51315-5469-Corrosion and Stress Cracking Corrosion of Austenitic Steels in Supercritical Water

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Product Number: 51315-5469-SG

ISBN: 5469 2015 CP

Author: Yimin Zeng

Publication Date: 2015

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The supercritical water-cooled reactor (SCWR) is one of six innovative Generation IV reactor concepts and merits further research and development with the intent of being pursued for implementation in the next 30 years. Based on established knowledge and experience from ultra-supercritical coal power plants (SCFP) supercritical water oxidation systems (SCWO) for hazard waste management and advanced materials development programs for existing nuclear reactor systems the materials that will be used for fabricating SCWR structural components such as calandria pressure tube and hot/cold let piping etc. can be reasonably identified and selected. To achieve optimum thermal efficiency however the Canadian SCWR concept requires a fuel core outlet temperature of 650 °C at 25 MPa with fuel cladding operating temperature possibly up to 850 °C therefore leading to the most challenging aspect of this novel reactor concept. During SCWR operation fuel cladding candidate materials must have very strong mechanical strength microstructure stability and excellent resistance to general oxidation/corrosion stress corrosion cracking (SCC) creep and radiation damage.A number of studies and investigations had been performed in the past years and several top-ranking austenitic steels including 310S 800H and SS347 have been pre-selected based on available information. To determine which alloy is suitable for the SCWR applications there are still a number of questions needed to be clarified. In this paper most recent corrosion and SCC experimental results obtained at CanmetMATERIALS are present. In an SCW autoclave a number of the alloys coupons were prepared and subsequently exposed to SCW condition (625 °C and 25 MPa) for about 1200 hours. Their corrosion rates are statistically measured using different methods and compared to those obtained at temperature < 600 °C. The effects of thermal cycles on the surface oxide formation and breakdown are assessed. The micrograph of the formed oxides and the variation of oxide and substrate microstructures during exposure are studied using advanced SEM/TEM techniques. The SCC susceptibility of these alloys is investigated using a high temperature and pressure loop with well controlled water chemistry under the designed SCWR operating conditions. The stress-stain curves of these alloys under SCW conditions are obtained and analyzed. The micrographs (including grown oxide and formed micro-cracks) of these SCC samples before and after SCW exposure are also characterized.