Fission recoil-induced microstructural evolution of the fuel-cladding interface [FCI] in high burnup BWR fuel

Understanding the structural evolution and reduction-oxidation behavior of nuclear fuel and cladding during operation is essential for predicting performance during and after service in light water reactors. Using TEM/STEM imaging of cross-sections of the fuel-cladding oxide interface region of high burnup BWR fuel, fission recoil radiation was demonstrated to not only stabilize the tetragonal phase of ZrO2 at temperatures well below the equilibrium temperature, but also to cause grain growth proportional to the fission recoil radiation damage. The tetragonal phase ZrO2 was exclusively present (no monoclinic phase) only in the region where fission product metal particles were found (∼6 μm depth). [Display omitted] •Fission recoil radiation stabilizes tetragonal ZrO2 below the equilibrium temperature.•Fission recoil radiation causes grain growth that is proportional to the radiation damage.•Tetragonal phase ZrO2 was exclusively present only where fission product noble metal particles were found (∼6μm depth).