Utilization of (U-Th)O2 as an alternative nuclear fuel for Small Modular Reactors

Small Modular Rector (SMR) cores are designed to stand for a complete cycle, without the need to be refueled, but they need to be strongly poisoned at the beginning of life. So, since thorium can be used as a poison and also a fertile fuel (finally can be converted to a fissile U-233 isotopes after a thermal neutron capture reaction), it could be a good option to be used as mixed oxide with uranium, and so we could reduce the burnable poison and also have an extended burnup cycle. In this study, we are trying to assess the possibility of using a mixed (U-Th)O2 fuel as an alternative nuclear fuel instead UO2 for SMRs. The Korean SMART reactor (the first integrated PWR to receive design certification) has been used as the basis of our calculations for SMRs. For the SMART core simulation and other neutronic parameter evaluations, MCNPX code has been used. In the parametric study, two concepts of mixed oxide fuel using homogeneous and heterogeneous (Radkowski seed and blanket) concepts have been used, and neutronic parameters during fuel cycle burnup have been evaluated. The results show that by using mixed (U-Th)O2 instead of UO2, we can achieve longer fuel cycle without increasing in the amount of U-235. Also the results show that at the end of cycle, there are amounts of U-233 that can be used as nuclear fuel, as well as an extended burnup, and a reduction in burnable poison and boron concentration in comparison with the original SMART core design.