Boron carbide powder of natural enrichment compacted into Type 304 stainless-steel cladding was irradiated in the EBR-II at temperatures of 1190 to 1350°F to exposures as high as 5% burnup of the 10B atoms. Particle breakup, microstructural effects, boron carbide/cladding interaction, and gas release were determined. The irradiation behavior was strongly dependent on temperature in the range investigated.