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.
　原発に影響を及ぼす巨大噴火に備えた「基本的な考え方」の案を原子力規制委員会が示した。前兆の可能性がある異常を検知したら、「空振りも覚悟の上」で原子炉の停止や燃料の運び出しを電力会社に求める。そのための判断基準についても、有識者を集め、検討を進めるという。

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.
　規制委が新規制基準に適合していると判断した九州電力川内１、２号機（鹿児島県）は、巨大噴火に襲われる危険性が全国の原発の中で最も高い、というのが専門家の一致した見方だ。本来なら原発の安全審査の前に、こうした検討を進めておくべきだった。日本は世界有数の火山国であり、規制委や電力会社は、噴火の脅威を侮ってはならない。

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.
　川内原発周辺には、阿蘇や鹿児島湾など、マグマの大量噴出で土地が陥没したカルデラ地形が複数ある。日本ではカルデラ式の巨大噴火が１万年に１回程度起きている。

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.
　昨年施行された原発の新規制基準は、原発から１６０キロ圏の火山の影響調査を電力会社に義務付けた。運用期間中に噴火が起き、火砕流や溶岩流が到達する恐れがあれば、立地不適格で原発は稼働できない。

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.
　九電は、川内原発の運用期間中にそうした噴火が起きる「可能性は十分低い」と評価し、桜島の噴火で火山灰が１５センチ積もる場合を想定すれば足りるとした。巨大噴火が起きるとしても、数十年前からマグマの蓄積が生じるので、地殻変動などを監視すれば事前に察知できるという。

In its safety evaluation, the NRA basically accepted Kyushu Electric Power Co.'s arguments.
　規制委は安全審査で、九電の考え方を基本的に了承した。

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.
　しかし、その後開かれた規制委の有識者検討会では「巨大噴火の時期や規模の予知は困難」との指摘が相次いだ。原発に影響する火山活動の監視では「電力会社任せにせず、国レベルの体制を作るべきだ」との意見も出された。

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.
噴火の影響を受ける恐れのある原子力関連施設は日本各地にある。川内原発は、それらの施設の火山対策の試金石となる。

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.
　そもそも、巨大噴火が起きれば日本という国の存亡にかかわる。

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.
　内閣府の検討会は昨年５月、東日本大震災をきっかけに火山活動が活発化する恐れがあるとし、監視体制の強化や避難計画の早期策定を提言した。巨大噴火に関する研究の遅れも指摘している。

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.
「想定外」を避けるためにも、規制委による判断基準の検討を、巨大噴火に関する研究や対策を促進する契機としたい。

毎日新聞　2014年09月08日　02時32分