NuScale SMR 3-D Modelling and Applied Safety Analyses with the System Code ATHLET in the Framework of the EU H2020 McSAFER

Research and development of small modular reactors (SMRs) is receiving increasing attention by several countries and organizations due to flexibility, cost reduction and advanced safety features. The SMR NuScale is modelled by Helmholtz-Zentrum Dresden Rossendorf (HZDR) in the framework of the EU H2020 McSAFER project. NuScale is a SMR of integral pressurized water reactor (PWR) type, operated with light water driven by natural circulation in all operation modes. This work summarizes the modelling approach of a thermohydraulic model of NuScale SMR with the system code ATHLET, that includes a state-of-the-art 3-D reactor pressure vessel (RPV). The paper presents results and discussion from a boron dilution sequence at hot full power based on the Design Certification Application (DCA) report. Simulation results show agreement at steady-state and transient calculation, thereby demonstrating ATHLET strong simulation capabilities on complex sequences in SMR designs. The results show a decrease in core nominal boron concentration and subsequent reactivity insertion by boron feedback. The reactor is tripped upon “high pressurizer pressure” function by the insertion of the control rod banks. The actuation of the decay heat removal system (DHRS) provides long term core cooling to bring the reactor to a safe shutdown condition and preservation of shutdown margin is met during the simulation thereby complying with acceptance criterion.