heoretical Derivation and MCNP5-Based Comparative Study of Neutron flux density Distribution in Annular Reactors

o bridge the theoretical gap in the analysis of neutron flux density distributions within annular reactors, this study derives closed-form solutions for the neutron flux density under critical conditions based on the monoenergetic neutron diffusion equation and validates them using MCNP5 simulations. The study categorizes annular reactors into three types according to inner radius: Type A ($a > 27\,\text{cm}$), where the inner neutron flux density approaches zero, is modeled using zero-flux boundary conditions at both inner and outer radii; Type B ($a 0.6$, neutron leakage increases sharply. This study fills a theoretical gap in modeling neutron flux density distributions in annular reactors and provides a robust foundation for geometry-based optimization in reactor core design.