SR 97. Processes in the repository evolution. Background report to SR 97

This report describes, in a comprehensive and coherent fashion, all identified internal processes of importance for the post-closure evolution and safety of a KBS-3 repository for spent nuclear fuel. The report has been written to be used in the SR 97 project, which has limited the time available for its preparation. Differences in the level of detail in descriptions of different processes do not always reflect differences in the significance of the processes. Discussions of different types of uncertainties could in many cases be broadened and deepened, and the stylistic quality could sometimes be improved. Like other background material for the safety assessments, the process report is also expected to require revision as site-specific conditions are progressively clarified. Today's version of the process report is therefore the first version of a report that will be revised prior to every safety report. The intention is to perform the first revision of the report after scrutiny of SR 97. The report describes the internal processes which over time lead to changes in a KBS-3 repository for spent nuclear fuel. The context of the material in the report is described in SR 97 Main Report and briefly entails the following: The repository has been divided into four subsystems: fuel/cavity, cast iron insert/copper canister, buffer/backfill and geosphere. A number of processes of importance for the post-closure evolution of the repository have been identified within each subsystem. This has been done with the aid of material in the so-called interaction matrices previously developed by SKB. The processes have been divided into the categories thermal, hydraulic, mechanical and chemical. Furthermore, there are processes related to radiation and radionuclide transport. The identified processes are documented in this report. Each subsystem has its own chapter, and each chapter is divided into radiation related, thermal, hydraulic, mechanical and chemical processes as well as radionuclide transport. Each chapter begins with a description of the subsystem in question plus an overview of the processes treated in the chapter. All processes are then described in a standard format with the following subheadings: Overview, Brief description of the process, what it is influenced by and influences, and its importance for safety. More detailed description of the process and the mechanisms involved. Description of model studies and/or experimental studies that have been performed to quantify the process. If possible to specify: On what timescale does the process lead to relevant changes? Sometimes several time perspectives need to be defined. Natural analogues wherever applicable (This report is a Swedish language version of report SKB-TR--99-07)