Thermo-migration of hydrogen isotopes in Eurofer and AISI 316L steel

Permeation driven by thermal gradients (the Soret effect) was evaluated for H isotopes fusion grade steels, specifically Eurofer 97–3 and AISI 316 L as a separate process from the most commonly known permeation related to a gas concentration gradient. A unique permeation measurement system was developed to isolate and quantify permeation driven by thermal gradients, independent from the conventional concentration gradient-driven permeation. Experiments were conducted under fusion-relevant conditions, covering a pressure range of 0.1 mbar to 1000 mbar and temperatures between 300 °C to 500 °C, with thermal gradients up to 100 °C/mm. The results show that permeation induced by thermal gradients can be significant, reaching magnitudes comparable to those of ordinary fluxes. These results indicate that the Soret effect should not be neglected in tritium retention and loss calculations, and suggest that future fusion reactor designs must incorporate these considerations for improved safety and efficiency. This research contributes a critical piece of knowledge to the field, with implications for both the development of fusion technology and the management of tritium in such systems.