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Understanding Radionuclide Migration From the D1225 Shaft, Dounreay, Caithness, UK

Published online by Cambridge University Press:  15 February 2011

David Savage
Affiliation:
Quintessa Limited, The Hub, 14 Station Road, Henley-on-Thames, RG9 1AY, UK
Claire Watson
Affiliation:
Quintessa Limited, The Hub, 14 Station Road, Henley-on-Thames, RG9 1AY, UK
James Wilson
Affiliation:
Quintessa Limited, The Hub, 14 Station Road, Henley-on-Thames, RG9 1AY, UK
Alex Bond
Affiliation:
Quintessa Limited, The Hub, 14 Station Road, Henley-on-Thames, RG9 1AY, UK
Warren Jones
Affiliation:
Dounreay Site Restoration Limited, Dounreay, Thurso, Caithness, KW14 7TZ, UK
Richard Metcalfe
Affiliation:
Quintessa Limited, The Hub, 14 Station Road, Henley-on-Thames, RG9 1AY, UK
Tony Milodowski
Affiliation:
British Geological Survey, Keyworth, Nottinghamshire, NG12 5GG, UK
Colin Munro
Affiliation:
Dounreay Site Restoration Limited, Dounreay, Thurso, Caithness, KW14 7TZ, UK
James Penfold
Affiliation:
Quintessa Limited, The Hub, 14 Station Road, Henley-on-Thames, RG9 1AY, UK
Sarah Watson
Affiliation:
Quintessa Limited, The Hub, 14 Station Road, Henley-on-Thames, RG9 1AY, UK
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Abstract

A 65 m vertical shaft was sunk at Dounreay in the 1950s to build a tunnel for the offshore discharge of radioactive effluent from the various nuclear facilities then under construction. In 1959, the Shaft was licensed as a disposal facility for radioactive wastes and was routinely used for the disposal of ILW until 1970. Despite the operation of a hydraulic containment scheme, some radioactivity is known to have leaked into the surrounding rocks. Detailed logging, together with mineralogical and radiochemical analysis of drillcore has revealed four distinct bedding-parallel zones of contamination. The data show that Sr-90 dominates the bulk beta/gamma contamination signal, whereas Cs-137 and Pu-248/249 are found only to be weakly mobile, leading to very low activities and distinct clustering around the Shaft. The data also suggest that all uranium seen in the geosphere is natural in origin. At the smaller scale, contamination adjacent to fracture surfaces is present within a zone of enhanced porosity created by the dissolution of carbonate cements from the Caithness flagstones during long-term rockwater interactions. Quantitative modelling of radionuclide migration, using the multiphysics computer code QPAC shows the importance of different sorption mechanisms and different mineralogical substrates in the Caithnesss flagstones in controlling radionuclide migration.

Type
Research Article
Copyright
Copyright © Materials Research Society 2009

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