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Baden, Switzerland

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Baden, Switzerland

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Zhang K.,Lawrence Berkeley National Laboratory | Zhang K.,Beijing Normal University | Croise J.,AF - Colenco Ltd | Mayer G.,AF - Colenco Ltd
Nuclear Technology | Year: 2011

Significant quantities of hydrogen can be produced by the corrosion of metal components. It is necessary to forecast gas migration and pressure buildup in the context of deep geological radioactive waste disposal. One of the major problems in representing gas migration in a radioactive waste repository is that of simultaneously modeling all gas sources and complex transfer pathways constituted by the network of underground drifts and the surrounding low-permeability rock. In 2006, the French National Agency for Radioactive Waste Management launched an international multiphase flow simulation benchmark exercise for modeling such a two-phase (gas and liquid) flow system. The exercise was designed to compare the performance of the numerical methods being used to resolve the designed problems. This paper presents the results of test case 2 of the exercise completed by the authors. The three-dimensional model represents a fraction of a repository for long-lived radioactive waste in a clay rock. The model simulates ambient pressure and flow conditions (considering influence of site evacuation on the flow system) after placement of wastes, with full consideration of two-phase initial and boundary conditions. Isothermal conditions are assumed. Time-dependent gas sources are applied to the model. Since the natural environment is unable to evacuate the entire amount of hydrogen in a dissolved state, a free gas phase is formed within the disposal structures. The model is used to study the dissipation of those gases to determine their influence on the transient phases throughout the lifetime of the repository, and to investigate possible pressure buildup, which may introduce a risk of damage to the host rock. We use the model to investigate how the presence of gas in the repository influences the nature of water flow around the disposal structures and the resaturation (process of saturation increasing) transient processes after closure of the repository. The TOUGH2-MP code, a parallel multiphase flow simulator, has been adopted for this study.


Poller A.,National Cooperative for the Disposal of Radioactive Waste | Enssle C.P.,AF - Colenco Ltd | Mayer G.,AF - Colenco Ltd | Croise J.,AF - Colenco Ltd | Wendling J.,Andra Inc
Transport in Porous Media | Year: 2011

The current design of a deep geological repository for high- and intermediate-level radioactive waste in France consists of a complex system of different underground structures (ANDRA, Dossier 2005 Argile, les recherches de l'Andra sur le stockage géologique des déchets radioactifs à haute activité et à vie longue, collection les Rapports. Châtenay-Malabry, France, 2005). For a comprehensive understanding of the long-term hydraulic evolution of the entire repository, numerical non-isothermal two-phase flow and transport simulation, taking into consideration the generation, accumulation, and release of hydrogen gas and decay heat, are compulsory. However, a detailed numerical model of the entire repository system would require a tremendous computational effort and pose a laborious task with respect to the operation of the model. To handle these difficulties, we have developed an efficient method for the numerical modeling of a complete repository system and its geologic environment. The method consists of the following steps: (i) subdivision of the repository plane into a large number of "sectors" based on the position of hydraulic seals and on other geometrical considerations, (ii) exploitation of existing symmetries (inside or between sectors), (iii) adoption of the "multiplying concept", and (iv) connection of the individual sectors at the drift interfaces to form the entire repository model. Each sector is modeled as a three-dimensional (3D) block, and the entire model is computed with TOUGH2-MP. The method allows for a massive reduction in overall finite-volume elements and, at the same time, provides an adequate representation of the small-sized structures in the repository. The main characteristics of the method and its application to an entire deep geological repository system in a clay host rock are presented. © 2011 Springer Science+Business Media B.V.


Croise J.,AF - Colenco Ltd | Mayer G.,AF - Colenco Ltd | Talandier J.,Chatenay Malabry | Wendling J.,Chatenay Malabry
Transport in Porous Media | Year: 2011

The corrosion of metals contained in intermediate-level long-lived waste (ILW) under reduced chemical condition will lead to the production of hydrogen gas during the post-closure phase of a deep geological repository for radioactive waste. According to previous investigations by Talandier et al. (Proceedings of TOUGH symposium 2006, Berkeley, 2006), the period of concern covers several 1,000 years after closure of a repository in a clay host rock (Callovo-Oxfordian). The limited hydrogen transport efficiency of the host rock will lead to significant saturation of the concrete waste canister pore space and voids with a gas phase and pressure build-up within the emplacement drifts. On the other hand, the water availability is limited as a result of (i) the low permeability of the clay host rock and (ii) the desaturation of the rock mass close to the drift wall due to the ventilation of the drifts during the operational phase of the repository. In former numerical simulations it was assumed that under the reducing chemical conditions prevailing in the repository, the corrosion rate would be a function of the available metal surface and the temperature only. In this paper, simulation results based on new phenomenological functions are presented, which were implemented in TOUGH2. These allow taking into account (i) a water saturation dependency of the hydrogen generation rate, (ii) the water consumption due to the corrosion process, and (iii) the total metal mass available for corrosion. The paper presents results of 1D radial and 2D vertical simulations of a typical cross-section of a waste emplacement drift and the surrounding rock mass. The interactions between water availability from the low permeable clay, the dependency of the hydrogen generation rates from the water saturation of the waste package and the hydrogen migration in the host rock are demonstrated. © 2011 Springer Science+Business Media B.V.


