More than 30 years ago, when its economy seemed invincible and the Sony Walkman was ubiquitous, Japan decided to build a recycling plant to turn nuclear waste into nuclear fuel.

It was supposed to open in 1997, a feat of advanced engineering that would burnish its reputation for high-tech excellence and make the nation even less dependent on others for energy.

Then came a series of blown deadlines as the project hit technical snags and struggled with a Sisyphean list of government-mandated safety upgrades. Seventeen prime ministers came and went, the Japanese economy slipped into a funk and the initial $6.8 billion budget ballooned into $27 billion of spending.

Now, Japan Nuclear Fuel Ltd, the private consortium building the recycling plant, says it really is almost done. But there is a problem: Japan does not use much nuclear power anymore.

The country turned away from nuclear energy after the 2011 Fukushima disaster, and only nine of its 35 reactors are operational.

It is a predicament with global ramifications. While waiting for the plant to be built, Japan has amassed a stockpile of 47 metric tons of plutonium, raising concerns about nuclear proliferation and Tokyo’s commitment to refrain from building nuclear arms even as it joins the United States in pressing North Korea to give up its arsenal.

In August, North Korea’s state-run Rodong Sinmun newspaper accused Japan of accumulating plutonium “for its nuclear armament.”

Japan pledged for the first time this past summer to reduce the stockpile, saying the recycling plant would convert the plutonium into fuel for use in Japanese reactors.

But if the plant opens as scheduled in four years, the nation’s hoard of plutonium could grow rather than shrink.

That is because only four of Japan’s working reactors are technically capable of using the new fuel, and at least a dozen more would need to be upgraded and operating to consume the plutonium that the recycling plant would extract each year from nuclear waste.

“At the end of the day, Japan is really in a vice of its own making,” said James M. Acton, a researcher at the Carnegie Endowment for International Peace in Washington.

“There is no easy way forward, and all those ways forward have significant costs associated with it.”

A handful of countries reprocess nuclear fuel, including France, India, Russia and the United Kingdom.

But the Japanese plan faces a daunting set of practical and political challenges, and if it does not work, the nation will be left with another problem: about 18,000 metric tons of nuclear waste in the form of spent fuel rods that it has accumulated and stored all these years.

A stora­ge facil­ity for spent fuel rods at Japan Nucle­ar Fuel Ltd.’­s plant in Rokka­sho, Japan­, Aug 2018.

Japan’s neighbours, most notably China, have long objected to the stockpile of plutonium, which was extracted from the waste during tests of the recycling plant and at a government research facility, as well as by commercial recycling plants abroad.

Most of this plutonium is now stored overseas, in France and Britain, but 10 metric tons remain in Japan, more than a third of it in Rokkasho, the northeastern fishing town where the recycling plant is being built.

Japan says it stores its plutonium in a form that would be difficult to convert into weapons, and that it takes measures to ensure it never falls into the wrong hands.

But experts are worried the sheer size of the stockpile — the largest of any country without nuclear weapons, and in theory enough to make 6,000 bombs — could be used to justify a nuclear buildup by North Korea and others in the region.

Any recycling plan that adds to the stockpile looks like “a route to weaponise down the road,” said Alicia Dressman, a nuclear policy specialist. “This is what really concerns Japan’s neighbours and allies.”

Japan maintains that its plutonium is for peaceful energy purposes and that it will produce only as much as it needs for its reactors. “We are committed to nonproliferation,” said Hideo Kawabuchi, an official at the Japan Atomic Energy Commission.

But the launch of the Rokkasho plant has been delayed so long — and popular opposition to restarting additional nuclear reactors remains so strong — that scepticism abounds over the plan to recycle the stockpile.

Critics say Japan should concede the plant will not solve the problem and start looking for a place to bury its nuclear waste.

“You kind of look at it and say, ‘My God, it’s 30 years later, and that future didn’t happen,’” said Sharon Squassoni, a nonproliferation specialist at George Washington University.

“It’s just wishful thinking about how this is going to solve their myriad problems.”