Investigation of Water Adsorption on OFP-, 6N, OF-Cu(100) Surfaces BT X-Ray Photoelectron Spectroscopy

The method chosen by Posiva Oy (Finland) and Svensk Kärnbränslehantering AB (Sweden) for the final disposal of spent nuclear fuel is the KBS-3 method. It entails disposal of spent nuclear fuel underground in canisters that have a protective exterior made of copper (Cu). At present, there is controversy over the extent of corrosion of Cu in anoxic water. Recent results suggest that Cu can corrode in anoxic water to a much larger extent than what has been predicted earlier.

In this report, surface sensitive X-ray photoelectron spectroscopy (XPS) is employed in the study of initial stages of water vapor adsorption on technologically relevant OFP-, 6N- and OF-Cu and on Cu(100) single crystal surface.
Experiments are conducted in an ultrahigh vacuum (UHV) research system that facilitates controlled water exposures up to mbar range and at variable surface temperatures. In particular, water adsorption is investigated on metallic and pre-oxidized Cu materials at 30 ºC – 100 ºC and at pressures of 2x10^-3 mbar and 21 mbar. The elemental composition of the surface, molecular bonds and any surface compounds are identified by XPS before and after the water exposure.

Our results show no evidence of Cu oxidation in the investigated pressure and temperature range: neither the metallic nor the pre-oxidized Cu materials become further oxidized under the present conditions, although formation of adsorbed hydroxyl groups cannot be conclusively ruled out due to experimental limitations.