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Values of DHC rates in Zr alloys are sensitive to measurement procedures. A standard method has been developed at the laboratories of AECL and evaluated in a round-robin involving ten IAEA member states. Two test materials were used—Zr-2.5Nb pressure tubes in the cold-worked (CANDU™) and heat-treated (RBMK) conditions. Cracks were grown from fatigued starter cracks in the axial direction on the axial-radial plane of the original tubes. To obtain the maximum value of Vc, specimens were heated to dissolve all their hydrogen, then cooled at 1 to 3°C/min to the test temperature before loading at 15 MPa√m. Although the start of cracking was detected by potential drop, the extent of cracking was measured directly on the crack faces. The values of incubation time to the start of cracking were highly variable but Vc was well behaved. The values of Vc were normally distributed with a range varying from a factor of 1.2 to 5.2. At 250°C the mean value of Vc from 80 specimens of cold-worked material was 8.9(±1.12)×10−8 m/s and from 41 specimens of heat-treated material the mean value of Vc was3.3(±0.64)×10−8 m/s. Tests were also done at six other temperatures between 144 and 283°C, using up to 22 specimens at each temperature. Both materials had an Arrhenius-type temperature dependence,
Zr-2.5Nb, delayed hydride cracking, standard method, strength, texture, microstructure
Coleman, Christopher E.
Researcher Emeritus, AECL, Chalk River Laboratories, Chalk River, Ontario
Inozemtsev, Victor V.
Nuclear Fuel Specialist, International Atomic Energy Agency, Vienna,