A numerical simulation model for studying the effects of stress levels, multi axial stress states and texture on hydride reorientation in Zr alloys

A numerical simulation model for stress reorientation of hydrides in zirconium alloys is proposed, to predict the orientation and distribution of the precipitated hydride. It was assumed in the model that all the hydrogen precipitates on the basal plane of α-Zr form transgranular hydrides, and the relative density of the precipitated hydride is proportional to the elastic strain energy induced by the positive strain along the c-axis in each crystal. Based on the model, the effects of changes in the stress states, crystallographic texture and heat treatment on the hydride precipitation properties were studied numerically and the following conclusions were reached. The typical circumferential hydride morphology observed in the tube cross-section under a stress free condition was successfully simulated when the texture of the tube was taken into consideration. The results obtained by the numerical method suggest that the radial hydride fraction, or Fn value, obtained from uniaxial tensile tests, will be useful for the substitute method of the internal pressurization tests to elucidate the hydride precipitation properties of the fuel cladding with internal pressure. The experimental data published in the literature, indicating that high fn, namely highly concentrated caxis to the tube radial direction, formed by the tube fabrication process decreased the radial hydride fraction Fn under stress free cooling, was interpreted by the proposed method. Macroscopic hydride morphologies on the cross sections of as cold worked (CW), stress relieved (SR), and recrystallization annealing heat treated (RX) tubes, cooled under a stress free condition, were estimated to be almost the same. A smaller change in the hydride reorientation was estimated for larger internal strains, which suggested that the RX tube was susceptible to stress reorientation as compared to the SR or CW tubes with larger internal strains