Buchli U.M.,SMEC International Pty Ltd | The Hung D.,PECC1 Joint Stock Company | Dredge A.,AF - Colenco Ltd | Morris D.,AF - Colenco Ltd | And 2 more authors.
International Journal on Hydropower and Dams | Year: 2010

The RCC dam for the Son La hydro project requires slightly more than 3 × 106 m3 of RCC, out of a total of 5 × 10 6 m3 of concrete for the whole project. The RCC was placed in a number of stages to allow various other parts of the project, to be started in accordance with the overall programme. In addition there was a gap in the placement to allow for large flows to pass over part of the dam. This paper describes the stages of construction and the construction methodology which it is expected to enable the RCC to be completed four months ahead of schedule.


Myint Zaw U.,Ministry of Electrical Power MOEP | Thaung Han U.,Ministry of Electrical Power MOEP | Rohrer Ch.,AF - Colenco Ltd | Steiger K.M.,AF - Colenco Ltd
Dams and Reservoirs under Changing Challenges - Proceedings of the International Symposium on Dams and Reservoirs under Changing Challenges - 79 Annual Meeting of ICOLD, Swiss Committee on Dams | Year: 2011

The paper gives an overview of the Upper Paunglaung project layout and the current situation of the construction and describes how the dam design was adapted for a rapid dam construction. It also describe the challenges of flood protection during construction, the unfortunate weather condition during the wet season, the challenging access to the site for transportation of the construction materials, as well as the initial stages of the RCC mix design and the performance of the RCC full Scale trial embankment in May 2010. © 2011 Taylor & Francis Group.


Baechler S.,AF - Colenco Ltd | Lavanchy J.M.,AF - Colenco Ltd | Armand G.,Andra Inc | Cruchaudet M.,Andra Inc
Physics and Chemistry of the Earth | Year: 2011

In order to investigate potential changes of the hydraulic properties of the EDZ over time in the Meuse/Haute-Marne underground research laboratory (URL), several hydraulic tests campaigns have been carried out between 2005 and 2008 in dedicated boreholes. After several test series, inconsistencies were noticed in the results, indicating, in particular cases, erratic, inexplicable property changes over time and spatial contrasts. It was therefore difficult to determine reliably potential trends of the EDZ hydraulic properties. It appeared necessary to re-evaluate both the interpretation concepts and assumptions applied to the numerical analyses of test data on the EDZ, trying to better constrain the flow model and the parameter variables. In order to improve the understanding of the geometrical, geomechanical and hydraulic properties of the EDZ, independent information from other investigation methods has been used to critically revise the conceptual model and formation parameters. In particular, results from a diffusion experiment and ultrasonic measurements allowed constraining the extent of the mechanical damaged zone around the borehole (BDZ). Storativity parameters were fitted due to their expected variability. Indeed, high storativity values can be presumed under the unsaturated conditions of the EDZ. The results of the reanalyses, performed with the numerical borehole simulator MULTISIM, demonstrated the good quality and consistency of the revised conceptual model with constrained BDZ and variable storativity. Overall the new simulation results obtained from selected test series are now very consistent. The revised conceptual model demonstrated its capacity to better represent the evolution and extension of the EDZ around a drift in Meuse/Haute-Marne URL. Further consistency checks are proposed to confirm the new model assumptions and the estimates of the single phase flow model in the EDZ. © 2011 Elsevier Ltd.


Enssle C.P.,AF - Colenco Ltd | Cruchaudet M.,Andra Inc | Croise J.,AF - Colenco Ltd | Brommundt J.,AF - Colenco Ltd
Physics and Chemistry of the Earth | Year: 2011

Andra is continuously investigating the Callovo-Oxfordian clay unit as a potential host rock for the deep disposal of long-lived medium and high-level radioactive waste at the Meuse/Haute-Marne underground research laboratory. A large number of hydraulic measurements have been performed in instrumented boreholes. In particular, hydraulic tests have been conducted for the determination of the average hydraulic conductivity and the formation pressure at the decimetre scale. Furthermore, the evolution of porewater pressure was measured for more than four years in test intervals at distances from a few decimetres to 20. m from the drift floor located at 492. m below ground level. These measurements, reflecting in particular the drainage and suction effect induced by the ventilated drift, present a unique set of data for the determination of the permeability of the Callovo-Oxfordian clay at the metre to decametre scale. The pressure data measured since the end of 2005 in four intervals of borehole PEP1001 were analysed by numerical modelling. Two different 2D models (vertical and axial-symmetric) were used considering also the rock desaturation and depressurisation processes due to the climatic conditions in the drift. The suction - related to the relative humidity of the ventilation air - was taken into account according to Kelvin's equation. Other transient effects, e.g. due to the seasonal temperature variation in the drift were also investigated. Eventually, sensitivity analyses to the key hydraulic parameters were performed. The best fit yielded a horizontal hydraulic conductivity of 7×10-13m/s and a vertical hydraulic conductivity of 4×10-13m/s in the Callovo-Oxfordian clay. The seasonal variation of the climatic conditions in the drift showed only little influence on the general pressure evolution and hence on the determination of the hydraulic conductivity. Further, the model results suggest that the measured pressure evolution in each interval of borehole PEP1001 is superimposed by local effects such as the thermal compressibility of the water in the steel lines, accounting for the seasonal pressure oscillations, and a possible borehole disturbance zone (BdZ) accounting for the relatively high pressure gradient directed towards the drift. © 2011 Elsevier Ltd.


