Validation and application of coupled thermal-hydraulics and neutronics model using sub-channel CFD and SERPENT

The novel coarse-mesh CFD tool Subchannel-CFD (SubChCFD) is coupled with the Monte Carlo transport code Serpent using a segregated multi-physics coupling algorithm. The multi-physics model is validated using the CASL VERA Core Physics Benchmark Progression Problem #6, showing good agreement of pin powers and exit coolant temperatures. The model is also used to simulate an assembly from the K-SMR soluble‑boron-free small modular reactor, which shows good agreement with a full-scale CFD model from the software STAR-CCM+, with the exception of a small gap region between two large control rod guide tube and burnable poison rods, which induces a periodic flow instability that SubChCFD cannot fully replicate. Nevertheless, the oscillatory characteristics of the instabilities modelled by both codes show some similarity. • Subchannel-CFD is a novel coarse-mesh CFD solver for nuclear thermal-hydraulics. • Subchannel-CFD successfully coupled with neutronics code SERPENT. • Validation: good agreement with results from VERA problem #6. • Application: model applied to K-SMR soluble‑boron-free reactor assembly. • Flow oscillation between large rods mostly captured by Subchannel-CFD.