Nuclear power plants are used around the world to provide clean, emission-free power. However, nuclear power plants do have inherent hazards, including highly radioactive fuels, potentials for accidents, and the necessity to store spent fuel after use. Today's nuclear power plants primarily use a uranium fuel cycle to generate power. However, other radioactive elements can be used, including thorium.
The Element Thorium
Thorium (atomic number 90) is a radioactive metal that occurs naturally in the Earth's crust. Thorium is widespread around the world, and is not limited to deposits in specific locations. It is estimated that the amount of thorium in the crust is about 3 to 4 times that of uranium, and does not require the intensive enrichment process of uranium to create fuel. Thorium is currently used as an alloy for high temperature applications, such as with magnesium in aircraft engines and with tungsten for electrodes in gas tungsten arc welding (GTAW).
Thorium as a Nuclear Fuel
Thorium on its own is not a fissile material. When exposed to slow neutrons, Thorium 232 will form Uranium 233, which is fissile. Thorium was first used as a nuclear fuel in the 1960s in light-water reactors, and was used as an alternative to uranium fuel in Oak Ridge National Laboratory's Molten Salt Reactor. All of these small-scale operations showed that thorium could be used as a viable nuclear fuel.
The abundance of uranium in most countries researching nuclear power and the ability of the resultant materials of the uranium cycle to be used for nuclear weapons encouraged research and development of the uranium cycle over the thorium cycle in the 1960s, but interest has been renewed due to the dangers and waste created by the uranium cycle.
Advantages and Disadvantages of Thorium as a Nuclear Fuel
The use of thorium as a nuclear fuel has many advantages over traditional nuclear fuels, such as:
- Thorium provides a variety of benefits over traditional nuclear fuels:
- Thorium is more widely available than uranium
- The thorium fuel cycle produces significantly less radioactive waste than uranium fuel cycle reactors
- The nuclear properties of thorium isotopes, such as thermal neutron absorption cross section and resonance integral are better than those of uranium isotopes
- The resultant uranium products contains both 232 and 233 isotopes. The presence of uranium 232 generally prevents the use of this material as weaponry.
However, thorium also has some inherent disadvantages over traditional nuclear fuels, including:
- Thorium does not naturally include any fissile isotopes, and has to be supplemented to achieve criticality
- If the uranium 233 is recycled as in a closed cycle, remote handling is required because of the significant radiation caused by the decay of uranium 232
- It would be difficult to convert many existing uranium-fuel power plants to a straight thorium fuel cycle
Despite the challenges that thorium fuel cycle plants can provide, many feel that the benefits outweigh the disadvantages.
Current Thorium Power Projects
India's Kakrapar-1 reactor uses thorium instead of depleted uranium to improve the operation of the plant at startup and achieve power flattening. India is also in the process of constructing a prototype heavy water reactor using thorium as a fuel. The country expects to have the prototype plant online in 2011 and five more plants are in the design pipeline.
While India is spearheading the thorium fuel switch, other countries such as the United States, Russia, and Norway, are considering the benefits of power plants that use thorium fuel instead of uranium fuel.
Thorium offers an alternative to conventional uranium cycle plants, but research and development is still needed to create a safe, viable power plant, fuel generation process, and waste management program.
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Susan Kristoff - Susan Kristoff is mechanical engineer by trade, but has a diverse set of professional and personal interests. The glue that binds all of ...
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