Abstract
Liquid lead-lithium in eutectic proportions (Pb-Li) is a candidate material for Breeding Blankets (BBs) in future Fusion Power Plants (FPP). BB design depends on the diffusivity and Sieverts’ constant (solubility) of tritium in this alloy, but literature reports a large scattering of measurements for these values. A model was developed to address one possible source of this scattering in static experiments, i.e., non-negligible loss of hydrogen gas through steel walls of containers. This model simulates the dissolution of gases into, and their diffusion through, metallic barriers for diffusivity and Sieverts’ constant as inputs. When implemented, it can be used to compute the pressure decrease in a metallic chamber, and comparison of simulated curves with experimental ones allows for estimates of the diffusivity and Sieverts’ constant. This approach was used to estimate these coefficients for deuterium in stainless steel, using experiments performed with a 316L steel chamber from an existing facility (the Vacuum Sieve Tray setup) and simulations in a quasi-2D representation of this chamber. This validated the model, which was then used to simulate the chamber containing Pb-Li, as a means of planning for future experiments.
Highlights
The European DEMOnstration Power Plant (EU-DEMO) is foreseen to consume more than 100 kg of tritium (T, or 31H) per full-power-year of operation [1]
Tritium must be produced in situ by Breeding Blanket (BB) systems, using a combination of Neutron Multiplier Material (NMM) and lithium compound
Liquid lead-lithium in eutectic proportions can act as both breeder and NMM, so it has been chosen for some BB concepts, including one of the current designs under Research and Development (R&D) focus, the Water-Cooled Liquid-Lithium (WCLL) concept [1]
Summary
The European DEMOnstration Power Plant (EU-DEMO) is foreseen to consume more than 100 kg of tritium (T, or 31H) per full-power-year of operation [1]. Static experiments attempt to infer the Sieverts’ constant by measuring: (a) how much of a fixed initial amount of hydrogen is absorbed by a Pb-Li sample; or (b) how much hydrogen desorbs from a Pb-Li sample previously exposed to a hydrogen atmosphere [6,7] In both cases, the eventual passage of hydrogen through the experimental container walls is non-negligible; walls are usually made of steel, which presents solubility, for the great majority of literature measurements, at least one order of magnitude higher than Pb-Li. In both cases, the eventual passage of hydrogen through the experimental container walls is non-negligible; walls are usually made of steel, which presents solubility, for the great majority of literature measurements, at least one order of magnitude higher than Pb-Li This can interfere with the accuracy of measurements and lead to an overestimation of absorption or underestimation of desorption. The model was applied to a simulated experiment with Pb-Li, to provide predictions and guidelines for future measurements with the setup (Section 5)
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