Capillarity in Concrete Disposal Vaults and Its Influence in the Behavior of Isolation Barriers at El Cabril Low and Intermediate Level Radioactive Waste Disposal Facility in Spain

El Cabril is a disposal facility commissioned in 1992 for Low level and Intermediate Level Radioactive Waste (LILW). Most waste is stored in 11 m3 concrete overpacks, placed inside 24 x 20 x 10 m concrete vaults. Beneath the disposal vaults, an inspection drift has been built containing 0.01 m3 control tanks that collect eventual seepage water from each vault. After 10 years of operation, small quantities of water started to be collected in the control tanks of some vaults. After thorough investigation, tests, and modeling effort, capillary rise was identified in the origin of this phenomenon, together with evaporation and condensation caused by temperature differences between the concrete blocks and the vaults wall surfaces, causing a sort of wick effect. With the support of research institutions as Instituto Eduardo Torroja (CSIC-IETCC), Instituto Jaume Almera (CSIC-IJA) and Technical University of Catalonia (UPC), a set of experiments as well as models were developed to study these processes and their effects in the concrete barriers and the potential migration of radionuclides. The Thermo-hydraulic model predicted two seasonal peaks (winter and summer), and has a good quantitative correlation with the amounts of water collected. According to the model, this process will not be significant in the long term, once the vaults will be covered by an earthen cap. The experimental work on the influence of this phenomenon in the different degradation mechanisms and the reactive transport models show a potential surface damage with a depth of two millimeters in 80 years, a period much longer than the expected duration before construction of the engineered cap. (authors)