2003:14 Exchange processes at geosphere-biosphere interfaceCurrent SKB approach and example of coupled hydrological- ecological approach

The design of the repository for final disposal of spent nuclear fuel proposed by SKB is based on a multi barrier system, in which the geosphere and biosphere are the utmost barrier surrounding the engineer barriers. This report briefly reviews the current approach taken by SKB to account for hydrological and ecological processes at the geosphere-biosphere interface (GBI) and their future plans in this area. A simple analysis was performed to shift the focus of performance assessment involving geosphere-biosphere interface modelling from the very simplistic assumption that the quaternary sediments are bypassed to one in which a more detailed model for sub-surface flows is included.

This study indicated that, for many assumed ecosystem descriptions, the presence of the GBI leads to lower maximum doses to individual humans compared to a case when the GBI is neglected. This effect is due to the additional "barrier" offered by the GBI. The main exposure pathways were assumed to occur through the food web. However, particularly the leakage on land through the stream-network and lakes can lead to higher doses due to ecosystem interaction with arable land. A scenario that gives particularly long duration of doses occurs due to land rise and with the transformation of the former bay and lake bed sediments into agricultural land. This effect is due to the significant retention or "accumulation" in aquatic sediment, which causes high activities to build up with time. Particularly, in combination with changing conditions in climate, humans life-style or geographic conditions (land rise, deforestation, etc.) doses to individual humans can be large.