Abstract
In the present study, the tensile creep behaviour of three various cladding tubes of the Zr1%Nb alloy has been studied in the α-Zr region at 350 °C, which corresponds to the operational service conditions of the cladding tubes in nuclear light-water reactors. Tensile creep tests under the high constant applied stress region from 150 to 260 MPa have been carried out at the transition from the power-law (PL) to the power-law breakdown (PLB) regimes. It was found that all dispersion strengthened Zr1%Nb cladding alloys under investigation reach the PLB regime at values of the compensated applied stress σ/G above approximately 8 × 10^–3, where the stress exponent n of the minimum creep rate ⋵_m (n = ∂ln⋵_m/(∂lnσ)_T) then dramatically increases from the value of ∼ 6 with increasing stress ratio σ/G. The fact that all experimental results for both the PL and PLB obey the Monkman-Grant relationship supports the idea that the creep mechanism in the PL and PLB does not change qualitatively and indicates a close link between the deformation and fracture processes in both creep regimes under investigation. However, future experiments could be carried out at different testing temperatures within the PLB regime to verify the controversial contemporary views. 1

Key words
zirconium alloy, creep testing, power-law breakdown, creep mechanisms, fracture

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