Rates of CO2 production from the microbial degradation of transuranic wastes under simulated geologic isolation conditions

Transuranic wastes containing organic matter can serve as an energy source for microbial growth. The rates of microbial respiration during decomposition of several transuranic-contaminated waste materials were measured under environmental conditions representative of a geologic waste repository in bedded salt. The major observed effect of microbial activity on organic-matrix wastes was the generation of CO2 gas. Experimental variables studied include: incubation temperature (250 to 700C), atmosphere (aerobic and anaerobic), moisture content, brine content, and plutonium contamination level (0 to 40 microcuries of alpha activity per gram of waste). The maximum rate of CO2 generation observed was 11 g/day per gram of waste. The addition of 300 μg (20 μCi) of defense-grade PuO2 per gram of waste reduced the rate of CO2 generation by approximately 70%. Results indicate that microbial activity in existing drums of defense-related transuranic wastes has the potential to generate significant quantities of gas under both aerobic and anaerobic conditions. Carbon dioxide was the only gas detected in these studies. 42 refs., 1 fig., 6 tabs