A coupled OpenFOAM-Modelica Modelling Framework for Analysing MSR Safety-Related Transients

In light of the licensing process of advanced reactor designs, a fundamental step to support the safety assessment consists of identifying and quantifying the uncertainties resulting from a lack of extensive practical knowledge and modelling assumptions. The uncertainty characterisation imposes specific requirements for the numerical tools employed to inspect safety-related phenomena. When dealing with Molten Salt Reactors (MSRs), the inherent characteristics of circulating fuel result in the need to perform multidimensional and multiphysics simulations to investigate the steady state and dynamic behaviour of the MSR concept. The multiphysics approach allows to capture the relevant governing phenomena strictly related to the strong coupling between neutronics and thermal-hydraulics. On the other hand, in the context of safety analysis, system codes have proven their suitability to represent the whole plant behaviour, implement submodules devoted to uncertainty quantification, and calibrate models with experimental data. In this work, a computational chain coupling system codes and high-fidelity multiphysics tools is developed to manage in the same environment different levels of detail. The modelling framework couples Modelica and OpenFOAM modelling tools thanks to Functional Mock-Up Interfaces, which define a container and an interface to exchange dynamic simulation models. This approach embraces a multidimensional and multiphysics model of the MSR core while preserving a global representation of the plant. The OpenFOAM-Modelica coupling chain is tested on a case study involving a symmetric portion of the Molten Salt Fast Reactor primary loop with a simplified representation of the intermediate salt circuit and Balance of Plant.