• In-Box LOCA
• Lithium-Lead
• SIMMER
• Water/PbLi interaction

The present research focuses on advancing the numerical modeling of the Lithium-Lead eutectic alloy and its interaction with water. Simulating these interactions is pivotal for the safety analysis of the Water-Cooled Lithium-Lead Breeding Blanket in the event of an In-Box LOCA. By addressing important open issues in key areas such as numerical modeling and coupling methodologies, this work contributes to the development of a robust framework for Deterministic Safety Analysis, which is essential for ITER and DEMO.
The research is divided into two distinct but related numerical activities. The first focuses on developing a coupling methodology to simulate a full-scale system, while the second addresses key challenges in how SIMMER models the Lithium-Lead alloy and its interaction with water. Additionally, the research is supported by an existing experimental database on the Lithium-Lead/Water interaction from the LIFUS5/Mod3 facility
The research begins with a sensitivity analysis of an experimental test conducted with the LIFUS5/Mod3 facility. This analysis highlighted two key areas for improving the SIMMER code's ability to accurately capture transient phenomena during In-Box Loss of Coolant Accidents (LOCAs), namely the development of a novel approach to modeling the chemical reaction between water and Lithium-Lead and the implementation of a realistic fluid behavior for the eutectic alloy.
A major component of this work was the development of a coupling methodology designed to simulate the In-Box LOCA in complex systems, such as the LIFUS5/Mod4 facility - a 1:1 scale representation of the ITER Lithium-Lead loop currently under construction. The coupling of the SIMMER-IV and RELAP5/Mod3.3 codes enabled, for the first time, the simulation of phenomena occurring during an In-Box LOCA. This represents an important starting point for developing a numerical methodology to conduct safety analyses at a system level.
The numerical modeling activities focused on two key areas of improvement identified in the earlier stages of this research, necessitating modifications to the original SIMMER source code. First, the Equation of State and thermophysical properties for the Lithium-Lead eutectic alloy were developed based on the SIMMER code framework, enabling the simulation of real fluid behavior. Second, a novel chemical reaction approach was implemented to account for the distinct properties of Lithium and Lead. This enhancement allowed the chemical reaction to occur only in the presence of Lithium, representing a more realistic behavior of the alloy. A preliminary approach to modeling the chemical reaction kinetics was also introduced, focusing on the limitations imposed by the diffusion of Lithium toward the reaction interface. Finally, a new variable was implemented to simulate the pressure drop in the gas phase caused by partially blocked flow passages due to solidified eutectic alloy.
Finally, the last section focuses on the comparison between experimental results, the new version of the SIMMER code, and its previous version. The analysis emphasized the quantitative results of the pressurization, highlighting the significant improvements achieved with the new version of the SIMMER code. However, key open questions regarding the reaction energetics and pathways were identified, underscoring the need for further investigation.
Overall, this work represents significant progress in enhancing the capabilities of the SIMMER code for nuclear fusion applications and its integration with RELAP5/Mod3.3. It establishes a robust foundation for safety analysis in fusion reactor systems. By addressing critical aspects of numerical modeling, it bridges important gaps in our understanding of PbLi/water interactions, supporting the design and development of fusion reactors such as ITER and DEMO.