[en] This document summarizes the discussions of the two working groups: decision making in the engineered barrier systems design process; confirmation and demonstration of the EBS in the context of confidence building. It provides also the workshop conclusions and recommendations. (A.L.B.)

[en] The 12-15 September 2006, at Tokyo, took place the fourth workshop on engineered barrier systems (EBS) in the safety case: design confirmation and demonstration. The barriers include the natural geological barrier and the engineered barrier systems. The workshop focused on strategies and methods to demonstrate that EBS designs will fulfill the relevant requirements for long-term safety, engineering feasibility and quality assurance. This document presents successively the eight invited presentations and the main focusing points of the corresponding discussions around the presentation. (A.L.B.)

[en] This paper discusses the evolution of the design of the potential repository at Yucca Mountain, Nevada, USA, in light of the various postclosure performance assessments conducted to prepare for regulatory reviews of a potential license application. The regulations require that any proposed repository design must meet both long-term performance and operational safety requirements. This paper surveys the evolution of the design of the potential Yucca Mountain repository, especially the engineered barrier system, and discusses the related performance assessments conducted by DOE in support of repository development and NRC in support of developing its capability to review a license application. The survey indicates that DOE design changes correlate well with release or dose-based performance criteria during the earlier part of design evolution. During the latter part, DOE design changes focused more on waste isolation and uncertainty reduction (strengthening the technical base ). NRC regulations recognize that the design may continue to evolve and performance confirmation information will continue to be collected until repository closure. (authors)

[en] The presence of several barriers serving complementary safety functions enhances confidence that radioactive waste placed in deep geological repositories will be adequately isolated and contained to protect human health and the environment. The barriers include the natural geological barrier and the engineered barrier system (EBS). The EBS itself may comprise a variety of sub-systems or components, such as the waste form, container, buffer, backfill, seals and plugs. Given the importance of this subject, the Integration Group for the Safety Case (IGSC) of the OECD Nuclear Energy Agency (NEA) sponsored a series of workshops with the European Commission to develop greater understanding of how to achieve the necessary integration for the successful design, testing, modelling and performance assessment of EBS for deep underground disposal of radioactive waste. These proceedings present the main findings from, and the papers delivered at, the fourth NEA-EC workshop on EBS, which took place in Tokyo, Japan, in September 2006. This final workshop of the series focused on strategies and methods to demonstrate that EBS designs will fulfill the relevant requirements for long-term safety, engineering feasibility and quality assurance. The workshop highlighted that large-scale experiments have confirmed the feasibility of techniques for manufacturing and installing engineered components in disposal systems and have also provided valuable lessons to improve designs and refine practical aspects to construct and implement EBS. (author)

[en] The Swedish Nuclear Fuel and Waste Management Company (SKB) is moving forward with plans for the disposal of spent nuclear fuel. SKB is planning to submit license applications for construction of an encapsulation plant in late 2006 and for construction of an underground waste repository for spent nuclear fuel in 2009. The latter will be based on results from currently ongoing site investigations at two sites in Sweden (Forsmark and Laxemar). SKB's concept for the disposal of spent nuclear fuel is known as KBS-3. According to the KBS-3 concept, SKB plans that after 30 to 40 years of interim storage, spent fuel will be placed in copper canisters and that these will be disposed of at a depth of about 500 m in crystalline bedrock. In the KBS-3 concept, the principal engineered barriers comprise an iron insert that will hold and support the spent fuel rods, a copper canister that will encapsulate the fuel and the insert, a layer of bentonite clay known as the buffer that will surround the canister, and a mixture of bentonite and crushed rock that will be used to backfill the waste deposition tunnels. As part of its programme, SKB has conducted a wide range of tests on engineered barriers within its underground laboratory at Aspo. (authors)

[en] SKB has been conducting research in the area of nuclear waste disposal in underground environment since the early 1980's. The early tests were conducted in the Stripa mine and in the late 1990's the first full scale tests of EBS installations were carried out in Aspo HRL that was built for the purpose of performing repository research and EBS development. This article focuses on lessons learned concerning the practical aspect of the EBS installation procedures. Specific practical issues as well as how the gained knowledge can be used in the continued. EBS design and optimisation are addressed. The article focuses on the workshop topic 'Confirmation of industrial scale feasibility emplacement of EBS components' but also addresses the topics: - demonstrations of compliance with specifications for emplaced EBS components; - demonstrations/examples of the EBS optimisation process; - identification of remaining key issues and uncertainties to be addressed in the next design optimisation cycle in relation to the scope of the envisaged safety case; - need for (re)assessment of repository and EBS design at later stages of development. (author)

