The link between performance assessment and quality of data

Performance assessments, using both individual and cumulative inventories, produce estimates of the risk or dose consequences for repository concepts. Unacceptable risk or dose for a given contaminant identify it as a problem contaminant. While risk or dose consequences are common outputs of safety assessments, results can also be reported as estimates of the safe inventory limit for each contaminant in a repository scenario. Once problem contaminants are identified, it may be useful to: validate the data used in the performance assessment; restrict contaminant inventories in the repository; or, improve the containment capability of the repository (including improved packaging). A key point is that performance assessments define the quality of data to be collected. If a contaminant's inventory will be far below its estimated safe inventory limit for a repository, then it is reasonable to accept inventory estimates that have high variances and low confidence. For contaminants that have a significant impact upon performance assessments, efforts must be made to provide the best inventory (source term) estimates practicable. One important goal of characterization programs should be to establish the adequacy of data used in performance assessments. There is little value in striving to improve confidence in data for some waste streams if they are assessed to have a minor impact upon repository performance. Streams that have a major impact upon performance deserve the time, attention and money to be characterized adequately. Waste acceptance must be linked to the quality of characterization data provided by generators. This link sets compliance monitoring requirements