Abstract
Several evaporite basins containing bedded salt and dome salt deposits in the USA and Europe are currently being investigated as potential repositories for radioactive waste. While salt has good geomechanical properties for the long-term isolation of radioactive wastes, all such deposits have undergone various degrees of dissolution by circulating unsaturated groundwater. The extent and rate of such dissolution poses a challenge to the geologists evaluating an area for a repository.
Detailed investigations at the Waste Isolation Pilot Plant (WIPP), a proposed repository for transuranic (TRU) radioactive wastes located in the Delaware Basin in Southeastern New Mexico, U.S.A., have outlined a broad dissolution front for the Salado formation. An approximate rate of advance of the dissolution front at 1 km per 100,000 years horizontally and 10 meters per 100,000 years vertically, has been calculated. Similar calculations have been performed for other basins with different degrees of uncertainty due to the limitations in surface mapping and core or well-log correlations. Unless such calculations can be performed satisfactorily, questions will remain about the future integrity of a repository located in such an area.
Résumé
Plusieurs bassins d'évaporites aux États-Unis et en Europe contenant des gisements de sel en couches et en dômes sont actuellement en investigation comme dépôts potentiels des déchets radioactifs. Tandis que le sel a de bonnes propriétés géomécaniques pour l'isolement à long terme des déchets radioactifs, tous ces gisements ont subi plusieurs degrés de dissolution par la circulation d'eau souterraine non saturée. L'étendue et la vitesse de cette dissolution présente un défi aux géologues qui évaluent un site pour un dépôt.
Des recherches détaillées sur l'emplacement du projet WIPP (Waste Isolation Pilot Plant), un des dépôts proposés pour déchets radioactifs transuraniques (TRU) situé dans le bassin Delaware au sud-est de l'état de New Mexico, États-Unis, ont tracé un large front de dissolution pour la formation «Salado». Un taux approximatif d'avance horizontal dufront de dissolution d'un km par 100 000 ans et en sens vertical de 10 mètres par 100 000 ans a été calculé. Des calculs similaires ont été faits pour d'autres bassins, avec différents degrés d'indétermination due aux limitations des levés de plan de la surface et à la corrélation entre sondages rotatifs. A moins que de tels calculs soient faits d'une manière satisfaisante, des questions demeureront sur l'intégrité future d'un dépôt situé dans un tel site.
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Lokesh, C. Evaluation of dissolution for radioactive waste repositories in salt deposits. Bulletin of the International Association of Engineering Geology 34, 11–14 (1986). https://doi.org/10.1007/BF02590230
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DOI: https://doi.org/10.1007/BF02590230