Pin-resolved resonance self-shielding methods in LWR direct transport calculations

Abstract

An essential component of deterministic reactor core analysis is the resonance self-shielding calculation, which is used to produce problem-specific multigroup cross sections. Equivalence theory and the subgroup method have been widely used to perform this task in the conventional two-step core analysis. However, recent progress with high-fidelity whole core direct transport methodology sets up new requirements for the associated self-shielding method, namely, being able to resolve within-pin effects such as multi-region depletion and non-uniform fuel temperature distribution. In the framework of whole core direct transport, the usability of existing self-shielding methods needs to be reexamined, and advanced self-shielding methods should be proposed to meet these new requirements. This paper reviews the important phenomena of resonance self-shielding that should be properly modeled in the direct transport calculation of light water reactor (LWR) applications. These phenomena include spatial self-shielding effects, resonance interference, non-uniform temperature effects and self-shielding of clad isotopes. We discuss the performance of four self-shielding methods, i.e., equivalence theory, the physical subgroup method, ESSM and ESSM-X, in addressing these basic and advanced requirements. The computational resources of these methods are also compared.