Nuclear Power from Thorium:Different Options

Abstract

Thorium is a fertile material that has drawn attention as a potential source of nuclear energy since the 1950s due to several attractive features of the Th-U 233 fuel cycle. In view of the renewed interest in thorium, the possibilities of thorium utilization in different reactor systems, namely pressurized heavy water reactors (PHWRs), light water reactors, molten salt breeder reactors (MSBRs), fast reactors and accelerator-driven sub-critical systems have been examined. Extraction of energy from thorium essentially requires prior conversion of thorium to fissile U 233 . For in situ burning of thorium, a high burn-up is therefore essential. It is shown that the use of thorium in currently deployed PHWRs will reduce the requirement of uranium by about 30% in once through fuel cycle, while MSBRs with closed fuel cycle can achieve near breeding capability in thermal reactors. The most effective thorium utilization can be achieved only by adopting a closed fuel cycle which will not only enhance the fissile inventory many fold but also reduce nuclear waste burden significantly. While in conventional fast breeder reactors, thorium, partly converted into U 233 in the blanket region, is reprocessed for the recovery of the fissile material; in the breed and burn concept, the converted material is transferred to the core region without any reprocessing. Availability of spallation neutrons produced by bombardments of high-energy protons on heavy nuclides can augment fertile to fissile conversion leading to thorium utilization. The various options, which appear technologically feasible for generating power from thorium and the key issues connected with these schemes, are discussed in this article.