Japan’s fast breeder reactor program was conceived in the Japan Atomic Energy Commission’s (JAEC) first Long Term Plan, published in 1956.1 Among various reactor types under review, the JAEC selected the fast breeder reactor and its closed fuel cycle as the preferred technologies for R&D and endorsed the importation of light-water reactor technology from the United States.2

A version of this chapter has been published in Science and Global Security 17 (2008): 68-76.

The JAEC’s 1967 Long Term Plan concluded that the fast breeder reactor should be the mainstream of future nuclear power generation3 and the Government established the Power Reactor and Nuclear Fuel Development Corporation (PNC) as the primary R&D institution for fast breeder reactor and nuclear fuel cycle development. The Plan envisioned that an experimental fast reactor would be built during the 1970s, and the first commercial fast breeder reactor by the late 1980s.

Japan’s first fast breeder reactor was the experimental Joyo (Eternal Sun), built at the Japan Nuclear Cycle Development Institute’s Oarai Engineering Center. Joyo achieved criticality in 1977 at an initial power level of 50 megawatt thermal (MWt). Power was increased to 75 MWt in 1979, and to 100 MWt with its Mark II core, which achieved criticality in 1982. From 1983 to 2000, Joyo operated as an irradiation test bed for fuels and materials for future Japanese fast reactors. Since 2003, Joyo has been operating at 140 MWt with its Mark III core, and in April 2007 it completed its 6th duty cycle. By 12 March 2007, Joyo had operated for 70,000 hours. Thus, in the 30 years between 1977 and 2007 Joyo operated approximately 27 percent of the time.

The prototype fast breeder reactor Monju (280 megawatt electric) was developed in parallel with Joyo, but construction was delayed and it did not achieve criticality until 1994. On 8 December 1995, Monju experienced a serious sodium leak and fire when intense vibrations caused the failure of a thermocouple attached to the secondary sodium loop. The sodium reacted with oxygen producing a fire that melted the steel structures in the room. No injuries were reported and no release of radioactivity occurred since the sodium in the secondary loop was not radioactive.

PNC’s cover-up of the accident caused a social and political uproar that delayed the repair and restart of Monju. In June 2001, PNC submitted a re-license application for Monju, which was granted in December 2002. Legal challenges against PNC surrounded the relicensing causing further delays and on 27 January 2003, the Kanazawa branch of Nagoya’s High Court reversed its 1983 approval to build the reactor. Just over two years later, on 30 May 2005, Japan’s Supreme Court ruled for PNC, thereby clearing all legal barriers for the restart of Monju. Restart was scheduled for October 2008 but as of January 2010 the reactor is still off-line.

Japan Atomic Power Company (JAPCO) finalized plans for a 660 megawatt electric (MWe) demonstration commercial fast breeder reactor in 1994. The project experienced delays because of the Monju accident and was eventually canceled in the late 1990s.

R&D on reprocessing fast reactor spent fuel started in mid-1970s, and reprocessing of Joyo spent fuel was conducted at the experimental Chemical Processing Facility (CPF) starting in 1982. Following the experience gained at the CPF, PNC started construction of a Recycle Equipment Test Facility (RETF) in 1995, which is the

first pilot-scale reprocessing facility for fast reactor spent fuel, the counterpart of the Tokai pilot reprocessing plant for light-water reactor spent fuel. The Tokai plant adopted imported French technology but the RETF intends to employ technologies currently under development under the cooperative program with Oak Ridge National Laboratory (ORNL) in the United States. The first phase of construction was completed in 2000, but its scheduled completion date is currently unknown.