Development of the Subgroup Projection Method for Resonance Self-Shielding Calculations

We investigate a new approach for resonance self-shielding calculations, based on a simplified and straightforward subgroup model, used in association with an improved Santamarina-Hfaiedh energy mesh. This subgroup model relaxes the need to represent the correlated slowing-down effects by optimizing the energy mesh. The resulting equations become sufficiently simple to reintroduce an accurate representation of other physical effects that are generally neglected, namely, the mutual shielding effect between different isotopes and the temperature correlation effect caused by an explicit temperature gradient in a resonant isotope. The resulting self-shielding model is shown to reach levels of accuracies that are similar to those of a Monte Carlo method.