China is planning to build a nuclear power plant on the edge of the Gobi Desert that would be the first in the world to use molten salt as the fuel carrier and coolant.
It would also be the first to use the radioactive metallic element thorium — named after the Norse god — as a fuel source instead of the uranium traditionally used in nuclear reactors.
Molten salt reactors are considered "inherently safer" than traditional water-cooled reactors, but face additional challenges such as the corrosion caused by the superheated radioactive salts and issues with waste disposal.
Plans for the thorium molten salt reactor (TMSR), first revealed by the South China Morning Post, were detailed in an environmental assessment report that was briefly posted to the website of the Shanghai Institute of Applied Physics (SINAP) before being taken down.
According to the report, , which was designed to produce 2 megawatts of thermal energy but no actual electricity, achieved criticality in October last year.
Building on the results of the prototype, the new facility will produce 60MW of heat that will be used to generate 10MW of electricity and hydrogen as part of a larger renewable energy research hub.
The project would "drive the development of a large number of materials and high-end equipment manufacturing technologies", the report said.
It cited advantages to molten salt reactors, including "high inherent safety, low nuclear waste, physical prevention of nuclear proliferation and better economics".
It also mentioned that because TMSRs don't require water, they could also be built underground and in arid areas.
Construction is due to start near Wuwei in China's northern Gansu Province next year with full operation expected in 2030.
Waste from the reactor is set to be stored underground in the Gobi.
SINAP did not respond to the ABC's request for comment.
The project is part of China's campaign to become carbon neutral by 2060, which has seen Beijing funding research into a wide variety of renewable energy technologies including new types of large nuclear reactors and small modular reactors (SMRs).
According to a paper previously published in the Chinese scientific journal Nuclear Techniques by the SINAP, China aims to begin producing 100MW TMSRs from 2030.
The reactors would be used for traditional civilian energy purposes but some have suggested they could also be used to power military ships, aircraft and even drones.
A Chinese shipyard last year revealed designs for a huge nuclear-powered container ship that would use a small TMSR.
'Inherently safer' than traditional nuclear reactors
Traditional water-cooled reactors have to operate at high pressures so the water doesn't turn into steam — like huge pressure cookers.
Molten salt vaporises at much higher temperatures, so the reactors don't need to be pressurised in the same way.
They also include a "frozen" salt plug designed to melt if the system overheats or loses power, allowing the molten salt to drain into a reservoir where it cools down and solidifies — stopping the nuclear reaction.
Experts say this means there is less danger of them having a catastrophic meltdown like at Fukushima and Chernobyl.
Australian Nuclear Association president Mark Ho said because molten salt reactors did not need to be pressurised, they could be smaller than water-cooled reactors.
Dr Ho said China could provide these "miniaturised" nuclear reactors to Pacific Islands nations where diesel generators provide most of the electricity.
"An unpressurised core [also] means an inherently safer design," Dr Ho said.
He said the initial success of China's molten salt reactor program showed how far behind Australia was on advanced nuclear power technology.
"Which is not helped by the ban on nuclear power," he said.
Thorium, meanwhile, has some potential advantages as a fuel over uranium, as it produces shorter-lived radioactive waste and is more difficult to use for nuclear weapons.
It is also much more abundant than uranium, particularly in China.
According to the SINAP report, China's proven thorium industrial reserves are about 280,000 tons — second only to India's, which are about 340,000 tons.
That's said to be enough to satisfy China's energy needs for 20,000 years.
The news has generated excitement in the scientific community because it suggests the Chinese researchers have had at least some success in overcoming the technical challenges that have made TMSRs unviable in the past.
They include the corrosive nature of the radioactive superheated salts and the difficulties involved in achieving fission with thorium.
Nuclear engineer Tony Irwin, an honorary associate professor at the Australian National University, said the TMSR was an "interesting technology that's got a lot of potential".
He pointed out that the higher operating temperature could also be used to supply process heat for industrial applications.
"[Chinese researchers] tend to go in very conservative steps," he said. "Start off slowly and demonstrate and then carry on for the next one."
He said the big challenge remained ensuring the plant would last for the expected 60-year lifetime of a commercial power plant.
"But there's huge progress being made with materials," he said.
Originally intended for aircraft
US scientists first started looking into molten salt reactors in the 1940s, hoping they could be built small enough to be installed in aircraft.
A functioning TMSR was built at the Oak Ridge laboratory in Tennessee but it endured a series of issues and malfunctions and was shut down in 1969, with thorium effectively abandoned in favour of uranium.
The 2MW TMSR built in the Gobi Desert was the first to achieve sustained fission since then.
China's researchers are not the only ones who have been working on the technology in recent years.
India, which has the world's largest known reserves, has long been trying to develop thorium as a power source, while Indonesia and other countries have expressed interest in TMSRs as well.
A number of private companies are also jostling to be the first to get a commercial thorium-powered and/or molten salt reactor up and running.
They include Bill Gates's TerraPower, which is planning to build a 345MW molten chloride salt-cooled reactor in Wyoming that would run on high-assay low-enriched uranium.
However, not everyone believes in the potential of TMSRs.
Researchers have raised concerns that waste from SMRs, including molten salt reactors, may be more harmful and difficult to dispose of than that from traditional nuclear reactors.
"Should molten salt reactors ever be constructed, they are unlikely to operate reliably," physicist MV Ramana wrote in Bulletin of the Atomic Scientists.
"And if they are deployed, they would likely result in various safety and security risks. And they would produce several different waste streams, all of which would require extensive processing and would face disposal-related challenges.
"Investing in molten salt reactors is not worth the cost or the effort."
Implications for Australia?
The federal opposition recently announced it would build a series of nuclear power plants if it won the next election.
However, Professor Irwin said molten salt reactors were still too far away to consider for Australia.
"I don't think that's a commercial path at the moment," he said.
"It's one that obviously everybody's looking at and monitoring, but the commercial path at the moment is still light water reactors in either large or small sizes for more immediate deployment."
Nigel Marks, an associate professor of physics at Curtin University, said it would be a "massive moment" if molten salt reactors proved commercially viable.
"If Australia decided to go nuclear, we should definitely look at it — geopolitics notwithstanding," he said.
He said finding a use for thorium would be great for the Australian mining industry,
"Australia has 10 to 15 per cent of the world's thorium," he said.
"For rare-earth miners such as Lynas, thorium is a thorn in their side as it creates a waste stream which is (mildly) radioactive."
He said that if thorium was a "bridge too far" then a molten salt reactor using uranium would have all the same safety benefits, apart from the waste being longer-lived.
He added that the problem of nuclear waste disposal had been "solved" with countries including Finland and Sweden set to put it deep underground.
"In Australia, we have great options for nuclear waste storage; not only do we have some of the oldest and most geologically stable rocks in the world, but we have excellent technology developed at ANSTO [Australian Nuclear Science and Technology Organisation]," he said.
Dr Marks said that from a broader perspective, China's progress with TMSRs showed the "power of innovation in science and engineering".
"The nuclear nay-sayers point to SMRs [Small Modular Reactors] and say 'long lead times, not yet commercially demonstrated' and so on, and all this is true.
"But it misses the point that there are lots of ways of skinning the nuclear cat, and if countries would just have the patience to invest for a decade or so, then the solutions will come.
"After all, finding a green solution for electricity (and heat and hydrogen) is a multi-generational task, so waiting five to 10 years to find a good path forward is nothing."
