W. Kickmaier

Development and testing of radionuclide transport models for fractured rock: examples from the Nagra/JNC Radionuclide Migration Programme in the Grimsel Test Site, Switzerland

The joint Swiss National Co-operative for the Disposal of Radioactive Waste (Nagra)/Japan Nuclear Cycle Development Institute (JNC) Radionuclide Migration Programme has now been on-going for over a decade in Nagras Grimsel Test Site (GTS). The main aim of the programme has been the direct testing of radionuclide transport models in as realistic manner as possible. Although it will never be possible to fully test these models due to the large time and distance scales involved, tests of the model assumptions in scaled down but otherwise realistic conditions will contribute to developing confidence in the predictive power of the models. In this paper, the Nagra/JNC approach is highlighted with examples from a large programme of field, laboratory and natural analogue studies based around the GTS. The successes and failures are discussed as in the general approach to the thorough testing of predictive transport codes which will be used in repository performance assessment (PA). Some of the work is still on-going and this represents the first presentation of a unique set of results and conclusions.

A review of research carried out in European rock laboratories

Research and development projects to support geological disposal options for nuclear waste have been carried out in underground research laboratories (URLs) for more than three decades and an extensive literature exists on the work carried out in these facilities. In this paper we focus on classification of URLs in terms of the particular orientation of their work programs. In addition, the evolution of URL work programs with time is overviewed with the particular aim of identifying trends in the types of experimental studies which are included.

Manganese occurrences in the Al Hammah Range — Wahrah Formation, Oman Mountains

Abstract The host rocks of the manganese in the Al Hammah Range (125 km S of Muscat) are red radiolarian cherts of Tithonian to Neocomian age, continuously exposed over 1000 km2. The stratigraphic sequence starts with fine-grained turbiditic limestones followed by a transition zone of coloured silt-mudstones and cherts which grade into almost CaCO3− free cherts, topped by 1–5 m of silicified limestones. The base of the Wahrah Formation is unknown. Sedimentological and geochemical features indicate that the cherts are of biogenic, non-hydrothermal origin. The stratiform manganese deposits are the result of sedimentary and tectonic enrichment processes. The single Mn-layers formed during periods of condensed sedimentation at the sediment-water interface. The different Mn-chert types (disseminated and layered ore and black Mn-rich cherts) can be explained by varying sedimentation rates of radiolaria, clay and manganese precipitation. Geochemically, the manganese deposits are characterized by high Mn/Fe ratios and by an extremely low minor element (e.g. Ni, Cu, Co) content. Using geochemical discrimination diagrams, the manganese deposits of the Wahrah Formation would be of hydrothermal origin. This contrasts with the sedimentary characteristics of the manganese-bearing cherts and with the field observations. Because of the Tithonian to Neocomian age of the Wahrah Formation cherts, the manganese enrichment can not be related to the formation of the Semail ophiolite. It is proposed that they might relate to a long distance discharge from the Owen fracture zone during the formation of the Masirah ophiolite.

Chert-Hosted Manganese Deposits in the Wahrah Formation: A Depositional Model

The non-metamorphic, stratiform manganese deposits in the Wahrah Formation (Al Hammah Range, 125 km south of Muscat) are of upper Berriasian to Hauterivian age. The manganese enriched horizons are continuously exposed over several 100 km2. Sedimentological and geochemical features prove that the host rock of the manganese deposits exclusively consisting of red cherts are of biogenic, non-hydrothermal origin, deposited in a distal part of the Hawasina basin. A depositional (geochemical) environment comparable to that of a siliceous ooze facies is highly likely. Geochemically the manganese layered cherts and nodules, with their extremely high Mn/Fe ratio and the low minor element content, are similar to hydrothermal deposits associated with volcanic activity or to diagenetic manganese enrichments in hemipelagic regions in sediments with relatively high organic-C contents. Diagenetic shallow water deposits are geochemical similar to the Wahrah Formation enrichment also. Regional geological considerations, mineralogical, sedimentological and REE-patterns evidences in the Wahrah Formation are, however in conflict with these models. Therefore, we propose a alternative manganese transport and accumulation model. “Continentally” derived manganese is introduced to the sea in suspended and/or dissolved form and deposited on the continental margin and -slope. Upward migrating pore fluids, diagenetically enriched in manganese, are released to the water column and horizontally transported through the Oxygen-minimum zone towards the open basin. During selective element scavenging onto different sinking particles and the formation of manganese-rich microparticles, element separation takes place. Sedimentary features indicate that manganese microparticles, precipitated in the water column and the sea water sediment interface, are mechanically enriched to fine laminae and thicker layers. Hydrodynamically controlled separation processes during transport of clay minerals, manganese-rich microparticles and biogenic particles (main element carrier phases) explain the geochemical composition. Geochemical differences and similarities of nodular and layered ore types are attributed to later minor element redistributions.

Grimsel test site - Phase VI: review of accomplishments and next steps

The Grimsel Test Site owned and operated by Nagra is located in the Swiss Alps (www.grimsel.com ). The sixth Phase of investigations was started in 2003 with a ten-year planning horizon. With the investigations and projects of Phase VI the focus is shifted more towards projects assessing perturbation effects of repository implementation and projects evaluating and demonstrating engineering and operational aspects of the repository system. More than 17 international partners participate in the various projects, which form the basic organisational ‘elements’ of Phase VI, each one further structured in field-testing, laboratory studies, design and modelling tasks, as appropriate. Each project phase is planned with a duration of 3 to 5 years, to facilitate all practical and administrative aspects, ensuring flexibility for updating the overall plan with the recent findings. Scientific and engineering interaction among the different projects is ensured via the annual international meeting and ad-hoc meetings, as appropriate. As Phase VI approaches its mid-term point, a review of the accomplishments to date is performed to provide a sound basis for the detailed planning of the next steps. The accomplishments to date are described and assessed below; the opportunities with the on-going projects as well as new projects – currently under discussion – are also presented and discussed. The on-going projects include: studies of the long-term diffusion with emphasis on the processes in the rock matrix (LTD); colloid studies under in-situ generation conditions and migration velocities closer to velocities expected in an actual repository site (CFM); studies of the long-term cement interactions with natural systems (LCS); evaluation of full-scale engineered systems under simulated heat production and long-term natural saturation (NF-Pro/FEBEX); gas migration through engineered barrier systems (GMT); emplacement of shotcrete low-pH plug (ESDRED/Module IV); test and evaluation of monitoring systems (TEM). In addition, various shorter term projects assessing, for example, new geophysical investigation tools, wireless transmission, testing new tools and training for in-situ tracer transport studies have been performed and/or are planned for the near future.Copyright