Cr-coated Zircaloy-4 Performance During Ramping Conditions

The development of accident tolerant fuel (ATF) concepts began as a result of the Fukushima nuclear accident in Japan. The primary objective of ATF cladding is to enhance the cladding corrosion resistance. The most prominent ATF cladding candidate is a chromium coated zirconium alloy. The material in this work involves a physical vapor deposition (PVD) Cr-coated Zircaloy-4 cladding. The test matrix included three sets of tubes that were all internally pressurized at elevated temperature (300 ℃) to simulate in-reactor ramping conditions. This included pressurization induced biaxial loading conditions, namely high hoop strain in addition to axial strain. The second and third set of tubes were additionally subjected to high temperature, and high purity hydrogen environments to simulate an accelerated hydrogen pickup through potential flaws in the Cr-coating. The third set of tubes was then tested at the severe accident test station (SATS) at Oak Ridge National Laboratory (ORNL) where the tube was pressurized and heated at a rapid rate until bursting. Each set of tubes were then sectioned to 4.0 mm lengths and imaged along the axial direction of the tube using the Neutron Microscope detector (NM) at the ICON beamline at the Paul Scherrer Institute (PSI). Radiography results showed that even a severely strained Cr-coating was effective at preventing hydrogen uptake. Radiography also provided insight into the differences in deformation that took place in the pre-strained versus the as-received Cr-coating near the opening of a burst tube. These results highlight the capabilities and challenges of high-resolution neutron radiography for materials with thin coatings.