Assessment of a new model for the linear and nonlinear stability analysis of natural circulation loops with supercritical fluids

• A new model for transient and linear stability analysis of natural circulation loops with supercritical fluids is presented.
• A code-to-code assessment addressing the effect of the presence of heating structures is performed.
• The new model is also applied in the analysis of an experimental loop.
• Conclusions are drawn on different parametric effects.

The paper describes the characteristics and the first applications of models recently developed to analyse both transient and linear stability of natural circulation loops, also accounting for the presence of heat structures. The models were conceived to be applied to loops containing fluids at supercritical pressure, though in principle they can be applied to a variety of fluids, even in usual single-phase and two-phase conditions. With respect to available system codes and already published models, the advantage of the twin programs set up in this work is to make use exactly of the same numerically discretised equations for transient and linear stability analyses, giving a clearer perspective of the obtained results, also including the effect of heat structures.For purpose of assessing the new models, a systematic comparison with the results obtained by the RELAP5 code results is performed, showing a very high level of coherence in very different conditions, including or not heat structures. The models are then applied to an experiment already addressed in previous work, better justifying the obtained conclusions.