Dottorato in ENERGIA E AMBIENTE

Titolo della tesi: Development of a System Magneto-Thermal- Hydraulics Code for the Modelling of Nuclear Fusion Reactors

This doctoral research focuses on the critical problem of modeling and understanding Magnetohydrodynamic (MHD) phenomena in the Liquid Metal Breeding Blankets (BB) within magnetic confinement fusion reactors. Conventional analytical and numerical methodologies have proven to be inadequate for capturing the complex interactions and phenomena inherent to the extreme conditions present in fusion environments. To address this lacuna, the study presents the development, Verification and Validation (V&V) of a novel Systems Thermal-Hydraulic (SYS-TH) computational tool, named RELAP5 Development for MagnetoHydroDynamics (REDMaHD). The foundation for REDMaHD is the well-regarded RELAP5/Mod 3.3 code, which has been widely validated for thermo-fluid-dynamic assessments of fission reactors. Adapting this code for fusion applications has led to a software platform with comprehensive capabilities, including the computation of distributed MHD pressure losses in various channel configurations and the evaluation of localized MHD pressure drops due to factors like bends, cross-sectional changes, and electrical conductivity discontinuities in the walls. The tool is also designed to work with fusion-relevant liquid metals, such as the lead-lithium eutectic alloy (PbLi) and sodium-potassium (NaK), further expanding its applicability. An extensive V&V procedure was conducted to establish the reliability and accuracy of REDMaHD. This involved not only the validation of individual subroutines but also the comparison of the code output against existing numerical simulations and empirical data from three Test Blanket Modules (TBMs) including the LLCB, HCLL, and WCLL. The validation process has shown that REDMaHD predictions deviate only minimally, by approximately 1% to 10%, when compared to these benchmark results, thus confirming its fidelity in simulating key electromagnetic effects relevant to fusion reactor design. Although REDMaHD has proven to be an advanced and dependable tool, it is important to note the existing limitations. The code currently lacks specialized modules for certain electromagnetic coupling phenomena and three-dimensional MHD losses, which impacts its ability to predict mass flow distributions in multi-channel configurations. The study outlines the future work needed to resolve these issues, including the integration of additional modules that can handle the newly identified requirements. By providing an advanced numerical tool with verified capabilities, this thesis significantly contributes to ongoing research efforts in fusion technology, offering a robust computational platform for tackling a wide range of engineering challenges in the design and operational analysis of future fusion reactors.