Abstract
The oxidation of 316 stainless steel (SS) was investigated in simulated Boiling Water Reactor (BWR) environments using coupons exposed to multistage oxidation tests under mixed water chemistry (H:O molar ratio ~8) at 288 °C. The coupons were initially oxidized for 500 h, then treated for 200 h to simulate On-Line NobleChemTM (OLNC) (either with or without 10 ppb Zn), and subsequently re-oxidized for 500 h in the same water chemistry as for the first stage, but this time with 0.2 ppb Co injection. The microstructure and chemical composition of the
oxide was analysed after each stage using a variety of characterisation techniques (SEM, TEM, STEM-EDX). In pure water, the duplex oxide formed without OLNC treatment was composed of a chromite spinel-based inner layer whilst the outer layer was a mixture of ferrite and magnetite. In contrast, the injection of Zn resulted in a thinner oxide and suppressed the formation of the outer magnetite in which Zn was not incorporated because it has low miscibility in magnetite which has an inverse spinel structure. A bilayer inner oxide developed after exposure to OLNC, which was attributed to the electrochemical potential gradient established near the surface where the Pt nanoparticles were deposited. It was also observed
that, in Zn-free water, Co was incorporated in the outer layer of the inner oxide whereas a negligible concentration of Co was detected in the oxide formed in Zn-dosed water, thus confirming the beneficial effects of Zn on the suppression of Co uptake in the oxide.
oxide was analysed after each stage using a variety of characterisation techniques (SEM, TEM, STEM-EDX). In pure water, the duplex oxide formed without OLNC treatment was composed of a chromite spinel-based inner layer whilst the outer layer was a mixture of ferrite and magnetite. In contrast, the injection of Zn resulted in a thinner oxide and suppressed the formation of the outer magnetite in which Zn was not incorporated because it has low miscibility in magnetite which has an inverse spinel structure. A bilayer inner oxide developed after exposure to OLNC, which was attributed to the electrochemical potential gradient established near the surface where the Pt nanoparticles were deposited. It was also observed
that, in Zn-free water, Co was incorporated in the outer layer of the inner oxide whereas a negligible concentration of Co was detected in the oxide formed in Zn-dosed water, thus confirming the beneficial effects of Zn on the suppression of Co uptake in the oxide.
| Original language | English |
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| Title of host publication | 21st International Conference on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactor |
| Publication status | Accepted/In press - 5 Aug 2023 |