Design Considerations for Utilising Thorium in Advanced Energy Systems

India has the largest thorium reserves in the world which has been recently estimated to be about 13.3% and its energy potential is calculated to be greater than 100,000 GWe years which is tremendously much larger than that of uranium. Unfortunately, thorium is not accompanied with fissile isotope and it will have to be irradiated in reactors to produce the U-233. In India, thorium has been successfully used in both in research facilities and in power reactors. The basic neutronic properties of thorium and the bred fissile isotope U-233 are superior to U-235. From a material standpoint, the thorium fuel has better thermal conductivity, higher melting point and the fuel matrix can withstand high irradiation because of the effective retention of the fission gasses. There is considerable experience in all aspects of the thorium fuel cycle from mining, to fabrication, to irradiation, and even post irradiation examination. This paper will highlight the use of thorium in advanced thermal reactors, where the superior neutronic characteristics of thorium have been exploited. The engineering considerations of these reactors and its fuel cycle will also be discussed. U-233 must be extracted from the spent fuel and recycled into reactors to enhance its energy potential. The radiological and reprocessing aspects of thorium fuel will also be presented. This paper will cover the design aspects of the thorium-based reactors namely, Advanced Heavy Water Reactor (AHWR), Molten Salt Reactor (MSR), High Temperature Reactor (HTR) and Accelerator Driven Sub-Critical Systems (ADSS) being designed at Bhabha Atomic Research Centre (BARC).