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Gaus I.,National Cooperative for the Disposal of Radioactive Waste | Wieczorek K.,GRS Society for plants and Reactor Safety | Mayor J.C.,Enresa S.A. | Trick T.,SOLEXPERTS | And 4 more authors.
Proceedings of the International Conference on Radioactive Waste Management and Environmental Remediation, ICEM | Year: 2011

The evolution of the engineered barrier system (EBS) of geological repositories for radioactive waste has been the subject of many research programmes during the last decade. The emphasis of the research activities was on the elaboration of a detailed understanding of the complex thermo-hydromechanical-chemical processes, which are expected to evolve in the early post closure period in the near field. It is important to understand the coupled THM-C processes and their evolution occurring in the EBS during the early post-closure phase so it can be confirmed that the safety functions will be fulfilled. Especially, it needs to be ensured that interactions during the resaturation phase (heat pulse, gas generation, non-uniform water uptake from the host rock) do not affect the performance of the EBS in terms of its safety-relevant parameters (e.g. swelling pressure, hydraulic conductivity, diffusivity). The 7th Framework PEBS project (Long Term Performance of Engineered Barrier Systems) aims at providing in depth process understanding for constraining the conceptual and parametric uncertainties in the context of long-term safety assessment. As part of the PEBS project a series of laboratory and URL experiments are envisaged to describe the EBS behaviour after repository closure when resaturation is taking place. In this paper the very early post-closure period is targeted when the EBS is subjected to high temperatures and unsaturated conditions with a low but increasing moisture content. So far the detailed thermo-hydraulic behaviour of a bentonite EBS in a clay host rock has not been evaluated at a large scale in response to temperatures of up to 140°C at the canister surface, produced by HLW (and spent fuel), as anticipated in some of the designs considered. Furthermore, earlier THM experiments have shown that upscaling of thermal conductivity and its dependency on water content and/or humidity from the laboratory scale to a field scale needs further attention. This early post-closure thermal behaviour will be elucidated by the HE-E experiment, a 1:2 scale heating experiment setup at the Mont Terri rock laboratory, that started in June 2011. It will characterise in detail the thermal conductivity at a large scale in both pure bentonite as well as a bentonite-sand mixture, and in the Opalinus Clay host rock. The HE-E experiment is especially designed as a model validation experiment at the large scale and a modelling programme was launched in parallel to the different experimental steps. Scoping calculations were run to help the experimental design and prediction exercises taking the final design into account are foreseen. Calibration and prediction/validation will follow making use of the obtained THM dataset. This benchmarking of THM process models and codes should enhance confidence in the predictive capability of the recently developed numerical tools. It is the ultimate aim to be able to extrapolate the key parameters that might influence the fulfilment of the safety functions defined for the long term steady state. Copyright © 2011 by ASME. Source


Uhlemann S.S.,British Geological Survey | Chambers J.E.,British Geological Survey | Alonso A.T.,Aitemin | De Gea A.E.,CTM | Falck W.E.,Miro Inc
Near Surface Geoscience 2015 - 21st European Meeting of Environmental and Engineering Geophysics | Year: 2015

This study shows the application of 3D Electrical Resistivity Tomography (ERT) to the characterization of a narrow and deep open-pit marble quarry, in order to develop near-surface geophysical methods as an aid to realize the concept of an invisible, low-impact quarry. The purpose of the survey was to prove the applicability of ERT to image the extent and shape of subvertical faults and cavities in a highly resistive hard rock environment, thus allowing for targeted extraction of the natural stone reserve and a reduction of mining waste. ERT faces a range of challenges when applied to a hard rock environment, namely very high contact resistances, preferential current flow through conductive surface layers, and pronounced topographic features, which have to be accounted for in the data inversion. Despite these challenges, results show that using 3D ERT it was possible to outline the extent of a cave below the lower quarry floor and to identify the location of the fault causing the karstification. Observations recorded during data acquisition correlated well with the features imaged in the 3D ERT surveys, indicating the reliability of the results. © (2015) by the European Association of Geoscientists & Engineers (EAGE). Source


Nabulsi S.,Aitemin | Rodriguez A.,Aitemin | Rio O.,Technical University of Madrid
Joint 41st International Symposium on Robotics and 6th German Conference on Robotics 2010, ISR/ROBOTIK 2010 | Year: 2010

