Extension and first validation of DASSH subchannel code for Liquid Metal Cooled Fast Reactors

This study presents the extension and first validation of the DASSH subchannel code for the thermal-hydraulic analysis of Liquid Metal Fast Breeder Reactor cores. Subchannel codes offer an effective compromise between computational efficiency and modeling fidelity. However, many existing tools rely on strong simplifying assumptions regarding both the solver and the geometrical domain. DASSH is a multi-assembly subchannel code, enabling whole-core thermal-hydraulic analyses with limited computational cost. The solver was originally developed for steady-state forced convection conditions. This work enhanced it extending its application domain to the mixed convection regime. This development has resulted in the tool becoming one of the few capable of analyzing liquid metal reactor cores with a high level of versatility in simulating different flow regimes, both in single and multi-assembly configurations. The predictive capability of DASSH for pressure drop, flow distribution and temperature fields is demonstrated using a test suite derived from publicly available experimental data focusing on wire-spaced bundles. The results show good agreement with measurements taken under forced convection conditions, and demonstrate significant improvements in temperature predictions under mixed convection, particularly in cases characterized by strong radial power gradients.