There is today a broad international consensus on the technical merits of the disposal of long-lived radioactive wastes in deep and stable geological formations. Through a system of multiple containment barriers, this strategy would isolate the wastes from the biosphere for extremely long periods of time, ensure that residual radioactive substances reaching the biosphere after many thousands of years would be at concentrations insignificant compared for example with the natural background of radioactivity, and render the risk from inadvertent human intrusion acceptably small. Such a final disposal solution would be essentially passive and permanent, with no requirement for further intervention or institutional control by humans, although it may be assumed that siting records and routine surveillance would in practice be maintained for many years if society evolves in a stable manner.
Other disposal options aiming at long-term isolation of wastes from the biosphere were also considered, but not pursued, during many years of evolution of the geological disposal strategy. They include:
New options might conceivably emerge over the next few decades. Certainly research on any credible alternative disposal option should be encouraged to allow, from time to time, a reappraisal of all potential options.
Currently, geological disposal can be shown to have the potential to provide the required level and duration of isolation. Moreover, it could be reversible, in contrast to the other disposal options considered. The principle of long-term isolation used in geological disposal is already the means by which the biosphere is protected from the vastly greater quantities of toxic and radioactive minerals naturally present in the earth. It is not a cheap waste management concept, but certainly in the case of nuclear power production its cost can be recovered according to the "Polluter Pays Principle", as a small fraction of the cost of nuclear electricity.
An essential aspect of the waste isolation strategy is that long-term safety of geologic disposal must be convincingly presented, and accepted, prior to actual waste emplacement. This can be achieved through safety assessments addressing timescales far beyond the normal horizon of social and technical planning, in practice many thousands of years. Scientific and technical assess-ments provide the principal means to investigate, quantify and explain long-term safety of any selected disposal concept and site to the appropriate authorities and the public. Their feasibility and reliability, including uncertainties unavoidably associated with the assessment of future situations, were addressed and confirmed in a previous international Collective Opinion published by NEA in 1991 (see Annex II for the Executive Summary of this Collective Opinion).
Another important element of the geological disposal strategy is the timing of the incremental process leading to the emplacement of waste, which in many national programmes would not occur until well into the next century. The main successive phases of this process consist of conceptual and technological development, site- screening, surface and in-situ characterisation studies, selection of a site, construction and operation (waste emplacement) of an underground facility and, eventually, sealing of all the accesses, dismantling of surface installations and closing of the facility to leave it in a passively safe state. Each phase of this long sequence will last many years, if not decades, and will be subjected to public debate and close scrutiny by the regulatory authorities, who will have to be satisfied with the results obtained before giving authorization to proceed with the next phase. It is important to note that technical safety is not dependent on any particular rate of progress through the incremental process since supervised storage of the wastes, whilst not an acceptable strategy for the long term, is itself a very safe interim procedure.
During this incremental process, scientific information will be continuously collected from observations at and around the site and will contribute to both a better understanding of the regional and local geology and to increasingly refined performance assessments. This process, which must be flexible in order to accommodate inputs from research programmes and from public consultation, would provide ample opportunity for review. At any point in the process, if there were an indication that the objectives of safe disposal could not be met, it would be possible to cease disposal operations and retrieve the wastes.
The geological disposal concept does not require deliberate provision for waste retrieval after site closure. Interventions will, in principle, never be needed after repository closure since the disposal concept requires that the presence of waste may safely be forgotten, after a period of institutional control to prevent early inadvertent intrusion. For the extreme case of retrieval from a sealed repository, engineering procedures might be difficult and costly, but not impossible, and somewhat analogous to the extraction of toxic mineral ores.
Retrievability is an important ethical consideration since deep geological disposal should not necessarily be looked at as a totally irreversible process, completely foreclosing possible future changes in policy. In this context, it should be noted that sealing of a site and its access will always require a specific decision and that such a decision could be delayed until well after the end of waste emplacement operations to continue to allow reversibility and flexibility in the process if considered necessary. Under such circumstances, the incremental process leading to the implementation of the geological disposal strategy incorporates the advantages of a temporary storage phase, as advocated by some, without letting this phase extend indefinitely.
It must be acknowledged that the most robust and passively safe system that can be devised by current generations may ultimately be compromised by the actions of a future society, through inadvertent intrusion. Consideration of the probabilities and consequences of such intrusions at well-chosen sites indicates that the risks would be very small.
Finally, the decision-making process involves representatives of the technical community and competent regulatory authorities at the national level, decision-makers at local and regional levels, and representatives of various public interest groups. An open process is required to ensure that ethical and social considerations are properly taken into account, necessitating, therefore, a broad range of participants in the process. All national geological disposal programmes recognize the need for such procedures, notably to allow the communities affected by the selection of specific sites to be consulted and to participate appropriately in decision-making.
What is clear is that environmental consciousness continues to evolve and will play an increasingly important role in technological decision-making. In the field of radioactive waste management, which is supported by strong international co-operation in research and development, experts have published a wealth of information on technical issues (including NEA "Collective Opinions"), but less attention has been drawn to the ethical basis of the plans. It is for this reason that the decision was taken to publish, in this Collective Opinion, the ethical principles which underly the strategies for deep disposal of radioactive wastes.