Safety analysis of the NuScale Small Modular Reactor: steady-state qualification and small break loss of coolant accident simulation using RELAP5/SCDAPSIM3.4.

This paper presents a comprehensive safety analysis of the NuScale Small Modular Reactor, a next-generation nuclear technology. The NuScale design emphasizes enhanced safety, flexibility, and efficiency, achieved through a natural circulation cooling system and robust passive safety functions. The analysis is conducted using the RELAP5/SCDAPSIM3.4 system code for high-fidelity thermal-hydraulic simulations. The first part details the steady-state qualification of the reactor model, a crucial step to establish a reliable baseline for normal operation and subsequent accident analyses. The study confirms the model's accuracy against key design parameters including temperature distributions, coolant flow rates, and system pressure validating its predictive capability. Building upon this qualified model, the second part investigates a severe beyond-design-basis accident scenario. The initiating event is the inadvertent opening of one Reactor Vent Valve, leading to an inside containment Small Break Loss of Coolant Accident. This breach is compounded by the postulated total failure of both the Emergency Core Cooling System and the Decay Heat Removal System, creating a fully unmitigated scenario. The progression of this severe accident, simulated for a duration of 500 s, critically assesses the reactor's passive safety features and inherent resilience. The system's response is analyzed in detail, with key findings showing a consistent behavior comparable to the results of similar scenarios documented in the literature.