Review of the Radkowsky Thorium reactor concepta

Abstract

A novel reactor‐design concept termed the Radkowsky Thorium Reactor (RTR) has been developed that shows potential for early application in conventional pressurized water reactors (PWRs). The RTR concept makes use of a seed‐blanket geometry with thorium as the fertile material, and uranium of less than 20 percent enrichment as fuel in both the seed and blanket regions. About 163 seed‐blanket units are employed in a 1,000 MWe RTR, and fuel shuffling during refueling is used to maintain an acceptable power distribution and a relatively‐low critical mass. Other key features of the RTR are: (1) irradiating the blanket fuel of mixed ThO2 and UO2 for a period of 10 years prior to removal, and (2) employing metallic uranium‐zirconium‐alloy as the seed fuel and irradiating it for 3 years. The high fuel burnups of both the blanket and seed fuels relative to that in a conventional PWR results in a substantial decrease in the plutonium present in RTR spent fuel, and to substantial increases in the percentages of Pu‐238, Pu‐240, and Pu‐242 in that plutonium. The RTR reactor design features are very similar to conventional PWRs, such that application of the general seed‐blanket arrangement could be implemented rather quickly if there were no reactor safety, technical, or economic concerns. In this review, the RTR is compared with a PWR considering key technical, safety, and economic features. Both reactors are operated with yearly refueling. Emphasis is on weapons proliferation resistance, fuel cycle costs, the comparative use of uranium and thorium fuel cycles, ability of the blanket fuel to be exposed for 10 years in an RTR environment, performance of RTR metallic seed fuel, and fuel shuffling/handling concerns. Relative to the PWR, the RTR shows a substantial increase in proliferation resistance to weapons production due to the low quality of the plutonium produced and to its lower production rate. However, PWRs operating on the once‐through uranium cycle are considered to have adequate proliferation resistance. Fuel‐cycle‐cost items were: fuel fabrication, natural uranium and thorium mining, Separative Work Units (SWUs) for fuel enrichment, fuel fabrication losses, chemical conversions, storage of fuel at the reactor site, and transporting fuel from the reactor to a storage/disposal location. Based on the reference conditions employed, the total fuel cycle costs of the RTR were 96 percent that of a conventional PWR. An important contribution to that result was the relatively‐low cost estimated for transporting/handling RTR fuel to an “away‐from‐reactor” storage/disposal location; when such transporting/ handling costs were not included, the RTR fuel cycle costs were 103 percent that of the PWR. The above differences in costs are small compared with uncertainties in cost parameters. Replacing the thorium with natural uranium will probably lower the RTR fuel cycle costs, and probably retain desirable non‐proliferation features. Overall, significant fuel and fuel‐shuffling R&D/Demonstration is required before the viability of the RTR concept can be assured. Primary concerns are: (1) the practicality of exposing zirconium‐alloy‐clad fertile fuel rods for very long times (‐10 years) and high burnups (‐100 MWd/kg) to a high‐temperature water environment containing small amounts of hydrogen; (2) the safety of metallic seed fuel having very high burnup (>150 MWd/kg) and high average seed power density (140 percent that of the PWR) when exposed to accident conditions; and (3) the impact on plant availability of extensive fuel shuffling of Seed‐Blanket Units (SBUs) combined with removing fully‐spent seeds from SBUs and reloading them with fresh seeds.