High-temperature creep behavior of Cr-coated optimized ZIRLO™ cladding via inverse analysis based on finite element method

• High-temp creep parameters for Cr-coated Optimized ZIRLO™ derived via inverse FEM. • PVD columnar grains make coated Cr properties differ from bulk Cr. • MERCURY–ISIGHT used for parameter identification. • Extracted parameters predicted burst behavior within set temperature range. • Cr coating delayed ballooning/burst, improving LOCA safety margins. After the Fukushima accident, nuclear power plant operators have required technologies that can prevent or delay the progression of a severe accident. For this reason, accident tolerant fuel (ATF) is being developed in many countries. As a near-term (NT) ATF cladding, chrome-coated cladding is the leading technology. The properties of the chromium coating layer change depending on the manufacturing process. It is inappropriate to directly apply bulk chromium properties to Cr coating due to significant microstructural differences. Since the thickness of the coating layer is tens of micrometers, it is difficult to obtain the properties by conventional experimental methods. This study presents a comprehensive approach to evaluate the high-temperature creep behavior of Cr-coated Optimized ZIRLO™ (Opt. ZIRLO) nuclear fuel cladding. The finite element method (FEM)-based fuel performance code MERCURY, developed by KAERI, was coupled with the commercial optimization tool ISIGHT to perform inverse analysis. Under the framework of the IAEA ATF-TS project, isothermal bust tests were conducted at two temperature levels (1080 K and 1180 K) with various internal pressure conditions. The high-temperature creep parameters for both the substrate and Cr coating layers as well as the effective parameter for a single-layer model were derived. The burst analysis using the derived properties showed good agreement with the burst test results. The analysis also confirmed the delayed start point of ballooning for the chrome-coated cladding.