Thorium Reactors: Why is this Technology Quite So Exciting

Since the world first learned to split the atom, nuclear energy has been a source of immense hope, and of lingering fear. By any human metric, the potential of nuclear power is all but limitless, with the potential for just a few hundred modern reactors to supply carbon-free energy to an entire continent at a time. Yet fears of catastrophic nuclear meltdown, longstanding concerns over radioactive waste, and the undeniable connection between world-changing nuclear energy and world-ending nuclear weapons, have long kept planet Earth from a true nuclear revolution.

But what if a new approach to nuclear energy came along, and changed the game? What if, not by magic or miracle but by straightforward nuclear physics, an atomic scientist near you promised that with a wave of a hand and a few billion dollars for research, they could provide a safer, cleaner, more peaceful alternative to the nuclear power industry we’ve known for so long? It isn’t some new uranium isotope, it’s not some new element from the depths of the Periodic Table, and it’s not nuclear fusion.

It’s thorium, an alternative fuel that many nuclear scientists believe to be not just a gateway to a massively improved nuclear industry, but a bridge between modern power infrastructure, and a nuclear fusion revolution that’s still decades away. Unlike fusion, thorium is ready now—and if the world can put theory into practice, then a whole lot of things are about to change.

The Principle; The Technology

Meet thorium. It’s element number ninety on the Periodic Table, sandwiched between a couple of elements the average person has never heard of, and for most of human history, thorium has been just another rock. First discovered in 1828, thorium is a relatively abundant silvery substance that can be extracted, in small amounts, from most rocks and sands.

It exists in nature in one single form, and while that form is technically unstable, it decays slowly enough that its half-life is multiple times the current age of planet Earth. It’s used in lightbulbs, high-refractive camera lenses, and ceramics, and it’s named after the Norse god of thunder, Thor.

But the thing that makes thorium special, is its properties relative to an element that the world has gotten to know a little bit better over the last century: Uranium. Thorium is situated just two spots away from uranium on the Periodic Table, and unlike uranium, thorium is not a material that can be useful as a nuclear fuel. Its only naturally occurring isotope, thorium-232, is fissionable, but not fissile; that is to say, it’s an atom that is more difficult to split in a nuclear reaction than uranium is. To get it to split, you’ve got to bombard it with high-energy neutrons, irradiating it until a fissile reaction finally takes place. Uranium-235, the fissile isotope of uranium that fuels nuclear power plants and nuclear bombs, is far easier to trigger into nuclear fission.

But when thorium is irradiated with sufficient energy to cause a fission reaction, it produces a different isotope of uranium than the isotopes that the modern nuclear industry relies on. Instead, the so-called fertile isotope thorium-232 can be used to create an artificial uranium isotope, uranium-233. While it’s the thorium fuel cycle that we’re discussing today, it’s this special sort of uranium, a by-product of the fissile reaction, that nuclear scientists are really after.

As for why it might be better to pursue nuclear power via thorium’s fuel cycle than via uranium’s, we’ll be diving deep in just a moment—but before we do, here are some of the highlights. Thorium is far easier to obtain, it’s much more abundant, it creates much safer by-products, and it is far harder to put the by-products of a thorium fuel cycle into a nuclear bomb.

With those sorts of advantages, it’s easy to see why thorium would generate some curiosity around the world. But the mere fact that thorium reactors are a hot topic in the 2020s, doesn’t mean that they’re a new concept. In fact, several nations, particularly the United States, have known about the potential value of the thorium fuel cycle for decades—and the reason why it hasn’t been adopted, is nothing to do with its efficacy.

See, thorium reactors were first worked out conceptually during the boom years of nuclear science, in the decade or two after the conclusion of the second World War. Around that time, scientists in the US were hard at work building uranium-based nuclear reactors, with the power and potential to do more than turn the lights on. They also created the isotope plutonium-239, today used as the primary fissile material in modern nuclear weapons.

But back in the 1960s, the US was still exploring alternatives to traditional uranium-fueled reactors, and one group in particular, at the Oak Ridge National Laboratory in the US state of Tennessee, got to work on a peculiar project: a so-called Molten Salt Reactor.

Back then, molten salt reactors were mostly known in the US government as a by-product of an embarrassing, decade-and-a-half-long attempt to build a nuclear-powered bomber aircraft. Oak Ridge had been responsible for building the reactor for the bomber, but their issues with building a reactor in the conventional style had led the laboratory to investigate other methods of nuclear power generation. At the time, the rapid expansion of nuclear power and the relative lack of naturally occurring uranium around the world had led many within the energy world to fear that uranium would eventually run out, even as, back in those days, much of the world believed that nuclear energy would be so cheap and abundant that it would practically be free to use.

