News : 11th NAWG Workshop 15th October 2009 (in conjunction with the ICEM ’09 conference Full details)

What is a natural analogue?

The generally accepted definition of the term 'natural analogue' (Côme &Chapman, 1986) is "...an occurrence of materials or processes which resemble those expected in a proposed geological waste repository." This has subsequently been refined by the addition; "The essence of a natural analogue is the aspect of testing of models - whether conceptual or mathematical - and not a particular attribute of the system itself." (McKinley, 1989) and by an IAEA review group which noted that; "Natural analogues are defined more by the methodology used to study and asses them than by any intrinsic physio-chemical properties they may possess." (IAEA, 1989). The progressive refinement of the definition reflects a maturation in the understanding and appreciation of natural analogues. In essence, natural analogue studies use information from the closest possible approximations, or direct analogies, of the long-term behaviour of materials and processes found in, or caused by, a repository to develop and test models appropriate to performance assessment work.

More recently, data from natural analogues have been used to explain complex repository concepts to non-technical audiences (e.g. Miller et al., 2000).

The advantage of natural analogues over short-term laboratory experiments is that they enable study of repository-like systems which have evolved over the geological time scales of relevance to a radioactive waste repository safety assessment (rather than the days to months usual in laboratory tests). The disadvantage is that the boundary conditions and source term are often unknown or poorly controlled.

In the light of more open discussion of radwaste programmes with a wider range of stakeholders than before, natural analogues are being used as solid examples of the long-term behaviour of materials used to construct radwaste repositories (e.g. Stuckless, 2002). For example, well-preserved ancient rock paintings in caves clearly show that even very delicate materials can survive millennia underground.

Formation of NAWG - Natural Analogue Working Group

Owing to the considerable upsurge of interest on the topic of natural analogues, a group of individuals working for or in national waste disposal programmes, took the initiative of establishing, in June 1985, NAWG, the Natural Analogue Working Group (originally under the auspice of the European Commission).

This was carried out to offer an international forum for:

• The discussion of natural analogue programmes from around the world.
• Assessing the relevance and appreciation of natural analogues to radioactive and toxic waste disposal - and now CO₂ sequestration..

These themes have been addressed at 10 international workshops.

• 10^th Workshop: Munich, Germany, 2007 where the workshop examined how current and future studies could be better focussed on providing appropriate data for the various end-users of natural analogue data.
• 9^th Workshop: Aarau, Switzerland, 2002, where the theme was the current international status of natural analogues.
• 8^th Workshop: Strasbourg, France, 1999, was devoted to a presentation of three, major international natural analogue projects, Oklo (II), Palmottu and Pena Blanca (EUR 19118);
• 7^th Workshop: Stein am Rhein, Switzerland, 1996, where one of the main themes of the workshop was the application of natural analogues to toxic wastes ( EUR 17851 EN);
• 6^th Workshop: Santa Fe, USA, 1994, where the intention was to review the "state-of-the-art" of several key issues in near-field and far-field processes and their importance to PA with the intention to provide a consensus view of the remaining areas requiring further research in natural analogues (EUR 16761);
• 5^th Workshop: Toledo, Spain, 1992, was held in association with the final workshop of the Alligator Rivers Analogues project (EUR 15176);
• 4^th Workshop: Pitlochry, Scotland, 1990, was devoted to review 5 years of NA studies and the final conclusions drawn from the Poças de Caldas study (EUR 13014);
• 3^rd Workshop: Snowbird, USA, 1988, where the application of natural analogues to repository performance assessment was discussed (EUR 11725);
• 2^nd workshop: Interlaken, Switzerland, 1986, where anthropogenic analogues and the role of colloids, complexes and microbes have been reviewed (EUR 10671);
• 1^st Workshop: Brussels, Belgium, 1985, where the theme was the interaction between the modellers and experimenters (EUR 10315).

• Studying natural analogues has greatly increased the understanding of repository-relevant processes and improved the capability to describe and effectively model them.
• The larger, multi-objective analogue studies are a very cost effective way of training site characterisation and performance assessment groups on real, complex systems.
• The application of analogues in broadening public perception of the natural context of waste disposal is under development.
• An increased awareness of the potential for studying natural analogues of chemotoxic waste.
• The significant role of natural analogues in understanding the long-term impacts of CO₂ sequestration