Neutronic Investigation on Thorium Mox Fuel in Vver-1000 Reactor Assembly

The accumulation of plutonium produced by LWR operations causes public concern related to its radiotoxicity and proliferation issue. Therefore, there is some interest in developing various methods for consuming plutonium through plutonium incineration i.e., by utilising thorium-based nuclear fuel. Thorium-plutonium mixed oxide fuel (Thorium MOX) is an attractive option considered for plutonium incineration. The aim of the study is to investigate the neutronic characteristics of Thorium MOX fuel in VVER-1000 nuclear reactor fuel assemblies. The VVER-1000 Benchmark model was utilised in the present study. A series of calculations were performed with the MCNP6 code and the ENDF/B-VII library. The calculation results show that a proper increase in Pu content could increase k_inf of ThMOX fuel, so it could have almost the same k_inf with MOX fuel or increase Pu content when needed. It was also shown that Thorium MOX fuel assembly had more negative Doppler reactivity due to neutron capture by thorium (²³²Th). The moderator temperature coefficient was found to be more negative than the Doppler coefficient, and it could be concluded that replacing uranium with thorium could reduce the amount of plutonium produced while increasing plutonium consumption.