This report describes research to identify the factors which govern or influence the long-term behaviour of the near-field of a nuclear waste repository. The near-field components include the engineered barriers and the natural rock mass although the behaviour of the rock mass is of greater significance over the long-term. The factors which govern the near-field behaviour consist of the processes which operate, and the properties or parameters of the rock mass which might be modified by them. The methods which are available for the prediction of the near-field behaviour have been identified, and the emphasis on computer based methods is noted. Summary details of generic computer techniques are provided for different process modelling requirements. An attempt is made to indicate how different processes will be important at various stages during the life of the repository and how the evaluation of performance assessment process modelling requires input from empirical models and the results of other process predictions. (Author).