[en] The sixteenth meeting of the Integration Group for the Safety case (IGSC) included a topical session titled: Handling extreme geological events in safety cases during the post-closure phase. The session included nine presentations on the handling of such events by various national programs, questions and answers on each presentation and ended with a general discussion period. The present document summarises the outcome of the meeting. The document is structured as follows: - Section 2 describes the types of extreme geological events discussed in the session and how these are identified, - Section 3 discusses the measures that can be taken to avoid such events and to mitigate their impact on repositories, - Section 4 describes how the likelihood and consequences of events are assessed, - Section 5 address experiences regarding interactions with regulators and other stakeholders, - Section 6 covers remaining issues and planned R and D to address these, and - Section 7 presents a recommendation for possible future collaborative work on this topic

[en] The regulatory requirements in the United States do not require any specific time frame for the duration of permanent marker systems to inform future generations of the presence of deep geologic nuclear waste repositories. The requirement is for markers to be 'as permanent as practicable'. For the Waste Isolation Pilot Plant in New Mexico, the U.S. Department of Energy chose a 10,000 year Passive Institutional Controls program goal. Passive Institutional Controls are to be designed prior to facility closure and implemented prior to the completion of the Active Institutional Controls program. Nuclear waste repositories across the world are actively developing marker and message systems, as required by their own regulations, for time frames either specified in those regulations or to be proposed to the regulator by the implementing organization. Time frames may be based upon the radioactive characteristics of the various isotopes being disposed of in the repository under consideration, or they may be based on some utility function that balances investment, practicability and risk. Scientifically, there are a number of time frames that make sense. However, an important determinant of effectiveness that has not been taken into consideration is the impact of the human connection, the receiver of the message. The major obstacle that the permanent marker systems need to overcome is the impact that humans will have over time. Historically, no monument has ever survived more than a few thousand years when humans come in contact with it. No matter what size of monument or topic the monument represents, humans have a history of destroying monuments beginning just a few generations after the monument's construction. The only way to ensure that a monument system can endure long time frames is to isolate it from humans. Eliminating contact with humans for whom the messages are meant defeats the very purpose of having an informative marker and message system. A more reasonable and historically supported time frame of 1,000 years would assure that no unreasonable cost would be incurred by current generations. Future generations could decide to continue maintaining the message, or not; and the likelihood of destruction of the markers by subsequent generations would be reduced since the knowledge of the markers and messages would have been transmitted within a more reasonable time frame over which language continuity, for example, would likely be manageable. Future preservation of the marker system and future human actions cannot be controlled, but the goal is to build a marker and message delivery system that reduces the likelihood of inadvertent future human disturbance of a deep geologic repository. This is the typical regulatory requirement on future information systems. Regulators who insist on an extremely long time frame for marker effectiveness should consider the historical realities of 'permanent' markers and monuments and propose a more reasonable time frame. Perhaps it would be more practicable to require 1,000 years for informing future generations and then allow them to determine what they wish to do to protect the future for another, perhaps similar, period of time. (authors)

[en] Radioactive waste repositories are designed to be intrinsically safe in that they are not dependent on the presence or intervention of humans. In response to this challenge, the Nuclear Energy Agency initiated the Preservation of Records, Knowledge and Memory (RK and M) Across Generations Initiative, calling on the international community to help create specific means to preserve RK and M. The concept of a key information file (KIF) emerged in response to the challenge presented by the large volumes of RK and M material generated by national disposal programmes. This concept has been developed into an important component of a RK and M preservation strategy. The KIF is designed to be a single, short document, produced in a standard format, with the aim of allowing society to understand the nature and intent of a repository, and thus to reduce the likelihood of unnecessary human intrusion. It should be made openly available and ultimately be widely distributed. This report describes the KIF concept in detail, in a manner that should enable those concerned with any particular repository to create their own versions. Three draft key information files, currently under development to support RK and M preservation in France, Sweden and the United States, are provided as examples.

[en] This paper presents examples from various disposal programmes and discusses lessons that may be drawn relating to disposal system design and the use of underground tests. Many useful large-scale experiments have been conducted in underground laboratories that have allowed an assessment of the feasibility of methods for tunnel construction, waste package emplacement, buffer and backfill emplacement, tunnel seal construction, etc. In general, these tests have been successful and have shown that the necessary techniques for manufacturing and installing EBS components are feasible and available. In some cases, tests have shown that designs or techniques need to be adjusted, or have enabled identification of the factors to be taken into account in future optimisation studies. Further trials of some methods are still required, particularly at the repository or industrial scale. Further experiments are also likely to be required to increase understanding of the long-term behaviour of the EBS after installation. (author)

[en] Communication has a specific role to play in the development of deep geological repositories. Building trust with the stakeholders involved in this process, particularly within the local community, is key for effective communication between the authorities and the public. There are also clear benefits to having technical experts hone their communication skills and having communication experts integrated into the development process. This report has compiled lessons from both failures and successes in communicating technical information to non-technical audiences. It addresses two key questions in particular: what is the experience base concerning the effectiveness or non-effectiveness of different tools for communicating safety case results to a non-technical audience and how can communication based on this experience be improved and included into a safety case development effort from the beginning? (authors)

[en] Radioactive waste repositories are designed to isolate waste from the living environment without human intervention over extended periods of time. Nevertheless, the intention is not to abandon the repositories, but to provide the oversight that is necessary to ensure that they are not forgotten by society. In response to this challenge, the Nuclear Energy Agency launched the international initiative 'Preservation of Records, Knowledge and Memory (RK and M) Across Generations'. As a result, an in-depth understanding of this issue was developed, as well as a specific methodology to address it. The RK and M preservation toolbox, for example, offers a menu with 35 different preservation mechanisms and guidelines on how to combine and implement them. This report may be used as a general guide to the RK and M preservation topic. It presents a historical review, addresses ethical considerations, analyses the fundamentals of RK and M preservation, outlines various mechanisms and indicates how to develop these mechanisms into a systemic RK and M preservation strategy. The report aims to inspire and assist a variety of actors so that they can discuss and develop national and repository-specific RK and M preservation strategies