Effect of the precipitates on the hydrogen desorption kinetics from zirconium-niobium alloys

This study aims at identifying and quantifying the rate-limiting steps of the hydrogen desorption process from unoxidized M5(Framatome) alloy. Gaseous deuterium charging, Thermal Desorption Spectrometry (TDS), Differential Scanning Calorimetry (DSC) and finite elements simulations of TDS results reveal that hydrogen desorption kinetics from the metal is limited by the surface molecular recombination (similarly to Zircaloy-4) and that part of the hydrogen originated from the elaboration process of M5(Framatome) and Zr-2.5%Nb is trapped by the Nb-rich precipitates. In the studied conditions and regarding M5(Framatome), the desorption flux corresponding to this initially trapped hydrogen reaches its maximum after the total dissolution of the precipitates, which releases hydrogen into solid solution. The kinetic constant corresponding to surface recombination identified on M5(Framatome) was identical to the one previously determined on Zircaloy-4. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study identifies and quantifies the rate-limiting steps of the hydrogen desorption process from unoxidized M5 alloy. It reveals that surface molecular recombination and trapping of hydrogen by Nb-rich precipitates are key factors affecting desorption kinetics. The kinetic constant for surface recombination on M5 alloy is found to be identical to that on Zircaloy-4.