The Test Blanket Module (TBM) experimental campaign in the International Tokamak Experimental Reactor (ITER) is expected to be a fundamental opportunity to characterize the wide range of phenomena expected to occur in a full-sized blanket. This component is of fundamental importance for a future Fusion Power Plant (FPP) since it will ensures the reactor fuel supply, power extraction, and radiation shielding. The EU is currently pursuing two different TBM mock-ups to be tested in ITER revolving around different breeder and coolant concepts. The objective of this research proposal deals with the Water-Cooled Lithium Lead (WCLL) mock-up that it is envisioned to employ water in PWR-like conditions as coolant and lithium lead eutectic alloy (PbLi) as tritium breeder and carrier. Since PbLi is electrically conductive, flow within the TBM is expected to interact with the tokamak magnetic field and to transition to a magnetohydrodynamic (MHD) regime. This phenomenon carries many subtle consequences for the blanket (and TBM) design, one of the most important being the enhanced pressure loss due to electromagnetic drag. This research proposal aims to perform a set of in-depth MHD analyses aimed to characterize the most relevant phenomena in the TBM breeding zone (BZ): 2D flow in rectangular duct with non-uniform conductivity, coupled counter-flow channels connected by a hairpin bend, 3D flow around complex geometry obstacles, and BZ/manifold entrance effect. The work proposed starts from the significant know-how accumulated by the DIAEE research group in the last years for the simulation of MHD flows in the WCLL blanket and it is structured in a progressive way from simplified to higher complexity numerical models. Obtained results will directly impact the R&D activities on TBM design, mostly by developing scaling laws for several magneto-hydraulic elements, that will make possible to optimize and streamline the PbLi flow path about pressure loss minimization.
Nuclear fusion is considered the most promising energy source to meet the ever-increasing world demand for electricity consumption in the 21th century due to nearly carbon-free emissions, very limited production of only short-lived radioactive wastes and employing deuterium as nuclear fuel (cheap, uniformly distributed and virtually inexhaustible). However, the most promising fusion reaction involves the use of tritium that, as opposed as deuterium, has no significant natural source. Therefore, the design of a blanket able to breed tritium from lithium and able to guarantee the self-sufficiency of the reactor is a non-negotiable condition to improve the technological readiness level of the power generation from nuclear fusion and make it a viable commercial source.
The TBM program will allow for the first time in history the opportunity to qualify a blanket component in conditions approaching those expected in a FPP. For this reason only, it can be considered a fundamental step forward in fusion research and it is almost needless to highlight its significance. An accurate design of the TBM could allow to maximize the gains from this historical campaign and can potentially bootstrap the blanket development for DEMO. Even more important, it constitutes an invaluable juncture to obtain high-quality experimental data for verification and validation (V&V) of numerical tools, which are essential to move forward the reactor development cycle.
High-quality experimental data in fusion-relevant conditions are particularly difficult to obtain to perform V&V of Computational Magnetohydrodynamics (CMHD) codes. Liquid metals are at best tricky to handle due to, among other issues, lack of transparency, chemical reactivity, toxicity, etc. For this reason, production of experimental data about liquid metal MHD flow is considerably more difficult than for other class of fluids and is relatively immature to more common fluids in industry like water or air.
This complexity is even further increased for fusion-relevant fluids, like PbLi, which require expensive heating systems and magnets to approach a usable parameter space (Ha ¿10^4). TBM data has the chance to further advance both fundamental MHD phenomena understanding and CMHD tools. Therefore, it is even more important to support this campaign with extensive pre-test simulations, of which TBM design R&D activities are an essential part. Flow feature characterization through numerical studies will aid the interpretation of the experimental data that will be gathered and could, even now, guide the TBM design toward an optimized solution and highlight the most interesting phenomena expected to happen in the mock-up.
Analyses envisioned for this study will significantly increase the body of knowledge for 3D MHD flow around obstacles in at least two classes of problems: cylinder transverse and aligned with streamwise direction. Flow around obstacles is a classic hydrodynamic problem and the MHD perspective is of direct concern for many industrial applications, most notably in metallurgy.