Effects of Radial Reflector Material on the Performances of Small LWR Core Using ThO₂-UO₂ and FCM Fuels

This paper is to analyze the effects of different radial reflector materials on the performances of the small LWR core using ThO₂-UO₂fuel pins and FCM fuels. In this work, a 2D whole core modeling using DeCART2D was used to accurately generate the radial reflector cross sections because the accuracy of the reflector cross sections is important in small reactor core design. We considered several candidate materials for solid reflector such as lead, SS303, beryllium metal, and graphite. In this work, we analyzed the effects of different reflector compositions on the neutronic performances of a small advanced LWR core having UO₂-ThO₂ pins and TRU FCM pins to effectively destroy TRU nuclides from LWR spent fuel and the results show that the reflector using SS303 or lead gives much better performance such as longer fuel cycle length, lower power peaking factors, higher TRU destruction rate and less negative MTC than the core having water reflector. Also, it was found that the cores graphite and beryllium reflectors has much longer cycle length but they shows larger thermal fluxes in the fuel assemblies adjacent to the reflectors, which leads to power rising in these fuel assemblies. And it was shown that the power peaking factors are acceptable in the core having graphite reflector. As conclusion, the advanced small LWR core having UO₂-ThO₂ pins and TRU FCM pins to effectively destroy TRU nuclides from LWR spent fuel can be designed to have better core performances using the solid reflectors such as lead and SS303