TOKYO (AP) -- Japan's nuclear watchdog announced Wednesday that the nation's trouble-plagued next-generation test reactor will not be allowed to restart due to safety violations, dealing a setback to the country's pro-nuclear government.
The Nuclear Regulation Authority's decision is the latest blow to the Monju fast-breeder reactor and Japan's nuclear fuel cycle program. The government of Prime Minister Shinzo Abe is hoping that Monju will be a key part of Japan's plans for disposing of atomic waste and reducing the nation's plutonium stockpile.
Monju uses plutonium fuel instead of conventional uranium and produces radioactive substances that can be reused as fuel. After nearly 50 years in the works, the problem-plagued reactor, located in the city of Tsuruga in western Japan, is still struggling to get online.
The watchdog's five commissioners unanimously agreed that the reactor's operator, the Japan Atomic Energy Agency, "is not ready to sufficiently secure the safety of Monju." They said the operator had repeatedly failed to conduct mandatory inspections on an array of equipment and come up with improvement plans.
Many experts have said Monju is a basket case and that Japan should abandon plans to achieve a full nuclear fuel cycle. The previous government tried to terminate Monju under its nuclear phase-out plan, but Abe's pro-nuclear government quickly reversed course as it pushes to resume commercial reactors that have been idle since a March 2011 earthquake and tsunami triggered a nuclear disaster at the Fukushima Dai-ichi plant.
Monju's operator can appeal the watchdog's decision, but an official suspension order is likely to come by the end of May, regulatory officials said. The operator needs at least until January to catch up with the delays in safety checks, but it is unknown when the suspension order can be lifted.
Watchdog chairman Shunichi Tanaka told reporters that Monju's operator systematically lacked a safety culture and deserved severe action.
"They repeated the same mistakes even though they said they were analyzing the root cause of the problem. I think they lack fundamental understanding about safety," Tanaka said. "Despite the lessons we learned from the Fukushima Dai-ichi accident, it seems safety culture is still insufficient in Japan."
Japan built Monju as a "dream reactor" to fulfill its energy needs, with the reactor meant to be a centerpiece of a self-sustainable fuel cycle. To complete the cycle, Japan has been building the Rokkasho fuel recycling plant in northern Japan to extract uranium and plutonium from spent fuel and fabricate hybrid fuel of the two radioactive elements.
But with both Monju and Rokkasho having technical problems, Japan has built up a large stockpile of plutonium extracted overseas and at home, causing international proliferation concerns.
Monju successfully generated power using MOX — mixed oxide fuel, a mix of uranium and plutonium — in 1995, but months later, massive leakage of cooling sodium caused a fire. Monju had another test run in 2010 but stopped again after a fuel exchanger fell into the reactor vessel.
Some experts also suspect that the Monju reactor sits on an active seismic fault. An independent team commissioned by the Nuclear Regulation Authority is set to inspect faults at Monju later this year.