5.50. In developing the models, it is necessary to identify and select the parameters that will be quantified, a process that is called model parameterization. Parameter values also have to be selected. In this process, the following should be ensured: @@- Parameter values used in the models and codes for assessment calculations should be documented, together with the justification for their use. The process of model parameterization should be traceable to source data.@@- Records should be kept of how site specific and system specific characterization data have been used to derive parameter values used in the assessment calculations. @@- Where a deterministic approach has been applied, a justification for the conservatism or realism of selected parameter values used in the calculations should be provided.@@- Where a probabilistic approach has been used in the assessments, a justification of the selected probability distributions should be provided.