Accuracy of a 2-level scheme based on a subgroup method for pressurized water reactor fuel assembly models

Until now, a typical computational scheme for the DRAGON5 lattice code was based on a resonance self-shielding method using the Subgroup Projection Method (SPM) coupled with a flux calculation using the Method of Characteristics (MOC), both solved over a 295-group Santamarina-Hfaiedh energy mesh (SHEM). We are investigating the accuracy of an optimized 2-level computational scheme based on a condensation stage from 295 to 26 energy groups. A first level flux calculation is performed using the Interface Current (IC) method on the 295-group mesh, followed by a detailed second level flux calculation using the MOC on the 26-group mesh. Here, we validate the 2-level scheme by comparison with the 1-level scheme and with Monte Carlo calculations at burnup 0 and with isotopic depletion. Validation results were obtained using Monte Carlo codes SERPENT2 and TRIPOLI4. This study shows that an optimized 2-level scheme is much faster than the corresponding 1-level scheme and leads to numerical results without a significant degradation in term of precision. The proposed 2-level schemes are therefore candidate for CPU-efficient production tools for generating multi-parameter reactor databases.