Repository Concept Research Articles

Repositório biográfico: singularidades de um modelo promissor

A Sociedade da Informação possibilitou o surgimento de novas ferramentas digitais, no qual suas metodologias são debatidas pelos seus pares cujo objetivo é aceitação pela comunidade científica. O Movimento de Acesso Aberto chancelou ao mundo dois dos seus principais pilares: os repositórios digitais (institucionais e temáticos) e os periódicos científicos. A presente comunicação se preocupa em discutir sobre o que se entende por “repositório biográfico”, inquietação que se originou a partir de um grupo de estudos oriundo do curso de Especialização em Informação Científica e Tecnológica em Saúde, do Instituto de Comunicação e Informação Científica e Tecnológica em Saúde, da Fundação Oswaldo Cruz no Rio de Janeiro. O procedimento metodológico aplica uma reflexão diante da literatura disponível sobre repositório, em relação aos preceitos estabelecidos pela memória. O trabalho pretende discorrer sobre as diferenças entre os repositórios institucionais e temáticos de forma a evidenciar as singularidades que promovem o conceito de repositório biográfico. Para tal, apoia-se nas áreas do conhecimento que abordam em seu contexto aspectos distintos de definição de documento, mas que convergem na finalidade de preservar e perpetuar a memória. Portanto, um repositório biográfico para ser conhecido como tal aplica elementos da Arquivologia, Biblioteconomia e Museologia, ainda que, as suas diferenças sejam evidentes.

Feasibility Analysis of the Multilayer and Multicanister Concepts for a Geological Spent Fuel Repository

For a spent fuel repository, the possible application of the concepts of a multilayer repository with a two- or three-story disposal tunnel and a multicanister repository in which two or three canisters are emplaced in a deposition hole is assessed from the viewpoint of temperature, mechanical stability, and nuclear criticality. The results show that the concepts of multilayer and multicanister repositories are applicable to the geological repository without deterioration of the mechanical stability and nuclear criticality safety. Their adoption in the spent fuel repository can improve the disposal density up to 200% to 400% depending on the applied peak temperature limit under the given thermal constraint and site conditions.

Safety assessment methodology for a German high-level waste repository in clay formations

In the ANSICHT project that was jointly carried out by DBE TECHNOLOGY GmbH, BGR, and GRS gGmbH, two generic geological site models were used to develop a first draft of a methodology to demonstrate the safety of a high-level waste (HLW) repository in argillaceous formations in Germany, taking into account the regulatory requirements. The main results of the project are characterised by the developed repository concepts adapted to the geological conditions. The specific quantifications of the integrity criteria and their exemplary application with calculational proofs were used to demonstrate the integrity of the host rocks. The development of site-specific FEP (features, events, and processes) cataloges provided a complete system description for evaluation of the repository evolution. The developed work flow of the demonstration concept illustrated the complete sequence of the safety proof in a transparent way. It shows that various steps have to be performed, possibly iteratively, to provide a successful safety proof. The results form a useful tool in the pending search for a HLW repository site, especially when providing a basis for comparing safety analyses of different sites in Germany.

Sorption of radium onto early cretaceous clays (Gault and Plicatules Fm). Implications for a repository of low-level, long-lived radioactive waste

