Thorium - The Key to the Future of Nuclear Energy

It is a popular belief that the world supply of uranium is sufficient to support the deployment of nuclear energy systems indefinitely, but this is not the case. If our usage of uranium remains as it is today, our supply will run out by the end of this century. And demand is not likely to remain what it is today.

The majority of the energy users in the 21st century are expected to be developing countries and other emerging users. As their energy demands grow, our current systems for generating and deploying nuclear energy will not be sustainable. A system that supplements uranium with thorium may prove essential for achieving sustainable global development in this century.

Thorium Is the Key To The Future of Nuclear Energy

Using thorium to supplement traditional uranium fuel has many advantages over the current approach of relying on uranium only.

•     Thorium fuel is more efficient and sustainable.
•     Thorium is more proliferation-resistant.
•     Thorium-based systems are more environmentally responsible.
•     Thorium-based systems allow for many applications.
•     Thorium-based systems can potentially be more economical.

For a more detailed explanation of the drawbacks of relying only on uranium, see Current Uranium Fuel Cycles. An article on the advantages of the thorium-based system can also be found on IAEA Bulletin.

Thorium Fuel is Efficient and Sustainable

Thorium, like uranium and plutonium, can be used as fuel in a nuclear reactor. Like U-238, Th-232 is not fissile and therefore cannot be used directly to sustain a fission reaction. However, both U-238 and Th-232 will absorb neutrons to produce fissile material.

A fission reaction initiated by U-235 is used to irradiate U-238 and Th-232 in order to generate new fissile material: Pu-239 and U-233. This method increases the amount of available fissile material by several hundred times, and makes nuclear energy almost as "renewable" as solar energy, with the added advantage of being more practical to deploy on a large scale.

Thorium is More Proliferation-Resistant

Proliferation is a major concern with the current generation of uranium-based nuclear energy systems. This is because plutonium (Pu-239), which can be obtained from uranium-based spent fuel, is the primary isotope used for the production of nuclear weapons. Thorium is an excellent supplementary or alternative fuel for these reasons:

- Thorium-based fuel cycles do not produce plutonium, and they produce many fewer minor actinides than do uranium-based fuel cycles. Plutonium and the minor actinides are responsible for the bulk of the radio-toxicity and heat generation of spent fuel in the hundreds-to-thousands years period.
- Some thorium-based reactors can facilitate the reduction of plutonium and other transuranic elements, and some even “consume” plutonium. This offers a practical and economical method for disposing of potential weapon materials.
- Some thorium-based reactors can be designed to “recycle” U-233 internally, eliminating the proliferation risk associated with removing it from the plant-site for reprocessing.

Although the U-233 produced by thorium fuel is theoretically a potential weapon material, a small admixture of U-232 invariably accompanies its production. The radioactive decay chain of U-232 contains a powerful emitter of a highly penetrating gamma ray. This gamma ray can be detected easily, so a weapon containing U-233 would be very difficult to conceal. Moreover, no weapon based on U-233 currently exists. Under the current testing moratorium, successful development of new weapon technology based on U-233 cannot be validated prior its real use. This makes U-233 much less attractive as a weapon material than plutonium.

Thorium-Based Systems Are More Environmentally Responsible

Many people are concerned about the environmental impact of nuclear energy systems. Systems supplemented with or based on thorium fuel have several advantages over uranium-based systems in terms of environmental responsibility.

- Thorium-based systems produce less high-level spent fuel per unit of energy generated than uranium-based systems. This spent fuel also has a much shorter half-life.
- Breeding U-233 from Th-232 is more efficient than breeding Pu-239 from U-238, and produces fewer minor actinides, or long-lived non-fissile isotopes.
- Long-term disposal is easier because less spent fuel is produced per unit of energy generated, as well as fewer minor actinides.
- The melting point of thorium dioxide is about 500 ºC higher than that of uranium dioxide. This high melting point is an added margin of safety in the event of a temporary power surge or loss of coolant in a reactor.

Thorium-Based Systems Have Many Applications

Thorium fuel has better thermal and physical properties than uranium fuel, as well as better irradiation performance. It is therefore an excellent fuel option for nuclear energy systems in general, and for those operating with higher temperatures in particular. Higher temperature operation makes possible many applications other than generating electricity.
In addition, the gamma rays produced by the U-232 that accompany the production of U-233 can potentially be used in many innovative applications, such as

 - sterilizing medical equipment
 - irradiating food
 - in radiation-therapy equipment
 - in medical diagnostic equipment

This flexibility in applications makes nuclear systems that use thorium relevant to the needs of emerging energy users, especially those in developing countries.

Thorium Fuel Can Be Economical

It has been suggested that thorium fuel is more costly to produce because of the handling of U-233 and the traces of the highly radioactive but short-lived U-232 that accompanies it. This argument is questionable when the following factors are considered:

- Unlike the uranium fuel cycle, thorium fuel cycles do not require enrichment.
- Fewer conversion processes are required to develop natural thorium oxide into fuel forms ready for first irradiation, compared to the conversion from natural U-3O8 to the conventional fuel form U-O2.
- The cost associated with the handling of U-233 and U-232 is expected to be significant only in the initial stage of introducing thorium fuel cycles, especially if the fuel is prepared on a small scale. As large-scale, highly automated thorium fuel fabrication facilities become operational, the extra cost will no doubt diminish.
- In the current generation of nuclear energy systems, the fuel cost component is typically less than 15% of the overall electricity generation cost. About 40% of this cost is related to enrichment, and about 10% is related to fuel fabrication. Therefore, even a hypothetical 400% higher cost of U-233 fuel fabrication will not necessarily make thorium more costly than conventional low-enriched uranium fuel on a unit-weight basis.
- The conversion from fertile Th-232 to U-233 is done during fission, while energy is generated, and the fissile U-233 can continue to undergo fission and produce energy for a very long time-practically as long as the fuel clad and supporting structure last.
- Thorium-based reactors can be designed to operate at very high temperatures, which will increase their thermal efficiency from the current peak of 34% to 50% or higher, reducing the fuel cost per unit of energy generated.

How Can We Realize the Potential of Thorium Fuel?

The biggest challenge facing the introduction of thorium fuel to commercial power generation is the lack of infrastructure needed for fuel fabrication. The industry is currently enjoying the availability of similar infrastructure for uranium fuel, an infrastructure made possible by past investments in non-civil applications.

The development of fuel-fabrication infrastructure for thorium fuel, however, is not currently driven by military or commercial considerations. It may take two decades or more before the strategic need for supplementary thorium fuel cycle technologies will manifest itself through the market force. This delay may have a significant negative impact on global sustainable development.