## 5 Simulation of Future VST Experiments with Pb-Li Using Literature-Averaged Dissolution Parameters  
The validated model presented in this work was then used to simulate an experiment similar to the one presented in Section 4, but this time including liquid Pb-Li in the UC. As an initial study to help plan for future experiments with the VST setup using Pb-Li, literature-averaged parameters for deuterium dissolution in both 316L steel (_vide_ Table 1) and Pb-Li (_vide_ below) were applied to these simulations, to evaluate the following averages: time required to reach dissolution equilibrium and expected pressure decrease in the chamber. Figure 9: Comparison between literature functions of \(\mathcal{D}_{\mathrm{D}}^{\mathrm{316L}}\) and \(\mathcal{S}_{\mathrm{D}_{2}}^{\mathrm{316L}}\) (coloured), and those determined by the curve-matching strategy (in _black_, _vide_ Table 2). As each experiment provided a set of dissolution parameters, the general behaviour of the Arrhenius Law around the temperature set for the experiment (_asterisk_ markers) is displayed by curve extensions (_dotted_ lines). (**a**) Comparison between literature functions of diffusivity for deuterium in 316L steel [12; 14; 44; 45], and from set of dissolution parameters (\(D_{\infty}\) and \(E_{d}\)) derived in this work. (**b**) Comparison between literature functions of Sieverts’ constant for deuterium in 316L steel [12; 14; 44], and from set of dissolution parameters (\(S_{\infty}\) and \(E_{s}\)) derived in this work. Simulating the VST Upper Chamber + Pb-Li System with Literature-Averaged Dissolution Parameters for Pb-Li  
Because of the large current scattering in measurements of dissolution parameters for hydrogen isotopes in Pb-Li, simulations were run using literature-averaged values. Table 3 shows the literature extremes and averages of dissolution parameters for deuterium in Pb-Li, derived using the logarithmic regression method (_vide_ Section 2 and Figure 2). Averages were obtained the same way as previously described. Some infinite-temperature diffusivity coefficients for deuterium were extrapolated from literature reports of hydrogen isotopes experiments, using Equation (6). In these cases, the activation energy was assumed to be the same for all isotopes. No extrapolation was performed for Sieverts' constants; only deuterium data directly found in literature was used. When applying literature-averaged dissolution parameters:  
* the calculated curve for the diffusivity of deuterium in Pb-Li is roughly _three_ orders of magnitude higher than in steel;
* the calculated curve for the Sieverts' constant of deuterium in steel is roughly _one_ order of magnitude higher than in Pb-Li. This implies that the gas diffuses more quickly through Pb-Li (as expected, since it is a liquid medium, while steel is a solid), so its profiles evolve faster than in steel. On the other hand, since the Sieverts' concentration (_vide_ Equation (3)) in Pb-Li is smaller than the one in steel, the BC experienced by steel surfaces that are covered by Pb-Li is smaller than the BC experienced by steel surfaces in contact with deuterium in gaseous form. This is true whenever the gas availability outside of the metals is not a limiting factor (i.e., \(c_{X}<c_{X}^{*}\) case, as opposed to case shown in Figure 4). Notice that this difference will be maintained during the dynamic evolution of the system, until the Pb-Li layer is completely saturated with deuterium (at which point steel will experience the same BC as steel surfaces in direct contact with the gas). Figure 10 shows the modelling approach applied to the UC, now containing Pb-Li. The interface between Pb-Li and the BASE in channel \(h^{\prime}\) can be treated using a Co-Dependent BC, as introduced in Section 3.2. Because of the Sieverts' constant scattering, its calculation relied on Equation (7) to ensure the continuity of the chemical potential instead of the concentration.