a major eruption. An opinion was also put forward that measures should not be left entirely in the hands of power companies but be addressed at the national level.

There are many nuclear facilities around Japan that could be affected by volcanic eruptions. The Sendai Nuclear Power Plant is a benchmark for those facilities in measures against eruptions.

NRA Commissioner Kunihiko Shimazaki, who currently serves as acting chairman of the regulator, says he doesn't know how far the body can go in setting standards for decisions pertaining to major eruptions. But unless officials remain on the safe side when forming standards, there could well be confusion when responding to an abnormality.  規制委の島崎邦彦委員長代理は、巨大噴火に関する判断基準の策定について「どこまでできるか分からない」と述べた。だが、安全サイドに立った基準をあらかじめ作成しておかなければ、異常が検知された時の対応に混乱が生じかねない。

Of course, if a major eruption does occur, it could threaten Japan's very existence.

In May last year, a Cabinet Office panel advised that monitoring be stepped up and evacuation plans quickly formulated, due to fears that volcanic activity could increase as a result of the March 2011 Great East Japan Earthquake. At the same time, delays in research on major eruptions have been pointed out.

To avoid an "unexpected event" such as the Fukushima nuclear disaster, we hope officials will take NRA's planned formulation of standards for its decisions as an opportunity to promote research and countermeasures against major volcanic eruptions.

毎日新聞 2014年09月08日 02時32分

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