The effect of high fluence neutron irradiation on the properties of a fine-grained isotropic nuclear graphite

A fine-grained isotropic nuclear graphite (IG-110), manufactured from a petroleum coke, was irradiated to a total neutron dose of 3.8 x 10(26) n/m(2) or 25 displacements per atom (dpa) at 600 degrees C in the high flux isotope reactor (HFIR) at Oak Ridge National Laboratory (ORNL). The effect of irradiation and the influence of post-irradiation thermal annealing on the properties of the graphite were evaluated. Volume change turnaround was clearly observed at 15-20 dpa and the return to original volume (Delta V/V-0 = 0) can be estimated to occur at similar to 30 dpa. Strength and elastic moduli of the irradiated graphite increased by a factor of 2-3, and maximums in the sigma/sigma(0), and E/E(0) curves were at similar to 20 dpa at 600 degrees C. Recovery of volume, fracture strength and thermal conductivity by thermal annealing were found, and thermal conductivity returned to better than about 30% of the unirradiated value after 1200 degrees C thermal annealing.