India, a country more than eleven times as densely populated as the United States, has been struggling to find its footing in today's technologically advanced economy over the past half-century.  Given the strong correlation between per capita energy consumption and quality of life, India finds itself in constant need of new sources of energy.  This search is made more difficult both by limited existing reserves of coal in India and by worldwide efforts to reduce the fossil fuel consumption and consequent CO2 production upon which today's more modernized economies built their foundations.  India has thus invested a great deal of energy and research into a cleaner alternative: Nuclear energy.
Nuclear energy typically brings to mind the use of uranium reactors, but India's uranium reserves are paltry. However, India is estimated to possess at least a quarter of the world's reserves of thorium, also a radioactive element.  According to the US Geological Survey, of the world's roughly 1.3 million tonnes of thorium, India is believed to hold about 300,000 tonnes.  The availability of thorium, combined with the country's great need for energy, has urged India to become a global leader in thorium fuels.  The country produced the world's first thorium nuclear reactor, the Kakrapar-1, in 1993, and as part of India's three-stage fuel cycle plan, a new Advanced Heavy Water Reactor (AHWR) is being designed, slated for operation in 2011. The country hopes to use thorium-based reactors to meet 30% of its electricity demands by 2050. 
Th-232, a fertile element, may be converted to U-233, a fissile element, upon neutron absorption and consequent β decay. Thorium is more abundant in the earth's core than uranium, and all the thorium that is mined may be used in a reactor, whereas less than 1% of natural uranium may be used. The 14-billion-year half-life of Th-232 also renders it safer than either uranium or plutonium.  The higher thermal conductivity of ThO2, the material used in reactors, is higher than that of UO2, permitting the use of lower fuel temperatures and thus reduced fission gas release. In addition, the thermal expansion coefficient of ThO2 is smaller than that of UO2, which reduces strain on the fuel clad. Further, thorium fuel cycles produce less plutonium and other transuranics than do uranium fuel cycles, and the technology to use the byproducts for nuclear weapons is not currently in place, thus improving control over nuclear proliferation.
The three-stage Indian nuclear power program began with natural uranium fueled pressurized heavy water reactors (PHWRs), then continued by reprocessing the irradiated spent fuel to extract plutonium, which was used in the nuclear cores of fast breeder reactors (FBRs). The final stage employs both U-233 and Th-232 in the breeder reactors, which are designed to maximize thorium usage.  FBRs are designed with a reactor core surrounded by a blanket of tubes containing a non-fissile element. In the AHWR currently underway, the reactor core is of U-233 and the blanket is of Th-232. Though many countries have suspended research behind such FBRs, the AHWR has a number of safety features that have permitted its construction to continue, including a reservoir of water above the primary containment vessel and direct injection of water into the fuel to cool the reactor, improved tube type design, low pressure moderation, on-power refueling, and a number of shut-down systems. FBRs typically run on mixed metal oxide fuels (e.g., a mixture of PuO2 and UO2). However, purely metallic fuels, which employ metal alloys rather than oxides, are much faster breeding, so Indian FBR research is focusing its attentions on the use of metallic fuels.  ThO2, which is a very stable oxide, does not oxidize, which optimizes its release of fission products in the event of a clad breach and permits the fuel to reside in the reactor for longer periods of time.
As India progresses with the third stage of its nuclear power plan, it works towards the use of an element abundantly available to it, thorium, as a commercial source of fuel, permitting the country to avoid having to import its energy source and providing it with long-term energy security. India is engaged in the construction and deployment of nuclear power plants within the country while maintaining a dedication to safety, which is made easier by the inherent advantages of thorium over uranium. The success of this project in India, as well as in other countries such as France, may encourage greater worldwide pursuit of nuclear energy as an alternative to fossil fuels.
© Koyel X. Bhattacharyya. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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