Fibre optic Raman spectroscopy has been used to characterise secondary-side deposits removed from CANDU steam generators. The deposits examined were in the form of powders, millimeter-sized flakes, and deposits on the surfaces of pulled steam generator tubes. The compositions of the deposits obtained using Raman spectroscopy compare favourably with the compositions obtained using other ex-situ analytical techniques. A semi-quantitative estimate of amounts of the
major components can be obtained from the spectra. It was noted that the signal-to-noise ratio of the Raman spectra decreased as the amount of magnetite in the deposit increased, as a result of absorption of the laser light by the magnetite. The conversion of magnetite to hematite by the laser beam was observed when high laser powers were used. The Raman spectra of larger flake samples clearly illustrate the inhomogeneous nature of the deposits. Keywords: Raman spectroscopy, fibre optics, corrosion products, iron oxides, steam generators