Japan's Nuclear Regulation Authority on March 28 approved a 30-year plan by the Japan Atomic Energy Agency for the decommissioning and dismantlement of the Monju prototype fast-breeder reactor.

Monju has a had troubled history, like other fast-breeder reactor (for details, see "Japan's Plutonium Breeder Reactor and its Fuel Cycle" by Tatsujiro Suzuki). Construction of Monju started in 1985. It went critical in 1994 but an accident led to its shut-down in August 1995. The reactor was restarted in May 2010, but suffered another accident about four months later, in September 2010. In total, the reactor operated for about a year until in 2016 the decision was made to shut it down. Japan has spent about 1 trillion yen ($9.46 billion) on Monju so far, and the cost of the decommissioning is estimated to exceed $3.5 billion.

The reactor was finally shut down in December 2017. The Japan Atomic Energy Agency expects to begin removing fuel from Monju in July 2018.

The decommissioning and dismantlement plan anticipates demolition of the reactor building by 2047. The plan does not however explain how the radioactive sodium coolant is to be removed.