India Advances Thorium Breeding Technology

Author: Koyel Bhattacharyya

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.  According to the United States 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 spurred India to become a global leader in thorium fuels.  The country produced the world’s first thorium nuclear reactor, the Kakrapar-1, in 1993. As part of India’s three-stage fuel cycle plan, a new Advanced Heavy Water Reactor (AHWR) has been designed, and slated for operation by 2017. The country hopes to use thorium-based reactors to meet 30% of its electricity demands by 2050.

Thorium-232 may be converted to uranium-233, a fissile element that can sustain a nuclear chain reaction.  Thorium is more abundant in the earth’s crust than uranium, and all of 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 due to the slow rate at which energy is emitted. The thermal conductivity of thorium oxide (ThO2), the material used in these reactors, is higher than that of uranium oxide (UO2).  This permits the use of lower fuel temperatures and thus reduces fission gas release. In addition, the thermal expansion coefficient of ThO2 is smaller than that of UO2, which reduces strain on the fuel clad, the outer layer of fuel rods that lies between the coolant and the fuel. Further, thorium fuel cycles produce less plutonium and other transuranic elements (those with an atomic number greater than 92, which are all radioactive) than do uranium fuel cycles.  The technology to use these byproducts for nuclear weapons is not currently in place, thus improving control over nuclear proliferation.

India’s three-stage nuclear power program began in the 1960s with natural uranium-fueled pressurized heavy water reactors (PHWRs) comprising the first stage. It continued with the second stage and the reprocessing of irradiated spent fuel to extract plutonium, which is used in the nuclear cores of fast breeder reactors (FBRs) currently being constructed. In such reactor designs, more nuclear fuel is generated than consumed.  The design of an Advanced Heavy Water Reactor (AHWR) is the third and final stage of the Indian atomic energy program, and employs both U-233 and Th-232 in the breeder reactors, which are designed to maximize thorium usage.  Though many countries have suspended research behind such FBR designs because they are not currently competitive, the AHWR has a number of safety features that have permitted its construction to continue.  These include a reservoir of water above the primary containment vessel and direct injection of water into the fuel to cool the reactor.

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. This will permit the country to reduce its dependency on foreign energy sources and provide it with long-term energy security. India is engaged in the construction and deployment of numerous nuclear power plants 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 may encourage greater worldwide pursuit of nuclear energy as an alternative to fossil fuels. China announced plans for a thorium molten-salt thermal breeder reactor at the beginning of 2011, and the U.S. is also considering the exploration of thorium as a nuclear fuel. Still, India’s large reserves of the element, as well as the country’s eagerness to develop an in-house system of sustainable energy, prepare the country to make great advances in thorium breeding technology.

Koyel X. Bhattacharyya is a graduate student in the Stanford Department of Chemistry. She works in the lab of Professor Matthew Kanan on the electroreduction of carbon dioxide.

References
L. Pham, “Considering an Alternative Fuel for Nuclear Energy,” New York Times, 19 Oct 09.
M. Benedict, T. H. Pigford and H. W. Levi, Nuclear Chemical Engineering, 2nd Ed. (McGraw-Hill, 1981), pp. 283-317.
R. Shrinivasan, “55% of India’s population poor: Report,” The Times of India, 15 Jul 2010.