ACCELERATED WEATHERING EXPERIMENTS OF TWO LOW-ACTIVITY WASTE GLASSES USING THE PRESSURIZED UNSATURATED FLOW (PUF) APPARATUS

Low Activity Waste (LAW) performance assessment models must account for the long term release rate from LAW glass formulations. The release rate is a key parameter affecting the overall performance of the LAW disposal facility. To address these and other issues, accelerated weathering experiments, using the pressurized unsaturated flow (PUF) apparatus, are currently being conducted to evaluate the corrosion rate of two radioactive glass formulations made with actual Hanford tank waste.

The PUF apparatus allows for accelerated weathering experiments to be conducted under hydraulically unsaturated conditions, thereby mimicking the vadose zone environment while allowing the corroding glass to achieve a final reaction state. The basic test apparatus consists of a column packed with crushed glass, a titanium porous plate, a computer data acquisition and control system, a fluid pump, and electronic sensors.

Results from the computer monitored sensors suggest that both glasses have a moderate corrosion rate consistent with rates measured for non-radioactive LAW glass formulations previously tested. Normalized release rates for ⁹⁹Tc and ²³⁸U show congruent release behavior with B, indicating little or no incorporation into alteration phases. In contrast, static experiments with several LAW glasses show significant incorporation of ⁹⁹Tc into alteration phases, principally zeolites. The discrepancy may be due to the limited mass of alteration phases (or different types) that have formed in the PUF tests to date.