Deformation and fracture of irradiated polygranular pile grade A reactor core graphite

► Mechanical properties of PGA nuclear graphite specimens were tested. ► Load-displacement characteristics were consistent with quasi-brittle behaviour. ► Micro-cracks observed in non-linear part of load-displacement curve pre-peak load. ► Micro-testing showed surface tilts consistent with twinning. ► Irradiated specimens failed at 20% lower load for 15% weight loss material.