Development of a model for radionuclide transport by colloids in the geosphere

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ISSN 1018-5593 * * European Commission Development of a model for radionuclide transport by colloids in the geosphere Report EUR 17480 EN European Commission nuclear science and technology Development of a model for radionuclide transport by colloids in the geosphere J. van der Lee, E. Ledoux, G. de Marsily1 A. Vinsot2 H. van de Weerd, A. Leijnse3 B. Harmand, E. Rodier, M. Sardin, J. Dodds4 A. Hernández Benítez5 1 Ecole des Mines de Paris, Fontainebleau, France 2 Intakta, Saint Maur des Fossés, France 3 RIVM, Bilthoven, the Netherlands 4LSGC/CNRS, Nancy, France 5 Ciemat, Madrid, Spain Contract No FI2W-CT91-0079 Final report This work has been performed under a cost-sharing contract with the European Atomic Energy Community, in the framework of its fourth R&D programme on 'Management and storage of radioactive waste' (1990-94) Part A, Task 4: Disposal ofe waste Directorate-General Science, Research and Development 1997 EUR 17480 EN A great deal of additional information on the European Union is available on the Internet. It can be accessed through the Europa server (http://europa.eu.int.

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ISSN 1018-5593
* *
European Commission
Development of a model for radionuclide
transport by colloids in the geosphere
Report
EUR 17480 EN European Commission
nuclear science
and technology
Development of a model for radionuclide
transport by colloids in the geosphere
J. van der Lee, E. Ledoux, G. de Marsily1
A. Vinsot2
H. van de Weerd, A. Leijnse3
B. Harmand, E. Rodier, M. Sardin, J. Dodds4
A. Hernández Benítez5
1 Ecole des Mines de Paris,
Fontainebleau, France
2 Intakta,
Saint Maur des Fossés, France
3 RIVM,
Bilthoven, the Netherlands
4LSGC/CNRS,
Nancy, France
5 Ciemat,
Madrid, Spain
Contract No FI2W-CT91-0079
Final report
This work has been performed under a cost-sharing contract with the European Atomic
Energy Community, in the framework of its fourth R&D programme on
'Management and storage of radioactive waste' (1990-94)
Part A, Task 4: Disposal ofe waste
Directorate-General
Science, Research and Development
1997 EUR 17480 EN A great deal of additional information on the European Union is available on the Internet.
It can be accessed through the Europa server (http://europa.eu.int.)
LEGAL NOTICE
Neither the European Commission nor any person acting on
behalf of the Commission is responsible for the use which might be made of the
following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1997
ISBN 92-827-9626-4
© European Communities, 1997
Reproduction is authorized, except for commercial purposes, provided the source is acknowledged
Printed in Luxembourg Contents
Executive summary 1
A. Objectives and scope
B. Work programme 2
C. Results obtained 3
D. Prospects 9
Bibliography 12
1 Radionuclide and colloid behaviour in geosphere systems: new model
development and analysis of the theory 13
2 Radionuclide migration by colloids with the
classical transport code TRUMP 81
3 Development of a model for coupled colloid and contaminant trans­
port (COLTRAP) 12
4 Contribution to the comprehension of colloidal capture processes:
development of a linear two sites model 18
5 Experimental studies with columns of granitic materials from El
Berrocal site 229 Executive summary
A. Objectives and scope
The overall objective of the project is to describe, understand and model radionuclide
migration by colloids in the geosphere. By studying the behaviour of colloidal systems
in laboratory conditions, we attempt to construct a consistent theoretical framework
to describe and predict the behaviour of colloids in natural conditions and on space-
and time scales that are relevant to final disposal of radioactive waste. Apart from
model development this, project also involves an experimental part, to support the
theoretical developments and develop databases used by the models. The study was
done jointly by the following laboratories and research institutes:
- ARMINES/École des Mines de Paris:
Association pour la Recherche et le Développement des Méthodes et Proces­
sus Industriels; École des Mines de Paris, Centre d'Informatique Géologique,
Fontainebleau, France.
- INTAKTA:
INTAKTA France SARL, Saint Maur des Fossés, France
- RIVM:
Rijksinstituut voor Volksgezondheid en Milieuhygiene, Bilthoven, the Nether­
lands
- LSGC/CNRS:
Laboratoire des Sciences du Génie Chimique, Centre National de la Recherche
Scientifique, Nancy, France
- CIEMAT:
Centro de Investigaciones Energéticas Medioambientales, Madrid, Spain
(Subcontracted by ENRESA, Spain) Β. Work programme
Globally, this research project can be described in terms of three major packages. The
first package consists of a literature survey, summarizing a number of aspects relevant
to colloids in far-field geosphere systems. The second package is of experimental na­
ture, designed to support the development of the theory and to provide parameters and
constants needed by theoretical models. The third major package is the development
of conceptual models for radionuclide and colloid behaviour in dynamic groundwater
systems.
