International Geologiical Congress - Oslo 2008

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NWG-01 Geology and disposal of nuclear waste: Global perspectives

 

Ice age influence on a nuclear waste repository in Sweden. A review of SKB's safety assessment SR-Can

 

Öivind Toverud, Statens kärnkraftinspektion (Sweden)
Per Holmlund, Stockholms universitet (Sweden)
 

 

As a rehearsal for the safety assessment (SA) SR-Site in 2009 the Swedish nuclear waste industry subsidiary the Swedish Nuclear Waste Management Co (SKB) presented the SA SR-Can (SKB TR-06-09) in November 2006. The SA has been jointly reviewed by the Swedish authorities the Swedish Nuclear Power Inspectorate (SKI) and the Swedish Radiation Protection Authority (SSI) with input from national and international consultants. However, this paper is based on the review of SR-Can carried out by SKI and focuses on three issues of the ice age scenarios; the climate record, the glacial hydrology and on sea level rise.

Poor knowledge on ice age air temperatures and ice sheet hydrology significantly influence uncertainties in the design and the placing of a future nuclear waste repository in Sweden. The SR-Can report underestimate the error bars in the modelled quantitative data. It does indirectly highlight lack of knowledge of the dynamics of ice sheets. The time perspective of the safety assessments linked to a nuclear waste repository spans up to a million years including several glaciations of unknown length and dignity.

In SR Can, SKB has made use of the Weichselian glaciation as a typical one, an approach which is pragmatic and probably realistic. Compared to a more or less educated guess of future climate and glaciations the knowledge of the Weichselian glaciation is very good. The crucial question is though; is it good enough for this purpose?

One important finding in the review is that the temperature record used for the Weichselian Scandinavia, primarily based on Greenland ice core data, is very uncertain in terms of quantitative information on air temperature. This is common knowledge but the uncertainty in the climate record is not transferred to calculations on permafrost extent and depth, on ice sheet temperature distribution and thus on estimations of glacial erosion. This is surprising as it adds significant error bars to successive calculations Another finding is that the knowledge of en-and subglacial ice sheet hydrology suffers from quantitative experiments from polar ice sheets such as the Greenlandic one.

The absolute majority of experiments of glacial hydrology have so far been performed on temperate glaciers which only to some extent is applicable to a polar ice sheet. A third comment to make is that future sea level rise due to enhanced global warming is to some extent neglected. This latter has impact on selected sites as the isostatic uplift from the previous glaciations differs significantly. At a more northern locality (Forsmark) the isostatic uplift will match a sea level rise including a melt off of the Greenland ice sheet. This is not the case for the more southerly located site (Laxemar) where the risk of saltwater intrusion will increase.

 

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