Pt catalytic effects on the corrosion and hydrogen chemisorption properties of Zircaloy-2

Noble metals are added to boiling water reactors (BWRs) to mitigate stress corrosion cracking of structural components made from steels and Ni-based alloys and this technology is referred to as Noble Metal Chemical Addition (NMCA) or NobleChemTM. There is a growing concern that NMCA can cause unwanted harmful effects on the corrosion and hydrogen uptake properties of Zircaloy-2 fuel cladding. To investigate this, we have subjected Zircaloy-2 fuel claddings to out-of-pile BWR conditions in a custom-built autoclave. These claddings are oxidized in pressurized hot water (280 °C, 9 MPa) for 25, 60 and 150 days, wherein Pt nanoparticles (~10 nm) were simultaneously injected. Cross-sectional focused ion beam cuts made at the oxide-metal interface reveal that the oxide growth is not significantly influenced by the local Pt loadings (≤ 1 µg·cm-2). Surprisingly, an inverse correlation was observed between oxide thicknesses and metal's hydrogen contents. Interestingly, Pt catalysts have led to diminished hydrogen absorption in specimens with liner exposed to the hot water. Overall, Pt catalysts exhibited no detrimental effects on the corrosion rate and hydrogen absorption in Zircaloy-2.