The Japan Atomic Energy Agency (JAEA) again failed to conduct checks on a device at its experimental Monju fast-breeder reactor and overlooked a warning signal from a maintenance management system for about three months, Japanese media reported on 22 July. JAEA, which recently was criticised for failing to inspect thousands of devices at Monju, is investigating the cause of the latest mishap and devising measures to prevent a recurrence. According to sources familiar with the matter, the device in question controls the temperature of sodium coolant for the prototype reactor.
JAEA was expected to complete the inspection by the end of March, after moving up the previous deadline, which was set at the end of May. Around the end of February, the maintenance management system installed at Monju started to display a warning signal. But it was not until 27 May that agency officials noticed it, the sources said. JAEA reported the problems to the Nuclear Regulation Authority (NRA) and completed the inspection of the temperature-controlling device on 31 May.
A massive sodium leak and cover-up attempt in December 1995 caused Monju’s operations to be suspended. It was eventually brought back online in May 2010, but halted againe because of technical prorblems in August the same year. In November 2012, it was found that JAEA failed to carry out maintenance checks on more than 10,000 devices at Monju, after which NRA effectively banned the JAEA from operating the reactor. In November 2015, NRA recommended to science and technology minister Hiroshi Hase that JAEA should be replaced as Monju’s operator. The ministry is studying the matter.