The repository of low-level and long-lived radioactive waste from REE purification and treatment is presently under investigation by the French National Radioactive Waste Management Agency (Andra). This waste consists of Ra-bearing solids, mainly Ra-barite (Ba,Ra)(SO4), along with other salts such as NH4NO3 and monazite. The current repository concept under study is based on a shallow (∼30 m deep) geological disposal in a clay formation. This work deals with the experimental study of the sorption of Ra onto two clay rocks from Lower Cretaceous geological formations in the Department of Aube, in France, the Gault (tégulines) Formation and Plicatules Formation.Clay samples were extracted from different boreholes from the both geological clay formations, and consisted mainly of illite, illite-smectite mixed layers (35–65% and 25–70%). Sorption experiments were carried out on raw materials as well as on samples exchanged with different cations (homoionic forms of Na, NH4, Ba and Ca, respectively). The results indicate that Ra sorption in raw materials is linear within the range of concentration investigated (10−8 - 10−11 M). In most of the samples, Kd values from 170 to 300 g·mL−1 were measured for Ra and from 30 to 70 g·mL−1 for Ba. The sorption experiments (from 1 h to 92 days) of Ra showed small kinetic effects as Kd values tend to increase with time from approximately logKd = 2.15 to 2.65. In all exchanged samples, a dependence of sorption on the ionic strength was observed -the higher the ionic strength, the lower Kd values-; except for Na, this dependence is consistent with an ionic exchange process and selectivity coefficients (Ra-Ca; Ra-Ba and Ba-Ca) have been determined. A non-negligible effect of pH on sorption was also observed that could be explained considering surface complexation on the amphoteric groups present at the solid surface. In these materials, the selectivity of Ra was higher than that of Ba (half an order of magnitude).The experimental results indicate that sorption of Ra in the studied clay formations is high enough to limit the radium migration in the near field of a low-level, long lived disposal site.

Inorganic anions as retarders for deep borehole disposal grouts

Deep borehole disposal (DBD) provides an alternative to comparatively shallow mined repository concepts for many high-level radioactive wastes. Filling the annular space around the waste containers with cement grout will support them during placement and seal against ingress of groundwater. The elevated temperature and pressure (∼120°C and 50 MPa) will cause acceleration of grout thickening and setting, so retardation is required. The DBD Research Group at The University of Sheffield has developed grouts based on class G oil well cement that use organic retarders, but their presence may increase the solubility of any radionuclides released from the waste packages. New DBD grout formulations using sodium phosphate and sodium borate as inorganic retarders are reported in this paper. To place the wet grout, the onset of thickening needs to be delayed for at least 4 h. Sodium borate was found to provide this retardation at 90°C (0·75% addition) and nearly retarded sufficiently at 120°C (1% addition). Sodium phosphate did not provide sufficient retardation at either temperature. Neither compounds influenced the phases formed, but may suppress the crystallisation of calcium silicate hydrates. This work demonstrates that the performance of these inorganic materials in this application is inferior to that of organic retarders.

Carbon Steel Corrosion in Simulated Anoxic Concrete Pore Water for Nuclear Waste Disposal Application

Carbon steel is a potential canister material for high-level waste disposal in underground geologic repository systems where reducing conditions dominate after the thermal period. For example, the super container concept in the proposed Boom Clay repository concept in Belgium comprises a carbon steel overpack containing the waste and an outer stainless steel liner forming the boundary of an annular region containing a cementitious material. The outer surface of the carbon steel overpack would be in contact with concrete pore water with pH near 12.5, expected to persist for thousands of years. This study investigated carbon steel passivity, corrosion rate, repassivation, hydrogen generation, and hydrogen induced cracking tendency in simulated concrete pore water under anoxic conditions, and the effects of possible anions in the pore water such as Cl−, , and S2−. Carbon steel maintained its passivity at 50°C and 80°C up to a test period of 6 months and passive corrosion rates were mostly in the range of 0.1...

Analyses of the Double-Layered Repository Concepts for Spent Nuclear Fuels

Analyses of the Double-Layered Repository Concepts for Spent Nuclear Fuels

Experiments on thermo-hydro-mechanical behaviour of Opalinus Clay at Mont Terri rock laboratory, Switzerland

