The thermal conductance of uranium dioxide/stainless steel interfaces was investigated in a disc-type apparatus under vacuum and with different interface gases (helium, argon, neon), and ranges of surface roughness (STA11 to 1417! x 10/sup -6/ cm, arithmetical mean height measured from Talysurf profile records), interface gas pressure (7 to 1226 mm Hg), contact pressure (0 to 570 lb/ in/sup 2/), mean interface temperature (55 to 410 deg C), and heat flux (1 to 5.5 cal/s cm/sup 2/). However, when the irradiation induced swelling in the matrix and fiber coating components was removed by recombination of point defects during high temperature annealing there was significant fiber/matrix separation. The fiber shrinkage is due to irradiation-induced grain-growth and recrystallization and the matrix swelling is due to accumulation of irradiation-induced point defects. These results suggest that during irradiation to 6 dpa or more radial swelling of the P圜 interface would compensate for the radial shrinkage of the Hi-Nicalon (Trademark) fiber and the SiC matrix swelling. Thermal diffusivity measurements in air, argon, helium and vacuum indicated that physical separation of the fiber/matrix interface was minimal after the irradiations, but was significant after annealing irradiated composites to 1200 degrees C. The ratio of the more » transverse thermal conductivity after to before irradiation K(sub-irr)/K(sub-zero) determined at the irradiation temperatures and predicted by the H2L model were: 0.18, 0.23 and 0.29 for the 330, 355 and 800 degrees C irradiations, respectively. Laser flash diffusivity measurements were made on representative samples before and after irradiation and after various annealing treatments. The composites were made with either a 1.044-micron (“thick”) or a 0.110-micron (“thin”) P圜 fiber coating and were irradiated in the HFIR reactor as part of the JUPITER 12J (355 degrees C, 7.1 dpa-SiC) or 14J (330 and 800 degrees C, 5.8 and 7.2 dpa-SiC, respectively) series. The H2L model was used to critically assess degradation within the individual fiber, fiber coating and matrix components for irradiated 2D-SiCf/SiC composite made with an ICVI-SiC matrix and Hi-Nicalon (Trademark) fabric.
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