Anisotropy of irradiation creep of Zr-2.5wt%Nb and Zircaloy-2 alloys

Stress relaxation in bending tests have been used to determine the creep anisotropy of Zr-2.5wt%Nb and Zircaloy-2 alloys during fast neutron irradiation at 570 and 320 K. The ratios of creep rates from longtidunal and transverse sections were found to be larger in Zr-2.5wt%Nb materials than in Zircaloys at both temperatures, and larger at 320 K than at 570 K for both alloys. The creep anisotropy a 570 K for both alloys can be related to crystallographic texture by a model in which the strains are produced by slip of dislocations of the type 1/3<1120>, 65% on prism planes an 35% on basal planes; at 320 K the ratios of prism to basal slip are 84/16 in Zr-2.5wt%Nb and 73/27 in Zircaloy-2. The latter difference is attributed to alloying. An important implication of these results is that the reduction of elongation rates in CANDU power reactors due to compressive end load is less than was previously believed. (orig.)