Accumulation of radioactive corrosion products on steel surfaces of VVER type nuclear reactors. Part I. Ag-110m contamination

Formation, presence and deposition of corrosion product radionuclides (such as Co-60, Cr-51, Mn-54, Fe-59 and/or Ag-110m) in the primary circuits of w ater-cooled nuclear reactors (PWRs) throw many obstacles in the way of norm al operation. During the course of the work presented in this series, accum ulations of such radionuclides have been studied at austenitic stainless st eel type 08X18H10T (GOST 5632-61) surfaces (this austenitic stainless steel corresponds to AISI 321). Comparative experiments have been performed on m agnetite-covered carbon steel (both materials are frequently used in some S oviet VVER type PWRs). For these laboratory-scale investigations combinatio n of the in-situ radiotracer 'thin gap' method and voltammetry is considere d to be a powerful tool due to its high sensitivity towards the detection o f the submonolayer coverages of corrosion product radionuclides. An indepen dent technique (XPS) is also used to characterize the depth distribution an d chemical state of various contaminants in the passive layer formed on aus tenitic stainless steel. In the first part of the series the accumulation o f Ag-110m has been investigated. Potential dependent sorption of Ag+ ions ( cementation) is found to be the predominant process on austenitic steel, wh ile in the case of magnetite-covered carbon steel the silver species are ma inly deposited in the form of Ag2O. The XPS depth profile of Ag gives an ev idence about the embedding of metallic silver into the entire passive layer of the austenitic stainless steel studied.