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Systems Analysis for a Dual-Purpose Repository

Objective

For a repository in rock salt accommodating both heat generating waste from reprocessing and spent fuel, the most favourable combination of waste/spent fuel conditioning technologies and disposal alternatives is sought. The annual arisings of spent fuel are subject to fuel reprocessing and direct disposal, respectively, whereby the extent of both paths is determined by the Entsorgung (versatile German term describing all steps at the back-end of the fuel cycle) ratio. This type of analysis gained of importance after the German government ruled in 1985 that the spent fuel disposal technology be developed so that it could be included in the German approach to spent fuel management. This analysis focuses on the underground part of the entire system, i.e. the repository. Beside the effects of heat in the near- and the far-field, the consequences of release scenarios are analyzed in order to assess the long-term performance of the underground system. In addition, economical and radiological aspects are considered, allowing to eventually compare the alternatives on a broad basis. The results will be included by the competent German authority submitting the licensing documents for the Gorleben exploratory mine.
The situation in Germany resulting from the Atomic Energy Act is such that spent fuel reprocesing is mandatory as long as the underlying technology is economically sound. However, in 1985 the German government ruled that direct disposal of spent fuel to be developed as a backup solution. This led, among other things, to the development of and adequate conditioning technology for spent light water reactor (LWR) fuel. Based on this technical boundary condition, the effects on the host rocksalt were evaluated for both reprocessing waste and spent fuel thereby anticipating a situation which is, most likely, going to be encountered in the prospective German repository.

The objective of the systems analysis is to establish the most favourable combination of waste/spent fuel conditioning technologies and disposal alternatives for the repository accommodating both heat generating waste from reprocessing and spent fuel. The analysis is based on 700 tons of spent fuel discharged annually from light water reactor LWRs and, with less emphasis, spent fuel form the German high tension reactor (HTR) programme. Beside the effects of heat in the near-field and the far-field, the consequences of release scenarios are analysed in order to assess the long term performance of the underground system. An additional concern of repository design is to make best use of the space available in the repository. This is accomplished by varying the emplacement pattern of the waste/spent fuel packages considered, taking fully into account a near-field design temperature of 200 C. Far-field analysis is focused on the interface between the salt dome and the overlying strata with special emphasis on possible tensile stress in this interface, thereby opening pathways to intrusion of brine. The possible consequences of such a scenario have been analysed.
Work programme:

1. Background: Fuel reprocessing is the German reference approach to spent fuel management but some sorts of spent fuel lend themselves to direct disposal.
2. Technical concepts: conditioning technologies for spent fuel and reprocessing waste are main requisites for making best use of the room available in model repositories.
3. Individual analyses: The thermal loading associated with various disposal concepts is key to thermal and thermomechanical effects in both the near- and the far-field.
4. Evaluation: Concepts are sought with score highest with respect to a series of evaluation criteria.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Forschungszentrum Karlsruhe Technik und Umwelt GmbH
Address
Weberstraße 5
76133 Karlsruhe
Germany