Development and Analysis of Scenarios for a Permanent Repository for Radioactive Wastes in Salt Rock
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Development and Analysis of Scenarios for a Permanent Repository for Radioactive Wastes in Salt Rock S. Keller Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover/Germany, Email: [email protected] ABSTRACT Scenarios were developed and analyzed as part of a long-term safety analysis of a permanent repository for radioactive wastes. A procedure is described by which features, events, and processes (FEP) at a specific site can be evaluated for the long-term safety assessment of a permanent repository for radioactive waste. These FEPs can be weighted according to selected criteria and combined to scenarios using a conceptual model of the site. INTRODUCTION BGR conducts geological, hydrogeological, and geomechanical studies on permanent repositories for radioactive wastes in salt rock. Within the scope of these studies, scenarios are developed and analyzed for the safety assessment of the repositories. Scenarios can be viewed as pictures of the futures. They show the changing conditions brought about by processes and events, for which the acronym FEP (features, events, processes) is used, that influence the permanent repository system. A method for developing and analyzing such scenarios is presented here that can be used to determine the most important scenarios for a safety assessment. SCENARIO DEVELOPMENT A NEA database [1] was used as a basis for developing the scenarios. This database contains FEPs that are of significance for the long-term safety of permanent repositories in different countries. To develop scenarios for a repository in a salt dome that take the geology of the site into consideration, 71 FEPs dealing with the host rock, repository depth, type of waste, repository design, retrievability, etc. were retrieved from the database. For a given site, this list must be modified on the basis of the site studies. A multibarrier system that will guarantee long-term retention of the radionuclides was assumed for the scenarios. In the case of a repository in salt rock, the multibarrier system consists of the "natural barriers", the salt rock (the host rock) and overlying sediments, and the "engineered barriers", consisting of the containers, packing material, backfill, and bulkheads, including the chemical aspects of these.
Dynamic exogenous and endogeneous geological processes, processes caused by the radioactive waste, and measures taken during the site exploration and repository operations affect the multibarrier system. Scenarios and the FEPs they are based on can be classified in various ways. For the BGR studies, a geological classification was chosen that does not include any assessment of the scenarios for the safety analysis: • • • • •
geotechnical scenarios hydrogeological scenarios climate scenarios geological scenarios extraterrestrial scenarios
The geotechnical scenarios deal with the effects of measures taken during site exploration, repository construction and operations and are thus of considerable significance for the long-term safety assessment. Because
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