Investigation of VVER-1200 pressurizer dynamics by adopting modelica based modeling

This work is conducted within the framework of developing a control-oriented modelling and simulation tool focused on the study of the generation III + VVER-1200 plant transient dynamics, in order to conduct necessary stability analyses aimed at providing essential feedbacks required to perform the model-based control system design. An object-oriented modelling technique was applied, based on the reliable, validated and well-documented Modelica language. The pressurizer was modeled based on the Åström and Bell non-equilibrium approach. The developed model was then adapted to predict the behavior of the VVER-1200 pressurizer free dynamics at different conditions, with different perturbations/excursions. The developed model has been successfully integrated inside a Modelica based VVER-1200 plant model and pressurizer transient response to plant different free dynamics was tested. Test and verification of the developed model were performed against multiple benchmarks, as well as a real reference plant. Good agreement was obtained. Test results has shown that the simulator has provided precise information regarding its steady state as well as transient behavior even for severe excursions. Uncertainty analysis was also performed and showed that the developed model is more sensitive to the input variables than the plant model parameters. The model is valid along the complete operating range, including run-up/down, fast runbacks, as well as violent transients. The produced model is non-linear, time variant, of low order and high-precision. The adopted technique is well suited to the task of performing assessed studies for system dynamics. It fills the gap and overcomes shortages and/or limitations associated with current control-oriented modeling techniques. •Most control strategies used in LWRs, are based on model-free heuristic techniques, no studies regarding the pairings between input and output.•A new modeling has been widely adopted for complex systems, individual parts of the model are described directly as equations rather than an algorithm•Modelica-based model of VVER-1200 pressurizer was developed to study pressurizer dynamics. Verification, and uncertainty analysis was performed.•The resulted model(s) can be adopted for : dynamic stability analysis, synthesis of automatic control systems, and construction of control algorithms,•The developed model has been integrated inside a Modelica VVER-1200 model and pressurizer response to different free dynamics