(The) influence of steam pressure on the nodular corrosion of zircaloy-4

Abstract

Oxidation of zircaloy-4 in high temperature, high pressure steam environment has been investigated. Nodular corrosion study was performed to find an evidence that physical property change in the oxide layer with steam pressure can be associated with the nodular corrosion. The steam test was done at $500\,^\circ\!C$, in a steam pressure of 10 atm, 40 atm, 70 atm, 100 atm. In contrast to uniform oxide, nodule nucleation was much influenced by steam pressure in terms of nodule number density, determining the extent of cracking after the noduyle coalesced. Uniform oxide formed at 40 atm affects subsequent nodular oxide in morphology at differently from that formed at 10 atm. Metallography divide the stages of development of a nodule, and shows that nodule growth rate and post-transition kinetics were influenced by steam pressure similarly. The effect of test pressure is similar to that of the test temperature ; both increase the discrimination capability of the steam test, associated with the microstructure of initial uniform oxide.