The effect of neutron irradiation on the fracture toughness of graphite

As a part of our irradiated graphite recycle program a small quantity of PCEA grade graphite was irradiated in the High Flux Isotope Reactor (HFIR) at ORNL. The graphite will provide the “raw material” for future recycle experiments. The geometry of the irradiated graphite allowed us to study the effects of neutron irradiation on the critical stress intensity factor, KIc, of graphite. The specimens were irradiated in two groups of 6 at an irradiation temperature of 900 °C in “rabbit” capsules to doses of 6.6 and 10.2 dpa, respectively. Following a full suite of pre- and post-irradiation examination, which included dimensions, mass, electrical resistivity, elastic constants, and thermal expansion (to 800 °C) the samples were notched and tested to determine their KIc using the newly approved ATSM test method for SENB fracture toughness of graphite. Here we report the irradiation induced changes in the dimensions, elastic constants, resistivity, and coefficient of thermal expansion of PCEA graphite. Moreover, irradiation induced changes in the critical stress intensity factor, KIc, or fracture toughness, are reported and discussed. Very little work on the effect of neutron irradiation on the fracture toughness of graphite has previously be performed or reported.