Long Term Diffusion (LTD) - Work Package Overview

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Long Term Diffusion (LTD)
Work Package Overview

Phase I of the LTD project runs from 2005 until 2008. During this time,four main experiments are being carried out in situ at the GTS.

	The monopole experiment
Aims:	To study matrix diffusion in undisturbed rock matrix and compare results of in situ, laboratory and modelling studies.
Overview:	To circulate a radionuclide cocktail around an interval deep in undisturbed rock matrix for one year to simulate radionuclide transport processes in the matrix. After circulation, the rock matrix will be removed by large diameter overcores and the radionuclide profiles will be analysed in detail to determine the extent of diffusion.
Outcomes:	Computer models for matrix diffusion will be verified via in situ testing.


	The in situ porosity experiment
Aims:	To study changes in porosity around a fracture system, to determine the extent of connected pore space in the matrix and to compare in situ and lab derived porosity values. See also the PSG experiment.
Overview:	To inject specialised resins (including radionuclide doped resins) into a shear zone, and the matrix rock surrounding a shear zone. New techniques for field characterisation will also be investigated. Investigate links between hydraulic testing, lab-derived diffusion co-efficients and porosity changes at increasing depths from a shear zone.
Outcomes:	Development of field characterisation techniques, derive correction factors for lab-based porosity determinations.


	Natural Tracer Study
Aims:	To find evidence of long term diffusion to support the in situ derived data.
Overview:	Use natural tracers (natural radionuclides, stable isotopes and chemical signals) in the rock to provide evidence for long term (on a repository time scale) matrix diffusion (see example on the right from sedimentary rock in Northern Switzerland).
Outcomes:	Techniques and understanding will be developed and evaluated to provide high quality data for PA calculations on the extend of matrix diffusion.


	Diffusion Process Study
Aims:	Locate and quantify Cs-137 concentrations in the rock matrix and examine structural and mineralogical associations.
Overview:	Samples from the former Excavation Project will be re-examined for evidence of radionuclide matrix diffusion from the earlier Migration experiment (see CRR - Radionuclide Migration Programme - RMP ) using beta autoradiography and gamma spectrometry techniques.
Outcomes:	Provide further evidence for matrix diffusion.

Long Term Diffusion (LTD) Experiment

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