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Stable water isotopes are useful tools for the characterization of groundwater recharge and the identification of evaporation and marine intrusion processes. This work compiles the isotopic values determined in rainwater samples and water collected in the river Záncara in the section between Zafra de Záncara and Villaescusa de Haro (Cuenca, Spain) from January 2013 to October 2015. The main purpose of this work is the exploration of the application of environmental isotopes to estimate the nature and magnitude of discharges to river Záncara along the section studied by using the δ2H, δ18O and δ13C values. Groundwater discharges are significant throughout the course of the river, reaching its maximum near Villar de Cañas. Os isótopos estáveis em amostras de água são ferramentas úteis para a caracterização de recarga de águas subterrâneas, identificação de evaporação e processos de intrusão marinha. Este trabalho reúne os valores isotópicos determinados em amostras de águas pluviais e água captada no rio Záncara no trecho entre Zafra de Záncara e Villaescusa de Haro (Cuenca, Espanha) desde janeiro de 2013 até outubro 2015. O principal objetivo deste trabalho é explorar as aplicações de os isótopos ambientais, a fim de estimar a natureza ea magnitude das descargas para o rio Záncara ao longo da seção estudada usando δ2H, δ18O e δ13C. As descargas de águas subterrâneas parecem significativas ao longo do curso do rio, atingindo o seu máximo perto de Villar de Cañas. [ABSTRACT FROM AUTHOR]

In the frame of the ENRESA natural analogue programme, the uranium ore from the “Mina Fe” (Salamanca, Spain) has been studied as a natural analogue of radioactive spent fuel behaviour. This uranium mine is hosted in highly fractured schistose rocks, a geological setting that has not been envisaged in the Spanish options for radioactive waste burial. However, some analogies with the processes that might be involved in the evolution of these geological repositories suggested this investigation.The pitchblende–pyrite–carbonate paragenesis has been studied “in situ” as natural analogue of the nuclear spent fuel behaviour under extremely oxidative dissolution conditions. Similarly, secondary Fe oxyhydroxides and clay minerals have also been considered as relevant analogue materials for the retention of uranium and other analogous trace metals. A multidisciplinary characterisation of the site has been performed in order to study these processes.Though the intense mining activities in the site hindered precise determination of the original hydrogeological and hydrochemical features of the investigated zone (Boa fault zone), the mineralogy and geochemistry of fracture fillings, mineralisation and associated clayey materials have allowed the geochemical evolution of the system to be established. Three geochemical zones have been clearly differentiated: (i) the oxidised zone, from the surface to approximately 20 m depth, (ii) the redox transition zone, from 20 to 50 m depth, and (iii) the reduced zone, located below the transition zone.The oxidised zone is characterised by the presence of the typical mineral association resulting from the strong acid conditions caused by the total oxidation of pyrite and other sulphides. The total oxidation, dissolution and leaching of U(IV), as uranyl–sulphate aqueous complexes, prevailed in this oxidised zone. The redox transition zone is characterised by the coexistence of the primary uranium paragenesis, oxidised minerals, as well as numerous secondary solid phases as a result of the physico-chemical changes in the environment. The optimal physico-chemical conditions for the coffinitisation of pitchblende and the co-precipitation of Fe(III)–U(VI) took place in this zone. In the reduced zone, where the primary uranium paragenesis is present, we currently find the necessary physico-chemical conditions to stabilise pitchblende, pyrite and carbonates.The physico-chemical conditions of the oxidised zone are not relevant to disposal conditions. In the transition zone, two main geochemical processes take place: (i) the coffinitisation of pitchblende, which may be an important process for the stability of spent fuel in reducing conditions, and (ii) the co-precipitation of the Fe(III) and U(VI) as oxyhydroxides, another relevant mechanism for the retention of uranium. The physico-chemical conditions that prevail below 50 m depth should be sufficient to stabilise a spent nuclear fuel repository, in the same way as they have been able to preserve the 34-Ma-old uranium deposit of the Mina Fe. [Copyright &y& Elsevier]