semigovernmental

Monju Nuclear Power Plant

is Japan's only fast breeder reactor. Located in Tsuruga, Fukui Prefecture in Japan, the reactor began construction in 1985 and first achieved criticality in April 1994.

Monju is a sodium-cooled, MOX-fueled loop type reactor with 3 primary coolant loops, producing 714 MWt / 280 MWe.

Monju was closed in 1995 following a serious sodium leak and fire. It is expected to reopen in 2008.

The successor to Monju is expected to be a larger demonstration plant that will be completed around 2025, built by the newly formed Mitsubishi FBR Systems company.

Monju sodium leak and fire

On Dec. 8, 1995, the reactor suffered a serious accident. Intense vibration caused a thermocouple pocket inside a pipe carrying sodium coolant to break, possibly at a defective weld point, allowing several hundred kg of sodium to leak out onto the floor below the pipe. Upon coming into contact with the air, the liquid sodium reacted with oxygen and moisture in the air, filling the room with caustic fumes and producing temperatures of several hundred degrees Celsius. The heat was so intense that it melted several steel structures in the room. An alarm sounded around 7:30 p.m., switching the system over to manual operations, but a full operational shutdown was not ordered until around 9:00 p.m., after the fumes were spotted. When investigators located the source of the spill they found as much as three tons of solidified sodium.

Fortunately, the leak occurred in the plant's secondary cooling system, so the sodium was not radioactive. However, there was massive public outrage in Japan when it was revealed that Power Reactor and Nuclear Fuel Development Corporation (PNC), the semigovernmental agency then in charge of Monju, had tried to cover up the extent of the accident and resulting damage. This coverup included falsifying reports and the editing of a videotape taken immediately after the accident, as well as the issuing of a gag order to employees regarding the existence of the real tapes.

Restart

On November 24, 2000, Japan's Atomic Energy Commission announced their intention to restart the Monju reactor. This decision was met with resistance by the public, resulting in a series of court battles. On Jan. 27, 2003, the Nagoya High Court's Kanazawa branch made a ruling reversing its earlier 1983 approval to build the reactor, but then on May 30, 2005, Japan's Supreme Court gave the green light to reopen the Monju reactor.

The restart is currently scheduled for October 2008, having been moved back five months.