Analysis of transient events without scram in a research reactor using theRELAP5/MOD3.2 computer code

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