Via their molten salt reactor, Oak Ridge was able to use the far more abundant thorium to derive uranium-233, and that, in turn, went back into the reactor to fuel it. By 1969, their thorium reactor was running at full power, and it would spend over 13,000 hours generating energy over the course of the experiment. In one documentary produced about the reactor decades later, nuclear scientist Kirk Sorensen would claim that if the US had continued working with the reactor and taking advantage of the technological gains that came with it, then America might have gone fully energy-independent by the year 2000.

But alas, it wasn’t to be. The reactor was plagued with technical issues, and its handlers couldn’t get it to produce nearly as much power as they’d initially hoped. Shutdowns were common, the electrical system was unable to handle the reactor—all told, it was underwhelming.

But that, alone, isn’t enough to outweigh the potential benefits of continuing the experiment and figuring out how to use a thorium reactor—and indeed, that isn’t what doomed the thing. Instead, the starry-eyed optimism around uranium reactors, and new realizations about uranium’s abundance, were enough to help leading atomic scientists decide that their more developed, uranium-based technology was the way of the future. The uranium fuel cycle was proven, the reactors were already way ahead of where thorium reactors had been at the time, and the clear safety benefits of the thorium reactors were deemed not quite important enough to continue their development.

Finally, the death of the thorium reactor was a product of its time—a time when words like “nonproliferation” could get a person laughed out of a meeting, and when the plutonium produced as part of the uranium fuel cycle was considered absolutely vital, to build more nuclear bombs. Thorium reactors wouldn’t just fail to produce anything that could go boom; their widespread adoption risked compromising the nuclear weapons supply chain. France would be the only other nation to seriously attempt a thorium reactor in the 20th century, and while their attempt, the Superphenix, would operate for over a decade, it was hamstrung by a long series of accidents and technical barriers.

Now, though, in the twenty-first century, thorium is back on the table—and in fact, it’s fast becoming an international sprint to the finish line.

Substantial Advantages

We’ve run through the basic list of positives related to thorium-reactor technology, but now, it’s time we dig into the details, where the most obvious asset of thorium over uranium, is its abundance. According to the International Atomic Energy Agency, some 6.2 million metric tons of the stuff is estimated to be hiding under the Earth’s crust. That’s about triple the estimated global reserves of uranium, making it roughly as abundant as lead.

It’s also far easier to get your hands on, with thorium ore, also known as monazite, typically containing significant amounts of thorium that can then be purified. It’s significantly safer and easier to physically mine than uranium, since thorium mining can take place in open pits.

And just as it’s safer to mine, it’s safer to use in reactors. In fact, thorium reactors, at least as the world currently understands them, cannot suffer a meltdown comparable to what a conventional nuclear power plant might experience. No Chernobyl; no Fukushima; no Three Mile Island. The reactors are built in a way where they can be easily drained of their fuel in case of emergency, and they cannot maintain nuclear reactions after powered mechanisms to stimulate the reaction are no longer functioning. Nor do thorium reactors require any complex lists of input materials; thorium is all they need, once the reaction is initiated. As a fertile isotope, thorium makes everything else that’s required to fuel the reactor—and it produces more fissile material than it consumes, meaning that no fissile material has to be introduced from outside, to sustain the reaction once it starts. Thorium doesn’t have to be enriched; its natural isotope is perfectly capable of producing uranium-233. And according to a Nobel laureate working with the European Organization for Nuclear Research or CERN, thorium is so efficient that it provides about two hundred times the yield of energy, for the same amount of substance as uranium. If that figure isn’t impressive enough, then fear not; thorium’s kilo-for-kilo power yield ratio, compared with coal, is one to three and a half million.

Also on the list of problems that thorium can solve, is that of nuclear waste. Thorium reactors are estimated to produce somewhere between one percent, and point-one percent of the nuclear waste that a uranium-fuel cycle reactor would—while, again, granting a yield of about 200 times as much energy in the process. The waste that it does produce, is more stable from the moment it’s generated—and it’s not as radioactive, either.

It’ll take only a few hundred years at most, for the radiation emitting from those sources to drop to safe enough levels that humans can get close to them—as opposed to tens of thousands of years, for the nuclear waste we produce today. Some thorium proponents suggest that by-products could drop to safe radiation levels after just a couple of decades, or maybe even faster.

