Simulation and analyses of a complete loss of electrical power supplies in the TRR using the RELAP5 code

In this paper, a complete loss of electrical power supplies or station blackout (SBO) is simulated and analyzed for the Tehran Research Reactor (TRR). The scenario is virtually traced in absent of active cooling systems and operators. The code nodalization is successfully benchmarked against experimental data of the reactor operating parameters. The passive heat removal system includes downward water cooling after pump breakdown by the gravity force (where the coolant streams down to the unfilled portion of holdup tank), safety flapper opening, flow reversal from downward to upward cooling direction, and then the upward free convection heat removal throughout flapper safety valve, lower plenum, and fuel assemblies. Both short-term and long-term natural core cooling have been simulated and investigated using the RELAP5 code; when short-term analyses focued on the safety flapper valve operation and flow reversal mode. Results are promising for pool-type MTRs due to investigate RELAP code abilities for MTR thermal-hydraulic simulations without any oscillation; and also the TRR is conservatively safe against a complete SBO.