[en] A cornerstone of national decision making and societal acceptance of deep geological disposal of radioactive waste is confidence that such repositories can protect humans and the environment both now and in the future. The safety case is the synthesis of evidence, analyses and arguments that quantify and substantiate a claim that the repository will be safe after closure and beyond the time when active control of the facility is ensured. For deep geological disposal, studies of the geosphere form a principal component of the safety case. Geo-scientific information is unique in that it can offer evidence and lines of reasoning that span geological timescales (millennia and even longer). The NEA Approaches and Methods for Integrating Geological Information in the Safety Case (AMIGO) project addresses the collection and integration of geo- scientific evidence, analyses and arguments that contribute to an understanding of long-term safety. The third and final AMIGO workshop on Approaches and Challenges for the Use of Geological Information in the Safety Case underscored that geo-scientific information plays a fundamental role in safety assessments. It is also increasingly used in the wider context of the safety case to provide evidence and arguments for the intrinsically favourable properties of a site, including its long-term stability. No single geo-scientific argument proves safety, but rather each supports some key element of the safety case and provides enhanced confidence in the safety case. The workshop also considered the links and feedback among the safety case; design, engineering and construction issues; and geo-scientific investigations. (author)

[en] The Dossier on Disposal Feasibility Assessment in Meuse/Haute-Marne (Callovo-Oxfordian Clay layers), which was submitted by ANDRA to the French Government in June 2005, is the result of a long way from the Preliminary Geo-scientific Survey in 1994 to the Safety Case. An iterative approach was used, three iteration loops were organised between acquisition of knowledge, architecture and design, safety studies and analysis with milestones in 1996, 2001 and 2005. At each step, the acquired geo-scientific data was used to refine the disposal design and then was integrated to the safety case. During raw data acquisition and interpretation, each value and model were discussed and presented in technical reports with its uncertainties of all kind (e.g. ranges of porosity and permeability, uncertainties on head values, etc). From the raw geo-scientific data, a first integration work (putting together measurements, results of modelling, lines of arguments) provided conceptual and phenomenological models which were the basis for description of the evolution of the repository (Phenomenological analysis of repository situations, PARS). (authors)

[en] The Waste Isolation Pilot Plant (WIPP) is the U.S. Department of Energy (DOE) deep geologic repository for transuranic (TRU) and mixed waste. The repository was constructed 655 m below ground surface in bedded halite of the Permian Salado Formation in southeastern New Mexico (Figure 1). Site-characterisation activities began in 1974, and WIPP became a licensed, operating repository in March 1999. The Culebra Dolomite Member of the Rustler Formation (Figure 2) is the most transmissive fully saturated unit above the WIPP repository horizon and the most likely groundwater pathway for radionuclides released from the repository by potential inadvertent human intrusion. Consequently, the Culebra is the focus of groundwater monitoring at WIPP. On-going monitoring has shown that Culebra heads are rising and that they respond to discrete, present-day events, an apparent contradiction of the original conceptual model for the Culebra which envisaged steady-state, or slowly declining, heads. Accordingly, the WIPP regulator, the Environmental Protection Agency (EPA), has requested that the DOE undertake additional studies of the Culebra and develop a revised conceptual model consistent with recent observations. (author)

[en] Swiss Legislation requires for all types of radioactive waste the safe and permanent disposal in deep geological repositories within Switzerland by stipulating a step-by-step procedure for site selection and licensing of the disposal facilities. Each step requires safety considerations or safety analyses which are reviewed by the Swiss Federal Nuclear Safety Inspectorate. The principle steps of radioactive waste disposal include: (i) Demonstration of disposal feasibility for all types of radioactive waste in Switzerland. (ii) Site selection process in three phases to narrow down the number of suitable sites to one for realisation (Sectoral Plan for Geological Repositories). (iii) Construction, operation and closure of the repositories according to Swiss legislation in five steps (licence for geological investigations, general licence (decision-in-principle), construction licence, operation licence, closure order). Step (i) has been completed in 2006 when the Swiss Federal Council approved the demonstration of disposal feasibility for high level and long-lived intermediate level waste submitted by the implementer in 2002. Currently the Swiss waste disposal programme is starting the site selection procedure according to (ii). This paper describes the safety requirements, presents examples of regulatory reviews and elucidates its feedback to site investigation. (authors)

[en] The research work summarised in the Dossier 2005 Argile has provided detailed information on each of the repository components but also on the determination, the analysis and the assessment of the main phenomena which are occurring within the repository. Their detailed representation associated with proposed repository architectures allowed the processing of the data in order to assess the robustness of the repository and to see how it would meet safety requirements. Through various indicators, the analysis showed that the three main safety functions preventing water circulation, limiting radionuclides release and immobilizing them in the repository and delaying and attenuating radionuclide migration were effectively fulfilled by the proposed system in both normal and much more penalizing situations. The PARS as well as the QSA already facilitated a systematic identification of uncertainties, then allowing covering them either trough cautious hypothesis, penalizing or conservative representation of some phenomena or components, sensitivity studies or altered evolution scenarios. Subsequently, the safety analysis revealed some residual uncertainties and margins for potential progress which will provide useful orientations for future research developments. While the safety analysis conducted reveals that the repository appears to be robust in all the configurations envisaged with respect to its safety functions, both CNE and safety authority evaluations focus on the necessity to provide more comprehensive and realistic modelling of the behavior of the repository (both exploitation and post-closure periods) and of the radionuclides. For example, it is requested not to consider the perturbed zone (EDZ) as a dead zone the characteristics and properties of which are set to zero in terms of transport. Similarly, when ANDRA constructed its safety case, an envelope hypothesis for conducting calculations led to consider the repository as fully saturated as soon as its closure. It has been asked to ANDRA to present for the next dossier a phenomenological approach of the hydric transient taking into account the gas production and migration issues but also the potential consequences of reversibility. Those recommendations led to set up a scientific programme for the 2008-2012 period that aims at improving the representation of repository evolutions over time, extract the relevant parameters for monitoring during the reversibility phases, reduce the parametric uncertainties and enhance the robustness of models for performance calculations and safety analyses. (authors)

