• Kyodo

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The Nagoya High Court reversed a lower court decision on Monday and nullified the national government’s 1983 go-ahead for construction of the trouble-plagued Monju fast-breeder nuclear reactor in Tsuruga, Fukui Prefecture — a ruling that could lead to the costly plant being mothballed.

In a landmark decision favoring residents seeking to halt construction or operation of nuclear reactors, the ruling supported the claim of the plaintiffs, who blamed a massive leak of sodium coolant at the plant in 1995 on shortcomings in the government’s preconstruction safety assessments.

“Flaws exist in the safety assessments needed to prevent an accident like leakage of radioactive material inside a reactor to the neighboring environment,” presiding Judge Kazuo Kawasaki said in the ruling at the court’s Kanazawa branch. “Thus the possibility of concrete threats cannot be discounted.”

Previously, only the ruling by the Matsuyama District Court in December 2000 had pointed out similar shortcomings in the government’s safety assessment for a nuclear reactor.

On Dec. 18, 1995, 640 grams of liquid sodium coolant leaked from a ruptured pipe in the secondary cooling system, triggering a fire. The 280,000-kilowatt reactor, which was operating at 40 percent of capacity when the leak occurred, has since been shut down.

The governmental operator of the plant came under fire after it was revealed that it tried to cover up damage from the accident and submitted a falsified report, incurring serious public distrust in the nation’s nuclear energy administration.

After receiving government approval in December, the state-run Japan Nuclear Cycle Development Institute was planning to start renovating the reactor, with a view to reactivating it in the near future.

The high court said, however, that the government’s approval of the renovation plan “will not affect the (court’s) conclusion that the (government’s original) approval is now annulled.”

By calling for the government to reassess the safety measures at Monju, the ruling is expected to make resumption of its operation extremely difficult.

The ruling raises doubts about the safety of Monju, which the government considers a key component of its nuclear fuel recycling policy. It is also likely to mark a setback for the state’s other nuclear energy programs, such as the use of plutonium-uranium mixed oxide (MOX) fuel at light-water reactors and reprocessing of spent nuclear fuel.

“This marks a crucial ruling that has overturned the basis of Monju, and it will no longer be possible for the reactor to be restarted,” a lawyer for the plaintiffs said. The plaintiffs later released a statement urging the national government and the Monju operator to scrap the reactor.

The ruling meanwhile sent shock waves through the Ministry of Economy, Trade and Industry, which had been preparing to reopen trouble-plagued Monju.

“You’re kidding!” exclaimed a senior official of the ministry’s Nuclear and Industrial Safety Agency upon hearing the news.

Atsuko Toyama, minister of education, culture, sports, science and technology, expressed regret over the ruling and insisted that perfecting fast-breeder reactor technology, which can produce more plutonium than it consumes, is essential to Japan, which lacks any natural energy resources of its own.

The government has begun consulting ministries and agencies involved to decide whether to appeal the high court ruling to the Supreme Court, government officials said.

Chief Cabinet Secretary Yasuo Fukuda told a separate news conference that electric companies’ nuclear power reactors will not be affected by the ruling.

The ruling concerned a fast-breeder reactor in the research and development stage, the government’s top spokesman said, denying there will be any adverse effect on nuclear reactors being operated for power generation.

Construction of Monju began in 1985 in Tsuruga, on the Sea of Japan coast, following the national government’s go-ahead in its safety assessments in 1983.

The 32 plaintiffs, mainly residents of Tsuruga, originally filed the lawsuit against the national government in 1985, seeking annulment of its permission to build Monju. They also filed a civil suit against Monju’s operator in a bid to halt its operation.

In March 2000, the Fukui District Court dismissed both suits, saying the fast-breeder reactor’s basic design was not at fault in the 1995 accident.

Monday’s ruling was handed down on the lawsuit against the government.

In the earlier ruling, the Fukui court said the reactor does not pose “any visible danger” to the lives or health of the plaintiffs despite the accident.

In the appeal, the plaintiffs said the lower court declared the reactor safe based on the basic design of conventional light-water reactors powered by uranium. They said the light-water type is completely different from fast-breeder reactors, which use MOX fuel.

They said almost no safety assessments were done based on fast-breeder reactors, and added the Fukui court ruling wrongly concluded that the reactor would be safe based on testimony by the defendants.

One major point of contention between the plaintiffs and the state was the safety of a metal sheet placed on the concrete floor of a room housing the sodium coolant pipes. The 6-mm sheet is designed to prevent leaked sodium from touching water in the concrete and setting off an explosion.

The plaintiffs pointed out that in the 1995 accident, the sheet was partially melted and decayed by the leaked sodium in a chemical reaction that was not considered in the government’s safety assessment.

They charged that the government committed a serious oversight by not taking the possibility of such a reaction, which could have triggered an explosion, into account, and said that the 6-mm sheet was insufficient for the intended purpose.

The government, meanwhile, counterargued that the thickness of the steel sheet was not specified in the basic reactor design it approved. It also insisted that the chemical reaction would not have created a hole in the sheet, although it partially damaged it.

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