A calculation module is developed for testing and validating the improved nodal equivalence techniques of reflectors for full-core nodal calculations. This module, BRISINGR, is a new implementation of the nodal expansion method developed by Delft University of Technology and Framatome, and has been inserted into the version 5 environment of Polytechnique Montréal, providing a fast prototyping setup used to assess the impact of different nodal equivalence approaches.

We focus our investigations on an open-source implementation of the legacy equivalence technique Baff-Refl originating from the SCIENCE platform at Framatome. The proposed improvements to Baff-Refl are twofold: modification of the nodal equivalence procedure and modification of the reflector diffusion coefficients. We review the Nodal Expansion Method (NEM) and Analytical Nodal Method (ANM) for reflector calculations, the discontinuity factor (DF) renormalization, the DF decorrelation, the albedo calculation, and the procedure for obtaining few-group reflector diffusion coefficients from fine-group leakage coefficients.

Our validation tests focus on the accuracy of the average nodal power of the fuel region in the downstream full-core calculation. A benchmark set of four two-dimensional 9 × 9 core configurations with Evolutionary Power Reactor-type assemblies with either steel or water reflectors was used for validation. The results on the core impact of the reflector model show that the Inscatter model for the calculation of diffusion coefficients improves the accuracy of the full-core power in all benchmark configurations. DF renormalization is another studied aspect of this paper, and has been shown to provide notable improvements. Actually, renormalization to assembly DFs provides better results than renormalization to 1, which is itself more preferable than none for accuracy. Finally, calculating reflector constants with ANM is shown to have no conclusive improvement over NEM.