## 1 Introduction  
In 2000, the United States Department of Energy (DOE) identified the need for advanced nuclear technologies and convened the Generation IV International Forum (GIF) to expand the mission of nuclear energy and further the development of future nuclear systems. The next generation advanced reactors seek to achieve (1) optimal resource utilization and waste minimization; (2) high proliferation resistance; (3) safety and reliability through passive safety systems that eliminate the likelihood of fission product release during accident scenarios [1]. Liquid-fueled molten-salt reactors (LFMSRs) have the potential to reduce the cost of electricity generation with an overall cycle efficiency that is higher than conventional reactors [2]. There is also no need to manufacture fuel pellets and rods since online refueling ensures that the reactor can continue operating. These objectives are realized by LFMSR systems since different salt compositions and fuel forms provide flexibility in temperature margins, neutron spectrum, and power density [1]. Other advantages to LFMSR systems include high-temperature process heat, minimal high-level nuclear waste, negative void and thermal reactivity feedback, and low-pressure operation. Researchers need advanced modeling approaches to obtain results with a reasonable computational efficiency while maintaining accuracy owing to the unique characteristic of the design such as liquefied fuel, complex core geometry, fast spectrum, and moving precursors. The key is to identify and model these multi-physics phenomena that impose the potential challenges to modeling and simulation of the reactors. In this study, GeN-Foam [3] is adopted as the main modeling and simulation tool for LFMSR. GeN-Foam is based on the Open-Source Field Operation and Manipulation (OpenFOAM) C++ library [4]. The LFMSR can be modeled using the GeN-Foam code to avoid a detailed Reynolds-Averaged Navier-Stokes (RANS) model of components such as heat exchangers and pumps. The flow and heat transfer in these components can be modeled using a porous k-epsilon approach, thereby saving a lot of computational expense and time. Most of the recent research efforts have been focused on studying the LFMSR, developing and verifying multi-physics codes for the LFMSR simulation [5]. The Safety Assessment of the molten-salt fast reactor (SAMOFAR) project coordinates research efforts on the molten-salt fast reactor (MSFR) concept in Europe. The MSFR is a fast-spectrum breeder reactor with a large negative power coefficient. The fast spectrum allows the reduction in the reprocessing requirements and enables a better reactor breeding ratio [6]. The reference MSFR concept is a 3000 MW\({}_{\text{th}}\) reactor with three different circuits: the fuel circuit, the intermediate circuit, and the power conversion system. Figure 1 illustrates a basic layout of the MSFR. The components of the primary fuel circuit are the fuel salt, the core cavity, the heat exchangers, the pumps, the inlet and outlet pipes, and the salt-bubble separators. The initial composition of the MSFR is 77.5 mol% of LiF and a 22.5% mol mixture of AcF\({}_{3}\) and AcF\({}_{4}\) (Ac indicates actinides, mostly \({}^{232}\)Th or \({}^{233}\)U). The total volume of fuel salt is about 18 m\({}^{3}\) in the fuel loop, and the average core salt temperature is approximately 725 \({}^{\circ}\)C. The fuel salt, upon exiting the core cavity from the top, flows into 16 different loops, each containing a pump and heat exchangers located around the core. The fuel salt circulates the loop in about 3-4 s [7]. The MSFR design has some potential advantages as discussed but also poses new challenges in terms of reactor design and safety. The presence of several phenomena  
Figure 1: Layout of the molten-salt fast reactor (MSFR) fuel circuit [7]. inherent to molten salts that do not exist in other reactor types requires the development of better modeling tools and new methodologies to perform the safety evaluation.