NUMO-TR-04-05

Proceedings ofthe International Workshop on
Bentonite-Cement Interaction in
Repository Environments
14-16 April 2004, Tokyo, Japan

Richard Metcalfe, Colin Walker
Quintessa Japan

October 2004
Nuclear Waste Management Organization of Japan (NUMO)

NUMO-TR-04-05

This report is equivalent to Posiva Working Report 2004-25.

Inquiries about copyright and reproduction should be addressed to:
Science and Technology Department
Nuclear Waste Management Organization of Japan
Mita NN Bldg. 1-23, Shiba 4-chome, Minato-ku, Tokyo
108-0014 Japan
Phone +81-3-4513-1114 Fax +81-3-4513-1599©原子力発電環境整備機構 2004
Nuclear Waste Management Organization of Japan 2004

NUMO-TR-04-05

Executive Summary
This report describes an international workshop on bentonite-cement interactions in possible
future repositories for High Level Waste (HLW) and/or Spent Fuel (SF). The meeting washosted by NUMO and POSIVA from 14th - 16th April 2004 in Tokyo, Japan and aimed to
overview comprehensively the present knowledge about these interactions. A goal was to
identify key uncertainties and how these might be reduced by modelling and laboratory tests,
including tests in Underground Research Laboratories (URLs).
The document reports 20 presentations covering various aspects of cement-bentonite
interactions, which were given during five sessions:•

Session I: Repository concepts and the uses of cement;•

Session II: Mineralogy during bentonite-cement interaction;•

Session III: Barrier performance and functions during bentonite-cement interaction;•

Session IV: Modelling - detailed research models versus Performance Assessment (PA)models;•Session V: Concluding discussions.

Discussions related to the presentations are also reported and associated abstracts are given in
an appendix.
The various proposed uses of cement and bentonite are overviewed. In many repository
designs, bentonite would be used in engineered barrier systems, to retard radionuclide
migration and/or to control groundwater flow. Cement-based materials could also form an
important component of the barrier system and/or be needed during repository construction.
Depending upon the design, cement could physically contact the bentonite, or be sufficiently
close that alkaline pore fluid from the cement may interact with the bentonite.
The workshop highlighted that a lot of data about cement-bentonite interactions have beenacquired and the main processes have been identified. Consequently, priorities for future
experimental, field and theoretical work can be suggested and a Performance Assessment(PA) framework can be proposed.
Important statements from the workshop are:•

Mass transfer (both ions and neutral species) can occur in both directions over aninterface of highly compacted bentonite and concrete (transport of Mg, Ca, OH- etc inand out).

•

Mass transfer rates as a function of time at the bentonite-cement interface, as well as atdifferent depths in both materials, should be recorded in experiments and simulations,whenever possible.

iNUMO-TR-04-05•

The effects of cement on bentonite are mainly governed by the concentration and rate at
which OH- ions enter the bentonite.

•

From the point of view of buffer performance, the contribution of cations entering thebuffer (e.g. Ca2+, Na+) to the chemical potential of species in the clay pore water isimportant, and at least partly governs the buffer’s physical properties.

•

Two important and inter-related effects of a high pH plume on montmorillonite andaccessory minerals in highly compacted bentonite, which may affect the buffer functionsare:mineralogical alteration of bentonite components, which will consume the chemical
buffering capacity of the bentonite and affect the pore water chemistry;osmotic effects (e.g. differences between the activities of ions in the external solution
and the activities of ions in the inter-lamellar water solution), which are a function of
the external pH and influence the temporal sequence of mineral dissolution andprecipitation.

•

Experimental studies should focus on determining dissolution rates under alkalineconditions.

•Non-compacted bentonite and highly compacted bentonite are structurally quite different
materials, and therefore experimental results are not directly transferable. However,experiments using non-compacted materials may give thermodynamic data and useful
information about reaction rates and reaction mechanisms.

•

The pH buffering capacity of highly compacted bentonite is a key parameter. There is afast (surface hydroxyl sites) and a slow (montmorillonite crystal lattice) component in thebuffering capacity. The maximum total buffering capacity of bentonite with amontmorillonite content of 75 wt% is approximately 9.5 moles of OH- ions per kg of clay.

•

It is important to thoroughly understand the relative propagation rates of diffusing OHions and the reaction front of the alteration processes in highly compacted bentonite.
Over timescales relevant to PA, significant propagation of a high pH plume in the buffer
seems to be possible, but the potential overall consequences depend on the disposal
concept.

•

There is a risk of cementation of the bentonite buffer affected by a plume of high pH.
With some exceptions (i.e. calcite, gypsum) all the accessory minerals will transform tosecondary minerals upon reaction with high alkaline solutions. Since neo-formed
precipitates often have larger molar volumes than the reactants, cementation may be
accompanied by a porosity decrease.

•

The mechanical (e.g. swelling pressure, plasticity) and transport-related (e.g. diffusivity)
properties of highly compacted bentonite altered by a high pH plume have not been
investigated thoroughly.

•

There is conflicting experimental evidence as to whether the transport of a high pH plumeii

NUMO-TR-04-05

originating from NaOH solution would be significantly faster than that of a high pH
plume originating from Ca(OH)2 solution. Some experiments suggest that the rates
would be faster, whereas others imply no difference.
•

Where massive cement or concrete surrounds or neighbours bentonite such as thicktunnel liner around the buffer, the formerly dry bentonite will be saturated by cement
pore water. Initially this saturation process will lead to reaction of hydroxide with thebentonite. As long as mass transport through the concrete is dominated by diffusion, these
phenomena are relatively easy to model. Potential consequences can be reduced by taking
care of mass balances (thickness of the buffer vs. thickness of the concrete layer).

In summary, varied mineral dissolution, precipitation and alteration reactions will cause interrelated temporal changes in porosity, permeability and mechanical properties of bentonite. A
holistic understanding of these changes is needed to evaluate the overall safety implications.
Additional work should focus on developing integrated interpretations using presently
available data and improved coupled models of bentonite alteration should be developed.
A need for a more unified approach to identifying and implementing potential solutions toproblems with using cement and bentonite in barrier systems was identified. In particular it
would be desirable to improve communication between management, researchersinvestigating cement-bentonite interactions, and engineers and workers in the constructionindustry who will design and implement the barrier systems. It was also pointed out that
regulatory frameworks usually lag behind technological innovations that may constrain theuse of materials other than cement, when account is taken of the timescales of repository
projects.

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Contents
1

INTRODUCTION

12PROPOSED USES OF CEMENT AND BENTONITE IN REPOSITORIES

2

2.1

Types of radioactive waste and disposal concepts2

2.2

Proposed uses of cement in repositories

4

2.3

Proposed uses of bentonite in repositories

8

2.4

Requirement for cement and bentonite to be used together in
repositories

11

Alternative concepts

11

2.5
3

MINERALOGY AND GEOCHEMISTRY OF CEMENT-BENTONITE SYSTEMS
3.1

Experimental approaches

14

3.2

Processes

17

3.3

4

14

3.2.1

Cement degradation

17

3.2.2

Bentonite degradation

19

Data

25

3.3.1

Thermodynamic data

25

3.3.2

Kinetic data

26

EVALUATING THE PERFORMANCE OF CEMENT-BENTONITE BARRIER
SYSTEMS

iv

27

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5

4.1

Numerical modelling

27

4.2

Towards PA modelling approaches

29

4.3

Natural/anthropogenic analogues

32

ISSUES FOR CONSIDERATION IN DESIGN AND PERFORMANCEASSESSMENT OF HLW/SF REPOSITORIES

33

5.1

Approach to presentation of major issues

33

5.2

Issues discussed in the workshop

33

5.2.1

Achievements of research to date and priorities for future
work

33

Issues concerned with repository concepts and the uses of
cement34

5.2.3

Issues concerned with bentonite and cement mineralogy

35

5.2.4

Issues concerned with barrier performance and functions

36

5.2.5

Issues concerned with modelling

39

5.2.6

Issues for project management

41

5.2.2

5.3

Responses to a questionnaire

42

Appendix 1 - Workshop Programme

A1-1

Appendix 2 – List of Participants

A2-1

Appendix 3 - Extended Abstracts

A3-1

v

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TablesTable 1 Functions and requirements of the cement-based material components in a
HLW repository.
7
Table 2 Functions and requirements of bentonite components of HLW disposal (basedon Vieno, McKinley et al.).
9
Table 3 Key roles of bentonite and their sensitivity to degradation by cement(McKinley et al.). Each key problem has been identified as a result ofinteraction with cement leachate and bentonite.
12
Table 4 Alternative concepts for avoiding or minimizing the effects of
cement/bentonite interaction. Many of the suggestions are known technologies
in the construction industry, but have received little attention from theradioactive waste management industry (McKinley et al.).
13
Table 5 Summary of experiments described during the workshop, designed toinvestigate cement/bentonite interactions.
15
Table 6 Mineral transformations as bentonite degrades under high pH conditions (Odaet al.; Gaucher; Lehikoinen). Precipitating minerals have been tentatively
assigned to different groundwater conditions, although differences may arise
from those suggested here depending on local conditions.
21
Table 7 Rate laws governing the dissolution of montmorillonite.

23

Table 8 Summary of numerical modelling approaches described during the workshop.
Different approaches were taken to confirm experimental results and predictboth chemical and physical changes in materials as they degrade.
28
Table 9 Summary of predictive models described during the workshop. These models
assessed the depth of degradation of materials in the EBS as a function of time. 30

vi

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FiguresFigure 1 Summary of radioactive waste classification in Japan (after Kitayama et al). L1,
L2 and L3 wastes are all LLW consisting of materials such as insides of coresand channel boxes (L1), liquid condensate and concentrated metal (L2), andconcrete blocks (L3).
3
Figure 2 Outline of kinds of geological disposal proposed or adopted for the disposal ofdifferent sorts of radioactive wastes in Japan (after Kitayama et al).
5
Figure 3 A view of the LLW repository at Rokkasho, Japan (Kitayama et al.). Cement based materials form a major component of most of the barriers, surrounding
the waste packages, the backfill material, liners and floors.
6
Figure 4 Examples of the use of cement in a tunnel section of a HLW repository
concept (Kitayama et al.).
7
Figure 5 Design and use of bentonite in the planned spent fuel repository in Finland(Hansen). Shown is the KBS-3V type design. The spent fuel assemblies will bepackaged in copper-iron canisters, which are surrounded by a buffer of highly
compacted bentonite in the deposition hole. The material for the tunnel
backfill has not yet been determined.
10
Figure 6 Schematic representation of ion release from degrading cement (10 ml of
cumulative volume correspond to 1 sample pore volume) (Berner). The
apparent double peak in the sulphate concentration represents an experimental
failure.
18
Figure 7 Layered structure of montmorillonite where Al ions are sandwiched between
two inward pointing sheets of linked SiO4 tetrahedra. The basal surface runs
parallel to the silicate sheets whereas the edge surface is perpendicular to thesheets. The dissolution of montmorillonite is along the edge surface, reactive
sites are shown in colour (Sato et al.; Ichikawa et al.).
20
Figure 8 Proposed two step dissolution mechanism of montmorillonite under high pH
conditions (Sato et al.).
20
Figure 9 Cement/Bentonite interaction as a coupled non-linear dynamical system(Takase).
31

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Figure 10 Preliminary PA model scheme (Takase).

31

Figure 11 Theoretical anion activity (Cl- or OH-) from NaCl or NaOH solutions in Namontmorillonite as a function of montmorillonite dry density.
43
Figure 12 Montmorillonite swelling pressure as a function of dry density. No. 1 denotes
the osmotic effect of 1.0 M NaOH solution, and No. 2 denotes the effect ofmass loss due to dissolution of cristobalite, quartz and montmorillonite in a
specific test. Note the logarithmic scale on the Y-axis.
46

viii

NUMO-TR-04-05

1 INTRODUCTION
This report summarises an international workshop on bentonite-cement interactions inrepository environments that was hosted by NUMO and POSIVA from 14th - 16th April 2004
in Tokyo, Japan. The workshop’s purpose was to overview comprehensively the present
knowledge about these interactions. It was aimed to identify key uncertainties and how thesemight be reduced by modelling and laboratory tests, including tests in Underground ResearchLaboratories (URLs).
The host organisations are seeking to construct deep geological repositories for High Level
Waste (HLW)/Spent Fuel (SF). It was expected that the workshop would lead to a clearer
definition of key issues that should be considered in the design and Performance Assessment(PA) of such repositories. However, many of the conclusions ought also to be applicable togeological repositories intended for other kinds of waste. Designs proposed for repositories of
Low Level Waste (LLW) and Intermediate Level Waste (ILW, here considered to include
TRU wastes which contain significant quantities of long-lived transuranic nuclides) were also
considered.
The need for the workshop arose because bentonite and cement are components of many
designs proposed for underground repositories. In many cases bentonite would be used in thesystems of engineered barriers to radionuclide migration, to retard radionuclide migration
and/or to control the flow of groundwater. Cement could also form an important componentof the barrier systems. Even designs in which cement has no barrier function usually envisagethat cement-based materials will be needed during the construction stage.
The fact that cementitious materials will be far from equilibrium with the natural groundwaterconditions and with any bentonite component of a barrier system needs to be taken into
account when designing a repository. The use of Ordinary Portland Cement (OPC) may cause
formation of a high-pH groundwater plume that could in turn cause problematic chemical
reactions. From the point of view of long-term safety it might perhaps be most prudent toavoid OPC completely close to the areas of waste emplacement in a HLW or SF repository
and in such areas seek to replace it by other materials. With this goal in mind low-pH
substitutes are being developed and tested for some repository applications. However, it is notclear whether such materials will be available within the time frames of many on-going
repository programmes. Therefore, there is a continuing need to assess the implications ofusing cement-based materials.
During the workshop various aspects of cement-bentonite interactions were addressed by 20
presentations that were given during five sessions:•

Session I: Repository concepts and the uses of cement;•

Session II: Mineralogy during bentonite-cement interaction;•

Session III: Barrier performance and functions during bentonite-cement interaction;•

Session IV: Modelling; detailed research models versus PA models;•Session V: Concluding Discussions.

1

NUMO-TR-04-05

Extended abstracts containing supporting information were also prepared by all thecontributors.
The present document aims to summarise objectively the research results presented during
these sessions and in the supporting extended abstracts, together with details of the associateddiscussions. To highlight the major issues identified during the meeting, each of the following
sections juxtaposes key findings and arguments that were presented during several
contributions. The extended abstracts themselves and other supporting literature are thenpresented in the appendix.

2 PROPOSED USES OF CEMENT AND BENTONITE INREPOSITORIES
2.1 Types of radioactive waste and disposal concepts
Internationally different types of radioactive waste are being, or are planned to be, disposed ofin different kinds of geological repository. The detailed design of such repositories reflects the
specific characteristics of the wastes.
Different countries classify radioactive waste differently, according to varying criteria. The
kinds of waste referred to in the workshop are:•

LLW is produced mainly by routine operations of nuclear facilities, and by certain
laboratories and medical facilities. Such waste will also be produced duringdecommissioning. It is primarily contaminated by low concentrations of beta- andgamma- emitting radionuclides, though some material contaminated by alpha-emitting
nuclides may be present. It does not usually require special handling, unless alphaemitting.

•

ILW contains higher concentrations of beta/gamma contamination and sometimes alphaemitters. These wastes usually require remote handling, but produce little heat. Suchwaste originates from routine power station maintenance operations, such as ion
exchange resins. The waste is sub-divided into short-lived (usually with radionuclides
having half lives of less than 30 years) and long-lived wastes.

•‘TRU waste’ is defined as a separate category of waste in some countries and consists ofwaste containing a significant component of alpha-emitting transuranic nuclides. In somecountries these wastes are included in the classification of ILW.

•HLW usually comprises spent fuel and highly active bye-products from fuel reprocessing(if re-processing is part of the fuel cycle). The waste contains high concentrations ofbeta/gamma emitting fission products and alpha emitting actinides. HLW is a long-lived
waste type that produces significant heat and requires remote handling.

The classification of wastes adopted in Japan is illustrated schematically in Figure 1. The
corresponding kinds of adopted or proposed geological disposal facilities are given in Figure
2. Generally the depth of any geological disposal facility depends on:•

the radio activity of the wastes;2

NUMO-TR-04-05

α nulides

HLW

Uranium Waste

TRU waste

L1
L2
L3
Below
Clearance

βγ nuclides
Figure 1:

Summary of radioactive waste classification in Japan (after Kitayama et al).
L1, L2 and L3 wastes are all LLW consisting of materials such as insides ofcores and channel boxes (L1), liquid condensate and concentrated metal (L2),and concrete blocks (L3).

3

NUMO-TR-04-05•

the half-lives of the nuclides present in the waste;•

bedrock conditions at the disposal site.

Generally, the higher the overall radioactivity of the waste and the longer the half-lives of thenuclides present, the deeper will be a geological repository (Figure 2).
However, a feature of the different disposal concepts is the reliance to a greater or lesser
degree on a multi-barrier system comprising both engineered and natural barriers. The
Engineered Barrier System (EBS) will comprise mainly cement based materials for
LLW/ILW repositories and/or bentonite for HLW repositories while the natural barrier will bea carefully selected geological formation1.

2.2 Proposed uses of cement in repositories
Cement-based materials will be used as a major component of most barriers in a LLW, ILW
or TRU waste repository. Cement has properties that are well suited to containing
radionuclides by both physical and chemical processes making it a very attractive material touse as the main component of the EBS. These properties include:•

Buffering capacity determines the long-term chemical conditioning provided by the
cement in its ability to buffer the pH of invading groundwaters to values ≥ 12.5. Most
radionuclides have a very low solubility under these high pH conditions. Microbialactivity will also be suppressed.

•

Mechanical strength affects the ability of the cement to prevent structural collapse of
excavated cavities.

•

Permeability affects the rate of groundwater flow into and out of the repository, lower
permeability favouring the slowing of any potential release of the radionuclide inventory.

•

Sorption on CSH gel phases which are the major components of hydrated cements willretard the migration of radionuclides.

Cement will therefore be used as the material for walls and floors, for encapsulating the waste,
to backfill gaps between waste packages, and as a sealant for tunnels and shafts. A design of a
LLW waste repository illustrating these uses is given in Figure 3.
In the case of a HLW repository, cement is not considered part of the barrier system. Instead
only its physical properties in adding mechanical strength and impeding groundwater flow inthe pre-closure phase are considered important. Functions and requirements of cement within
the EBS depend on waste/repository type and whether pre- or post- closure, summarized inTable 1.
These components are represented in a schematic tunnel section of a HLW repository in
Figure 4.
1

e.g. a mudrock such as the Opalinus Shale in Switzerland (McKinley et al.) or a crystalline rock such as themigmatic mica gneiss that has been chosen in Finland (Hansen).

4

NUMO-TR-04-05
Reuse

L3
Front-end
Facility

L2
L1

Back-end
Facility

TRU Waste

HLW

Figure 2:

Industrial
waste
Controlled Disposal

Belowclearance

Ground Surface

～２ｍ
～１0ｍ

５０～
１００ｍ

Over
severalhundredmetersDeep Geological
Disposal

Power
Plant

Outline of kinds of geological disposal proposed or adopted for the disposal ofdifferent sorts of radioactive wastes in Japan (after Kitayama et al).

5

NUMO-TR-04-05

Figure 3:

A view of the LLW repository at Rokkasho, Japan (Kitayama et al.). Cement based materials form a major component of most of the barriers, surrounding
the waste packages, the backfill material, liners and floors.

6

NUMO-TR-04-05

Table 1:

Functions and requirements of the cement-based material components in a
HLW repository.
Components

Figure 4:

FunctionsPre-closure
requirements

Post-closure
requirements

Ensure mechanical
Structural liner stability of tunnels andshaftsMechanical strength

No detrimental effects
on other barriers

Grout – backwall

Provide contact between
liner and host rock
Suppress water inflow

Low permeability

No detrimental effects
on other barriers

Cover grouting

Suppress water inflow
through fractures

Low permeability

No detrimental effects
on other barriers

Confine andMechanical plug mechanically support
backfill material

Mechanical strength

No detrimental effects
on other barriers

Examples of the use of cement in a tunnel section of a HLW repository concept(Kitayama et al.).

7

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2.3 Proposed uses of bentonite in repositories
Highly compacted bentonite will be used as the buffer material around the waste package andas such, forms the bulk of the EBS. Water-saturated highly compacted bentonite is an ideal
barrier material because of its physical and chemical properties (Arthur et al.). These
properties include:•

diffusion barrier behaviour, which is due to the very low hydraulic conductivity that inturn causes the migration of any solutions through bentonite to be by diffusion only;•

low permeability, which should nevertheless be high enough to allow the passage ofgases generated from the corrosion of metallic components in the EBS, without cracking
or rupturing;•

colloid filtering behaviour, which is due to the very small grain size that effectively stops
the migration of any colloid-sized particles;•

ability to prevent growth of microbes, which is due the low water activity (availability offree water) in the highly compacted bentonite;•

sorption capacity, which is very significant for adsorbing any radionuclides that may bereleased from a canister and that is a consequence of the very high surface area with
abundant reactive sites and surfaces;•

thermal conductivity, which should be sufficiently high to ensure rapid dissipation ofradiogenic heat and is particularly important in the safe disposal of HLW;•

swelling pressure, which should be sufficiently high to sustain good contact with the hostrock and EBS, but not so high as to deform other components in the EBS or fracture thehost rock;•mechanical buffering/plasticity, which should be high enough to absorb rock movements,
but not so high as to cause the position of EBS components to shift in their deposition
holes or drifts.

Functions and requirements of bentonite within the EBS depend on waste and repository type.
Bentonite will only be used in LLW or TRU repositories as an outer layer between the cement
barriers and the host rock to ensure near-field solute transport is diffusion dominated(Kitayama et al.).
In the case of a HLW repository, the EBS will comprise almost exclusively bentonite, though
backfill may possibly also include crushed rock. In contrast cement is only to be used forstructural purposes. The functions and requirements of bentonite in the HLW repository aresummarized in Table 2.
The use of the bentonite buffer is shown in the conceptual design of the planned spent fuelrepository at Olkiluoto in Finland in Figure 5 (Hansen).

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Table 2:Components

Functions and requirements of bentonite components of HLW disposal (basedon Vieno, McKinley et al.).

Main functions

BufferEncase waste package
and:Protect the canister
against minor rockdisplacements
Act as animpermeable barrier
to the mass transport
by ground water
Provide geochemical
buffering andretardation capacity
Act as a colloid filter
prevent growth of
microbes
Conduct heat fromcanister to rock

Sealing plug

Confine backfill material
and retard release ofradionuclides

Backfill

Have lowpermeability forground water
Keep the canister andthe buffer in place
Help keep the tunnel
mechanically stable

Pre-closure
requirements
Restrict mass transfer
rates between thecanister and host rock
Have chemical andmechanical stability
No harmful effects on
the other barriers

Post-closure
requirements
Restrict mass transfer
rates between thecanister and host rockBe sufficiently
permeable to gases
Have chemical andmechanical stability
No harmful effects on
the other barriers

Restrict mass transfer
rates along back-filled
tunnels/shafts
Have chemical andmechanical stability
No harmful effects on
the other barriers
Restrict mass transfer
rates along back-filled
tunnels/shafts
Be chemically andmechanically stable
Have no harmful
effect on otherbarriers

Restrict mass transfer
rates along back-filled
tunnels/shafts
Have chemical andmechanical stability
No harmful effects on
the other barriers
Restrict mass transfer
rates along back-filled
tunnels/shafts
Be chemically andmechanically stable
Have no harmful
effect on otherbarriers

9

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Figure 5 :Design and use of bentonite in the planned spent fuel repository in Finland(Hansen). Shown is the KBS-3V type design. The spent fuel assemblies will bepackaged in copper-iron canisters, which are surrounded by a buffer of highly
compacted bentonite in the deposition hole. The material for the tunnel
backfill has not yet been determined.

10

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2.4 Requirement for cement and bentonite to be used together in
repositories
Most proposed repository concepts have cement-based materials and bentonite in close
proximity. However, high pH cement-conditioned water has undesirable effects on theproperties of bentonite, summarized in Table 3.

2.5 Alternative concepts
Strategies for avoiding cement/bentonite interaction have been suggested and include:•

Alternative materials could replace bentonite components in the cases of LLW and TRU
waste repositories and cement in the case of HLW waste repositories.

•

Alternative designs could avoid the close proximity of cement based materials andbentonite.

•

Removal of cement used in pre-closure phases could be carried out before the final
closure of a repository.

•

Low-pH (less alkaline than conventional cements) could be developed.

A summary of these concepts is given in Table 4.
In practice, however, it may not be possible to avoid using cement-based materials andbentonite in close proximity in a repository environment. These reasons may include:•

Regulatory issues affecting alternative construction materials in a repository environment
remain largely unaddressed. Cement, however, is a widely used construction material andits mechanical, physical and chemical properties have been identified (although notnecessarily understood) and will therefore behave in a predictable manner.

•

Scheduling may have been largely decided (as is the case in Finland) and could limit thescope for additional research into new materials and technologies and the development of
new working repository concepts.

11

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Table 3:Key roles of bentonite and their sensitivity to degradation by cement(McKinley et al.). Each key problem has been identified as a result ofinteraction with cement leachate and bentonite.

Bentonite role

Significance of cement
leachate for bentonite
role

Diffusion barrier

Major

Colloid filter

Major

Radionuclide sorption

Some

Plasticity (gas flow)

Major

Thermal conductivity

None

Mechanical buffer

Some

Microbe barrier

Some

12

Key potential
problem
Cementation/
cracking,
Montmorillonite
dissolution
Cementation/
cracking,
Montmorillonite
dissolution
Ion exchange,
Montmorillonite
dissolution
Cementation,
Montmorillonite
dissolution
Not Applicable
Cementation,
Montmorillonite
dissolution
Cementation/
cracking,
Montmorillonite
dissolution

NUMO-TR-04-05

Table 4 :Type

Alternative concepts in avoiding or minimizing the effects of cement/bentonite
interaction. Many of the suggestions are known technologies in theconstruction industry, but have received little attention from the radioactive
waste management industry (McKinley et al.).

TRU

Component/
strategy used tominimisecement/bentonite
interaction
Hydraulic cage

TRU

Colloid filter

HLW

HLW

Repository design(e.g. aligning
tunnels)
Retrieving
cement before
closureStructural liner

HLW

Cover grouting

HLW

Mechanical plug

HLW

Floors

HLW

Material

Advantages

Disadvantages

Relatively highpermeability material
such as gravel

Avoid
advective
flow driven by
hydraulic gradients
Minimises effectsof cementation or
cracking
Avoids release ofgas by acting as a
macro-porous
buffer.
Filters colloids that
may bind withradionuclides

Long-term performance
unknown

Reduces total amountof cement in
repository
Reduces total amountof cement in
repository
Reduces total amountof cement in
repository
Reduces total amountof cement in
repository

Long-term mechanicalstrength of repository
may be compromised
Long-term mechanicalstrength of repository
may be compromised
Long-term performance
unknown

Reduces total amountof cement in
repository
Reduces total amountof cement in
repository

Long-term performance
unknown

Special plastic
Self-healing
concretes
Zeolites
Not applicableNot applicable
Steel
Ceramics
Natural stone
Resin
Clay
Carbonate/silicate
cements
PEM(Prefabricated
EBS
Module)1Natural stone
MetalsGravelNaturalpavingstone

1Long-term performance
unknown

Long-term performance
unknown (organics
should probably be
avoided in HLW/SF
repositories)

a pre-fabricated module consisting of multiple barrier components such as bentonite inside a steel liner,
surround by sacrificial material (crushed tuff, volcanic glass etc) and a concrete liner on the outside.

13

NUMO-TR-04-05

3 MINERALOGY AND GEOCHEMISTRY OF CEMENTBENTONITE SYSTEMS
Cement/bentonite interaction is a key issue in the longevity of a TRU or HLW repository. The
main problem is the degradation of the bentonite barrier as a result of groundwater that has
been conditioned by the adjacent cement. Through experimentation, key
chemical/geochemical processes have been identified.

3.1 Experimental approaches
A lot of detail regarding the cement/bentonite interaction has been obtained throughexperimental studies. Experimental approaches reported during the meeting included:•

Batch reactors:
Bentonite and crushed rock with synthetic saline waters
Cement in H2O•

Flow through reactors:
Bentonite and crushed rock with synthetic saline waters
Bentonite with NaOH-NaCl, KOH-KCl and Ca(OH)2-CaCl2 solutions (most common
approach)
OPC and H2O•

Diffusion flow reactors:
Sand/bentonite mixture in synthetic cement/groundwater

Details of the experiments are given in Table 5.
Additionally, there was some discussion of studies of experiments that are reported in the
published literature. It was highlighted that most published data are for experiments withmudrocks rather than isolated smectite. Furthermore, experiments have been carried out undera wide range of conditions and the results are difficult to compare in a meaningful fashion.
Similarly, when bentonite has been used in experiments, there is a question as to the purity ofthe smectite present.
It was noted that the solubility of NaOH and Ca(OH)2 in pure water is of quite a different
order: at 20°C, c.44 mol/L and c.0.04 mol/L, respectively. Hence experiments with NaOH
solutions can reach much higher pH values/OH--ion concentrations.

14

Karnland
et al.

Sato
et al.

15
30,
50, or70

Room

0.3M NaOH

Acid added to
pH = 4, Alkali
added to pH =10

0.1, 0.3 or
1.0M NaOH,
1M KOH,
0.02M
Ca(OH)2(saturated) ,1M NaCl and
H2O

Namontmorillonite

Namontmorillonite

Namontmorillonite

Namontmorillonite

Na-, K- or Caexchanged
MX-80
bentonite(dominantly
montmorillonite)

In situ within
AFM
chamber

In situ within
AFM
chamber

Batch reactor

Titration

Batch
diffusion cell

50

1.0M NaOH NaCl

Namontmorillonite

Flowthrough cell

0.3M NaOH

0.3M NaOHNaCl or 0.3M
KOH-KCl

OPC

25

25

30,
50, or70

25

Deionized H2O(replaced every
24 hours)

Accelerated
batch reactor

T
(°C)

25

Solutions

Deionized H2O

OPCBatch reactor

Otsuki

SolidsExperiment
design70 to 100days

Not
applicable

6 to 33days< 1 dayc. 1.5hours and2-8 days

7 to 10
days

c. 9
weeks

c. 1 week

Duration

Yes

Determine
dissolution
rates andmechanism

Determine
dissolution
mechanisms

Determine pH
buffering
capacity,changes inmineralogy,
swellingpressure, CEC

pH as afunction of time
CationExchange
Capacity(CEC),
mineralogy,
mineral andpore watercompositions(including pH),and swellingpressure

Starting andfinal mineralparticle size

Mineral particle
size over time

Mineral particle
size over time
Determine
dissolution
rates andmechanism
Determine
dissolution
rates andmechanism

Yes

Determine
dissolution
rates andmechanism

Solutioncomposition
over time

No

Test a model
for leaching of
calcium from
cementCementchemistry andcompressive
strength

Yes

Yes

Yes

Yes

No

Test a model
for leaching of
calcium from
cementCementchemistry andcompressive
strength

Reactionmechanisms

Main PurposeMainparameters
tested

Yes

No

Yes

Yes

Yes

Yes

Yes

Yes

Kinetic

No

No

No

No

No

No

No

No

Thermodynamic

Yes

No

No

No

No

No

Yes

Yes

Mass
balances

Major types of information obtained

No

No

No

No

No

No

Yes

Yes

Transport
parameters

Summary of experiments designed to investigate cement/bentonite interaction described during the workshop.

Contributor

Table 5:

No kinetic parameters orrate laws were deduced

Particle sizes measured
by AFM during reaction.
Kinetic parameters were
derivedParticle sizes measured
by AFM after reaction.
Kinetic parameters were
derivedParticle sizes measured
by AFM during reaction.
Kinetic parameters were
derivedA rate law and kinetic
parameters were derived

Experimental results
were not used to derive amodel, only to test it No
kinetic parameters or rate
laws were deduced

Experimental results
were not used to derive amodel, only to test it No
kinetic parameters or rate
laws were deduced

Comments

NUMO-TR-04-05

16

BernerIto et al.

Yamaguchi
et al.

Vuorinen
et al.

