Accumulation of radioactive corrosion products on steel surfaces of VVER-type nuclear reactors. II. Co-60

In the case of intact fuel claddings, the predominant source of radioactivi ty in the primary circuits of water-cooled nuclear reactors is the activati on of corrosion products in the core. The most important corrosion product radionuclides in the primary coolant of pressurized water reactors (PWRs) a re Co-60, Co-58, Cr-51, Mn-54, Fe-59 (as well as Ag-110m in some Soviet-mad e VVER-type reactor). The second part of this series is focused on the comp lex studies of the formation and build-up of Co-60-containing species on an austenitic stainless steel type 08X18H10T (GOST 5632-61) and magnetite-cov ered carbon steel often to be used in Soviet-planned VVERs. The kinetics an d mechanism of the cobalt accumulation were studied by a combination (coupl ing) of an in situ radiotracer method and voltammetry in a model solution o f the primary circuit coolant. In addition, independent techniques such as X-ray photoelectron spectroscopic (XPS) and ICP-OES are also used to analyz e the chemical state of Co species in the passive layer formed on stainless steel as well as the chemical composition of model solution. The experimen tal results have revealed that: (i) The passive behavior of the austenitic stainless steel at open-circuit conditions, the slightly alkaline pH and th e reducing water chemistry can be considered to be optimal to minimize the Co-60 contamination. (ii) The highly potential dependent deposition of vari ous Co-oxides at E > 1.10 V (vs. RHE) offers a unique possibility to elabor ate a novel electrochemical method for the decrease or removal of cobalt tr aces from borate-containing coolants contaminated with Co-60 and/or Co-58 r adionuclides. (C) 2001 Elsevier Science B,V. All rights reserved.