Hydrogen isotope transport parameters in materials for tritium extraction systems. Focus on the low pressure

Abstract

This work aims to fill a gap in the H transport database for niobium and vanadium, materials proposed for the fabrication of tritium extraction systems. The permeability, key parameter for this application, has not been properly determined in niobium so far. Values are given for H2 and D2 permeability in two different Nb samples from different suppliers but with similar microstructure from ¿300 °C to 500 °C and tested with loading pressures from 20 mbar to 500 mbar: For vanadium, new measurements for material from different suppliers and with very different microstructure allow to confirm values for the permeability recently published (in contrast to the traditionally accepted values indirectly derived from solubility and diffusivity). In this work, the following expression is given for deuterium: There are very few documented attempts to measure surface rate constants for either of the two materials under consideration. These parameters are especially important and define the permeation process under certain conditions, in particular at low pressures. Hydrogen and deuterium permeation data in Nb and V has been therefore obtained in a wide range of pressures, with special focus in the low pressure region, the role of the microstructure being also evaluated. Surface rate constants and which are fundamental parameters for the modelling of H isotope transport through the materials, have been determined in vanadium and niobium with different surface finishes, this factor resulting determinant of the result.