Waste Form Performance Modeling

Division researchers participate in the modeling and assessment of the metal and ceramic waste forms, which incorporate the radioactive wastes generated during electrometallurgical treatment of spent nuclear fuel. These waste forms must be qualified to meet the regulatory requirements on radionuclide release and thermal performance within a geologic repository. Acceptable limits on temperature and radionuclide release must also be met under on-site interim storage and transportation conditions. The qualification relies on both testing and modeling.

Thermal Analysis Results that Demonstrate the Potential Increase in the Amount of Recycle Waste That Could Disposed as Compared to Direct Disposal of Spent Nuclear Fuel. (See full-size image)

NE's modeling efforts are coordinated with testing activities conducted by CMT and Idaho National Laboratory (INL) investigators. The activities encompass (a) thermal and radiation-shielding analyses of waste package configurations, (b) modeling of waste form degradation and radionuclide retention as functions of time and environmental conditions of storage and final disposition, and (c) integrated assessment of waste form long-term performance in a geologic repository. Specific modeling and analysis activities include:

• Developing models of the long-term degradation behavior and radionuclide release mechanisms of the ceramic waste. The modeling effort currently focuses on interpretation of experimental results of waste qualification tests provided by the waste form development and testing groups-with the objective of applying these results to the long time scales and environmental conditions of interest in repository performance evaluation. Such phenomena as radiation damage and humid corrosion are considered in the models. This empirical modeling approach is complemented by molecular-level simulations to provide insights into the experimental results and to provide a theoretical basis for future predictive models.

• Creating and maintaining an electronic database of metal and ceramic waste performance data generated by experimental groups in the CSE Division and at INL. This database supports waste form design optimization and performance modeling. The database is being made accessible to project personnel via World Wide Web technologies.

• Developing a repository performance assessment model to be used for scoping studies and parameter sensitivity studies. This model is being developed in collaboration with Golder Associates, Inc., and Duke Engineering/TRW (the DOE Management and Operating Contractor for the Yucca Mountain Project). When completed, the model will be available to allow individual waste storage sites to perform preliminary repository performance evaluations to support decisions related to the benefits of treating spent fuel by the electrometallurgical process prior to disposal.
• Developing waste packaging designs compatible with both on-site interim storage and geologic permanent disposal. Analyses include transportation considerations, thermal evaluations, and dose calculations. As part of this process, working relationships have been established with the National Spent Nuclear Fuel Program, Duke Engineering/TRW, the DOE Standardized Canister Working Group, and performance assessment specialists at Sandia National Laboratory.

Repository Performance Assessment Results that Demonstrate the Potential Decrease in Dose to the Public for Disposing Recycle Wastes Compared to Direct Disposal of Spent Nuclear Fuel. (See full-size image)