Thin chromium coatings applied to the surface of cladding tubes can reduce the severity of accident transients through superior oxidation kinetics. The nuclear industry is interested in the potential for increased economics of nuclear reactors using Cr-coated cladding by way of licensing for increased discharge burnup limits and fuel enrichment. Preceding burnup extension licensing, the benefits of Cr-coated cladding must be well understood.
A single rod test facility was constructed to study the thermal and mechanical performance of Cr-coated cladding during simulated loss of coolant accident conditions (LOCA). The facility is designed to investigate two LOCA phenomena: balloon and burst of the cladding, and reflood quenching. Balloon and burst tests are conducted by pressurizing the cladding tube and ramping the furnace temperature to induce high temperature creep deformation and rupture. Post-burst analysis aims to quantify how Cr-coatings affect the temperature and pressure conditions for the onset of balloon and bursting as well as the resulting rupture size and shape. The BISON fuel performance code is used to further study the effect of Cr-coatings on balloon and burst behaviors, with experimental data planned for validation or extension of ATF material models. Reflood tests are conducted by heating the cladding tube to postulated LOCA temperatures (600-1200 C) before injecting subcooled water into the channel to quench the cladding. A Photron Nova R3-4K camera is used to obtain high speed video of the reflooding and quenching process to investigate the complex two-phase dynamics during the transient. The effect of quenching on the cladding is studied using surface profilometry, optical microscopy, scanning electron microscopy, and ring compression testing to quantity post-quench ductility. Collaborators on these projects include Idaho National Laboratory, Westinghouse Electric Company, and Pohang University of Science and Technology.
[1] C. Dunbar, W.H. Jung, R. Armstrong, K. Sridharan, M. Corradini, H. Yeom, “Fuel performance analysis of Cr-coated Zircaloy-4 cladding during a prototypical LOCA event using BISON”, Annals of Nuclear Energy, vol. 200, p. 110411, Jun. 2024.