And finally, thorium reactors have little, if any potential to create byproducts that would be functionally useful in a nuclear weapon. Thorium itself is useless inside a bomb unless it’s quite literally dropped on somebody’s head. Uranium-233 is fissile, and thus, can be used to create a nuclear weapon, but it’s an impractical way to create a bomb even under the best conditions. Thorium reactors do produce some plutonium as a by-product, but only a small fraction of what conventional uranium reactors produce, and even the plutonium that does come out, is woefully unsuitable for use in a bomb. In fact, thorium might even turn out to be a way to get rid of some of the plutonium waste that humanity already has. That same plutonium is useful in starting a thorium reaction, so although thorium reactors aren’t a way to burn up all the excess plutonium the world has, it can at least put a dent in the pile overall. Other by-products of uranium-233 that could technically be used to build a bomb, are a poor choice to do so; they give off gamma rays that make them easily traced and tracked, as well as posing a risk to their handlers.

Make no mistake; thorium reactors, like every other emerging technology, certainly have their naysayers. But the arguments against thorium, have much more to do with start-up costs and minor trade-offs than any major barriers to widespread adoption. As its detractors often point out, the thorium fuel cycle will require major investment and research before it can be harnessed via modern technology. There is no guarantee of a payoff at the end of all that research, and past attempts to build thorium reactors have been beset by a wide variety of issues. Getting thorium ready for reactor use does cost more than conventional uranium preparation, at least right now while technologies are still emerging and production lines aren’t yet built. It’s pulled from monazite ore that’s also used as a source of rare-Earth elements, demanding changes to current mining practices to prioritize thorium extraction and retention. The heat required to melt thorium oxide and make a thorium fuel poses a challenge, when designing the equipment to bring it to that temperature. And one of the byproducts of thorium reactors, the unstable isotope uranium-232, does emit gamma rays, requiring a different set of measures and mechanisms to keep a reactor’s human operators from harm. But each of these barriers is far outweighed by the potential benefits—and much of the world seems to know it.

A Coming Energy Revolution?

The nation that’s put the most into thorium reactors across history isn’t the USA, or Russia, or China, but India, a nation where uranium is scarce, but where the largest thorium supply in the world lurks just underneath its citizens’ feet. India kept up research into thorium reactors long after the rest of the world passed it by, and that work has now paid off. Development and testing of promising thorium-reactor technology has been ingoing there for over a decade, although plans to build and finish a full-scale thorium reactor have yet to be realized.

India is pushing hard to achieve large-scale power production via thorium over the course of the next two decades or so, and hopes to cover a large proportion of its electricity needs via thorium, not long after. India’s leaders, both past and present, recognize that their nation is ideally suited to be a leader on thorium-derived nuclear energy, and it’s been enshrined in India’s civilian nuclear program since the founding father of that program, a physicist named Homi Bhabha, made it a top priority over half a century ago. The country’s push for thorium hasn’t always been fruitful; part of the reason that progress has been so slow, is that India has refused to sign the Nuclear Non-Proliferation Treaty and was thus iced out of global resource pools that might otherwise have resolved its thorium problems by now.

But in 2024, its Prototype Fast Breeder Reactor was finally completed, and it’s expected to go operational by the end of the year.

And just across a frigid Himalayan border, the nation of China is well on its way to matching, if not outpacing India within a few short years. China has been working toward a thorium reactor since at least 2011, and like India, China has undertaken the work almost entirely by itself. China, however, had the luxury of doing so by choice.

The same laboratory that built a molten salt reactor back in the 1960s, Oak Ridge, has since become one of the few foreign scientific entities to partner with China on that mission. At the time of writing, China has multiple thorium-fuel-cycle reactors in construction out in the Gobi Desert, and just this year, 2024, China confirmed that one of those reactors will start operating in 2025. That pilot plant will produce only about two megawatts of electricity when fully operational, but because of the broader robustness of China’s nuclear industry, the act of building a working thorium reactor will probably be more challenging than simply proliferating them later on.

China hopes to eventually build numerous thorium plants across its deserts, and spread them to dozens of nations involved with its Belt and Road Initiative across the globe.

In the United States, after some early whispers of collaboration with China in the 2010s, the drive to build a thorium reactor is still flagging. The idea picked up early traction in the US Congress, even before 2010, and in 2020, the US Department of Energy began an initiative to bring two prototype next-generation reactors online, with the door wide open to making an attempt at thorium. In 2022, however, Congress introduced a bill entitled the Thorium Energy Security Act, calling for the US to invest in the procurement of uranium-233 with the goal of building a national stockpile, and eliminating any potential future dependency on other nations for the stuff. Although that particular bill never made it to a floor vote before either house of Congress, a later bill, signed in 2024, put aside healthy sums of money to gather uranium-233 and called for the development of fuels for use in, “future molten salt and high-temperature gas reactor designs.”

