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Geosphere retention of radionuclides can be an important component of the safety case for deep geological disposal of radioactive wastes. Methods to evaluate and model the migration of radionuclides in the geosphere have been developed intensively over many years. The RETROCK project, "Treatment of Geosphere Retention Phenomena in Safety Assessments", has examined how the retention and transport of radionuclides are dealt with in performance assessment (PA) models for deep geological repositories and how this could be further developed and improved. RETROCK is a part of Euratom's research and training programme and, as a Concerted Action, its work is based on existing background knowledge. The environment considered in RETROCK is saturated, sparsely fractured rock in the socalled ‘far-field’ (between the repository and the biosphere), where the interconnected fracture network provides flowpaths for groundwater that could transport radionuclides. The results of the project are also applicable, with some constraints, to other geological environments. The phenomena in the focus of RETROCK are related to matrix diffusion, sorption and the distribution of groundwater flow. These, along with radioactive decay, provide the key terms to the transport equations of PA models. Some other processes are discussed but more cursorily: colloid-facilitated transport, the influence of microbes, gas-mediated transport, precipitation and dissolution, off-diagonal Onsager processes, effects originating in the near-field and the impacts of climate change. The RETROCK participants acknowledge that the currently applied priorities to develop the treatment of the processes under discussion are well-reasoned - considering also that the project did not reveal new issues that could call for significant reprioritisation. It looks likely that further work on retention mechanisms and modelling will be at the level of gradual improvements within the existing main directions.

Additional information

Authors: No Author stated, European Commission, DG Research, Brussels (BE)
Bibliographic Reference: EUR 21230 EN (2005), 76pp. Free of charge
Availability: (Catalogue Number: KI-NA-21230-EN-C)
ISBN: ISBN: 92-790-0130-2
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