Nanostructure and local properties of oxide layers grown on stainless steel in simulated pressurized water reactor environment

• Passive films grown on stainless steel in high temperature water analysed by C-AFM.
• Electrical resistance of grains and grain boundaries measured at nanometre scale.
• Local electrical resistance influenced by changes in resistivity of the oxide film.
• Local resistivity assigned to balance in Fe(II)/Cr(III) composition of inner layer.
• Grain boundaries of outer layer would promote Cr(III) enrichment of inner layer.

The morphology and local electrical resistance of duplex oxide films formed on 316L stainless steel at 325 °C in simulated primary coolant of pressurized water reactor have been investigated at the nanometre scale with Conductive Atomic Force Microscopy. The electrical resistance varies over ∼1 order of magnitude for most oxide grains and over 2–3 orders of magnitude locally at grains and grain boundaries. This is rationalized in terms of local variation of the composition and thus resistivity of the mixed Fe(II)–Cr(III) barrier inner layer of the oxide films with grain boundaries of the outer layer possibly promoting Cr(III) enrichment.