Nuclear systems and reactors stand out by their intrinsic complexity and the wide range of scientific and technical disciplines they involve. The design, modeling, and operation of a reactor rely on the close interdependence between neutronics, thermal-hydraulics, and thermomechanics, complemented by the description of the thermodynamic cycle of the secondary circuit and the plant's control and instrumentation systems. Historically, each of these fields has led to the development of specialized computational codes, recognized for their reliability and accuracy. However, integrating these tools into comprehensive simulation frameworks has quickly raised major challenges related to interoperability, data consistency, and the heterogeneity of physical and numerical models.
To address these challenges, the standardization of code coupling interfaces has attracted growing interest, particularly following the release of the Functional Mock-up Interface (FMI) standard. This standard provides a unified framework for the systematic coupling of models from different domains, thereby facilitating communication between heterogeneous software tools. In this context, three coupling strategies were developed, analyzed, and applied to various nuclear systems: coupling through a heat exchanger between two thermal systems, pressure-velocity coupling between distinct thermal-hydraulic circuits, and a multiscale coupling linking the reactor core to detailed fuel pin models.
These coupling strategies were illustrated through several representative case studies. The first application focused on the simulation of load-follow operation in a simplified nuclear power plant. The second addressed the modeling of a simplified nuclear propulsion system during a trans-lunar injection. Finally, the third examined the effects of beam trips on the fuel pins of an Accelerator Driven System.
Overall, these studies demonstrate the feasibility and relevance of multi-code coupling based on the FMI standard for the integrated simulation of complex nuclear systems. The results confirm that this approach represents a promising pathway toward more flexible and interoperable modeling tools for reactor design and safety analysis.
