HZP and HFP rod ejection analysis in a SMART-like reactor model using the GUARDYAN-SUBCHANFLOW coupled code system

GUARDYAN is a dynamic 3D Monte Carlo reactor physics code with continuous energy handling developed for GPU hardware that has recently been coupled to the SUBCHANFLOW (SCF) subchannel thermal hydraulics solver. In this paper two control rod ejection accident scenarios will be presented in a Small Modular Reactor (SMR) geometry: a transient starting from Hot Zero Power (HZP), and one starting from Hot Full Power (HFP) conditions, both of them using Beginning of Cycle (BOC) material composition. Both the time dependent core-wise data and the node-wise data at certain times calculated by the GUARDYAN-SCF coupled code system exhibit the tendencies expected during such transients, with the thermal hydraulic properties mostly inside their safe limits. Relative variances estimated from 8 independent realisations suggest the results are credible. To further support our findings the HZP results are presented alongside data from PARCS-SCF and Serpent2-SCF calculations provided by Karlsruhe Institute of Technology (KIT), while for the HFP case we were able to compare some of the quantities to PARCS-SCF results. • Pin-by-pin neutronics coupled with subchannel thermal hydraulics. • Rod ejection transient in an SMR model. • GUARDYAN GPU based time dependent Monte Carlo.