The 1.18 million-kW No. 3 reactor at Kyushu Electric Power Co.'s Genkai nuclear power plant in Saga Prefecture, which is Japan's first reactor using plutonium-uranium mixed oxide (MOX) as fuel, attained nuclear criticality last Thursday and started trial operations Monday (commerical operations are to start on Dec. 2). Thus "pluthermal" power generation has begun, but many problems remain unresolved.
MOX fuel, made of plutonium extracted from spent nuclear fuel and uranium, was primarily intended for use in a fast breeder reactor (FBR), the core of Japan's nuclear fuel-cycle plan. But the prototype FBR Monju in Tsuruga, Fukui Prefecture, has remained shuttered since a major accident in 1995. As a secondary step, the government in 1997 decided to adopt pluthermal power generation, which burns MOX fuel in ordinary light water reactors. But mishaps delayed its start by 10 years.
Under an international obligation to prevent nuclear proliferation, Japan has to burn its accumulated plutonium. Since the 1970s, Japan has entrusted reprocessing its spent nuclear fuel to France and Britain. As of the end of 2008, Japan had 32 tons of fissile plutonium — 25 tons in France and Britain — enough to make several hundred Nagasaki-type plutonium bombs. The power industry plans to start using MOX fuel in 16 to 18 reactors by fiscal 2015.