An in-line diffuse reflection spectroscopy study of the oxidation of stainless steel under boiling water reactor conditions

A novel cell unit was constructed to measure in-line the oxide layer build-up on a stainless steel sample by Diffuse Reflection Spectroscopy (DRS; ultraviolet, visible, near infrared) under boiling water reactor (BWR) conditions. The stainless steel samples, observed in the cell through a sapphire window, are contacted with oxidising hot water (300oC, 9.0 MPa). Using a cold finger with the optical fibre probe, the spectroscopic investigations (200-1000 nm wavelength) were performed at a fixed position from the sapphire window. The DRS spectra are the result of the coupling of both absorption (chemical) and interferometric (physical) processes. Analysis of these spectral components allows the independent determination of the oxide layer thickness. The build-up of the oxide layer may be directly observed and quantified, nanometre by nanometre, from 2 to 200 nm. This powerful technique may be used to study the early corrosion rates of stainless steel under BWR conditions and should allow the development of a strategy to reduce corrosion. (Author)