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

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 a combinat ion of the in situ radiotracer 'thin gap' method and voltammetry is conside red to be a powerful tool due to its high sensitivity towards the detection of the submonolayer coverages of corrosion product radionuclides. An indep endent technique (XPS) is also used to characterize the depth distribution and chemical state of various contaminants in the passive layer formed on a ustenitic stainless steel. In the first part of the series the accumulation of Ag-110m has been investigated. Potential dependent sorption of Ag+ ions (cementation) is found to be the predominant process on austenitic steel, while in the case of magnetite-covered carbon steel the silver species are mainly depleted in the form of Ag2O. The XPS depth profile of Ag gives an e vidence about the embedding of metallic silver into the entire passive laye r of the austenitic stainless steel studied. (C) 1999 Elsevier Science B.V. All rights reserved.