The research project was divided into a set of tasks:
• Task 1:
A literature survey covering field and laboratory studies involving colloids and
state-of-the-art modelling of colloid migration;
• Task 2:
First conceptual model formulation based on findings from task 1, screening of
important phenomena with simplified models;
• Tasks 3,4:
Planning and executing laboratory experiments, focussing on advection and dis­
persion processes of particles in purified and natural media;
• Task 5:
Second conceptual model formulation;
• Task 6:
Design and execution of laboratory migration experiments using field materials
from El Berrocal;
• Tasks 7,8:
Model development, verification, application to laboratory experiments (database
development) and application to performance assessment scenarios;
• Task 9:
Project management and coordination, editing of intermediate reports and the
final report. C. Results obtained
Literature survey (task 1)
A bibliographical report was compiled during the first year of the project. It cov­
ers all the major aspects of colloid transport relevant to model development. Each
partner provided a specific chapter and the final editing was by ARMINES/Ecole des
Mines de Paris and INTAKTA. The report, entitled "A bibliographical review of col­
loid tramsport through the geosphere" was published by the European Commission in
1994 [10].
Preliminary modelling studies (task 2)
In a first attempt to assess the impact of colloid formation after uranium leakage from
a waste repository, a macroscopic parametric transport model was developed and
applied to hypothetical deep-waste repository scenarios [9]. It showed that colloids
may considerably enhance radionuclide transport. The predicted breakthrough of
radionuclides is, however, highly sensitive to lumped parameters such as distribution
coefficients. The maximum adsorption capacity of the medium with respect to colloids
appears to be a key parameter, deserving more refined modelling than previously
proposed.
A second approach therefore included a different colloid-medium interaction model
based on the theory of electrostatic force-field development (the so-called DLVO-
theory). Colloid adsorption is described in terms of first-order rate laws (i.e. time-
dependent fluxes towards the surface), as a function of ionic strength and surface
potential. The results were published in the second and third progress reports, as well
as in van der Lee et al. [8].
The RIVM provided an analytical solution based on the theory of hyperbolic dif­
ferential equations for colloid-facilitated transport of contaminants when colloids are
not retained by the medium [11]. This model is proposed as a qualitative tool for
estimating the impact of colloids on the behaviour of radionuclides in natural systems.
On the basis of the findings in this preliminary modelling step, the decision was
taken to follow two parallel paths towards the final objective: a "parametric" approach
that is precise enough to model the data at different scales, but macroscopic enough
to remain practical and fast (the macroscopic approach); a "phenomenological" mod­
elling approach including all microscopic phenomena, down to the scale of the colloids
and solutes themselves (the microscopic approach). Eventually, this method could be
used to provide lumped parameters for predictive simulations with the macroscopic
approach. Laboratory experiments (tasks 3,4,6)
The LSGC studied transport of latex colloids in a natural sand using to a common
chromatographic method. The porous medium is a natural sand from Entraigues
(south of France) containing 81% of quartz. The clay fraction of the raw material is
relatively low (0.2 to 0.32% of the total mass) and was eliminated by washing.
The colloid suspension consists of spherical and mono-dispersed carboxyled poly­
styrene beads, so-called lattices. Three lattice diameters were used: 0.79 μηι, 0.21 μπι
and 0.11 μπι. In a common range of ionic concentration (10-4 M to 0.1 M) and pH
(3 to 10), the zeta potential of the lattices and the sand are negative; therefore the
elements of the system are expected to repel each other.
The experimental device is a classical liquid chromatographer where the particle
concentration is measured by optical density. Most of the experiments were made at
pH 5-6 which is the pH of aqueous solutions in contact with the atmosphere. The
dynamic behaviour of the artificial colloids was studied as a function of the following
parameters:
• colloid size
three different particle diameters were used, i.e. 0.11, 0.21 and 0.79 μηι. These
experiments indicate a lower retention capacity of the larger-size particles, pos­
sibly due to the fact that they are restricted to the largest pore sizes;
• flow rate
five different flow rates were used; an earlier (normalized) breakthrough was
found for higher flow rates. This suggests a possible effect of adsorption kinetics;
• ionic strength
three different concentrations of NaCl were used; the fastest breakthrough was
obtained for lower ionic strengths. This is explained by the electrostatic effects
on retention.
The conclusion from the experimental results on sand columns is that flow rate
and ionic concentration influence the retention of particles. The size of the colloidal
particles is important because the retention time can be very high if the particles are
very small. Capture by filtration may be important for latex colloids.
The contribution by CIEMAT involved characterization of a fractured granitic
medium, adsorption batch experiments and transport of colloids and radionuclides
through an isolated fracture in a granite core.
The adsorption coefficient of radionuclides with respect to the fracture infilling ma­
terial is an important quantity in the modelling. However, not enough of this material
was available for the batch experiments. Instead, CIEMAT obtained distribution co­
efficients of 60Co, '5Se and 13'Cs with different constituent minerals of the granite, i.e.