In-line measurement of the oxide layer build-up on Zircaloy under boiling water reactor (BWR) conditions using diffuse reflection spectroscopy

Diffuse reflection spectroscopy (DRS) can be used successfully to monitor in situ the early and pre-transition stages of the corrosion of Zircaloy at high temperature under simulated boiling water reactor (BWR) conditions. Measurements were carried out with a UV-vis-NIR spectrometer connected to a flow-through cell using an optical fibre bundle. In the cell the sample was illuminated through an optical window and the water from a test loop (550 K, ; that is, about C, 90 bar ). Spectral investigations in the wavelength range 200-1000 nm allow in-line measurements of oxide layer thickness from some nanometres to the micrometre range. The precision of the experimentally determined thickness is about (i stands for the order of interference). The time necessary to record one spectrum is less than 1 min. The method allows the study of the oxide layer build-up over several weeks.