Comparison of thorium-plutonium fuel and MOX fuel for PWRs

Thorium-plutonium (Th,Pu) oxide fuels will provide an evolutionary way to simultaneously reduce plutonium volumes and capture energy from this material. In this work we compare the neutronic properties of Th,Pu-fuel and MOX fuel with different Pu isotope vectors. For these studies, burn-up simulations are performed for a regular MOX PWR fuel assembly and for a thorium-plutonium PWR fuel assembly of the same geometry. The neutronic properties and performance of the assemblies are investigated by lattice calculations using CASMO-5. The plutonium content of the two fuel types is chosen so that the same total energy release per fuel assembly is achieved, which demanded a somewhat higher plutonium content in the thoriumplutonium case. The assemblies are then analyzed with regards to temperature coefficients, delayed neutron fractions, control rod and boron worths, coolant void reactivity (CVR) and decay heat. Overall, the results show that MOX and Th,Pu-fuel have fairly similar neutronic properties in existing PWRs. Th,Pu-fuel offers an advantage over MOX fuel with regards to CVR values and plutonium consumption. The conclusion is therefore that introducing Th,Pu-fuel would improve these factors without imposing any major hurdles from a reactor physics point of view.