β-85 wt % Nb precipitates: the effect on in-reactor diametric creep of pressure tubes

By linking the microstructure evolution of an α-Zr crystal with the macroscopic behaviour, the deformation of an in-service reactor pressure tube is calculated. Microstructure evolution is considered through rate theory modelling of the interaction between point defects and sinks. Different densities of β-85 wt % Nb precipitates are proposed to be distributed inside the α grains and act as point defect sinks, doing a screening effect on the grain boundaries. From the interatomic pair potential which is used to describe the material, positive tangential deformation rates (on the other hand negatives) are obtained when these densities in the c-crystal direction are bigger than a minimum value. (author)