In order to validate predictive models of the very long-term processes which affect the performance of radioactive waste repositories, there has been an increased interest in the information and understanding which can be obtained from studying similar mechanisms in natural systems. These "natural analogues", as they are known in the jargon of waste management, have been studied sporadically for many years, but there has been a considerable rejuvenation of interest in the last four years, possibly owing to the fact that performance assessment methodolo gy is gradually maturing to the point where it needs the kind of support which analogues can offer. Since 1982, the Commission of the European Communities has been involved in specific work on natural analogues in the framework of its activities on radioactive waste management, principally within the MIRAGE project which concerns migration of radionuclides in the geosphere. As a consequence, the Commission took the initiative, in 1985, of establish ing a Natural Analogue Working Group (NAWG) whose members can benefit from the overall expertise available for managing their own natural analogue research programmes. In this group, modeller' s requirements and the results of field research are exchanged at regular intervals. A number of wide-ranging investigation programmes, both on national and international scales. are currently underway or being initiated, and several of these have been discussed recently at the NAWG.

Many countries are currently exploring the option to dispose of highly radioactive solid wastes deep underground in purpose built, engineered repositories. A number of surface and shallow repositories for less radioactive wastes are already in operation. One of the challenges facing the nuclear industry is to demonstrate confidently that a repository will contain wastes for so long that any releases that might take place in the future will pose no significant health or environmental risk. One method for building confidence in the long-term future safety of a repository is to look at the physical and chemical processes which operate in natural and archaeological systems, and to draw appropriate parallels with the repository. For example, to understand why some uranium orebodies have remained isolated underground for billions of years. Such studies are called 'natural analogues'. This book investigates the concept of geological disposal and examines the wide range of natural analogues which have been studied. Lessons learnt from studies of archaeological and natural systems can be used to improve our capabilities for assessing the future safety of a radioactive waste repository.

In order to validate predictive models of the very long-term processes which affect the performance of radioactive waste repositories, there has been an increased interest in the information and understanding which can be obtained from studying similar mechanisms in natural systems. These "natural analogues", as they are known in the jargon of waste management, have been studied sporadically for many years, but there has been a considerable rejuvenation of interest in the last four years, possibly owing to the fact that performance assessment methodolo gy is gradually maturing to the point where it needs the kind of support which analogues can offer. Since 1982, the Commission of the European Communities has been involved in specific work on natural analogues in the framework of its activities on radioactive waste management, principally within the MIRAGE project which concerns migration of radionuclides in the geosphere. As a consequence, the Commission took the initiative, in 1985, of establish ing a Natural Analogue Working Group (NAWG) whose members can benefit from the overall expertise available for managing their own natural analogue research programmes. In this group, modeller' s requirements and the results of field research are exchanged at regular intervals. A number of wide-ranging investigation programmes, both on national and international scales. are currently underway or being initiated, and several of these have been discussed recently at the NAWG.

A unique and scientifically most difficult aspect of predictive safety analysis of repositories for long lived wastes is the extrapolation of short term field and laboratory data to the long periods of time required by regulatory agencies for performance assessment. Natural analogues may be the only way of obtaining data on the cumulative effect of the migration of radionuclides over the time-scales of interest. This report briefly summarizes the state of the art in this field for technical specialists and may also serve as an introduction to the subject for managers.

The first purpose of this book is to provide a comprehensive review of the state of development of natural analogue studies with emphasis on those studies which are relevant to the following repository designs: Nagra (Switzerland) disposal concepts for high-level waste/low and intermediate-level waste; SKB (Sweden) disposal concepts for spent fuel/low and intermediate-level waste; and Nirex (UK) disposal concept for low and intermediate-level waste. The book's second aim is to discuss the expanding application of natural analogues for non-performance assessment purposes, especially their potential for presenting the concept of geological disposal to various interested audiences in a coherent, understandable and scientifically legitimate manner. Much of the discussion of the book is relevant to concepts for geological disposal of radioactive wastes by other countries, and is concerned only with those physico-chemical processes which control the release of radionuclides from the near-field, and their subsequent retardation and transport in the geosphere.

Many countries are currently exploring the option to dispose of highly radioactive solid wastes deep underground in purpose built, engineered repositories. A number of surface and shallow repositories for less radioactive wastes are already in operation. One of the challenges facing the nuclear industry is to demonstrate confidently that a repository will contain wastes for so long that any releases that might take place in the future will pose no significant health or environmental risk. One method for building confidence in the long-term future safety of a repository is to look at the physical and chemical processes which operate in natural and archaeological systems, and to draw appropriate parallels with the repository. For example, to understand why some uranium orebodies have remained isolated underground for billions of years. Such studies are called 'natural analogues'. This book investigates the concept of geological disposal and examines the wide range of natural analogues which have been studied. Lessons learnt from studies of archaeological and natural systems can be used to improve our capabilities for assessing the future safety of a radioactive waste repository.

The safe disposal of radioactive wastes by burial in deep geological formations requires long-term predictions of the future behaviour of the wastes and their engineered repository. Such predictions can be tested by evaluating processes analogous to those which will occur in a repository, which have been long active in the natural geochemical environment. The Pocos de Caldas Project is a comprehensive study of two ore deposits in Minas Gerais, Brazil, aimed at looking at uranium and thorium series radionuclide and rare-earth element mobility, the development and movement of redox fronts, and the nature of natural groundwater colloids. A multidisciplinary team of experts from 27 laboratories carried out a fully integrated study of the geology, geomorphology, hydrogeology, geochemistry, hydrochemistry and geomicrobiology of the two sites for nearly four years. This book contains 20 papers covering the detailed findings, with particular emphasis on their significance for radioactive waste disposal, especially on the use of the data in testing models of radionuclide movement. It will interest economic geologists, geochemists and performance assessment modellers involved in the geological disposal of radioactive wastes.