Feasibility study of minor actinide transmutation in light-water reactors with various AM/CM separation efficiencies

Implementing a viable solution for the disposition of used nuclear fuel (UNF) raises concerns due its high radiotoxicity and decay heat generation over long time periods. The major contributors to these are the minor actinides (MA) that are contained in the UNF. The strategy of Partition and Transmutation (P&T) separates the components of UNF to treat each separated stream in the manner that is most appropriate. The MA stream can be reprocessed and fabricated with MOX fuel and recycled in a reactor. Through transmutation, reductions in the radiotoxicity and decay heat of UNF can be achieved, which reduces the length of time that UNF must be sequestered from the environment. Because of the greater fission to capture cross section ratio in a fast neutron spectrum, the transmutation of MA is most effective in fast spectrum systems. However, MA transmutation can be carried out, albeit less effectively, in a thermal spectrum. This work examines MA transmutation in a thermal spectrum because there are no currently operating commercial fast spectrum reactors in the U.S. The goal of this study was to examine the feasibility of americium transmutation in a typical light water reactor. Due to similar chemical properties of americium and curium and the difficulty associated with their chemical separation, the separation efficiency of these two elements was also considered. Three separation efficiencies for the MA content were considered, and these were 99.9%, 99.0%, and 90.0% separation of Cm from Am. In addition, the homogeneous and heterogeneous additions of MA to MOX fuel were considered. Similar to current MOX loading schemes, the study simulated a reactor core with 30% of the fuel assemblies composed of MOX fuel bearing MA. This study measured the feasibility of MA transmutation by the reactivity of individual MOX+MA fuel assemblies and full cores, the coefficients of reactivity such as the Doppler Coefficient, Moderator Temperature Coefficient, and Moderator Void Coefficient, MA transmutation efficiency, and attainable burnup. Results show that the transmutation of MA in a light water reactor is feasible from a reactor safety and operation point of view. The reductions of the Am inventory in the UNF were between 40% and 60%. Despite these reductions, there was a significant increase in the Cm inventory, mostly due to the neutron capture of Am in the thermal spectrum.