Nuclear safety called into question
(From The Japan Times April 7 issue)

原発に運転停止命令：金沢地裁

    Saying that there is a problem with the earthquake-resistance design of the reactor, the Kanazawa District Court ordered Hokuriku Electric Power Co. to halt the operation of the nuclear power station — the first ruling to order such a halt from among 30 lawsuits filed by citizens concerned about the safety of nuclear power stations.

    As the company has appealed the ruling, the reactor continues to operate. But the ruling could greatly affect the nation's energy policy and power industry. If it is upheld by the Supreme Court, it will call into question the safety foundation upon which the nation's 55 power reactors — supplying about one-third of the nation's electric power — are built and could lead to their temporary closure.

    A total of 135 citizens from 17 prefectures, most of them residents of Ishikawa and neighboring Toyama prefectures, filed a lawsuit against Hokuriku Electric, the operator of the No. 2 reactor at its Shika nuclear power station in Ishikawa Prefecture, in August 1999 shortly after construction of the reactor began. The lawsuit initially demanded the reactor not be built.

    The 1,358-megawatt, advanced boiling-water-type reactor is the nation's 55th nuclear reactor and the second largest in terms of output. The plaintiffs contend that the reactor, whose design is based on the quake-resistance design guidelines drawn up in September 1978 by the Atomic Energy Commission, is vulnerable to damage in a large quake. The ruling came nine days after the reactor began operation.

    In the trial, the power company explained that the reactor was designed to withstand a magnitude 6.5 earthquake whose focus is just below the reactor, the largest earthquake predicted to hit the area. But the ruling contended the scale and intensity of the largest earthquake assumed in the reactor design is too small.

    The ruling in part mentioned an earthquake with a magnitude 7.2 that occurred off Miyagi Prefecture on Aug. 16, 2005, and its effect on Tohoku Electric Power Co.'s Onagawa nuclear power station in the prefecture. Three reactors at the plant automatically shut down because vibrations at the site were larger than had been factored into the quake-resistance design.

    The district court ruling said that the calculation method to determine possible vibrations for use in a reactor design was inadequate.

    In their argument, the plaintiffs said that the Shika reactor design failed to take into account the activity of the 44-km Ochigata fault line in Ishikawa Prefecture and east of the nuclear power station.

    In March 2005, the government's Earthquake Research Committee said that there is a 2 percent probability that an earthquake with a magnitude of 7.6 could occur within 30 years if the entire fault line shifted. The power company said that the committee's approach is different from that employed by the reactor's designers. It said that there is no need to suppose that the whole fault line would shift.

    But the ruling said that the committee's prediction is tenable and should be taken into consideration in the reactor design.

    The ruling concluded: "There is a possibility that earthquake vibrations beyond the power company's expectations can occur, causing an accident at the nuclear power station and exposing residents to radiation." It said that in the event of a large quake, radioactive material exceeding the permitted levels would be released and would seriously affect the lives and health of local residents. It even said that plaintiffs living in Kumamoto Prefecture, about 700 km from the nuclear power station, could be exposed to radiation far exceeding the permitted levels.

    The basis of the state's quake-resistance design guidelines for nuclear power stations is that they must be built on bedrock located away from active fault lines and be designed to safely withstand the estimated largest possible earthquake that could take place in the area. The significance of the ruling is that it has cast doubt on the adequacy of the guidelines.

    The Great Hanshin Earthquake, which devastated the city of Kobe in Hyogo Prefecture in 1995, has heightened people's concern about the safety of nuclear power stations. The ruling pointed out that earthquakes with a magnitude of 6.5 or more have occurred even in places where the existence of active fault lines was not confirmed, including an earthquake with a magnitude of 7.3 in western Tottori Prefecture in October 2000.

    The Nuclear Safety Commission started work to revise the quake-resistance design guidelines in July 2001 but has not reached a conclusion. Since Japan is a quake-prone country, it is imperative that it finishes the revision work as soon as possible, taking into account the latest seismological studies and other scientific findings.

    The nation's nuclear reactors are aging, with 11 more than 30 years old. This makes the safe operation of nuclear power stations all the more important.

The Japan Times Weekly: April 15, 2006
(C) All rights reserved

    原発の安全性をめぐる30件の訴訟で、運転停止が命じれらたのは初めてである。しかし、北陸電力は直ちに控訴し、原発の運転は継続している。

    今回の判決は国のエネルギー政策、電力業界に大きな影響を持つと予想される。もし最高裁が地裁の判決を支持すれば、国内電力供給の3分の1を占める55の原発全基の運転停止に至る可能性もある。

    訴訟の原告は、石川県、富山県を中心にした17都道府県の住民135名で、1358メガワットの出力を持つ改良型沸騰水型原子炉について1999年に提訴、当初は建設中止、建設後は運転中止を求めていた。

    北陸電力は、問題の原発はマグニチュード6.5の直下型地震に耐えられると主張した。しかし判決は、同社が想定する地震の規模は小さすぎるとして耐震設計の不備を突いた。

    政府の地震調査委員会は昨年3月、志賀原発の東側にある邑知潟断層帯で30年以内にマグニチュード7.6の地震が発生する確率を2％と評価している。判決は、この評価を原発の設計に考慮すべきと判断した。

    判決は「北陸電力の想定を超えた地震で原発事故が起こり、地域住民らが被ばくする具体的可能性がある」と判断した。

    原発は活断層から離れた岩盤上に設置し、予想される最大規模の地震に耐えられるようせねばならない、としているのが国の原発耐震設計指針だが、判決はこの指針に疑問を呈している。

    1995年の阪神淡路大震災は、原発の安全性に関する国民の不安を浮き彫りにした。判決は、活断層の存在が確認されていない地域でも、マグニチュード6.5以上の地震が起きていると指摘した。たとえば、2000年に起きた鳥取西部地震（マグニチュード7.3）がひとつの例だ。

    原子力安全委員会は01年に原発の耐震設計指針の改訂作業を始めたが、まだ結論を出していない。できるだけ早く改訂作業を完成させることが望まれる。国内の原子炉のうち11基は設置後30年以上経過しており、原発の安全性は非常に重要だ。