Effect of the precipitates on the hydrogen desorption kinetics from zirconium-niobium alloys
Résumé
This study aims at identifying and quantifying the rate-limiting steps of the hydrogen desorption process from unoxidized M5Framatome 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 M5Framatome and Zr-2.5%Nb is trapped by the Nb-rich precipitates. In the studied conditions and regarding M5Framatome, 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 M5Framatome was identical to the one previously determined on Zircaloy-4.
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