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In-reactor stress-relaxation tests were done on zirconium alloys with different compositions, grain sizes, heat-tratments, cold-work, and specimen stress directions at 568 ± 5 K in a fast neutron flux (E > 1 MeV) of 2.0 × 1017 neutrons (n)/m2s, for up to 8200 h with initial stresses up to 300 MPa. The relaxation behavior can be represented by σ/σo = D exp (-Kt) where σ/σo is the ratio of the unrelaxed stress at time t to the initial stress, D is a constant which approximates the stress ratio after a rapid initial drop, and K is a relaxation rate constant.
The effects of the metallurgical variables on the in-reactor stress relaxation of zirconium alloys is small. Variations in composition and heat-treatments change the relaxation rate constant by factors of 2 to 4, while variations due to cold-work and working direction change the constant by factors of up to 2. Stress-relieving (or aging) following cold-work decreases the initial stress drop.
zirconium, irradiation, zirconium alloys, cold working, stress relieving, aging(metallurgy)
Atomic Energy of Canada Limited, Chalk River Nuclear Laboratories, Chalk River, Ontario