Thermalhydraulic study of research reactor is still continously improved to considered that there are many postulated accidents cases in safety analysis report (SAR). Thermalhydraulic aspect analysis of research reactor using RELAP/SCDAP was performed. This analysis began with steady state condition calculation for variation of reactor power, then followed by accidents condition considerd in safety analysis report (SAR) such as reactivity insertion accident (RIA), loss of flow accident (LOFA) and loss of coolant accident (LOCA) due to primary cold leg break and beam tube rupture. For steady state calculation, to adjust the flow to the core, the calculation result using computational fluid dynamic (CFD) was used. Then, the results were compared with modified STAT code and measurement. For reactivity insertion accidents simulations were performed with power and reactivity variation inorder to find the worst case, in this thesis paper shown that at low power RIA causes power excursion very high. During loss of flow accident simulation was assumed primary pump trip and without SCRAM, a natural circulation in the reactor tank was established and negative fuel temperature reactivity feedback that maintained the power and fuels temperature were still low. During loss of coolant accident simulation, in case of primary cold leg break at the lowest part, the break flow was stopped by siphon breaker holes existing at the discharge and suction pipe and the water level was remained at that holes level. In case of the beam tube rupture simulation, water level descent to the middle of the core. This simulation assumed that water level monitor gives emergency signal, reactor scram and emergency core cooling system was actuated when water level at 5 m below normal level.
Keywords: thermal hydraulic, research reactor, reactivity insertion accident (RIA), loss of flow accident (LOFA), loss of coolant accident (LOCA), and RELAP/SCDAP