Contributor

OPC

OPC

OPC

Batch

Flow throughFlowthroughDeionized H2ODeionized H2O
or 1M NaNO3

Deionized H2O

0.5M and
10-5M NaOH

Compacted
sand and Namontmorillonite (Kunigel
V1)

Diffusion
cell

Flowthrough cell

Batch reactor

Crystalline
rock from
Olkiluoto andMX-80
montmorillonite

Batch
reactor

Na-Cl-OH
water,
0.1, 0.3, 1 M
NaOH

High pHsynthetic NaCa-Cl waters(fresh andsaline pH =12.5; saline pH= 13.5)Synthetic fresh
ground water,
Na-Ca-Cl waterand high pH
Na-Ca-Cl water(fresh + saline,
pH = 8.8 and
8.3; saline pH= 12.5)

Crystalline
rock from
Olkiluoto or
MX-80
montmorillonite

Compacted
sand and Namontmorillonite (Kunigel
V1)

Solutions

SolidsExperiment
design

Room

20

20

10 to
90

50 to
170

c. 25

c. 25

T
(°C)

Yes

Determinesecondaryminerals,
alteration
reactions andpropagation ofan alkaline
plume
Determine
dissolution
rates andmechanisms

Mineral andsolutioncompositions(out-flow andpore water),
CEC
Mineralogy,
remainingmontmorillonite and Si, Al
and Caconcentrations
in solutions

Solutioncomposition

2 years

To >3
years
(3000
pore
volumes)

Yes

No

Determinechemicalmechanicalhydraulicproperties

Hydraulic andmechanicalproperties

Determinesolutioncomposition as
a function of
time

No

Determinechemicalmechanicalhydraulicproperties

Hydraulic andmechanicalproperties

2 years

Yes

Determinediffusivity ofalkali solutions
in bentonite

Yes

Yes

Reactionmechanisms
Determinesecondaryminerals,
alteration
reactions

Mineral andsolutioncompositions

Main purpose

Dissolution
rates

18 to 28
weeks

4 to 8weeks

1 year and
1.5 years

1 week to
1.5 years

Duration

Table 5. Continued.
Mainparameters
tested

Yes

No

No

Yes

Yes

Yes

Yes

Kinetic

Yes

No

No

No

No

No

No

Thermodynamic

No

No

No

Yes

Yes

Yes

Yes

Mass
balances

Major types of information obtained

No

Yes

Yes

Yes

No

Yes

No

Transport
parameters

Only experiments
described by Berner thatwere carried out at PSI
are considered. No rate
laws or parameters
derivedLeaching tests provided
material suitable formechanical testing

Leaching tests provided
material suitable formechanical testing

Kinetic parameters were
derivedKinetic parameters were
derivedNo kinetic parameters orrate laws were deduced

No kinetic parameters orrate laws were deduced

Comments

NUMO-TR-04-05

NUMO-TR-04-05

3.2 Processes
3.2.1 Cement degradation
Variations in the chemistry of pore water released from cement as a function of time aresummarised in Figure 6. Cement dissolution releases mainly Na, K, OH (early), and Ca, OH(later).
The initial high Na and K concentrations are a consequence of the non-restricted solubility of
NaOH and KOH present in freshly hydrated cement. The following increasing/high Ca
concentration is a result of Ca(OH)2 solubility. The peak in SiO2 reflects SiO2 release from
CSH phases (Berner).
The effect on cement of releasing these components is to increase porosity and permeability
and to lower compressive strength (Otsuki; Ito et al.). The last two effects have been found to
be a function of the former. However, these effects are countered by cementation processes(e.g. carbonation/calcite precipitation), which can lower the effective porosity, and therefore
the permeability, to almost zero (Berner).
Local groundwater flow and transport conditions have a major influence on the release andtransport of cement and subsequently on the magnitude of the high pH plume (Vieno).
Important controlling factors include:•

Sub-horizontal fracture zones divide the flow pattern into layered zones. It is unlikelythat a significant amount of cement above or from major sub-horizontal zones would betransported into the sparsely fractured rock below the zones.

•

The water leaving a grouted rock spot will not have the pH and other properties of
cement pore water, but is diluted by the groundwater flowing around/through the
grouted area. This source term dilution is enhanced by the fact that grouting is carriedout at fracture zones and other locations where flow rates are highest.

•

Further buffering and dilution take place during transport in the geosphere. In open
fractures with a limited buffering capacity and a small WL/Q (half of the “flow wetted”
surface divided by the flow rate), the leachate may, however, be transported over long
distances.

•

Transfer of OH- ions from water-conducting fractures intersecting a deposition hole islimited by the boundary layer (film) resistance between the flowing groundwater andthe stagnant pore water in the buffer. The fraction of OH- ions entering the buffer
decreases with an increasing flow rate of groundwater along the fractures.

17

NUMO-TR-04-05

Figure 6:

Schematic representation of ion release from degrading cement (10 ml of
cumulative volume correspond to 1 sample pore volume) (Berner). The
apparent double peak in the sulphate concentration represents anexperimental failure.

18

NUMO-TR-04-05

3.2.2 Bentonite degradation
One of the most predictable changes is an increase in the pH of the buffer pore water(Gaucher). This increase influences significantly both the chemical and physical properties ofthe buffer including:•

The structure of montmorillonite consists of superimposed layers, each of which contains
a plane of Al ions sandwiched between two inward pointing sheets of linked SiO4
tetrahedra. These layers are separated by a cation exchange layer, shown in Figure 7(Sato et al.; Ichikawa et al.).
Montmorillonite dissolves along the edge surface whereas the basal surface remains
relatively un-reacted, apart from minor pitting (Sato et al.). A two-step mechanism for the
dissolution of montmorillonite is shown in Figure 8.
Reaction between the hydroxyl groups in the cement leachate and bentonite gives asignificant release of silicon (Karland et al.). Initially silicon in solution is controlled by
the dissolution of silica polymorphs (cristobalite and quartz) followed by the dissolutionof montmorillonite (Karnland et al.).
The release of silicon from montmorillonite is shown to by some studies to beincongruent (silicon is released preferentially compared to the concentration of othercomponents) and conditions move towards the stability field of beidellite (Karnland etal.). This behaviour is supported by the presence of beidellite in the results of Vuorinen et
al. Conversely, Sato et al. suggest the dissolution of montmorillonite is congruent basedon the concentrations of silicon and aluminium in both NaOH and KOH solutions
corresponding to the stoichiometry of montmorillonite.

•

Secondary minerals will form as a result of the interaction between cement leachate andbentonite. The types and abundances of secondary minerals will reflect the compositionof the solution phase (pH, pe, cations etc). The important minerals associated with thedegradation of bentonite are identified in Table 6.
Some of these phases are believed to be metastable on the timescales relevant to thesafety assessment of a waste repository. Given enough time these solids could transform
into other more stable phases under the prevailing local conditions (Oda et al.; Gaucher).
Some potential reaction paths are:Montmorillonite -> Illite -> Zeolites
Montmorillonite -> Illite -> Saponite -> Clinochlore
Montmorillonite -> Illite -> Phillipsite -> K-Feldspar
Problems still persist in predicting which of these secondary phases will be importantbecause of the poor knowledge of possible reaction products (including some which may
not yet have been identified), mineral dissolution rates and growth kinetics which are
subject to considerable uncertainty (Lehikoinen).

19

NUMO-TR-04-05

Figure 7:

Layered structure of montmorillonite where Al ions are sandwiched between
two inward pointing sheets of linked SiO4 tetrahedra. The basal surface runs
parallel to the silicate sheets whereas the edge surface is perpendicular to thesheets. The dissolution of montmorillonite is along the edge surface, reactive
sites are shown in colour (Sato et al.; Ichikawa et al.).

Figure 8:

Proposed two step dissolution mechanism of montmorillonite under high pH
conditions (Sato et al.).

20

NUMO-TR-04-05
Table 6:

Mineral transformations as bentonite degrades under high pH conditions(Oda et al.; Gaucher; Lehikoinen). Precipitating minerals have beententatively assigned to different groundwater conditions, although differences
may arise from those suggested here depending on local conditions.
Precipitating minerals (theoretical and observed)

Original minerals
in bentonite

Dissolving
minerals

NaOH
dominant
solution

Namontmorillonite

Namontmorillonite

NaBeidellite

GypsumGypsumAnalcime

AlbiteAlbiteSilicapolymorphs

Silicapolymorphs

KOH dominantsolution

Ca(OH)2 dominantsolution

Other

IlliteCa –Montmorillonite

HalitePhillipsite

CalciteCSH

K-Feldspar

Chlorite
CAH

Muscovite

QuartzCASH

Calcite21

NUMO-TR-04-05•

Cation exchange reactions may occur at the same time as the mineral transformations inTable 6. Notably, Mg-exchanged sites (MgX2) in the unaltered bentonite will become Naexchanged (NaX) in NaOH solutions, K-exchanged (KX) in KOH solutions and Caexchanged (CaX2) in Ca(OH)2 solutions.

•

Cation Exchange Capacity (CEC) is significantly increased on exposure to strong NaOH
solutions (>0.3M) (Karnland et al.) and synthetic high pH Na-Ca-Cl waters (molar ratios
of Na/Ca ~ 2.4, 24 and 2330; Vuorinen et al.). In contrast, solutions exposed only to NaCl
and Ca(OH)2 saturated solutions show no significant change. Although replacement of
Na in the montmorillonite by Ca was found for the experiments conducted in the
Ca(OH)2 saturated solutions (Karnland et al.) and controlled replacement could beachieved using a CaCl2 solution (Ito et al.).

•

Dissolution rates of minerals in bentonite are strongly dependent on pH and temperature.
The dissolution rate increases with an increase in pH and/or temperature (Sato et al.).
The rate of dissolution at any time will also depend on the degree to which equilibrium isapproached. Solids that are far from equilibrium with respect to a particular solution will
dissolve much faster than solids that are close to equilibrium (Takase).
Similar rates are obtained from Si and Al concentrations, and NaOH and KOH
experiments, showing no effects of interlayer cation on dissolution rates (Sato et al.).
A summary of the dissolution rate laws presented at the workshop is given in Table 7.

•

The buffering capacity of unpurified bentonite may be controlled by silica polymorphs in
the early stages of degradation because of their faster dissolution when compared tomontmorillonite (Lehikoinen).
The buffering capacity of montmorillonite is the sum of two contributions:the edge surface hydroxyl sites (see Figure 7) which undergo very fast reactions;the montmorillonite structure itself, which tends to undergo slow reactions and will
not buffer the pore fluid chemistry until the edge surface sites have been exhausted.
The interaction between the montmorillonite and hydroxide ions takes place accordingto:Na-montmorillonite + 6H2O + 4.67 OH- => reaction products (Lehikoinen)orNa-montmorillonite + 2H2O + 4.68 OH- = reaction products (Takase)
Meaning one mole of Na-montmorillonite consumes 4.67 moles of OH-, or 12.7 moles of
OH- are buffered per kilogram of clay. This is deemed acceptable to keep the pH below
11, by neutralizing at least 0.5 moles of OH- per kg of clay (Lehikoinen).

22

NUMO-TR-04-05

Table 7:

Worker:Rate laws governing the dissolution of montmorillonite, mentioned during theworkshop.

Yamaguchi et al.

−48000RT

Rate law: R A = 0.8[OH ] e
Source:Experimentally derived
T (°C):
50 - 170
pH:
13 - 14
Comments: Also used by Takazawa et al.
Worker: Sato et al.
Rate law:177⋅ e20.4/ RT ⋅ aOH+
0.0297⋅ e23.5/ RT ⋅ aOH+ −6−39.6 / RT
−69.7 / RT
R A =  4.74⋅10 ⋅ e⋅+1.70⋅ e⋅
1+177⋅ e20.4/ RT ⋅ aOH+
1+ 0.0297⋅ e23.5/ RT ⋅ aOH+ 



− 1.4

∆G

( −6⋅10−10 )⋅( r )6 RT 
⋅  1− e
Source:Experimentally derived
T (°C):
30, 50 and 70
pH:
8 - 13.5
Worker: Lehikoinen−12.31
0.34⋅ aOH−
Rate law: R A = 10
Source:Huertas et al. (2001)
T (°C):
25
pH:
12.5
Worker: Takase  Q  6 
−0.34
Rate law R A = k.A.(aH + ) .1− exp−alog    K  
(1):−0.34 QRate law
R A = k.A.(aH + ) .1− 
 K
(2):
Source:Fujiwara et al. (2003)
T (°C):
pH:
Comments: a = 6e-10 and logK = -17.1
Rate law 1 is based on the empirical model suggested in Cama et al. (2000) andRate law 2 is derived from transition state theory

Where: RA is the specific rate (usually molm-2s-1) k is the rate constant; a and A are constants; Q is the ion
activity product for the montmorillonite; K is the equilibrium constant for the dissolution of montmorillonite; R
is the gas constant (8.314 Jmol-1K-1); T is the absolute temperature.

23

NUMO-TR-04-05

In highly compacted bentonites, the pH buffering capacity is at a maximum because thesolution migration is diffusion controlled (Lehikoinen).
•

Solution modelling predicts that with the precipitation of zeolites, associated with themineralogical changes, the pH of the cement leachate is neutralized, which in turn may
inhibit further dissolution of the bentonite (Oda et al). Swelling pressure is reduced on
exposure to high concentration NaOH and NaCl solutions (>0.3M). A major difference
was that NaCl gave a rapid decrease to a new stable pressure value, while contact with
the NaOH solution gave a gradual decrease (Karnland et al.). Low concentration NaOH
solution and Ca(OH)2 saturated solution had no effect on the swelling pressure (Karland
et al.).
Consolidation tests show that the greater the difference between the pre-consolidationstress (overburden pressure) and the current overburden pressure (i.e. unloading ofoverburden pressure due to adjacent cement dissolution) the greater the tendency for thematerial to swell (Ito et al.).

•Precipitation/cementation processes are difficult to evaluate. Depending on experimental
set up (e.g. flow through reactors), some workers found that precipitation/cementation
effects were not significant. However, this may not be truly representative of a realsystem where secondary minerals are likely to grow in situ (see precipitating minerals in
Table 6).
Cementation may be a significant issue because of the increased chance of the bentonite
barrier cracking and solution transport being advective as opposed to diffusive(McKinley et al.).

•Porosity has been described as either increasing or decreasing as a function of dissolution
and precipitation rates of the primary and secondary minerals. In the long term this will
depend on the stability of these secondary phases once formed (Arthur et al.). Where only
dissolution of the bentonite is considered (e.g. Kato et al.), the porosity increases. If
considering the growth of alteration products they are likely to form in situ (cementation)and so decrease the porosity (e.g. Berner; Gaucher).

•

Permeability and porosity are strongly dependent on each other. Similarly, permeability
will increase or decrease as a function of the dissolution and precipitation of the primaryand secondary minerals.

•

Hydraulic conductivity is related to the permeability and porosity of the bentonite.
Predictive modelling has shown the hydraulic conductivity to generally increase withongoing exposure to a high pH plume (Kato et al.). Similarly this is dependent on the
dissolution and precipitation rates of the primary and secondary minerals.

•

Diffusivity of bentonite has been predicted to decrease as a function of time (Kato et al.).
This can be attributed to the decreasing difference in solution concentration across the
EBS and the decrease in porosity due to cementation by secondary minerals.

•

Sorption will be important and an intact bentonite has excellent sorption capability, oneof the main criteria for using it. However, assessing the sorption capability of secondary24

NUMO-TR-04-05

minerals is difficult and results in uncertainty as to the evolution of sorption capacity as afunction of time.
•

Shear strength (the ability to resist failure by a shear motion stress field) is independent of
sodium replacement calcium in montmorillonite (Ito et al.).

Other relevant factors which were mentioned, but not addressed, include:•density;•settling;•

swelling of corrosion products;•

construction defects;•

microbial activity;•

gas generation.

3.3 Data
3.3.1 Thermodynamic data

There is a great need for better thermodynamic data to access the significance of potential
geochemical reactions under different scenarios pertinent to the needs of a particular country.
General issues relevant to this problem, which apply to both cement and bentonite are given
below.
•The mineralogy, structural formulae and crystallinity of secondary solids are not welldefined.

•Thermodynamic properties of representative clay minerals, zeolites and CSH/CASH
solids/gels are poorly known.

•

Minerals formed initially tend to be metastable and may transform into other more stablephases over the timescales involved.

•

Precipitates may be amorphous or poorly crystalline and may persist metastably withrespect to their crystalline counterparts for a very long time.

•

Crystalline solids are often complex solid solutions that exhibit a wide range ofcomposition depending on the chemistry of the coexisting aqueous phase. Currently solid
solution modelling is not employed in repository degradation models.

•

Databases are of variable and often uncertain quality and notably:data for a particular phase of importance for radioactive waste PA is often missing;25

NUMO-TR-04-05

databases often have internal inconsistencies;
peer-review of data entries is often lacking.
•

There are poor data for aqueous species at high pH (especially Si- and Al- species).

A particular issue in the case of cement is that Ca(OH)2(s) solubility is not well known anddepends on the method used for deriving activity coefficients. This is critical because theselection affects further high pH items in databases. (e.g. CaOH+ reactions).
Some of these issues can be addressed by:•using a peer reviewed database as a starting point, such as SPRONS.JNC, to which data
are systematically added;•

using numerical approaches that allow reasonable estimates to be made and uncertainties
to be assessed;••

carrying out additional experiments for key phases to support these estimations;estimating bounding parameter values;•

assigning the same bounding parameter values (e.g. equilibrium constants) to groups ofsimilar minerals;•

deriving relevant data for all the different minerals which may form in the EBS system asa result of cement/bentonite interaction.

A key issue for consideration is the validity of estimation techniques. Is it realistic to rely on
estimated thermodynamic quantities or should the focus remain on deriving the relevant data
for all the different minerals (the approach adopted by Gaucher)?
3.3.2 Kinetic data

There is similarly a great need for more reliable kinetic data for relevant mineral phases, inthe cases of both cement and bentonite.
Significant progress has been made in bounding rates and determining relative rates ofreaction. An important issue is whether this progress is adequate for the needs of barrier
design and ultimately PA.
However, compared to uncertainties associated with thermodynamic data, even greater
uncertainties are associated with kinetic data.
Problems still persist in the derivation of reliable kinetic data, notably:•

It is particularly difficult to obtain reliable rates under high pH and temperature
conditions, whether in the cases of bentonite or cement.

•

In the cases of experiments aimed at understanding cement and/or bentonite alteration
most workers tend to choose specific experimental conditions. This was partially26

NUMO-TR-04-05

addressed by Sato et al. who conducted their experiments over a range of temperatures,from 30 - 90°C.
•

Bentonite is a mixture of different minerals containing primarily montmorillonite, butalso gypsum, silica polymorphs, albite and calcite. Purification of montmorillonite isparticularly difficult and so experimental studies invariably investigate the dissolution ofa mixture of these minerals.

•

Dissolution of the primary minerals verses the growth of secondary minerals in bentonite
is largely unknown. Combined with the variability in groundwater conditions (pH, pe,temperature, species in solution, etc.) gives a large number of kinetic controlling factors
which are poorly constrained.

•

In the cases of minerals present in bentonite or cement, different rate laws can be derived
from the same experiment depending on the fitting parameters and assumptions made.

As in the case of thermodynamic data, a potentially fruitful approach is to either estimate rates
or obtain experimental rates for groups of chemically and crystallographically similar
minerals.

4 EVALUATING THE PERFORMANCE OF CEMENTBENTONITE BARRIER SYSTEMS
4.1 Numerical modelling
Numerical modelling provides a very useful tool in predicting mineral (both chemical andphysical) and solution properties in the long term evolution of a HLW repository. The major
available modelling approaches are equally applicable to both bentonite and cement alteration.
However, though a multitude of these different approaches were discussed during theworkshop, not all were applied to both bentonite and cement in Table 8.
In summary, the main modelling approaches are:•forward modelling (equilibrium and kinetic);•

inverse modeling;•

coupled chemical/mass transport modelling (mostly using 1D transport codes);•coupling handled by a single code;•

different aspects handled by different codes (e.g. PHREEQC handling chemistry and aseparate 1D transport model);•2D coupled modelling showing calcite growth while treating diffusion;•ion-migration models (dealing with the relationship between electrochemical potentials,
transport and reaction);•

coupled chemical/mechanical/hydraulic (Finite Element Model, FEM) codes;

27

NUMO-TR-04-05

Table 8:WorkerSummary of numerical modelling approaches described during the workshop.
Different approaches were taken to confirm experimental results and predictboth chemical and physical changes in materials as they degrade.

ApproachOda et al.

Forward equilibrium
modelling

Vuorinen et al.

Forward and inverse
equilibrium modelling

OtsukiSequential calculation oftransport - kinetic
reaction - physicalproperties

Takazawa et al.

Sequential calculation oftransport - kinetic
reaction - physicalproperties

Gaucher

Ito et al.

Lehikoinen

Kato et al.

Ichikawa et al

BernerTakaseMass transport
CouplingofComputer codes
Applied to
Maximumchemistrydimensionandtransport?
Yes,
Bentonite,
PHREEQC
1D
diffusion
CementYes(FEMLAB)
Combined
PHREEQC,
3D
bentonite andadvection
FEMLAB(FEMLAB)androck
diffusion
Concrete/cement

Compacted
bentonite/sand mixture

Forward equilibrium
modelling along a flow
MX-80
path, with overall reaction
bentonite,rate controlled byJurassic mudrock
transport, calculation ofmineralogy and porosity
Sequential calculation ofstress – boundary
conditions – chemistry Bentonite,mechanical properties –
cementdeformation - physicalproperties
Sequential calculation oftransport - kinetic
Montmorillonite
reaction - physicalproperties
Sequential calculation oftransport - kinetic
Kunigel V1
reaction - physicalbentonite, cement
properties
Calculation of transport physical properties (MD/HA)
Calculation of transport kinetic reaction - physicalproperties
Simultaneous calculationof transport - kinetic
reaction- physicalproperties

Un-named
numerical
calculation

1D

Yes,
diffusion

1D

Un-namedYes,
numerical
calculation
advectionand(includes chemical
diffusion speciation using
PHREEQC)

1D

Yes,
diffusion

PHREEQC

2D

Yes,
advection

MACBECE(developed byauthors)

1D

Yes,
diffusion

Un-named
numerical
calculation

1D

Yes,
advectionanddiffusionYes,
advectionanddiffusion

Un-named
numerical
calculation
Un-named code,developed byauthors

Kunipia-F
bentonite

2D

Cement2D

Yes,
diffusion

MCOTAC

1D

Yes,
advectionanddiffusion

RAIDEN

Bentonite

28

NUMO-TR-04-05•

macro-properties estimated from micro-scale(MD)/Homogenization Analysis (HA)).

processes(Molecular

Dynamics

The capability of these models to accurately predict the performance of the components in an
EBS as a function of time is limited by:•appropriate mineral representation, especially the secondary minerals, including:
CSH-phases (there is still an on-going debate concerning the nature of appropriate
analogous CSH phases);zeolites;smectites.

•

formulation of key underlying models/laws/functions, especially:solid solution models - these have yet to be incorporated into modelling of EBS;
activity coefficient models - using different methods provides different answers interms of the activity of a species in solution;
rate laws - both dissolution and precipitation of relevant phases in the system;hydrological constraints - including groundwater velocity, advection vs. diffusion,
porosity, permeability, and hydraulic conductivity.

•

differences between actual and modelled phases, notably:chemical differences;
degree of crystallinity (which is very hard to determine as mineral phases may bepresent as gels, or be semi- or wholly- crystalline and different states of the same canhave solubilities ranging over several orders of magnitude).

Several of the models were used to predict the depth of degradation as a function of time andare summarized in Table 9.

4.2 Towards PA modelling approaches
Additional work is needed before an adequate model for assessing the performance of
cement-bentonite barrier systems can be produced. Notably it is necessary to:•define an appropriate simplification of the cement-bentonite system;•

demonstrate appropriate levels of conservatism in the models.

However, considerable progress has been made so far and a general approach to developing
such PA models can now be suggested.
Some of the important mechanisms controlling the degradation of the buffer by the cement
leachate have been identified and investigated. These can be represented schematically as
shown in Figure 9 (Takase).

29

NUMO-TR-04-05

Table 9:

Summary of predictive models described during the workshop. These models
assessed the depth of degradation of materials in the EBS as a function of time.

WorkerMaterial

Phenomena
investigatedOtsuki

OPC

Porosity
increase

Lehikoinen

Namontmorillonite

Gaucher
TakaseNamontmorillonite
Namontmorillonite

Timeframe(years)
10
100
1000

Porosity vs.
secondaryminerals
Secondaryminerals
Secondaryminerals

Depth affected
(cm)
5
10
30
Porosity lost < 10
Reaction products>35

Validation against
real systems?

100,000

65

No1,000,000

50 - 200

No

1,000

30

Yes
No

NUMO-TR-04-05

Figure 9:

Cement/Bentonite interaction as a coupled non-linear dynamical system(Takase).

Figure 10:

Preliminary PA model scheme (Takase).

31

NUMO-TR-04-05

Representing cement/bentonite interaction in this way has several advantages:•

Modifications to this diagram are simple to implement as more mechanisms andcouplings are found.

•

Magnitudes of the mechanisms can be indicated.

•

The representation facilitates simplification of the system by visualizing mechanism
interaction.

•

Helps to define conservative models where all mechanisms can be considered in terms of
their importance.

Alternative possible approaches consider the degradation of the buffer to be limited by three
distinct controls:•

mass balance, whereby there is a sufficient amount of bentonite to buffer the pH of thecement leachate;•mass transport, whereby not all OH- released from the cement will necessarily react withthe buffer because of the low diffusion rates in the buffer in comparison with advective
transport around the tunnel;•

reaction kinetics, whereby the total amount of buffer left intact at a specific time isgoverned by its dissolution rate.

A final PA assessment of the EBS for HLW considering cement/bentonite interaction could
follow the guidelines represented in Figure 10 (Takase).

4.3 Natural/anthropogenic analogues
Natural and anthropogenic analogues to the EBS system do exist and were mentioned, butthey were not discussed in detail. This can be attributed largely to the subject matter of theworkshop, where the focus was specifically on the interaction of cement and bentonite.
However, using natural and anthropogenic analogues have potentially important benefits,notably:•providing a better insight into key mechanisms;•

giving insights into the later stages of the time frames considered by the PA of a HLW
repository;•

allowing for the evaluation of the extent of localized verses macro-scale hydrologicalmechanisms (e.g. diffusion verses advection).

Two natural analogues of particular interest, which were mentioned during the workshop andwhich provide information on cement-buffered hyperalkaline groundwaters are:32

NUMO-TR-04-05•

Maqarin, Jordan;•

Khushaym Matruk, Jordan.

Although these sites have already been studied extensively, a re-examination may provide
more confidence and further insights in assessing the mechanisms of cement leaching andalteration. However, little new information is likely to be provided about cement-bentonite
interaction. It would be worthwhile to examine available information from actual
underground investigation sites (URLs) where cement has been used during construction.
Such evaluations may give useful information about the eventual formation of an alkaline
plume and are presently being undertaken on some data from the Äspö Hard Rock Laboratory
in Sweden.

5 ISSUES FOR CONSIDERATION IN DESIGN ANDPERFORMANCE ASSESSMENT OF HLW/SFREPOSITORIES
5.1 Approach to presentation of major issues
Issues to be considered in the design and performance assessment of HLW/SF repositories are
considered in two sub-sections. In the first part, issues that were discussed during theworkshop are summarised, based on questions that were asked of each speaker, responses tothose questions and comments that were made following each presentation. Since at different
times similar questions were offered and similar answers were given, the issues discussed
have been consolidated and are not presented on a presentation-by-presentation basis.
The issues have been classified generally according to the topics of the sessions in theworkshop. However, the first and last sub-divisions of the topics discussed do not correspondto particular sessions but highlight research achievements and management issues
respectively. Additionally, not all issues discussed in each session are presented together. Thisapproach is necessitated by the fact that sometimes an issue raised in one session was more
appropriate to the theme of another.
It is stressed that there was not necessarily a consensus concerning the accuracy of thestatements that were made. However, these discussion points highlight the range of opinions
that were expressed by the workshop participants.
The second subsection summarises the responses to a questionnaire. The section aims tohighlight areas of agreement and areas of disagreement.

5.2 Issues discussed in the workshop
5.2.1 Achievements of research to date and priorities for future work

The discussions highlighted that a lot of data have been acquired and key processes have been
identified. There was considerable discussion of the most appropriate uses of this information.
Issues that were highlighted are:33

NUMO-TR-04-05•

Priorities for future experimental, field and theoretical work can be suggested based upon
the work completed already.

•A framework for PA can be suggested based on these data.

•

Additional work should focus on developing integrated interpretations from the diverse
data that are available already.

•

Additional experiments to verify present understanding should be undertaken.
Additional information on the long-term evolution of cement-barrier systems would
be desirable.
Consideration should be given to long-term experiments.
Analogues could yield useful information.
There are underground lab facilities, such as the Mol URL in Belgium, which havebeen operating for 20 to 30 years and could be used to give useful information onthese time-scales.

•

It is desirable for new materials to be considered in place of cement and to question‘conventional wisdom’ which states that cement is the best material to use forconstruction and barrier functions in many circumstances.

•

It is desirable to develop low pH cements (pH ≤ 11, but not so low as to promote
excessively rapid corrosion of steel materials) with particular properties for certain
applications, such as grouting where water-rock interactions at higher pH would havedetrimental effects•

It is important to identify which of the possible problems that have been highlighted byexperimental and theoretical investigations would actually be encountered in realrepository environments.

•

There is a need to identify what research and development can and should be done within
the available timescales.

5.2.2 Issues concerned with repository concepts and the uses of cement

The discussions highlighted that, since the roles of bentonite in different kinds of repository
are quite different, interactions between bentonite and cement have different implications forsafety.
Three general topics where considered by the discussions:•

To some extent the amount of cement used will be dependent on the disposal concept.
For example, the KBS-3H concept would use less cement than the KBS-3V concept
where the volume of excavations is large due to the deposition tunnels.

•

The relative spatial distributions of cement and bentonite will be different in different
disposal concepts. For example grout will be distributed heterogeneously through therock mass, depending upon the characteristics of the fracture network in the host rock.
34

NUMO-TR-04-05

At Olkiluoto the rock is more fractured nearer to the surface than at greater depths.
More grout will be required in this upper fractured zone than in deeper rock.
Major inflows will be from major fracture zones, which will consequently be thefeatures where most grout is used. At Olkiluoto, typically there will be 40 – 70 m
between the water-conducting features (WCF) at the waste emplacement depth.
•

If groundwater flows are high, there may need to be some low-permeability material or ahydraulic cage to ensure adequate longevity of any cement barrier system (this is an
issue for TRU repositories). It is currently generally considered that bentonite is the mostsuitable low-permeability material, but consideration should be given to developing
alternatives such as:
new concrete technologies, for example fibrous concretes;
low-permeability concrete surrounding a higher-permeability cement barrier;special materials stable at high pH (e.g. zeolites).

An important implication of the second point for repository design is that the impact ofgrouting cement on bentonite used in a barrier system will not be uniform throughout thebarrier, because of the heterogeneous distribution of grouted fractures.
When developing new concrete technologies, particularly low-permeability concretes,
consideration also needs to be given to the possibility of fractures developing. If such
fractures are heterogeneously distributed, one effect could be heterogeneous leaching ofalkaline water from the concrete.
The practicality of grouting and alternatives to cement-based systems (e.g. resins, clays) are
important issues.
5.2.3 Issues concerned with bentonite and cement mineralogy

A key theme of the discussions was the importance of the pH versus time relationship as acontrol on both the stability and sequence of mineral formation. It was highlighted that
information is needed concerning the relationship between the concentration gradient ofhydroxide across a bentonite barrier and the rate at which an alkaline plume migrates.
Strongly alkaline pore fluids would cause alteration of bentonite, but there is some doubt as to
the relative importance of alteration of accessory minerals and montmorillonite for reducing
swelling pressures at different stages of the evolution:•

Possibly, prior to breakthrough, swelling pressure could be a combination of swelling ofunaltered material and a reduction in swelling due to alteration.

•

There would be a change in swelling pressure across an alkaline front migrating througha bentonite barrier.

