Four alternative hybrid breeding blankets have been compared using probabilistic risk assessment (PRA) methodology. Included in the comparison were uranium and thorium fast-fission blankets, a thorium fission-suppressed blanket, and a pure fusion blanket. Three accident initiating events, a blanket cooling duct failure, a tritium vent system pipe break, and a plasma disruption were chosen and event sequences and radioactivity release pathways determined. Event trees were constructed for the four blanket designs and reliability data applied to obtain branch probabilities. These were then combined with the results of consequence analyses, providing a limited risk profile.