Fixed Contamination on Steel Surfaces: First Use of Quartz Crystal Microgravimetry to Measure Oxide Growth on Process Steels Under Conditions Typical of Nuclear Reprocessing

Boxall, Colin and Woodhouse, Becky and Wilbraham, Richard (2012) Fixed Contamination on Steel Surfaces: First Use of Quartz Crystal Microgravimetry to Measure Oxide Growth on Process Steels Under Conditions Typical of Nuclear Reprocessing. MRS Online Proceedings Library, 1383: mrsf11-138. ISSN 1946-4274

Abstract

During the lifetime of a nuclear facility, radioactive material may become deposited onto process and structural material surfaces. Due to their high corrosion resistance, steels comprise the largest class of metal-based materials encountered on nuclear sites. A greater understanding of the mechanisms of how contaminant radionuclides interact with and attach to process steels in nuclear plant environments is required in order to enable informed decisions to be made about the design and effective application of decontamination techniques, reducing secondary wastes. There is limited literature relating to radionuclide sorption mechanisms on steels. Key studies have found that sorbed contamination is almost entirely located in the outermost oxide layers formed at steel surfaces. Thus, a molecular level investigation of contaminant uptake during induced oxide formation would be beneficial in developing steel decontamination strategies. Stainless steel 316L is commonly employed in the nuclear industry in process streams and pipework. Thus, we describe work carried out on electrochemically accelerated oxide growth on 316L and SS2343 (a 316L analog) in nitric acid media and its characterisation using combined voltammetric and microgravimetric measurements. These allow identification of active, passive, high voltage passive, transpassive and secondary passivation regimes in the associated current voltage curves. EQCM on SS2343 coated quartz crystal piezoelectrodes, combined with potentiodynamic polarisation data have allowed us to determine that fastest net growth of surface oxide occurs in the low voltage passive regime. Further, we have directly measured the growth of that layer by using in situ microgravimetry for the first time. We will be shortly using the methods described above and radionuclide surrogates for the study of contaminant uptake during oxide formation and uptake onto preformed oxide layers. XPS will be used to determine layer composition and mode of contaminant uptake.