Analysis and burnup modeling of the GEM^∗STAR accelerator-driven system

The purpose of this paper is to evaluate the neutronics and fuel burnup of the GEM^∗STAR accelerator-driven reactor design. The GEM^∗STAR design uses a molten salt fuel, with graphite moderation in a subcritical configuration with supplemental neutrons provided by an accelerator-driven proton spallation source. This allows for very safe operation since no criticality accidents are possible. A continuous extraction of spent fuel and addition of fresh fuel allows for the reactor to run at an equilibrium state of power and isotopic concentrations. Further, the liquid fuel and subcritical nature allow for higher burnup and more flexible fueling options. In previous analysis of the reactor, several simplifying assumptions were made about the neutronics modeling. In this study, these assumptions are eliminated, and a more detailed study is performed using MCNP6, Monteburns, and CINDER90 for neutronics and burnup calculation. Although there are some differences between the old and new analyses, equilibrium isotopic concentrations are within 10%, while electric multiplication factors are within 20%. Burnup analysis shows that the approach to equilibrium takes approximately two years for natural uranium fuel. By decreasing the fuel feed rate, the burnup can be increased at the cost of slightly lower electric multiplication. The performance of several feed materials are examined including natural uranium, LWR spent fuel and plutonium.