Unveiling damage mechanisms of chromium-coated zirconium-based fuel claddings at LWR operating temperature by in-situ digital image correlation

• Published in: Surface & coatings technology 2022-01, Vol.429 (C), p.127909, Article 127909
• Main Authors: Roache, David C., Bumgardner, Clifton H., Harrell, Timothy M., Price, Morgan C., Jarama, Alex, Heim, Frederick M., Walters, Jorie, Maier, Benjamin, Li, Xiaodong
• Format: Article
• Language: English
• Subjects: Acoustic emission; Axial stress; Chromium; Claddings; Coated cladding; Cracking (fracturing); Deformation; Digital image correlation; Digital imaging; Expanding plug testing; Fracture mechanics; Fracture mechanisms; Fuel systems; High temperature; Light water reactors; Mechanical tests; Nuclear fuel elements; Operating temperature; Oxidation; Oxidation resistance; Strain; Zirconium
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2021.127909

Here, we investigate the coupled thermomechanical fracture mechanisms of coated nuclear fuel claddings at Light Water Reactor (LWR) operating temperatures. These coated claddings are a highly attractive, near-term solution, which addresses the demands for accident-tolerant fuel systems and provide greater oxidation resistance. However, the fracture mechanisms of these coatings, which may create channels for oxidation ingression, must be fully understood prior to implementation. Thus, high-temperature expanding plug experiments were conducted on coated cladding specimens at a temperature of 315 °C, consistent with the operating environment of LWRs. In-situ thermomechanical deformation was measured with stereo digital image correlation during heating and mechanical testing to separately resolve contributions of thermal and mechanical strain. Digital image correlation, supported by acoustic emissions (AE) detection, was also leveraged to track cracking activity during loading. Coating fracture was found to initiate at total hoop strains of 0.34%. The thermal deformation of the coated claddings was investigated via finite element simulations, revealing a bidirectional stress-state within the coating with axial and circumferential strains of 0.026 and 0.031%. This bidirectional stress-state was attributed with the generation of off-axis fracture pattern within the coating as identified via post-experiment scanning electron microscopy. Thus, this study unveiled critical, coupled thermomechanical mechanisms governing the coating fracture of coated claddings at LWR temperatures. •Thermal expansion mismatch resulted in a multidirectional coating stress state•Axial and residual thermal strains were found via FEA•Coating fracture initiation was determined at combined thermal and mechanical strain•Surface crack orientation more angled for 315 °C compared to room temperature•Through thickness crack propagation was similar between 315 °C and room temperature