Thorium is a mildly radioactive metal with a handful of practical uses, the most significant being its potential as nuclear fuel. It also shows up in welding electrodes, vintage camera lenses, and gas lantern mantles. Three to four times more abundant than uranium in the Earth’s crust, thorium has long attracted interest as a more sustainable energy source, and recent breakthroughs in China have brought that closer to reality.
Nuclear Fuel
Thorium’s biggest potential use is generating electricity in nuclear reactors. It doesn’t split (fission) on its own the way uranium-235 does. Instead, thorium-232 absorbs a neutron inside a reactor and gradually converts into uranium-233, which is fissile. This extra step has historically made thorium harder to use, but it also comes with real advantages: the fuel cycle produces less long-lived nuclear waste, achieves higher burn-up (meaning more of the fuel actually gets used), and is more resistant to nuclear weapons proliferation than conventional uranium fuel. Thorium also has a higher melting point and better thermal conductivity than uranium, which gives reactor designers more safety margin.
For decades, thorium reactors existed mostly on paper or in small experiments. That changed in October 2024, when China’s experimental molten salt reactor, TMSR-LF1, became the first reactor in the world to successfully add thorium to a working molten salt system and convert it into usable uranium fuel. Located in Wuwei, Gansu Province, the 2-megawatt thermal reactor first achieved a sustained chain reaction in October 2023 and has been continuously generating heat through fission since then. China’s next goal is a 100-megawatt demonstration reactor by 2035.
India has also pursued thorium energy for decades, motivated by its large domestic thorium reserves and limited uranium supply. India’s long-term nuclear strategy includes a three-stage power program designed to eventually run on thorium fuel.
Gas Lantern Mantles
Before thorium was a nuclear fuel candidate, it was a lighting material. In the late 1800s, manufacturers discovered that fabric mantles soaked in thorium and cerium compounds would glow brilliant white when heated by a gas flame. When the mantle is first burned, the thorium and cerium convert to their oxide forms, and these oxides emit intense visible light at the high temperatures inside a gas lantern. Thoriated gas mantles were the dominant lighting technology before electric bulbs took over, and you can still buy them today for camping lanterns. The thorium content makes these mantles mildly radioactive, though the dose from normal use is extremely small.
Welding Electrodes
Thorium is widely used in tungsten inert gas (TIG) welding. Welding rods made of tungsten are often alloyed with 1 to 2 percent thorium oxide by weight. Adding this small amount of thorium improves arc stability, makes the electrode easier to strike, and helps it last longer under the intense heat of the welding arc. These “thoriated tungsten” electrodes have been an industry standard for decades, particularly for precision welding of stainless steel and other metals. Because grinding the electrodes can release radioactive dust, some shops have shifted to alternatives made with cerium or lanthanum oxide, though thoriated rods remain popular due to their reliable performance.
High-Quality Camera Lenses
From the 1940s through the 1970s, optical glass manufacturers added thorium oxide to camera lenses. The reason comes down to how glass bends light. Lens designers want glass with a high refractive index, which bends light more sharply and allows the lens to be made thinner and lighter. The problem is that high-refractive-index glass usually also has high dispersion, meaning it splits white light into its component colors and introduces chromatic aberration. Thorium oxide solves this tradeoff: it pushes the refractive index above 1.6 while keeping dispersion low. Some lens formulations contained up to 28% thorium oxide.
Companies like Canon, Pentax, and Kodak produced thoriated lenses during this era. These lenses are prized by vintage photography collectors today, though they’re known for developing a yellowish tint over time due to radiation damage to the glass. Manufacturers eventually replaced thorium with lanthanum oxide and other rare-earth compounds that achieve similar optical properties without the radioactivity.
Why Thorium Keeps Getting Attention
The core appeal of thorium is simple: there’s a lot of it. Thorium is three to four times more abundant than uranium in the Earth’s crust, found in mineral sands and granite deposits on every continent. Countries like India, Brazil, Australia, and the United States hold large reserves. Unlike uranium, thorium doesn’t require expensive enrichment before it can enter a reactor fuel cycle.
The waste profile is also better. Thorium fuel cycles produce far less plutonium and fewer of the long-lived radioactive isotopes that make spent uranium fuel dangerous for tens of thousands of years. The reactor designs being developed for thorium, particularly molten salt reactors, also operate at lower pressures than conventional water-cooled reactors, which reduces the risk of the kind of pressure-driven accidents that have defined nuclear disaster scenarios.
The tradeoff is that the technology is still in its early stages. No commercial thorium power plant exists yet, and the fuel cycle requires reprocessing steps that haven’t been proven at industrial scale. China’s successful demonstration is a milestone, but scaling from a 2-megawatt experiment to grid-level power generation will take years of engineering work. For now, thorium’s everyday uses remain limited to niche industrial applications, while its biggest promise sits on the horizon.