Safety-oriented CFD analysis of the PeLUIt-40 pebble-bed HTGR under partial flow and LOCA scenarios

In this study, the thermal–hydraulic behavior of the Indonesian Micro Reactor PeLUIt-40, a 40 MWt modular pebble-bed high-temperature gas-cooled reactor (HTGR), was analyzed under reduced coolant flow and loss-of-coolant accident (LOCA) conditions. Three-dimensional computational fluid dynamics (CFD) simulations using a porous-media core model and volumetric heat sources from neutronic analysis were performed. Steady-state simulations were conducted for helium flow rates from 100% to 25% of nominal, and a transient LOCA was simulated by reducing flow to zero over ten seconds. The results show that maximum core temperatures increased nonlinearly with reduced flow, exceeding TRISO fuel limits at 25% flow, while outlet duct temperatures remained well homogenized. During the LOCA, passive buoyancy-driven circulation limited temperature rise, stabilizing around 1026 °C. These findings provide preliminary insight into PeLUIt-40 thermal hydraulics, highlighting the need for further validation and extended transient analysis to confirm safety margins.