Coupling Radioactive Waste Glass Dissolution Measurements in Generic Groundwaters With Reactive Transport Modeling of Repository Scenarios

Abstract

AbstractThe reliable simulation of radionuclide migration away from the near field of a geological repository for safety analyses requires a fundamental understanding of processes in the near field. We focus this study on investigating the behavior of UK MW25 waste glass (a nonradioactive simulant of U.K. Magnox glass) and other near‐field components in a geological repository over long periods of time. The approach used involved a two‐step process: waste glass dissolution measurements and modeling in potential repository groundwaters, and reactive transport simulation of radionuclide release and transport in the near field. The Stage 1 rate of MW25 measured in lower‐strength‐sedimentary‐rock groundwater was found to be slightly higher than that measured in higher‐strength‐rock groundwater. Experimental results show the critical role of groundwater chemistry on waste glass dissolution kinetics. Reactive transport model parameterization was accomplished by coupling direct laboratory measurements and literature data with transport processes. The results revealed that 79Se, 99Tc, and 237Np are the radionuclides that will have the greatest impact on the environment at long times. The performance assessment results show that the improvement afforded by the addition of a copper canister in the waste package, as opposed to having only a steel canister, is marginal and higher strength rock would be a more effective barrier at long time than lower strength sedimentary rock in terms of restricting the transport of the radionuclides. Our model provides deep insights into the contribution of waste glass durability and other near‐field components in the containment and retardation of radionuclide transport.