Direct experimental measurement of the solubility of hydrogen isotopes in the Eurofer-97 RAFM

• The gas evolution absorption–desorption technique was used for the evaluation of the Sieverts’ constant of protium and deuterium in Eurofer-97. • The absorption–desorption technique allows the direct measurement of solubility, avoiding indirect measurements that have been used traditionally. • Solubility values have been provided in terms of Sieverts’ constant for protium and deuterium in Eurfofer-97 at three different temperatures (350 °C, 450 °C and 550 °C). • No isotopic effect has been observed and experimental values show good agreement with literature. Accurate knowledge of hydrogen isotopes transport properties in structural materials of interest for Breeding Blankets (BB) and Tritium Extraction and Recovery (TER) systems is fundamental for experiments, modelling, safety and design activities. This work aims at measuring these transport properties in Eurofer-97 at laboratory conditions, providing a reliable measure, at relevant operational conditions, on which a degree of uncertainty exists. The solubility of protium and deuterium, expressed in terms of the Sieverts’ constant ( K S ), is commonly derived indirectly from permeation experiments, assuming Sieverts’ law and diffusion-limited regimen (DLR). In this work, aiming the goal of avoiding these indirect procedure, solubility of protium and deuterium in Eurofer-97 was directly measured by means of the gas evolution absorption–desorption technique at the facility located in the University of the Basque Country (EHU). This facility has been previously used and validated for the direct determination of hydrogen isotope solubility in other reduced-activation ferritic–martensitic steels (RAFM). Absorption–desorption experiments were carried out using Eurofer-97 samples at three different temperatures, for both protium and deuterium. The resulting values of Sieverts’ constants expressed in [mol m −3 Pa −0.5 ] for protium at have been 8.75 × 10 −3 at 350 °C, 1.13 × 10 −2 at 450 °C and 1.33 × 10 −2 at 550 °C, while for deuterium values of 7.88 × 10 −3 , 1.15 × 10 −2 , and 1.26 × 10 −2 have been obtained at the same respective temperatures. Within the experimental uncertainty, no clear isotopic effect on solubility can be confirmed in the temperature range investigated, which is consistent with classical transport theory. Likewise, the measured values are in good agreement with literature data, especially with the most recent results. This study provides, for the first time for Eurofer-97, a fully direct experimental determination of the solubility of hydrogen isotopes, which contributes to reducing uncertainties in the modelling of hydrogen transport for fusion applications.