Reactor dynamic simulation to analyze possible scenarios after a spurious opening of the safety flapper valve of TRR during the normal operation regarding the inherently safety features and Design Extension Conditions (DEC) by using the RELAP5 code

Abstract

LOFA is one of the most important PIE in nuclear reactors. For the pool-type research reactor, the safety flapper valve is usually located below the reactor core and have a very important rule on the reactor safety especially during the loss of the pump accident. In this paper, TRR has been simulated and analyzed against the spurious opening of the safety flapper valve during normal full power operation. First of all, the steady state parameters are successfully benchmarked against the operational data of TRR. Then, the reactor dynamic calculations are successfully benchmarked against a sophisticated experimental dynamic test to evaluate the reactor power changes due to reactivity feedback. Then three different types of possible scenario including both types of DBA and DEC are simulated and analyzed. Furthermore, inherently safety features are evaluated against temperature rises. Results indicate that if the anticipated emergency shutdown signal is triggered successfully, the reactor core remains safe against any physical damage. If the reactor reactivity control system is completely disabled, the inherently safety features of the reactor decrease the reactor power effectively via negative reactivity feedback and the reactor fuel assemblies remain safe again. But if the fault diagnosis system of the spurious opening of the safety flapper valve fails to detect the occurrence or it does not send the emergency shutdown signal, and at the same time, the automatic power regulation system keeps the normal operating conditions, the hot spot may reach to the fuel melting point just a few seconds after the accident occurrence.