Loss of flow accident analysis in Atucha II nuclear power plant using RELAP5 model

Abstract

The loss of flow accident (LOFA) in nuclear power plants (NPP) is considered a design base initiating event (DBIE) and it is broadly analyzed in safety and licensing evaluation. Therefore, this is commonly chosen to assess computational models. The current paper addresses the simulation of LOFA under single and total main coolant pump (PMP) trips during full power in Atucha-II Pressurized Heavy Water Reactor (PHWR). RELAP5-mod3.3 NPP was used for solving the thermal-hydraulics, neutron kinetics, and control and safety logic in steady-state and LOFA events. Simulations were assessed against real plant data recorded during a single-PMP trip obtaining very good agreement. After that, the total-PMP trip was simulated, showing that the plant also reached a safe steady condition, guaranteeing the removal of decay heat by natural flow circulation. The very good agreement in terms of the main thermal-hydraulics parameters demonstrated the capability of the computational model to reproduce the overall NPP behavior.