| Abstract Scope |
As chromium-coated zirconium fuel cladding nears deployment in light-water reactors, it promises to broaden the operating envelope and provide safety and economic benefits to reactor operation. While gains in hydrothermal corrosion resistance, steam oxidation resistance, reduced hydrogen pickup, and improved fretting are well established, the nature of the mechanical benefits, especially under accident scenarios, are not fully understood. Oak Ridge National Laboratory has developed chromium coated Zr alloy cladding to assess coating integrity during off-normal conditions. Laboratory loss-of-coolant accident (LOCA) testing has demonstrated clear improvement in the burst performance of internally pressurized claddings compared to claddings without coatings. In sharp contrast, high-temperature mechanical tests performed exclusively in the axial direction showed little or no benefit. Analysis of ORNL Cr coatings revealed large compressive residual stresses in the tangential direction, contrasting with near-neutral stresses in the axial direction. This stress anisotropy helps explain the discrepancy, where the compressive hoop stress drives the enhanced burst integrity, while the neutral axial stress accounts for the standard behavior observed in axial tension. This talk synthesizes five years of development and characterization at ORNL, outlining the implications of these nuances for Cr-coated cladding deployment. Ultimately, these results highlight that "enhanced performance" is not a blanket attribute, but a directionally dependent phenomenon. Capturing this nuance is essential for avoiding uncertainty in safety margins and qualification. |