Thorium - the future of nuclear energy?

Vyom Sharma

Nuclear power is viewed as the future of sustainable energy for the planet, due to its tremendous energy density and reliability, providing a consistent and steady supply of energy. In contrast, renewable sources like wind and solar power are less reliable, and can only generate electricity in certain conditions. However, the big issue with nuclear power is radioactive waste, which continues to emit harmful radiation for thousands of years after its formation.
Traditional nuclear fuels like uranium-235 and plutonium-239 produce radioactive waste that remains hazardous for tens of thousands of years. Managing and storing this waste safely has been a long-standing issue for governments and energy providers worldwide.
In 1996, a potential breakthrough came with the development of a new type of nuclear reactor in Kalpakkam, India. This reactor used thorium-232 as its fuel instead of the usual uranium or plutonium isotopes. Thorium could prove to be a game-changer for the future of nuclear power, as thorium-232 is far more abundant in nature. About 99.98% of natural thorium exists as this specific isotope, while uranium-235 makes up only about 0.7% of natural uranium. This means that the huge monetary investment of building an enrichment facility is not needed, money which could build more thorium reactors and help the UK achieve its goal of reaching net zero by 2050.

But what exactly is the future of thorium reactors, and how do they work?

The idea behind using thorium as a nuclear fuel is to avoid a potential shortage of uranium and to find safer, cleaner alternatives to uranium. Thorium itself is not fissile (able to undergo nuclear fission). However, it is possible to add a neutron to create thorium-233, which then naturally undergoes two sequential beta decays, eventually becoming uranium-233, which is fissile and suitable for use in reactors. The transformation from thorium-232 to uranium-233 takes approximately 27 days. In this context, thorium is referred to as a “fertile” fuel,meaning it can be converted into fissile fuels through a nuclear process, often inside what's known as a breeding reactor. These reactors are specially designed to create more fissile fuel than they consume.

Advantages of Thorium reactors over traditional nuclear reactors/other fertile fuels.

This leads to the question: why thorium and not something else? Uranium-238, another fertile material, can also be converted into plutonium-239, which is commonly used in reactors. However, thorium has several advantages. It has a higher likelihood of being converted into a usable fissile isotope compared to uranium-238, which doesn't convert as efficiently. This means a greater proportion of thorium can be used as nuclear fuel, resulting in better fuel efficiency.
Thorium is also significantly more abundant than uranium, with estimates suggesting it is about three times more common in the Earth’s crust. This is largely due to thorium’s much longer half-life—about 14 billion years compared to uranium’s 4.5 billion. Because of this, thorium has remained more available in nature. Despite these differences, the energy released by one nucleus of uranium-233 (produced from thorium) is nearly identical to that released by uranium-235: about 200 million electron volts (MeV), which makes thorium a viable alternative in terms of energy output.
The main problem surrounding nuclear power is the huge amounts of nuclear waste it produces . This is partly due to uranium-235 or plutonium-239 isotopes absorbing a neutron (in a reactor core) without the nucleus dividing/undergoing fission. This is how transuranic elements (elements heavier than uranium) are formed, and these are usually highly radioactive and difficult to manage. This means that heavier isotopes are formed when neutrons continue to be fired at them, and these become increasingly radioactive and have long half-lives. With uranium-235, approximately 1/6 of nuclei absorb the neutron rather than undergoing fission, and for uranium-233 this occurs for approximately 1/8 of nuclei, which shows a huge benefit of using thorium (uranium-233 is formed via decay of thorium). Furthermore, the radioactive waste produced in thorium reactors decays to safe levels within 300-500 years, while the waste produced by uranium/plutonium can remain dangerously radioactive for tens of thousands of years. The products from the decay of thorium fuel are less suited for use in weapons production, as they are often contaminated by a highly radioactive element, meaning that the threat of thorium secretly being used in nuclear weapons.
Safety is another important benefit of thorium-based nuclear energy. Traditional uranium reactors use solid fuel rods that must be kept cool using large pools of water. If this cooling system fails, the rods can overheat and potentially melt down, releasing dangerous levels of radiation into the environment (as happened in the tragedies of Fukushima and Chernobyl). Thorium, on the other hand, can be used in molten salt reactors (MSRs). In these reactors, the fuel is mixed with a molten salt that acts as both fuel carrier and coolant. Since the molten salt is already in liquid form and operates at lower pressures, it reduces the risk of explosions or meltdowns. It also removes the need for large bodies of water, meaning thorium reactors can be built in remote or dry areas where traditional reactors wouldn’t be viable.

Drawbacks of thorium

One issue is the lack of research and design so far – much more development is required until thorium can be widely implemented into nuclear reactors around the world.
Furthermore, certain countries such as India, Brazil, Australia and the USA hold a majority of the world’s thorium, meaning that it may not be as accessible to poorer countries without exportation of thorium on shipping vessels, which would not only cost huge sums of money, but would also be detriment the environment, effectively defeating the point of using clean energy in the first place.
Another issue with thorium reactors is that Uranium-232 is also produced in unwanted side reactions during the breeding process of thorium,such as when a uranium-233 nucleus is hit by a fast neutron,causing the uranium-233 to jump to an excited state which leads it to lose two neutrons, leaving uranium-232. Uranium-232 is hard to handle, however it also makes the entire mixture of waste much harder to use in nuclear weaponry as it is very easy to detect (gamma radiation is very penetrating and has a long range) and is difficult to use in bombs without extreme shielding.

Future of thorium?

Thorium power has a lot of potential for the world of sustainable energy, solving many of the previous issues with nuclear power and offering a cleaner and more versatile fuel source. However, the likelihood of thorium power being introduced around the world is low, due to the huge research and design costs to convert the existing experimental reactors into functioning energy infrastructure, as well as the hundreds of years of uranium reserves the earth still has means world governments are unlikely to pool millions in funding towards this technology, where they could instead invest that money into building/upgrading tried and tested energy infrastructure.