STP1447

    On the Mechanism of Irradiation Embrittlement Enhancement in Reactor Pressure Vessel Steels at High Neutron Fluences

    Published: Jan 2004


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    Abstract

    The DBTT shift in irradiated VVER pressure vessel steels is represented by standard guidelines with a power law dependence on fast neutron fluence multiplied by a material constant. However, from recent data on surveillance specimens for several units of VVER-440, an irradiation embrittlement enhancement has been observed at neutron fluences above (2–3)×1020 n/cm2 (E>0.5 MeV) with a significant deviation from the standard guideline. This suggests an additional mechanism of irradiation embrittlement at high fluences.

    In the present work it was supposed that such a mechanism could be intergranular embrittlement caused by grain boundary phosphorus segregation. A threshold dose was used that accounts for intergranular embrittlement, that occurs after sufficient phosphorus segregation, when the critical stress for intergranular fracture falls below that for cleavage fracture. The modeling of phosphorus accumulation on grain boundaries is performed taking into account the radiation-enhanced phosphorus diffusion by both vacancy and interstitial mechanisms, the radiation-induced segregation in the matrix near grain boundaries, and the Gibbsian adsorption on grain boundaries. Predictions of such a composite model are in agreement with surveillance data for VVER-440.

    Keywords:

    pressure vessel steels, irradiation embrittlement mechanisms, grain boundaries, phosphorus accumulation, modeling


    Author Information:

    Pechenkin, VA
    Head of Laboratory, Principal Research Scientist and Research Scientist, State Scientific Center of Russian Federation (SSC RF), Institute of Physics and Power Engineering (IPPE), Obninsk, Kaluga region,

    Konobeev, YV
    Head of Laboratory, Principal Research Scientist and Research Scientist, State Scientific Center of Russian Federation (SSC RF), Institute of Physics and Power Engineering (IPPE), Obninsk, Kaluga region,

    Stepanov, IA
    Head of Laboratory, Principal Research Scientist and Research Scientist, State Scientific Center of Russian Federation (SSC RF), Institute of Physics and Power Engineering (IPPE), Obninsk, Kaluga region,

    Nikolaev, YA
    Leading Research Scientist, Russian Scientific Center “Kurchatov Institute”, ORM, Moscow,


    Paper ID: STP11224S

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP11224S


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