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King-Clayton, L.M.; Smith, P.A.; Dverstorp, B.
Proceedings of the 1996 international conference on deep geological disposal of radioactive waste1996
Proceedings of the 1996 international conference on deep geological disposal of radioactive waste1996
AbstractAbstract
[en] Site-scale radionuclide transport calculations have been carried out for a hypothetical deep repository at the Aespoe site, southeast Sweden. The work complements and utilizes results from regional-scale, variable density flow modelling in which the groundwater flow field is time-dependent, reflecting the impact of climate evolution over the next 130,000 years at the site. The climate evolution and its impacts are qualitatively described in the Central Climate Change Scenario, which specifies a hypothetical evolution of the local climate over the period modelled, including the periodic development of permafrost conditions and ice sheet advance and retreat. The work summarised here is complementary to the transport calculations undertaken as part of the SKI SITE-94 performance assessment project, with the specific objective of quantifying the impact of transient changes in flow direction and magnitude. The spatial evolution of 79Se and 129I contaminant plumes, released from the hypothetical repository under the influence of time-dependent (step-wise varying) head boundary conditions associated with ice sheet and permafrost development, is compared with that of a steady-state Base Case based on continuing present-day conditions. The results indicate that temporal changes in flow conditions due to future climate changes can have a significant effect on the transport of radionuclides from a source at depth. A case with high sub-ice sheet recharge and taliks (ie. gaps in the permafrost), creating groundwater fluxes up to an order of magnitude greater than the Base Case, has the greatest impact on radionuclide flux out of the geosphere, with a maximum 79Se flux of over three orders of magnitude greater than that of the Base Case. The maximum 129I flux is nearer one order of magnitude greater than the Base Case. In all cases modelled with time dependent boundary conditions, the greatest radionuclide fluxes occur towards the end of the main glacial periods (periods with ice sheet coverage), and correspond to periods of high groundwater discharge at the margin of the modelled ice sheets. These short-term flux maxima may exceed the corresponding fluxes from the near-field and represent a relatively rapid 'flushing out' of radionuclides from the repository host rock. Fluxes to the biosphere may, for limited periods (∼2000 years or less), be 3 times higher than those from the near-field. The occurrence of these peak fluxes requires careful consideration in any performance assessment which wishes to take account of future changes in groundwater flow conditions. The study has provided a quantitative way of illustrating the possible effects of future glaciations on radionuclide transport from a repository. Such effects are likely to be significant in any potential siting area predicted to be affected by future periods of ice cover. (author)
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Canadian Nuclear Society, Toronto, Ontario (Canada); 1 v; ISBN 0-919784-44-5;
; 1996; p. 3.93-3.101; International conference on deep geological disposal of radioactive waste; Winnipeg, Manitoba (Canada); 16-19 Sep 1996; Available from Canadian Nuclear Society, 144 Front Street, Toronto, Ontario M5J 2L7; 6 refs., 3 tabs., 3 figs.

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Book
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Conference
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