STP1354

    Evolution of Dislocation and Precipitate Structure in Zr Alloys Under Long-Term Irradiation

    Published: Jan 2000


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    Abstract

    Tubes from zirconium-base alloys are used widely in the pressure tube reactor core. The lifetime of the zirconium component in the reactor core will be determined by structure changes and alloy properties under long-term neutron irradiation. The studies were carried out using Zr-1Sn-1Nb-0.4Fe (E635) and Zr-2.5Nb (E125) alloy samples cut out of a pressure tube (PT) in the initial condition and after 7 and 15.5 years operated (42 000 and 95 000 effective hours) under irradiation to the neutron fluxes of 3 × 1017 and 2 × 1017 n/m2 s (E > 1 MeV) at 304°C in RBMK-1000 and 314°C in RBMK-1500, respectively. The E125 alloy PTs were in two conditions, as cold worked and annealed (A) and as thermomechanically treated (TMT-1) (B). The E635 alloy PTs were cold worked and annealed (A) (Tablel). The examinations were implemented using analytical transmission electron microscopy (TEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) analyses. New data showing the microstructure changes are presented. Both the alloys have a partially recrystallized grain structure with a high density of intragranular dislocations in the initial state. The main part of dislocations belong to ⟨a⟩ type. Density of secondary phase precipitates is high. They are β-Nb (bec) in Zr-2.5Nb. In Zr-1.3Sn-1Nb-0.4Fe, precipitates consist of Zr, Nb, and Fe, and the constituent ratio is close to 1:1:1 Zr(Nb,Fe)2 (hcp). Linear dislocations (Type a) are annealed under irradiation, while the density of ⟨c⟩-component dislocations is not practically changed. Grain structure of the Zr-2.5Nb alloy is retained, and it is practically completely recrystallized in Zr-1.3Sn-1Nb-0.4Fe. The phase structure and microchemical composition are modified by irradiation. Nb concentration changes in β-Nb are observed in Zr-2.5Nb. A substantial decrease of Fe concentration and irradiation defect accumulation are observed in the intermetallic precipitates Zr(Nb,Fe)2 in the E635 alloy. This leads to crystal lattice disordering and new precipitates Nb-enriched are formed. Dislocation loops are formed under irradiation. Loop dimensions vary widely in Zr-2.5Nb. They show a tendency to ordering under high-fluence irradiation. Uniform structure of loops with a high tendency to ordering is formed in the alloy Zr-l.3Sn-lNb-0.4Fe; 70% of them are interstitial loops of the ⟨a⟩ type. Irradiation-induced Fe depletion of intermetallic particles and a Fe content increase in saturated α-Zr matrix may be a cause of the microstructure and performance changes in E635 alloy pressure tubes. The correlation between irradiation-induced dislocation structure and hardening of the E125 alloy is discussed.

    Keywords:

    irradiation growth, electron microscopy, dislocation, microstructure, zirconium alloys, neutron irradiation, precipitates


    Author Information:

    Averin, SA
    Senior researcher, researcher, head of laboratory, and deputy director, SB RDIPE, Zarechny, Sverdlovsk region

    Panchenko, VL
    Senior researcher, researcher, head of laboratory, and deputy director, SB RDIPE, Zarechny, Sverdlovsk region

    Kozlov, AV
    Senior researcher, researcher, head of laboratory, and deputy director, SB RDIPE, Zarechny, Sverdlovsk region

    Sinelnikov, LP
    Senior researcher, researcher, head of laboratory, and deputy director, SB RDIPE, Zarechny, Sverdlovsk region

    Shishov, VN
    Leading researcher and professor (head of laboratory), State Science Centre, R.F., A.A. Bochvar VNIINM, Moscow,

    Nikulina, AV
    Leading researcher and professor (head of laboratory), State Science Centre, R.F., A.A. Bochvar VNIINM, Moscow,


    Paper ID: STP14297S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP14297S


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