浜岡原発―津波だけではない

2011/05/11
--The Asahi Shimbun, May 10
EDITORIAL: Tsunami not the only safety concern for Hamaoka plant
浜岡原発―津波だけではない

Chubu Electric Power Co. decided on May 9 to halt, for the time being, operations of all reactors at its Hamaoka nuclear power plant, which is located right above what seismologists say will be the focus of an expected Tokai earthquake.
　東海地震の想定震源域の真上にある浜岡原発のすべての炉が当面は止まる。

The company made the decision in an emergency board meeting in response to Prime Minister Naoto Kan's unusual request for the action.
菅直人首相による異例の求めを中部電力が受け入れた。

The March 11 Great East Japan Earthquake has triggered a disastrous accident at the Fukushima No. 1 nuclear power plant, operated by Tokyo Electric Power Co., shattering the myth of the safety of nuclear power generation.
　東日本大震災によって東京電力福島第一原発の事故が起き、原子力の安全神話は崩れた。

There is clearly a compelling case for shutting down the nuclear power plant in Shizuoka Prefecture, which is considered the most dangerous in Japan, and taking fresh measures to bolster the safety of the plant.
　国内で最も危険といわれてきた原発を止め、安全対策を強めるのは当然の決断と言えよう。

One troubling element in the move is that the suspension of reactor operations requested by Kan is limited to the period until medium- to long-term safety measures, like the construction of levees, have been implemented at the plant.
　ひとつ気になるのは、首相の要請が防潮堤づくりなどの中長期対策が施されるまで、となっていることだ。

This raises the question of whether the plant is strong enough to withstand the violent shaking of the ground caused by powerful seismic waves in the first place.
地震の揺れそのものに対しては大丈夫なのか、という心配が残る。

The medium- to long-term safety measures have been called for by the Nuclear and Industrial Safety Agency in light of the crisis at the Fukushima No. 1 plant. They are aimed at enhancing defenses against massive tsunami and potential losses of power sources.
　中長期対策は、福島第一の事故を受けて、原子力安全・保安院が、津波に対する備えや、それによって起こる電源喪失などへの対策を確実にするために求めた。

Besides building levees, Chubu Electric says that it will also install watertight doors, a backup reactor cooling system and additional power sources for emergencies.
　中部電の計画では、防潮堤のほか防水扉、非常用の炉心冷却系や電源を充実させる、と説明している。

But the blueprint doesn't contain measures for checking and enhancing the safety of the plant against quakes themselves.
そこには、揺れそのものに対する安全度の確認や補強策は含まれていない。

The principal concern about the Hamaoka plant has been whether it can withstand the force of the expected Tokai earthquake, a mega-quake that occurs at the boundaries of tectonic plates.
　浜岡原発がこれまで不安視されてきたのは、なによりもプレート境界型の巨大地震である東海地震の揺れに耐えられるか、ということだった。

In response to the concern, Chubu Electric announced in 2005 plans to strengthen the quake resistance of the plant. Other electric power companies have followed suit.
　そのこともあって、中部電は早めに手を打ち、２００５年に補強を表明した。ほかの電力会社も追随した。

But NISA's assessment of the quake resistance of the Hamaoka plant based on the new quake safety standards adopted in 2006 is not yet over.
　それでも、０６年に改定された新耐震指針による浜岡原発に対する保安院の審議は、まだ終わっていない。

The assessment has been delayed by the safety implications of some recent seismic events, including the 2007 Niigata Chuetsu-oki Earthquake, which shook the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture with a far stronger intensity than TEPCO had expected.
　長引く背景には、０７年の新潟県中越沖地震で東京電力柏崎刈羽原発が想定を大きく超える揺れに見舞われるなど、新しい事態に直面したことがある。

It is also necessary to glean lessons from the Great East Japan Earthquake.
　東日本大震災からも、教訓を得る必要がある。

Regarding the accident at the Fukushima No. 1 plant, attention has been focused on the height of the tsunami that struck the facilities.
　福島第一原発の事故では、津波の高さばかりに目が向いている。

But it is possible that the piping of the reactors might have been seriously damaged by the intense shaking before the tsunami hit.
だが、原子炉の配管系が津波襲来より前の強い揺れで大きく損傷した可能性がある。

The March 11 earthquake was marked not just by its strong peak ground acceleration but also by the unusual length of the shaking.
そして、揺れの最大加速度だけではなく、その継続時間の長さにも特徴があった。

What is crucial in taking safety precautions is not to focus too much on a single aspect.
　安全対策で忘れてならないのは、一つのことに目を奪われてはならぬということだ。

The Fukushima No. 1 plant suffered unexpectedly serious damage from a tsunami, a factor that had not been given much attention in preparations for a natural disaster.
　福島第一原発は、それまで関心の低かった津波によって予想外の大打撃を受けた。

But it would be foolish to go to the opposite extreme and concentrate only on the danger of tsunami in taking precautionary measures to make the Hamaoka plant safer.
浜岡で、その逆の愚をおかしてはならない。

Let us not forget the destructive force of the shaking of a mammoth quake.
地震の揺れを忘れまい。

New important discoveries have been made almost annually about the mechanisms and risks of earthquakes that occur in areas surrounding the Japanese archipelago.
　日本列島周辺の地震の仕組みや危険度については年々、新しいことがわかってきている。

Such new knowledge should be used for the sake of making more informed decisions on whether to keep or stop operating specific reactors.
新知識をとり込みながら、原発を動かすか止めるかを決める。

A greater dose of flexibility is needed for the government's nuclear power policy.
　そういう柔軟な原発政策が、いま求められている。