STP1502

    Application of Subsize Specimens for Irradiation Embrittlement Monitoring of VVER-440∕213 RPV Steels

    Published: Jan 2009


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    Abstract

    Results of VVER-440∕213 reactor pressure vessel (RPV) surveillance specimens studies showed that all surveillance impact bend specimens were irradiation with a lead factor more than 20 compared to irradiation of the pressure vessel inner surface. This is a special problem of radiation embrittlement assessment for VVER-440∕213 RPV materials. Prediction of radiation embrittlement of RPV materials using surveillance specimens is efficient on the basis of accelerated irradiation compared to irradiation of the RPV inner surface. However, the lead factor, which is the ratio of neutron flux affecting surveillance specimens to neutron flux affecting the RPV inner surface in the maximum irradiated zone, should be not too high, when acceleration of steel irradiation would not cause qualitative changes in physical processes of irradiation damage. It is generally assumed that irradiation with a lead factor less than 3–6 provides adequate assessment of radiation embrittlement dependence on the damage dose. In the top part of the chains with VVER-440∕213 surveillance specimens, fast neutron flux decreases ∼20 times and the top capsules are irradiated with a neutron flux range close to the flux maximum on the inner surface of the reactor pressure vessel; i.e., the lead factor there is around 1. This concerns both reactors with full core and with dummies on the periphery of the core. The gradient of the neutron flux in the top and bottom parts of chains is great enough; hence, the volume of homogeneously irradiated metal is low. However, there is an opportunity to use material from the top capsules of irradiation sets for correct evaluation of the transition temperature using subsize specimens. As surveillance specimens in the top capsules are irradiated at the same conditions as the pressure vessel, their study allows precise determination of radiation embrittlement of RPV materials. The results of studies of irradiation embrittlement of VVER-440∕213 RPV steels using subsize specimens are discussed.

    Keywords:

    reactor pressure vessel, radiation embrittlement, ductile-to-brittle transition temperature, subsize impact bend specimens, specimen reconstitution


    Author Information:

    Nikolaev, Yu. A.
    Lab Head and Senior Research Scientist, Russian Research Center “Kurchatov Institute,” IRMT, Moscow,

    Nikolaeva, A. V.
    Lab Head and Senior Research Scientist, Russian Research Center “Kurchatov Institute,” IRMT, Moscow,


    Paper ID: STP48729S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP48729S


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