Xiangkun Ru

Distribution and Characteristics of Oxide Films Formed on Stainless Steel Cladding on Low Alloy Steel in Simulated PWR Primary Water Environments

The properties of oxide film formed on stainless steel (SS) cladding on low alloy steel (LAS) after immersion in simulated PWR primary water environments with different dissolved oxygen contents are investigated. The HAZ in the LAS consist of overheated crystal region, complete recrystallized region and incompletely recrystallized region, while SS cladding consist of austenite zone and austenite and ferrite mixing zone. Pitting appeared on 309L SS after immersion in high temperature water due to the dissolution of inclusions existed previously on 309L SS which contain higher ferrite content. Raman spectra and TEM results show that the outer layer is mainly Fe-rich spinel oxides while the inner layer is mainly Cr-rich oxides. Ni is mainly concentrate at the oxide/substrate interface due to the low oxygen affinity. The inner oxide layer on 308L SS is thinner than that on 309L SS, implying that ferrite distributed on austenite is not favorable for the growth of oxides. Reducing the oxygen content in PWR primary water favored the formation of spinel oxides.

Properties of Oxide Films on Ni–Cr– x Fe Alloys in a Simulated PWR Water Environment

The iron content in Ni–Cr–xFe (x = 0–9 at.%) alloys strongly affected the properties of oxide films formed in a simulated PWR primary water environment at 310 °C. Increasing the iron content in the alloys increased the amount of iron-bearing polyhedral spinel oxide particles in the outer oxide layer and facilitated the local oxidation penetration into the alloy matrix from the chromium-rich inner oxide layer. The local oxidation penetration was caused by the pile-up of the cation vacancies.