Thermal conductivity degradation of graphites due to nuetron irradiation at low temperature

Several graphites and carbon/carbon composites (C/C's) have been irradiated with fission neutrons near 150°C and at fluences up to a displacement level of 0.24 dpa. The unirradiated room temperature thermal conductivity of these materials varied from 114 W/mK for H-451 isotropic graphite, to 670 W/mK for a unidirectional FMI-1D C/C composite. At the irradiation temperature a saturation reduction in thermal conductivity was seen to occur at displacement levels of approximately 0.1 dpa. All materials were seen to degrade to approximately 10 to 14% of their original thermal conductivity after irradiation. The significant recovery of thermal conductivity due to post-irradiation isochromal anneals is also presented.