Resumen: The mobility of natural U is compared among four boreholes in a fractured granite using Ra isotopes and geochemical modelling. Rn-222/Ra-226 activity ratios (ARs) spanning an order of magnitude underline differences in reactive surface area. (Ra-224/Ra-228)(ARs) up to 9 indicate recent changes in hydrogeochemistry, and (Ra-226/Ra-228)(ARs) 0.6-30 indicate variable deposition of U. Dissolved U is related to dissolution of a solid U(VI) phase by groundwater with HCO3- > 20 mg.L-1. U reduction is hindered by Ca2UO2(CO3)(3)(0). Idioma: Inglés DOI: 10.1016/j.proeps.2016.12.122 Año: 2017 Publicado en: Procedia Earth and Planetary Sciences 17 (2017), 484-487 ISSN: 1878-5220 Financiación: info:eu-repo/grantAgreement/EC/FP7/290336/EU/Metal Transport in the Environment/MetTrans Tipo y forma: Artículo (Versión definitiva) Área (Departamento): Área Petrología y Geoquímica (Dpto. Ciencias de la Tierra)