Rock matrix diffusion as a mechanism for radionuclide retardation

European Commission Directorate-General For Research And Innovation

Description

Natural radioelement migration in relation to the microfractography and petrophysics of fractured crystalline rock (Report on Phase 1)
Nuclear energy and safety

Informations

• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION
• Nombre de lectures: 12
• Langue: English
• Poids de l'ouvrage: 8 Mo

Extrait

ISSN 1018-5593
European Commission
nuclear science
and tedinolo^
Rock matrix diffusion as a mechanism for
radionuclide retardation: natural radioelement
migration in relation to the microfractography and
petrophysics of fractured crystalline rock
(Report on Phase 1) European Commission
nuclear science
and technology
Rock matrix diffusion as a mechanism for
radionuclide retardation: natural radioelement
migration in relation to the microfractography and
petrophysics of fractured crystalline rock
(Report on Phase 1
March 1991 - February 1993)
Compiled by
M. J. Heath
Earth Resources Centre, University of Exeter
North Park Road
Exeter EX4 4QE
United Kingdom
Participating Organizations
Earth Resources Centre, University of Exeter (United Kingdom)
University of Oviedo (Spain)
CEA (France)
University of Liverpool (United Kingdom) y of Oxfordd)
University of Franche-Comté, Besançon (France)
AEA Technology (United Kingdom)
Contract No Fl2W-CT91-0082
Topical report
Work as part of the European Atomic Energy Community's shared cost programme (1990-94) on
management and disposal of radioactive waste
Task 4: Disposal of radioactive waste
Directorate-General
Science, Research and Development
1995 EUR 15977 EN 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, 1995
ISBN 92-827-0152-2
© ECSC-EC-EAEC, Brussels · Luxembourg, 1995
Printed in Luxembourg Research Team, Rock Matrix Diffusion Project Phase 1:
M. J. Heath Earth Resources Centre, University of Exeter
J. Camp (UK)
R. Barillon
M. Montoto Area de Petrologia, Departamento de Geología,
A. Rodríguez-ReyUniversidad de Oviedo (España)
V. G. RuizdeArgandoña
Β. Menendez
Α. Martinez-Nistal
M. T. Ménager Centre d'Etudes Nucléaires de
C. Montjotin Fontenay-aux-Roses, Commissariat à l'Energie
Atomique (France)
A. G. Latham Archaeological Sciences, University of Liverpool
(UK)
G. A. D. Briggs Department of Materials, University of Oxford
(UK)
A. Chambaudet Laboratoire de Microanalyses Nucléaires,
C. Dubois Université de Franche-Comté, Besançon (France)
S Bassot
M. Rebetez
Isotope Geoscience Section, Harwell Laboratories M. Ivanovich
(UK) S. E. Hasler
A. Hernandez
Anatomisches Institut, Universitet Bern (CH) L. M. Cruz-Orive
(sub-contractor to University of Oviedo).
Ill ABSTRACT
Rock matrix diffusion is a potentially important radionuclide
retardation mechanism. To predict retardation, mathematical
models need data from actual sites. This study aims to provide
such data by investigating the petrophysical, microstructural,
geochemical and uranium series disequilibrium characteristics of
rock adjacent to fractures in El Berrocal granite (Spain).
Ultrasonic tests on cores EB4 (borehole S-16, ~38 m) and EB5 (S-
14, ~161 m) suggest microstructural changes adjacent to
fractures. Acoustic microscopy has revealed anisotropy in surface
wave velocity in thin sections; fluorescence microscopy has
allowed quantification on microcrack orientation which appears
anisotropic.
Uranium microcartography (fission track analysis and alpha-
autoradiography) has revealed three modes of U distribution: (1)
dispersed within primary phases; (2) point sources associated
with accessory minerals; and (3) linear distributionsd
with microfractures.
Uranium series/geochemical work on EB4 has shown a correlation
of U mobility with iron oxidation. The EB5 profile shows no
chemical U enrichment but the activity ratio suggests recent 234U
enrichment. The EB6 profile (S-14, -120 m) shows U enrichment on
the fracture, but the activity ratios suggest geologically-recent
U mobilisation in the entire profile.
These profile data are being used in the development of a
mathematical diffusion model. Chemical U profiles can be modelled
easily in terms of diffusion, but isotopie data are more
difficult to model. It appears that simple "matrix diffusion" has
not taken place, the observed migration resulting from a
combination of matrix diffusion and chemical interaction. CONTENTS
Abstract
Summary 1
1. Objectives 3
2. Project methodology
3. Work carried out during Phase 1, 1st March 1991
- 28th February 1993. 4
3.1. Field sampling and sample preparation
3.2. Petrographical and mineralogical studies 5
3.2.1. General characteristics 6
3.2.2. Major rock-forming minerals
3.2.3. Alteration products
3.2.4. Accessory minerals 7
3.3. Petrophysical studies and microscopy 8
3.3.1. Introduction
3.3.2. Anisotropy and elastic property profiles:
Non-destructive testing 9
Acoustic microscopy 12
3.3.3 Elemental physical properties and hydric
property profiles:
Physical and hydric properties6
Mercury porosimetry8
3.3.4. Determination of pétrographie profiles:
Stereological and digital image
processing data9
Quantification of cracks in quartz grains 23
Confocal laser scanning microscopy data 25
3.4. Uranium microcartography (fission track
analysis and alpha-autoradiography) 2
3.4.1. Fission track analysis8
3.4.2. Alpha-autoradiography
3.5. Uranium series investigations 30
3.5.1. Interlaboratory comparison, alpha
spectrometry2
3.5.2. Uranium series profile. Core EB4
3.5.3. Uranium series. Core EB53
3.5.4.ms.e EB6 3
VII 3.6. Geochemistry 33
3.6.1. Intertechnique comparison 3
3.6.2. Trace element geochemistry5
3.6.3. Uranium and thorium
3.6.4. Rare Earth spectra6
3.6.5. Iron chemistry
3.6.6. Other elements8
3.7. Uranium series diffusion modelling9
3.7.1. Assumptions and model 3
3.7.2. Results of simulations 40
3.7.3. Identification of processes affecting
fracture profiles
3.7.4. Fractures2
3.7.5. Uranium concentration variations4
3.7.6. Diffusion-modelled profiles7
3.7.7. Progress in model development9
4. Discussion and preliminary conclusions 50
5. Acknowledgements 5
6. References
Annex I. Neutron activation analysis: analytical
parameters and standards 55
Annex II. Results of geochemical analyses6
Figures 60
Vlil