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This paper briefly reviews work by the author identifying and describing in-reactor deformation mechanisms of materials and structures used in nuclear reactors, in particular, Zircaloy-2, Zircaloy-4, and Zr-2.5Nb, and the CANDU fuel channel (comprising Zr alloy pressure tubes, calandria tubes, and spacers). The discussion is set in the context of contemporary findings of other workers in the international community. The following themes are highlighted: The contributions of creep and growth to deformation; c-component dislocations and the fluence dependence of irradiation growth; anisotropy of irradiation growth; deformation equations and pressure tube-to-calandria tube contact in CANDU reactors; low temperature flux (damage rate) dependence of deformation rates. The first developments were reported in 1976 at the third conference in this series and there are ongoing developments in all areas. The linear low temperature flux dependence of creep and growth rates is yet to be satisfactorily explained.
High creep strain experiments have been carried out under irradiation using cold worked Zircaloy-2, cold-worked Zr-Nb, and heat treated Zr-Nb 0.6-in.-diameter tubes in DFR, DMTR, and PLUTO reactor. The tests in PLUTO were found to be the most useful since full creep curves were obtained using neutron radiography techniques. Creep strains of up to 9 percent were obtained on cold-worked Zircaloy-2 tubes without failure, thus substantiating the recommended pressure tube creep strain limit of 3 percent. Up to 5 percent creep strain was observed with cold-worked Zr-Nb tubing, but since one tube failed at only 1.8 percent strain it is not yet possible to specify a realistic yet safe creep limit for this material.
The anistropy of creep deformation of Zr-2.5Nb pressure tubes during service in CANDU reactors is related to the anisotropic physical properties of the hexagonal crystal structure of zirconium. These physical properties contribute to the development during fabrication of an anisotropic microstructure, including crystallographic textures, grain morphologies, and dislocation structures. A number of studies tried to relate the anisotropic deformation of the polycrystalline zirconium alloys to those of their individual grains by accounting for the microstructural features, particularly the crystallographic texture, but they suffered from a lack of experimental data from biaxial creep tests on materials that have crystallographic texture similar to that of the pressure tubes. This experiment contributes to the development of a reliable model for Zr-2.5Nb tubes by using two batches of small tubes, one of which has a crystallographic texture similar to that of the CANDU power reactor pressure tubing, the other having a texture that is completely different. The results are analyzed in terms of texture using a self-consistent model to account for the effects of the grain interactions.