Dimensional Stability of Neutron Irradiated Molybdenum

    Published: Jan 1975

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    Polycrystalline molybdenum specimens were irradiated to fast neutron fluences between 1.1 × 1019 neutrons (n)/cm2 and 1.0 × 1022 n/cm2 at a temperature range of 70 to 480°C. The irradiation-induced length changes and subsequent changes during postirradiation annealing were measured using a high vacuum dilatometer. The effects of neutron fluences, at reactor ambient temperature of ∼70°C, were to increase the length changes up to the neutron fluence of ∼1020 n/cm2 and then level off at the higher fluences. The length change data were compared with the resistivity data and the ratio of resistivity to length changes was calculated as 2.7 × 10-3 Ω-cm.

    Specimens irradiated to very high neutron fluence, 1 × 1022 n/cm2 at 430°C, showed very large length changes which were about 15 times those of low fluence specimens. This was attributed to the formation of voids in these specimens. The bulk density measurements of the specimens irradiated to 1 × 1022 n/cm2 at the temperature region of 430 to 1000°C are presented along with the void swelling data.

    A postirradiation anneal study of the irradiation induced length changes was made in the temperature region of 70 to 1600°C. A total of five different recovery stages was observed at the temperature regions of: 0.16 Tm (Stage III), 0.22 Tm (Stage IV), 0.31 Tm (Stage V), 0.36 Tm (Stage VI), and 0.54 Tm (Stage VII), respectively. The specimens irradiated at 70°C revealed four recovery stages ranging from Stage III to VI.

    Those specimens irradiated to 1 × 1022 n/cm2 at 430°C revealed an additional recovery stage at 0.54 Tm, and this recovery stage coincided with the thermal annealing of voids.


    radiation, molybdenum, neutron irradiation, dilatometry, annealing, radiation effects, defects, voids, swelling, density

    Author Information:

    Jang, HI
    Graduate student and professor, University of Cincinnati, Cincinnati, Ohio

    Moteff, J
    Graduate student and professor, University of Cincinnati, Cincinnati, Ohio

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP33702S

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