STP1046V2

    Application of a United Kingdom Magnox Steel Irradiation Model to the HFIR Pressure Vessel

    Published: Jan 1990


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    Abstract

    This report discusses the application of a model of irradiation hardening, originally developed for U.K. Magnox pressure vessel steels, in describing embrittlement in High Flux Isotope Reactor (HFIR) pressure vessel steels. In common with the HFIR, the steel pressure vessels of Magnox reactors were constructed from carbon-manganese mild steels in the 1960s and have since operated while receiving a high energy (E>1MeV) neutron flux of 1011 to 1.6×1013nm2s1. The operational temperature of Magnox vessels at “cold” locations (i.e. 167°C (333°F) to 225°C (437°F)) is somewhat higher than that of the HFIR vessel (50°C (122°F)). The model assumes that hardening has two contributors: a “radiation damage” term, which depends on neutron fluence, but not flux, and a copper precipitation term, which is flux dependent.

    Good agreement is found between model predictions of embrittlement and experimental data from the HFIR surveillance program. The agreement can be further improved with only a small adjustment to the value chosen for the activation energy for copper diffusion. Contrary to limited experimental data obtained from higher flux irradiations in the Oak Ridge Research Reactor (ORR), the model does not predict a flux dependence in the range 1011 to 1017 n · m−2 s−1. Various suggestions are discussed that could rationalize this behavior, but further experimental data are required for more conclusive explanations.

    Model predictions of embrittlement with continued operation of the HFIR at full power suggest that linear extrapolations of existing surveillance data with time are conservative—that is, they overestimate the actual embrittlement.

    Keywords:

    radiation embrittlement, radiation hardening, toughness, pressure vessel steels


    Author Information:

    Druce, Stephen G.
    Principal scientific officer, Harwell Laboratory, Atomic Energy Authority, Oxfordshire,


    Paper ID: STP49442S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP49442S


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