Gas Generation And Migration In Deep Geological Radioactive Waste Repositories

Understanding the behaviour of gases in the context of radioactive waste disposal is a fundamental requirement in developing a safety case for the disposal of radioactive waste. Of particular importance are the long-term performance of bentonite buffers and cement-based backfill materials that may be used to encapsulate and surround the waste in a repository, and the behaviour of plastic clays, indurated mudrocks and crystalline formations that may be the host rocks for a repository. The EC Euratom programme funded project, FORGE, has provided new insights into the processes and mechanisms governing gas generation and migration with the aim of reducing uncertainty. This volume brings together papers on aspects of this topic arising from both the FORGE project and work undertaken elsewhere. This has been achieved by the acquisition of new experimental data coupled with modelling, through a series of laboratory and field-scale experiments performed at a number of underground research laboratories throughout Europe.

This Special Publication highlights the importance of clays and clayey material, and their multiple roles, in many national geological disposal facilities for higher activity radioactive wastes. Clays can be both the disposal facility host rock and part of its intrinsic engineered barriers, and may be present in the surrounding geological environment. Clays possess various characteristics that make them high-quality barriers to the migration of radionuclides and chemical contaminants, e.g. very little water movement, diffusive transport, retention capacity, self-sealing capacity, stability over millions of years, homogeneity and lateral continuity.

This volume contains 11 case studies of toxic waste repositories that use geologic isolation in order to accomplish the permanent and safe isolation of dangerous materials. It describes past and currently active facilities and also discusses generic considerations of the isolation capability of average crustal rock, apparently in an effort to convince audiences of the safety of these facilities.

It is internationally accepted that the safest and most sustainable option for managing radioactive waste is geological disposal, utilizing both engineering and geology to isolate the waste and contain the radioactivity. This Special Publication contains 25 scientific studies presented at the 6th conference on ‘Clays in natural and engineered barriers for radioactive waste confinement’ held in Brussels, Belgium in 2015. The conference and this resulting volume cover many of the aspects of clay characterization and behaviour considered at various temporal and spatial scales relevant to the confinement of radionuclides in clay, from basic phenomenological process descriptions to the global understanding of performance and safety at repository and geological scales. The papers in this volume consider research into argillaceous media under the following topic areas: large-scale geological characterization; general strategy for clay-based disposal systems; geomechanics; mass transfer; bentonite evolution and gas transfer. The collection of different topics presented in this Special Publication demonstrates the diversity of geological repository research.

Geological disposal has been internationally adopted as the most effective approach to assure the long-term, safe disposition of the used nuclear fuels and radioactive waste materials produced from nuclear power generation, nuclear weapons programs, medical, treatments, and industrial applications. Geological repository systems take advantage of natural geological barriers augmented with engineered barrier systems to isolate these radioactive materials from the environment and from future populations. Geological repository systems for safe disposal of spent nuclear fuels and radioactive waste critically reviews the state-of-the-art technologies, scientific methods, regulatory developments, and social engagement approaches directly related to the implementation of geological repository systems. Part one introduces geological disposal, including multiple-barrier geological repositories, as well as reviewing the impact of nuclear fuel recycling practices and underground research laboratory activities on the development of disposal concepts. Part two reviews geological repository siting in different host rocks, including long-term stability analysis and radionuclide transport modelling. Reviews of the range of engineered barrier systems, including waste immobilisation technologies, container materials, low pH concretes, clay-based buffer and backfill materials, and barrier performance are presented in Part three. Part four examines total system performance assessment and safety analyses for deep geological and near-surface disposal, with coverage of uncertainty analysis, use of expert judgement for decision making, and development and use of knowledge management systems. Finally, Part five covers regulatory and social approaches for the establishment of geological disposal programs, from the development of radiation standards and risk-informed, performance-based regulations, to environmental monitoring and social engagement in the siting and operation of repositories. With its distinguished international team of contributors, Geological repository systems for safe disposal of spent nuclear fuels and radioactive waste is a standard reference for all nuclear waste management and geological repository professionals and researchers. Critically reviews the state-of-the-art technologies, scientific methods, regulatory developments, and social engagement approaches related to the implementation of geological repository systems Chapters introduce geological disposal and review the development of disposal concepts Examines long-term stability analysis, the range of engineered barrier systems and barrier performance