Hydrogen Embrittlement of Duplex Stainless Steel 2205 and TiPd Alloy in a Synthetic Bentonite Pore Water Available to Purchase

This work is focused on evaluation of the susceptibility of spent nuclear fuel repository canister structural materials to hydrogen embrittlement. The materials studied in these experiments were duplex stainless steel 2205 (UNS S32205/S31803) and titanium alloy with palladium. Both hydrogen absorption kinetics and mechanical properties were studied. Both materials were tested in a solution of sulphuric acid with arsenic trioxide and in the synthetic bentonite pore water. Laboratory temperature, 40°C and 90°C and current densities of 0.2 A/m², 10 A/m², and 100 A/m² were used for this work. Some samples were exposed to gamma radiation in an irradiation facility to verify the possibility of hydrogen absorption due to water radiolysis. Hydrogen absorption kinetics were evaluated by means of thermal desorption spectrometry and x-ray diffraction. Mechanical properties were observed by means of a slow strain rate tensile test, U-bend test, and impact toughness. Hydrogen absorption in the synthetic bentonite pore water is possible even at low current densities, which is proportional to galvanic corrosion. Water radiolysis did not lead to hydrogen absorption. Hydrogen absorption in titanium alloy causes titanium hydride formation, accompanied by total disintegration of the material. Lower current densities paradoxically can lead to faster hydrogen uptake at the beginning stage of charging because formation of the hydride layer is delayed. Saturation of duplex stainless steel with hydrogen leads to significant loss of ductility, but fracture is possible only under a load that is higher than the ultimate tensile strength. The loss of ductility is more significant at lower temperatures. The results obtained in this study showed that hydrogen absorption into TiPd alloy and duplex stainless steel is possible even in neutral bentonite pore solution at low current densities. Water radiolysis under low gamma irradiation does not lead to hydrogen absorption.