Limits of hydrogen analysis by atom probe tomography targeting Zr(Fe,Cr)2 second phase particles in Zr-based fuel cladding from reactor operation

We report results from atom probe tomography (APT) experiments capturing Zr(Fe,Cr)2 second phase particles (SPPs) in Zircaloy-2-type fuel cladding after reactor operation. In light of recent reports of H trapping around SPPs, we assess the feasibility of H analysis in modern commercial atom probe instruments on this system. To this end we employed voltage and laser pulsing APT on specimens prepared by focused ion beam (FIB) at room and cryogenic temperature. Room temperature FIB caused transformation of the α-Zr matrix into δ-hydride, but left SPPs mostly unaffected. This indicates that α-Zr has a higher affinity for H than SPPs. However, even under optimized conditions, we were not able to find evidence for H trapping near SPPs located within the α-Zr matrix in cryogenically FIB sharpened specimens, where no hydride transformation occurs.