No abstract available

[en] Addressing the issues of reversibility and safety of radioactive waste disposal in geological formation, and the interaction between reversibility and safety, this contribution discusses how uncertainties and risks are managed within the frame of a safety approach when safety relies on site and parcel characteristics and on design and organisation measures. Besides design and technological choices, various monitoring actions are planned, as well as means to limit impacts on workers and to intervene during exploitation if necessary. Reversibility and safety are also taken into account in immediate protection and safety requirements, and in the protection of future generations and of their environment

[en] In recent years, it has become more and more evident that repository development will involve a number of stages punctuated by interdependent decisions on whether and how to move to the next stage. These decisions require a clear and traceable presentation of technical arguments that will help in giving confidence in the feasibility and safety of the proposed concept. The depth of understanding and technical information available to support decisions will vary from step to step. A safety case is a key item to support the decision to move to the next stage in repository development. Progress is noted, in the past decade, in the performance and safety assessment areas, particularly in the methodologies for repository system analysis. Progress is also observed regarding the understanding of the natural system and its characterisation, treatment of uncertainties, and modelling. Some areas are under active development, e.g. the area of scenario development and analysis. Finally, to increase confidence, rigorous quality assurance procedures need to be implemented, as well as the factoring of the contribution of R and D in underground research laboratories. The paper summarises the lessons learnt within relevant NEA initiatives as they evolved over the course of a decade and now allow a comprehensive view of what constitutes a safety case. (author)

[en] Most countries producing nuclear energy are considering, or actively pursuing, a deep geologic repository for radioactive waste. As part of the assessment of the performance or safety of such a repository, radionuclide transport through the heterogeneous, geologic environment must be modelled. In most cases, an important migration mechanism is transport in groundwater and developing an understanding and modelling capability for how radionuclides might migrate away from the repository through the surrounding geosphere is an integral part of making the safety case for a repository. This understanding has been significantly improved through the NEA GEOTRAP Project, the results of which have been documented in a final synthesis report summarizing the outcomes of the five GEOTRAP workshops held between 1996 and 2001

[en] The French National Radioactive Waste Management Agency, or ANDRA, has, among its roles in management of radioactive waste, to ensure the protection of man and the environment from all radioactive waste generated in France. In order to verify compliance to the safety objectives, radiological and chemical impact evaluations are to be assessed. The objective of the paper is to present the overall approach for assessing the post-closure safety of French nuclear waste disposals in particular on the Geological Disposal. (authors)

[en] In France, low- and intermediate-level radioactive wastes are disposed in a near-surface facility, at Centre de l'Aube disposal facility. This facility, which was commissioned in 1992, has a disposal capacity of one million cubic meters, and will be operated up to about 2050. It took over the job from Centre de la Manche, which was commissioned in 1969 and shut down in 1994, after having received about 520,000 cubic meters of wastes. The Centre de l'Aube disposal facility is designed to receive a many types of waste produced by nuclear power plants, reprocessing, decommissioning, as well as by the industry, hospitals and armed forces. The limitation of radioactive transfer to man and the limitation of personnel exposure in all situations considered plausible require limiting the total activity of the waste disposed in the facility as well as the activity of each package. The paper presents how ANDRA has derived the activity-related acceptance criteria, based on the safety analysis. In the French methodology, activity is considered as end-point for deriving the concentration limits per package, whereas it is the starting point for deriving the total activity limits. For the concentration limits (called here LMA) the approach consists of five steps: the determination of radionuclides important for safety with regards to operational and long-term safety, the use of relevant safety scenarios as a tool to derive quantitative limits, the setting of dose constraint per situation associated with scenarios, the setting of contribution factor per radionuclide, and the calculation of concentration activity limits. An exhaustive survey has been performed and has shown that the totality of waste packages which should be delivered by waste generators are acceptable in terms of activity limits in the Centre de l'Aube. Examples of concentration activity limits derived from this methodology are presented. Furthermore those limits have been accepted by the French regulatory body and constitute a key point of ANDRA waste acceptance criteria. (author)

