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Used Fuel Degradation: Experimental and Modeling Report

The primary purpose of this report is to describe the strategy for coupling three process level models to produce an integrated Used Fuel Degradation Model (FDM).  A multi-laboratory collaborative approach to the used fuel degradation and radionuclide mobilization activities includes experimental work, process model development and model integration; models intended to feed the generic disposal system performance assessment model is a focus of activities.  The primary output connection to the PA model is the fractional degradation rate (FDR) of the used fuel matrix (radiolysis and mixed potential models are used to evaluate this).  A second output has been generated to represent the instant release fractions (IRF) of radionuclides that are released virtually instantaneously upon breach of the cladding.  Within the process models, the radiolysis model (RM) and the mixed potential model (MPM) are employed to evaluate (a) generation rate of radiolytic oxidants in a water film on the surface of a used fuel pellet, and (b) degradation rate of used fuel at the pellet-water film interface for a given generation rate of radiolytic oxidant, respectively.  Underpinning these continuum modeling approaches are experimental studies and first principles models of uranium dioxide and the major corrosion products expected.  Individual, integrated and coupled model development, implementation, verification and validation exercises are presented.  Options for future model development, integration and testing, and use of the DAKOTA code are also presented.