A metallographic study of the terminal solubility of hydrogen in zirconium at low hydrogen concentrations

Experimental Results and Theoretical Interpretations of Solvus Relationships in the Zr–H System

“…Therefore, according to the accommodation energy model of TSS, the c-hydride phase might be expected to have a slightly different solvus relationship if it were actually the stable phase at those low temperatures as suggested by Mishra et al [26] if also the chemical binding energies of the two phases are similar (which is likely: see Domain et al [6]). Cann and Atrens [3], therefore, carried out a separate linear regression fit of the data for the temperature range over which the c-hydride phase was the only one observed. The results provide a straight line on a van't Hoff plot having a slightly different slope than that given by Kearns' regression fit to all the data from unalloyed Zr available at the time.…”

“…To provide data for TSSD to lower temperatures, Cann and Atrens [3] used a metallographic technique. With this technique, using unalloyed Zr samples doped with total hydrogen contents ranging from 230 to 4 wppm, the authors obtained TSSD data down to *156°C.…”

“…For this extreme anisotropy of the transformation strain, using an expression given by Puls [35] for an aspect ratio of 0.1, the elastic accommodation energy is reduced by a factor of *6.5 compared to the value obtained for a hydride precipitate of the same shape but with transformation strains assuming hydride formation occurred by a pure lattice strain transformation. 3 It could, however, be reduced to zero if all the stresses resulting from the misfit strains of the precipitates are relieved through diffusion of the atoms of the underlying lattice structure with respect to which the misfit strains are imposed.…”

“…In contrast, such reduction is possible for the accommodation energy (for a finite-sized defect such as a precipitate) because large shear stresses that can be plastically relaxed can be generated by this term depending on the shape of the precipitate. The image interaction component of the total coherency energy thus represents an energy contribution to the total energy that cannot be dissipated by plastic deformation during phase conversion, 3 while its sign and magnitude would vary across the twophase average composition range. It is proposed, therefore, that this component of the total coherency energy is the sought-for source of hysteresis since it requires a finite increase in chemical free energy to overcome it from which follows a finite phase boundary movement and, hence, internal entropy production.…”

Potential corrosion and degradation mechanisms of Zircaloy cladding on spent nuclear fuel in a tuff repository

“…3OO0C, but only 1 ppm at 20°C (Sawatzky and Wilkins, 1967;Simpson and Cann, 1979;Cann and Atrens, 1980). When the solubility is exceeded at any particular temperature, brittle hydrides precipitate.…”