The H diffusivity (tables 198 and 199) was determined by measuring the H concentration along the length of samples which had been made by resistance-welding H-bearing studs to H-free studs. No measurable differences were found between the coefficients for these 3 materials, nor was any effect of grain size or cold-working observed. However, small differences were found which depended upon the sample orientation in rolled sheet. The results, combined with an analysis of the crystallographic texture of the sheet, indicated that the ratio of the single-crystal diffusion coefficients parallel to, and perpendicular to, the c-axis of the hexagonal structure was greater than unity; but probably not more than two.

Diffusion Coefficient of Hydrogen in Alpha Zirconium, Zircaloy-2 and Zircaloy-4. J.J.Kearns: Journal of Nuclear Materials, 1972, 43[3], 330-8