Shaun Burnie with Mycle Schneider

It was reported on 6 January 2013 that computer hackers had accessed and may have stolen private data held on a computer system at the idle Monju Fast Breeder Reactor, in Tsuruga, Japan. Monju is managed by the Japan Atomic Energy Agency (JAEA). The data on the computer consisted of 42,000 emails and staff training reports. On 2 January, one of the eight computers in the reactor control room was found by the server administrator to have been accessed from outside 30 times in the previous five days. This occurred after a free software update took place on 26 December 2013. JAEA officials stated that none of the accessed data was crucial to the safety of the reactor.

It was reported that the stolen data had been requested through a website 'based' in the Republic of Korea. There is no suggestion that this has anything to do with Korea's own fast breeder reactor research program. In fact, international collaboration is on-going for the development of so-called Generation IV reactors, with Korean efforts focusing on the Kalimer-600 sodium cooled reactor. Japan and Korea are both members of the Generation IV International Forum.

On 6 November 2013, Japan's Nuclear Regulation Authority (NRA) admonished Monju's operator for lax security at the plant, including failing to take appropriate measures to protect nuclear material at its premises from possible terrorist attacks and other malicious acts.

The Monju reactor is not operating due to major technical failures, seismic reviews, and as a result of an investigation by the NRA in 2012 which found that the JAEA had failed to inspect thousands of components at the reactor. In May 2013, the NRA effectively barred the restart of Monju until major changes in inspection methods were adopted. The reactor has been off-line since a sodium fire in December 1995.