A Neutronics Study of the Initial Fuel Cycle Extension in APR-1400 Reactors: Examining Homogeneous and Heterogeneous Enrichment Design

In this study, we conducted a neutronics analysis of a soluble-free-boron APR-1400 reactor core. Our goal was to explore the possibility of extending the fuel life cycle from 18 to 24 months. To achieve this, we examined both homogeneous and heterogeneous fuel enrichment designs while maintaining the original fuel geometries of the reactor. The proposed fuel enrichments for the homogeneous reactor core were 3.0%, 3.5%, 4.0%, 4.5%, and 4.95%. For the heterogeneous reactor core, they were (3.6%, 4.0%, 4.5%, and 5.0%) and (3.4%, 3.8%, 4.5%, and 5.0%). To suppress excess reactivity at the beginning of the fuel cycle (BOC), we applied an Integral Fuel Burnable Absorber as a thin coating layer on the outer surface of the fuel pellets. The coating was distributed uniformly throughout the core. In addition, we also studied the use of selected cladding materials as a replacement for the conventional zircaloy used in the fuel rods. The neutronics calculations for the modified APR-1400 core configuration were performed using the Serpent 2.1.31 Monte Carlo reactor physics code. We evaluated the behavior of the APR-1400 core by analyzing the effective multiplication factor, flux spectrum, pin power distribution, and radial power profile. Both the homogeneous and heterogeneous cores were compared with the reference APR-1400 core configuration. Our results indicate that it is possible to extend the fuel cycle to up to 24 months in both the homogeneous and heterogeneous cores. We also conducted a thorough analysis of the initial cycle for heterogeneous cores to consider more realistic scenarios.