Aspects of the design of experiments to investigate these phenomena received considerable
attention. Important issues that were mentioned are:•

When interpreting the results of experiments designed to investigate the alteration of35

NUMO-TR-04-05

bentonite by alkaline pore fluids, it is important to recognize that CSH phases might
precipitate.
•

It is important to understand the dissolved carbonate system if the alteration of bentonite
in alkaline pore fluids is to be understood. As a consequence, it would be valuable toimpose a constant partial pressure of CO2 on experimental bentonite-alkaline pore fluid
alteration experiments.

•

Care is needed to take into account the possibility that trace cristobalite and quartz may
remain in purified smectite when using dissolved silica concentrations to conclude thatincongruent dissolution of smectite has taken place.

•

Extrapolation of the results of laboratory tests, for example cement leaching tests, orobservations on old man-made cement, to timescales relevant to repository safetyassessments is problematical.

•

Techniques exist to accelerate processes such as leaching in the laboratory (e.g. byincreasing diffusion rates using an electric field), but these techniques may be
accompanied by a change in the mechanisms of chemical and/or migration processes.
One approach to solving this problem is to combine the results of un-accelerated andaccelerated laboratory tests.

•

When experimental solutions are varied it is important to ensure that the ionic strength ofthe different solutions is constant in order that results can be compared.

There was little discussion of redox conditions, but the potential reduction of carbonate tomethane was mentioned. It was pointed out that this process will not occur unless there is
microbial activity, though it is difficult to assess whether microbial activity would occur ornot.
Other topics that were discussed are as follows:•

Specific reactive surface areas change during reactions, but during the course of alaboratory experiment these effects are not always significant because reaction rates may
be too slow.

•

In experimental alteration of bentonite or bentonite-sand mixtures, rates of pH variations
with respect to time may not be constant, suggesting that the reaction rates vary over time.
Possible causes are:formation of preferential migration pathways through a sample and/or
formation of inert mineral coatings on the surfaces of migration pathways.

•

The potential corrosion of steel components in low-pH cement need not be a problem, if
such components can be removed prior to repository closure.

5.2.4 Issues concerned with barrier performance and functions

Much of the discussion focused on the potential undesirability of using cement and bentonite
together in barrier systems. Key issues for safety that were highlighted are:36

NUMO-TR-04-05•

The evolution of porosity in bentonite is important.
The initial porosity is very high.
If cement-bentonite alteration results in porosity reduction that causes a permeability
decrease there could be an adverse effect on safety since the potential for gas
pressures to rise, leading to eventual cracking of the barrier, might be enhanced.

•

It is unclear whether or not there would be an increase in the total volume of minerals anda corresponding decrease in pore space near to the boundary between cement andbentonite.
There is a need not only to consider relatively low-pH evolved cement pore fluids,
but also original high-pH fluids rich in NaOH and KOH.
If there is insignificant K in the fluids, then illitization will not occur, but the generalsequence of appearance of the other phases will be broadly similar.

•

The different swelling properties of Ca-bentonite and Na-bentonite could cause a change
in the mechanical characteristics and hydrogeological properties of a bentonite barriersystem during interaction with cement.

•

It is necessary to consider the possibility that alteration may lead to the formation ofregions with high porosity next to regions with low porosity and cause mechanicalinstabilities.

•

Gas migration could be affected significantly by bentonite-cement interactions.
Volumes of gas could be significant in TRU repositories and will need to escape.
If bentonite is used and cementation occurs during alteration then fracturing could
occur.

Although the use of cement and bentonite together in an engineered barrier system may have
undesirable consequences for safety, it is unlikely that interactions between cement used in a
repository and a natural mud rock host formation will be problematic. Favourable factors are:•

The volume of cement relative to the volume of the host formation will be very small
hence the host formation will be able to buffer chemical conditions.

•

In a mud-rock transport is likely to be dominated by diffusion, which will result in only avery small migration of alkaline pore fluid originating in the cement.

•

The width of the disturbed zone in such a rock will be negligible.

The chemical instability of cement in fractures in contact with ambient groundwater was also
discussed. This instability will cause the properties of the cement and wall-rocks to evolve.
•

The chemical stability of cements may not be relevant for repository safety if the cement
is used for grouting, the purpose of which is to control groundwater inflow over the
relatively short interval of repository construction and operation.
37

NUMO-TR-04-05•

In circumstances where a barrier function is required, then alternative materials should beconsidered.

•Effects on the transport properties/sorption/retardation properties in fractures need to beevaluated.

The discussions highlighted that variations in transport properties of a bentonite barriersystem as a function of interaction with cement pore fluids is somewhat uncertain. In
particular, the effect of alteration processes on the transport mechanism is unclear.
•

In experimental alteration of bentonite by alkaline pore fluids, the possibility that themass transport mechanism may change from diffusion-dominated to advection-dominated,
as a result of the alteration of bentonite, needs to be considered.

•

There is a possibility that, if high-specific molar volume phases such as CSH phases form
during alteration of bentonite, the permeability of the bentonite will remain low. As aresult, even if there is significant alteration, the transport mechanism will remain
diffusion dominated.

•

Conversely, there could be mass transport driven by gas evolution, which might influence
the pore fluid chemistry and hence the chemical reactions that occur and the performanceof the barrier.

The degree to which chemical conditions would be buffered by chemical reactions in the
bentonite was discussed and the consequences of this for safety were considered. It was
highlighted that it is important to distinguish the pH-buffering capacity of bentonite
interactions from the ‘buffering intensity’ of these reactions. Relevant issues are:•

Buffering capacity is a mass balance constraint, which represents the total amount ofalkaline pore fluid that can be buffered by a particular mass of bentonite.

•

Buffering intensity represents the rate of change of pH as a function of reaction progressand effectively controls the actual value of pH as a function of reaction.

•

A high chemical buffering capacity does not necessarily ensure safety, since suchbuffering implies significant reaction and alteration. If this reaction and alteration
compromises the physical integrity of the barrier, then there may be negative
consequences for safety. Nevertheless, buffering is a key barrier role for EBS materials inmany repository concepts.

The possible cementation of bentonite by silica was pointed out as a process that could havenegative consequences for safety. It was suggested that such a process could be a negative
effect of using sacrificial material (which will react preferentially with alkaline pore fluid
originating in cement, thereby increasing pH) if silica dissolves and causes cementation.
However, this risk could be eliminated by use of a Pre-fabricated EBS Module (PEM), whichuses a steel container to enclose and protect a bentonite barrier.

38

NUMO-TR-04-05

5.2.5 Issues concerned with modelling

The discussions of research models focused on four main themes:•

the availability and limitations of thermodynamic data;•

the availability and limitations of kinetic data;•

simulations of transport processes;•

simulations of mechanical processes.

A major limitation with simulations of cement-bentonite interactions is the availability ofthermodynamic data for relevant primary and secondary phases in both cement and bentonite.
Potential approaches for addressing these limitations were discussed, highlighting that:•

Chemically and structurally similar phases could be grouped together and uncertainties inthermodynamic data estimated from the ranges of reported thermodynamic parametervalues across the entire group.

•

Many simulations of reactions involving cement and bentonite could be done using
different combinations of phases selected from each group of structurally and chemicallysimilar minerals. For example, if a particular reaction produced a certain zeolite, thenseveral simulations could be done, each one using thermodynamic data for a different, but
structurally and chemically similar zeolite.. Such calculations would establish whether
poor thermodynamic data for a particular phase would be significant for the overall
alteration.

The discussions emphasised that care needs to be taken when using data for one phase to
carry out simulations of a related phase. For example, using thermodynamic data formuscovite to represent mixed-layer smectite-illite during the alteration of bentonite would beinvalid. However, it was also pointed out that it is possible to test thermodynamic propertiesof minerals that are estimated from thermodynamic properties of the constituent oxides.
Possibilities that were suggested are:•Observed mineral assemblages in natural groundwater systems can be compared withmineral assemblages that are predicted using the estimation techniques.

•Predictions of the mineral parageneses actually occurring in natural analogues such as
Maqarin can be made.

The validity of the range of kinetic laws employed received some consideration it wassuggested that Transition State Theory (TST) rate laws should not normally be used underhigh pH conditions and that reaction affinities are uncertain under these conditions. It waspointed out that:•

There is no theoretical treatment that relates affinity to reaction rate at high pH.

•

Empirical equations, such as that of Cama et al (2000) can be used.

39

NUMO-TR-04-05

It was mentioned that simulations of the coupling between the migration of an alkaline pore
fluid plume and chemical reactions are very sensitive to the choice of rate law and the valuesof kinetic parameters. For example:•

Depending upon the reaction kinetics, quartz or montmorillonite are predicted to dissolve
in simulations of quartz-bentonite alteration by alkaline pore fluids.

•

Depending upon the reaction kinetics, montmorillonite dissolution could lead to increases
in permeability of several orders of magnitude.

However, there was also some discussion as to the merits of assuming equilibrium conditions
when carrying out simulations. It was suggested that under high-pH conditions where thereacting mineral phases have high surface areas, it might be appropriate for simulations toassume that reactions equilibrate rapidly.
•

Experiments have tended to produce results that are not far from equilibrium.

•

The assumption of equilibrium in simulations will often be conservative since they willthen predict the maximum amount of mineralogical transformation.

The discussions pointed out that simulations of alkaline pore fluid migration from cement into
bentonite or a mudrock formation have tended to concentrate on diffusion-controlled transport.
•

Such an approach is valid for systems where low-permeability formations such as
mudrock will host a repository, but under certain circumstances advection may occur (e.g.
where cement grout-bearing fractures in certain crystalline rocks are juxtaposed against
bentonite barriers) and then the approach may not be valid.

•

If advection occurs, metastable phases could be important.

Other issues that were discussed in connection with research models are:•

When modelling the deformation of bentonite as a function of alteration and groundwater
flow, the effect on bentonite strength of confining pressure due to overburden needs to beconsidered.

•

When developing molecular dynamics (MD)/ homogenization analysis (HA), it would
be valuable to consider that different solutes show different migration behaviour anddifferent portions of the total porosity can be accessed by different solutes.

•

Variations in the dielectric constant of water in bentonite should be taken into account by
MD/HA.

•

When simulating cement alteration it is desirable to consider the variability in thecomposition of interacting groundwaters (notably potentially adverse effects of dissolved
Mg, Ca, SO4 and Cl and ionic strength of waters).

Key issues that were considered in connection with the development of PA models are:•

When developing approaches to PA of cement-bentonite systems, it is important to40

NUMO-TR-04-05

consider the range of secondary minerals that may form and the temporal sequences inwhich they form.
•

Care should be taken when representing actual mineral phases by pure phases in PA
calculations.

•

The coupling between mechanical, transport and chemical processes must be consideredby PA.
Is it possible to predict these couplings?
Swelling pressures can be calculated, but how can these be related to other processes
adequately?

5.2.6 Issues for project management

A need for a more unified approach to identifying and implementing potential solutions toproblems with using cement and bentonite in barrier systems was highlighted. In particular it
would be desirable to improve communication between management, researchersinvestigating cement-bentonite interactions and engineers and workers in the constructionindustry who will design and implement the barrier systems.
It was pointed out that regulatory frameworks usually lag behind technological innovations
and may constrain the use of materials other than cement, when account is taken of thetimescales of repository projects.
The timescale available to develop alternatives to cement is an important issue.
•

Alternatives to OPC need to be developed before the start of disposal, for example
development of low pH cements (pH< 11).

•

Alternatively, the acceptability of using cement needs to be confirmed before the start ofdisposal.

•

These requirements need not necessarily interfere with the initial development of arepository since cement can possibly be used in parts of the excavations that are remotefrom the emplacement localities. For example, the underground rock characterisation
facility ONKALO at Olkiluoto has been designed in such a manner that it can later
function as access routes and auxiliary rooms of the repository. It is considered that OPC
can be used in the upper parts of the ONKALO excavations even if it is later proved that
other materials are more suitable close to the actual deposition galleries.

41

NUMO-TR-04-05

5.3 Responses to a questionnaire
Prior to the workshop, a list of key questions was distributed to the invited experts. The
answers obtained from the invited experts, as well as from other workshop participants are
summarised below. Answers by one expert are shown as an example in bold; additional
answers and comments from other respondents are provided in italics.
1.

Does mass transfer occur over an interface of highly compacted bentonite and concrete(both directions)?
Yes, both ions and neutral species can pass over the interface. The ion
concentrations in the clay are likely to be governed by ion equilibrium. The
equilibrium conditions are electric neutrality and the same ion activity productinside and outside the bentonite. The concentration of introduced ions will thereby
be significantly lower than in the surrounding groundwater since highly
compacted bentonite has a high concentration of exchangeable cations.

OH-, Na+, K+, Ca2+, and maybe SO42- will diffuse from the concrete into the bentonite.
Mg2+, CO32-, H3SiO4-, Cl- and maybe SO42-, depending on the relative concentrations,will diffuse from the bentonite into the concrete. Mass transfer depends on the diffusion
coefficients in the two media and on the evolution of these parameters (e.g. due toclogging of the porosity).
It was pointed out that mass transfer is the key process. Mass transfer rates asa function of time at the bentonite-cement interface as well as at different depths in bothmaterials should be recorded in experiments and simulations, whenever possible.
2.

What governs the effects of cement on bentonite? Are they governed by the rate at
which OH- ions enter the buffer Is the pH (i.e. concentration of OH- ions in the enteringsolution) actually irrelevant and the effects on bentonite governed only by the flux of
OH- ions (moles per year) entering the buffer?
No, for several reasons. One is the ion equilibrium effect (see answer to Question 1).
A high groundwater solute concentration will lead to a small difference between
groundwater and pore water concentrations. Theoretically, a 1.0 M NaOH
concentration in free water will decrease to a 0.3 M concentration in the porewater (decrease ~3 times; Figure 11). However, a low groundwater concentration
will lead to a much larger difference. Theoretically, a 0.1 M NaOH solution will be
reduced to 0.002 M in the pore water (decrease ~50 times).

42

NUMO-TR-04-05

Introduced ion concentration
10.000
1.000

0.1 M

[Cl-], M

1.0 M

3 times
0.100

50 times

0.010
0.001
0

500

1000

1500

2000

2500

3.0
1.0
0.3
0.1
3.0
1.0
0.3
0.1
0.00
0.1
1.0

Dry density, kg/m3

External solution
Figure 11:

KBS3 Buffer

Theoretical anion activity (Cl- or OH-) from NaCl or NaOH solutions in Namontmorillonite as a function of montmorillonite dry density.

43

NUMO-TR-04-05

Furthermore, different initial pH will lead to different silica solubility anddifferent equilibrium conditions, resulting in the formation of different secondary
minerals.

Are the entering cations (e.g. Ca2+, Na+) important from the point of view of buffer
performance?
Yes, they contribute to the chemical potential in the clay pore water, which at least
partly governs the physical properties (item 1 in Question 4).

As long as thermodynamic equilibrium is not reached and kinetics are fast enough,inward migrating OH- will react with bentonite. Resulting products depend on local
composition, particularly on the pH, but also on the cocktail of cations. The
stoichiometry of the actual transformation determines the buffer capacity.
It was noted that the pH scale depends on temperature. From the point of view of
buffering the invading alkaline solution, the mass transfer rate of OH- ions is the key
factor, i.e. the buffering capacity of the bentonite in terms of moles of OH- ions per kg ofclay is not considered to be significantly dependent on the pH (see also answer to
Question 6). However, the effects on the bentonite depend on the pH, i.e. different
reactions dominate at different pH levels. The cations (e.g. Ca2+, Na+, K+) and the ionicstrength (salinity) of the intruding groundwater (and cement pore water) are importantfrom the point of view of mineralogical transformations in the bentonite. Also the local
chemical conditions in the bentonite, in particular the pCO2, have a great impact on thebuffering reactions. However, dissolution of cementitious materials will not affect theionic strength significantly. Ca ions produced from cementitious materials will affectthe type and fraction of inter-layer cations. In general, Ca-smectite shows higher
permeability and lower swelling properties. The link between the pH of the bentonite
pore water and the bentonite’s dry density should be considered. This aspect has notbeen incorporated in geochemical codes.
3.

If the dissolution rate of montmorillonite (smectite) were low enough, the effects of
cement would not be so significant. From this point of view, the investigations of the
dissolution rate under alkaline conditions should be a focus of experimental studies.
How does the dissolution rate of montmorillonite (smectite) govern the kinetics of thecement/bentonite interaction processes?
The montmorillonite dissolution reaction seems to be very fast according toexperiments on both un-compacted and highly compacted bentonite. The mainquestion is therefore what the governing conditions are. Probably, the silica
activity is the most important factor.

It was noted that if the dissolution rate of montmorillonite is low, the buffering capacity
would also be low. The mineralogical perturbation of the bentonite would be low, but
the extent of the high pH plume might be significant. The effects of the alkaline solution
on the accessory minerals of the bentonite should also be taken into account. However,even if the rates of reaction are such that bentonite alteration does not affect thechemistry of the alkaline plume, the plume’s chemistry will still evolve over time as aresult of the cement being leached by flowing groundwater. If even a small amount ofbentonite cementation occurs, the secondary minerals formed could coat the primary44

NUMO-TR-04-05

minerals and decrease the dissolution rate of smectite, thereby causing the alkaline
plume to extent over a wider volume of the bentonite.
4.

What are the effects of a high pH plume on montmorillonite and accessory minerals inhighly compacted bentonite? Which effects are the most important ones for the
performance of the buffer?
At least two different effects are important:
1) Osmotic ion equilibrium effects, i.e. the ion activity of the external solution in
relation to the activity of ions in the interlamellar water solution (see answer to
Question 2).
2) Mineralogical alteration of bentonite components.
Dissolution of accessory minerals may lead to reduced buffer functions if the
dissolution products are transported away and/or if the secondary products havehigher densities than the original minerals. On the other hand, the porosity will
decrease if neo-formed minerals have lower density than the original minerals.
However, apart from general cementation by secondary phases the most important
effect is doubtless dissolution of montmorillonite, which will lead to reduced buffer
functions under almost any conditions. Several probable neo-formed minerals
have indeed lower density than the original montmorillonite, which leads to a
reduced porosity, but the governing condition for most of the physical buffer
properties is the ratio between montmorillonite and water masses. This ratio will
decrease if neo-formed minerals have a density higher than the mean
montmorillonite - water density, which is set to 2000 kg/m3 in the KBS-3 concept.
Of minerals that may possibly form, only some sulphates have lower densities.
Further, the effect of montmorillonite dissolution will also be large for relatively
small changes in montmorillonite content due to the fact that several of thephysical properties are exponentially dependent on the montmorillonite - water
ratio (Figure 12).

Dissolution and precipitation are the most important processes. Ion exchange (Na ↔
Ca) will take place and may change the properties of the buffer, but will be lessimportant. Concerning the effects on the buffer performance, see also answer to
Question 9. Dissolution of accessory minerals may act to decrease the rate at whichsmectite dissolves. For example dissolution of accessory quartz will increase theaqueous SiO2 content and inhibit smectite dissolution.
5.

How can experimental results obtained in non-compacted conditions be applied tohighly compacted system?
These data may give reaction rates (for example), and can be used in modellingwhere transport is taken into account. An important application is that the results
enable the effects of ion equilibrium to be determined.

45

NUMO-TR-04-05
1E+5

Swelling Pressure, kPa

Swelling Pressure, kPa

1E+4

1E+4
1E+3
1E+2
1E+1
0

Figure 12:500 1000 1500
Dry density, kg/m3

1

2

1E+3
1200
1600
Dry density, kg/m3

2000

0.0
0.1
0.3
1.0
3.0
0.0
0.1
0.3
1.0
3.0
26i
26f

Montmorillonite swelling pressure as a function of dry density. No. 1 denotes
the osmotic effect of 1.0 M NaOH solution, and No. 2 denotes the effect ofmass loss due to dissolution of cristobalite, quartz and montmorillonite in a
specific test. Note the logarithmic scale on the Y-axis.

46

NUMO-TR-04-05

It was noted that non-compacted bentonite and highly compacted bentonite are
structurally quite different materials, and therefore experimental results are not directlytransferable. There is no mechanistic model which adequately explains cementbentonite interaction in compacted systems. Generally this problem is addressed bydefining conservative analysis cases. In a highly compacted bentonite, the structure of
the water molecule is influenced by the surface of the clay (owing to the electric double
layer). This effect will decrease the activities of the ions in the pore water. Presently
available geochemical modelling codes cannot really address this effect.
Highly compacted clay is also inhomogeneous. It is probable that some zones will bepreserved (intact islets) and not affected by the diffusion of the alkaline plume. Thiseffect will diminish the chemical buffering capacity of the barrier from a mass-balance
point of view.
6.

What is the buffering capacity of highly compacted bentonite, i.e. its ability to keep thepH, say below 11 or 10, in terms of moles of OH- ions per kg of clay? Is this quantity arelevant measure of the buffering capacity of the buffer?
The following equilibrium conditions are valid according to PHREEQC modellingusing the Minteq database. The pH decrease caused by reaction with cristobalite isaround 19 mole of [OH-] per kg cristobalite. The reaction ceases at silica
equilibrium, which means that 1.0 M NaOH solution drops in pH from 13.8 to 12.0,
and a solution of pH 12.4 will show a decrease in pH to 10.8 if the high pH solution
does not contain silica at the start of the reaction. Other reactions (i.e.
precipitation or transport) have to take place for further pH reactions.
The pH reduction capacity is smaller for montmorillonite (around 5 moles [OH-]per kg montmorillonite). The capacity of quartz to reduce pH is intermediate
between that of cristobalite and that of montmorillonite.

Buffering capacity is a key parameter. There is a fast (surface hydroxyl sites) anda slow (montmorillonite crystal lattice) component to the total buffering capacity. The
maximum total buffering capacity of bentonite with a montmorillonite content of 75
wt% is approx. 9.5 moles of OH- ions per kg of clay (see presentations by Lehikoinen
and Takase). Precipitation of CSH phases (e.g. tobermorite) may also buffer the pH.
7.

What are the relative propagation rates of diffusing OH- ions and the reaction front
characterised by the buffering and alteration processes in highly compacted bentonite?
Is it possible that, due to the kinetics of reactions, the plume of high pH could reach awaste canister surface (and penetrate into a defective canister) before the buffering
reactions neutralise the high pH?
This has to be thoroughly modelled in order to take into account the transport andreaction kinetics in each specific geometry. The diffusion rate was very fast in the
ECOCLAY tests with compacted bentonite (regardless of accessory minerals), anda fast breakthrough was noticed at sufficiently high pH gradients. Also take into
account the answer to Question 6.

According to experiments relatively fast propagation of a high pH plume in the buffer
seems to be possible (see presentation by Karnland et al.). However, the low diffusion

47

NUMO-TR-04-05

coefficient and relatively high reactivity of the mineral system in the bentonite suggest
that, the occurrence of such phenomena may be of low probability. The potential
overall consequences depend, of course, on the disposal concept (thicknesses of thebuffer and a possible concrete liner surrounding it; and on the different roles ofbentonite and cement in the ILW/TRU and HLW/SF repository designs). Generally it is
to be expected that if the dissolution rates of primary minerals are lower, then the pH at
the surface of the canister will tend to be higher. However, the variation of pH with timeat the surface of the canister will depend on many inter-related parameters. Notably, it
will depend on the dissolution kinetics of primary minerals in the bentonite buffer, thekinds of secondary minerals produced, the precipitation kinetics of secondary minerals,
and the diffusivities of both unaltered and altered bentonite buffer materials.
8.

Concerning the effects of dissolution and (re)precipitation of siliceous and aluminous
species and other accessory minerals of cement, ballast, rock and bentonite: Is there arisk of cementation of the bentonite buffer affected by a plume of high pH, when the pH
eventually drops again?
Yes, the silica activity may reach molar values at pH 14, and the risk for
cementation effects is obvious. I do, however, not know anything about the
precipitation mechanisms. Laboratory experiments are planned for the near
future.

The term “cementation” is often used in a broad sense to describe effects of chemical
and mineralogical processes which can lead to various changes in the rheologicalproperties of the buffer material, for example increased mechanical strength, brittlenessor reduced swelling capacity. A number of completely different processes may cause
similar effects, and the underlying reactions can occur directly in the montmorillonite
mineral, in the interlaminar space between montmorillonite layers, or in accessory
minerals. The resultant cementation does not necessarily have to appear in the same
area as the underlying process, since released chemical species can be transported in
the buffer by various prevailing gradients (thermal, concentration, etc.) and be
precipitated in various locations and in various forms. (SR 97 Process Report, SKB TR99-07).
It was noted that with some exceptions (i.e. calcite, gypsum) all the accessory minerals
would form secondary minerals upon reaction with highly alkaline solutions. Since neoformed precipitates often have larger molar volumes than the reactants, cementation
may occur in the buffer.
9.

What are the mechanical (e.g. swelling pressure, plasticity) and transport-related (e.g.
diffusivity) properties of highly compacted bentonite altered by a high pH plume?
See answer to Question 4.

The properties of altered bentonite have not been investigated thoroughly. The likely
and potential effects include, for example, loss of swelling capacity and plasticity,
increase of permeability, loss of filtering capacity for colloids, and erosion at the
bentonite–rock interface. Ion exchange resulting in conversion of Na-bentonite to Cabentonite reduces the swelling capacity and increases the permeability of the buffer.

48

NUMO-TR-04-05

10.

In experiments, the transport of a high pH plume originating from an NaOH solution
has been significantly faster than that of a high pH plume originating from a Ca(OH)2
solution. Is such a relationship between plume chemistry and migration rate likely tooccur in an actual barrier?
No such fundamental conclusion can be drawn from the experiments we have
performed. NaOH solutions with a concentration gradient of 1.0 and 0.3 M over 5
mm distance led to a high pH breakthrough, but a gradient of 0.1 M over 5 mm
did not. Neither did 0.02 Ca(OH)2 (saturated) solution lead to a breakthroughduring the test time.

Is this effect only due to the higher concentrations of OH- ions in the NaOH solutions
used, compared to those in the Ca(OH)2 solutions, where the OH- concentration islimited by the solubility of Ca(OH)2?
Different secondary minerals may be formed in each case and thereby lead todifferent pH and transport conditions in the system.

The experiments by Karnland et al. seem to indicate that the faster penetration of thehigh-concentration, high-pH solution in the highly compacted bentonite cannot
explained only by the higher concentration gradient. Besides simple diffusion and massbalance reactions, there seem to be other phenomena related, for example, to the
Donnan effect and/or to the structure of the highly compacted bentonite affecting thepenetration rates (see presentation by Karnland et al. and his answers above.). It wasnoted that longer experiment periods (or higher temperatures) should be used to see if
the low-concentration solution also eventually penetrates through the highly compacted
bentonite. However, it is noted that Na+ and K+ will control the concentration of OHonly in the early stages of cement degradation. These concentrations are each about 0.1
mol/L. After leaching of Na+ and K+ from cement, concentration of OH- is limited by
the solubility of Ca(OH)2.
11.

What are the issues specific to systems where massive cement or concrete surrounds orneighbours bentonite, such as where a thick tunnel liner occurs around the buffer?
The bentonite will be saturated by cement pore water, which initially will cause ion
disequilibrium phenomena, leading to a faster chemical attack.

It was noted that this case, as long as mass transport is dominated by diffusion, isrelatively easy to analyse. Potential consequences can be reduced by taking care ofmass balances (thickness of the buffer vs. thickness of the concrete layer).

49

NUMO-TR-04-05

50

NUMO-TR-04-05

Appendix 1 - Workshop ProgrammeInternational Workshopon
Bentonite – Cement Interaction in Repository Environments
April 14-16, 2004
AIJ Hall (Kenchiku Kaikan), Tokyo, Japan
Cement-based materials are normally used in rock construction for various purposes such as grouting,supports and tunnel floors. However, in the design of nuclear waste repositories the introduction of
any foreign materials is considered with caution as they may effect adversary changes in the chemical
conditions of the repository or the host rock. In this respect the use of normal Portland cements has
been pointed out as a problem because of the high pH groundwater plume that it may give rise to.
From the point of view of long-term safety it might be easiest and perhaps most prudent to avoid it
completely and search for other materials to replace it. To this effect low pH substitutes are being
developed and tested for some repository applications, but, especially for grouting purposes, it is still
not clear whether such materials will be available at the time the need arises. Therefore, there
continues to be interest to assess the implications of the use of cement-based materials on a broad
basis.
For high-level waste repositories the main concerns as regards long-term safety, are related to thealteration of bentonite, the stability of the fuel matrix, and the validity of the performance assessment
databases in a high pH (>11) environment. In the past years a large number of studies on bentonite
alteration due to cement-bentonite interaction have been performed both in international projects(European Union 5th Framework Programme) and at national levels.
A number of questions have been identified, such as the buffering capacity and alteration of bentonite,
alteration products, and the properties of the altered clay in highly compacted bentonite. Additionalquestions being discussed are e.g., the relative propagation rates of diffusing OH- ions and the reaction
front of the buffering and alteration processes in the highly compacted bentonite, and the fate andeffects of dissolving siliceous and aluminous reaction products in the long-term.
In order to get a comprehensive overview on the present knowledge on the bentonite-cement
interaction, and to identify key issues and how these should be approached by modelling and tests inUnderground Research Laboratories and other laboratories, NUMO and POSIVA are launching thisworkshop. The expected outcome is a clearer definition of the key issues of bentonite-cement
interaction to be considered in the design and performance assessment of HLW/SF repositories.

A1-1

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Wednesday, April, 14

13:30 Welcome address and working format
NUMO (Kazumi Kitayama and Hiroyoshi Ueda)
Posiva (Marjut Vähänen)13:50 Session I: Introductory session: Repository concepts and use of cement
Chairs: Hiroyoshi Ueda and Marjut Vähänen
13:50-14:20 General overview on the use of cement in repositories for HLW and otherradioactive wastes
Kazumi Kitayama1, H. Ueda1, N. Sasaki2 and M. Hironaga3
1
NUMO, 2 JNFL, 3 CRIEPI
14:20-14:50 Planned use of cement in ONKALO, in a KBS-3V type and KBS-3H type
repository in crystalline rock
Johanna Hansen Posiva
14:50-15:10

Coffee15:10-15:40 Main issues in the use of cement in a spent fuel repository – what are we seeking
answers for?
Timo Vieno VTT Processes
15:40-16:10 The bentonite/cement interaction problem; cutting the Gordian knot
Ian G. McKinley, R. Alexander, W. Kichmaier and
F. Neall Nagra
16:10 Session II: Mineralogy under B-C interaction
Chair: Seichi Sato Hokkaido Univ.
16:10-16:55 Evaluation methods for ion migration in concrete & prediction methods forconcrete deterioration caused by chloride attack or calcium leaching
Nobuaki Otsuki
Tokyo Institute of Technology
16:55-17:40 Dissolution mechanism and kinetics of smectite under alkaline conditions
Tsutomu Sato1, M. Kuroda1, S.
Yokoyama1, M. Tsutsui1,
K. Fukushi2, T. Tanaka3 and S.
Nakayama3
1
Kanazawa Univ.,
2
AIST, 3 JAERI
17:40 End of Day 1

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NUMO-TR-04-05

Thursday, April 15

9:30 Session III: Barrier Performance and functions under B-C interaction
Chair: Patrik Sellin SKB
9:30-10:30 Experimental study on changes of bentonite mineralogy and physical properties
as a result of exposure to high pH solutions
Ola Karnland1, U. Nilsson1, S. Olsson2 and P. Sellin3
1
Clay Technology, 2 Geochimica, 3 SKB
10:30-11:00 Effects of saline alkaline attack on bentonite and crushed rock – experimental
and modelling studies – ECOCLAY II
Ulla Vuorinen1, Ari Luukkonen2, Jarmo Lehikoinen1 and Heini Ervanne3
VTT Processes, 2 VTT Building and Transport, 3 University of Helsinki

1

11:00-11:20

Coffee

11:20-11:50 Experimental study on dissolution of montmorillonite in compacted sandbentonite mixture under Na-Cl-OH pore-water conditions
Tetsuji Yamaguchi1, Y. Sakamoto1, M. Akai1, M. Takazawa1,
T. Tanaka1, S. Nakayama1 and T. Sato2
1
JAERI., 2 Kanazawa Univ.
11:50-12:20 Modelling of variation in permeability of compacted bentonite with alkaline
fluid for long-term safety assessment of geological disposal system
Mayumi Takazawa, T. Yamaguchi, Y. Sakamoto,
M. Akai and S. Nakayama JAERI
12:20-13:20

Lunch (lunch box provided by NUMO)

13:20 Session III continues
Chair: Patrik Sellin SKB
13:20-13:50 Cement-bentonite interaction issues, buffering capacity of bentonite
Jarmo Lehikoinen VTT
13:50-14:20 A long-term performance assessment for engineered barriers – study on barriermaterials alteration –Hiroyasu Kato1, H. Asano1 and N. Yamada2
1
RWMC, 2 Mitsubishi Materials

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NUMO-TR-04-05

14:20-14:50 An analysis of cement-bentonite interaction and evolution of pore waterchemistry
Chie Oda1, A. Honda1 and D. Savage2
1
JNC, 2 Quintessa
14:50-15:20 Development of MACBECE: Mechanical Analysis system considering
Chemical transition of BEntonite-based and Cement-based materials
Hiroyuki Ito, M. Mihara and T. Ohi JNC
15:20-15:40

Coffee15:40 Session IV: Modelling; Detailed research models vs. PA models
Chair: Masao Shiotsuki JNC
15:40-16:40 Modelling diffusion of an alkaline plume in two types of clayey systems
Eric Gaucher BRGM
16:40-17:10 Potential complications in the development of a thermodynamic database for
hyperalkaline, argillaceous systems
Randy Arthur1, Hiroshi Sasamoto2 andMikazu Yui2
1
Monitor Scientific, 2 JNC
17:10-17:40 Nano/macro-based cation/water transport and adsorption in bentonite
Yasuaki Ichikawa1, S. Prayongphan1, S. Suzuki2 and K. Kawamura3
1
Nagoya Univ., 2 IRI, 3 TokyoTech.
17:40 End of Day 2
19:30 Workshop Banquet hosted by NUMO

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NUMO-TR-04-05

Friday, April 16

9:30

Session IV continues

Chair: Margit Snellman SROY
9:30-10:30 Status of cement modelling – future investigations in the view of
cement/bentonite interactions
Urs Berner PSI
10:30-11:00 Discussion on PA model development for bentonite barriers affected bychemical interaction with concrete: Do we have enough evidence to support
bentonite stability?
Hiroyasu Takase Quintessa Japan
11:00-11:30

Coffee11:30 Session V: Concluding Discussions and Wrap-up (Conclusions from each session)
Chair: Hiroyuki Umeki NUMO
12:30 End of Workshop

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NUMO-TR-04-05

Deliverables
We are planning to compile a proceedings report of the workshop as POSIVA and NUMOTechnical Reports, which will be open to the public and distributed to the workshop
participants.

