1D Modelica Modeling of the DYNASTY-eDYNASTY Coupled Natural Circulation Loops

In developing safety systems for advanced nuclear reactors, such as the Gen-IV Molten Salt Fast Reactor (MSFR), the study of natural circulation is of primary importance. The MSFR is a particular type of reactor characterized by natural circulation in the presence of an internally distributed heat source during shutdown due to the fluid fuel being mixed with the thermal carrier. To analyze natural circulation with a distributed heat source, the DYNASTY facility was designed and built in Politecnico di Milano and later extended with the eDYNASTY facility to study natural circulation on coupled systems. The coupled facility analyzes the influence of a secondary natural circulation loop on the behaviour of the primary DYNASTY facility, simulating the presence of the intermediate loop in the MSFR design. This work focuses on modelling the coupled DYNASTY-eDYNASTY natural circulation loops using DYMOLA®, an integrated development environment based on the Modelica Object-Oriented a-causal simulation language. The 1D Modelica approach allows for building highly reusable and flexible models, easing the modelling effort on complex systems such as the DYNASTY-eDYNASTY coupled facility and allowing eventual model updates without the need to rewrite the whole model from scratch. This work analyzes the behaviour of the DYNASTY-eDYNASTY coupled facility models when influenced by the addition of distributed heat losses with the environment. The simulation results are presented, discussed, and compared with the ones available in the literature, showing remarkable differences between the model's results. The simulation outcomes are then used to identify the most critical aspects of the models, preparing them for the experimental comparison.