Reducing the plutonium stockpile around the world using a new design of VVER-1200 assembly

Abstract

The broad goal of this work is to use the accumulated plutonium around the world in peaceful uses of energy production rather than for military purposes. This work investigates the feasibility of burning the Pu vector that is extracted from the spent fuel of light water reactor or from the nuclear warheads stockpile. MCNPX code version 2.7 has been used to design two assembly models, conventional assembly and Blanket-seed (BS) assembly. The conventional assembly is fueled with UO2 while the BS assembly is fueled with ThO2 in the blanket region and Pu vector either in the form of reactor grade plutonium (rgPu) or weapon grade plutonium (wgPu) in the seed region. Using of Th-232 as a fertile material in the blanket region prevents from more Pu breeding and enables a longer fuel burnup rate. Five different fuel models are studied to investigate the optimum concentration of Pu vector that is used in the seed region. MCNPX code is used to simulate the neutronic characteristics of the presented fuels. The multiplication factor Keff values of the suggested fuel in the BS assembly have been analyzed and compared with that obtained in the conventional assembly. Some parameters related to safety operation such as moderator temperature coefficient (MTC) and effective delayed neutron fraction (βeff) have been calculated. The Pu vector concentrations have been investigated with burnup to distinguish the effectively of the suggested models to burn how much of the used Pu in the seed region. Using of Th-232 as a fertile material in the blanket region enhance the ability of BS assembly to bred more fissile material (U-233). Therefore, the suggested fuel assemblies achieve a higher conversion ratio (CR). The radioactivity of the actinides and non-actinides elements has been investigated with burnup. Due to the poising effect of fission products on the reactivity of the reaction, it is important to investigate the concentrations of the most important fission product at the presented fuel.