PNNL

Abstract

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. The composites were made with either a 1.044-micron (“thick”) or a 0.110-micron (“thin”) PyC 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. Laser flash diffusivity measurements were made on representative samples before and after irradiation and after various annealing treatments. The ratio of the 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. 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. These results suggest that during irradiation to 6 dpa or more radial swelling of the PyC interface would compensate for the radial shrinkage of the Hi-Nicalon (Trademark) fiber and the SiC matrix swelling. 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. 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.