The decision last week by the Hiroshima High Court to order Shikoku Electric Power Co. to suspend operations of a reactor comes as yet another reminder of the many hurdles faced by nuclear power plants in the wake of the 2011 Fukushima disaster. Power companies should re-examine their strategy of counting on restarting their idled reactors, which will reduce their imported fuel costs, as a key to rebuilding their financial health. The government, meanwhile, should review the feasibility of its energy plan that envisions having nuclear power account for more than 20 percent of the nation’s electricity supply in 2030.

In the first high court decision to issue such an order, the Hiroshima High Court ruled that reactor No. 3 at Shikoku Electric’s Ikata nuclear power plant in Ehime Prefecture cannot be restarted, saying the potential impact of a major volcanic eruption of Mount Aso in central Kyushu — about 130 km away — on the plant’s safety has not been properly assessed. Shikoku Electric was operating the reactor since August last year, following the Nuclear Regulation Authority’s approval of its updated measures against big natural disasters, until it was taken offline for a routine inspection. The court injunction remains in effect through the end of next September, and the company’s plan to resume its operation next month is now doomed unless another court decision reverses the order.

Since the nation’s nuclear power plants were taken offline following the March 2011 meltdowns at Tokyo Electric Power Company Holding’s Fukushima No. 1 plant, only five reactors at plants run by Kyushu Electric, Kansai Electric and Shikoku Electric have been reactivated following NRA screening based on a 2013 revamped nuclear power plant safety standard. Under its basic energy plan, the government sets a target of having nuclear power account for 20 to 22 percent of Japan’s electricity supply in 2030, but that would require 25 to 30 reactors in operation by that point.

Meanwhile, doubts over the safety of nuclear power triggered by the 2011 Tepco plant disaster have led to dozens of lawsuits being filed against the operation of nuclear power plants across the country. Some district courts have handed down rulings or issued injunctions ordering a halt to plant operation, but all such decisions were later reversed at the high court level. This time, however, the Hiroshima High Court reversed a March lower court ruling that rejected a plea by residents of Hiroshima for an injunction ordering suspension of the Ikata plant reactor’s operation.

In its decision, the high court pointed out that the evaluations given by the NRA and Shikoku Electric concerning the potential risk posed to the Ikata plant by a major volcanic eruption of Mount Aso were insufficient. An NRA guideline established after the 2011 Fukushima crisis necessitates an evaluation of the risks from volcanic eruptions such as pyroclastic flow and volcanic ash hitting a nuclear power plant if the facility is located within 160 km of a volcano that is active, and stipulates that such a plant must not be built on a site where the risk of damage from eruption cannot be deemed sufficiently low. The high court determined that such a risk cannot be judged low enough for the Ikata plant, noting that the possibility cannot be ruled out that pyroclastic flow reached the Ikata plant site when Mount Aso erupted some 90,000 years ago — estimated to be its biggest eruption ever.

The court decision should trigger more discussions on volcanoes and nuclear power plant sites. Japan has more than 100 active volcanoes, and the Meteorological Agency constantly monitors 50 of them. Some nuclear power plants — in Hokkaido and Kyushu — are located relatively close to such volcanoes, but it is still reportedly difficult to be able to accurately forecast the timing or magnitude of an eruption, including a major, disastrous one.

In many of the earlier court decisions on lawsuits that sought to halt the operation of nuclear power plants in the relative vicinity of volcanoes, the risk from a massive eruption was regarded as negligible if the frequency of eruptions was low. However, one of the lessons from the March 2011 Great East Japan Earthquake and tsunami, which led to the meltdowns at the Tepco plant in Fukushima, was that the nation must be on guard for natural disasters whose chances of happening may be low but will have catastrophic consequences if they take place. The power companies, the NRA and the government should take the high court ruling seriously.

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