Neutronic analysis of thorium MOX fuel blocks with different driver fuels in advanced block-type HTRs

Abstract

The use of thorium-based fuels is an attractive option to achieve high burnup level and relatively longer reactor operation period. This also includes some other potential advantages, such as, low proliferation risk and high conversion ratio, etc. It is interesting to utilize thorium-based fuels in advanced high temperature reactors (AHTRs), because they are a better choice for their high burnup limit and inherently-safe HTRs with a low-pressure operation condition. The neutronic performance of thorium MOX fuel blocks, including infinite multiplication factor, conversion ratio, discharge burnup and the neutron spectra in AHTRs, has been investigated by the DRAGON V4 code for four different driver fuels, U-233, reactor-grade plutonium (RGrPu), weapon-grade plutonium (WGrPu) and weapon-grade uranium (WGrU). Based on a typical fuel block of AHTRs, the influence of varying heavy metal loading and effective enrichment on the neutronic performance of the four fuel blocks is firstly investigated. The heavy metal loading of 5 kg and effective enrichment of 12% are selected for the neutronic comparisons. The further comparisons of the four thorium fuels with different driver fuels show that the Th/RGrPu and Th/WGrPu fuel blocks have intermediate neutron spectra, while Th/U233 and Th/WGrU fuel blocks have thermal neutron spectra. The Th/U233 fuel achieves the highest infinite multiplication factor at beginning of life because of its high thermal η value. Th/RGrPu fuel achieves the highest conversion ratio and the highest discharge burnup.