Thorium, a potential source of energy for the future

Thorium is used to strengthen magnesium and cover the tungsten wire in electric devices.  It is also used to manufacture camera lenses and scientific instruments, heat-resistant ceramics, airplane engines and lightbulbs.

In the search for clean and sustainable energy sources, thorium is an alternative to uranium as a nuclear fuel. It could help overcome some of the challenges presented by traditional nuclear generation of electricity.

Thorium, which is listed on the periodic table of the elements with symbol Th and atomic number 90, was discovered by Swedish chemist Jöns Jakob Berzelius, who named it after the Nordic god Thor. In 1828 it was isolated for the first time, and years later the physicist spouses Pierre and Marie Curie discovered its radioactivity.

This element, belonging to the actinide series, can be found in small amounts in most rocks and grounds, in minerals such as monazite, thorite and thorianite. It is approximately three times more abundant than uranium. In its pure state, it is a soft silver-white metal which turns black as it gradually oxidizes.

It is estimated that there are around 12 million tons of thorium in the world. India has the greatest registered thorium deposits on its Southern and Eastern coasts. There are also significant deposits in countries like Australia, Brazil, Canada, the United States, Greenland, Norway, Russia, South Africa and Venezuela.

Advantages of thorium as a nuclear fuel

• Greater abundance

Thorium is significantly more abundant in the Earth's crust than uranium, the main fuel used in most nuclear reactors. This makes thorium much more adequate for long-term energy sustainability.

• Greater output

Practically all the thorium that is extracted may be used in a reactor. In uranium, however, only its U-235 isotope - which represents just 0.7% of natural uranium- is usable in current reactors.

• Less radioactive waste

To use thorium as an energy source, the Th-232 isotope must be converted into U-233. This conversion can be done in specific reactors such as the fast and subcritical models. These reactors can produce less plutonium and transuranic elements in comparison to conventional uranium reactors. This way waste management is simplified and radioactive material management is reduced.

• Prevention of nuclear proliferation

The uranium-233 produced during the thorium fuel cycle contains uranium-232, which produces intense gamma radiation when it breaks down. For this reason it is not suitable for military use. This characteristic adds a safety layer against nuclear proliferation.

Molten salt reactors

As fuel, thorium is especially suitable for Molten Salt Reactors (MSR).  MSRs use a mix of liquid thorium fuel and fluoride salts, which facilitates efficient heat transfer and improves safety mechanisms. The liquid form of the fuel allows for continuous processing, eliminating fission byproducts in real time and preventing fuel overheating. This design minimizes fusion risks from the nucleus.

Challenges, obstacles and research

Although thorium offers many promising advantages, there are certain barriers that must be overcome before its general deployment. Research is necessary in order to develop efficient methods to turn thorium into usable fuel, as well as to optimize reactor designs and fuel processing technologies. Moreover, the economic viability of thorium-based reactors must be fully assessed. The main challenges are the costs.

• Extraction costs:

The mineral known as monazite is one of the greatest sources of rare earth elements and thorium. If it was not for the current demand of rare earth elements, monazite would not be extracted and its thorium contents would not be used. Since Thorium is a byproduct, its extraction requires methods that are more expensive than those of uranium extraction. This situation could change if there was a demand of thorium and its application in nuclear electric energy.

• Research costs:

The costs of research, development and testing related to the nuclear sites that use thorium are also high, due to lack of experience. For many years, uranium has been the traditional fuel in nuclear power.

Current developments and future perspectives

Several countries, including India, China and the United States, have invested in thorium-based research and development programs. India's Advanced Heavy Water Reactor (AHWR) Project is dedicated to demonstrating the viability of thorium-based fuel cycles. China is also looking into thorium, as is shown by its interest in MSR technology. While these initiatives are very interesting, the generalized use of thorium-based reactors is still in its experimental and developmental stage.

 

Sources: IAEA, World-nuclear.org