Small-Scale Approaches to Evaluate the Mechanical Properties of Quasi-Brittle Reactor Core Graphite

Abstract

A range of small scale, from centimetre scale to micrometre scale, mechanical testing techniques have been used to measure the properties of nuclear reactor core graphite, including Pile Grade A (PGA) graphite and Gilsocarbon graphite. These testing methods include four-point bending (centimetre scale), diametral compression (millimetre scale), micro-scale cantilever bending (micrometre scale) and nano-indentation (micrometre scale). These methods provide both a measure of mechanical properties including elastic modulus and fracture strength and detailed information concerning the deformation and fracture mechanisms. For each test, an example using a particular specimen geometry is given and discussed with respect to the particular mechanical property evaluated and compared with macro-scale data. Nano-indentation was carried out as a conventional approach to validate and assist the understanding of the mechanical properties obtained via other small scale tests. The use of small scale test specimens offers benefits when handling irradiated reactor core graphite. The results are discussed with respect to the potential benefits, difficulties and value of small scale mechanical tests for this particular application.

In-situ neutron diffraction measurement and numerical modelling of macro- and micro-strains in two porous synthetic graphites

“…Recently, synchrotron X-ray computed micro-tomography was performed at different temperatures ranging between ambient to 1000°C for investigating damage tolerance of Gilsocarbon graphite [27]. Miniaturised specimens were used for material characterisation at smaller length-scales using micro-cantilever beams [28,29].…”