Language
The workshop language is English. Oral Japanese is allowable with simultaneous translation
provided.

Discussion time
Discussion time is proposed as follows:
5 min. discussion for 30 min. presentation;
5 min. discussion for 45 min. presentation;
10 min discussion for 60 min. presentation;
These are flexibly changeable under the control of the chair person.

Practical information
Meeting time and place
The meeting starts on Wednesday, April 14th at 13:30 and ends on Friday, April 16th at 12:30.
It takes place at AIJ Hall (http://www.aij.or.jp/eng/about/map.html or see the map attached.
The hall is familiar to Japanese as “Kenchiku Kaikan”.), 5-26-20, Shiba, Minato-ku, Tokyo
Hotel
Celestine Hotel, http://www.celestinehotel.com/us/index.html, is located close to AIJ Hall (7minutes walk).
Information about Tokyo
Information in detail is available from WEB as:

http://www.tourism.metro.tokyo.jp/english/index.html
http://www.tcvb.or.jp/en/index_en.htm
http://www.jnto.go.jp/eng/
http://www.jnto.go.jp/mapindex/E/Tokyo.html

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NUMO-TR-04-05

Appendix 2 – List of Participants

BELGIUM
Tel: +32 14 333236
Fax: +32 14 323553
E-mail: lwang@SCKCEN.BE

Wang, Lian
Belgian Nuclear Research Center
SCK・CEN
Boeretang 200 B-2400 Mol,
Belgium
FINLAND
Hansen, Johanna
Design Coordinator,
Repository Technology
Posiva Oy
27160 Olkiluoto,
FinlandTel: +358 2 8372 3738
Fax: +358 2 8372 3709
E-mail: johanna.hansen@posiva.fi

Lehikoinen, Jarmo
Senior Research Scientist
VTT Processes
P.O. Box 1608
FIN-02150 VTT,
FinlandTel: +358 0 456 6371
Fax: +358 9 456 6390
E-mail: jarmo.lehikoinen@vtt.fi

Snellman, Margit
Saanio & Riekkola Oy
Laulukuja 4 FIN-00420
Helsinki,
FinlandTel: +358-9-53065450
Fax: +358-9-5663354
E-mail: margit.snellman@sroy.fi

Vähänen, Marjut
Research Coordinator,
Long-term Safety
Posiva Oy
27160 Olkiluoto,
FinlandTel: +358 2 8372 3746
Fax: +358 2 8372 3709
E-mail: marjut.vahanen@posiva.fi

Vieno, Timo
Chief Research Scientist
VTT Processes
P.O. Box 1608
FIN-02150 VTT,
FinlandTel: +358 0 456 5066
Fax: +358 9 456 6390
E-mail: timo.vieno@vtt.fi

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NUMO-TR-04-05

Tel: +358 0 456 6389
Fax: +358 9 456 6390
E-mail: ulla.vuorinen@vtt.fi

Vuorinen, Ulla
Senior Research Scientist
VTT Processes
P.O. Box 1608
FIN-02150 VTT,
Finland
FRANCE

Tel: +33 2 38 64 35 73
Fax: +33 2 38 64 30 62
E-mail: e.gaucher@brgm.fr

Gaucher, Eric
Environment and Process Division
BRGM (Bureau de recherches géologiqueset minières)3 Avenue Claude Guillemin
BP 600945060 Orléans Cedex 2
FranceJAPAN
Aoyama, Yuji
Executive Consultant
Quintessa Japan707 Queen's Tower A,
2-3-1 Minato-mirai, Nishi-ku,
Yokohama, 220-6007,
Japan

Tel: +81-45-222-6375
Fax: +81-45-222- 6376
E-mail: aoyama@quintessa.co.jp

Asano, Hidekazu
Advanced Waste Systems Research
Project
RWMC (Radioactive waste management
funding and research center)No.15. Mori Bldg.
2-8-10, Toranomon,
Minato-ku, Tokyo 105-0001,
Japan

Tel: +81-3-3504-1081
Fax: +81-3-3504-1297
E-mail: asano@rwmc.or.jp

Ashida, Takashi
Manager, Planning Section,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1512
Fax: +81-3-4513-1599
E-mail: tashida@numo.or.jp

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NUMO-TR-04-05

Aso, Ryoji
Senior Manager,
Department of Fuel Cycle Safety Research
JAERI (Japan Atomic Energy ResearchInstitute)
Tokai-Mura, Naka-gun,Ibaraki, 319-1195
Japan

Tel: +81-29-282-6759
Fax: +81-29-282-5842
E-mail: aso@masant.tokai.jaeri.go.jp

Danda, Hiroaki
Deputy Manager,
Research and Development,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1533
Fax: +81-3-4513-1599
E-mail: hdanda@numo.or.jp

Deguchi, Akira
Manager, Planning Section,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1512
Fax: +81-3-4513-1599
E-mail: adeguchi@numo.or.jp

Fujihara, Hiroshi
Group Manager,
Nuclear Power Engineering Department
TEPCO (Tokyo Electric Power Company)
1-1-3, Uchisaiwai-cho,
Chiyoda-ku, Tokyo, 100-001,
Japan

Tel: +81-3-4216-4973
Fax: +81-3-3596-8562
E-mail: fujihara.hiroshi@tepco.co.jp

Fujita, Tomonari
CRIEPI (Central Research Instituteof Electric Power Industry)
2-11-1 Iwatokita, Komae-shi,
Tokyo 201-8511
Japan

Tel: +81 3 3480 2111
Fax: +81 3 3480 3564
E-mail: tfujita@criepi.denken.or.jp

Hanamoto, Mareki
Deputy Manager,
International Affairs and TechnicalCooperation Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1583
Fax: +81-3-4513-1599
E-mail: mhanamoto@numo.or.jp

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NUMO-TR-04-05

Hironaga, Michihiko
CRIEPI (Central Research Instituteof Electric Power Industry)
1646 Abiko, Abiko-shi,
Chiba-ken 270-1194
Japan

Tel: +81 4 7182 1181
Fax: +81 4 7182 2243
E-mail: hironaga@criepi.denken.or.jp

Honda, Akira
Assistant senior engineer,
Material Research Group,
Waste Isolation Research Division,
Tokai WorksJNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-1540
Fax: +81-29-282-9328

Ichikawa, Yasuaki
Associate Professor,
Environmental Engineering andArchitecture,
Graduate School of Environmental Studies
Nagoya Univ.
Furo-cho, Chikusa-ku,
Nagoya, 464-8601,
Japan

Tel: +81-52-789-3829
Fax: +81-52-789-1176
E-mail:YIchikawa@nucc.cc.nagoya-u.ac.jp

Imoto, Harutake
CRIEPI (Central Research Instituteof Electric Power Industry)
1646 Abiko, Abiko-shi,
Chiba-ken 270-1194
Japan

Tel: +81 4 7182 1181
Fax: +81 4 7182 2243
E-mail: imoto@criepi.denken.or.jp

Ito, Hiroyuki
Engineer,
Material Research Group,
Waste Isolation Research Division,
Tokai WorksJNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-1540
Fax: +81-29-282-9328
E-mail: itou.hiroyuki@jnc.go.jp

Jintoku, Takashi
JNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-3695
Fax: +81-29-282-9295
E-mail: jintoku.takashi@jnc.go.jp

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NUMO-TR-04-05

Kato, Hiroyasu
Advanced Waste Systems Research
Project
RWMC (Radioactive waste management
funding and research center)No.15. Mori Bldg.
2-8-10, Toranomon,
Minato-ku, Tokyo 105-0001,
Japan

Tel: +81-3-3504-1081
Fax: +81-3-3504-1297
E-mail: hiro@rwmc.or.jp

Kawaguchi, Mitsuo
Senior Scientist,
Nuclear Chemistry and Chemical
Engineering Center (NUCEC),
Kashiwa Laboratory
IRI (Institute of Research and Innovation)
1201 Takada, Kashiwa,
Chiba, 277-0861
Japan

Tel: +81-4-7144-8997
Fax: +81-4-7144-7602
E-mail: mkawaguchi@iri.or.jp

Kitayama, Kazumi
General Manager of Science andTechnology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1501
Fax: +81-3-4513-1599
E-mail: kkitayama@numo.or.jp

Kurasige, Isao
CRIEPI (Central Research Instituteof Electric Power Industry)
1646 Abiko, Abiko-shi,
Chiba-ken 270-1194
Japan

Tel: +81 4 7182 1181
Fax: +81 4 7182 2243
E-mail: kurasige@criepi.denken.or.jp

Matsui, Hiroya
Geotechnical Science and EngineeringGroup,
Horonobe Underground Research Center
JNC (Japan Nuclear Cycle Development
Institute)
Miyazono-machi 1-8,
Horonobe-cho, Hokkaido, 098-3207
Japan

Tel: +81-1632-5-2022
Fax: +81-1632-5-2344
E-mail: matsui@tono.jnc.go.jp

Metcalfe, Richard
Principal Consultant
Quintessa Japan707 Queen's Tower A,
2-3-1 Minato-mirai, Nishi-ku,
Yokohama, 220-6007,
Japan

Tel: +81-45-222-6375
Fax: +81-45-222- 6376
E-mail: metcalfe@quintessa.co.jp

A2-5

NUMO-TR-04-05

Mihara, Morihiro
Assistant senior engineer,
Material Research Group,
Waste Isolation Research Division,
Tokai WorksJNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-1540
Fax: +81-29-282-9328
E-mail: mihara@tokai.jnc.go.jp

Naito, Morimasa
Manager,
Research and Development,
Science and Technology Division
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1532
Fax: +81-3-4513-1599
E-mail: mnaito@numo.or.jp

Nishida, Takahiro
Research Associate, Concrete Lab.
Department of International Development
Engineering,
Graduate School of Science andEngineering
Tokyo Institute of Technology
2-12-2 O-okayama,
Meguroku, Tokyo, 152-0033,
Japan

Tel: +81-3-5734-2585
Fax: +81-3-5734-2585
E-mail: nishida@ide.titech.ac.jp

Oda, Chie
Assistant senior engineer,
Material Research Group,
Waste Isolation Research Division,
Tokai WorksJNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-1540
Fax: +81-29-282-9328
E-mail: oda.chie@jnc.go.jp

Otsuki, Nobuaki
Professor, Department of International
Development Engineering,
Graduate School of Science andEngineering
Tokyo Institute of Technology
2-12-2 O-okayama,
Meguroku, Tokyo, 152-0033,
Japan

Tel: +81-3-5734-2594
Fax: +81-3-5734-2585
E-mail: otsuki@ide.titech.ac.jp

A2-6

NUMO-TR-04-05

Owada, Hitoshi
Advanced Waste Systems Research
Project
RWMC (Radioactive waste management
funding and research center)No.15. Mori Bldg.
2-8-10, Toranomon,
Minato-ku, Tokyo 105-0001,
Japan

Tel: +81-3-3504-1081
Fax: +81-3-3504-1297
E-mail: owada@rwmc.or.jp

Sakabe, Yasushi
Group Manager for Research andDevelopment,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1532
Fax: +81-3-4513-1599
E-mail: ysakabe@numo.or.jp

Sasaki, Noriyuki
JNFL (Japan Nuclear Fuel Limited)
Aza Nozuki Oaza Obuchi Rokkasho-mura
Kamikita-gun, Aomori 039-3212
Japan

Tel: +81-175-72-3305
Fax: +81-175-72-3226
E-mail: noriyuki.sasaki@jnfl.co.jp

Sasamoto, Hiroshi
Team Leader
JNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-3695
Fax: +81-29-282-9295
E-mail: sasamoto.hiroshi@jnc.go.jp

Sato, Seichi
Professor,
Division of Quantum Energy Engineering,
Graduate school of Engineering
Hokkaido Univ.
Kita 13, Nishi 8,
Kita-ku, Sapporo 060-8628,
Japan

Tel: +81-11-706-6686
Fax: +81-11-706-7139
E-mail: sato@qe.eng.hokudai.ac.jp

Sato, Tsutomu
Institute of Nature and Environmental
Technology
Kanazawa Univ.
Kakuma-machi, Kanazawa 920-1192,
Japan

Tel: +81-76-264-5725
Fax: +81-76-264-5746
E-mail:tomsato@kenroku.kanazawa-u.ac.jp

A2-7

NUMO-TR-04-05

Shibata, Katsuaki
Director of International Affairs andTechnical Cooperation Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1504
Fax: +81-3-4513-1599
E-mail: ktshibata@numo.or.jp

Shimizu, Tomofumi
JNFL (Japan Nuclear Fuel Limited)
Aza Nozuki Oaza Obuchi Rokkasho-mura
Kamikita-gun Aomori 039-3212
Japan

Tel: +81-175-72-3305
Fax: +81-175-72-3226
E-mail: tomofumi.shimizu@jnfl.co.jp

Shiotsuki, Masao
Group Leader,
Material Research Group,
Waste Isolation Research Division,
Tokai WorksJNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-1540
Fax: +81-29-282-9328
E-mail: siotuki@hq.jnc.go.jp

Sugita, Yutaka
Deputy Manager,
International Affairs and TechnicalCooperation Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1582
Fax: +81-3-4513-1599
E-mail: ysugita@numo.or.jp

Sugiyama, Daisuke
CRIEPI (Central Research Instituteof Electric Power Industry)
2-11-1 Iwatokita, Komae-shi,
Tokyo 201-8511
Japan

Tel: +81 3 3480 2111
Fax: +81 3 3480 3564
E-mail: daisukes@criepi.denken.or.jp

Suzuki, Satoru
Researcher,
Nuclear Chemistry and Chemical
Engineering Center (NUCEC),
Kashiwa Laboratory
IRI (Institute of Research and Innovation)
1201 Takada, Kashiwa,
Chiba, 277-0861
Japan

Tel: +81-4-7144-8972
Fax: +81-4-7144-7602
E-mail: kakusuzuki@iri.or.jp

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NUMO-TR-04-05

Suzuki, Yohei
NSRA(Nuclear Safety Research Association)
5-18-7 Shinbashi
Minato-ku, Tokyo 105-0004
Japan

Tel: +81-3-5470-1986
Fax: +81-3-5470-1991
E-mail: ysuzuki@nsra.or.jp

Takahashi, Yoshiaki
Deputy Manager,
Planning Section,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1515
Fax: +81-3-4513-1599
E-mail: ytakahashi@numo.or.jp

Takase, Hiroyasu
Managing Director
Quintessa Japan707 Queen's Tower A,
2-3-1 Minato-mirai, Nishi-ku,
Yokohama, 220-6007,
Japan

Tel: +81-45-222-6375
Fax: +81-45-222- 6376
E-mail: htakase@quintessa.co.jp

Takazawa, Mayumi
Department of Fuel Cycle Safety Research
JAERI (Japan Atomic Energy ResearchInstitute)
Tokai-Mura, Naka-gun,Ibaraki, 319-1195
Japan

Tel: +81-29-282-6184
Fax: +81-29-282-5934
E-mail:takazawa@sparclt.tokai.jaer.go.jp

Takeuchi, MitsuoGroup Manager for Safety Affairs,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1571
Fax: +81-3-4513-1599
E-mail: mtakeuchi@numo.or.jp

Tsutsui, Masanori
Department of earth sciences
Kanazawa Univ.
Kakuma-machi, Kanazawa 920-1192,
Japan

Tel: +81-76-264-5725
Fax: +81-76-264-5746
E-mail:tsutsui@earth.s.kanazawa-u.ac.jp

Ueda, Hiroyoshi
Manager,
Research and Development,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan

Tel: +81-3-4513-1534
Fax: +81-3-4513-1599
E-mail: hueda@numo.or.jp

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NUMO-TR-04-05
Tel: +81-3-4513-1503
Fax: +81-3-4513-1599
E-mail: humeki@numo.or.jp

Umeki, Hiroyuki
Director for Research and Development,
Science and Technology Department
NUMO
1-23, Shiba 4-chome,
Minato-ku, Tokyo, 108-0014,
Japan
Yamada, Norikazu
Energy Project & Technology Center,
Radioactive Waste Management Dept.
Mitsubishi Materials Corporation
Koishikawadaikoku Bldg.
1-3-25, Koishikawa,
Bunkyo-ku, Tokyo,112-0002,
Japan

Tel: +81-3-5800-9311
Fax: +81-3-5800-9375
E-mail: yamata@mmc.co.jp

Yamaguchi, Tetsuji
Department of Fuel Cycle Safety Research
JAERI (Japan Atomic Energy ResearchInstitute)
Tokai-Mura, Naka-gun,Ibaraki, 319-1195
Japan

Tel: +81-29-282-6676
Fax: +81-29-282-6678
E-mail:yamaguch@sparclt.tokai.jaeri.go.jp

Yamamoto, Takeshi
CRIEPI (Central Research Instituteof Electric Power Industry)
1646 Abiko, Abiko-shi,
Chiba-ken 270-1194
Japan

Tel: +81 4 7182 1181
Fax: +81 4 7182 2243
E-mail: t-yama@criepi.denken.or.jp

Yokozeki, Kosuke
Senior Research Engineer,
Materials and Life Cycle EngineeringGroup,Kajima Technical Research InstituteKajima2-19-1, Tobitakyu,
Chofu-shi, Tokyo, 182-0036,
Japan

Tel: +81-424-89-7816
Fax: +81-424-89-7073
E-mail: yokozeki@kajima.com

Yui, MikazuGroup Leader
JNC (Japan Nuclear Cycle Development
Institute)4-33, Muramatsu, Tokai-mura,Naka-gun, Ibaraki, 311-1194
Japan

Tel: +81-29-287-3695
Fax: +81-29-282-9295
E-mail: yui@tokai.jnc.go.jp

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NUMO-TR-04-05

Tel: +81-45-222-6375
Fax: +81-45-222-6376
E-mail: colin.walker@macmail.com

Walker, Colin
Consultant
Quintessa Japan707 Queen's Tower A,
2-3-1 Minato-mirai,
Nishi-ku, Yokohama, 220-6007,
Japan
SWEDEN
Karnland, Ola
Clay Technology AB
IDEON Research Center,
Scheelev. 19F,
S-223 70 Lund,
SwedenTel: +46 (0)46 286 25 76
Fax: +46 (0)46 13 42 30
E-mail: ok@claytech.se

Sellin, Patrik
SKB
Box 5864
S-102 40 Stockholm
SwedenTel: +46 (8) 459 8522
Fax: +46 (8) 662 4974
E-mail: patrik.sellin@skb.se

SWITZERLAND
Berner, Urs
Waste Management Laboratory,
Department Nuclear Energy and Safety
PSI (Paul Scherrer Institut)
CH-5232
Villigen PSI
Switzerland

Tel: +41 56 310 24 32
Fax: +41 56 310 28 21
E-mail: urs.berner@psi.ch

Kaku, Kenichi
Project Manager
Engineering, International Services andProjects
Nagra
Hardstrasse 73,
CH-5430 Wettingen,
Switzerland

Tel: +41-56-437-1308
Fax: +41-56-437-1317
E-mail: kenichi.kaku@nagra.ch

McKinley, Ian G.
Director,
International Services and Projects
Nagra
Hardstrasse 73,
CH-5430 Wettingen,
Switzerland

Tel: +41-56-437-1289
Fax: +41-56-437-1317
E-mail: ian.mckinley@nagra.ch

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NUMO-TR-04-05

U.S.A.
Tel: +1 303 985-0005
Fax: +1 303 980-5900
E-mail: rarthur@monitorsci.com

Arthur, Randy
Monitor Scientific, LLC
3900 S. Wadsworth Blvd.
#555 Denver,
CO 80235
USA

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Appendix 3 - Extended Abstracts
Kitayama K., Ueda H.1, Sasaki N.2, and Hironaga M.3 ‘General Overview on the Use of
Cement in Repositories for HLW and Other Radioactive Wastes’. 1Nuclear Waste
Management Organization of Japan (NUMO), 2Japan Nuclear Fuel Limited (JNFL) and3
Central Research Institute of Electric Power Industry (CRIEPI), Japan.
Hansen J. ‘Planned use of Cement in ONKALO, in a KBS-3V type and KBS-3H Type
Repository in Crystalline Rock’. Posiva, Finland.
Vieno T. ‘Main Issues in the Use of Cement in a Spent Fuel Repository – What are We
Seeking Answers for?’. VTT Processes, Finland.
McKinley I., Alexander R., Kickmaier W., and Neall F. ‘The Bentonite/Cement Interaction
Problem: Cutting the Gordian Knot’. Nagra, Switzerland.
Otsuki N. ‘Evaluation Methods for Ion Migration in Concrete’ and ‘Prediction Methods forConcrete Deterioration Caused by Chloride Attack or Calcium Leaching’. Tokyo Institute ofTechnology, Japan.
Sato T.1, Kuroda M.1, Yokoyama S.1, Tsutsui M.1, Fukushi K.2, Tanaka T.2, and Nakayama
S.3. ‘Dissolution Mechanism and Kinetics of Smectite Under Alkaline Conditions’.
1
Kanazawa University, 2National Institute of Advanced Industrial Science and Technology(AIST) and 3Japan Atomic Energy Research Institute (JAERI), Japan.
Karnland O.1, Nilsson U.1, Olsson S.2, and Sellin P.3 ‘Experimental Study on Changes of
Bentonite Mineralogy and Physical Properties as a Result of Exposure to High pH Solutions’.
1
Clay Technology AB (CT), 2Geochimica and 3Svensk Kärnbränslehantering AB (SKB),
Sweden.
Vuorinen U.1, Luukkonen A.2, Lehikoinen J.1, and Ervanne H.3 ‘Effects of Saline Alkaline
Attack on Bentonite and Crushed Rock – Experimental and Modelling Studies – Ecoclay II’.
1
VTT Processes, 2VTT Building and Transport and 3University of Helsinki, Finland.
Yamaguchi T.1, Sakamoto Y.1, Akai M.1, Takazawa M.1, Tanaka T.1, Nakayama S.1, and SatoT.2 ‘Experimental Study on Dissolution of Montmorillonite in Compacted Sand-Bentonite
Mixture Under Na-Cl-OH Pore-Water Conditions’. 1Japan Atomic Energy Research Institute(JAERI) and 2Kanazawa University, Japan.
Takazawa M., Yamaguchi T., Sakamoto Y., Akai M., Tanaka T., and Nakayama S. ‘Modelingof Variation in Permeability of Compacted Bentonite with Alkaline Fluid for Long-Term
Safety Assessment of Geological Disposal System’. Japan Atomic Energy Research Institute(JAERI), Japan.
Lehikoinen J. ‘Cement-Bentonite Interaction Issues, Buffering Capacity of Bentonite’. VTTProcesses, Finland.
Kato H.1, Asano H.1 and Yamada N.2 ‘A Long-Term Performance Assessment for Engineered
Barriers – Study on Barrier Materials Alteration’. 1Radioactive Waste Management Funding
and Research Center and 2Mitsubishi Materials Corporation, Japan
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Oda C.1, Honda A.1 and Savage D.2 ‘An Analysis of Cement-Bentonite Interaction and
Evolution of Pore Water Chemistry’. 1Japan Nuclear Cycle Development Institute (JNC),
Japan, and 2Quintessa Limited, UK.
Ito H., Mihara M. and Ohi T. ‘Development of MACBECE: Mechanical Analysis system
considering Chemical transition of Bentonite-based and CEment-based materials’. Japan
Nuclear Cycle Development Institute (JNC), Japan.
Gaucher E. ‘Modelling Diffusion of an Alkaline Plume in Two Types of Clayey Systems’.
Bureau of Geological and Mining Research (BRGM), France.
Arthur R.1, Sasamoto H.2 and Yui M.2 ‘Potential Complications in the Development of a
Thermodynamic Database for Hyperalkaline, Argillaceous Systems’. 1Monitor Scientific,
USA, and 2Japan Nuclear Cycle Development Institute (JNC), Japan.
Ichikawa Y.1, Prayongphan S.1, Suzuki S.2, and Kawamura K.3 ‘Nano/Macro-BasedCation/Water Transport and Adsorption in Bentonite’. 1Nagoya University, 2Institute of
Research and Innovation (IRI) and 3Tokyo Institute of Technology, Japan.
Berner U. ‘Status of Cement Modelling – Future Investigations in the View ofCement/Bentonite Interactions’. Paul Scherrer Institut (PSI), Switzerland.
Takase H. ‘Discussion on PA Model Development for Bentonite Barriers Affected by
Chemical Interaction with Concrete: Do we have Enough Evidence to Support Bentonite
Stability?’. Quintessa Japan, Japan.

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General overview on the use of cement in repositories for
HLW and other radioactive wastes
Kazumi Kitayama1, Hiroyoshi Ueda1, Noriyuki Sasaki2 and Michihiko Hironaga3
1

Nuclear Waste Management Organization of Japan (NUMO)
2
Japan Nuclear Fuel Limited (JNFL)
3
Central Research Institute of Electric Power Industry (CRIEPI)Introduction
The high-level radioactive waste, HLW, denotes in Japan the vitrified waste from thereprocessing plant, which includes fission products and minor actinides. All the otherwastes from the reprocessing plant, the power plant and so on are categorized as LLW,
low-level radioactive waste, which includes wastes from the operation and thedecommissioning of the plants. LLW is categorized as L1, L2 and L3 wastes, TRU
waste and Uranium waste according to their origins and radioactivity. L1, L2 and L3
wastes are generated from the operation and decommissioning of the power plants. The
disposal of LLW is already started in Rokkasho site. TRU waste is generated from thereprocessing plant and includes relatively long-lived nuclides. Its disposal is still underdiscussion. LLW from the fuel fabrication plan is particularly called “Uranium waste”.
Each waste is disposed of according to its own disposal concept as shown in Fig. 1. L1, L2 andL3 wastes are disposed of near the surface or relatively shallow. The controlled disposal isapplied to these wastes, i.e., there will be the period of monitoring and control for several
hundred of years, after closure of the facility. On the other hand, HLW and TRU waste will bedisposed of several hundred meters deep.
Reuse

L3
Front-end
Facility

L2
L1

Back-end
Facility

TRU Waste

HLW

Industrial
waste

Ground Surface

～２ｍ
～１0ｍ

Controlled Disposal

Belowclearance

５０～
１００ｍ

Deep Geological
Disposal

Power
Plant

Fig. 1 Disposal concepts for radioactive wastes.

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Over
severalhundredmetersNUMO-TR-04-05

Use of cement
ground surface
The disposal of L2 waste
cover soil
is already under operation
at Rokkasho site. A viewof its No.1 facility is
bentonite/sand mixture
shown in Fig. 2. This
concrete pit
shows details of theengineered barrier system
for L2 waste. Cement isused for the mortar
waste
backfill around the waste
porous concrete layer
drain pipe
packages, the porous
cement base backfill
inspection
concrete and the structural
tunnelbedrock
concrete. Bentonite/sandmixture is used for the
bedrock
cover soil. Table 1
summarizes the functions
and requirements of
cement components in L2
Fig. 2 View of No.1 disposal facility in Rokkasho.
disposal concepts. It
should be mentioned that cement is considered as the barrier material particularly for relatively
short-lived nuclides, expecting its low permeability and high sorption capacity.

Table 1 Functions and requirements of the cement components of L2 disposal.

Functions for EBS
Components

Operational period

Period of decay of short-lived nuclides(monitored and controlled)

Long-term period(uncontrolled)

Isolation of nuclides

Restriction of nuclide migration

Requirements

Mortar backfill

SealingHigh sorption capacity

Structural concrete

Mechanical strength

Requirements

Requirements

Diffusive transport
High sorption capacity

Use of cement in HLW repository has been
discussed so far. The liner, grout andmechanical plug are provisionallyconsidered as shown in Fig. 3. The liner isneeded for a soft rock formation to ensure
mechanical stability of tunnels or shafts.
Grouting with cement is considered asmeasures against water inflow during thepre-closure period. The mechanical plugconfines and mechanically supports the
backfill material for tunnels or shafts.

High sorption capacity

Sealing plug
(Bentonite)

Mechanical plug
Fracture Zone

Liner

Grout

Overpack
Buffer(Bentonite)

Fig. 3. Use of cement in HLW repository concept (examples).

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NUMO-TR-04-05

Regarding HLW repository concept, cement is not considered as any barrier material, but asmaterial for construction which functions during the pre-closure period as shown in Table 2.
Relatively short-lived nuclides are isolated mainly with glass matrix and the overpack, notsimilarly as LLW disposal concept in which cement is used as the barrier material for shortlived nuclides. It may be mainly because cement is not suitable for the initial period of high heatgeneration of HLW due to the decay of short-lived nuclides.
Table 2 Functions and requirements of the cement components of HLW disposal (examples).
Components

Pre-closure

Post-closure

Functions

Requirements

Functions

Requirements

Mechanicalplug

Confine and mechanicallysupport backfill material

Mechanical strength

No detrimental effect onbarriers

Liner

Ensure mechanical stabilityof tunnels and shafts

Mechanical strength

No detrimental effect onbarriers

Grout

Suppress water inflow
through fractures

Low permeability

No detrimental effect onbarriers

Conclusion
It was illustrated how cement is employed or planned to be employed in the repositories withrespect to each category of radioactive waste in Japan. The concept of the cement employment
is fairly different between HLW and LLW disposal depending on the characteristics of thewastes. Cement is used only as “pre-closure” material for HLW while the barrier material toisolate short-lived nuclides for LLW. This is understandable in terms of the initial heatgeneration of HLW due to the decay of short-lived nuclides.

