Non-destructive Correlative 3D Characterization of Nuclear Graphite: From the Micro-scale to the Nano-scale.

Graphite is a key material in the design and operation of a wide range of nuclear reactors because of its attractive combination of thermal, mechanical, and neutron interaction properties. In all its applications, the microstructural evolution of nuclear graphite under operating conditions will strongly influence reactor lifetime and performance. However, measuring the 3D microstructural characteristics of nuclear graphite has traditionally faced many challenges. X-ray tomographic techniques face limitations in achievable resolution on bulk (mm-sized) specimens while serial sectioning techniques like FIB-SEM struggle to achieve adequate milling rates for tomographic imaging over representative volumes. To address these shortcomings, we present here a multiscale, targeted, correlative microstructural characterization workflow for nuclear graphite employing micro-scale and nano-scale x-ray microscopy with a connected laser milling step in between the two modalities. We present details of the microstructure, including porosity analysis, spanning orders of magnitude in feature size for nuclear graphite samples including IG-110