Contribution to Nirex review of a deep brine repository concept

Barnes, R.P.; Chadwick, R.A.; Darling, W.G.; Gale, I.N.; Kirby, G.A.; Kirk, K.L.. 2005 Contribution to Nirex review of a deep brine repository concept. British Geological Survey, 65pp. (CR/05/230N) (Unpublished)

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Nirex has developed a multi-barrier concept for a deep repository for the phased disposal of intermediate level (ILW) and certain low level (LLW) solid radioactive wastes, making use of both engineered and natural barriers to form a containment system. As part of the generic studies being carried out by Nirex, a concept is being examined in which a repository is constructed within rocks containing dense brines in which, on the basis of currently available data, groundwater flow rates are expected to be low and travel times for transport of repository derived radionuclides are expected to be long. If a repository could be constructed within an area containing dense brines it could potentially offer significant benefits in terms of enhanced long-term radiological performance. Currently, a feasibility report is being prepared by Nirex to further examine the dense brines concept. As part of this exercise, to illustrate the way such a concept could be delivered, the potential of creating a repository in the dense brines known to exist close to Sellafield in west Cumbria is being used as an illustration based solely on the fact that there is some existing information on which to base the study. It does not indicate or imply that the site has been selected for detailed consideration as a potential site for an actual repository. Although there is a substantial amount of existing geological information from the Sellafield area that is relevant to the dense brines study, the information is not currently in a suitable form for direct incorporation in the study. Furthermore, there has not been an assessment to evaluate the degree of confidence that is associated with such information. The objectives of the work package are to: • Prepare a series of maps and plans to present the geological structure of areas adjacent to Sellafield in a form suitable for use in the feasibility report currently under preparation by Nirex; • Provide an assessment of the levels of confidence that can be assigned to the various items of geological information presented in the plans, such as the range of uncertainty that is associated with the positions of subsurface boundaries between geological units, the locations of faults and the location of contours on salinity; • Provide an assessment of the likely geological succession, including the presence of halite bands, within the Mercia Mudstone Group in the area extending approximately 30 km offshore from the coast near Sellafield and to provide an evaluation of the level of confidence that can be assigned to the estimated geological succession. The basis on which the succession has been assessed is to be explained. • Provide an evaluation of whether additional information is available that could be used for improving the levels of knowledge or understanding regarding the above aspects of the Sellafield dense brines, geological structure or geological succession, e.g. by reprocessing and reinterpretation of existing geophysical data. • Provide an assessment of locations of dense brine bodies present in onshore UK and offshore within 40 km of the coast. The evidence on which knowledge of the locations of these dense brine bodies is based is to be explained and levels of confidence assigned to this knowledge is to be evaluated. This report provides collated and cartographic information in a form suitable for use in the preparation of the feasibility report. The four main sections of this report provide information on a specific aspects of the feasibility study. Chapter 2 describes the methodology used in preparing four ‘available thickness’ maps for the main geological units in the off-shore Sellafield area and the production of a ‘level plan’ at a depth of 1600 m below OD for the Sellafield area. The resulting maps are provided as enclosures to this report. Chapter 3 provides an assessment of the geological succession present within the Mercia Mudstone Group within the area covered by the above plans showing the position and thickness of any identified halite and mudstone horizons present within the sequence. Availability of new information that has been acquired since the work undertaken in the Sellafield area by Nirex during their Sellafield investigations is identified at the end of the chapter. Chapters 4 and 5 provide an assessment of locations of dense brine bodies present in onshore UK and offshore UK territorial waters within a buffer 40 km from the coast to depths of up to about 2 km, respectively. Chapter 6 identifies additional data that may be available or data processing that could be undertaken to improve information provided in this report. An indication of the confidence levels associated with the assessments is provided. It is stressed that this report is not a premature initiation of a new site selection exercise for a radioactive waste disposal facility, but a conceptual study to provide general information and guidance to help those charged with designing any future site selection process. The decision on how to select individual sites and which sites to investigate will rest with Government.

Item Type: Publication - Report
Programmes: BGS Programmes > Chemical and Biological Hazards
Funders/Sponsors: NIREX
Additional Information. Not used in RCUK Gateway to Research.: This item has been internally reviewed but not externally peer-reviewed
NORA Subject Terms: Earth Sciences
Date made live: 29 Sep 2010 12:24 +0 (UTC)

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