Repositories for deep geological disposal of radioactive waste rely on multi-barrier systems to isolate waste from the biosphere. A multi-barrier system typically comprises the natural geological barrier provided by the repository host rock – in our case the Opalinus Clay – and an engineered barrier system (EBS). The Swiss repository concept for spent fuel and vitrified high-level waste (HLW) consists of waste canisters, which are emplaced horizontally in the middle of an emplacement gallery and are separated from the gallery wall by granular backfill material (GBM). We describe here a selection of five in-situ experiments where characteristic hydro-mechanical (HM) and thermo-hydro-mechanical (THM) processes have been observed. The first example is a coupled HM and mine-by test where the evolution of the excavation damaged zone (EDZ) was monitored around a gallery in the Opalinus Clay (ED-B experiment). Measurements of pore-water pressures and convergences due to stress redistribution during excavation highlighted the HM behaviour. The same measurements were subsequently carried out in a heater test (HE-D) where we were able to characterise the Opalinus Clay in terms of its THM behaviour. These yielded detailed data to better understand the THM behaviours of the granular backfill and the natural host rock. For a presentation of the Swiss concept for HLW storage, we designed three demonstration experiments that were subsequently implemented in the Mont Terri rock laboratory: (1) the engineered barrier (EB) experiment, (2) the in-situ heater test on key-THM processes and parameters (HE-E) experiment, and (3) the full-scale emplacement (FE) experiment. The first demonstration experiment has been dismantled, but the last two ones are on-going.

The anaerobic corrosion of carbon steel in saturated compacted bentonite in the Swiss repository concept

ABSTRACTCarbon steel is a candidate disposal canister material for high-level radioactive waste and spent fuel in the Swiss deep geological repository concept and so a long-term laboratory-based corrosion experiment was undertaken to measure the anaerobic corrosion behaviour and corrosion rate of carbon steel in compacted bentonite under simulated anoxic repository conditions. The corrosion rate was measured using barometric gas cells over a period of more than 5 years, until quasi-steady-state conditions were reached. The measured corrosion rates are in agreement with weight loss measurements and with previous tests under similar conditions. The carbon steel and surrounding bentonite removed from one cell after 3 years were analysed with a range of analytical techniques, weight loss measurements and mineralogical characterisation. The results provide an insight into the prevailing corrosion mechanisms under repository conditions.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Reaction of native copper in contact with pyrite and bentonite in anaerobic water at elevated temperature

ABSTRACTCopper pellets were reacted with different solutions, reference minerals, and well-characterised bentonites to investigate the effect of different bentonites on the stability of native copper in repository concepts for high-level radioactive waste. The reaction of Cu in contact with bentonite used as barrier material to store high-level radioactive waste was significantly affected by the presence of sulphides (e.g. pyrite) leading to a specific corrosion. Bentonites free of pyrite are not actively involved in a reaction with Cu. Nevertheless, slightly different Cu mass losses were found for different bentonites. For different bentonites, different coatings were found on the Cu surface. The characteristics of these coatings are probably responsible for different Cu mass losses of Cu in contact with different bentonites. As an example, particularly dense coatings led to a decrease in Cu mass loss. No relation of the Fe-corrosivity of different bentonites with Cu mass loss was found, which proves that the Fe-corrosion mechanism differs from the Cu-corrosion at the metal/bentonite interface. The experiments also demonstrated the importance of the presence even of traces of oxygen.

In-situ experiments on bentonite-based buffer and sealing materials at the Mont Terri rock laboratory (Switzerland)

Repository concepts in clay or crystalline rock involve bentonite-based buffer or seal systems to provide containment of the waste and limit advective flow. A thorough understanding of buffer and seal evolution is required to make sure the safety functions are fulfilled in the short and long term. Experiments at the real or near-real scale taking into account the interaction with the host rock help to make sure the safety-relevant processes are identified and understood and to show that laboratory-scale findings can be extrapolated to repository scale. Three large-scale experiments on buffer and seal properties performed in recent years at the Mont Terri rock laboratory are presented in this paper: The 1:2 scale HE-E heater experiment which is currently in operation, and the full-scale engineered barrier experiment and the Borehole Seal experiment which have been completed successfully in 2014 and 2012, respectively. All experiments faced considerable difficulties during installation, operation, evaluation or dismantling that required significant effort to overcome. The in situ experiments show that buffer and seal elements can be constructed meeting the expectations raised through small-scale testing. It was, however, also shown that interaction with the host rock caused additional effects in the buffer or seal that could not always be quantified or even anticipated from the experience of small-scale tests (such as re-saturation by pore-water from the rock, interaction with the excavation damaged zone in terms of preferential flow or mechanical effects). This led to the conclusion that testing of the integral system buffer/rock or seal/rock is needed.

