Design Boiling Water Reactor Core Model Using MCNPX for Studying the Burnable Poisons and the Axial Enrichment Fuel Effect on the Neutronic Characteristics

Abstract

The incorporation of gadolinium directly into nuclear fuel is important for improving the reactor behavior and satisfying the safety criteria during the core lifetime. MCNPX (Monte Carlo N–Particle code extended) has been used for designing Advanced Boiling Water Reactor model. MCNPX code based on Monte Carlo method, is used to design a three-dimensional model for a BWR fuel assembly in a typical operating temperature and pressure conditions. This model has been designed to study the effect of Gd₂O₃ on the power, total neutron flux, and normalized power. The effects of axial fuel enrichment and control rod on the total neutron flux and normalized power have been studied also. The initial fuel enrichment has been increased, which means that the additional amount of fissile material (U²³⁵) in the reactor core has to be compensated by the introduction of additional neutron absorber material. The use of a burnable poison in nuclear reactors provides the necessary negative moderator reactivity coefficient at the beginning of core life and helps shape core power distributions. In this study, the influences of the burnable poisons on the main parameters of the reactor such as multiplication factor, burn-up, soluble poison concentration, moderator temperature coefficient over the reactor lifetime are investigated. It is found that the axial fuel enrichment distribution flat the power through the axial core distance. The spent fuel in the reactor can be recycled, and plutonium and its isotopes can be extracted from it. The extracted plutonium can be used as a fuel.