Paper 31. The electrokinetic nature of colloidal corrosion products in LWRs

A Mixed-Conduction Model for the Oxidation of Stainless Steel in a High-Temperature Electrolyte

“…The values of the diffusion coefficients of ionic current carriers are in fair agreement with those estimated earlier in hightemperature electrolytes. 1,56 The relatively high values of the diffusion coefficient of ionic defects suggests the predominance of a grain-boundary diffusion mechanism, which is in agreement with the presumed nanocrystalline structure of the barrier layer.…”

“…The development of knowledge of the oxide film composition and behavior, as well as the knowledge of the local coolant chemistries, has converged considerably during the last few years. 1,2 It is hence known that the oxide films formed on stainless steels and nickel-based alloys in high-temperature water have basically the same main structure and that the important compounds ensuring the protective character of the oxide film ͑nickel ferrite and nickel and iron chromites͒ are essentially the same for all the nickel-based materials and stainless steels. [3][4][5][6][7][8][9][10][11][12][13][14][15] In addition to the increased understanding of growth and restructuring of oxide films, recent development of radiolysis codes allows the modeling of the chemistry resulting from the radiolysis in virtually any location where the coolant is in contact with any material in light water reactors.…”

Mixed-Conduction Model for Stainless Steel in a High-Temperature Electrolyte: Estimation of Kinetic Parameters of Inner Layer Constituents

“…The values of the apparent diffusion coefficients in the outer layer of the oxide at 300°C ͑Table III͒ are close to those estimated from the interpretation of mass gain and/or thickness vs time data for oxidation of stainless steel in nuclear power plant coolants at comparable temperatures based on a parabolic growth law. 1,2,27 Their variation with potential is negligible, which supports the hypothesis that the potential drop in the outer layer can be omitted from the simplified approach outlined in the present paper. Because the bilayer structure of the oxide film was clearly evident only at a temperature of 300°C, the activation energies for the transport in the outer layer could not be determined at this stage.…”

“…They act as a deposit base for radioactivity incorporation in the reactor primary circuit, which is a potential risk for personnel safety during maintenance and shutdown periods. [1][2][3] During the almost 50 years of commercial use of LWRs, a considerable experience has been gained about the material's behavior in addition to the technical materials test results. Yet, the increasingly faster change of the environmental conditions have made it difficult to test all possible combinations of materials and environments in order to assess the long-term behavior of the protective oxides on the materials, in these new combinations of environments.…”

“…Yet, the increasingly faster change of the environmental conditions have made it difficult to test all possible combinations of materials and environments in order to assess the long-term behavior of the protective oxides on the materials, in these new combinations of environments. [1][2][3][4][5] The inference is that a full assessment of the material's behavior in LWRs cannot be gained only through materials testing in simulated or even real LWR environments, because the oxide film stability and protectiveness will depend on a large number of factors, and so will the materials integrity. We need a more fundamental understanding for each kind of oxide film and the impact of environmental factors on the film behavior.…”