The Probabilistic Risk Assessment (PRA) of Savannah River Plant (SRP) reactor operation is evaluating the offsite risk due to tritium releases during postulated full or partial loss of heavy water moderator accidents. Preliminary determination of the frequency of average partial moderator loss (including incidents with leaks as small as 0.5 kg) yields an estimate of ∼1 per reactor-year. The full moderator loss frequency is conservatively chosen as 5×10−3 per reactor-year. Conditional consequences, determined with a version of the MACCS code modified to handle tritium, are found to be insignificant. The 95th percentile individual cancer risk is 2×10−8 per reactor-year within 16 km of the release point. The full moderator loss accident contributes about 80% of the evaluated risks. “Nuclear Power Safety Goals in Light of the Chernobyl Accident,” Nucl. Safety, 29(1), 20 (1988).