Thorium 

Thorium is a naturally occurring radioactive metal belonging to the actinide series of elements, symbolised as Th with atomic number 90. It is a silvery-white, malleable, and ductile metal that tarnishes slowly when exposed to air, forming thorium dioxide. Named after the Norse god Thor, thorium is found in small quantities within most rocks and soils, typically at concentrations of about 6 to 10 parts per million, which makes it more abundant than uranium. Its unique physical and nuclear properties have attracted scientific, industrial, and economic interest, particularly as a potential alternative energy source.

Background and Discovery

Thorium was discovered in 1828 by the Swedish chemist Jöns Jakob Berzelius, who isolated it from a mineral sample provided by a Norwegian priest. The mineral, later named thorite, contained significant amounts of thorium silicate. During the early 20th century, thorium gained attention for its radioactive properties and became widely used in the manufacture of gas mantles before the discovery of safer materials.
Thorium’s natural isotope, thorium-232, is fertile but not fissile; it cannot sustain a chain reaction by itself but can absorb neutrons to form uranium-233, a fissile isotope. This property gives thorium immense potential as a nuclear fuel in breeder reactors, leading to renewed global interest as nations seek cleaner and more sustainable energy solutions.

Industrial Applications

Thorium’s industrial relevance spans across various sectors, including metallurgy, nuclear technology, and materials science.
1. Nuclear Energy: Thorium is regarded as a promising alternative nuclear fuel due to its abundance, safety, and lower production of long-lived radioactive waste compared to uranium. In a thorium-based fuel cycle, thorium-232 absorbs neutrons and transmutes into uranium-233, which can undergo fission. Several countries, such as India, Norway, and China, have conducted extensive research on thorium reactors, particularly molten salt reactors (MSRs), which offer enhanced safety and efficiency. India’s nuclear energy programme has a well-defined three-stage strategy focused on utilising its vast thorium reserves in the long term.
2. Metallurgy: Thorium is used to improve the high-temperature strength of magnesium, aluminium, and tungsten alloys. These thorium-based alloys exhibit superior creep resistance and mechanical stability under extreme conditions, making them valuable in aerospace applications, such as in jet engines and gas turbines. However, health and environmental concerns over radioactivity have led to reduced industrial use in modern times.
3. Optical and Electronic Devices: Thorium dioxide (ThO₂), also known as thoria, possesses a very high melting point and excellent refractive properties. It was historically employed in the production of high-quality optical lenses and camera components due to its low dispersion and high refractive index. Although newer, non-radioactive materials have replaced it in most applications, some scientific instruments still utilise thoria for specialised optical coatings and cathodes.
4. Catalysis and Chemical Applications: Thorium compounds, particularly thorium oxide, act as efficient catalysts in several industrial chemical reactions. They are used in petroleum cracking, ammonia synthesis, and the production of nitric acid. Thorium-based catalysts are valued for their high thermal stability and resistance to poisoning, contributing to their persistence in niche industrial processes.

Everyday Uses and Decline of Consumer Applications

Historically, thorium had several everyday applications, most notably in gas mantles for portable lanterns and streetlights. When heated, thorium oxide produced an intense white light, making it ideal for illumination before the widespread adoption of electric lighting. However, due to the recognition of thorium’s radioactivity and the availability of safer alternatives, its use in consumer goods has dramatically declined.
In earlier decades, thorium was also employed in certain television tubes, camera lenses, and laboratory equipment, but these uses have been largely discontinued. Modern safety regulations restrict thorium’s use in consumer products to avoid exposure risks, particularly from alpha radiation.

Economic Importance and Global Distribution

Thorium is relatively abundant in the Earth’s crust, estimated to be about three to four times more plentiful than uranium. It occurs mainly in the minerals monazite and thorite. Major thorium reserves are located in India, Australia, the United States, Brazil, and Norway. Among these, India possesses one of the world’s largest reserves, concentrated along its coastal sands.
Economically, thorium’s significance lies in its potential as an energy resource. The transition to a thorium-based nuclear economy could diversify global energy portfolios, reducing dependency on fossil fuels and uranium. Since thorium cannot be directly weaponised and produces less transuranic waste, it presents both economic and strategic advantages for countries seeking secure and sustainable nuclear programmes.
However, commercial deployment of thorium reactors remains limited due to several challenges:

• Lack of established thorium fuel fabrication and reprocessing technology.
• High initial costs of developing thorium-based reactor infrastructure.
• Regulatory hurdles associated with handling radioactive materials.
• Competition from well-established uranium fuel cycles.

Despite these obstacles, the long-term economic potential of thorium remains significant, especially in regions with large untapped deposits and growing energy demands.

Environmental and Safety Considerations

Thorium offers potential environmental advantages over conventional nuclear fuels. The thorium fuel cycle produces less long-lived radioactive waste and lower amounts of plutonium and minor actinides, reducing the long-term hazards associated with nuclear waste storage. Furthermore, thorium reactors can be designed with inherent safety features, such as passive cooling systems and lower risks of meltdown.
Nevertheless, thorium’s radioactivity poses occupational health risks during mining, handling, and processing. Radioactive dust and waste from monazite sand extraction can pose hazards if not managed properly. Stringent safety measures and regulatory oversight are essential to ensure responsible utilisation.

Research and Future Prospects

Ongoing research focuses on developing advanced reactor systems that can fully harness thorium’s potential. These include molten salt reactors (MSRs), accelerator-driven systems (ADS), and high-temperature gas-cooled reactors (HTGRs). Such technologies aim to achieve higher fuel efficiency, enhanced safety, and lower waste production.
India’s Kalpakkam-based prototype fast breeder reactor and China’s thorium molten salt experimental reactor in Gansu province are notable projects demonstrating renewed global interest. International collaborations under agencies such as the International Atomic Energy Agency (IAEA) continue to evaluate thorium’s feasibility for sustainable energy generation.