K. Varga et al., Accumulation of radioactive corrosion products on steel surfaces of VVER-type nuclear reactors. II. Co-60, J NUCL MAT, 298(3), 2001, pp. 231-238
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.