Assessment of pressurizer dynamic performance for nuclear hybrid energy system modelling: Comparison between equilibrium and 1D non-equilibrium approaches

The importance of the pressurizer for the control and safe operation of pressurized water reactors translates into the need to develop accurate dynamic models to simulate the response of this component in various scenarios. This study compares two modelling paradigms, classified into equilibrium and non-equilibrium approaches, implemented in the Modelica language. Specifically, the non-equilibrium version adopts a 1D modelling approach with a user-defined number of control volumes. The objective is to assess the prediction accuracy by comparing simulation results with experimental data. The analysis identifies the models’ applicability limits as well a relevant phenomena affecting the outcomes. Additionally, the investigation is extended to a Small Modular Reactor (SMR) pressurizer architecture, exploring the impact of its features and different control strategies to mitigate pressure fluctuations. The latter analysis represents an initial step towards the development of a SMR-driven integrated energy system simulator, which will encompass the most suitable pressurizer model. The outcomes of this work indicate that the equilibrium model is able to capture overall system dynamics despite its strong simplifying assumptions. As for the SMR pressurizer, the distinctive geometry affects the system's response to the considered transients, resulting in the requirement of designing control strategies tailored to its characteristics.