Development of a reverse permeation model for the calculation of hydrogen transport parameters

Determining the diffusion parameters of the hydrogen isotopes in fusion materials is essential for the design of fusion reactors. Measuring these parameters is usually performed at relatively high pressures. However, these same measurements at low pressures are problematic. Maintaining a constant pressure at low pressures is technically challenging, which complicates traditional direct diffusion experiments. The main objective of this work is to provide a solution to that technical limitation. For this purpose, a reverse permeation method is proposed, using the permeation facility at the Bilbao School of Engineering. This method consists of using the final stage of a direct permeation experiment as the initial stage of a new diffusion experiment. Three experimental measurements have been carried out with Eurofer, AISI 316 and AISI 4130 samples. This method allows measurements to be made in a low-pressure range using the entire setup used for the direct diffusion experiment. However, since the pressure is not maintained constant during the experiment, a mathematical model is required to relate the measurements to the diffusion parameters. In this work we have developed a mathematical model, which tries to adjust these curves in order to parameterise them. A precise qualitative description has been achieved, and its quantification is still to be perfected.