Hydrogen-induced micro-void formation in copper used for spent nuclear fuel disposal canisters

Spent nuclear fuel is planned to be deposited in the 50 mm thick copper canisters at about 500 m depth in the bedrock. Hydrogen uptake may occur in the disposal conditions in copper due to corrosion reactions and effects of irradiation. Therefore, it is important to know in which conditions the hydrogen uptake results in the formation of pressurized hydrogen bubbles near the copper surface. During the thermal desorption spectroscopy (TDS) measurements the existing hydrogen bubbles grow due to accumulation of dissolved hydrogen and build-up of hydrogen gas pressure inside the voids. The further growth of the voids occurs by plastic deformation and results opening of the voids near the copper surface due to increasing temperature. The friction-stir weld metal samples of phosphorous-doped oxygen-free copper were cathodically charged with hydrogen in a 1.0 N H2SO4 solution with added 10 mg/L thiourea at various electrochemical potentials, -0.95…-1.3 VSCE. A threshold potential of -1.10 VSCE was found for the marked increase of hydrogen uptake and hydrogen-induced void formation near the copper surface.