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Impact of repository depth on residence times for leaking radionuclides in land-based surface water

Wörman A., Marklund L., Xu S., Dverstorp B.

Acta Geophysica

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2007

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Vol. 55, no. 1

73-84

EN

The multiple scales of landscape topography produce a wide distribution of groundwater circulation cells that control the hydro-geological environments surrounding geological repositories for nuclear waste. The largest circulation cells tend to discharge water into major river reaches, large freshwater systems or the nearby Baltic Sea. We investigated numerically the release of radionuclides from repositories placed in bedrock with depths between 100 to 2000 meters in a Swedish coastal area and found that leakage from the deeper positions emerges primarily in the major aquatic systems. In effect, radionuclides from the deeper repositories are more rapidly transported towards the Sea by the stream system compared to leakage from more shallow repositories. The release from the shallower repositories is significantly retained in the initial stage of the transport in the (superficial) landscape because the discharge occurs in or near low-order streams with high retention characteristics. This retention and residence time for radioactivity in the landscape control radiological doses to biota and can, thus, be expected to constitute an essential part of an associated risk evaluation.

2

Tracer test in Hobol Creek, Norway, under different flow conditions

Wörman A., Klove B., Wachniew P., Czupryński P., Packman A.

Acta Geophysica Polonica

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2005

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Vol. 53, nr 4

517-526

EN

The current paper describes a repetition of a tracer test using tritiated water in Hobol Creek, Norway, under two markedly different flow conditions in August and in October 2002. By carefully fitting a one-dimensional model of the solute trans-port in the creek, various mixing parameters could be evaluated and compared be-tween the two occasions. The change in residence time in and exchange rate with the hyporheic zone caused by the difference in flow could be well accounted for in terms of the "pumping" theory. The pumping theory represents the hydro-mechanics of the exchange flow. Further, we found that at least 70% mass recovery is needed to provide an accurate evaluation of model parameters and this can only be achieved up to a limited stream distance.

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Kinematic model of solute transport in stream networks: example with phosphate retention in Morsa Watershed, Norway

Wörman A., Klove B., Wachniew P.

Archives of Hydro-Engineering and Environmental Mechanics

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2004

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Vol. 51, nr 1

41-53

EN

A theoretical description of reactive solute transport in a network of stream channels is derived by convoluting unit solutions based on a physical representation of transport and topographical information of the distributions of solute load as well as pathways. The theory is applied to a generic analysis of the phosphate export in Morsa watershed due to the load from 620 individual households with a local wastewater treatment. Essential factors for the phosphate export is filtering of the water in stream-bed sediments through a distribution of hyporheic flow paths of various lengths. This generic study indicates that a significant portion of phosphate is retained in the hyporheic zones for a long time. The 90\% recovery time following a hypothetical remediation action in the households is expected to be in the order of one decade.