Modeling of In, Tl, Ga, Sb, and Pd as lanthanides binding agents in U-Zr metallic nuclear fuels
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Modeling of In, Tl, Ga, Sb, and Pd as lanthanides binding agents in U-Zr metallic nuclear fuels Guillermo Bozzolo1, Abdellatif M. Yacout1, Gerard L. Hofman1, and H. O. Mosca2 1 Nuclear Engineering Division, Argonne National Laboratory, Argonne, IL, 60439 U.S.A. 2 Gerencia de Investigaciones y Aplicaciones, CAC, Comisión Nacional de Energía Atómica, San Martín, Buenos Aires, Argentina ABSTRACT Atomistic modeling is used to study the role of different alloying additions to metallic U-Zr nuclear fuels in terms of their ability to reduce lanthanide migration to the outer surface of the fuel and thus reduce their interaction with cladding. The Bozzolo-Ferrante-Smith (BFS) method for alloys is used to examine the behavior of each addition, the resulting phase structure, and the evolution of the fuel surface. Different behaviors are observed for each of the additives (In, Tl, Ga, Sb, Pd), all a result of the competition between the formation of bulk precipitates and the tendency of each additive to segregate to the surface. For each case, characteristic temperatures are determined indicating the range of temperatures in which each additive performs a different role. Sb and Pd additives are determined to be the most effective additions, properly balancing their ability to bind lanthanides in the fuel with their own segregating tendencies. INTRODUCTION The use of metallic U-Zr fuels in fast reactors can be limited by the migration of fission products to the periphery of the fuel at the fuel operating temperatures ranging between abour 450 °C to 750 °C, with a deleterious effect on the fuel/cladding interface (the interface temperature can be up to 650 °C) [1]. Several options have been put forward to mitigate this problem, such as the inclusion of alloying additions in the fuel or cladding, the deposition of a protective layer in the interface, or, more radically, the use of different fuels. The first option is probably the most economical and practical, but due to the large number of participating elements, it is not easy to determine what alloying additions could be best suited for such task. As most of the known information comes from binary phase diagrams or some other previous multi-element experimental source of data, the overall behavior of arbitrary elements is largely unknown. In this work we present computational modeling results addressing the behavior of five different candidates (In, Tl, Ga, Sb, Pd), concentrating on their role in diminishing lanthanide migration to the surface. The results are obtained from numerical simulations using the Bozzolo-Ferrante-Smith (BFS) method for alloys [2], which has shown to be an appropriate tool to describe, albeit in an approximate way, the behavior of such complex multielement systems [3-6]. The necessary steps to validate both the usefulness of the method for the current problem and its parameterization have already been taken. The method calculations successfully reproduced some of the basic properties of the U-Zr fuel [3], explained the rationale behind the migration of
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