Enssle C.P.,AF - Colenco Ltd | Croise J.,AF - Colenco Ltd | Poller A.,AF - Colenco Ltd | Mayer G.,AF - Colenco Ltd | Wendling J.,Andra Inc
Physics and Chemistry of the Earth | Year: 2011

An important question related to the long-term safety performance of a repository for long-lived medium and high-level radioactive waste in the Callovo-Oxfordian clay unit is the impact of heat and gas generated in the waste emplacement areas on the gas and water pressure and on the water saturation in the backfilled repository and in the host rock. The current design of such a repository consists of a multitude of different underground structures, such as emplacement drifts for waste canisters and other types of waste packages, access and ventilation drifts, and access shafts in the central part of the repository. The individual underground structures exhibit different thermo-hydraulic and geometrical properties yielding a large and complex system for the flow and transport of gas, water and heat. A detailed 3D modelling of the entire repository would require a tremendous computational effort, even when using high performance simulator codes. A newly developed method (Poller et al., 2011) allows for the 3D modelling of the two-phase gas-water flow and thermal evolution in the entire repository/host-rock system in a simplified manner. Besides accounting for both the detailed structures at local scale and the global geometry of the drift network, it also allows for an assessment of the gas phase pressure as well as the hydrogen and heat fluxes developing over the complete lifetime of the repository system. In this paper, the results of a reference scenario are presented. The assessment focuses on the two dominant processes, i.e. the dissolution. and. diffusion of the generated hydrogen, and the advective migration of the forming hydrogen gas phase in space and time (up to 1. million years). Further, the main findings of a sensitivity analysis on different features, physical processes and parameter uncertainty are presented. © 2011 Elsevier Ltd.


Poppei J.,AF - Colenco Ltd | Mayer G.,AF - Colenco Ltd | Hubschwerlen N.,AF - Colenco Ltd | Pepin G.,Andra Inc | Wendling J.,Andra Inc
Nuclear Technology | Year: 2011

The calculation of relative humidity in tunnels is a fundamental task when designing a repository ventilation system in a clay host rock. It requires complex numerical modeling of transient (forced) convective and conductive heat and fluid transport. The humidity of the tunnel air primarily depends (along with the meteorological conditions at the entrance) upon the thermal-hygric transitional conditions at the exposed rock surface of the tunnel walls. Some portions receive water influx while others receive heat influx from the waste already emplaced in other parts of the host rock. The coupling between the transport processes in the host rock and the transfer processes along the tunnel wall are treated in a simplified manner. The processes described by coefficients for heat (Nusselt number) and vapor (Sherwood number) both depend on the ventilation velocity (Reynolds number). We discuss an approach involving supportive TOUGH2 computations for complex transport problems in the host rock. The results are processed and applied to the transient analysis of temperature and humidity changes in the ventilation air. Analysis of the evaporation along a tunnel wall is supported by a one-dimensional radially symmetric EOS9 model. Results from the TOUGH2 computations with different Sherwood numbers are parameterized accordingly. The prevailing humidity along the tunnel wall is then determined with an iterative approach, whereby the humidity is controlled by either the ventilation (i.e., through the Sherwood number) or the leakage capacity of the host rock. Finally, the humidity changes in the ventilation air are derived from the computed diffusion of vapor along the boundary layer. To calculate the heat transfer into the tunnel along its walls, we used the results from a complex geometric TOUGH2 model. The model considers different thermophysical parameters as well as the transient rates of heat production by the waste. At any given time, the heat transfer along the tunnel wall-with consideration of the then-prevailing heat production and ventilation velocity-causes a rise in air temperature and a corresponding decrease in relative humidity.


The article describes experiences made from a number of full scale trial tests conducted for current large RCC dams in Southeast Asia. The focus is on the Son La Hydropower Project in Vietnam with its 138 m high RCC gravity dam. The first RCC for the dam has been placed in January 2008, 1 Mio.m 3 RCC have been placed after only eight months. The processes tested within the full scale trials and which have contributed to the considerable placement rates and related good RCC quality are further described in the article.

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