| Sumario: | The FEBEX in situ test simulated the engineered barrier of a nuclear waste repository and was in operation for 18 years under natural conditions. The water retention curves of bentonite samples retrieved during dismantling of the in situ test were determined in wetting paths under isochoric conditions with the vapour transfer technique. The water retention curve relates suction (or relative humidity) to bentonite water content. Samples taken from the drier blocks in the barrier –i.e. those closest to the heater that simulated the waste container– and those from the core of the barrier in cool areas were used, since the aim of the tests was to check the effect of prolonged and intense drying on the water retention capacity of the bentonite. For the samples tested the initial water content conditioned the retention capacity for suctions above 10 MPa. In contrast, the samples closest to the heater, which had the lowest water contents, reached higher water contents for the lowest suctions than the rest of the samples, which attest that the water adsorption capacity was not lost as a result of prolonged drying. The comparison of the water retention curves obtained in the retrieved samples with those for the FEBEX reference bentonite compacted at similar densities shows that there were no changes in the water retention capacity during operation and that the water adsorption capacity of the bentonite under constant volume conditions is mostly conditioned by dry density.
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