Comprehensive investigation of the corrosion state of the heat exchanger tubes of steam generators. Part I. General corrosion state and morphology K. Varga a, * , Z. Ne ´meth a , A. Szabo ´ a , K. Rado ´ a , D. Oravetz b , Z. Homonnay c , J. Schunk d , P. Tilky d , F. K} oro ¨si e a Department of Radiochemistry, University of Veszpre ´m, P.O. Box 158, H-8201 Veszpre ´m, Hungary b Department of Silicate and Materials Engineering, University of Veszpre ´m, P.O. Box 158, H-8201 Veszpre ´m, Hungary c Department of Nuclear Chemistry, Eo ¨ tvo ¨ s University, P.O. Box 32, H-1518 Budapest, Hungary d Paks NPP Ltd., P.O. Box 71, H-7031 Paks, Hungary e Department of Physics and Process Control, Szent Istva ´ n University, Pa ´ ter Str. 1, H-2100 Go ¨do ¨ll} o, Hungary Received 8 October 2003; accepted 16 September 2005 Abstract The present work, constituting the first part of a series of two, deals with a systematic investigation of the general cor- rosion state of 22 heat exchanger tubes originating from different steam generators of the Paks NPP (Hungary). While the passivity of the inner surface of the stainless steel tube specimens was studied by voltammetry, the morphology and chem- ical composition of the oxide layer formed on the surfaces were analyzed by SEM–EDX method. Based on the measured corrosion characteristics (corrosion rate, thickness and chemical composition of the protective oxide layer) a strong depen- dence of these parameters on the decontamination history of the steam generators was revealed. It is well documented that the chemical decontamination carried out by a non-regenerative version of the AP-CITROX procedure does exert, on the long run, a detrimental effect on the corrosion resistance of steel surfaces. Therefore, process restrictions and modifications to minimize corrosion damages have be defined. Ó 2005 Elsevier B.V. All rights reserved. PACS: 82.55.+e; 81.65.Kn 1. Introduction In accordance with international trends, the life- cycle prolongation of the nuclear reactors of type VVER-440/213 at Paks NPP is a fundamental issue in the energy policy of Hungary. Recent investiga- tions [1] have shown the potential for an additional 20–25 year operation cycle over the 30 years, pre- dicted earlier. This possibility should not be an underestimated resource for the development of the national economy. Long lasting and continuous availability of the electricity supply for the industry and community 0022-3115/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jnucmat.2005.09.012 * Corresponding author. Tel./fax: +36 88 427 681. E-mail address: vargakl@almos.vein.hu (K. Varga). Journal of Nuclear Materials 348 (2006) 181–190 www.elsevier.com/locate/jnucmat