This paper summarizes the development of the technologies used to produce high quality sprayed concrete layers by robotizing a commercial shotcreting machine and automating the process used in the tunnelling construction industry. The proposed method provides the control system with the information of the properties of the pumping process, controlling the quality of the concrete layer by adjusting in real-Time the trajectory of the shotcreting machine. Given the unstructured nature of the tunnelling construction method there is an inherent difficulty in the automation of the shotcreting process. A complete description of the implemented control architecture of the shotcreting machine, the automated shotcreting process, the real-Time quality layer prediction and the analysis of the tests made in real sites are shown in this paper. Source


Villar M.V.,CIEMAT | Martin P.L.,CIEMAT | Barcena I.,Aitemin | Garcia-Sineriz J.L.,Aitemin | And 2 more authors.
Engineering Geology | Year: 2012

This paper summarises the information gathered in the last 15. years on the saturation of compacted bentonite obtained from different laboratory-scale tests, a large-scale mock-up test, and a real-scale in situ test, that were performed to simulate the conditions of the bentonite barrier in a high-level radioactive waste repository and to better understand the hydration/heating processes. In all the tests the bentonite used was the Spanish FEBEX bentonite, the maximum temperature in the system was 100. °C and the water used was of the granitic type, with low salinity. Some of the tests were running for more than thirteen years.The migration of water vapour in areas affected by the high temperature induced by the radioactive waste decay is very rapid, its extent depending on the actual temperature and bentonite porosity. The water vapour condensates in cooler areas and this causes water content increases in internal zones of the barrier where the liquid water coming from the host rock has not yet arrived. The hydration kinetics is initially quicker when the temperature is high, provided no vapour phase is formed. Nevertheless, the major effect of the thermal gradient on saturation is a delaying of it in the inner parts of the barrier, which can be very persistent and depends on the actual thermal gradient and consequently, on the barrier thickness and boundary conditions.During the transient period in which the barrier is saturating, important changes in the water content and dry density of the bentonite are generated, which induce bentonite density and water content gradients along its thickness. These gradients could eventually disappear once the barrier is fully saturated, depending on the irreversibility of the deformations.The average density of the water in the saturated barrier will be higher than 1g/cm 3, due to the predominance of high-density, interlayer water in the compacted bentonite, and consequently, more water than expected, according to calculations made considering the density of free water, would fit in the bentonite pores.The rate of hydration of the barrier depends on the bentonite and surrounding media hydraulic properties (that is, water availability), waste temperature and buffer thickness and geometry. © 2012 Elsevier B.V. Source


Garcia-Sineriz J.L.,Aitemin | Villar M.V.,CIEMAT | Rey M.,Aitemin | Palacios B.,Aitemin
Engineering Geology | Year: 2015

The EB experiment was a large-scale test performed in the Underground Research Laboratory of Mont Terri (Switzerland) for the demonstration of an engineered barrier concept for nuclear waste disposal consisting of the simultaneous use of high-density bentonite blocks and a lower-density bentonite pellets mixture (the granular buffer material, GBM). For that purpose, a gallery was excavated in the Opalinus clay and a dummy waste canister was placed on a bed made of bentonite blocks and surrounded by the GBM material. The bentonite barrier was artificially hydrated with Pearson water and after 10.5. years of operation at isothermal conditions it was considered that the bentonite was completely saturated and the dismantling of the barrier was undertaken. A sampling campaign was done to assess the final state of the bentonite barrier with regards to dry density and water content.Upon dismantling, the GBM looked perfectly homogeneous, with every void and gap between the different elements (blocks/GBM, GBM/host rock, GBM/canister, etc.) having been sealed. Full saturation had been reached all through the barrier. Moreover, the dry density of the blocks had decreased to values similar to those of the GBM, and the average water contents for both kinds of materials were similar. Nevertheless, the initial conditions of the system did have a certain impact on the final distribution of dry density and water content: the bottom of the barrier had a chance to quicker and higher water uptake (due to the heterogeneities in the initial porosity and characteristics of the artificial hydration system), which gave place to immediate swelling that resulted irreversible, with permanent higher water contents and lower dry densities towards the floor and back of the gallery, particularly in the GBM. Despite these heterogeneities, the water contents and dry densities of the whole barrier (GBM and blocks) were much more homogeneous than at the beginning of the test and remained within a relatively narrow range. The bentonite degree of saturation was homogeneous and very close to 100% all through the barrier.The feasibility and performance of this kind of initially heterogeneous barrier was proved in that it had an optimal sealing capacity and developed acceptable swelling pressures between 1.3 and 2.2. MPa. © 2015 Elsevier B.V. Source

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