The Nuclear Safety Commission of Japan made assurances Tuesday over the safety of using plutonium-uranium mixed oxide, or MOX, fuel at nuclear plants.

It recommended that safety measures at plants be stepped up in an effort to ease public concerns about safety that have so far prevented the fuel’s debut in Japan.

In a white paper on nuclear safety, the commission affiliated with the Cabinet Office also effectively conceded that the lack of a cohesive safety inspection system was to blame for an accident in November at the Hamaoka nuclear plant in Shizuoka Prefecture.

According to the report, a technological basis has already been established to ensure the safe use of plutonium at light-water reactors, provided the ratio of MOX to total fuel for a reactor is one-third or less.

It said the technology to ensure safety when MOX fuel is used in the so-called pluthermal process does not vary greatly from that for existing light-water reactors because one-third of the energy generated comes from plutonium produced as a result of burning uranium.

In the pluthermal process, plutonium extracted from spent nuclear fuel is combined with uranium oxide to create MOX fuel, which is then burned in light-water reactors instead of being stored for future use in fast-breeder reactors.

The process therefore differs from conventional nuclear power generation only in that the fuel contains plutonium from the outset and that the composition of plutonium is higher than levels seen in conventional generation, according to the paper.

The commission called for special measures to ensure safe plutonium use, citing the fuel’s extremely high radioactivity level, about 200,000 times that of regular uranium fuel.

On the accident at Chubu Electric Power Co.’s Hamaoka No. 1 reactor, the paper called on plant designers and engineers to take into account the possible impact that a change in fuel would have on the system.

In the Nov. 7 accident, a carbon steel pipe in the emergency cooling system ruptured, resulting in a leakage of steam and some radioactive material.

The accident only heightened public distrust of the government’s assurances on nuclear safety.

The commission is awaiting the results of an ongoing probe to determine what caused the accident, but it suspects that the pipe that ruptured had been previously replaced, an official supporting the commission said in a media briefing.

Replacement parts are usually safety tested by the commission.

The paper thus also directs the call for overall safety management of nuclear safety authorities, including the commission itself, as the local checks could be partly responsible for the Hamaoka accident, the official conceded.

The possibility that MOX fuel will be used soon in Japan was reduced to almost nil last May when local residents voted against a plan by Tokyo Electric Power Co. to introduce the fuel at its Kashiwazaki-Kariwa plant in Niigata Prefecture.

The Tepco plan for the plant was one of three nationwide to introduce the fuel. The other two plans, by Kansai Electric Power Co. and Tepco, to use the fuel at the Takahama nuclear complex in Fukui Prefecture and a plant in Fukushima Prefecture, had already been suspended.

The earliest Kepco plan was suspended after British Nuclear Fuels PLC, from which the Osaka-based company imported MOX fuel, was found to have falsified manufacturing data for the fuel.

Tepco’s plan in Fukushima was opposed by the governor.

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