SIMS depth profiling, line scanning and imaging analyses of the oxide layer on in-reactor corroded cladding specimens with high lateral resolution

The distribution of the reactor water components lithium and boron in the oxide layer of in-reactor corroded Zircaloy fuel rod cladding specimens was investigated by depth profiling, line scanning and imaging analyses using secondary ion mass spectrometry (SIMS). The exact thickness of the oxide layer on the specimens was measured by scanning electron microscopy (SEM). The SIMS analyses showed that lithium and boron were not homogeneously distributed in the oxide layer. The peak concentration of lithium was found close to the reactor water/oxide interface of the specimens whereas boron showed no relevant variations in the bulk of the oxide layers investigated. The concentration of both elements decreased rapidly at a significant distance close to the oxide/metal interface. Conclusions were drawn to improve the understanding of the in-reactor corrosion process of fuel rod claddings consisting of zirconium based alloys.