Japanese fast breeder reactor Monju restarted after 14-year shutdown

On 6 May 2010 the Japanese fast breeder reactor Monju located in Tsuruga restarted for the first time after it was shutdown on 8 December 1995, following a major sodium leak and fire. The extent of the accident had been covered up and the operator had first released a forged version of video footage shot by a technical team shortly after the event. The revelation of the manipulation led to massive loss of confidence in nuclear operators in Japan.

National authorities and the Fukui Prefecture authorized the restart of the 280 MW (gross) reactor in spite of continuous protests by environmentalists, scientists and mainstream media (see a report on Asahi Shimbun editorial) over safety and proliferation concerns. The reactor had been connected to the grid on 29 August 1995, less than three and a half months prior to the accident, and has since been consuming power - especially for the necessary permanent heating of the sodium to maintain its liquid form - rather than generating electricity for the grid.

According to the Japan Times the Monju project cost about ¥900 billion ($7.5 billion) so far, including ¥600 billion ($5 billion) for construction. The accident contributed significantly to the costs. It was caused by a broken thermocouple in the secondary sodium loop that gave way to a massive sodium leak estimated at 640 kg, some of which ignited. Sodium is highly reactive in contact with air and water.

The Tokyo Citizens' Nuclear Information Center (CNIC) was not alone to raise concerns over the restart. "Monju was built 20 years ago to meet a design basis that was set 30 years ago", CNIC stated in a press release. "We believe that Monju is an accident waiting to happen and that it is, therefore, irresponsible to restart the plant", CNIC concludes.

In March 2010 twenty-nine scientists signed a declaration opposing the restart of Monju stating that "hardly any checks of coolant system piping, tests to detect non-penetrating cracks and holes in the steam generator heat transfer tubes, or studies of the integrity of fuel assemblies in the reactor core have been undertaken, so there is no knowing what defects might be lurking."

The scientists also claim that "in the course of preparations to restart Monju, it was discovered by accident, as a result of false alarms, that hundreds of contact-type sodium detectors had not been checked". Hours after the restart, one in three gas detectors started indicating a leak. When the detector kept sending signals the following day that were identified as false alarms, "they have concluded the equipment has developed problems", reported Japan Times on 8 May 2010.

Monju is part of a Long Term Plan that envisaged as early as 1967 that the fast breeder reactor should be the mainstream of future nuclear power generation. The first commercial breeder was then thought to start operating in the late 1980s. By that time the commercialization of breeders was pushed back to around 2030. A 2006 policy paper by the Japan Atomic Energy Commission (JAEC) pushes the target date of commercialization to 2050.

As former IPFM member Tatsujiro Suzuki, now Vice-Chairman of JAEC, indicates in his detailed review of the history of Japanese fast breeder development (see IPFM Research Report No. 8, Chapter 4), the Monju accident "triggered a significant shift in Japan's fast breeder reactor program". The effect was that the debate was opened to critics and, according to Suzuki, the fast breeder reactor commercialization date "has receded far into the future while the fast breeder reactor R&D budget has been shrinking. Japan's continued commitment to the fast breeder reactor appears largely driven by socio-political factors affecting Japan's management of the back-end of the light-water reactor fuel cycle and R&D management".