Pedro Luis Martín

Pore waters extracted from compacted bentonite subjected to simultaneous heating and hydration

A compacted clay block of montmorillonite clay has been simultaneously subjected to heating and hydration by parallel and opposite fronts, in order to determine the physico-chemical effects of the thermohydraulic process on the clay and on its pore water. The pore waters of the clay have been extracted at ambient temperature after the thermal-hydration treatment by a compaction at high pressure (60 MPa) technique. They have been analyzed, and the chemistry has been evaluated by using the speciation program EQ3NR. The movement of salts towards hot areas has been observed as a result of the thermo-hydraulic gradients, but it is conditioned by anionic retention processes, which mainly affect the mobility of SO42− anions. The distributrion of the exchangeable cations is modified by the thermal gradient.

Gas-breakthrough pressure of FEBEX bentonite

Abstract The gas-breakthrough pressure values in saturated FEBEX bentonite were determined for different dry densities and sample sizes. They increased clearly with dry density and were always higher than the swelling pressure of the bentonite. In high-density samples, gas flow tended to stop abruptly after breakthrough, whereas, in lower density samples, gas flow decreased gradually until a given pressure gradient was reached. The permeabilities computed after breakthrough (which usually did not stabilize) were inversely related to dry density. This would indicate that, despite the fact that flow took place through preferential pathways, the bentonite matrix and its swelling conditioned the ease of pathway formation. These paths sometimes closed quickly after breakthrough and others remained open, allowing a gradual decrease in gas flow. After resaturation of the bentonite, the same breakthrough pressures and permeabilities were found, pointing to the perfect healing of these preferential pathways. A sealed interface along the bentonite did not seem to affect the breakthrough pressure or permeability values.

Polarity effect on fluorescence of styryl derivatives of quinolizinium salts in micellar media

Abstract The styryl derivatives of quinolizinium salts show a marked solvatochromic effect. The p -amino and p -hydroxy derivatives exhibited the greatest effect. The fluorescent intensity of the salts dissolved in nine different solvents is shown to be related to their polarity parameters. The emission was highest for hydroxylic solvents. For all solvents the changes in the fluorescence of the styryl derivatives in the presence of various surfactants is also studied; a great increase in intensity was produced in the presence of sodium dodecylsulfate. This enhanced emission was not observed for non-ionic surfactants. This behaviour is discussed ansd also related to solvent polarity.

Gas and water permeability of concrete

Abstract Concrete is used as a barrier on surface or near-surface facilities for the final disposal of low- and intermediate-level radioactive waste, where gas can be generated and affect the hydraulic properties and the processes taking place in concrete. In this framework, gas-transport properties of concrete samples were investigated using two different laboratory test set-ups: a non-steady-state equipment working under low injection pressures; and a newly fine-tuned steady-state set-up working under different pressures. Permeability decreased with water content increase but was also greatly affected by the hydraulic history of concrete (i.e. if it had been previously dried or wetted). The intrinsic permeability determined with gas flow was about two orders of magnitude higher than that determined with liquid water (10−16 v. 10−18 m2), probably due to the chemical reactions taking place during saturation (carbonation). The relative gas permeability of concrete increased sharply for water degrees of saturation smaller than 50%. The boundary conditions also affected the gas permeability, which seemed to be mostly conditioned by the back pressure and the confining pressure, on the whole decreasing as the effective pressure increased. It is considered that the Klinkenberg effect was not relevant in the range of pressures applied.

State of a bentonite barrier after 8 years of heating and hydration in the laboratory

The conditions of the bentonite in an engineered barrier for HLW disposal have been simulated in a laboratory test. Six cylindrical blocks of bentonite compacted at a dry density of 1.64 g/cm{sup 3} were piled up in a hermetic Teflon cell. The total length of the clay column inside the cell was 60 cm. The bottom surface of the bentonite was heated at 100 deg. C while the top surface was injected with granitic water. The duration of the test was 7.6 years. The water intake was measured during the test and, at the end, the cell was dismounted and the dry density, water content, mineralogy, geochemistry, and swelling capacity of the clay were measured in different sections along the column. At the end of the test no full water saturation was reached and water content and dry density gradients were found along the column. No mineralogical changes have been detected, although the pore water chemistry and the exchangeable complex of the smectite have changed along the bentonite. None of these changes affect drastically its swelling capacity, which remains high. The material used in this test is the FEBEX bentonite. (authors)

Experimental Investigation of Gas Transport in the Shaly Facies of Opalinus Clay

An experimental setup was designed to measure gas permeability and gas breakthrough pressures in Opalinus clay samples. The confining pressures applied were higher than the maximum in situ stress, and the tests were performed by slowly increasing the injection pressure whereas backpressure was kept atmospheric and the outflow was measured. The breakthrough pressure perpendicular to bedding was generally higher than 18 MPa, which is consistent with the air entry values deduced from mercury intrusion porosimetry tests for this material, which was between 19 and 36 MPa. In samples with degrees of saturation lower than 70% flow occurred for lower gas injection pressures, and the effective gas permeability measured was in the range from 8 · 10−21 to 4 · 10−23 m2, decreasing with confining pressure. The gas transport mechanism in those cases was probably 2-phase flow.

Tests in Thermo-Hydraulic Cells to Simulate the Behavior of Engineered Barriers

Laboratory tests in thermo-hydraulic cells that simulate the conditions of the sealing material in a radioactive waste repository are very useful to identify and quantify processes taking place in the engineered barrier. This kind of tests have gone on at CIEMAT for the last 20 years, evolving from simple designs in which just temperatures inside the material were measured, to the current designs that involve the measurement of temperature and relative humidity, total pressure and water intake. Tests kept running for different periods of time (up to several years) and the analysis of the material upon dismantling included mineralogical, geochemical, microstructural, hydro-mechanical and chemical studies, what allowed gaining insight into the time evolution of the properties of the barrier.