STP956

    Fission Fragment Induced Hardening in Uranium Mononitride

    Published: Jan 1987


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    Abstract

    Fission fragment-induced hardening of uranium mononitride (UN) was examined by the Knoop indentation technique. Measurements were done at a variety of indentation loads (25 to 500 g) and for specimens with various fission doses (2.7 × 1021 to 5.3 to 1024 f/m3). The hardness showed a gradual increase with fission dose until 1023 f/m3. After that, however, for irradiations in JRRs (a lower thermal neutron flux and low irradiation temperature), the hardness attained a maximum at around 5 × 1023 f/m3 followed by a successive decrease. By contrast, in the Japan Material Test Reactor (JMTR), in which the thermal neutron flux and irradiation temperature were 7 × 1017 n/m2s and 400°C, respectively, the hardness increased monotonically up to 5.3 × 1024 f/m3. In the thermal annealing process, on the other hand, the hardness exhibited two recovery steps at 650 and 950°C, to which two types of extended defects caused by fission fragment damage could be attributed. It is concluded here that dislocation loops and vacancy clusters contributed to the fission fragment-induced hardening of UN.

    Keywords:

    irradiation hardening, uranium mononitride, neutron irradiation, fission fragment damage, Knoop hardness, thermal annealing, interstitial cluster, vacancy cluster, defect identification, post-irradiation examination


    Author Information:

    Tamaki, M
    Research associate, research associate, and Emeritus professor, Nagoya University, Nagoya,

    Matsui, H
    Research associate, research associate, and Emeritus professor, Nagoya University, Nagoya,

    Kirihara, T
    Research associate, research associate, and Emeritus professor, Nagoya University, Nagoya,


    Paper ID: STP25676S

    Committee/Subcommittee: E10.14

    DOI: 10.1520/STP25676S


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