Novel application of an in-situ radiotracer method in the field of nuclear corrosion

In response to the need for the better understanding of the kinetics and mechanism of corrosion and contamination processes emerged in nuclear power plants, the first step is the application of laboratory measuring systems. The methods used on laboratory scale should be able to combine advantages of the experimental techniques of radiochemistry, electrochemistry and corrosion science to explain the relevant issues. Nowadays, combined applications (couplings) of the radiotracer and electrochemical methods play an important role in the investigations of mass- and charge transport processes at the solid electrode/liquid electrolyte interfaces [1]. Our laboratory has traditions and some experience in in-situ radiotracer studies of nuclear corrosion and contamination-decontamination processes ([1-3] and references therein). During the last two decades significant part of our research activities has been focused on the extension of the applicability of the so-called 'foil' method. The main disadvantage of the 'foil' method is that it cannot be used to study the surface properties of compact constructional material surfaces. This drawback can be eliminated by applying the so-called 'thin gap' method. However, the original version of the 'thin gap' method cannot be utilized for studies of the oxide-covered (rough) surfaces of metal samples having industrial importance. With a combination of the 'foil' and the 'thin gap' method we may obtain an effective technique to solve the above problem. As a fundamental demand in this regard, the expressions elaborated for quantitative evaluations have to be refined in some aspects. Our present contribution is focused on the following main issues: 1) Further development of the theoretical relationships of the 'thin gap' radiotracer method for the investigations of the sorption phenomena on the rough surfaces of compact metals. 2) The experimental validation of the equations at platinum black surface/chloride (labelled with ³⁶Cl) containing electrolyte systems. 3) The determination of the adsorption of SO₄^2-/H₂SO₄ (labelled with ³⁵S) and Cl^- (labelled with ³⁶Cl) on different steels covered with porous layers. Naturally, with the extension of the basic principles of the radiotracer technique, the determination of the surface excess of various species can be performed on a great variety of porous metal electrodes. Consequently, following the methodological development outlined above we can get some important findings on adsorption, contamination-decontamination, and corrosion processes that have never been studied earlier by in-situ radiotracer method. (authors)