Understanding irradiation growth through atomistic simulations: Defect diffusion and clustering in α-zirconium and the influence of alloying elements - 2016-0093
- Materials Design, Inc., 12121 Scripps Summit Dr., Suite 140, San Diego, CA 92131 (United States)
- Zircology Plus, 36848 Montecito Dr., Freemont, CA 94538 (United States)
- Westinghouse Electric Sweden, Fredholmsgatan 22, SE-721 63, Vaesteraas (Sweden)
- Global Nuclear Fuels, PO Box 780, MC A-75, Wilmington, NC 28402 (United States)
- Electric Power Research Institute, 4960 Shadow Creek Dr., Idaho Falls, ID 83401 (United States)
Irradiation-induced structural changes of α-zirconium alloys and in particular the effect of iron were investigated by molecular dynamics simulations using embedded atom potentials derived from first-principles calculations. The simulations revealed that at temperatures between 500 and 600 K self-interstitial atoms (SIAs) diffuse rapidly in a cooperative movement, preferably parallel to basal planes (a directions; ), forming nano-clusters with an extension in and . Vacancies diffuse more slowly than SIAs and remain isolated for a longer period of time. Nano-clusters associated with SIAs cause a pronounced overall expansion in a directions, as well as local strains. Under compressive strain in the c direction, vacancy diffusivity increases in the c direction. In contrast, the diffusivity of SIAs increases in the c direction under a tensile strain in the c direction. SIA nano-clusters are highly mobile within basal planes. Vacancy clusters grow by merging, leading to a contraction in the a direction, compensating for the expansion caused by SIA nano-clusters and possibly contributing to the plateau in growth after the initial rapid expansion. At the onset of breakaway growth, possibly due to stress buildup, the vacancy nano-clusters can condense into c loops, thereby diminishing the compensation effect. The alloying elements iron, nickel, chromium, and niobium liberated from secondary phase particles under irradiation or already in solution are attracted to vacancies and SIAs and are found inside vacancy and SIA loops. The interaction of alloying elements with defect clusters is discussed, with a particular focus on iron. Iron has been found to promote cluster formation in zirconium, and the structures of zirconium-iron clusters have been analyzed. Tin is repelled by SIA clusters and only weakly attracted by vacancies. Niobium impedes the diffusion of SIAs (and therefore may increase annihilation rates with nearby vacancies) and does not destabilize vacancy or SIA clusters. Ab initio calculations of the dimensional and elastic coefficients of the intermetallic phases occurring in secondary phase particles, such as Zr{sub 2}Fe and Zr{sub 3}Fe, are presented, allowing an assessment of local strains in a zirconium matrix. Thus, novel results from extended molecular dynamics simulations provide new insights and contribute to a deeper understanding of the complex mechanisms causing irradiation-induced dimensional changes and the breakaway growth of zirconium alloys. (authors)
- Research Organization:
- ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA, 19428-2959 (United States)
- OSTI ID:
- 22788437
- Resource Relation:
- Conference: 18. International Symposium on Zirconium in the Nuclear Industry, Hilton Head, SC (United States), 15-19 May 2016; Other Information: Country of input: France; 78 refs.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Breakthrough in Understanding Radiation Growth of Zirconiu
The Influence of the In-Situ Clad Staining on the Corrosion of Zircaloy in PWR Water Environment