Propagation of Nuclear Data Uncertainties for Reactor Physics Parameters in Fluorine-19-based Molten Salt Reactors

Abstract: It could be argued that a renaissance is taking place for the global interest in nuclear power - especially for the development of the next generation of reactor systems that aim at solving the problems with contemporary energy production with nuclear technology. One such proposed concept for Gen IV nuclear power is a Molten Salt Reactor (MSR), in which the nuclear fuel is in solution of a salt - often based on fluorine or chlorine. The historical experience of MSRs is limited in both scope and time, but significant developments have been made in the past few years. In order for such technologies to become commercially viable, it is important that investigations are conducted into the behaviour of the materials involved. In this work, the propagation of uncertainty in nuclear data for the isotope F-19 is investigated in a fluorine-based MSR. Uncertainty quantification is important in reactor physics as calculations that are based on Best Estimate Plus Uncertainty often leave more margin to the regulatory requirements compared to conservative calculations. The quantity of interest is the reactivity of the system at hand, and three different levels of moderation were investigated in order to observe any differences that the hardness of the neutron spectrum might impose on the reactivity uncertainty. In addition, the individual neutron-nucleus interaction channels are analyzed separately in order to deduce which channels that contribute the most to the reactivity uncertainty. The nuclear reactor cores were simu- lated with the Monte Carlo-based neutron transport code OpenMC, and the uncertainty quantification was performed using the Total Monte Carlo (TMC) methodology with perturbed nuclear data that was generated using the tools SANDY and NJOY. The results from the uncertainty quantification showed that the nuclear data uncertainty from F-19 gave rise to reactivity uncertainties of approximately 60-200 pcm, depending on the amount of moderation rods that were inserted. The less moderated systems were more susceptible to the F-19 uncertainties, which could be explained by the fact that those systems gave more room for the fluorine- based fuel, and hence they would be more exposed to the uncertainties of F-19. It was also observed that the elastic scattering, neutron capture, and alpha production reaction channels contributed the most to the uncertainties in the most moderated reactor, while the least moderated reactor was most susceptible to the uncertainties due to elastic scattering, inelastic scattering, and alpha production. These findings show that significant improvements needs to be made in the measurements and evaluations of nuclear data for F-19 if it is to be implemented in MSRs of the future.