Comments on the paper: 'hydrogen effected defects evolution in zirconium items of light-water reactors' by S.V. Ivanova

摘要

Recently, we presented a new DHC model [2-4] where a driving force for DHC is the hydrogen concentration gradient, not by the stress gradient as argued by the old DHC models [5-9], which arises from stress-induced precipitation of hydrides at the tip of a notch or crack subjected to a higher tensile stress. Thus, our new DHC model suggests that the first process of DHC must be precipitation of the hydrides only at the crack tip, followed by the migration of hydrogen from the bulk region to the crack tip as opposed to the contention of the old DHC models. This suggestion fully agrees with theoretical analyses of Flanagan et al. [12], Birnbaum [13,14] and Puls [15] who have demonstrated that tensile stresses promote precipitation of the hydride phase in the stressed volume such as the crack tip region, leading a hydrogen solubility in this stressed region to reach the solubility of hydrogen on a heating [16]. A sufficient condition for hydride precipitation is a supersaturation of hydrogen either by undercooling or AT from the terminal solid solubility of hydrogen (TSSD) temperature or by increasing the charged hydrogen concentration by an increase of the hydrogen gas pressure in an isothermal condition when no transformation of hydrides is considered.