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PLANNED USE OF CEMENT IN ONKALO, IN A KBS-3V TYPE AND
KBS-3H TYPE REPOSITORY IN CRYSTALLINE ROCK
Johanna Hansen, Posiva
1. INTRODUCTION

The Posiva plans to construct a KBS-3 type repository for spent fuel in the crystalline bedrockon the Olkiluoto Island on the coast of the Baltic Sea. The Olkiluoto nuclear power plant, with
two operating reactors and one under construction, and the VLJ Repository for low andintermediate level waste are also located on the island.
Underground rock characterisation facility (URCF) ONKALO will be constructed ahead ofdeep repository to confirm the suitability of site and bedrock masses. The excavation of
ONKALO starts at summer 2004 and based on continued characterisation the investigation
data needed for construction licence for repository should be available early 2010th decade.
Construction of ONKALO will be done mainly with conventional excavation methods, but
the requirements set to the repository should be fulfilled. The construction should not cause
major disturbances in surrounding bedrock nor impair the long-term safety. Fulfilment ofthese requirements among other things set restrictions in use of stray materials and limits theseepage water in to the ONKALO and repository. This paper deals the planned use of cementin during the underground construction.
2. CONCEPT FOR FINAL DISPOSAL

The safety concept is based on multi barrier system, which guarantees the long-term isolationof spent fuel assemblies. Engineered barriers consist of durable copper-iron canisters, highly
compacted bentonite buffer and the tunnels, which will be sealed by backfill materials andsealing structures. The crystalline bedrock offers a natural barrier for repository, which will
be located at the depth of 400-700 metres. The repository design is of KBS-3V or KBS-3H
type (Figure 2). In a KBS-3V type repository, a canister is emplaced in a vertical deposition
hole bored in the floor of a tunnel. In the KBS-3H type repository, several canisters are
emplaced in a horizontal deposition hole with a length up to 300 metres (Autio et al. 1996 &Birgersson et al. 2001). In both concepts, the space between the canister and rock is filledwith highly compacted bentonite clay.

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NUMO-TR-04-05

Fig. 2. KBS-3V and KBS-3H alternatives.

The design basis for repository may accommodate 5800 tU spent fuel from the Loviisa (2 x
488 MWe VVER-440 type PWR) and Olkiluoto (2 x 840 MWe BWR) nuclear power plants
and also from the fifth reactor (OL3 1600 MWe PWR), which is under construction.
3. DESCRIPTION OF SITE CONDITIONS

Olkiluoto is an island (approx. 10 km2), close to the mainland, on the coast of the Baltic Sea.
The topography is flat and thin layer of sandy tills covers the sparsely outcropped bedrock.
The bedrock consists of Svecofennian metasediments and plutonic rocks of 1800-1900
million years in age. Migmatitic mica gneiss is the most abundant rock type, and is intruded
by foliated grey gneisses and massive coarse-grained granites and pegmatites. At the depth ofabout 500 metres, the majority of the rock mass at Olkiluoto consists of intact rock between
fracture zones and has been estimated as “normal” from the point of constructability (Anttila
et al. 1999). This means that excavation and rock support can be carried out using
conventional methods and materials generally used in underground constructions. Close to thedepth of 700 metres, the rock has been estimated as “demanding” or “very demanding” interms of its constructability, because of its relatively low uniaxial compressive strength (σucs =80 – 140 MPa) and the higher stress field (σH = 35 – 40 MPa at 700 metres). Severe spallingof the rock may occur, and special methods and materials (including for example shorter
blasting rounds, temporal supporting with bolts and shotcrete, and pregrouting) may beneeded when excavating and supporting the rock (Äikäs et al 2000).
In the upper parts of the bedrock the fracturing occur more intensively and hydraulicconductivity is somewhat larger. Fresh groundwater (content of Total Dissolved Solids (TDS)< 1 g/l) is found to the depth of about 150 metres, and brackish (TDS between 1 and 10 g/l),
sulphate-rich groundwater between 100 and 400 metres. Deeper groundwaters are saline(TDS > 10 g/l). At the depth of 500 metres, TDS varies between 10 and 25 g/l. The mostsaline waters at depths greater than 800 metres have TDS values between 30 and 75 g/l. These
deep saline waters seem to have been undisturbed during the most recent glaciation and evenmuch longer in the past.

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NUMO-TR-04-05

Table I. Main Water Types at Olkiluoto and Their Interpreted Origins and Formation Ages
(Anttila et al. 1999 and Pitkänen et al. 1999). Table is taken from Vieno (2000).
Depth ofoccurrence(metres)

Water type

Origin of dominant
end-members

Age estimate of dominant
end-member type(years)above 150

Fresh-brackish
HCO3-rich water

Meteoric water andpresent Baltic Sea water0 – 2500

100 – 300

SO4-rich brackish Na-Cl

Litorina Sea water

2 500 – 7 500

100 – 500

Brackish Na-Cl water

Pre-Litorina water containing
fresh glacial meltwater

7 500 – 10 000

below 500

Saline Ca-Na-Cl water

Preglacial to Precambriansaline water>> 10 000

During the construction and operation phases groundwater will be drawn into ONKALO andlater into the repository from the surrounding bedrock. A design basis TDS value of 35 g/l has
been recommended for a repository excavated at the depth of about 500 metres at Olkiluoto(Vieno 2000). All repository systems and engineered barriers should perform properly at leastat groundwater salinities ranging from fresh water to 35 g/l (Autio et al. 2002).
4. DESCRIPTION OF URCF ONKALOONKALO consist of a system of exploratory tunnels accessed by a shaft and an access tunnel.
The main objective of ONKALO work is to enhance the current geoscientific understandingof the site to allow the submission of the application for a construction licence for the deep
repository. ONKALO efforts possibility also to test interactions between the rock and theengineered barrier system (Posiva 2003).

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Fig. 3. Preliminary lay-out of ONKALO. A) ramp, B) shaft, C) upper characterisationlevel, D) main characterisation level, E) demonstration tunnels, F) lower
characterisation level.

The ONKALO will be excavated by conventional drill and blast method. The total length of
the spiral access ramp is 5 kilometres and the inclination of the ramp is 1:10. The preliminary
dimensions of the ramp are 5.5 metres in width and 6.35 m in height with broadened bendings.
The other access routes consist of few raise bored shafts, with height of 420-520 metres. The
main characterisation level is located at the depth of 420 metres. Minor characterisation levelat depth of 520 metres is connected to the main characterisation level by ramp. Combined
length of the tunnels, characterisation loops, auxiliary rooms and shafts are 8 500 metres (Fig.
3). Total volume of the ONKALO underground facilities is approximately 330 000 m3. The
influence of excavation will be monitored continuously during construction of the facility.
The ONKALO construction should not cause any major disturbances for surrounding natural
conditions (Posiva 2003).

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5. USE OF CEMENT DURING CONSTRUCTION PHASESThe implementation of underground construction will be started in the middle of 2004.
Support and sealing of crystalline bedrock will be performed by using of cementitious
materials. The water conducting fractures will be grouted by micro cement. Usually
pregrouting is used for sealing while post grouting may not be effective enough. The amountof injection grout should be limited because it is not removable from rock fractures. For
ONKALO, the quantity of cement needed for injection has been estimated to be 3 000 000 kg,
of which 2 500 000 kg is used in the access tunnels and ventilation shaft (Riekkola et al.
2003). For the other parts in the repository the current estimation is that about 2 000 000 kg of
cement will be needed. (Hjerpe 2003) The bedrock surfaces will be covered by shotcrete forbedrock stabilisation purpose. Rock bolts and anchors will be grouted into the bedrock withcement. Several temporary and permanent construction installations will be made from
cement based materials. Cast concrete is used for floors and walls. The elevators and theventilation systems will be mounted in elements built inside the shafts. The final design is not
yet determined. Here it is assumed that the elements will be made of 200 mm thick concrete(cement contents of 300 kg/m3), supported by steel meshes. In the access tunnels the cement
amount in the concrete linings is estimated to be 1 400 000 kg. For the ventilation shaft a
300 mm thick lining will be used in the upper 100 m. (Hjerpe 2003)
6. REMAINING QUANTITIES OF CEMENT AFTER CLOSURE OF REPOSITORY

The removal efficiency for cement used for miscellaneous construction purposes is estimatedto be 98%. Almost all concrete floors, walls etc are removable. Shotcreting is in theory
removable but in the design it will most probably remain in the repository. There are several
methods to remove the shotcrete, like excavation, mechanical pick dressing, hydraulic pickdressing and mechanical routing. The need of the removal of shotcrete will be evaluated later.
(Hjerpe 2003)
Grout for sealing the fractures and rock bolts cannot be removed and it creates the largest
quantities of cementitious materials, which will remain in the repository after closure. The
estimated quantity is 5 300 000 kg. Each deposition tunnel is sealed with a plug of massive
concrete that will remain after sealing in the repository. The plugs are 6 m long having a
volume of 138 m. The estimated quantity of cement needed for plugs is totally 4 700 000 kg.
(Haaramo 1999, Hjerpe 2003)
7. REFERENCES
Anttila, P., Ahokas, H., Front,K., Hinkkanen, H., Johansson, E., Paulamäki, S.,
Riekkola, R., Saari, J., Saksa, P., Snellman, M., Wikström, L. & Öhberg, A. 1999. Finaldisposal of spent nuclear fuel in Finnish bedrock - Olkiluoto site report, POSIVA 99-10.
Autio, J., Hautojärvi, A., Salo, J.-P. & Vieno, T. 2002. Backfilling concept for a spent fuelrepository at Olkiluoto. 6th International Workshop on Design and Construction of Final
Repositories “Backfilling in Radioactive Waste Disposal” ONDRAF/NIRAS - Brussels,
11-13 March 2002. Transactions, Session II, Paper 3.

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Autio, J., Saanio, T., Tolppanen, P., Raiko, H., Vieno, T. & Salo, J.-P. 1996. Assessmentof alternative disposal concepts, POSIVA 96-12.
Birgersson, L., Pers, K. & Wiborgh, M. 2001. Project JADE, "Long-term function andsafety – Comparison of repository systems,” Swedish Nuclear Fuel and Waste Management
Co (SKB), Technical Report TR-01-18.
Bäckblom, G. & Öhberg, A. 2002. The observational method applied to engineering andconstruction of the access to the ONLALO facility, Posiva Working report 2002-48.
Haaramo. M. 1999. Structural design of the concrete structures used to plug deposition
tunnel, Posiva Working Report 99-71 (in Finnish).
Hjerpe, T. 2003. Engineering and Stray Materials in the Repository for Nuclear Waste
Estimation of Quantities after Backfilling, Posiva working report 2003-72 (in print).
Pitkänen, P., Luukkonen, A., Ruotsalainen, P., Leino-Forsman, H. & Vuorinen, U. 1998.
Geochemical modelling of groundwater evolution and residence time at the Olkiluoto Site,
POSIVA-98-10.
Posiva Oy. 2000. Disposal of spent fuel in Olkiluoto bedrock – Programme for research,development and technical design for the pre-construction phase, POSIVA 2000-14.
Posiva Oy. 2003. ONKALO Underground Rock Characterisation Facility – Main Drawings
Stage, Posiva working report 2003-26, Posiva Oy, 80 p.
Posiva Oy. 2003. ONKALO Underground Characterisation and Research Programme(UCRP),POSIVA report 2003-03, 142 p.
Riekkola, R., Sievänen, U. & Vieno, T. 2003. Controlling of disturbances due togroundwater inflow into ONKALO and the deep repository, Working Report 2003-46, Posiva
Oy.
Vieno, T. 2000 Groundwater salinity at Olkiluoto and its effects on a spent fuel repository,
POSIVA 2000-11, 36 p.
Äikäs, K.(editor), Hagros, A., Johansson, E., Malmlund, H., Sievänen, U., Tolppanen, P.,
Ahokas, H., Heikkinen, E., Jääskeläinen, P., Ruotsalainen, P. & Saksa, P. 2000.
Engineering rock mass classification of the Olkiluoto investigation site, POSIVA 2000-08.

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MAIN ISSUES IN THE USE OF CEMENT IN A SPENT FUELREPOSITORY– WHAT ARE WE SEEKING ANSWERS FOR?
Timo Vieno
VTT Processes, P.O. Box 1608, FIN-02044 VTT, Finland

Safety-related reasons to use cement

Besides engineering reasons and operational safety, there are reasons related to the longterm safety to use cement in a repository for spent nuclear fuel in crystalline bedrock.
Inflow of groundwater into the excavations during the construction and operation phase
may namely cause drawdown of groundwater table and significant movement and mixingof groundwater masses giving rise to•desaturation and intrusion of air in the drawdown zone•
intrusion of superficial water – containing oxygen, carbon dioxide and organic
substances – into the host rock•at islands and coastal areas, intrusion of seawater – percolated through sediments andbeing rich in sulphate, bicarbonate and possibly in ammonia and organic substances•
upconing of deep saline groundwater towards the excavations•
consumption of the redox and pH buffering capacity of fracture fillings and rockmatrix.
The disturbances can be reduced by applying methods commonly used in rock engineering,grouting of rock with cement and hydrostatic liners, to limit inflows (Riekkola et al. 2003).
Posiva has recently started the construction of an underground rock characterisation
facility, called ONKALO, at the Olkiluoto island at the coast of the Baltic Sea (Posiva
2003a-c). The facility consists of a system of exploratory tunnels accessed by a tunnel anda shaft. The main characterisation level will be located at a depth of about 400 metres andthe lower level at a depth of about 500 metres. The total underground volume of
ONKALO will be approx. 330 000 m3 with the combined length of tunnels and shafts ofapprox. 8500 metres (Posiva 2003d). ONKALO is designed in such a manner that it canlater function as access routes and auxiliary rooms of the repository for spent fuel.
If no sealing of rock were made, the inflow of groundwater into ONKALO could be as
high as 600 000 m3/yr and drawdown of groundwater table and upconing of deep saline
groundwater several hundred metres (Vieno et al. 2003a). The salinity of groundwater inthe vicinity of the tunnels at the characterisation levels might locally rise up to 50 g/l,
whereas it ranges in the present natural state from 10 to 25 g/l. A major part of the inflow
comes from the subhorizontal fracture zones, which the access tunnel and shaft intersect at
a depth between 70 and 330 metres. To minimise the disturbances, the leakages into the
excavations will be limited to a level as low as practically achievable. The amount of
cement remaining in the host rock after the closure of the repository has been estimated to
be about 5400 tons for the ONKALO excavations and in total 10000 – 23000 tons fora repository containing about 5800 tons of spent fuel (Hjerpe 2003a-b).

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Cement-related issues: general

A review of potential effects of cementitious leachate in the vicinity of a spent fuelrepository highlighted the following issues (Vieno et al. 2003a–b)•
Alteration of the bentonite buffer may take place.
•
The redox stability of spent fuel is questionable if it comes in contact with a high pH
solution. It was noted that the spent fuel itself also contains alkaline and earthalkaline metals, notably cesium, which, when released from the fuel, may increase
the pH inside the canister.
•
Solubility and sorption databases specific to the KBS-3 concept and crystalline rockat high pH conditions are scarce. Databases developed for cementitious
LLW/ILW/TRU disposal concepts are, of course, available, but the databases usedin past assessments of the KBS-3 concept cannot reliably be extrapolated to pH >11.
•
The effects of superplasticizers and other (organic) admixtures of cement andconcrete are not well known.
•
In the long term degrading concrete structures – for example, injection boreholes,
liners and floors – may become preferential flow and transport pathways.
Less significant concerns were associated with the effects of cement on fracture fillings
and rock matrix (Baker et al. 2002) as well as with potential generation of colloids at sharp
pH gradients. The reviews of corrosion of the copper canister (King 2002) and of thezircaloy cladding of the fuel pins (Johnson & McGinnes 2002) indicate no significant
negative impacts due to alkaline conditions.
Mass transport analyses of cement

Assessment of release and transport of cement in the geosphere and its intrusion into theEngineering Barrier System (EBS) of the repository is an inverse problem to radionuclide release and transport. The same modelling concepts can be used, but in the
cement case the source term is dispersed in heterogeneous conditions in the groutedrock around the excavations. The analyses of groundwater flow and transport of cementin the vicinity of ONKALO show (Vieno et al. 2003a) that•
The subhorizontal fracture zones, which the access tunnel and shaft intersect at
depths of 70 – 130 metres and 290 – 330 metres divide the flow pattern intolayered zones. It is unlikely that significant amount of cement from these zones orfrom the sparsely fractured rock between and above them would be transported
into the sparsely fractured rock below the lower zone.
•
The water leaving a grouted rock spot will not have the pH and other properties of
cement porewater, but is diluted by the groundwater flowing around/through the
grouted area. This source term dilution is enhanced by the fact that groutings are
made at fracture zones and other locations where flow rates are highest.
•
Further buffering and dilution take place during transport in the geosphere. In
open fractures with a limited buffering capacity and a small WL/Q (half of the“flow wetted” surface divided by the flow rate), the leachate may, however, betransported over long distances.
•
Transfer of OH- ions from water-conducting fractures intersecting a deposition
hole is limited by the boundary layer (film) resistance between the flowing
groundwater and the stagnant porewater in the buffer. The fraction of OH- ionsentering the buffer decreases with an increasing flow rate of groundwater along
the fractures.
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In the assessment of the effects of OH- ions entering the buffer from rock fractures,
one must take into account that the attack is localised. The shape and volume of
the affected bentonite are governed by diffusion processes and reactions between
the intruding solution and the clay.

In general, it was estimated as fairly unlikely to encounter a plume with a pH
significantly higher than 11 at a distance of several tens of metres (which corresponds tothe minimum distance between the ONKALO excavations and the deposition galleries)
from the nearest grouted spot. In the case of ONKALO, the groundwater flow and masstransport analyses showed that it is very unlikely that cement transported fromONKALO, especially from the major subhorizontal fracture zones and from the sparsely
fractured rock above and between them, could significantly impair the key functions of
the bentonite buffer and other components of the EBS in the deposition holes of therepository.
Recommendations and areas deserving further studies: general

Cement-bentonite interaction is a key issue. In all modelling studies special attention
should be paid on mass balances and mass transport rates.
Uncertainties in the transport analyses could be reduced by further experiments andmodelling studies on transport and effects of cement in fractured rock. Posiva is
considering participation in the proposed second phase, Long-term Cement Studies(LTC), of the Hyperalkaline Plume in Fractured Rock (HPF) project in the Grimsel rocklaboratory in Switzerland.
Grouting experiences could be revisited to check whether any indications of a high pH
plume can be found. Most convincing evidences could be obtained by systematic
measurements of groundwater pH around past groutings in backfilled and saturated
excavations in deep crystalline bedrock, if such can be found, or around cemented deep
boreholes.
As concerns radionuclide release and behaviour, areas deserving further studies include
stability of the spent fuel and performance assessment databases for the KBS-3 concept
in a high pH environment.
Potentially harmful effects of cement could, of course, be minimised by minimising theamount of ordinary cement remaining in the host rock. Posiva is developing low-alkali
cementitious and non-cementitious grouts in cooperation with NUMO and SKB. Effects
of new materials introduced into the host rock need, of course, be studied carefully. The
effects of superplasticizers and other admixtures of cements and grouts need to bestudied, too.
Main issues of cement-bentonite interaction

In short, the main issues of cement-bentonite interaction are•
What happens to the bentonite buffer and cement/concrete, if they are in contact witheach other, for example, within a sealing structure?
•
What happens to the bentonite buffer affected by cementitious leachate?
•
Can cementitious leachate penetrate through the bentonite without significant
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buffering and attack the canister and spent fuel?
Ten questions (and some comments) on cement-bentonite interaction

1.
2.

3.

4.

5.

6.
7.
8.
9.

10.

Mass transfer over an interface of highly compacted bentonite and concrete (bothdirections). In the simulations, the mass transfer rates as a function of time should
be recorded also at different depths in the materials.
Are the effects on bentonite governed by the entering rate of OH- ions into thebuffer? Is the pH (i.e. concentration of OH- ions in the entering solution) actuallyless important and the effects on bentonite governed only by the flux of OH- ions(moles per year) entering the buffer? Are the effects of 10 litres/yr of pH 11
solution similar to those of 1 litre/yr of pH 12 solution? Note also that the pH
scale is temperature-dependent: at higher temperatures, ion product and soluteconcentrations of OH- and H+ increase, while pH decreases. What is the role ofthe cations (e.g. Ca2+, Na+, K+) and ionic strength (salinity) in the solution
entering the buffer?
In experiments with highly compacted bentonite, the transport of a high pH plumeoriginating from NaOH solution has been significantly faster than that of a highpH plume originating from Ca(OH)2 solution. Is this only due to the higher
concentration of OH- ions in the used NaOH solutions, and thus a higher diffusive
mass transfer rate, than from the Ca(OH)2 solutions, where the OH- concentration
is limited by the solubility of Ca(OH)2?
Extension and shape of the altered bentonite layer as a function of time? Note thatthe attack from rock fractures or through the repository excavations may belocalised. Is the growth of the altered zone governed by diffusion processes andreactions between the intruding solution and the clay?
Relative propagation rates of diffusing OH- ions and the reaction front of thebuffering and alteration processes in highly compacted bentonite. Is it possible
that, due to the kinetics of reactions, the plume of high pH could reach the canister
surface (and penetrate into a defective canister) before the buffering reactions
neutralise the high pH? What are the effects of alkaline and earth-alkaline metals(e.g. cesium) released from the spent fuel on the solution chemistry inside thecanister?
What are the effects of a high pH plume on montmorillonite and accessory
minerals of highly compacted bentonite? Which effects are the most importantones for the point of view of buffer performance?
What is the buffering capacity of highly compacted bentonite, i.e. its ability tokeep the pH, say below 11 or 10, in terms of moles of OH- ions per kg of clay? Is
this quantity a relevant measure of the buffering capacity of the buffer?
Mechanical (e.g. swelling pressure, plasticity) and transport-related (e.g. porosity,
diffusivity, sorption) properties of highly compacted bentonite altered by a highpH plume.
Effects of dissolution and (re)precipitation of siliceous and aluminous species andother accessory minerals of cement, ballast, rock and bentonite: Is there a risk of
cementation of the bentonite buffer affected by a plume of high pH, when the pH
eventually drops again?
Effects of superplasticizers and other admixtures of cement on bentonite andradionuclide mobility.

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References

Baker, A.J., Bateman, K., Hyslop, E.K., Ilett, D.J., Linklater, C.M., Milodowski, A.E.,
Noy, D.J., Rochelle, C.A. & Tweed, C.J. 2002. Research on the alkaline disturbed zone
resulting from cement-water-rock reactions around a cementitious repository. NIREX
Report N/054.
Hjerpe, T. 2003a. Engineering and stray materials in the underground rockcharacterisation facility ONKALO – Estimation of quantities at the time of backfilling.
Posiva Working Report 2003-48.
Hjerpe, T. 2003b. Engineering and stray materials in the repository for nuclear waste –Estimation of quantities after backfilling. Posiva Working Report 2003-72.
Johnson, L.H. & McGinnes, D.F. 2002. Partitioning of radionuclides in Swiss powerreactor fuel. National Cooperative for the Disposal of Radioactive Waste (Nagra),Technical Report 02-07.
King, F. 2002. Corrosion of copper in alkaline chlorine environments. Swedish Nuclear
Fuel and Waste Management Co (SKB), Technical Report TR-02-25.
Posiva 2003a. Baseline conditions at Olkiluoto. POSIVA 2003-02.
Posiva 2003b. ONKALO Underground Characterisation and Research Programme(UCRP). POSIVA 2003-03.
Posiva 2003c. Programme of monitoring at Olkiluoto during construction and operationof ONKALO. POSIVA 2003-05.
Posiva 2003d. ONKALO Underground Rock Characterisation Facility – Main drawings
stage. Posiva Working Report 2003-26.
Riekkola, R., Sievänen, U. & Vieno, T. 2003. Controlling of disturbances due togroundwater inflow into ONKALO and the deep repository. Posiva Working Report
2003-46.
Vieno, T., Lehikoinen, J., Löfman, J., Nordman, H. & Mészáros, F. 2003a. Assessmentof disturbances caused by construction and operation of ONKALO. POSIVA 2003-06.
Vieno, T., Lehikoinen, J. & Nordman, H. 2003b. Cement issues in the assessment of the
disturbances caused by the underground rock characterisation facility ONKALO at
Olkiluoto. Workshop on Qualification of Low-pH Cement for a Geological Repository,
October 15 – 16, 2003, Stockholm, Sweden.

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Extended Abstract
The bentonite/cement interaction problem: cutting the Gordian knot
Ian McKinley, Russell Alexander, Wolfgang Kickmaier, Fiona Neall
Nagra, Switzerland
Introduction

A basic principle which contributes to our ability to make confident predictions of thesafety of deep geological repositories for long-lived waste is avoiding high energy
systems. The geological environment itself is (usually!) selected to be stable with lowhydrologic, thermal and geochemical driving forces. The engineered barriers
emplaced should, ideally, maintain this situation. It is, therefore, desirable to avoid
use of materials which are mutually incompatible or are incompatible with the hostrock.
A particular problem arises due to the extensive use of cement and concrete in
the civil engineering and mining industries. Very extensive practical experience
with well-characterised and relatively cheap cementitious materials makes them thenatural choice for many applications involved in repository construction. Such use is,however, incompatible with the use of highly compacted bentonite as a key safetybarrier; the interactions between these materials being the main focus of most papers
presented at this workshop.
Despite the efforts being expended, we feel that there is no possibility of rigorously
excluding significant long-term degradation of bentonite barriers which interact withcement leachates - at least within the foreseeable future. Even if understanding of thedegradation processes increases, such a dynamic system with time-varying properties
will be extremely difficult to characterise. In such a case, modifying designs to ensurethat such interaction does not occur in the first place seems a more robust approach.
Two cases are distinguished, "TRU" type long-lived ILW - where replacement ofbentonite is suggested - and HLW / SF where we recommend protecting bentonite
from any interaction with cement leachate.
TRU

The case for TRU is relatively clear; concrete is a major component of the packaged
waste and hence there is no point in restricting use of cement and concrete forconstruction. The question is thus - what role does bentonite serve and can it be takenover by another material?
The geochemical environment within the monolithic, microporous near-field in mostTRU designs ensures effective immobilisation of most radionuclides. Actinides, inparticular, are likely to display low solubility and high sorption. The most problematicradionuclides are those which are highly mobile in such situations - e.g. anions (I-129),
organics (organic C-14) and alkali metals (e.g. Cs-135). Even for these, releases may
be greatly limited within a low permeability concrete.

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One role attributed to bentonite is to further reduce these releases by ensuring thatsolute transport through the near-field is dominated by diffusion. For this particularcase, there are certainly alternative approaches and materials which could provide thesame net effect - the most robust of which is probably a high permeability hydrauliccage (assuming that a host rock cannot be found which provides such a situation
naturally – e.g. Opalinus Clay).
The problems mainly arise when the evolution of the concrete monolith is considered.
Over a relatively short period cracking is quite likely, for example due to:•settling / earth movements (creep, fault movement, ...)•

gas production•swelling of corrosion products (rebars, canisters, ...)•

biodegradation•

construction defects, monitoring equipment and other anthropogenic
influences

In such a case, a number of problematic scenarios need to be considered:
1. advective water flow; driven by hydraulic gradients
2. advective water flow; driven by gas pressure
3. release of gaseous radionuclides (e.g. C-14 methane)
4. release of radionuclides as colloids, macromolecular complexes or associatedwith microbes
The presence of an intact, highly-compacted bentonite barrier would avoid (1) and (4)above, but do little for (2) and (3). A simple hydraulic cage would also avoid (1) inthe case of minor cracking and might reduce the effects of (3) by providing amacroporous gas buffer which might minimise direct gas release to the geosphere.
The problem with the bentonite barrier is its uncertain long-term performance. Even if
mineralogical alteration is slow, cementation due to carbonate or silicate precipitation
may be relatively rapid. Coupled with gas production, this leads to cracking scenarios
which would result in loss of both advective flow barrier and colloid filtration roles.
By comparison, the hydraulic cage is much more robust. Cementation / cracking
causes little significant effect and massive precipitation with a major reduction inporosity would be needed to cause a decrease in hydraulic conductivity.
If an enhanced barrier is needed, an external hydraulic cage can be combined with anadditional colloid filter with low permeability, but this should be immune todegradation by hyperalkaline conditions. Candidates would be special plastic (or selfhealing) concretes or zeolites. As the latter are often identified as the end-products ofbentonite alteration, their stability is well supported. Zeolites have wide ranges ofproperties, which include molecular filtration and highly-specific sorption, indicatingthat an optimised solution is possible. It should be noted that, in this regard, much can

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also be done in terms of designing the waste emplacement system for improved longterm performance.
HLW

A particular problem occurs with the use of cement and concrete in repositories
for HLW (or SF) in which bentonite plays a key barrier role (Table 1). The option of
replacing bentonite is not considered here; instead we focus on avoiding any
processes which could affect its longevity. The best option is to avoid all use of
cementitious materials in the vicinity of waste emplacement zones. For hard hostrocks, a lot can be achieved by careful design and construction, aligning tunnels for
maximum mechanical stability, using construction techniques which cause minimum
mechanical damage and support systems which do not involve use of concrete. An
example of this approach is described in the recent Entsorgungsnachweis project.
Even when massive structures are required (tunnel seals); use of concrete can be
avoided by a bit of lateral thinking (e.g. use of natural stone plugs).
The challenge is to replace all the planned use of cementitious materials in sensitive
areas. Such uses include:
tunnel / borehole liners
tunnel / borehole plugs & seals
grouts for hydraulic sealing
floors, walls and other structural elements
In the case of liners, it is worth distinguishing between the cases where such liners are
required for mechanical support and those where they are needed only to reduce water
inflow during the operational period. In the former, alternative materials which can beconsidered include steel, ceramics and natural stone. Although there may be somecost consequences, these must be seen in terms of total project costs and opportunities
for global cost optimisation. In the latter, there may additionally be options for sealingof “wet areas” using resins and / or simply amending the EBS design to allow
practical operation with higher water inflow rates (e.g. use of pre-fabricated EBS
modules – PEMs).
As noted above, in many cases concrete can be avoided in plugs by use of naturalstone. There certainly are a number of options for use of other designs using metal
plugs or packers – especially where the plug is required only during the operational
period. Costs are unlikely to be critical here and alternative designs may even havesignificant advantages (especially if remote handled emplacement is considered).
Replacing conventional cement-based hydraulic grouts for sealing major water inflow
zones is probably the biggest challenge at present. Many alternative materials are
possible – for example clay-based, alternative carbonate- or silicate-cementation
systems or resins. The main problem is the lack of a development programme for suchmaterials which includes accumulation of experience under relevant conditions (manysystems which work well in the laboratory fail when tested in-situ). Nevertheless,with the rapid advances in materials technology, this should not be regarded as ahopeless option – especially when combined with efforts to better characterise

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problematic features at a potential site and minimise sealing requirements by
optimisation of layout.
The structural used of concrete are, in contrast, generally easiest to work around;avoid entirely by design changes (e.g. replace floors by rails directly on the rock /liner) or use of alternative materials (e.g. concrete floors replaced with gravel plus
natural stone paving).
It is quite probable, if avoiding use of concrete is taken to be a design prerequisite,
alternative options can be found for most host rocks presently considered.
Although maybe a second-best choice for most disposal concepts, if the use of
concrete liners or cement grouts cannot be avoided, there are options to protect
bentonite from degradation – particularly during the initial high temperature / highalkalinity phase where risks are greatest.
Two examples are illustrated (although others are certainly possible). The first is avariant of the PEM theme, where the bentonite is protected for a period of time due tothe external steel handling shell. To maximise protection, pozzolanic or glassy
material (e.g. crushed tuff) is used to backfill the annulus around the PEM. This
material reacts rapidly at high pH and hence acts as a pH buffer. As it has no
particular barrier role apart from space-filling, this reaction will have no effect onlong-term performance.
An alternative is the CARE option considered by NUMO. In this design massive,casks containing around 20 HLW packages are emplaced in caverns which are kept
open for a planned period of 300 years before sealing and closure of the repository.
Even if concrete liners and floors are used in this design, the problems are greatly
reduced by very extensive carbonation of all such structures during the long period ofhigh temperatures and active ventilation.
Conclusions

It will be very difficult to make a safety case which depends on the longevity ofbentonite which can be degraded by interaction with cementitious materials. Rather
than expend effort to better understand this degradation process, it may be better toavoid it by design.
For TRU, the best approach is to replace bentonite with an alternative material. A
good option seems to be a hydraulic cage with an inner zeolite layer. In any case, forsuch waste there is great optimisation potential by considering the EBS design as awhole.
In the case of HLW, it is best to avoid all use of concrete in critical areas. A numberof alternatives have been suggested. If concrete must be used, design changes toreduce the risk of interaction with bentonite can be examined.

