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Workreport 2007-24

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Name:

A Concept for Radionuclide Transport Modelling

Writer:

Poteri, A.

Language:

English

Page count:

56

Summary:

This report drafts a modelling methodology that can be applied to assess transport and retention properties along flow paths in fractured rock. Transport properties are assessed for the main geosphere retention processes: matrix diffusion and sorption. Data extracted from the flow model is used to characterise release paths and to derive appropriate geosphere performance measures that can be applied in the radionuclide transport calculations, performance assessment and safety case.

The proposed transport concept is based on application of the site scale DFN model. It is able to take into account heterogeneity in all scales. Computational feasibility can be ensured by focusing the detailed scale fracturing only to the regions of the model that have active flow paths or that are of special interest. The present transport concept takes advantage of the one dimensional nature of the solute transport through the fractured rock. In practice, this means that the transport channels are identified by particle tracking using the simulated DFN flow field.

Enhancements of the present approach compared to the previous analyses are, for example: site evolution is taken into account in the flow conditions, heterogeneity of the fractured rock is taken into account by explicitly including small scale fracturing into the model where it is appropriate, heterogeneity of the rock mass and geological materials is taken into account by taking advantage of the generalised retention models and varying sorption properties, in space or in time, can be taken into account.

Transport and retention simulations have important interfaces with DFN flow modelling, geology, geochemistry, biosphere modelling and performance assessment. DFN flow model has a central role in defining the flow characteristics, geology describes and parameterise the generalised retention models (immobile zones), geochemistry provide sorption data that are connected with the retention models and biosphere modelling provides the upper model boundary of the geosphere transport and retention model. Finally, performance assessment defines calculation scenarios and performance measures for the geosphere transport paths.

Keywords:

groundwater flow, transport of solutes, performance assessment,

File(s):

A Concept for Radionuclide Transport Modelling (pdf) (758.8 KB)


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