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U/Th-isotopes as natural analogues for the mobility of actinides in granitic rocks

By K. Mengel, A. Gerdes and Clausthal-Zellerfeld (Germany). Inst. fuer Mineralogie und Mineralische Rohstoffe Technische Univ. Clausthal

Abstract

The short-lived decay products of "2"3"8U ("2"3"4U and "2"3"0Th) can be used as natural analogues for actinides in a hard rock repository. Their mobility in the past may serve as a key for understanding actinide migration in the future. For generally old calcites of the HRL Aespoethe age of disturbance of "2"3"8U/"2"3"4U and "2"3"4U/"2"3"0Th activity ratios ranges from 30 000 to 436 000 years at degrees of disturbance ranging from 0.5 to 6.7. The results obtained imply that during the past 440 000 years U was mobile throughout the tunnel sections of the HRL Aespoeinvestigated here. For the FL Grimsel, the disequilibrium states of the "2"3"4U/"2"3"8U and "2"3"0Th/"2"3"4U activity ratios in fracture minerals (calcites silicates) also imply that the reactions causing isotopic disturbances have occurred within the past 500 000 years. The U/Th-isotope data of both the samples from the HRL Aespoeand the FL Grimsel have in common the mobilization of U in secondary fracture minerals by migrating solutions within the past 500 000 years. As for the question of a final disposal of radioactive waste in granite host rocks, the transport of U - and thus of similarly behaving actinides - in migrating underground solutions can therefore not be ruled out, if suitable hydraulic systems are considered. (orig.)SIGLEAvailable from TIB Hannover: F02B977+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Topics: 03E - Radioactive pollution, nuclear waste, RADIONUCLIDE MIGRATION, RADIOACTIVE WASTE DISPOSAL, RADIOACTIVE WASTE FACILITIES, RISK ASSESSMENT, URANIUM 238, URANIUM 234, THORIUM 230, GRANITES, CALCITE, GEOLOGIC MODELS, ISOTOPE DATING, CHEMICAL REACTION KINETICS
Year: 2001
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Provided by: OpenGrey Repository
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