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Bentonite role
Degradation by cement
Diffusion barrier
Major
Colloid filter
Major
Radionuclide sorption
Some
Plasticity (gas flow)
Major
Thermal conductivity
None
Mechanical buffer
Some
Microbe barrier
Some

Key problem
Cementation / cracking
Cementation / cracking
Ion exchange
Cementation
Cementation
Cementation / cracking

Table 1 Key roles of bentonite and their sensitivity to degradation by cement.

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DISSOLUTION MECHANISM AND KINETICS OF SMECTITE UNDERALKALINE CONDITIONS
Tsutomu Sato1, Masato Kuroda2, Shingo Yokoyama2, Masanori Tsutsui2, Keisuke Fukushi3,
Tadao Tanaka4 and Shinichi Nakayama4
1

Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa, Ishikawa, 9201192, Japan
2
Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa, 9201192, Japan
3
Research Center for Deep Geological Environments, National Institute of Advanced Industrial Scienceand Technology, Tsukuba, Ibaraki 305-8567, Japan
4

Department of Fuel Cycle Safety Research, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, JapanINTRODUCTION

Extensive use of cement for encapsulation, backfilling, and grouting purposes is envisaged
in geological repositories of radioactive waste. Degradation of cement materials in therepositories can produce a high pH pore fluid initially ranging from pH 13.0 to 13.5. The pHof fluid progressively decreases to moderately alkaline range with the formation and evolutionof subsequent materials (Atkinson, 1985). The high pH pore fluids can migrate from therepository and react chemically with the host rock and bentonites which were employed toenhance repository’s integrity. These chemical reactions can affect the capacity of the rocks
and bentonites in retarding the migration of radionuclides. Smectite, main component ofbentonite, can lose some of their desirable properties at the early stages of bentonite-cement
fluid interaction. This has been a key research issue in performance assessment of radioactive
waste disposal. The effect of high pH fluid on the chemical and physical behavior of smectite,
especially dissolution behavior and rates is of utmost importance.
A mineralogical conversion during the interaction with high pH fluids and its effect on
swelling and sorption capacities have been roughly understood (for example; Johnston &Miller, 1984, Duerden, 1992, Savage et al., 1992, Eberl et al., 1993, Bauer & Berger, 1998,
Amaya et al., 1999 and Sato, 2001). However, most of the previous studies have focused
mainly on the mineral conversion under high pH and high temperature conditions. Only a few
studies on smectite dissolution rate under different pH conditions and relatively low
temperature expected in the repository have been systematically carried out In the above
studies, reliable data was probably obtained because the experiments were carefully
performed under the given conditions. However, as following two reasons, the experimental
results are difficult to compare a priori for discussing the pH effects on the dissolution rate ofsmectite. Firstly, most of the authors used not an almost pure smectite but a bentonite
containing other minerals such as cristobalite, quartz, calcite, feldspar, and so on. The sample
studied by Cama et al. (2000) was mainly composed of an illite/smectite interstratified
mineral with about 85-90% smectite. Secondly, the dissolution rates have been obtained fromthe different systems, i.e., flow-through (open) or batch (close) systems. In the batch system
performed by many authors, the degree of saturation (i.e., deviation from equilibrium) should
be changed as function of time, and then the smectite dissolution does not attain a constantrate (Oelkers et al., 2001). In this context, stirred-flow-through dissolution experiments werecarried out to determine reliable dissolution rates of smectite from neutral to highly alkalinecondition and to formulate the effect of pH and temperature on smectite dissolution rate.
Atomic force microscopy (AFM) using fluid cell also performed to determine the reactive

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surfaces and reliable dissolution rate in smectite dissolution and to understand mechanism of
the dissolution under alkaline condition.
EXPERIMENTS
Flow-through system was employed in this study because the flow-through experimentsallow us to measure the dissolution rate under steady state condition. Experiments werecarried out using stirred-flow Teflon® reactors with long cylindrical shape. To avoid pHchange due to the solution-CO2 interaction, the preparation, stock and collection of thesolution were performed in glove box filled with N2 gas atmosphere.
The experiments were performed for mixed NaOH-NaCl or KOH-KCl aqueous solutions
with ionic strength of 0.3 M. Purified smectite (Kunipia-P® provided from Kunimine
Industry Co Ltd) was reacted at the pHs from 8-13 and constant temperature of 30, 50 and
70°C. For each experiment, 120 mg of the sample was added to the 120 ml of the solution in
the reactor. The concentrations of Al in the contacted aqueous solutions were determined byusing inductively-coupled plasma mass spectroscopy (ICP-MS), and Si was determined as
SiO2 through molybdenum-blue spectrometry. The dissolution rates were calculated from thesteady-state Si and Al concentrations.
Adsorption of protons and hydroxyl ions with the sample was investigated by acid/basetitration. The titration was performed under N2 gas bubbling to exclude CO2, constant ionicstrength (0.3 M NaCl) and at temperatures used in the experiments (T = 30, 50 and 70ºC).
Acidimetric titrations were performed until pH 4, while alkalimetric titration were conducteduntil pH 10.
The following three setups for the dissolution experiments by AFM observations wereprepared (referred here as Run X); Run I: short-term in situ batch dissolution experiment atroom temperature (22°C); Run II: long-term in situ flow-through dissolution experiment atroom temperature (22ºC); and Run III: long-term dissolution experiments at 50°C. The
dissolution experiments were conducted under highly alkaline conditions (pH 13.3 ± 0.1)
using 0.3 M NaOH solutions. For Run III, the samples mounted on mica plates were
immersed and heated in 50 mL 0.3M NaOH solutions inside Teflon containers. The samples
are allowed to react for a period ranging from 6 to 33 days at 50ºC and then placed inside thefluid cell of the AFM to prevent further dissolution with entrained alkaline reacting solution.
The samples mounted on the mica plate were observed under AFM at 22ºC to detect changes
in particle volume after the dissolution reactions. A hundred particles were observed to bestatistically viable.
RESULTS AND DISCUSSION
In the present study, possibilities of other variables were except for pH and temperatureeliminated by conducting all experiments at constant of the factors. Therefore, the observed
difference in the dissolution rates should be attributed to the difference in the pH andtemperature of the solution. From the rates obtained in the dissolution experiment, it isunambiguously shown that the pH strongly affects the dissolution rate under alkalinecondition, and the rates increase with an increase in the pH. Fig. 1 is plot of the logarithm of
the rate versus the pH of the solution. Good linear relationships are observed between pH andlog rate. The rate laws were calculated by fitting the dissolution log rate to the pH value, andyielded the following equations:−0.15
Rate(mol −2 s −1 ) = 10 −13.58 a H +(in 30˚C NaOH solution)Rate(mol −2 s −1 ) = 10 −13.84 a H +

−0.24

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(in 50˚C NaOH solution)

NUMO-TR-04-05

Rate(mol −2 s −1 ) = 10 −13.52 a H +−0.27(in 70˚C NaOH solution)

The dissolution rates calculated cover a range of alkaline pH. The rates become more pHdependent with increasing temperature.
The changes in ln rate at constant pH as a function of 1/T are shown in Fig. 2. The
calculated values of Eexp for smectite dissolution range from 37.89 to 63.88 kJ mol-1. The
lowest values are at near neutral pH but the rates increase with increasing pH. The changes in
Eexp as a function of pH are shown in Fig. 3. The variation in activation energy with pH
causes rates to become increasingly sensitive to pH at elevated temperature. Above pH 8, theobtained relation between pH and activation energy is shown following equation:
E exp = 6.80 pH − 18.07

In order to formulate the effect of pH and temperature on the dissolution rate, model of
two parallel reaction paths are proposed according to Cama et al. (2002), givesb1 ⋅ a H +b2 ⋅ a H +Ratei= k1 ⋅ F1+ k 2 ⋅ F2
ρr
1 + b1 ⋅ a H +1 + b2 ⋅ a H +where Fi is the maximum surface coverage of protons on site i, bi is a constant related to theenergy of adsorption on site i and aH+ is the activity of protons in solution.
A pH-independent apparent activation energy for each of the reaction paths is calculated byplotting an Arrhenius plot of the rate coefficients (k'1 and k'2) at 30°C, 50°C and 70°C, whichwere obtained from the fitting of the experimental data to the proposed model. The apparent
activation energies were determined from a best-fit of rate coefficients that were obtained byfitting the experimental results at each temperature. The following equation was obtained byfitting the whole data set into a single equation
177⋅ e20.4 / RT ⋅ aOH+
0.0297⋅ e23.5 / RT ⋅ aOH+
−6
−39.6 / RT
−69.7 / RT
Rate= 4.74⋅10 ⋅ e⋅+1.70⋅ e⋅
1+177⋅ e20.4 / RT ⋅ aOH+
1+ 0.0297⋅ e23.5 / RT ⋅ aOH+
The proposed model shows that smectite dissolution rate may be described by a rate law using
activation energies being pH-independent. The dissolution mechanism can be interpreted interms of surface complexation theory. In this study, the surface properties of smectite atdifferent temperature, reactive surface parameters and distribution of reactive sites as afunction of pH were systematically investigated. As the result of investigations, the first andsecond reaction sites in the above equation are Si site and Al site, respectively. Combining theabove equation (the terms of effect of temperature and pH) and f(∆Gr) obtained from Cama etal. (2000) into the general rate law (Lasaga 1995, 1998) gives
177⋅ e 20.4 / RT ⋅ aOH+
0.0297⋅ e 23.5 / RT ⋅ aOH+
−6
−39.6 / RT
−69.7 / RT
Rate= (4.74⋅10 ⋅ e⋅+1.70⋅ e⋅)
1+177⋅ e 20.4 / RT ⋅ aOH+
1+ 0.0297⋅ e 23.5 / RT ⋅ aOH+
( −6⋅10−10 )⋅(∆Gr)6RT⋅ (1− e)In Run I, the observed reduction in smectite particle volume can be attributed solely toedge surface dissolution. Dissolution rate calculated based on the surface area defined by the
ESA (observed edge surface area) is 1.30×10-9 mol/m2•sec. On the other hand, there were no
detectable changes in particle volume in Run II which is already achieved a steady state fordissolution. The relatively faster dissolution in Run I was also observed at the initial stage inthe flow-through dissolution experiments. The dissolution rates were therefore different
between at initial and steady state conditions. In Run III, the dissolution rate was calculated
based on the median values of the basal surface areas of particles. The reduction in particle
volume is mainly attributed to dissolution along edge surface areas despite the formation of a

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few etch pits on the basal surface. Based on the surface areas defined by the ESA, thedissolution rate was 1.11 ×10-11 mol/m2•sec. The rate is fairly close to that obtained from theflow-through dissolution experiment at 50°C and pH 13.3 (1.20×10-11 mol/m2•sec). From
AFM observation, the dissolution rates derived at longer observation periods were directlycomparable with the results from the flow-through dissolution experiments. Furthermore, theactual reactive sites (e.g. ESA) in the dissolution reactions were determined and used in thecalculations of dissolution rate, which reflect the real dissolution rate of smectite. On thecontrary, the rates obtained from flow through dissolution experiments were sufficiently
reliable because of the above correspondence in the obtained dissolution rates
ACKNOWLEDGEMENT
This is a part of study funded by Radioactive Waste Management Funding and ResearchCenter, Japan.
-10.0

-23
70℃：Rate=10-13.52aH+

ln rate（mol/m2)

50℃：Rate=10-13.85aH+0.24

-11.5
-12.0

-13.0

-25
-26
-27
-28

30℃：Rate=10-13.58aH+0.15

-12.5

-29
2.9

7

8

9

10

11

12

pH12.0pH11.0pH10.0
pH9.0
pH8.3

□
○
▲
■
●

-24

-11.0

13

3

3.1

3.2

3.3

3.4

1000/TpH

Fig. 2 Arrenius plots of smectite dissolution rate at different
pH of the solution.

Fig. 1 Relationship between logarithm of the dissolution rates
and the pH of NaOH solution each temperature (30, 50, 70ºC).

Basal surface area (nm2)70
Activation Energy (kJ/mol)

log rate (mol/m2s)

-10.5

0.27

60
50
40

Eexp=6.80pH-18.07

9

10

11

62000
60000
58000

Y = -0.75X + 63583
r = 0.999
0

1000

2000

3000

4000

5000

Reaction time (sec)

ESA：
2.74×10-9mol/m2/sec
TSA：
2.11×10-11mol/m2/sec

30
20
8

64000

12

pH
Fig. 3 Experimental activation energy (Eexp) for dissolutionof smectite as a function of pH.

Fig. 4 Changes in AFM images and basal surface area of thesample particle in the dissolution process (22˚C, pH=13.3).
Calculated dissolution rates based on edge surface area and total
surface area also shown in this figure.

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Experimental study on changes of bentonite mineralogy and physicalproperties as a result of exposure to high pH solutions
Ola Karnland1, Ulf Nilsson1, Siv Olsson2, Patrik Sellin3
1
Clay Technology AB, ok@claytech.se, 2Geochimica, Lund, 3SKB, Stockholm

INTRODUCTION AND OBJECTIVS

In a repository for spent nuclear waste, it will be most practical to use concrete in many
constructions, and cement for sealing rock fractures. In the Finnish ONKALO
underground facility, the estimated quantity of injected cement is 3E6 kg, and in the
Swedish planned KBS3 repository the corresponding figure is around 9E5 kg. The highpH in cement pore water may affect the stability of repository components, and istherefore of concern for the performance and safety assessment analyses. In a KBS3type repository, the high pH may influence fracture minerals, the bentonite buffer,canister components, and the spent fuel in case of a canister failure. The pH evolution in
the bentonite is of special interest, since it completely surrounds the fuel canisters andtherefore may protect the canister and fuel. Such pH buffering capacity may be due toaccessory mineral reactions, montmorillonite surface reactions and montmorillonite
crystal lattice reactions. Fresh cement may raise pH to values between 13 and 14, and inmatured cement materials pH is governed by portlandite (Ca(OH2)), which gives a pHof around 12.4. Compared to ground water conditions this leads to an increase of thecation/proton activity ratio and into the stability field of Feldspars, and up to four ordersof magnitude higher silica activity.
Several studies have been made concerning the interaction between bentonite andcement pore-water, of which most have been batch experiments with high water/solid
ratio. The present study focuses on highly compacted bentonite since e.g. ionequilibrium and transport restrictions significantly may affect possible reactions andreaction rates. The overarching objectives were to gather information concerning pH
evolution in compacted bentonite, pH buffering capacity, changes in mineralogy,changes in swelling pressure, and possible specific effects of accessory minerals on theabove items,.
EXPERIMENTAL

Commercial Wyoming bentonite from American Colloid Co. (MX-80) was used as
starting material for all tests. The original material was used to produce almost purehomo-ionic montmorillonite with Na+, K+, and Ca2+ as exchangeable cations,
respectively. Tests were made with the purified and the original material. The test
solutions were chosen to be 0.1, 0.3 and 1.0 M NaOH, and saturated Ca(OH)2 solution.
The corresponding pH values as calculated by PHREEQC are 12.9, 13.3, 13.7 for the
NaOH solutions, 12.4 for the Ca(OH)2 solution. The samples had a 35 mm diameter,
and a 55 mm height. The proposed KBS3 buffer density of 2000 kg/m3 at full water
saturation was aimed at in all tests.

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NUMO-TR-04-05

A-sidepH measured
0.5 L NaClload cellsample0.5 L NaOH
pH controlled
B-sideFigure 1

Schematic drawing and photo of a sample holder.

Air dry test material (water ratio ~10%) was slightly over-compacted compared to theintended density and placed in the cylindrical sample holders made of titanium and
PEEK (Figure 1). The samples were water saturated by slowly circulating 0.5 L deionized water behind the filter by means of a peristaltic pump. After reaching pressure
equilibrium, the water was changed to the predefined chloride solutions, and after
reaching new pressure equilibrium, the chloride solutions at the bottom side (B) werechanged to 0.5 L hydroxide solutions (high pH), and the 0.5 L isotonic chloride solution
were left on the upper side (A). In a few tests the same solution was used on both sidesof the samples and successively changed on both sides. At test termination the solutions
were disconnected and the samples were quickly removed, split, and characterized withrespect to physical and mineralogical properties.
MEASUREMENTS AND ANALYSESThe temperature and swelling pressure were automatically measured every half hour,and pH was measured virtually daily in the low pH solutions, and weekly in the high pH
solutions. The type of exchangeable cations was determined by exchange withammonium ions, and the cation exchange capacity was determined by exchange withcopper(II) triethylenetetramine. XRD scans were made both of random powders and asoriented samples. Mineralogical quantification was made by use of the Siroquant
software based on Rietveld technique. Element analyses were made by use of ICP/AES
for both the clay and the test solutions. Anions were analysed by use of ion
chromatography (IC). Scanning electron microscopy and microanalyses (EDX) wereused to study microstructure and mineral distribution.

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RESULTS

The measurements and analyses were fully carried out for the 12 separate tests.
Significant reductions in swelling pressure were found for the samples contacted to highconcentrations of sodium chloride and hydroxide solutions. A major difference was,though, that the chloride solutions gave a fast drop to a new stable pressure value, while
contact to the hydroxide solution led to a continuous lowering of the swelling pressure.
Figure 2 (left) shows the pressure response from one sample successively exposed topure water, 1.0 M NaCl, 1.0 M NaOH, 1.0 M NaCl, and finally pure water. A
significant continuous swelling pressure reduction was also observed for all samples
exposed to 0.3 M NaOH solutions. However, no swelling pressure change was noticed
in the samples exposed to 0.1 M NaOH or to saturated Ca(OH)2 solution.
1.0 M

NaCl

4000

6000
Swelling Pressure, kPa

Swelling Pressure, kPa

5000

NaOH

3000
H2O

2000

NaCl

1000
0

MX-80
NaCl

4000

0.1 M
0.3 M

2000

1.0 M

0
0

20

40

60

80

NaOH

0

Time, days

20 40 60 80 100 120
Time, days

Figure 2. Left: Pressure response from a MX-80 sample successively exposed to purewater, 1.0 M NaCl, 1.0 M NaOH, 1.0 M NaCl, and finally pure water. Right: Swellingpressure evolution in three MX-80 samples. All samples were initially saturated withpure water, subsequently exposed to the chloride solutions (5 days), and finally to thehydroxide solutions on one side (60 days).
A pH increase in the NaCl solutions was measured in the four tests exposed to 1.0 M
and 0.3 M solutions. Logically, the increase came earlier and was more pronounced in
the tests with the highest concentration. A systematic release of silica was found inthese tests (Table 1). No pH increase was measured after 45 days in tests with 0.1 M
solutions, and neither after an exposure time of 110 days in the four tests with saturated
Ca(OH)2 solutions..
Table 1. ICP/AES analyses of solutions from tests with MX-80 exposed to NaOH
solutions. Concentrations are expressed in mM.
Sample
pH
Al
Ca
Mg
K
Si
Ti
NaCl side

21
22
23

n
11.8
12.3

0.001
0.000
0.000

0.185
0.416
0.170

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0.084
0.132
0.000

0.394
0.421
0.605

0.119
0.620
1.336

0.000
0.000
0.000

NUMO-TR-04-05

NaOH side

21
22
23

12.9
13.3
13.7

0.004
0.005
0.013

0.013
0.000
0.000

0.000
0.000
0.000

0.231
0.305
0.463

0.419
1.890
4.167

0.000
0.003
0.041

A significant increase in CEC was noticed for all samples exposed to the NaOH
solutions. The increase was significant on both sides of the samples except for the NaClside of the MX-Na sample exposed to the 0.1 M solutions. No significant change in
CEC was measured in the samples exposed only to NaCl solutions (sample 31 and 32),
or to the four samples exposed to the 0.015 M Ca(OH)2 solutions. No neoformation ofminerals was indicated in any of the MX-Na samples. A small amount of soft gelmaterial was found outside of the filter on the low pH side in one test. The ICP/AES
element analyses show that the silica/aluminium ratio decreased significantly in samples
exposed to the NaOH solutions, and an Si/Al gradient from the NaOH to NaCl solutions
side.
DISCUSSION AND CONCLUSIONS

It is obvious from the present results that a pH plume may pass through highly
compacted bentonite at a sufficiently high pH gradient. It is also obvious that it isstrongly affected by reactions between the hydroxide and bentonite minerals, and theeffective transport is not well described by diffusion parameters only.
In the present experiments the bentonite swelling pressure was strongly reduced byexposure to 0.3 (pH 13.3) and 1.0 M (pH 13.7) NaOH solutions. The reduction seems tobe due to an instant osmotic effect, and to a continuous dissolution of silica minerals
leading to mass loss. The decrease rate due to dissolution was reduced after a relatively
short time, and a subsequent almost constant decrease rate was observed. The initial
decrease rate is likely governed by dissolution of cristobalite, and the latter due todissolution of montmorillonite and quartz when cristobalite is depleted.
A significant increase in CEC was observed in samples exposed to the NaOH solutions.
The structural formulas of the exposed montmorillonite were calculated based on the
ICP/AES and CEC data, and show a significant release of silicon from themontmorillonite structure. This incongruent dissolution leads to a charge increase in thetetrahedral layers and a first step towards beidellite. This observed moderate charge
increase can be seen as a minor problem with respect to the buffer functions. However,the physical properties of the clay will change dramatically if this reaction continues
until a high charge mineral is formed, or a general breakdown of the structure takes
place. The silicon release rate from montmorillonite in this specific geometry wasdetermined to be 1.6E-9 g*g-1clay*s-1 for the 1.0 M NaOH solutions conditions and 5E10 g*g-1clay*s-1 for the 0.3 M conditions. No effect on swelling pressure was found in
the samples exposed to 0.1 M NaOH (pH 12.9) and saturated Ca(OH)2 solutions (pH12.4). No mineralogical/chemical effect except ion exchange from sodium to calcium
was found in the samples exposed to the Ca(OH)2 solution.

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The similar pressure response of bentonite exposed to NaCl and NaOH solutions
indicate that ion-equilibrium is established between the external hydroxide solutions
and the clay pore-water, which then leads to reduced pH inside the clay. This effectincreases theoretically with bentonite density and with decreasing pH in the external
solution (groundwater). The chemical reactions between the introduced hydroxide andthe clay will therefore be less intense, more localized, and lead to lower final pH. At
moderately high pH, the combined effect leads to a large calculated difference between
batch experiments and experiments with highly compacted bentonite with respect tomineralogical alteration rate. Ion equilibrium conditions may consequently explain theminimal physico-chemical changes in the samples exposed to 0.1 M NaOH andsaturated Ca(OH)2 solutions.

Acknowledgments
The authors wish to acknowledge that this paper is a result of work funded by the
Swedish Nuclear Fuel and Waste Management Company (SKB) and the European
Commission.

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EFFECTS OF SALINE ALKALINE ATTACK ON BENTONITE AND CRUSHED ROCK –EXPERIMENTAL AND MODELLING STUDIES – ECOCLAY II
Ulla Vuorinen*, Ari Luukkonen#, Jarmo Lehikoinen*, *VTT Processes, #VTT Building andTransport, FIN-02044 VTT, Finland,
Heini Ervanne, Department of Chemistry, Laboratory of Radiochemistry, FIN-00014 University of
Helsinki, Finland

INTRODUCTION
The use of concrete and shot crete in constructing a deep disposal vault for spent fuel has raisedquestions about the effects of an alkaline perturbation on the buffer materials used and the possible
consequences to the safety of the final disposal system. In order to facilitate an assessment of the
propagation of an alkaline plume in the bentonite buffer and to detect alterations brought about bysuch a plume laboratory studies were initiated within the European 5th frame work project
ECOCLAY II.
EXPERIMENTAL
Six flow-through cylinders, each containing site specific crushed rock (<1.5 mm) from Olkiluoto,
Finland in one half, and compacted bentonite (2 000kg/m3) (commercial Wyoming bentonite MX80) in the other half. Thecylinders were subjected to an attack of a slow flow of solution. The
solution rate used was 2.5mL/day, comparable to groundwater flow rate in deep disposal conditions.
Three different solutions were used, saline alkaline (pH=12.5), saline (pH=8.3) and fresh (pH=8.8)
solutions, one solution for each cylinder in the two sets of cylinders. Both cylinder sets were started
at the same time and ran simultaneously. The experiments were performed at ambient temperatureinside a glove-box with nitrogen atmosphere in order to avoid disturbances of atmospheric CO2 on
the alkaline system. Solution samples were collected at the out-flow end for analyses andmeasurement of pH. The first set of three cylinders were dismantled after about a year and the otherset of three after about 1.5 years. The solids, crushed rock and compacted bentonite, were sectioned
and analysed for mineral alterations. Bentonite pore water was analysed in several bentonite
specimen sampled along the cylinder length, as well as the amount of exchangeable cations (Na, Ca,K, Mg).
Batch experiments were also conducted using the same solid materials as in the flow-throughcylinder experiments. The solids were treated separately with three alkaline solutions (fresh alkaline
pH 12.5, saline alkaline pH 12.5 and saline hyper alkaline pH 13.5). The solid/solution ratio used
was 1/10 and the equilibration periods 1 week, 1 month, 6 months, 1.5 years. The batch experiments
were also conducted in nitrogen atmosphere at ambient temperature. After completion of eachperiod the phases were separated by centrifugation and filtration. Both the solutions and solids wereanalysed. The mineral alterations were more prominent in the batch experiments than in the flowthrough experiments. The solution analysis results were the basis in the modelling (inverse) of themineral reactions occurring.
RESULTS AND DISCUSSION
Flow-through experiments

The saline alkaline solution affected bentonite throughout the entire column to some extent as all
the determined exchangeable cation capacities (CEC) either increased or decreased when compared
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NUMO-TR-04-05

to the initial MX-80 bentonite values (Figure 1). There was a clear decreasing trend in the column
with more prominent changes at the in-flow end. However, the pH values in the bentonite porewater samples (Figure 2) supported alkaline changes only near the interface with a clear decreasing
trend towards the cylinder end. The out-flow solution had reached a pH value around 9.5 by the endof the experiment and showed an increasing trend (Figure 3). If the alkaline pH was to keep its
trend the estimated time needed for the out-flow solution pH value to reach a value around 11
would be about 6 years and to reach the initial value of 12.5 would take about 10 years. In the saline
and fresh experiments the out-flow solution pH values levelled off at around 9.5 and about 8,
respectively.

[meq/g of bentonite]

0.8

0.20

Na

0.6

0.15

0.4

0.10

0.2

0.05

0.0

0.00

1

2

3

4

5

6

7

0.010
[meq/g of bentonite]

Ca

8

9

K

1

2

3

4

5

6

7

8

0.06

9

Mg

0.008

0.04

0.006
0.004

0.02

0.002
0.000

0.00
1
A1

2
3
4
5
6
B1
B2
C1
D1
E1

7
8
9
F1
F1
F2

1

2

3

4

5

6

7

8

9

Figure 1. Measured CEC (cation exchange capacity) values (meq/g of bentonite) for the four
elements in the saline alkaline case. The red bar on the left shows the initial CEC of MX-80. The
text box in the figure indicates the bentonite samples along the flow-through column(A=in-flow end,
F=outflow end, 1=interfac specimene, 2=below interface specimen) in each category.
12.5

OL-SA

12

11.5

10

ALL-MR I

ALL-MR II

OL-SA initial

OL-SA I

OL-SA II

OL-SS initial

OL-SS I

OL-SS II

10.5

360 d

6

560 d

pH

pH

8

ALL-MR initial

4
2

9.5

8.5

0
1
A1

2
A2

3
B1

4
B2

D15

6
D2

7
F1

7.5
0

200

400

600

800

1000

1200

mL

Figure 2. Bentonite pore water pH in thesaline alkaline experiment for both the 360 d
and 560 d cylinder.

A3-48

Figure 3. pH values of the out-flow solutions
during the experiment versus the amount ofsolution (mL) passed through the cylinders. In
green the saline alkaline values (I=360d,
II=560d).

NUMO-TR-04-05

The initial saline solutions did not contain K+, Mg2+, SO42-, or Si(aq). The levels of K+ were quite
similar in both saline cylinder experiments, both in the determined exchangeable cations and in theout-flow solutions indicating that interactions with bentonite were well reflected in the out-flow
solution composition. This was also true for SO42- and Si(aq), based on pore water and out-flow
solution results. In the case of exchangeable Mg2+ the amount left in the bentonite samples of thesaline alkaline case was less than in the saline case, but this was not reflected in the Mg2+ contentsof the out-flow solutions even if the pore water analysis showed depletion of Mg2+. This indicatesthat Mg2+ remained to some extent inside the alkaline column undergoing possible reactions.
The depletion of Ca2+ in the pore water and the decreasing trend in the out-flow solutions in thesaline alkaline case, which was contrary to the increasing trends in the other two experiments,
supports the retention of Ca2+ in the column and possible undergoing reactions as well.
An increase in the CEC of bentonite in all alkaline experiments and also in the saline flow-throughexperiment was observed. The increase was more significant in the batch experiments. The cause of
the increase is not quite clear at this point, especially in the saline experiment, but in the alkaline
cases partial alteration of montmorillonite to beidellite can be an explanation as indicated by themineral analyses.
Batch experiments

As expected greater changes to the initial solution pH values occurred in the bentonite batches(Table 1), nevertheless, the pH decreased somewhat in all cases.
Table 1. The measure pH values of the contacting solutions after phase separation.

duration
days
6
30
180
540

Rock
fresh

salinesaline hyper

MX-80
fresh

salinesaline hyper

alkalinealkalinealkalinealkalinealkalinealkaline

12.3
12.4
12.6
12.4

12.4
12.5
12.2
12.1

13.5
12.6
12.9
13.1

11.6
11.5
11.4
11.2

10.8
10.6
10.3
10.2

13.5
13.4
12.8
12.9

The most prominent changes in the solution chemistries were met in the saline hyper alkaline
experiments (Table 2), but the trends were rather similar in the other solutions as well;- Ca content decreases, Si content increases, except in the fresh alkaline MX-80
solution which gave the highest concentration after 6d and thereafter decreased(gel-formation).
- More Al appears in the rock solutions than MX-80 solutions

A3-49

NUMO-TR-04-05

Table 2. The analysis results of the contacting solutions. The initial solution composition is given in
the yellow row.
durationin
Bentonite

Rock

Na

Ca

K

Mg

Al

Si

Cl

SO4

EC

mg/L

mg/L

(mS/m)

Fe

days

mg/L
17710

mg/L
12.8

mg/L
mg/L
<2 < 0.1

mg/L
0.21

mg/L
mg/L
6.97 < 0.03
13700 < 1

6

18480

0.25

38.4 < 0.1

0.19

981

< 0.03

13900

304

9200

30
180

18740

0.52

26.5

0.16

0.22

1215 < 0.03

13300

321

5000

17563

0.73

45.5 < 0.1

0.28

1965 < 0.03

15750

300

4750

540

16640

<0.1

21.0 < 0.1

0.22

2346

0.08

13800

310

6

18860

3.58

36.4 < 0.1

19.0

38.7

0.58

13700 < 1

11000

30
180

18160

1.41

39.1 < 0.1

41.2

65.3

0.99

14100 < 1

11000

17800

0.55

45.1 < 0.1

95.9

141

0.5

11000

540

17570

0.43

67.8 < 0.1

91.8

155

0.49

11500 < 1

9800

7.02

3900

9900
6100

Mineralogical summary

Crushed rock alterations
The crushed rock was prepared from Olkiluoto mica gneiss (75 wt%), granite pegmatite (20 wt%)
and tonalite (5 wt%). The rock material was crushed to grain sizes <1.5 mm. All materials,
including the fine fractions were mixed together. The mineralogy of the mixture is given in Table 3.
Table 3. Estimated initial mineral composition (in wt%) for crushed rock used in the experiments.
Mineralwt%

Mineralwt%

Mineralwt%

QuartzOligoclase
Microcline
BiotiteCordierite

23.2
19.2
17.1
20.1
8.3

Sillimanite
Muscovite/Sericite
Hornblende
Chlorite
Epidote/Saussurite

5.4
2.9
1.6
1.2
0.3

ZirconCarbonate
ApatiteSulphides

0.2
0.1
0.1
0.3

In the batch experiments (Table 4) microcline was found to react. A corresponding increase insericite was interpreted from the hyperalkaline case. The dissolution of oligoclase was probable inall experiments. In the hyperalkaline experiment the low Ca2+ solute concentration promoted
dissolution of the anorthite part of oligoclase, and possibly minor production of saussurite. In the
fresh alkaline experiment the albite part of oligoclase was believed to dissolve more readily. It
seems that the high Na+ solute concentrations in the saline experiments inhibited dissolution of
albite. The saline experiments also indicated dissolution of hornblende and cordierite. It issuggested that a significant part of hornblende was altered to chlorite, and Mg2+ needed for thisconversion was partially produced from the decomposition of cordierite. The final water results ofthe batch experiments indicated a sink for Na+. In the saline experiments small precipitation ofhalite was a partial sink. It is believed that the newly-formed surface edge sites of the recently
crushed rock were a distinct Na+-sink as well. The overall mass transfer in the crushed rock batch
experiments was low. However, as a response to the small drops in pH, the batches produced
minute amounts of CSH-gel. This gel gave a sink for Ca2+.
In the flow-through experiments (Table 4) minimal detectable changes in the crushed rock occurred.
The reactivity of bentonite is much higher than that of crushed rock. In the saline alkaline flow-

A3-50

NUMO-TR-04-05

through experiment similar changes to those in the saline alkaline batch experiment were assumed.
Interpretations were, however, subject to ambiguities because of the compositional variations in the
crushed mixture. In the near-neutral-pH experiments the crushed silicates were expected to be nonreactive. Small amounts of precipitated halite were observed in the saline flow-through experiments.
It was also assumed that the fresh surfaces of crushed minerals were potential for Na+ adsorption.
Table 4. Summary of the crushed rock mineralogical observations interpreted from the batch andflow-through cell experiments.
+ increase in final bentonite,– decrease in final bentonite,() inferred but not observed.