[en] Clear international evolution from performance and safety assessments (dose and risk) to safety cases - a collection of arguments in support of the long term safety of a repository - better exploitation and presentation of the full range of arguments (quantitative and qualitative) - serving different audiences - predictions versus illustrations (bounding assessments) - multiple function system - Regulations are reflecting this evolution - further guidance needed - weighting of indicators and arguments in different time frames

[en] The December 30, 1991 French Waste Act entrusted ANDRA, the French national agency for radioactive waste management, with the task of assessing the feasibility of deep geological disposal of high- and medium-level long-lived waste (HLW and ILW, respectively C-waste and B-waste types in French) plus spent fuel (CU in French). In that context, the 'Dossier 2005 Argile' submitted by ANDRA presents the feasibility assessment - with regard to the technical capacity to accommodate all wastes, to reversibility, and to safety - of a radioactive waste disposal in a clay formation studied at the Meuse/Haute-Marne URL. This report was built upon an iterative approach between site characterisation, design, modelling, phenomenological analysis and safety analysis, in which two principles always guided the elaboration of the safety case: the principle of robustness - repository components must maintain their functionality given reasonable solicitations, taking into account uncertainties on the nature and level of these solicitations; and the principle of demonstrability - safety must be verified without requiring complex demonstrations, and based on multiple lines of evidence/argument (numerical simulation, qualitative arguments such as use of natural analogues, experiments and technological demonstrators). In that respect, the EBS definition, demonstration and confirmation of design is a part of the overall safety case. The 'Dossier 2005 Argile' was submitted to three independent peer reviews. The aim. of this article is to present the methodology that ANDRA implemented in the context of 'Dossier 2005 Argile' for defining, demonstrating and confirming the EBS design as well as the future programme with respect with the new Act of 28 June 2006. (author)

[en] The analysis conducted within the Dossier 2005 exercise (ANDRA 2005b) shows that in all envisioned situations (normal or altered) through complementary indicators, the repository and surrounding host rock fulfill the three major safety functions, without relying excessively on any single component no elements that jeopardize the technical feasibility. In any event, the Callovo- Oxfordian host rock plays a major role in immobilizing radionuclides and in delaying and reducing their migration to the environment. In all scenarios even accidental or altered the repository performance provides significant margins to the dose objective recommended by the RFS III.2.f. In conclusion, Dossier 2005 Argile supports, with both qualitative and quantitative arguments as results from a robust methodology and a multidisciplinary iterative process, the feasibility of a reversible and safe repository in Meuse-Haute-Marne Callovo-Oxfordian clay. Some key design features and orientations have been developed to meet safety requirements. The various reviews of the ANDRA Dossier Argile that was published in 2005 and the existing design experience has helped to identify the key areas needing further development and design evolution in order to apply for a license to build a repository in 2015 according to the new French Act of 2006. (A.L.B.)

[en] Andra is currently in the license application process for a deep geological disposal facility for high level waste (HLW) and intermediate level waste (ILW) in a clay formation, the Callovo-Oxfordian, in the eastern part of France. This process started in 2011 by the development of an industrial design phase that consists of a proposed overall underground architecture for the repository and the definition of the operating principles, and the name given to the project was defined: the “Centre industriel de stockage en milieu géologique” (Cigéo, Industrial Center for Geological Disposal). The files and in particular the safety case that will support the license application result from a continuous increase in knowledge, project development, and associated safety assessment for several decades. Since the French Act in 1991 on the long term plan for the management of ILW and HLW in France, Andra is running a comprehensive research project including a broad combination of laboratory research, surface and drilling based site investigations, research in the Bure URL and model development. The preparation of the license application is thus the result of a stepwise accumulation of knowledge and iterative process including several safety cases as well as their regulatory review. The safety case development plays a key role in supporting the development of the technical solutions to manage HLW and ILW. It is based on successive “knowledge/design /safety” iterations. Each iteration involves scientific and technological knowledge acquisition, study of the layout designs consistent with this knowledge and safety assessment. Each safety case is associated with key milestones (reliability, siting, underground research, industrial design development, safety options, licensing) based on the “knowledge/design /safety” iteration providing lessons learnt. The successive iterations gradually help to guide the choice toward design solutions, R&D programmes, and safety studies. Andra collects and documents knowledge R&D data and analyses residual uncertainties in the knowledge. (author)