On The Interation of Injected Zinc With Oxide Films Formed On Stainless Steel Under Cyclic Oxidising and Reducing Conditions

摘要

Zinc injection technology has been widely used in light water reactors as remedy for plant radiation field build-up and corrosion of reactor materials. The possible mechanisms about the role of zinc in reducing incorporation of radionuclides such as Co-60 in the oxide films on stainless steels are, however, not completely understood. In recent years several laboratory loop studies have been performed at Studsvik to understand the effects of zinc and other metal dopants in reactor water on activity build-up under normal water chemistry condition. In this paper, we present some experimental evidences that would shed some light on the reactivity of injected zinc with the duplex layers of oxide films formed under cyclic oxidising and reducing conditions. The results show that under the oxidising condition there was no detectable zinc in the outer oxide layer but there was up to 2 at% of zinc in the inner oxide layer. Following an exposure under the reducing condition with mixed dopants of Fe, Ni and Zn species for a short period of time, a constant zinc concentration profile could be detected in the very surface region of a nickel ferrite grain but not in any place in the non-nickel ferrite grains in the outer oxide layer. The present findings are discussed in the light of some existing findings in literature and the results of activity build-up in the same loop study that is also presented in this conference.