Eighteen boron carbide specimens were irradiated for 355 effective full-power days in the Experimental Breeder Reactor II to maximum burnups of 82 x 1020 capture /cm3. Baseline specimens were patterned after Fast Flux Test Facility reference boron carbide, and material variables of 10B enrichment, pellet density, grain size, and stoichiometry were investigated in the test. Irradiation temperatures ranged from 1175 to 1570°F (635 to 855°C). Each specimen was individually instrumented to measure temperature and helium release continuously during irradiation.Postirradiation examination provided information on pellet integrity, swelling, tritium retention, and compatibility with stainless-steel containment components.