Implementation of the full-scale emplacement (FE) experiment at the Mont Terri rock laboratory

Opalinus Clay is currently being assessed as the host rock for a deep geological repository for high-level and low- and intermediate-level radioactive wastes in Switzerland. Within this framework, the ‘Full-Scale Emplacement’ (FE) experiment was initiated at the Mont Terri rock laboratory close to the small town of St-Ursanne in Switzerland. The FE experiment simulates, as realistically as possible, the construction, waste emplacement, backfilling and early post-closure evolution of a spent fuel/vitrified high-level waste disposal tunnel according to the Swiss repository concept. The main aim of this multiple heater test is the investigation of repository-induced thermo-hydro-mechanical (THM) coupled effects on the host rock at this scale and the validation of existing coupled THM models. For this, several hundred sensors were installed in the rock, the tunnel lining, the bentonite buffer, the heaters and the plug. This paper is structured according to the implementation timeline of the FE experiment. It documents relevant details about the instrumentation, the tunnel construction, the production of the bentonite blocks and the highly compacted ‘granulated bentonite mixture’ (GBM), the development and construction of the prototype ‘backfilling machine’ (BFM) and its testing for horizontal GBM emplacement. Finally, the plug construction and the start of all 3 heaters (with a thermal output of 1350 Watt each) in February 2015 are briefly described. In this paper, measurement results representative of the different experimental steps are also presented. Tunnel construction aspects are discussed on the basis of tunnel wall displacements, permeability testing and relative humidity measurements around the tunnel. GBM densities achieved with the BFM in the different off-site mock-up tests and, finally, in the FE tunnel are presented. Finally, in situ thermal conductivity and temperature measurements recorded during the first heating months are presented.

Corrosion processes and microbial activity of carbon steel in the context of geological repository in clay environment

Carbon steel (C-steel) is studied to be the reference material for the metallic components in the high level waste (HLW) repository concepts of several European countries such as France, Switzerland, Belgium. Electrochemical impedance spectroscopy (EIS) was performed over a period of 7 years, to determine the instantaneous corrosion rate (CR) of carbon steel (C-steel) in contact with clay porewater in diffusive regime. The study was conducted at the Mont Terri underground research laboratory (URL) located in Switzerland. The test chamber was at a depth of 8 m under anoxic conditions at 90°C in a vertical and descending borehole drilled in Opalinus clay (OPA). Microbial and chemical investigations were conducted on porewater in contact with C-steel as well as directly on C-steel surface further to dismantling. The results showed clearly a decrease of the CR over time followed by a steady state below 1 µm/year. Sulphate and thiosulphate reducing bacteria were observed in porewater and at the metal surface, with a higher concentration of mesophilic and thermophilic bacteria respectively. The metal surface characterizations revealed the presence of magnetite, mackinawite, hydroxychloride and siderite with local traces of oxidizing species such as goethite.

Collaborative gathering and continuous delivery of DevOps solutions through repositories

Collaboration is a key aspect for establishing DevOps-oriented processes because diverse experts such as developers and operations personnel need to efficiently work together to deliver applications. For this purpose, highly automated continuous delivery pipelines are established, consisting of several stages and their corresponding application environments (development, test, production, etc.). The DevOps community provides a huge variety of tools and reusable artifacts (i.e. DevOps solutions such as deployment engines, configuration definitions, container images, etc.) to implement such application environments. This paper presents the concept of collaborative solution repositories, which are based on established software engineering practices. This helps to systematically maintain and link diverse solutions. We further discuss how discovery and capturing of such solutions can be automated. To utilize this knowledge (made of linked DevOps solutions), we apply continuous delivery principles to create diverse knowledge base instances through corresponding pipelines. Finally, an integrated architecture is outlined and validated using a prototype implementation.

