Closed down in late 1995 after a serious accident, the local government in Fukui prefecture and the national nuclear authority want the prototype plant operating again within two years.
But not everyone in the prefecture is buying the official line that it is completely safe - and thousands of residents are hoping that an imminent ruling by Japan's Supreme Court will ensure the reactor will not go on line.
The charm offensive launched by the nuclear industry to convince the public that Monju is the answer to the country's long-term energy problems and poses no threat, is slick and professional.
Laser indicators, power-point presentations and colourful graphics are used to drive home the message that an experimental reactor on the coast of northern Japan is the way forward.
At a recent press conference in Tokyo, Yuichi Tonozuka, president of the Japan Nuclear Cycle Development Institute, stated the case for restarting the prototype plutonium reactor, nearly 10 years after a massive leak of sodium coolant caused a fire.
Yuichi Tonozuka preaches the
virtues of fast-breeder tech
"If the fast-breeder nuclear fuel cycle can be brought on line, then it will be far more efficient than present uranium reactors, while it will also profoundly lessen the burden on the environment because it produces far less waste," he said.
A fast-breeder nuclear reactor uses a combination of plutonium-uranium mixed oxide (MOX) fuel and is designed to produce more plutonium than it consumes, providing a perpetual source of energy.
Tonozuka said: "As well as producing electric power, the fast-breeder technology allows us to produce precious metals, including platinum, as a by-product and although this technology is at present far more expensive than a conventional light-water reactor, we believe that our research will make it competitive by 2015."
Work on Monju, near the coastal town of Tsuruga in northern Japan, began in 1985 and the reactor reached criticality - the point at which a nuclear reactor is self-sustaining - in April 1994.
The Japanese government has made Monju a key pillar of its energy policy because of the country's reliance on imports of declining deposits of oil.
In February, Fukui Governor Issei Nishikawa approved plans to repair and upgrade the reactor, which had been mothballed since December 1995, when an estimated 750kg of molten sodium leaked from the cooling unit and caused a fire.
The public outcry from the accident was made worse when it quickly became apparent that the operator of the plant had tried to conceal the scale of the problem.
"If the fast-breeder nuclear fuel cycle can
be brought on line, then it will be far more efficient than present uranium reactors"
Japan Nuclear Cycle Development Institute
The accident was the largest reported sodium leak in a reactor in the world. An inquiry subsequently determined that it had been caused by a fundamental design flaw involving a thermometer well combined with an inefficient detection system.
Sodium burns when is released into the air and reacts violently if it comes into contact with water. The chemical reaction in the chamber ate into the metal lining to a depth of 3cm.
"For almost 10 years, the plant has been undergoing safety inspections and a modification programme has been drawn up that will allow us to rehabilitate the plant," Tonosuka said.
The improvements include modifications to steam generators and thermometers, which failed in the 1995 accident, but opponents of the plan area adamant - Monju poses a threat to their lives.
Critics say Japan cannot afford
a large-scale N-plant accident
"Not enough research has been done on Monju, which is an immature nuclear reactor that should never be put into operation," 69-year-old Miwako Ogiso, who lives just 40km from the plant, said.
"The last accident was not foreseen by the safety reviews - which clearly cannot be trusted - and I predict that if Monju reopens, then there is a high possibility of simultaneous multiple ruptures of pipes from the steam generators.
"If there is another accident, a vast area of the country would be contaminated," she said.
"That's why I refuse to move away; I'll stay to continue the fight against the Monju programme."
Tonozuka admitted Japan is currently storing "excessive" stockpiles of plutonium - much of which is of weapons grade - but played down concerns voiced recently by Muhammad al-Baradai, of the International Atomic Energy Agency, that it could lead to proliferation.
"Nuclear proliferation is a global issue and one that we have to have grave concerns about," he said. "But the peaceful utilisation of nuclear energy is also a concern of the world community.
"Even if you ask the most pro-nuclear experts, they say that in a best-case scenario, Monju will produce just 1% of Japan's energy by 2050. Is that really the way we want to go?"
Aileen Mioko Smith,
head, Green Action Kyoto environmental group
"I admit that we have excessive amounts of plutonium, but our purpose is for research," he added.
In tandem with the local residents' demonstrations against the reactor, the case against Monju is also being fought through Japan's courts.
The Supreme Court is due to hand down a decision in the next few weeks in response to an appeal filed by the national government against a ruling by the Nagoya High Court in 2003 that found the government's approval in 1983 for the construction of Monju to be invalid, according to Aileen Mioko
Smith, head of the environmental group Green Action Kyoto.
"At the final hearing, on 17 March, the government side summed up its case in about five minutes," she said.
The destructive power of nuclear
technology is familiar to Japan
"Their arguments in the case were contradictory and it was a pretty poor performance. Our side used the entire hour that we were allotted.
"The legal struggle has been going on for 19 years and it has been brought by people in the prefecture who are worried about their safety," she said.
"More than 200,000 people in the prefecture - that is, one-third of the entire population - have signed a petition to the governor asking that Monju not be reopened.
Best case scenario
"Yes, we agree that Japan is energy-poor, but this is by far the worst option open to the government to solve that problem," Smith said, pointing out that Monju has been a cornerstone of the national nuclear policy for nine consecutive five-year plans - and in all that time has produced just one hour of electricity to the grid.
"The cost of the fast-breeder project is over Y2 trillion ($1.9 billion), of which 80% is taxpayers' money," she said.
"And even if you ask the most pro-nuclear experts, they say that in a best-case scenario, Monju will produce just 1% of Japan's energy by 2050. Is that really the way we want to go?"