Real time nanogravimetric monitoring of corrosion for nuclear decommissioning

Monitoring and understanding of corrosion on nuclear sites plays a key role in safe asset management (predicting plant life, assessing efficacy of corrosion inhibitors for plant lifetime extension) and supporting informed choice of decontamination methods for steels due for decommissioning. Recent advances in Quartz Crystal Nanobalance (QCN) technology offer a means to monitor corrosion in-situ in radiologically harsh environments, in real time and with high sensitivity. Oxalic acid has been widely used in nuclear plants and installations as a corrosion inhibitor for carbon steels and as a decontamination cleaning agent due to its ability to remove rust from the surface of ferritic metals and alloys. As an exemplar system for decontamination, the corrosion behavior of mild carbon steel and pure iron samples in 1 wt% to 8wt% oxalic acid solutions have, for the first time, been measured and compared in real time and in situ using the QCN. Corrosion rates measured using the QCN are found to agree with those obtained using corrosion current (iCORR) measurements, with the added advantages of: (i) real time and potentially in situ and higher sensitivity measurement; (ii) reduced uncertainty in the conversion of the QCN measured frequency change to a mass change-based corrosion rate compared to the conversion of the icorr measured by LSV with Tafel extrapolation to similar; (iii) the provision of mechanistic insights into the action of oxalic acid on Fe-rich steels