Ab Initio Study of Advanced Metallic Nuclear Fuels for Fast Breeder Reactors
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Ab Initio Study of Advanced Metallic Nuclear Fuels for Fast Breeder Reactors Alexander Landa1, Per. Söderlind1, Blazej Grabowski1, Patrice E.A. Turchi1, Andrei V. Ruban2, and Levente Vitos2 1 Condensed Matter and Materials Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, L-045, 7000 East Avenue, Livermore, CA 94551-0808, U.S.A. 2 Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, Brinellvägen 23, SE-100 44 Stockholm, Sweden ABSTRACT Density-functional formalism is applied to study the ground state properties of J-U-Zr and J-U-Mo solid solutions. Calculated heats of formation are compared with CALPHAD assessments. We discuss how the heat of formation in both alloys correlates with the charge transfer between the alloy components. The decomposition curves for J-based U-Zr and U-Mo solid solutions are derived from Ising-type Monte Carlo simulations. We explore the idea of stabilization of the G-UZr2 compound against the D-Zr (hcp) structure due to increase of Zr dband occupancy by the addition of U to Zr. We discuss how the specific behavior of the electronic density of states in the vicinity of the Fermi level promotes the stabilization of the U2Mo compound. The mechanism of possible Am redistribution in the U-Zr and U-Mo fuels is also discussed. INTRODUCTION The US Reduced Enrichment for Research and Test Reactors (RERTR) program was created in 1978 with a purpose to develop technology necessary to enable the conversion of civilian facilities using high enriched uranium (HEU, U235 > 85 at. %) fuels to the use of low enriched uranium (LEU, U235 < 20 at. %) fuels in research and test reactors [1]. In 2004 the RERTR program was absorbed into Global Treat Reduction Initiative (GTRI) [2, 3], which purpose is to reduce and protect vulnerable nuclear and radiological materials at civilian sites. From nuclear performance standpoint, a comparable amount of fissile material (U235) is required to maintain reactor power for both the LEU and HEU designs. As was mentioned in Ref. [4], the LEU design requires a fuel material with uranium density at least 5 times higher than the current HEU compounds in order to compensate for the reduction in enrichment. Another requirement for the LEU fuel is its capability to withstand the structural damage caused by the fission events occurring inside the material [4]. Early on, metallic fuels (pure U and Pu) have been considered because of their high thermal conductivity (with the very significant safety benefits) in comparison with MOX fuels (e.g., UPuO2) used in thermal reactors. However, the low melting temperature of pure U, Pu, and the U-Pu alloys makes them unsuitable for hightemperature applications due to the danger of penetration of molten actinides to the cladding. That is why addition of some high-melting temperature elements, such as Cr, Mo, Nb, Re, Ru, Ti, V, or Zr, is considered in order to boost the liquidus curve in the U-Pu system thus enhancing thermal and mechanical stability [3,
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