PNNL

Abstract

Understanding the structural evolution of nuclear fuel and cladding during operation is essential for predicting performance during and after service in a light water reactor. In this work, we utilized focused ion beam-based preparation techniques to make transmission electron microscopy samples of the cross-section of the fuel-cladding interface oxide region of high burn-up BWR fuel. Using diffraction contrast STEM imaging and precession electron diffraction, we demonstrated that not only does fission product radiation stabilize the tetragonal phase of zirconium oxide at temperatures well below the equilibrium temperature, but it also causes grain growth that is proportional to the fission production radiation damage. The tetragonal phase ZrO2 was exclusively present only in the region where fission product metal particles were found (~6µm), and then the tetragonal phase was also present, but mixed with monoclinic phase, up to the max depth at which fission product radiation is expected to be reached - ~8µm. Also, the grain size distribution of tetragonal phase was proportional to the integrated damage (excess vacancies generated) profile of the implanted fission product atoms.