%0 Journal Article
%T Cohesive Relations for Surface Atoms in the Iron-Technetium Binary System
%A Christopher D. Taylor
%J Journal of Metallurgy
%D 2011
%I Hindawi Publishing Corporation
%R 10.1155/2011/954170
%X Iron-technetium alloys are of relevance to the development of waste forms for disposition of radioactive technetium-99 obtained from spent nuclear fuel. Corrosion of candidate waste forms is a function of the local cohesive energy ( ) of surface atoms. A theoretical model for calculating is developed. Density functional theory was used to construct a modified embedded atom (MEAM) potential for iron-technetium. Materials properties determined for the iron-technetium system were in good agreement with the literature. To explore the relationship between local structure and corrosion, MEAM simulations were performed on representative iron-technetium alloys and intermetallics. Technetium-rich phases have lower , suggesting that these phases will be more noble than iron-rich ones. Quantitative estimates of based on numbers of nearest neighbors alone can lead to errors up to 0.5£żeV. Consequently, atomistic corrosion simulations for alloy systems should utilize physics-based models that consider not only neighbor counts, but also local compositions and atomic arrangements. 1. Introduction The development of long-term containment strategies for spent nuclear fuel requires a combination of careful experiments and theoretical studies so that the realistic lifetimes of these strategies can be confidently predicted. Currently, a number of different containment strategies are being considered, one of which involves the storage of certain fission products within a metallic alloy waste form [1]. Chief among these fission products is technetium-99, which has a half-life of ~105 years [2]. Studies have demonstrated that technetium can be alloyed with stainless steel with significant mass-loadings and that these waste forms have considerable corrosion resistance [3]. Predictions of the long-term stability of this material can be obtained through the coupling of the results of accelerated testing studies with a rigorous, physics-based theoretical model. Corrosion is believed to be the chief process by which stored, spent nuclear fuel will degrade over time and have the potential to release radionuclides to the environment [1, 4, 5]. Modeling corrosion at long-time scales requires a thorough and fundamental understanding of the electrochemical stability of such systems, particularly the surface phenomena (Figure 1) [6]. Surface processes that are important to consider include passivation (formation of protective oxide films), depassivation (the rupture of such films by localized dissolution, mechanical damage, or presence of deleterious chemistries), mass-transport (at the
%U http://www.hindawi.com/journals/jm/2011/954170/