Thorium Fuel: A Safer Uranium Alternative?

Uranium has been the dominant nuclear fuel for decades, but there is growing interest in using thorium as an alternative. Thorium is more abundant in nature than uranium, and it has several potential advantages as a nuclear fuel, including superior physical and nuclear properties, and reduced nuclear waste production. However, there are also challenges to using thorium as a nuclear fuel, including higher costs of extraction and fuel fabrication, and the need for a separate fissile material to trigger and maintain a chain reaction. While there have been experiments and research into thorium-based nuclear reactors, it is not clear if any country has completely switched from uranium to thorium fuel.

Thorium is more abundant in nature than uranium

Thorium is a naturally-occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder. It is very insoluble, which is why it is plentiful in sands but not in seawater, unlike uranium.

Thorium is a silvery, slightly radioactive metal commonly found in igneous rocks and heavy mineral sands. It was named after Thor, the god of thunder in Norse mythology.

Thorium's greater abundance is one of several potential advantages of a thorium fuel cycle over a uranium fuel cycle. Other advantages include superior physical and nuclear properties, reduced plutonium and actinide production, and better resistance to nuclear weapons proliferation when used in a traditional light-water reactor.

Thorium's greater abundance is also often cited as a key benefit of using it as a fuel. However, one source notes that if closed fuel cycles or breeding ever become mainstream, this benefit will be irrelevant because both the thorium-uranium and uranium-plutonium fuel cycles will last well into the tens of thousands of years.

Thorium is harder to weaponize

Uranium-233, the isotope that results from the nuclear fission of thorium, can be used in a nuclear weapon. However, the process of creating U-233 also creates U-232, which is intensely radioactive and emits gamma rays. This makes U-233 difficult to handle and necessitates careful shielding and attention. Separating U-232 from U-233 is possible but requires the same facilities needed to enrich U-235. Due to these challenges, U-233 has been considered less useful than U-235 or Pu-239 for weaponization.

Thorium itself is not fissile and cannot be used directly in a thermal neutron reactor. It is classified as a "fertile" material, meaning it requires a separate fissile material like uranium or plutonium to initiate and sustain a nuclear chain reaction. This adds complexity to the fuel fabrication process.

Additionally, thorium-based fuels produce hard gamma emissions, which can damage electronics and limit their use in bombs. The presence of U-232 in spent thorium fuel further complicates weaponization efforts as it creates strong gamma radiation, making handling difficult and detection easier.

In summary, while not impossible, weaponizing thorium and its by-products is challenging due to the presence of radioactive isotopes, the need for specialized facilities, and the handling difficulties they pose. These factors contribute to thorium's reputation as a fuel with low weaponization potential.

Thorium reactors produce less nuclear waste

Thorium is a fertile material that can be used as nuclear fuel. It is not fissile and therefore cannot be used to generate power on its own. However, when irradiated, thorium-232 (the only naturally occurring isotope of thorium) can be converted into uranium-233, which is fissile and can be used as nuclear fuel.

Thorium-fuelled reactors could be much more environmentally friendly than their uranium counterparts. In addition to the fact that nuclear power does not emit greenhouse gases, thorium reactors also produce less long-lived nuclear waste than uranium-fuelled reactors. The radioactivity of the waste produced in thorium reactors drops to safe levels after just a few hundred years, compared to tens of thousands of years needed for current nuclear waste to cool off.

However, there are some challenges to using thorium as a fuel. The extraction of thorium is currently expensive, and the research, development, and testing of thorium-powered nuclear installations are costly due to a lack of experience with the material. Additionally, being a fertile and not a fissile material, thorium requires a "driver" such as uranium or plutonium to trigger and maintain a chain reaction.

Despite these challenges, thorium has the potential to be a more abundant and efficient substitute for uranium, the dominant nuclear fuel.

Thorium is more efficient to mine

Thorium is safer and more efficient to mine than uranium, making it more environmentally friendly. The percentage of thorium found in its ore is generally greater than the percentage of uranium found in its ore, making it more cost-efficient. Thorium mines have an open pit, which does not require ventilation, whereas uranium mines are closed off and can reach potentially dangerous radon levels.

Thorium is about three to four times more abundant than uranium in the Earth's crust. It is found in small amounts in most rocks and soils. Soil contains an average of around 6 parts per million (ppm) of thorium. It is very insoluble, which is why it is plentiful in sands but not in seawater, unlike uranium.

The most common source of thorium is the rare earth phosphate mineral, monazite, which contains up to about 12% thorium phosphate, but 6-7% on average. Thorium recovery from monazite usually involves leaching with sodium hydroxide at 140°C, followed by a complex process to precipitate pure ThO2. Thorite (ThSiO4) is another common thorium mineral. A large vein deposit of thorium and rare earth metals is found in Idaho.

Thorium is a naturally occurring, slightly radioactive metal discovered in 1828 by the Swedish chemist Jons Jakob Berzelius, who named it after Thor, the Norse god of thunder. When pure, thorium is a silvery-white metal that retains its lustre for several months. However, when contaminated with oxide, thorium slowly tarnishes in the air, turning grey and eventually black. When heated, thorium metal ignites and burns brilliantly with a white light.

Thorium is safer to use

Less radioactive waste

Thorium-fuelled reactors produce less high-level nuclear waste than Uranium-fuelled ones. The radioactivity of the waste from a Thorium reactor also drops to safe levels after just one or a few hundred years, compared to Uranium waste, which needs tens of thousands of years to cool off.

Less weapons-grade plutonium

Thorium reactors produce plutonium at much lower levels than Uranium reactors, and this plutonium is also harder to use in nuclear weapons. Uranium-233, the fissile material produced in Thorium reactors, is contaminated with Uranium-232, which is a strong gamma-ray emitter. This makes Uranium-233 extremely difficult to handle and easy to detect.

Less proliferation risk

Thorium-based power reactor fuels would be a poor source of fissile material for illicit use in explosive devices. The gamma radiation field created by the presence of Uranium-232 and its decay products creates significant handling problems and boosts detectability.

Less mining danger

Thorium's ore, monazite, generally contains higher concentrations of Thorium than the percentage of Uranium found in its respective ore. This makes Thorium a more cost-efficient and less environmentally damaging fuel source. Thorium mining is also easier and less dangerous than Uranium mining, as Thorium mines are open pits, whereas Uranium mines are often underground, where radon levels can be harmful.

Failsafe measures

Liquid Fluoride Thorium Reactors (LFTRs) are designed to be meltdown-proof. In the event of a power failure or if temperatures exceed a set limit, a fusible plug at the bottom of the reactor melts, draining the fuel into an underground tank for safe storage.

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