STP1467

    Effect of Irradiation on the Fracture Properties of Zr-2.5Nb Pressure Tubes at the End of Design Life

    Published: Jan 2005


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    Abstract

    To determine the fracture properties of Zr-2.5Nb pressure tubes irradiated until the end of design life, cantilever beam, curved compact toughness, and transverse tensile samples were prepared from a typical pressure tube and irradiated in the high flux reactor OSIRIS at CEA, Saclay, France. Experiments were conducted on two batches of samples mounted in two irradiation inserts. Each insert held sixteen samples of each type of specimen. The first insert was irradiated to a fluence corresponding to approximately half of the design life in a CANDU3 reactor. The experimental results were reported in [1]. Samples in the second insert were irradiated for 10.5 years in OSIRIS and received a maximum neutron fluence of 2.61 × 1026 n/m2 (E > 1 MeV), being equivalent to 2.98 × 1026 n/m2 (E > 1 MeV) in a CANDU reactor, i.e., corresponding to ∼30 years operation in CANDU reactors at 80 % capacity factor. The present report describes the results of tensile, fracture toughness, and Delayed Hydride Cracking (DHC) tests and XRD microstructure analysis from the second batch of specimens. A continuous and gradual evolution in tensile, fracture, DHC properties, and dislocation densities is demonstrated without any evidence of a sudden change following the initial transitient at very low fluence. In the whole high fluence range, there is a very slow rate of increase in c-component dislocation density, strength, and DHC velocity and a slow reduction in elongation and Nb concentration in the β-phase. The a-type dislocation density and fracture toughness remain approximately constant. The results from the second insert of specimens confirm that, following the initial transient at very low fluence, there is little further change in the fracture properties of Zr-2.5Nb pressure tube material. Therefore, material properties behave in a stable and predicable manner to the end of a 30 years design life for CANDU reactor pressure tubes.

    Keywords:

    Zr-2.5Nb alloy, pressure tube, neutron radiation damage, tensile strength, elongation, fracture toughness, delayed hydride cracking, microstructure evolution, x-ray diffraction, dislocation density


    Author Information:

    Pan, ZL
    Research Scientist, AECL Chalk River Laboratories, Chalk River, Ontario

    St Lawrence, S
    Research Scientist, AECL Chalk River Laboratories, Chalk River, Ontario

    Davies, PH
    Senior Research Scientist, AECL Chalk River Laboratories, Chalk River, Ontario

    Griffiths, M
    Senior Research Scientist, AECL Chalk River Laboratories, Chalk River, Ontario

    Sagat, S
    Senior Research Scientist, AECL Chalk River Laboratories, Chalk River, Ontario


    Paper ID: STP37534S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP37534S


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