Corrosion monitoring in nuclear systems

Cost effective operation of nuclear power plants at very high safety levels requires implementation of optimised, strategic and proactive plant aging and life management methods. The continuing occurrence of corrosion phenomena like flow accelerated corrosion or stress corrosion cracking (SCC) in light water reactors worldwide clearly demonstrates a need for the development of advanced, non-destructive, continuous corrosion monitoring tools, e.g. for the early detection of SCC initiation in the technical precrack stage.

After a successful workshop on ‘Corrosion monitoring in nuclear systems’ during EUROCORR 2007 in Freiburg, Germany and publication of a ‘Green book’ of the European Federation of Corrosion (EFC Publication no. 56), a second workshop was organised during EUROCORR 2011 in Stockholm, Sweden. Nine very interesting papers were presented at the workshop, of which three were selected for consideration by Corrosion Engineering Science and Technology. One paper is available in CEST Vol. 47 (4) with the remaining two papers published in this issue together with four additional papers dealing with the wider theme of nuclear corrosion.

The first paper reviews the most promising corrosion monitoring techniques, which appear suitable for the early detection of SCC in light water reactor environments.¹ Out of a rather large number of techniques only few have the potential to monitor the early stages of SCC in high temperature water (∼300°C) in the lab and even less are feasible for plant applications. Research on monitoring of the early stages of SCC in stainless steels on the lab scale is described in the second paper. Kovac et al. performed electrochemical impedance spectroscopy measurements during tensile tests at room temperature.² The third paper highlights the capabilities and limitations of Guided Wave monitoring of buried piping systems within nuclear installations and discusses some examples.³

Three additional papers related to SCC in high temperature water are published together with the papers from the workshop. The first one deals with On-line NobleChem^TM technology.⁴ The Platinum deposition behaviour on stainless steel specimens exposed to simulated boiling water reactor environment has been investigated. The second and third paper describe how Ruthenium addition to AISI 304 stainless steel may improve the resistance towards SCC in high temperature water environment,⁵ whereas Palladium alloying additions did not reveal beneficial effects (shown by constant load tests and transmission electron microscopy crack tip and oxide film investigations).⁶

An autoclave study with zirconium alloys completes the collection of nuclear corrosion papers.⁷ The effect of heat treatment and hydrogen charging on the corrosion behaviour of different zirconium alloys has been investigated under simulated pressurised water reactor conditions.

We hope the current papers will be useful for scientists and engineers for future corrosion mitigation work. We finally would like to thank all the contributors to the workshop and to the current issue as well as the reviewers. We also appreciate the support by Working Party 4 (‘Nuclear corrosion’) of the EFC and by the European Cooperative Group on Corrosion Monitoring of Nuclear Materials (ECG-COMON).