Investigation of effects of alternative thorium based fuels on neutronic performance in VVER-1200 reactors with Monte Carlo methods

Thanks to the developing technology, an immense amount of studies is carried out to reduce nuclear wastes, dependency on uranium and reduction of fuel costs in nuclear power plants. The fact that known uranium reserves are limited lead to find alternatives to uranium dioxide fuel, today commonly used fuel in nuclear reactors. Given that thorium sources are much more than uranium sources, studies on thorium-based fuels become increasingly important. In this study, the effects of using low enriched uranium and thorium mixture (UO2+ThO2), reactor grade plutonium and thorium mixture (rgPuO2 + ThO2), weapon grade plutonium and thorium mixture (rgPuO2 + ThO2) in a VVER-1200 fuel assembly on neutronic performance, changing of fuel composition according to burnup rates and some safety parameters related to safe and secure operation of reactor were investigated. Considering the findings obtained from this study, it is evaluated that the use of 235U can be minimized by the utilization of thorium-based fuels and the dependence on 235U can be decreased. With the use of plutonium-based fuels, VVER-1200 power reactor can have higher burnup rates or operating times under similar operating conditions without any change in the fuel lattice geometry, thereby fuel cycle costs can be reduced. Thorium-based plutonium fuels have been found to have much higher thorium and plutonium consumption rates compared to traditional thorium-based uranium fuels. Therefore, it emerges as a promising fuel mixture due to its possibility to be used in light water reactors without any significant changes in its design.