Objective
The hydrogeological role of potentially hydraulically conductive features, such as faults and fracture clusters (hereafter termed faults), is a principal cause of uncertainty in the movement of fluid around a deep radioactive waste repository. In order to predict the rate of migration of radionuclides through a disposal system, it is important to understand the structure of fluid flow paths along faults, as well as their hydraulic significance in the context of the regional flow field. This includes the need to consider the evolution of fault hydrogeology as a consequence of fault reactivation (resulting from, for example, glacial loading and unloading).
Extant models of faults do not take account of the internal heterogeneity of flow paths, or the hydrodynamic effects of renewed displacements. Fluid flow models typically assume faults to be simple static planar structures of higher hydraulic conductivity than the surrounding rock. This project aims to develop numerical models of fluid flow and radionuclide transport in fault zones, that can be used to evaluate the importance of considering detailed fault hydrogeology in predictions of disposal system performance. Use of such models will help to reduce uncertainty in safety assessments of radioactive waste disposal sites.
The proposal involves the development and application of existing models, FRACAS and FLAC, to address these issues of fault hydrogeology. FRACAS is a 3-D model of fluid flow and transport in an interconnected fracture network. FLAC allows the structure of localized deformation zones to be represented, and can be used to simulate pressure reduction within active fault zones. The principal objectives of the project are:
* To develop the 2-D FLAC code to evaluate the hydrodynamical effects of fault reactivation on flow and radionuclide transport.
* To develop a detailed 3-D model of fluid flow and radionuclide transport and retardation in a fault zone using FRACAS, incorporating a range of identified hydrogeological structures.
* To evaluate the models against experimental observations in underground laboratories and other available field data to be identified as part of the project.
* To use the models to evaluate the influence of fault heterogeneity and fault movement on fluid flow and radionuclide retardation.
* To develop constitutive expressions for flow and transport in fault zones that are computationally tractable for use in performance assessment models.
This work falls under Section 3.6 of the European Commission Nuclear Fission Safety 1996 work programme concerned with radionuclide migration. It meets the objectives of the work programme by developing new techniques for evaluating the flow and retardation properties of fault zones.
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CSC - Cost-sharing contractsCoordinator
LE15 6AX Oakham (leicestershire)
United Kingdom