[en] Repository site selection in the Japanese HLW disposal programme is based on a volunteering approach, which places special constraints on the process of developing repository designs. In particular, a high degree of flexibility is needed in order to respond to conditions in the specific geological environments in the communities that may come forward. In order to meet this challenge, NUMO has developed a structured process for tailoring repository concepts to siting environments, which considers many options for each design components and assesses them with regard to a number of design goals, long-term safety, operational safety, engineering feasibility, etc. Various associated design demonstration activities have been carried out by R and D organisations. such as JAEA and RWMC, to support the NUMO structured approach. Such activities are presently focused on engineering feasibility and the long-term safety of a range of repository design options. The preliminary results from such demonstration tests have useful feedback for further design improvements. This suggests that optimisation of repository design can be achieved by world rig systematically through an iterative process of design and assessment followed by re-evaluation and design refinement. (authors)

[en] In the context of the technological project ESDRED: 'Engineering Studies and Demonstration of Repository Designs', the national waste management agencies ANDRA, ONDRAF/NINAS and NAGRA are currently in the process of demonstration testing the construction of the buffer/backfill component inside the disposal drifts for high level waste (HLW). ESDRED is co-funded by the European Commission (EC) as part of the sixth Euratom research and training Framework Programme (FP6) on nuclear energy (2002-2006). The work aims to demonstrate the technical feasibility at an industrial scale of the construction of the buffer around the disposal package and/or the associated activity of backfilling the remaining voids within the disposal drift. The tests described in this paper are performed in a workshop on the surface, which will enable a better control over the test conditions and facilitate the evaluation of the test results. The following configurations are being tested: - a prefabricated buffer in a horizontal disposal cell (representative of the ANDRA design); - granular and grout backfills in a horizontal disposal drift (representative of the ONDRAF/NIRAS design); - a combination of a prefabricated and a granular buffer in a horizontal disposal drift (representative of the NAGRA design). After the preceding stages of defining the functional requirements of the buffer/backfill component, computer simulation, laboratory testing and designing the buffer prototypes or disposal drift mockups, the work is currently focused on the execution phase of the demonstration testing. The work, although conducted by the agencies in parallel, is characterised by frequent mutual status reporting and exchange of 'lessons-learned' within the context of ESDRED. The work on the in-workshop demonstrators is scheduled to be finalized by the end of 2006. (authors)

[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] In the former German Democratic Republic the abandoned salt mine of Bartensleben was selected to serve as a repository for low and intermediate level (LLW, ILW) radioactive waste. Located near the village of Morsleben in the Federal State of Saxony-Anhalt, this mine was named 'Repository for Radioactive Waste Morsleben (ERAM)'. The decision to establish the repository was based on safety and technical-economic studies performed in the 1960's. It was designed, constructed and commissioned between 1972 and 1978. Following several studies and the successful demonstration of the disposal technologies used, a first operational licence was granted in 1981. The licence did not cover repository closure. After the German reunification (October 3, 1990) the Federal Government of Germany took over the responsibility for the repository. The Federal Office for Radiation Protection (Bundesamt fur Strahlenschutz, BfS) acts on behalf of the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU), which represents the German Federal Government. DBE then became operator of the repository on behalf of the BfS. The final disposal of waste was stopped in 1998. In accordance with the German Atomic Energy Act (AtG) a licence application for repository closure is being prepared by the BfS. In this context, BfS concluded contracts concerning the backfilling and closure of the Morsleben repository, which is presently being planned. According to the closure concept 21 drift seals have to be constructed. Situated in the access drifts to the disposal areas these drift seals are important components of the multi barrier system. To guarantee compatibility of all closure measures planned, salt-concrete is the preferred construction material for the seals. The conceptual design of the ERAM drift seals was presented at the Oxford workshop, the optimisation process of drift seal design within a rock salt environment was described at the Turku workshop. The alteration of salt concrete and the related process model applied to the ERAM drift seals were presented in the Las Vegas, and the treatment of the drift seal performance within the safety assessment was described in the La Coruna workshops, respectively. This paper focuses on the proof of structural reliability, the confirmation of producibility, demonstration of compliance with specifications for emplaced drift seals, and methods for demonstrating that design requirements have been met in a regulatory environment. The relevant design criteria used to prove structural reliability determine the type and general set-up of the experiments. (authors)