Explicit Burnable Absorber Modeling for Pressurized Water Reactor Core Reload Design Applications

A model is developed to generate homogenized, two-group cross-section data for pressurized water reactor (PWR) fuel assemblies loaded with burnable absorbers by explicitly incorporating the effects of the neutron poison into the unpoisoned group constants. This provides the calculational freedom to use the assembly burnable absorber loading as an independent variable in dynamic search methods for optimizing low-leakage PWR core reloads. To achieve an accuracy of better than 0.2% in the assembly k_∞, separate consideration is given to the absorption and scattering perturbations, as well as to the spectrum-hardening effects caused by the presence of burnable absorbers in the assembly. The model was validated first by comparison of unit assembly cross sections to data from reference calculations and then by use of the model in the Electric Power Research Institute nodal code SIMULATE-E and comparison to reference core power distributions.