The Japanese government formally decided to scrap the Monju prototype reactor. Spent fuel from the reactor will be removed by 2022 and the dismantlement is expected to be completed by 2047. The dismantlement is estimated to cost about ¥375 billion ($3.2 billion). A recent estimate suggested that restarting the reactor would take about eight years and ¥540 billion (about $4.82 billion) to operate.

The 350-MWe Monju prototype fast-neutron reactor was operational for only very brief period. It reached criticality in 1994 and was connected to the grid in August 1995, but was shut down four months later by a fire caused by leakage of its molten sodium coolant. It was restarted again 15 years later, in May 2010, but was shut down again three months later by a refueling accident. In November 2015, Japan's Nuclear Regulatory Authority announced that the current operator of the reactor, the Japan Atomic Energy Agency, is unfit for purpose when it discovered a number of problems during a safety inspection.

However, the shutdown of the Monju reactor does not seem to affect Japan's plan to invest in fast neutron reactor or the policy regarding reprocessing of the spent fuel of its light-water reactors.