Unveiling damage mechanisms of chromium-coated zirconium-based fuel claddings by coupling digital image correlation and acoustic emission

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2020-02, Vol.774 (C), p.138850, Article 138850
• Main Authors: Roache, David C., Jarama, Alex, Bumgardner, Clifton H., Heim, Frederick M., Walters, Jorie, Romero, Javier, Maier, Benjamin, Li, Xiaodong
• Format: Article
• Language: English
• Subjects: Accident conditions; Acoustic emission; Bending; Chromium; Coating; Coatings; Cracking (fracturing); Critical loading; Digital imaging; Electron microscopy; Failure mechanisms; Finite element analysis; Fracture mechanics; Fuel systems; High temperature; Mechanical properties; Mechanical tests; Nuclear fuel elements; Oxidation; Oxidation resistance; Stress/strain measurements; Two dimensional models; Zirconium alloys; Zirconium base alloys
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2019.138850

Coated nuclear fuel claddings offer a promising, near-term solution to address the demand for next-generation, accident-tolerant fuel systems. It is expected that they will possess superior mechanical properties and greater oxidation resistance compared to current cladding technology, allowing for improved performance during beyond design-basis accident conditions. Here, we present a methodology to determine the failure mechanisms of chromium-coated zirconium-alloy claddings under expected, critical loading conditions. Three-dimensional digital image correlation and acoustic emission techniques were used in situ to monitor spatial strain and crack development of the claddings under two key, de-coupled loading conditions: expanding plug and four-point bending. Critical strain levels, at which cracking initiated, were determined to be 0.4% εhoop and 0.4% εxx for expanding plug and four-point bending, respectively. A two-dimensional fracture model was also developed for the expanding plug loading condition based on inputs determined from mechanical testing. It was concluded that coating fracture of expanding plug specimens was axisymmetric across the specimen circumference and occurred rapidly through the thickness of the chromium coating. Subsequent high temperature steam oxidation experiments on tested (cracked) expanding plug specimens showed no signs of oxidation degradation to the underlying zirconium alloy, thereby showcasing the effectiveness of the chromium coating. This comprehensive, multi-scale study is intended to inform future testing of next-generation, coated claddings and identify the resulting failure mechanisms that arise in beyond design basis accident conditions. •Cracking of chromium-coated zirconium alloy nuclear fuel claddings was investigated.•In situ 3D-digital image correlation mechanical testing with acoustic monitoring.•Determined initial cracking strain for expanding plug and four-point bend testing.•Rapid cracking observed by finite element modeling and scanning electron microscopy.•No oxidation ingression through cracks in 1200 °C steam environment.