Long-Term Disposal Research

Radioactive waste management, disposal and decommissioning are important areas of European research. Attention has focussed on evaluation of long-term disposal systems, including packaging policies and properties. Different aspects of waste retrieval are also under consideration. Underground facilities provide the best means of characterising potential disposal sites and for investigating different concepts of deep geological disposal. They are also required for data collection on the performance of the different barriers of protection. The performance of different types of rock ranging from clay, salt, marl or crystalline rock is being considered at possible sites. Within the EU, there are underground research facilities in the Asse salt mine in Germany and in the Hades facility in the Boom clay layer beneath Mol in Belgium. In France, some experimental activities are on-going in existing mines, e. g. the Amelie mine; sites for other underground laboratories are being considered.

Research tasks cover the testing of different methods of disposal, the methods of backfitting and scaling of repositories. They have also included the investigation of the long-term behaviour of components and groundwater flow and the migration of radionuclides.

An important objective of the research is to gain an improved understanding of the essential phenomena. The main requirement is to understand the release of radionuclides from the waste packages and their migration through the repository barriers to the environment. Characterisation of the different levels of waste in the waste volume is useful, to reduce the volume of highly active waste for disposal in deep underground repositories. Research is carried out into characterising the different waste forms and matrices (cement as a containment and barrier material, spent fuel itself and glass matrices of vitrified material). The quality control of nuclear waste packages and waste forms is being promoted to facilitate standardisation of checking methods, a common under­standing of R & D requirements and unification of test methods, etc.

The mechanical and chemical stability of the engineered barriers and the surrounding host rock is influenced by groundwater movements, thermal energy transfer effects at the interface and beyond and the radionuclide transport. It is important to understand any long-term degradation of these engineered barriers. The generation of gas can occur due to a number of processes affected by the nature of the waste, waste package, buffer and backfill materials and the nearby host rock. This could result in the build-up of pressure and possible structural problems in the repository.

Radionuclide migration research focuses on the thermodynamics of the solid-liquid phases’ equilibria and complexes with organic materials. These include groundwater colloid generation and transport, transport and retardation processes through porous and fractured rock systems and chemical thermodynamic and kinetic processes associated with radionuclide transport through the engineered barriers.

Studies have been performed on natural geological sites and have provided qualitative and some quantitative data on geochemical aspects (e. g. container corrosion, waste form degradation, radionuclide solubility and transport processes).

Palaehydeogeological studies also provide information on site evolution over geolo­gical time scales. Information of ancient flow patterns can provide understanding of past rates of uplift, erosion and of other, e. g. climatically induced changes of groundwater behaviour.

In addition to technical research, there are EU research programmes to enhance public understanding of the impact of waste disposal and to establish better methods of achieving public confidence and trust (European Commission, 2001). The objectives include gaining an understanding of the origins of public mistrust, evaluation of better means of communication and evaluation of decision making at different levels (e. g. local, national and international).

The decommissioning of nuclear installations is the final chapter in closing the nuclear fuel cycle. Research programmes are in place to develop innovative dismantling techniques to collect technical performance data, including data on specific wastes and doses arising from decommissioning.

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