[en] In Sweden and Finland the spent nuclear fuel will be disposed of in a KBS-3 type repository in crystalline rock. Extensive surface based studies at Forsmark and Laxemar sites by SKB in Sweden and at the Olkiluoto site by Posiva Oy in Finland show that the bedrock in general will provide suitable and sufficiently stable conditions for a repository. Still, there are certain site specific features, e.g.: extensive deformation zones, volumes of relatively low mechanical strength in relation to the rock stress, sparse occurrence of highly transmissive fractures or very highly saline groundwaters that may affect the safety of the repository. The KBS-3 concept aims at long-term isolation and containment of the spent fuel assemblies in the copper canisters. Consequently, the safety functions of the host rock are a) to isolate the waste from the biosphere, b) provide favourable mechanical, geochemical and hydrogeological conditions for the engineered barrier system and c) to limit and retard inflow to repository and releases of harmful substances from the repository. This paper presents an approach, how to derive the criteria for selecting suitable canister positions from the general safety functions of the host rock. An intermediate step is definition of the safety function indicators and related criteria, which consider properties and conditions under which the barriers will fulfill the safety functions. Examples of the current status of the development work are given highlighting the different aspects of applying such criteria for design, safety assessment and practical testing in tunnel conditions. (authors)

[en] The main themes of the workshop, which include the topics covered both by the plenary sessions and Working Group sessions, can be stated as follows: Has geo-scientific information been effectively integrated and addressed in safety cases? To what extent (and how) does geo-scientific data influence the development of the safety concept, the repository design, and the safety case? To what extent (and how) does the development of the safety case influence R and D priorities and site investigation or other geoscience activities? The presented synthesis summarises the main points raised on these themes in the course of the workshop. (A.L.B.)

[en] A discrete-feature model was used to integrate deterministic and stochastic geo-scientific information, to support the Swedish regulatory authorities review of SR-Can. The discrete-feature approach was used to replicate the main geometric features of the proponents models of the two candidate sites, including: (1) deformation zones on scales of 1 km to 10 km which are treated deterministically, (2) deterministic rock domains, (3) discrete fractures on scales of 2 m to 1 km which are treated stochastically, (4) excavation-disturbed zones around repository tunnels, where the tunnels are adapted to the deformation zones, and (5) deposition holes which are adapted to each realisation of the stochastic fractures, to avoid fractures for which mappable characteristics would indicate unacceptable seismic or hydrologic risks. Application of this approach in the SR-Can review provided independent estimates of key safety parameters including utilisation factors (the percentage of usable deposition-hole positions in a given layout), distribution of groundwater flow to canisters, and retention properties and release points for discharge paths to the biosphere. These results were provided as input to a compartment model (AMBER) which was used for both deterministic and probabilistic risk calculations. Discrete-feature model variants were used to scope uncertainties in deformation-zone properties and boundary conditions, as well as the potential for enhanced transport due to spalling of deposition holes at one of the sites which has a strongly anisotropic stress field. This application showed that a discrete-feature model with realistic complexity can provide independent evaluation of key geo-scientific factors for safety, in the regulatory context. (authors)

[en] The dossier on disposal Feasibility Assessment in Meuse/Haute-Marne, which was submitted by ANDRA to the French Government in June 2005, is the result of a long way from the Preliminary Geo-scientific Survey in 1994 to the Safety Case. An iterative approach was used, three iteration loops were organised between acquisition of knowledge, architecture and design, safety studies and analysis with milestones in 1996 (URL licensing application), 2001 (intermediary report) and 2005 (Dossier 2005 feasibility assessment). At each step the acquired geo-scientific information was used to refine the disposal design and then was transferred to the safety case. Our knowledge has been more and more growing; up scaling and simplification processes have been more and more important issues in qualitative and quantitative safety analyses. (author)

[en] Site characterisation is a very complex, multidisciplinary process that may extend over many years and involve development of an optimised programme that balances the diverse and often contradictory requirements of the many specialists involved in this work. To make things even more difficult, the end users who use this input to steer repository implementation programmes the designers of waste disposal concepts and the assessors of their safety require processed data that may involve many steps of synthesis and integration before it is in a form that is applicable for their purposes. For the additional requirements of repository licensing, the entire process termed geo-synthesis in the paper should be transparent and fully documented. Indeed, in a perfect world, the methodology should be user-friendly and capable of providing feedback to set priorities in the field programme and provide guidance in the (likely) event of surprises occurring. As a step towards this goal, JAEA is developing a geo-synthesis methodology and testing its application with real data. The paper describes the geo-synthesis methodology and its applicability to site selection in Japan, which involve provisional safety case development to support key decisions. Using the JAEA database for the two URLs at Mizunami and Horonobe, the maturity of the existing technology will be illustrated and key challenges for future development discussed. (authors)