Hoop expansion deformation and cracking behavior of Cr-coated Zr cladding at 320 ℃: A comparative study before and after hydrothermal corrosion

Hoop expansion deformation is used to study deformation behaviors for Zr cladding tubes, simulating a reactivity-initiated accident in pressurized water reactor nuclear power plants. In this paper the expansion deformation behavior at high temperature of Cr-coated zirconium alloy cladding tubes of both as received and after hydrothermal corrosion at 360 °C /18.7 MPa for 270 days have been investigated in detail. After expansion deformation at 320 °C, obvious plastic deformation was observed in the Cr coating of the cladding tubes. Cr coating exhibits transgranular crack propagation in expansion deformation. Compared to the as-deposited Cr-coated cladding, hydrothermal corrosion has little effect on the yield strength of the cladding. However, it has a significant effect on the cracking initiation behavior of Cr-coated zirconium alloy cladding tubes during deformation. The crack density of Cr-coating after 270-day hydrothermal corrosion was significantly lower than that of as-received Cr coating in expansion deformation, due to Cr nanograins coarsening when corrosion at 360 °C for 270 days. The results indicate that size and morphology of Cr nanograin size adjacent Cr-Zr interface has important effect on deformation and damage of Cr coating.