Batch Experiments

Hornblende
Chlorite
Cordierite
Microcline
Sericite
Oligoclase
Na-part (albite)
Ca-part (anorthite)
Saussurite
HaliteCSH-gel (Tobermorite?)
NaX

Fresh
Alkaline
(–)
(+)
–
+
–
–

+
+

Flow-through Experiments

SalineAlkaline

Saline .
Hyperalk

Fresh

Saline

–
(+)
–
–
+
–

–
(+)
–
–
+
–

–
(+)
–
–
+
–

–
(+)
+
+
+

–
+
+
+
+

–
(+)
+
+
+

+
+

+

SalineAlkaline

MX-80 alterations
In the batch experiments (Table 5) the initial Nax-montmorillonite was found to alter partially toNax-beidellite. The degree of conversion was related to the Na/Ca ratio of the initial solution and
pH. The long-term (e.g. 540 days) hyperalkaline attack produced smectite that indicated goodresemblance to crystallography of Nax-beidellite. The main sink for Na+ was apparently the cationexchange sites of the altered smectite. However, according to Hong and Glasser (1999, 2002) also
CSH gel is a Na+-sink especially in high Na+ solute conditions. The CEC studies with altered solids
indicated an increase in the exchange sites as a result of the alterations. The other main cations werereleased from bentonite. K+ remained in the final solution, while Mg2+ assumably adsorbed or
precipitated into CSH gel (cf. Taubald et al. 2000). The main sink for Ca2+ was CSH gel and to aminor extent calcite. Especially in the hyperalkaline case quartz dissolved partially and albite
almost completely. Significant amounts of halite precipitated in the saline batch experiments.
In the flow-through cylinder experiments (Table 5) the changes in smectite were found to be diverse.
The dilute near-neutral-pH fresh water injection resulted in complexly fluctuating cation
distributions in bentonite. The constant release of Na+ and silica from bentonite seems to havecaused interlayer deficiencies in montmorillonite. Due to the relatively low Na/Ca ratio, the nearneutral-pH saline water caused smectite to transform towards Cax-montmorillonite. The saline
alkaline water interaction indicated comparable smectite alteration to the equivalent batch
experiment. The near-neutral-pH experiments released Na+ while the alkaline experiment adsorbed
Na+ into the cation exchange sites. In the near-neutral-pH saline experiment, the released Mg2+ wasleft to final solution while in the saline alkaline experiment Mg2+ was apparently caught by CSH gel.
In all experiments, the sink for Ca2+ was either Cax-montmorillonite or CSH gel. Small amounts ofcalcite were precipitated in all cylinders. In the near-neutral-pH experiments no formation of CSH

A3-51

NUMO-TR-04-05

gel occurred, and apparently no significant increases in the CEC. In the saline experiments a small
amount of halite precipitated in bentonite.
Table 5. Summary of the bentonite mineralogical observations interpreted from the batch and flowthrough cell experiments.
+ increase in final bentonite,– decrease in final bentonite,() inferred but not observed.

Batch Experiments

Nax-Montmorillonite
Cax-Montmorillonite
Nax-Beidellite
Deficient Montmorillonite
GypsumAlbiteQuartzHaliteCalciteCSH-gel (Tobermorite?)
NaX
KX
CaX2
MgX2
CEC increase

Flow-through Experiments

Fresh
Alkaline–

SalineAlkaline–

Saline.
Hyperalk
–

+

+

++

–
(–)
(–)
+
++
+

–
+

–
–
(–)
++
+
+
+
–
–
––
+

–
––
–
++
+
+
++
–
––
––
++

Fresh

Saline––+SalineAlkaline
–
+

+
–

–

+

+
+

––

––
–
++
–

–
–
(–)
+
+
+
+
–
–
––
+

Modelling

A simple thermodynamic forward model developed for montmorillonite was applied to describe theuptake of sodium and calcium on MX-80 bentonite reacted with saline hyper-alkaline solution. The
experimental findings were adequately explained by the model, provided that sorption of calcium
takes place predominantly by way of precipitation of calcium-bearing mineral phases.
Forward modelling considered quartz, calcite, microcline and albite as primary accessory minerals
of MX-80. In the hyper-alkaline modelling, the minor solid assemblage of bentonite was completely
destroyed upon reacting with the solution, which resulted in the formation of zeolite and silicate
phases. At the point of modelling, the mineralogical interpretation of the secondary solid phases
was fraught with uncertainties, however.
The inverse modelling results for MX-80 and crushed rock replicated most mineralogical alteration
processes identified in the mineralogical studies. In MX-80 the important processes were the partial
conversion of smectite (from Nax-montmorillonite to Nax-beidellite), complete dissolution of albite
and partial dissolution of quartz. Laboratory observations indicated significant production of CSHgel and that was interpreted analogous to structurally defect 14Å-tobermorite. In the crushed rockexperiments the main alteration processes were partial dissolution of microcline and hornblende.
Since the geological conditions otherwise are similar to the bentonite experiments, CSH-gel was
assumed to form accordingly. Evidently, however, the reaction rates in the crushed rockexperiments are lower due to the overall smaller reactive surface area than in the bentonite batches.
In the inverse modelling of the hyperalkaline experiments significant difficulties were met withcharge balancing the analytical results. Uncertainties in the concentrations of Na+, Cl- and OH- wereA3-52

NUMO-TR-04-05

reflected as difficulties to adjust the cation exchange to the correct level in both MX-80 and crushedrock batch experiments.
Acknowledgements

The authors wish to acknowledge the European Commission and Posiva Oy for funding the work
presented here, which was carried out under a cost-sharing contract with the European Atomic
Energy Community (EURATOM) within specific programme on ″Nuclear Energy″ (1998-2002),
Key Action on Nuclear Fission, Area: ″Safety of the Fuel Cycle − Waste and Spent FuelManagement and Disposal″.
REFERENCES
Hong, S.-Y. and Glasser, F.P., 1999. Alkali binding in cement pastes. Part I. The C-S-H phase.
Cement and Concrete Research 29, 1893–1903.
Hong, S.-Y. and Glasser, F.P., 2002. Alkali sorption by C-S-H and C-A-S-H gels. Part II. Role ofalumina. Cement and Concrete Research 32, 1101–1111.
Muurinen, A. and Lehikoinen, J. 1999. Porewater chemistry in compacted bentonite. Helsinki,
Finland, Posiva Oy, Posiva 99-20, 46 p.
Müller-Vonmoos, M and Kahr, G. 1983. Mineralogische Untersuchungen von Wyoming Bentonit
MX-80 und Montigel. Baden, Switzerland, NAGRA, Technisher Bericht 83-12, 15 p.+app. 13 p.
Taubald, H., Bauer, A., Schäfer, T., Geckeis, H., Satir, M. and Kim, J.I., 2000. Experimental
investigation of the effect of high-pH solutions on the Opalinus shale and the Hammerschmiede
smectite. Clay Minerals 35, 515–524.
Vuorinen, U., Lehikoinen, J., Luukkonen, A. and Ervanne, H. 2003. Effects of salinity and high pH
in crushed rock and bentonite – experimental work and modelling in 2001 and 2002. Olkiluoto,
Finland, Posiva Oy, Working Report 2003-22, 33 p.

A3-53

NUMO-TR-04-05

Experimental study on dissolution of montmorillonite in compacted sandbentonite mixture under Na-Cl-OH pore-water conditions
Tetsuji Yamaguchi1, Yoshifumi Sakamoto1, Masanobu Akai1, Mayumi Takazawa1
Tadao Tanaka1, Shinichi Nakayama1, Tsutomu Sato2
12

Department of Fuel Cycle Safety Research, JAERI, Tokai, Ibaraki 319-1195 Japan
Institute of Nature and Environmental Technology, Kanazawa University, Kanazawa,
Ishikawa 920-1192, JapanINTRODUCTION
Highly alkaline environments induced by cementitious materials in radioactive waste
repositories are likely to alter montmorillonite, the main constituent of bentonite buffermaterials, and are likely to cause the physical and/or chemical properties of the buffermaterials to deteriorate. We focus our experimental efforts on predicting long-term variations
in permeability of compacted sand-bentonite mixture because the variations induce major
uncertainties in the radionuclide migration analysis and have not been quantitatively
understood. The dissolution rate of montmorillonite and the diffusivity of hydroxide ions in
the compacted sand-bentonite mixtures are essential parameters, which quantify the effects ofalteration caused by the alkaline environments on the permeability of a bentonite buffer.
There are not a few studies on the dissolution rates of clays in near neutral to alkaline
solutions (Bauer et al., 1998; Bauer and Berger, 1998; Cama et al., 2000; Huertas et al., 2001;
Sato et al. 2002). In these studies, the rates were obtained for far from equilibrium conditions,where the solid/solution ratio employed in their experiments is much lower than the disposal
conditions. It is of concern if the rates are straightforward applicable to predict alteration ofcompacted bentonite under disposal conditions. For this reason, we have performedexperiments to acquire quantitative data on the rate of dissolution of montmorillonite anddiffusivity of the alkaline source in compacted, cylindrical bentonite samples under highly
alkaline, saline groundwater conditions. This experimental configuration was employedbecause it reflects repository conditions such as the use of compacted bentonite and saline
groundwater that is nearly saturated with respect to silicon and aluminum.
EXPERIMENTS
The dissolution rate of montmorillonite wasobtained through a time-dependent variation in
the quantity of montmorillonite in sand-bentonite
mixtures. The mixtures of granules of Na-type
bentonite (Kunigel V1, [Ito et al., 1993]) andsilica sand of two different granule sizes (0.1 –0.85 mm: SiO2 94.6%, 0.85 – 2 mm: SiO2 99.78%[Suzuki & Fujita, 1999]) were compacted tocylindrical specimens of 20 mm in diameter and
10 mm in thickness. The mixture ratio of thebentonite and silica sands was 70:15:15 in dry
weight. The density of the specimens was 1.6 Mg
m-3. Alteration experiments using compacted
specimens require much longer time periods thanA3-54

Si- and Al-saturated
NaOH solution

Teflon® container
Specimen holder
Specimen:
Compacted sandbentonite mixture;
20 mmφ x 10 mmt
1.6 Mg m-3

Fig .1 Schematic drawing of theexperimental configuration for
the alteration experiment.

NUMO-TR-04-05

those using granules. Temperatures were selected to be 50oC to 170oC, and pH values were13.0 to 14.0 to observe montmorillonite dissolution over a reasonable time period. The results
will be extrapolated to repository conditions. A specimen set in the holder in a Teflon®
container, schematically shown in Fig. 1, was contacted with 0.08 dm3 of pH-adjusted,simulated alkaline, saline groundwater. The simulated groundwater was prepared byequilibrating NaCl-NaOH mixed solutions of the Na concentration of 1 M with bentonite
granules under the same temperature (50 to 170oC) as those employed in the alteration runs
for the equilibration period of 4 to 8 weeks. The container assembly (Fig. 1) was placed in asealed stainless steel container and kept at desired temperatures in ovens. Each of theassembly was taken from the oven at the fixed sampling time and the compacted mixture
specimen was removed from the holder, freeze-dried at –110oC, and the amount ofmontmorillonite that remained was determined by the methylene-blue adsorption titration
method. The reacted solid was analyzed by X-ray powder diffraction (XRD). The
concentrations of Al and Ca in the contacted aqueous solutions were determined by using
inductively-coupled plasma mass spectroscopy (ICP-MS), and Si was determined as SiO2
through molybdenum-yellow spectrometry.
The diffusivity is the rate of spreading of the alkaline plume in the sand-bentonite
mixtures, and it also gives some indication as to whether the dissolution of montmorillonite or
the transport of hydroxide ions limits the alteration of bentonite. For this reason, the two
phenomena, alteration of bentonite andButyl rubber packing
diffusion of hydroxide ions in bentonite, have tobe quantified separately. The diffusivity ofhydroxide ions in compacted sand-bentonite
Compacted sandmixtures was obtained by the through-diffusion
Filterbentonite mixture;holdermethod using an polysulphon diffusion cell as
20 mmφ x 10 mmt
1.6 Mg m-3
shown in Figure. 2. The specimens ofcompacted sand-bentonite mixtures, which areSintered SUS
the same in size and in mineral composition as
filter; 1 mmt
those used in the alteration experiment, were
employed in the hydroxide ion diffusion
experiment. The water in one of the reservoirs(referred to as “high-pH reservoir”) was
Butyl rubber O-ring
replaced with simulated cementitious water, andreservoir:
Low-pH reservoir: simulated
the other (referred to as “low-pH reservoir”) High-pH
simulated cementitious
fresh-type groundwater;
with simulated fresh-type groundwater. The water; [OH-] = 0.5 M[OH-] = 1x10-5 M
experimental runs were conducted in thetemperature range 10 to 90oC. The through- Fig. 2 Schematic drawing of the throughdiffusion cell used in the hydroxide
diffusion runs were conducted under theion diffusion experiment.
ambient atmospheric condition. At 7-day
intervals, the pH of the aqueous solutions in thetwo reservoirs was measured.
RESULTS AND DISCUSSION
The amount of montmorillonite in the compacted sand-bentonite mixtures decreased ina few days to several months under the employed conditions of pH and temperature, as seenin Fig. 3. X-ray diffraction patterns of sand-bentonite mixtures indicated the decrease ofmontmorillonite. Crystalline silica also dissolved, and a secondary mineral, analcime

A3-55

NUMO-TR-04-05

lo g R alog RA(Mg･m-3･s-1)

Monmorillonite density (Mg･m-3)(NaAlSi2O6), was formed. The linear decrease in the amount of montmorillonite with timeclearly differs from the widely-accepted
exponential decrease in dissolution of
0.8
○：90℃
minerals (e.g., Stumm & Morgan, 1996).
△：130℃
0.6□：170℃
The linear decrease can be expressed as
0.4
W (t ) = W (0) − R A t , where W (t ) denotes
the density of montmorillonite (Mg of
0.2
montmorillonite/m3 of sand-bentonite
0.0
mixture), W (0) the initial density (1.758
0
50
100
150
200
250
Time (day)Mg/3.14 m3 = 0.56 Mg m-3), R A (Mg m-3s-1) the rate of density decrease and t (s) Fig. 3 Dissolution curves of montmorillonite incompacted sand-bentonite mixture as a
the time after the contact with thefunction of time at [NaOH] ～ 0.3 M.
simulated groundwater. The R A is a-5function of pH and temperature as shown●:50℃
in Fig. 4, and can be expressed as-6○:90℃
RA = 0.8 [OH-]1.4 e-48000/RT(1)△:130℃-7
where R the gas constant (8.314 J mol-1□:170℃-1K ). The activation energy of 48±10 kJ-8-1
mol is close to that of formation of-9analcime, 52 – 60 kJ mol-1 (Kim, 2001),
and higher than that of dissolution of
-10
-1
-3
-2
-1
0
1
montmorillonite, 30 kJ mol (Huertas etg O Hloglo[OH](M)
al., 2001). The alteration rates estimatedby Eq (1) were compared with previous Fig. 4 Dependence of the montmorillonite
dissolution rate, RA (Mg m-3 s-1) ondata from batch dissolution experiments
temperature and on [OH-].
for smectite obtained in hyperalkaline
solutions at 35oC and 80oC (Bauer andBerger, 1998) in Fig. 5. The dissolution rates of montmorillonite obtained for compacted
sand-bentonite mixtures in [Mg-montmorillonite / m3-bentonite / s] were converted to [mol-Si/ m2 / s] using the SiO2 content in the montmorillonite of 61.3 % (Ito et al., 1993) and thespecific surface area of 2.7x104 m2 kg-1 (Shibutani et al., 1999). The dissolution rates ofmontmorillonite obtained for compacted sand-bentonite mixture are lower than those in thebatch dissolution experiments by one order of magnitude or more. The dependence on
concentration of OH- is higher for compacted sand-bentonite mixture than that in the batch
dissolution experiments. The dissolution of montmorillonite in compacted sand-bentonite
mixture is likely to result from some different mechanisms from that occurring in the farfrom-equilibrium batch dissolution experiments.
In the hydroxide ion diffusion experiments, it took a few tens of days for the ions todiffuse through the 10 mm-thick compacted sand-bentonite mixture disks. Hydroxide ionswere mainly consumed by dissolution of soluble silicate minerals during the delay. After thedelay, the activity in the low-pH reservoirs began increasing. The increasing rate becomes
-

A3-56

NUMO-TR-04-05

-9

-21

-10

-22

ln D e (m2s-1)

log dissolution rate (mol-Si m-2 s-1)

close to the decreasing rate of the activity in the high-pH reservoirs, and when the two valuesof the rate were identical, the steady state flux of hydroxide ions was established in thespecimens. The diffusivity was calculated by using the identical values of the rate. The
obtained De values were (3.9±0.6)x10-11 m2 s-1 at 10oC, (4.6±2.3)x10-11 m2 s-1 at 20oC,(1.1±0.4)x10-10 m2 s-1 at 30oC, (8.9±2.2)x10-11 m2 s-1 at 40oC, (1.1 – 2.3)x10-10 m2 s-1 at 50oC,(1.8±0.7)x10-10 m2 s-1 at 70oC and (0.9 – 5.4)x10-10 m2 s-1 at 90oC, which are summarized inFig. 6. The dependence of De on temperature follows the Arrhenius equation of De = exp(15.1 - 21000/RT). The diffusivity of ions in compacted bentonite materials is known todepend strongly on their bulk density, ρ (Mg m-3), and to be proportional to e-5.4ρ for I(Mihara et al., 1999) which is analogous monovalent anion to OH-. The effective diffusivity
of hydroxide ion in compacted bentonite materials can be expressed as a function of thetemperature and the bulk density as
De = exp(-7.8 - 21000/RT – 5.4ρ)
(2)

-11
-12

Bauer, 80℃
Bauer, 35℃
Eq (1), 80℃
Eq (1), 35℃

-13
-14
-2

-1

0

1

log [OH -] (M)Fig. 5Comparison between dissolution
rates of montmorillonite obtainedin this study and those obtainedby Bauer and Berger (1998).

-23
-24

-25
0.00250.003

0.00350.004

1/T (K-1 )Fig. 6 Effective diffusivity, De (m2 s-1),of hydroxide ion in compacted
sand-bentonite mixture at thetemperature of 10 – 90 oC.

CONCLUSIONS
Dissolution of montmorillonite and diffusion of hydroxide ions in compacted sand-bentonite
mixtures were measured under the simulated alkaline groundwater environments. Dissolutionof montmorillonite followed the linear dependence on time under the employed experimental
conditions of pH 13 to 14 and temperatures of 50 to 170oC. The slope gives the dissolution
rate, RA. The dissolution rate is a function of pH and temperature (K), and expressed as RA =0.8[OH-]1.4 exp(-48000/RT), where R is the gas constant. The effective diffusivity was foundto be in the order of 10-10 to 10-11 m2/s at 10 to 90oC and expressed as De = exp (-7.8 21000/RT – 5.4ρ). These equations will be provided for the long-term prediction on thepermeability of a bentonite buffer. The dissolution rates we obtained in this study are smaller
than previous data which were obtained by far-from-equilibrium batch dissolution
experiments. Dissolution mechanisms under high solid/solution ratio and near-equilibrium,

A3-57

NUMO-TR-04-05

which is representative of the waste repository, is required to be understood to provide
reliable data for the long-term prediction of the bentonite buffer performance.
ACKNOWLEDGEMENT
This is a part of study funded by the Japanese Ministry of Economy, Trade and Industry.
REFERENCES
Bauer, A., Berger G., 1998. Kaolinite and smectite dissolution in high molar KOH solutionsat 35oC and 80oC. Appl. Geochem., 13, 905-916.

Bauer, A., Velde, B., Berger G., 1998. Kaolinite transformation in high molar KOH solutions.
Appl. Geochem., 13, 619-629.
Cama, J., Ganor, J, Ayora, C., Lasaga, C. A., 2000. Smectite dissolution kinetics at 80oC andpH 8.8. Geochim. Cosmochim. Acta, 64, 2701-2717.
Huertas, F. J., Caballero, E., Jiménez de Cisneros, C., Huertas, F., Linares, J., 2001. Kinetics
of montmorillonite dissolution in granitic solutions. Appl. Geochem. 16, 397-407.
Ito, M., Okamoto, M., Shibata, M., Sasaki, Y., Danhara, T., Suzuki, K., Watanabe, T., 1993.
Mineral composition analysis of bentonite. PNC TN 8430 93-003, Power Reactor andNuclear Fuel Develop Corporation (in Japanese).
Kim, S.-Y., 2001. Experimental investigations of the effect of alkali fluids on montmorillonite,
albite and quartz. JNC TN8400 2001-008, Japan Nuclear Fuel Cycle Development Institute(in Japanese).
Mihara, M, Ito, M., Kato, H. and Ueta, S., 1999. Effective diffusion coefficients of HTO, Cs
and I in compacted Ca-bentonite. JNC-TN 8430 99-011, Japan Nuclear Fuel Cycle
Development Institute (in Japanese).
Sato, T., Kuroda, M., Yokoyama, S., Fukushi, K., Nakayama, S. 2002. Effect of pH on
smectite dissolution rates under alkaline conditions, Proc. Int. Conf. Clays in Natural andEngineered Barriers for Radioactive Waste Confinement.
Shibutani, T., Kohara, Y., Oda, C., Kubota, M., Kuno, Y. and Shibata, M. 1999. PhysicoChemical Characteristics of Purified Na-Smectite and Protonation/Deprotonation Behavior ofSmectite Surface in NaCl Media. JNC TN8400 99-066, Japan Nuclear Fuel Cycle
Development Institute (in Japanese).
Suzuki, H., Fujita. T., 1999. Swelling characteristics of buffer material, JNC TN8400 99-038,
Japan Nuclear Fuel Cycle Development Institute (in Japanese).
Stumm, W., Morgan, J. J., 1996. Aquatic Chemistry – Chemical Equilibria and Rates in
Natural Waters, 3rd Ed., Wiley Interscience, New York.

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Modeling of variation in permeability of compacted bentonite withalkaline fluid for long-term safety assessment of geological disposal
system.
Mayumi Takazawa, Tetsuji Yamaguchi, Yoshifumi Sakamoto
Masanobu Akai, Tadao Tanaka, Shinichi Nakayama
Department of Fuel Cycle Safety Research,
Japan Atomic Energy Research Institute, Tokai, Ibaraki, 319-1195, JapanINTRODUCTION
Uncertainties should be quantitatively assessed in a long-term assessment ofradioactive waste disposal. We focus our experimental efforts on parameters that induce
major uncertainties in the radionuclide migration analysis and that have not been
quantitatively understood. Alteration of the bentonite buffer material by highly alkaline
environments induced by cementitious materials used in geological disposal facilities isa prioritized study. The highly alkaline environments may alter montmorillonite, themain constituent of bentonite buffer materials, and are likely to cause the physicaland/or chemical properties of the buffer materials to deteriorate. Mathematical models
have been developed to predict long-term alteration of bentonite such as permeability (1).
However, the relationship between changes in the mineralogical composition of
bentonite and variations in its permeability has not been understood for reliable longterm prediction.
APPROACH
The purpose of our investigation is to quantify the effect of alteration caused by
the alkaline environment on permeability of bentonite buffer. Our goal is to predict the
time- & space-dependent permeability of compacted sand-bentonite mixtures inradioactive waste repositories. The structure of the approach is shown in Figure 1. The
amount of remained montmorillonite, M(x, t), is predicted by Coupled Masstransport/Chemical-reaction Analysis as a function of time and space. The analysis
needs a number of input parameter values including thermodynamics on minerals,chemistry of groundwater, configuration of waste package and structural materials, andboundary conditions on the alkaline source and natural barriers. The predicted M(x, t) is
combined with M- & ionic-strength-dependent permeability values, k(M, I), to finallyyield the time- & space-dependent permeability, k(x, t), of compacted sand-bentonite
mixtures. Data of M-dependent permeability values, k(M, I), are obtained throughmeasurements and literature survey (Permeability Measurement & Literature Survey).
A series of year-long permeability measurements (Long-term Permeability Experiment)
will be carried out for the purpose of validation of this approach.
COUPLED MASS-TRANSPORT/CHEMICAL-REACTION CODE
A conceptual model of one-dimensional coupled mass-transport/chemical-reaction
for geological disposal system is illustrated in Fig. 2. This model allows us to predict
long-term alteration of bentonite buffer accompanied with space- and time-dependentchanges in porosity, permeability and diffusivity. The flow of the model calculation isshown in Fig. 3. A widely-used and verified geochemical code, PhreeqC ver. 2.8 (2), isin charge of the chemical reaction calculations.

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A trial calculation was performed to reproduce hydroxide ion diffusion at 70 oC(preceding report(3)). The one-dimensional model for the calculation is shown in Fig. 4.
In this calculation, the dissolution rate of montmorillonite in a sand-bentonite mixture
was given as RA (Mg m-3 s-1) = 0.8 COH1.4 exp(-48000/RT) where COH (mol L-3) is theconcentration of OH- in pore water, R (8.314 J mol-1 K-1) the gas constant and T (K) theabsolute temperature. The results of the calculation are compared with the experimental
data in Figs. 5 and 6. The calculation reproduced the time-dependent variations in OHconcentration in through-diffusion experiments (Fig. 5), and concentrations of Na and
Ca (Fig. 6). This comparison illustrates that the coupled-mass transport/chemical
reaction code we are developing expresses quantitatively the mass transfer in a sandbentonite mixture under highly alkaline conditions. The concentration of Si was slightly
overestimated in the calculation probably because kinetics of the dissolution of SiO2
was not considered. The overestimation of the concentration of Si probably led to theunderestimation of the concentration of Al because they are related by the solubility
products of analcime, NaAlSi2O6.
According to the structure of the approach shown in Figure 1, our next step is toverify the computer code by using long-term variations in permeability that will beobtained through Long-term Permeability Experiment.
ACKNOWLEDGEMENT
This is a part of study funded by the Japanese Ministry of Economy, Trade andIndustry.
REFERENCES
1) Savage, D. et al. : Modelling the interaction of bentonite with hyperalkaline fluids,
Applied Geochemistry 17, pp. 207-223, 2002.
2) Parkhurst, D. L. and Appelo, C. A. J.: User's Guide to PHREEQC (Version 2)--A
Computer Program for Speciation, Batch-Reaction, One-Dimensional Transport,
and Inverse Geochemical Calculations, U.S. Geological Survey, Warer-Resources
Investigations Report 99-4259, Denver, Colorado 1999.
3) Yamaguchi, T. et al. : Experimental study on dissolution of montmorillonite incompacted sand-bentonite mixtureunder Na-Cl-OH pore-water conditions, in Proc.
Int. Workshop on Bentonite – Cement Interaction in Repository Environments,
Tokyo, Japan, 2004.
Alteration Experiment
Dissolution rate : RA (OH-, T)

Permeability Measurement& Literature Survey
Permeability coefficient : k (M, I)

Alkali Diffusion Experiment
Diffusivity : D (T,ρ)

Coupled Mass-transport / Chemical-reaction Analysis
Mass of montmorillonite ： M (x, t)

Prediction of time- &space-dependent permeability
coefficient : k (x, t)

Verification:
Long-term(～year)
permeability experimentFig.1 Structure of the approach to predict effects of bentonite alteration on permeabilityof altered compacted sand-bentonite mixture.
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Cement materials
Sand-bentonite mixtures
flow &
diffusion

Waste
Groundwater
conceptual model ofgeological disposal facility

Cement pore watercomposition

flow & diffusion

Output from performance assessment( Input of safety assessment )One dimension model of changes in
performance of compacted bentonite

time & space dependent,・pore water composition・solid composition・porosity・diffusion coefficient・permeability coefficientFig. 2Conceptual model for a geological disposal facility and one-dimensional
calculation cell of the coupled mass-transport/chemical-reaction code.

Start

Groundwater flow calculations

Mass transport calculations
Geochemical reaction calculations(PhreeqC)

Computation of porosity andmontmorillonite gel density
Reset of permeability anddiffusivity

End

Fig. 3 Flow of the calculation in the coupled mass-transport/chemical-reaction analysis
code

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NUMO-TR-04-05(cementcontacted
water)

High-pH
reservoir(simulated
groundwater)

Low-pH
reservoir

volume110 mlhydroxide ion diffusion
experiment container

High-pH reservoir(cement-contacted water)

Sand-bentonite
mixturesLow-pH reservoir(simulated groundwater)

1cm
Diffusion

Fig.4

Schematic drawing of the through-diffusion cell used in the hydroxide ion
diffusion experiment for compacted sand-bentonite mixtures.

OH- concentraion [mol/l]

0.6High-pH
reservoir(simulated)
Low-pH
reservoir(simulated)
High-pH
reservoir(experiment)
Low-pH
reservoir(experiment)

0.5
0.4
0.3
0.2
0.1
0.0
0

50

100

150

Time [day]Fig.5 Concentrations of OH- in high- and low-pH reservoirs in a through-diffusion
experiment. The plots are experimental results from Yamaguchi et al.(3).

1.E+0Concentraion [mol/l]

1.E-1
1.E-2
1.E-3
1.E-4
1.E-5
1.E-6
1.E-7
0

50

100
Time [day]150Na(simulated)Si(simulated)Ca(simulated)Al(simulated)Na(experiment)
Si(experiment)
Ca(experiment)
Al(experiment)

Fig.6 Concentration of Na, Si, Ca and Al in the low-pH reservoir in a through-diffusion
experiment. The plots are experimental results from Yamaguchi et al.(3).

