Tests were conducted in 500 C steam to determine the cause of a second transition point observed to occur during the oxidation of zirconium alloys. While oxygen penetration into the samples was not entirely discounted as a possible cause for the second increase in the oxidation rate, tests pointed strongly to hydrogen accumulation as being largely responsible for this change. It was found that this second transition occurred only in those alloys which showed severe absorption of hydrogen during corrosion in steam. Tests indicated that increases of up to a factor of four on the initial post-breakaway rate came about at high hydrogen concentrations. Comparison with oxygen diffusion data showed that this latter phenomenon did not occur fast enough to account for the change in kinetics observed.
3.8.4, 6.3.20, 4.6.2
