“…This results in enhanced crack growth rates because either (a) the dissolved sulfides decrease the repassivation rate, which increases the amount of metal dissolution for a given oxide rupture rate:72 or (b) the dissolved sulfide poisons the recombination of H atoms liberated by 25 NUREG/CR-6583 corrosion, which enhances H uptake by the steel at the crack tip.83 A change in fracture appearance from ductile striations in air to brittle facets or cleavage-like fracture in LWR environments lend the greatest support for hydrogen-induced cracking. 67,70,78,79 In crack growth studies in long cracks, brittle fracture is generally associated with MInS inclusions and spreads like a fan from these incl~sions,78,~9 which is reminiscent of ithe quasi-cleavage facets produced in hydrogen-charged specimens. In LWR environments, fracture surface often has a terraced appearance produced by linkage of main crack with the hydrogen-induced cracks ahead of the crack tip at inclusion matrix interface.…”