The critical reactor header break and the thermosiphoning experiments in the RD-14 test facility were simulated with the RELAP5/MOD3.1 code. The RELAP5 code has been developed for best-estimate transient simulation of pressurized water reactors and associated systems, but it has not been assessed for a Canada deuterium uranium (CANDU) reactor. Therefore, this study has been initiated with an aim to identify the code applicability in a CANDU reactor by simulating some of the tests performed in the RD-14 facility. The RD-14 test facility at Whiteshell Nuclear Research Establishment is a full-scale pressurized-water loop. The RD-14 is not a scale model of any particular CANDU reactor. Rather, it possesses many geometric features of a CANDU reactor heat transport system and is capable of operating at conditions similar to those expected to occur in a reactor under normal operation and some postulated accident conditions. In this study, two critical reactor header break tests (B8711 and B8713) and three thermosiphoning tests (T8513, T8515, and T8517) were analyzed with the RELAP5 code. The results were compared with experimental data and those of CATHENA performed by Atomic Energy of Canada Ltd. The RELAP5 analyses demonstrate the code's capability to predict reasonably the main phenomena occurring in the transient, in both the qualitative and the quantitative view. However, some discrepancies after the emergency coolant injection for the critical break case and also related to the behaviors of the mass flow rate and the primary pressure for the thermosiphoning case were observed.