TOKYO -- Japan is set to start decommissioning its troubled Monju fast-breeder reactor after decades of accidents, cost overruns and scandals. It is the beginning of the end of a controversial project that exposed the shortcomings of the country's nuclear policy and the government's failure to fully explain the risks and the costs.

In July, the Japan Atomic Energy Agency will begin decommissioning what was hailed as a "dream" reactor that was expected to produce more nuclear fuel than it consumed. The government has so far spent more than 1 trillion yen ($9.44 billion) on the plant, which has barely ever operated.

The plan approved by the Nuclear Regulation Authority on March 28 to decommission the reactor, located in central Japan's Fukui Prefecture, calls for the extraction of spent nuclear fuel to be completed by the end of the fiscal year through March 2023. Full decommissioning is expected to take about 30 years.

Total costs to shut down the reactor are currently estimated at 375 billion yen, but that could climb, as the full technical requirements and the selection of the nuclear waste sites are not well understood.

Japan does not have the technological ability to manage the decommissioning process on its own, and must enlist the help of France, which has more experience with fast-breeder reactors. Among the technical challenges is handling the plant's sodium coolant, which is highly reactive and explodes on contact with air.

Many of the problems with Japan's nuclear policy were brought to light by the Fukushima Daiichi nuclear disaster caused by the tsunami and earthquake of March 2011. Such problems have included the high costs of plants, the selection of nuclear disposal sites, and the threat of shutdowns due to lawsuits. Japan's nuclear policy has largely been gridlocked since the disaster.

But the Monju project had many problems before the Fukushima catastrophe.

Planning for the project began in the 1960s. Its fast-breeder technology was considered a dream technology for resource-poor Japan, which had been traumatized by the oil crisis of the 1970s. The reactor was supposed to generate more plutonium fuel than it consumed.

The reactor finally started operating in 1994, but was forced to shut down the following year due to a sodium leak. It has been inoperative for most of the time since. The decision to decommission it was made in December 2016 following a series of safety scandals, including the revelation that many safety checks had been omitted.

Recent experience suggests the government's estimated cost of 375 billion yen to decommission Monju could be on the low side. In 2016, the estimate for decommissioning the Fukushima Daiichi plant ballooned to 8 trillion yen from an initial 2 trillion yen in 2013, largely due to inadequate understanding of the decommissioning process.

While "the JAEA will try to keep costs down," said Hajime Ito, executive director with the agency, the process of extracting sodium, the biggest hurdle, has yet to be determined. Future technical requirements will also involve significant costs.

The Monju reactor is not the only example of failure in Japan's nuclear fuel cycle policy -- the cycle of how nuclear fuel is handled and processed, including disposing nuclear waste and reprocessing used fuel.

Central to this policy is a nuclear fuel reprocessing plant in the village of Rokkasho in northern Aomori Prefecture that was supposed to extract plutonium and uranium by reprocessing spent nuclear fuel to be reused at nuclear plants.

More than 2 trillion yen has been spent on the plant so far. Construction was begun in 1993, but completion has been repeatedly postponed due to safety concerns. On Wednesday, the NRA decided to resume safety checks on the plant, but if it chooses to decommission it, the cost would be an estimated 1.5 trillion yen.

Had Japan taken into consideration the costs of decommissioning plants and disposing of spent nuclear fuel, it probably would not have been able to push ahead with its nuclear policy in the first place, said a former senior official of the Ministry of Economy, Trade and Industry, who was involved in formulating the country's basic energy plan.