Cement-bentonite-iron interactions on small scale tests for testing performance of bentonites as a barrier in high-level radioactive waste repository concepts

Nuclear power plants produce high-level radioactive waste, which has to be stored. Many countries plan to encapsulate their high-level radioactive waste (HLRW) in iron or steel canisters, which will be surrounded by highly compacted bentonite. The bentonite may be in contact with cement. Bentonite, discussed as the geotechnical barrier, is currently tested to find out which type has the best properties for a final repository. Considering the variety of bentonites in their behaviors regarding processes in contact with iron or cement, comparative methods are exceedingly valuable. In addition, when operating a repository a quality management (QM) regarding bentonite qualities will be required.In this study a small scale setup was tested that included the performance of bentonite in contact with the bentonite-iron and bentonite-cement interfaces. The tests proved that the different bentonites reacted differently. The mini-tests could be an appropriate way to test the behavior of bentonite in the final repository taking into account the appropriate proportions of cement, bentonite, and iron considered in the repository. The excess of cement used in this study has shown that the cement reacts very aggressively, which masked the reactions taking place at the bentonite-iron interface. A first overview of quantitative data about bentonite performance can be an example gained from both the mass loss of the metal pellet and the drop of cation exchange capacity (CEC) of the bentonite after the tests. Taking both these values into account does not permit deep understanding of the complex processes but allows for a quantitative comparison of the performance of different bentonites. Amongst the three bentonites tested the Ca-bentonite B36 from Slovakia showed on average less loss of swelling capacity (CEC) and hence is regarded superior to both other materials.

Thermal–hydraulic–mechanical behavior of bentonite and sand-bentonite materials as seal for a nuclear waste repository: Numerical simulation of column experiments

Depending on the repository concept, buffer materials around the canister may play an important role for the performance of deep geological repositories for high-level radioactive waste (HLW). Coupled thermo-hydro-mechanical (THM) processes are initiated in the buffer material, as heat produced by the HLW typically causes an initial drying of this sealing layer, which may be followed by re-saturation with fluid from the host rock. In this study, a fully coupled and process-oriented numerical model was applied to simulate laboratory experiments investigating two buffer materials, i.e. clay pellets as well as a sand-bentonite mixture. The developed models account for heat transport, multiphase flow and mechanical effects from swelling and thermal expansion. Model calibration was achieved by first determining the most sensitive parameters for heat and multiphase flow effects. A good fit between experimental data and model results was achieved for temperature, relative humidity, water intake and swelling pressure measurements. It is found that a unique set of thermal parameters for the insulation materials of the two experiments can be identified, which allows for a reliable estimate of the heat balance of the experiments. The most important parameters identified are the intrinsic and relative permeability, the water retention curve and the saturation dependent thermal conductivity of the buffer materials. It is further shown that the transient saturation state of the buffer material strongly influences its hydraulic and thermal behavior. The buffer material behavior thus identified contributes to the evaluation of larger scale in-situ experiments, and to better design deep geological repositories.

Modeling early in situ wetting of a compacted bentonite buffer installed in low permeable crystalline bedrock

AbstractThe repository concept for geological disposal of spent nuclear fuel in Sweden and Finland is planned to be constructed in sparsely fractured crystalline bedrock and with an engineered bentonite buffer to embed the waste canisters. An important stage in such a deep repository is the postclosure phase following the deposition and the backfilling operations when the initially unsaturated buffer material gets hydrated by the groundwater delivered by the natural bedrock. We use numerical simulations to interpret observations on buffer wetting gathered during an in situ campaign, the Bentonite Rock Interaction Experiment, in which unsaturated bentonite columns were introduced into deposition holes in the floor of a 417 m deep tunnel at the Äspö Hard Rock Laboratory in Sweden. Our objectives are to assess the performance of state‐of‐the‐art flow models in reproducing the buffer wetting process and to investigate to which extent dependable predictions of buffer wetting times and saturation patterns can be made based on information collected prior to buffer insertion. This would be important for preventing insertion into unsuitable bedrock environments. Field data and modeling results indicate the development of a de‐saturated zone in the rock and show that in most cases, the presence or absence of fractures and flow heterogeneity are more important factors for correct wetting predictions than the total inflow. For instance, for an equal open‐hole inflow value, homogeneous inflow yields much more rapid buffer wetting than cases where fractures are represented explicitly thus creating heterogeneous inflow distributions.

