Analyses of primary side oxide layers on steam generator tubes from PWRs and radiochemical issues on the contamination of primary circuits

Abstract

Auger electron spectroscopy, X-ray photoelectron spectroscopy and γ-spectroscopy have been used to investigate primary-side oxide layers on steam generator tubes from three PWRs. The distribution of iron, chromium, nickel and oxygen in the depth of the oxide layer as well as the valency states of these elements show FeCr 2O 4 to be the main chemical compound forming the oxide layer. Nickel occurs in the entire oxide layer in the elementary state. Only a top few nanometer of the oxide layer contain some NiO besides elementary Ni. 60Co is homogeneously distributed in the entire oxide layer. Considering other radiochemical measurements performed in these three plants, it can be stated that only the ionic fraction of the 60Co in the coolant is able to explain the build-in distribution of this radionuclide in the oxide layer and is thus responsible for the primary circuit contamination.