The test run of the prototype fast-breeder reactor (FBR) Monju in Tsuruga, Fukui Prefecture, is now expected to start after Golden Week, after prefecture Gov. Issei Nishikawa on April 28 gave the go-ahead for test runs to be conducted. The 280,000 kW reactor — an important part of Japan's planned nuclear fuel cycle — has been inoperative for the 14 years and five months since Dec. 8, 1995, when some 640 kg of secondary-coolant sodium leaked and caused a fire.

This will be the first time for Japan to restart a reactor that has been out of operation for such a long time. Sodium reacts strongly with air and water. Some deterioration of the reactor's components due to old age cannot be ruled out.

In March 2008 the Japan Atomic Energy Agency, the operator of Monju, admitted that a 15-km-long active seismic fault runs only about 500 meters from Monju, and that another 18-km-long active seismic fault runs directly under the reactor, about 5 km below ground level. The agency cannot be too careful in conducting test operations at Monju.