Simulations of two different events without scram were conducted for a hypothetical research reactor, based on the High-Flux Australian Reactor (HIFAR) moderated and cooled by heavy water circulating under atmospheric pressure. The simulations were performed with the RELAP5/MOD3.2 computer program. Although the simulations neglected reactivity feedback effects, the focus on the thermal-hydraulic aspects represents a step toward full analyses of hypothetical events in HIFAR. Two simulations focused on events associated with the failure of the primary coolant circulation pumps, and three simulations focus on the events associated with the reduced heat removal via the nonavailability of heat exchangers. The critical heat flux subroutine of the RELAP program was modified to account for the concentric annular fuel element geometry of HIFAR fuel elements.