Across the rest of the world, Denmark stands out as a leader on thorium energy, with the company Copenhagen Atomics announcing in 2024 that its molten salt reactor, the Waste Burner, is finally ready for a real-life attempt to reach criticality. The Waste Burner is a small reactor, meant to be packed up and transported in a shipping container if need be, and it uses plutonium derived from spent nuclear fuel to activate and begin the reaction process with fertile stores of thorium. The Waste Burner is expected to come online for the first time in Switzerland, in 2026.

Elsewhere, Canada has made some progress toward a thorium reactor, Israel and Japan had both shown some interest, and one South African company is working overtime to design a thorium reactor that could alleviate the country’s serious energy problems. Indonesia and Norway have each demonstrated some willingness for research and development, too.

As the race to a commercial thorium reactor really kicks off in the next few years, the nations involved are sure to find reasons to engage in friendly, or sometimes, quite-unfriendly competition. But just like the thorium fuel cycle offers myriad advantages over conventional nuclear power, a thorium technology race promises to be a whole lot less intense than some of the other resource-based competitions around the world. A big part of the reason why, has to do with resource availability. According to the World Nuclear Association, India has the world’s largest set of thorium reserves, estimated at about 850,000 metric tonnes; next is Brazil, 632,000 metric tonnes; then Australia and the US, each barely below 600,000 metric tonnes. Egypt, Turkey, Venezuela, Canada, Russia, South Africa, and China are all believed to have 100,000 metric tonnes of reserves or more, and often, much more. Unlike, say, cobalt, an incredibly important substance that the world depends largely on the Democratic Republic of the Congo to mine, thorium is available in major reserves across many world nations—but even more important, it’s available on both sides of stark geopolitical gaps that only seem to be getting more extreme. Russia, China, and the US all have substantial reserves of their own; India and Brazil are likely to be very pleased to sell some of their thorium to Russia and China to make up for America’s head start; Turkey, along with the Scandinavian nations, can combine to yield 600,000 tons of the stuff or more for the European nations of NATO; Venezuela will be more than happy to sell to Russia; and Egypt, likewise to China. Whatever the race to thorium power looks like, it won’t look like the current fight over rare-Earth elements, by example, where one major power, China, controls much of the market.

Nor is thorium an area where scarcity is likely to be an issue. At its current levels of power consumption, the United States, by example, is expected to have enough thorium in the ground to power it for the next 1,000 years—after which time, it’s true, America would need to explore other options. So would other world nations, in the year 3024, be having intense conversations about what to do when the thorium runs out—if, that is, they were still dependent on thorium at all. But that’s highly unlikely to be the case, because the thing about the thorium fuel cycle, is that it’s best understood as a bridge technology. Truly next-generation sustainable energy resources—namely, nuclear fusion—aren’t expected to yield substantial energy production until around 2050, and more conservative estimates can fall back to 2060 or even 2070. But let’s be really pessimistic for a moment, and say that fusion won’t be scaled up to that level for another century, until the 2120s. Even then, the US, assuming it maintains its level of energy consumption, will have burned through just ten percent of the thorium it already knows about. The same is true for the world’s thorium reserves, which are, in aggregate, enough to power several centuries of better, more sustainable, more peaceful nuclear energy before the next energy revolution inevitably arrives for the generations that come after ours.

Make no mistake; the road to mass adoption of the thorium fuel cycle will be a bumpy one. The technologies involved will still need to mature, and policymakers the world over will need to choose thorium to complement, or even replace, more time-tested renewable and conventional energy sources. The thorium-fuel-cycle industry, as it emerges, will have to sustain withering attacks from fossil fuel corporations, conventional nuclear power advocates, and more. And while the multilateral technology race may not be quite so bitter as some of the other ones the world is currently fighting—it certainly won’t be easy, for anybody involved.

But the payoff waiting at the end, is one of those potential futures that seems almost too good to be true—except with the distinct advantage of actually being true. As far as humanity can tell, the thorium fuel cycle does work, it does have concrete promise and potential to meet specific technical thresholds, and if the world can figure it out, then the contentious, and often painful slog to fully renewable energy can get a hell of a lot easier.

Key Takeaways

• Thorium reactors offer a safer alternative to traditional nuclear power, with no risk of meltdowns like Chernobyl or Fukushima.
• Thorium is more abundant and easier to mine than uranium, making it a more accessible fuel source.
• Thorium reactors produce significantly less radioactive waste, which decays faster than waste from uranium reactors.
• The thorium fuel cycle is seen as a bridge technology to nuclear fusion, providing sustainable energy for centuries.
• Multiple countries, including India, China, and Denmark, are actively developing thorium reactor technology.

Sources

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• Hero image source by IAEA Imagebank / openverse, by.

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