In December 1995, the Monju fast-breeder reactor at Tsuruga sprang a leak in its sodium-cooling circuitry.

ECONOMIST: Japan

With plutonium no longer needed for use in the world's abandoned fast breeder reactor programmes and nuclear powers getting rid of their atomic weapons, large stockpiles of the highly toxic plutonium metal are starting to build up.

BBC: More suspect nuclear fuel found

Also on Wednesday, the watchdog decided to freeze further steps to bring the Monju prototype fast-breeder nuclear reactor online, criticizing Japan Atomic its operator for a series of significant safety lapses.

WSJ: Panel: Active Fault Runs Beneath Japan Reactor

In the 1970s and 1980s the federal government poured billions of dollars into the Synthetic Fuels Corporation to develop liquid and gas fuel from coal, and into the fast-breeder nuclear reactor.

ECONOMIST: How the government can help things along

Also on Wednesday, the watchdog decided to freeze further steps to bring the Monju prototype fast-breeder nuclear reactor online, criticizing the Japan Atomic Energy Agency its operator for a series of significant safety lapses.

WSJ: Panel: Active Fault Runs Beneath Japan Reactor

And the fast-breeder type of nuclear reactor in which plutonium was used as fuel is no longer economic.

ECONOMIST: The nuclear industry