DIMENSIONAL AND PROPERTY CHANGES OF GRAPHITES IRRADIATED AT HIGH TEMPERATURES

The linear dimensional changes of anisotropic and near-isotropic graphites were measured after irradiation in the range 300 to 1500°C to 3.3 × 1021 n/cm2 (E > 0.18 MeV). The presence of a nongraphitizing impregnant coke in an anisotropic needle-coke graphite increased its volume contraction, reduced the anisotropy of dimensional contraction, and retarded turnaround in the direction perpendicular to extrusion. No changes in the thermal expansivities were observed but all graphites studied exhibited a single linear relationship between thermal expansivity and linear dimensional change at 320 to 615°C. A separate linear relationship was observed for anisotropic or near-isotropic graphites at 840 to 1500°C. There was a shift toward higher contraction for the near-isotropic graphites. Thermal conductivities, measured at room temperature, were lower than the preirradiation conductivities. Fractional reductions ranged from 85 per cent after irradiation at 300°C to 35 per cent after irradiation at 1250 to 1500°C. After irradiation at 1200°C conductivity changes were annealed out of anisotropic graphites at 1500°C, while 2600°C was necessary to remove the changes from a near-isotropic graphite. © 1968.