Corrosion at the carbon steel⿿clay borehole water and gas interfaces at 85 °C under anoxic and transient acidic conditions

In order to understand the corrosion processes of low-alloyed carbon steel (C-steel) materials in contact with porewater and/or gas in clay environments under reducing conditions at 85°C, an in situ experiment called ⿿MCO-Gravimetry⿿ has been carried out in the Meuse/Haute⿿Marne Underground Research Laboratory (Bure, France). In a test chamber drilled in clay rock, samples of C-steel were exposed either to ⿿clay porewater⿿ (actually a liquid phase initially made of synthetic clay porewater gradually replaced by water seepage) or to an atmosphere of gases released by the host rock and by corrosion processes. Samples series were removed from the test chamber at given times (between 3 and 30 months), and the metal loss and corrosion rate (r) were quantified by gravimetric measurements. Characterisations of certain coupons were performed by using micro-Raman and X-Ray Diffraction analyses. Chemical and microbial analyses of the water seepage were also performed.Gravimetric measurements showed that r was lower in the gas phase (about 5μm/yr) than in the liquid phase (up to 200μm/yr). Two trends were observed in the liquid phase, one with an active behaviour (high r of about 200μm/yr) and one with a passive behaviour (low r <30μm/yr). The high r could be explained by the presence of an acidic pH transient that occurred 100days after the experiment had started and lasted for 200days. The rods with very low r may have been shielded in the setup, which could explain the comparatively limited damage, even under acidic conditions. Corrosion products (CPs) characterisation mainly showed the presence of siderite. In addition, Fe hydroxychloride was detected at the metal/corrosion product interface on coupons with high r. Finally, results from microbial analysis revealed the presence of sulphate- and thiosulphate-reducing bacteria (SRB and ThRB) in both media. The SRB/ThRB metabolism may explain the presence of sulphide in the CPs.Overall, this study highlights the potential risk of an acidic pH transient that would promote high corrosion rates for the C-steel structural barriers in a high-level nuclear waste repository. Therefore, HLW French repository concept has been modified by adding a cement-bentonite based grout between the host rock and casing. This is expected to neutralise the potential acidity and bring the C-steel surface to the passivity domain.

The effect of organic retarders on grout thickening and setting during deep borehole disposal of high-level radioactive waste

Deep borehole disposal (DBD) is being increasingly seen as a viable and potentially superior alternative to comparatively shallow mined repository concepts for disposal of some high-level radioactive wastes. We report here details of proof-of-concept investigations into the use of cementitious grouts as sealing/support matrices for use in low temperature DBD scenarios. Using the cementitious grout to fill annular space within the disposal zone will not only support waste packages during placement, but will also provide a low permeability layer around them which will ultimately enhance the safety case for DBD. Grouts based on Class G oil well cement are being developed. The use of retarders to delay the accelerated onset of thickening and setting (caused by the high temperature and pressure in the borehole) is being investigated experimentally. Sodium gluconate and a polycarboxylate additive each provide sufficient retardation over the range 90–140 °C in order to be considered for this application. Phosphonate and sulphonate additives provide desirable retardation at 90 °C. The additives did not affect grout composition at 14 days curing and the phases formed are durable at elevated temperature and pressure.

Trusted by whom? TDRs, standards culture and the nature of trust

The first part of this paper examines the notion of trust within the suite of standards that anchor the trustworthy digital repository (TDR) concept. The second part traces the short and confusing trajectory of the TDR project at Library and Archives Canada (LAC) and explores the extent to which the failure of LAC TDR should be understood in relation to organizational funding, operational decisions, TDR standards culture or other factors. In the conclusion I suggest that the notion of trust within TDR standards culture is itself evolving in a positive direction that emphasizes user perceptions of trust rather than seeking to establish objective evidence of trust.