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CEMENT-BENTONITE INTERACTION ISSUES, BUFFERINGCAPACITY OF BENTONITE
Jarmo Lehikoinen
VTT Processes, FIN-02044 VTT, Finland
Introduction
The main concern when clay minerals are exposed to a high-pH environment created by leachingcementitious materials relates to their stability on prolonged contact. The mineralogical alterationsof the smectite clay could lead to disadvantageous changes in its hydraulic and mechanicalcharacteristics, such as plasticity and swelling capacity, which could impair its performance as abuffer.
The cement-bentonite interaction is one between two thermodynamically incompatible materials,
which contradict rather than complement (Glasser, 2002). To mitigate this incompatibility, thedevelopment of low-pH cementitious materials has been initiated and is now underway.
Buffering capacity
In the present context, the buffering capacity is understood as a measure of bentonite’s ability toexert control on the solution pH. The buffering capacity of montmorillonite, the main componentof bentonite, is the ‘sum’ of two contributions,
1. The surface hydroxyl sites (≡SOH) situated along the edges of the clay platelets.
2. The montmorillonite crystal lattice itself.
The buffering of the ≡SOH sites is based upon their amphoteric nature, that is, they can protonate(≡SOH2+) or deprotonate (≡SO–), depending on the solution pH. The capacity of these sites, which
has usually been determined in short-term titration experiments 1 , is about 10% of the cationexchange capacity of the clay (i.e., <0.1 moles per kg of clay).
The rate of pH buffering by the ≡SOH sites is fast, while that of the montmorillonite matrix isgoverned by reaction kinetics. Once the capacity of the ≡SOH sites is used up, the second
component begins to operate.
The interaction between the montmorillonite crystal and hydroxide ions takes place according to
Na-montmorillonite + 6 H2O + 4.67 OH– → reaction products
Hence, the dissolution of 1 mole of Na-montmorillonite consumes 4.67 moles of OH–. This meansthat the theoretical buffering capacity of montmorillonite is 12.7 moles of OH– per kg of clay. The
capacity of the ≡SOH sites is therefore very limited in comparison to the second component (lessthan 1%). A bentonite with a montmorillonite content of 75 wt% (such as MX-80) has a buffering
capacity of 0.75×12.7 = 9.5 moles of OH– per kg of clay.
In what follows, with reference to the buffering capacity of bentonite, no differentiation between
montmorillonite crystal lattice conservative or destructive processes will be made per se.
In laboratory scale batch experiments, interactions of clays with highly alkaline fluids have beenreported to yield as reaction products (Vieno et al., 2003),••
1

Ca/Mg (aluminium) silicate hydrates
Framework silicates or zeolites

Therefore, it tacitly assumes chemical inertness of the montmorillonite crystal lattice.
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Hydroxides
Carbonates
Sheet silicates, such as illite or mixed-layer clays

The rise of temperature and the increase of time, solution pH and the solution-to-solid ratio tend
to favour the reaction progress. In addition, the nature of reaction products is strongly affected by
the cation content of the reactant fluid.
The potential of bentonite to consume OH– released from concrete was examined by Oscarson etal. (1997), who carried out alkalimetric titrations on pre-equilibrated smectitic clays by adding
solid Ca(OH)2 in amounts ranging from ∼5 to 80 mg to the suspensions and allowed them to react
for two weeks. The results from the titrations for Avonlea bentonite (∼80 wt% smectite) aredepicted in Figure 1a. In comparison to the theoretical pH as a function of added Ca(OH)2 withouta clay in Figure 1b, Avonlea bentonite is seen to exhibit a substantial buffering capacity. Also,
Jefferies et al. (1988) stated that for the three smectite-containing clays they investigated, at least
one mole of OH– per kg of clay was required to reach a high pH (>11). Based on these results, it
was considered in Vieno et al. (2003) that bentonite can retain the pH below 11 by neutralizing atleast 0.5 moles of OH– ions per kg of clay before the buffering capacity is used up.
Supporting evidence that the buffering capacity of bentonite could be ≥0.5 moles per kg of clay
was gained from the results of the recent ECOCLAY II project. In one of the experiments, 3.8 g
of MX-80 bentonite was let to react for 540 d at room temperature with 38 ml of a fresh alkaline,
saline alkaline and saline hyper-alkaline aqueous solution (Vuorinen et al., 2004). The starting pH
for these solutions was 12.5, 12.5 and 13.5, respectively. At the end of the reaction period, the‘equilibrium’2 pH attained was 11.2, 10.2 and 12.9. It can be estimated that approximately 0.36,
0.43 and 3.07 moles of OH– per kilogram of MX-80 was neutralized in these experiments.
According to the X-ray diffractograms of the reacted solid phases, a significant montmorillonite
component was present in the first two solutions (thus, MX-80 would still possess buffering
capacity against further alkaline attack). For the saline hyper-alkaline solution, a fraction of themontmorillonite appears to have transformed to beidellite (a smectite).

a)

12

b)

pH

11
10
9
8
7
0.0

0.5

1.0

1.5

2.0

m o l OH -/kg clay

Figure 1. a) Experimental titration curve for Avonlea bentonite (Oscarson et al., 1997); b)
Theoretical pH for Ca(OH)2 – synthetic granitic ground water of Oscarson et al. (1997) with noclay added. Open symbols denote saturation with respect to Ca(OH)2.

2

True equilibrium was likely not established, and the dissolution of montmorillonite was stillin progress. Upon approaching equilibrium, the rate of dissolution will decrease, however.
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Mass balance considerations
Assume that the total amount of cement remaining in ONKALO at the time of the backfilling of
the repository is at most 5 400 tonnes (Vieno et al., 2003). Hydrated ordinary Portland cement(OPC) contains about 20% of portlandite (Ca(OH)2), i.e. 5.4 moles of OH– per kg of cement,
which constitutes the main chemical threat to bentonite in the long term. The 5 400 tonnes of
cement could thus release ~3 107 moles of OH–. A repository of the KBS-3V type contains about
60 000 tonnes of bentonite clay in the buffer in the deposition holes. Therefore, this amount ofbentonite can theoretically buffer about 64 107 moles of OH–, which is 20 times the maximum
imaginable release of OH– from OPC.
However, in Vieno et al. (2003), a value of 0.5 moles of OH– per kg of clay (~5% of thetheoretical value) was (quite conservatively as it seems) selected for the buffering capacity ofbentonite, which is, in theory, just the limit to alter all the bentonite in the deposition holes.
Although it is highly unlikely that the OH– from cement could be transported without any
buffering and dilution into the deposition holes, the question of the extent of OH– attack bentonite
can, in practice, tolerate remains.
Model calculations
A potential means of gaining a deeper insight into the extent of alteration of compacted bentonite
subjected to a long-term high-pH attack could be by way of model calculations and optimisationof the parameters in long-term laboratory experiments, carried out in parallel.
So far, predictive model calculations on the long-term evolution of the bentonite buffer in contact
with high-pH solutions have been highly speculative, the model results ranging from a small
amount of montmorillonite dissolution in one million years to total removal of primary bentonite
minerals up to 60 cm from the contact with cement in about 1 000 years (Vieno et al., 2003).
Unfortunately, integrated mass flow rates of OH– ions and other solutes entering the bentonite
from concrete were not recorded in any of these simulations. A common problem with all themodel calculations with complex mineral assemblages is poor knowledge of possible reaction
products and of mineral dissolution and growth kinetics, which are thus subject to considerable
uncertainty.
Simple model calculations
The dissolution kinetics of montmorillonite in Huertas et al. (2001) has been incorporated into a
simple one-dimensional non-linear diffusion-reaction equation. The underlying assumptions of themodel are• only one solute, OH–, is involved• at the solid-solution interface, pH = 12.5 (25 °C)• the fate of OH– is determined by diffusion and consumption by montmorillonite dissolution• the diffusivity is given by the Bruggeman equation, D = φ3/2 D0, where φ is the volume
fraction of pores and D0 = 5 10–10 m2/s has been selected arbitrarily• the volume is made up of the montmorillonite, porosity and reaction products, φm + φ + φr =1
• initially, the pore fluid pH is 8.5, φ ≈ 0.43 and φr = 0• the changes in the volume fractions φm and φr are related by, dφr = –κ dφm, where κ is 0.5,
1.0 and 1.5.
The results of the calculation at t = 1 ka are shown in Figure 2. Depending on the value of κ, 1 to
8 cm of montmorillonite will convert to secondary phases. The extent of this conversion is seen to
be a strong function of the evolution of porosity. Albeit highly simplified, the model results
readily allow the calculation of the consumption of OH–.

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1.0a)Volume fraction

0.8

φ
0.6

0.4

φm
0.2

φr

0.0
0

2

4

6

8

10

12

14

10

12

14

10

12

14

Distance / cm
1.0b)Volume fraction

0.8

φ

0.6

0.4

φr

φm

0.2

0.0
0

2

4

6

8

Distance / cm
1.0

0.8

Volume fraction

c)

φ

0.6

φr
0.4

φm
0.2

0.0
0

2

4

6

8

Distance / cm

Figure 2. Volume fractions of montmorillonite, pores and reaction products after 1 ka as afunction of distance from the solid-solution interface for a) κ = 0.5, b) κ = 1.0 and c) κ = 1.5.

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Discussion and questions
The functional form for the pH dependence of the dissolution rate, k (mol/m2/s), is typically of theform, log k = α + β pH, where β = 0.34 for montmorillonite (Huertas et al., 2001). Upon lowering
the solution pH from 11 to, say, 10, will the difference in log k be significant enough to improve
the long-term stability of bentonite, and, if so, would there be a need to one reconsider the pH
limit of 11, which seems to have been selected more or less arbitrarily (Bradbury and Baeyens,1997)?
In addition to montmorillonite, bentonite may have as accessory minerals other powerful pH
buffers, such as quartz (15 wt% in MX-80), which have a faster dissolution kinetics thanmontmorillonite. Uncertainty about the role the accessory minerals in bentonite play in thechemical buffering of the solution pH in these experiments remains, however. It would be ofinterest to know how much of the buffering capacity of bentonite can be assigned to these minor
solids in practice.
The solid-to-solution ratio (s/s) is an important parameter when assessing the interaction between
the clay and highly alkaline solution. In Vuorinen et al. (2004), this ratio was relatively low, 1:10
(3.8 g:38 ml). It is likely, however, that the solution pH will be buffered to lower values by
bentonite when the solid-to-solution ratio is increased. This anticipated trend would then also
pertain to repository conditions, where compacted bentonite (s/s ≈ 1:0.26 for the bentonite dry
density of 1.6 g/cm3) is in contact with its own pore fluid and diffusion-control prevails.
Interesting in this context is the extent to which bentonite is able to buffer the ingress of anaggressive alkaline plume close to the solid-solution interface, where far-from-equilibrium
conditions result in the highest montmorillonite dissolution rate, and if the solid reaction products
possess enough molar volume to reduce or even clog the pore space of the altered bentonite.
When investigating mineral transformations in batch systems, the whole surface area of the clay istypically exposed to the high-pH solution. However, in systems where compacted clay is put indirect contact with a leachate from a cementitious material, the alteration of the clay will be
diffusion-controlled. Mineral transformation in compacted bentonite under diffusion control is
expected to be a powerful chemical buffer against a high-pH solution, which is supported by the
scarcity of hard evidence for the propagation of such a plume (Vieno et al., 2003). However, apotential exception is the study by Ichige et al. (2001), who discovered a non-negligible zone ofzeolitization in only 20 days for compacted Kunipia-F bentonite (smectite content ∼99%) in
contact with a solution pH of 14 at elevated temperatures (130 °C and 200 °C). The extent ofzeolite formation was a function of temperature. On the other hand, the same experiments
performed with a solution saturated with portlandite (pH 12.5) gave only small zeolite peaks in 6
months. Also, the relatively fast diffusion of hydroxide ions through bentonite with apparently
little chemical buffering (Karnland et al., 2003) clearly warrants a closer look into the topic. In
particular, the propagation of OH– in relation to the buffering rate of compacted bentonite and thepotential of slowly-dissolving siliceous species to precipitate and cause cementation of the highly
compacted bentonite should be investigated in more detail.
The effect of a high-pH fluid on the mineralogical stability of clays and the concomitant buffering
capacity has also been studied with percolation tests. Usually no or minor mineralogicalalterations and insignificant buffering of the injection fluid pH were observed within the durationof the tests, which can be explained by the relatively high flow rates used to percolate the fluid.
Under these conditions the potential of the clay to buffer the chemistry is bound to be limited in
short-term experiments. By adjusting the flow rate and/or composition of the percolating fluid tobetter conform to sluggish mineral dissolution and growth rates, it was possible to observe a
buffering effect of the clay on the effluent pH (Vieno et al., 2003; Vuorinen et al., 2004).

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Future research
It is suggested that continued effort be put on• Performing long-term alkalimetric titrations to find out the buffering capacity of untreatedand purified bentonite for a number of solid-to-solution ratios.
• Clarifying the extent to which compacted bentonite is able to buffer the ingress of anaggressive alkaline plume at the solid-solution interface, where far-from-equilibrium
conditions prevail and the montmorillonite dissolution rate is the highest (i.e. thepropagation of OH– in relation to the buffering rate of compacted bentonite). On-line
monitoring of the evolution of pH inside the bentonite (see Figure 3).
• Performing experiments on systems, where the degrees of freedom are constrained to aminimum (for example, pure homoionic montmorillonite in contact with NaOH or Ca(OH)2).
This way, uncertainty of the neoformed secondary phases is also minimized. If possible,
keep a record of mass balances to ensure back calculation.
• Investigating in more detail the potential of slowly-dissolving siliceous species to precipitateand cause cementation of the highly compacted bentonite.
• Conducting a careful analysis of the reaction products.
• Carrying out supporting numerical calculations. Acknowledging the uncertainties associatedwith chemical kinetics, sensitivity analyses might be needed. A successful blind predictionof a simplified system would lend credence to the capability of geohydrochemical models to
reproduce the observed phenomena.

Figure 3. Schematic view of the diffusion cell for on-line monitoring of the evolution of pH incompacted bentonite (courtesy of Dr. A. Muurinen, VTT, Finland).

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References
Bradbury, M. H., and Baeyens, B. 1997. Far-field sorption data bases for performance assessmentof a L/ILW repository in a disturbed/altered Palfris marl host rock. Report PSI Bericht Nr. 97-16.
Glasser, F.P. 2002. Characterisation of the barrier performance of cements. Mat. Res. Soc. Symp.
Proc., 713, 721–732.
Huertas, F.J., Caballero, E., Jiménez de Cisneros, C., Huertas, F., and Linares, J. 2001. Kinetics ofmontmorillonite dissolution in granitic solutions. Appl. Geochem., 16, 397–407.
Ichige, S., Kubo, H., Kuroki, Y., Savage, D., Rochelle, C., Noy, D., and Mihara, M. M. 2001. The
effect of high pH cement solution on bentonite buffer. Presented at the Crystalline Group
Workshop on the Use of Cement in Construction of Underground Facilities, Helsinki, May 10–11,
2001.
Jefferies, N.L., Tweed, C.J., Wisbey, S.J. 1988. The effects of changes in pH within a clay
surrounding a cementitious repository. Mat. Res. Soc. Symp. Proc., 112, 43–52.
Karnland, O., Nilsson, U., Olsson, S., Sellin, P. 2003. Laboratory experiments with compacted
bentonite in contact with high pH solutions. In press for the final report of the ECOCLAY II
project.
Oscarson, D.W., Dixon, D.A., and Onofrei, M. 1997. Aspects of clay/concrete interactions.
Report AECL-11715, COG-96-562-1.
Vieno, T., Lehikoinen, J., Löfman, J., Nordman, H., and Mészáros, F. 2003. Assessment ofdisturbances caused by construction and operation of ONKALO. Report POSIVA 2003-06.
Vuorinen, U., Lehikoinen, J., Luukkonen, A., and Ervanne, H. 2004. Effects of salinity and highpH in crushed rock and bentonite. In preparation as a POSIVA report.

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A long-term performance assessment for engineered barriers- Study on barrier materials alteration H. Kato1, H. Asano1, N. Yamada2
1

Radioactive Waste Management Funding and Research Center, Japan2
Mitsubishi Materials Corporation, Japan

Introduction
In TRU waste repository, large amount of cementitious materials will be used as waste form,
fillings, structure and lining. Bentonite material also will be used as buffer material in order torestrict groundwater movement into the repository. Quantitative ratio of cementitious materials tobentonite materials at the TRU waste repository is larger than that of HLW repository. Therefore
bentonite-cement interaction is one of the important phenomena to evaluate long-term
performance of engineered barriers.
In the first progress report on TRU waste disposal in Japan 1), the performance of engineered
barriers had been pessimistically evaluated because of uncertainty of their long-term behavior.
However, at present, more realistic evaluation might be possible by accumulation of recent
experimental knowledge for alterations of cementitious materials and bentonite materials in therepository environment, development of modeling and numerical analysis method for theiralteration process.
In this study, based on a recent knowledge, numerical analysis for a long-term alteration ofengineered barrier system (EBS) was performed as a preliminary calculation. From this result, key
technical issues on engineered barriers alteration process were identified in order to improve thereliability of a long-term performance assessment for EBS in TRU waste repository
Alteration analysis of EBS
A long-term evolution of EBS of TRU waste repository was evaluated based on the most recent
knowledge about chemical, mineralogical, hydrological and mechanical processes in the system.
Then, according to the influence on the performance of the repository system, important processes
were selected.
Coupled geochemistry and mass transport calculation code (PhreeqC-Trans) was used in theseanalysis.(Figure 1) This code treats geochemical reactions and mass transport (diffusion andadvection). In this code, hydraulic conductivities, diffusion constants and porosities were renewedin accordance with the change of mineralogy and concentration in EBS, and mass transportconditions were recalculated at regular time intervals.
Because of the uncertainty which lies in the parameters and models, several sensitivity analysis
were performed under different parameters or models listed below.
・ Cement minerals to be considered in the geochemical analysis
・ Bentonite minerals to be considered in the geochemical analysis
・ Source of thermodynamic database
・ Effect of the change in hydraulic conductivity of cementitious materials/bentonite materials
・ Effect of the change in diffusion constants of cementitious materials/bentonite materials.
・ Dissolution model of bentonite minerals.
・ Types of the groundwater・ Groundwater flow rate in host rock

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NUMO-TR-04-05

Geochemical
reaction

Change of thephysical properties

・equilibrium・speciation
・dissolution andprecipitation
・ion exchange・porosity・diffusivity
・hydraulic conductivity

Mass transport
・advection・diffusion（・dispersion)

Hydrology
・ground water flow rate and direction

Figure 1 Phenomena and their coupling on the alteration analysis of EBS

System configuration for numerical analysis
Geometry of the analysis is shown in Figure 2. TRU waste repository system consist of waste
package, filling mortar, concrete structure, buffer material (bentonite/sand mixture), concrete
lining and rock. Representative section of this system was selected and modeled as 1 dimensional
mesh. In the alteration analysis, ordinary portland cement and kunigel V1® are considered as
cementitious and bentonite materials respectively.

Concrete lining 0.5ｍ Buffer material 1.0ｍ
structure1.0ｍ

rock

Filling mortar 0.5ｍ

Upstream side of the repository tunnel ismodified to 1-dimensional geometry.

ﾋﾟｯﾄ層

waste

Geochemical-transport analysis area
充填
ﾓﾙﾀﾙ層

Groundwater flow analysis area

Figure 2 Geometry of the analysis

Results
Figure 3 shows a typical result of the analysis. Dissolution of chalcedony was confirmed in the
bentonite/sand mixture layer. Most of montmorillonite was altered to analcime at the interface ofbentonite/sand mixture layer and concrete structure. Portlandite in cementitious material dissolved
to form low Ca/Si ratio CSH with silica ions from chalcedony. As the result of these reactions,porosity increased in the bentonite/sand mixture layer. On the contrary, porosity at the interface ofconcrete structure and bentonite/sand mixture layer significantly decreases by the precipitation of
low Ca/Si ratio CSH.

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Figure 4 shows the change of hydraulic conductivity and diffusivity in accordance with alterationof the properties of EBS. The numbers of the layers shows the calculative mesh positions in eachbarrier material, and the 1st layer is the most outer layer. Hydraulic conductivities of the bentonite
material increased, at first, by the ion exchange of inter layer Na to Ca, and alteration ofmontmorillonite to analcime. The long-term change is caused by the dissolution of chalcedony.
The diffusivities in the structure decreased by the precipitation of CSH, and the diffusivities in thefilling mortar slightly increase by the dissolution of portlandite.
As a result of sensitivity analysis, following important parameters, which affect the resulting total
performance of EBS, were confirmed.
- Different thermodynamic data shows quantitatively and qualitatively different timedependent mineralogical change.
- Different dissolution rate of montmorillonite shows qualitatively different time dependentof montmorillonite alteration.
- High concentration of CO32- and NaCl can change the mineralogy of cementitious
materials and montmorillonite respectively.

The change of porosity with
geochemical interaction

Porosity change (-)

5

10

5
- -Dissolution
10
Dissolutionofof0 . 15
0. 1

4- -Alteration
Alterationof
ofmontmollironite
montmollironite
into
intoanalcime
analcime- -Precipitation
Precipitationof
ofCSH
CSH

4

10

10
Time [y]Time [y]0 . 050-0 . 05

3

10

Typical alteration eventschalcedony
chalcedony

0. 2- -Dissolution
Dissolutionof
ofPortlandaite
Portlandaite103-0 . 1-0 . 15

Rock

C on crete B -S M ix t u reConcrete Mort ar

WastesWaste
form
Bentonitematerials

0.3
0.3
2 (OHafter)2 10,000 years
10Ca
CSH
C3 AHRock6
Co ncre t e B -S Mi x ture Concrete
C3
0.2 ASH 4
0.2
C2 ASH 8
C3 AS3AFt
空隙率の変化量の経時変化
Ca lc it e
0.1
Br uci te
Ch al ce don y
An al ci me
0.0Na
0.0 -Mo nt

Volumefraction
固相
体 積割
合[-]
[-] [ - ]固相体積割合-0 . 2

102

岩

Rock
岩

覆工

ベン トナイ ト

ベン トナ イ ト
混合土

混合土Concrete
Bentonite
覆工

M ort arWastesCa(OH)2CSH
C3AH6
C3ASH4C2ASH8
C3AS3
AFt
CalciteBruciteChalcedony

Analcite
Na-Mont
モルタ

モル タ廃棄物層
Waste
廃棄物層
ル

構造躯体

ル
Concrete
構 造躯体 Mortar

Volume fractions of minerals in thebarrier materials after 10,000 years

Cementitious
materials

E.B. system

Figure 3 Typical alteration events and porosity change occurred in engineered barriers.
(GW type: FRHP)
1.0E-09

実効 拡 散係 数 [ms ]Diffusivity [m2/s]

2 -1

1st layer
0.075
nd layer20.225rd layer
30.4
th layer
40.6
th layer50.7750.925
6th layer

1.0E-09-1

係 数 [m s [m/s]]Hydraulic透水
conductivity

1.0E-08

1.0E-101.0E-11

1.0E-12100

1.0E-101.0E-11
1000

10000

100

100000

1000

10000

Structure
1st layer
1.075
2nd layer
構
1.225
造
1.4
3rd layer躯
1.6
4th layer
1.775
体
5th layer
1.925
6th layer
2.05
モMortar2.15
1st layerル
2.25
2nd layer
タ
2.35
ル
3rd layer
2.45
4th layer
100000
5th layer

経過時間[y]Time [years]

Time[years]
経過時間[ y](a) Change of the hydraulic conductivity of bentonite materials(b) change of the diffusivity of cementitious materials

Figure 4 Evaluated barriers performance as a function of the time

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Discussion
Through the above preliminary alteration analysis, following key technical issues on evaluation ofa long-term alteration of EBS are identified from a view point of improvement of reliability on along-term performance assessment for EBS in TRU waste repository
1. Considering of ignored components in engineered barrier on modeling・ Necessity of consideration of aggregates in mortar or concrete and mixed sand in bentonite
materials on the analysis.
・ Treatment and modeling of crack in cementitious materials
2. Experimental acquisition of parameters and its review- Geochemical model・ Initial minerals composition of hydrated cement in the model
・ Thermodynamic data of montmorillonite and analcime about bentonite alteration- Geochemical reaction
・
Thermodynamic model of C-A-S-H, and change of more stable minerals by
thermal effect in cementitious materials
・Experimental identification of secondary minerals and dissolution rate underalkaline condition in bentonite materials- Mass transport
・ Effect of pore structure, hydraulic conductivity and diffusivity in extremely low porosity.
3. Experimental validation of typical alteration events to be predict from the analysis
・ Remarkable decrease of the porosity ant the vicinity of cement/bentonite boundary caused
by precipitation of secondary minerals such as calcite, C-S-H and ettringite
・ Selective dissolution of chalcedony, reverse alteration reaction of analcime intomontmorillonite, montmorillonite dissolution rate close to its saturated concentration andsignificant alteration of montmorillonite into analcime in saline water in bentonite materials.
*This study was commissioned by METI, Japan.

Reference
1) TRU coordination office, Progress report on Disposal Concept for TRU Waste in Japan, March,
2000.

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An Analysis of Cement-Bentonite Interaction and Evolution of Pore Water
ChemistryC. Oda*, A. Honda* and D. Savage*** Japan Nuclear Fuel Cycle Development Institute, 4-33 Muramatsu, Tokai-mura, Naka-gun,Ibaraki-ken, 319-1149, Japan.
** Quintessa Limited, 24 Trevor Road, West Bridgford, Nottingham, NG2 6FS, United
Kingdom
INTRODUCTION

Performance assessments for TRU waste repositories have shown that soluble and poorly
sorbing nuclides such as I-129 and Cl-36 dominate the dose [1]. These nuclides are expected
to migrate with groundwater flow, hence hydraulic conditions and their evolution with timein the repository are key issues for repository safety. Cementitious material will be used for
waste packaging, backfilling and structural material in a TRU waste repository. Bentonite isalso expected to be used for some TRU wastes to provide the function of a hydraulic barrierin the disposal system. It is known that the logarithm for the dissolution rate of smectite is
proportional to the logarithm for the activity of hydroxide ion [2]. Therefore there is concernthat the coexistence of cementitious material and bentonite cause the alteration of smectite
due to interaction with hyperalkaline leachates and consequent deleterious perturbation of thefunction of bentonite as a hydraulic barrier. Many research studies have been performed to
identify possible mechanisms of cement-bentonite interaction. However, uncertainties still
exist in our understanding of the precise chemical scheme of bentonite alteration in highly
alkaline conditions, especially the spatio-chronological variation of secondary mineraloccurrences.
In this work, the possible multiple scenarios of chemical-mineralogical evolution wereconsidered on the basis of the information of both experimental results and observations of
natural systems. The range of variable chemical conditions according to each scenario was
examined in terms of the potential for locally-attained chemical equilibrium. These analyses
have been intended to provide reasonable assumptions on simurations using the chemistrytransport-hydrology coupling models that aimed at estimating possible evolution of hydraulicconditions of bentonite in a TRU waste repository.
Understanding alteration processes of bentonite

There have been several experimental studies on smectite alteration under hyperalkalineconditions at low temperature and these are summarized below. From the experimental results,
it is likely that different parageneses of secondary minerals are possible.
- Mineral stability with respect to the composition of the solution phase
The types and abundances of secondary solid phase will reflect the composition of thesolution phase (e.g. pH, the concentration of alkali/alkali earth elements, and the Si/Al ratio).
Under hyperalkaline conditions produced by the presence of KOH, illite and phillipsite havebeen observed in the experiments [3][4][5][6]. In Na-rich conditions, analcime, a zeolite
mineral mainly formed in experiments at temperatures in excess of 373 [K], is formed, evenat low temperature [7]. In highly alkaline conditions due to the presence of Ca(OH)2 or the
combination of Ca(OH)2, NaOH and KOH, CSH, CAH, CASH minerals, mixed-layer
minerals, analcime and phllipsite have been observed in experiments [8]. Zeolites have been

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observed as products of many laboratory experiments and natural analogues of hyperalkaline
water-rock interaction.
Mariner et al. [9] showed that the Si/Al ratio of zeolites decreased with increasing pH.
Accordingly, analcime and phillipsite (low Si/Al ratio zeolite) preferentially form at high pH,
whereas mordenite and clinoptilolite (high Si/Al ratio zeolite) preferentially form in anenvironment of lower pH. Savage [10] hypothesized that the Si/Al ratio of zeolites potentiallyforming in the hyperalkaline disturbed zone of a waste repository should increase with
distance away from the source of hyperalkaline fluid, mirroring the decrease in pH with
distance away from the repository.
- Transformation of solid phases from a metastable to a thermodynamically stable state
On the other hand, the sequential variation of secondary minerals from metastable phases tostable phases was also observed in laboratory experiments using high pH solutions at low
temperature as follows:・ Opalinus Clay → CASH and mordenite → illite and calcite [11]・ smecite → Iillite → phillipsite →K-feldspar [3]These reactions seem to be controlled by kinetic factors rather than by attainment ofthermodynamic equilibrium. The formation of the metastable phases occurring occasionallyin sedimentary rocks is explained by the empirical Ostwald step rule, where the surface freeenergy and degrees of supersaturation are important factors. Consequently, rapidly-growing
metastable phases which lower the overall free energy of the system may be observed, rather
than phases which are thermodynamically more stable [18].
Transformation from metastable to stable phases appears in natural environment, forexample:・ mordenite, phillipsite → clinoptilolite, analcime, K-feldspar [12]・ phillipsite → clinoptilolite, analcime [13]・ smecite → illite [14]These findings from natural environments of lower pH show similar trends to thoseexperiments at high pH and low temperature conditions, indicating that the high-pH
conditions greatly increase reaction rates [11][15].
The relationship between natural zeolite formation during burial diagenesis of sedimentaryrocks and thermal history has been reported extensively in the literature. From these studies, it
is concluded that at low temperatures zeolites with a high Si/Al ratio (e.g. clinoptilolite, andmordenite), form whereas at greater burial depths (higher temperature) , zeolites with a lower
Si/Al ratio (e.g. heulandite and analcime), formed, and where even higher temperature existed,laumontite was produced [16]. This observation seems also to follow an Ostwald step rule
postulating that the precipitate with the highest solubility (i.e. the least stable solid phase) will
form first in a sequential precipitation reaction [17].
It could be regarded that the formation of zeolites with a higher Si/Al ratio is faster thanthat of zeolites with a lower Si/Al ratio, so that pH may control the reaction rates in analogy
with the effect of temperature. Furthermore, it is considered that a wide range of secondary
minerals, CSH, CAH, CASH, clay minerals (illite, mixed-layer mineral, low Si/Al zeolite,
high Si/Al zeolite) and K-feldspar could appear due to the variation of pH with time and space
under repository conditions. The formation of K-feldspar may, however, take more than 1
million years at low temperature [18].

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Analysis using Geochemical Modeling CodeThe chemical conditions in the engineered barriers will change sequentially during thealteration of cement and bentonite over the long term. It is hard to determine precisely to what
degree the alteration may progress over PA timescales. To estimate the range of possible
chemical evolution, an analysis of spatio-chronological variation of mineralogy and porewater chemistry in the cement-bentonite system was conducted with consideration of the local
equilibrium and sequential transfer of solutes between modeled regions.
- Bentonite Alteration Scenarios
Bentonite alteration scenarios for this analysis were determined on the basis of theinformation mentioned above.
At first, the guidelines for making scenarios for smectite alteration were considered asfollows:
Guideline 1 : The precipitate with the highest solubility (i.e. the phase of least positive
saturation index) forms first in a sequence of precipitation reactions.
Guideline 2 : The Si/Al ratio of zeolite increases with decreasing pH.
Guideline 3: The alteration of mineral assemblages progresses rapidly at high pH and more
slowly at lower pH.

The temperature in repositories is assumed to be less than 353[K], and the maximum pH in
the engineered barrier systems lies between that of ambient groundwater and that of thehyperalkaline pore fluid typical of cement. Some minerals were selected as being
representative of mineral types likely to form in such systems as follows:- CSH, CASH: metastable in all the range of environmental conditions- illite, mixed-layer minerals: metastable in hyperalkaline condition, but more stable thansmectite- analcime: alkalic zeolite stable over the wide range of environmental conditions- laumontite: calcic zeolite stable in hyperalkaline conditions, but difficult to form at low
temperature- (K, Na)-phillipsite : alkalic zeolite stable in weakly alkaline conditions- (Ca, Na)-clinoptilolite: calcic and alkalic zeolite stable in weakly alkaline conditions- (Na, Ca)-mordenite: alkalic and calcic zeolite stable in neutral – weakly alkaline conditions- K-feldspar: Stable over the wide range of environmental conditions, however difficult toform at low temperature
Waste/concrete construction
Ordinary portland cement

Cement pore waterTime

A set of scenarios was prepared inaccordance
with
the
above
classification and the guidelines. A
schematic of the scenarios is shown in
Fig.1. The bentonite region is adjacentto the cementitious region. A model
groundwater is equilibrated with thehydrated cement and the consequent
cement pore water is transferred into
the bentonite region. The cement porewater changes with time according toregions I, II and III [19]. The bentonite
pore water builds up through theinteractions of cement leachate andpH>12.5 （Region I）↓
pH=12.5 （Region II）↓↓
pH<12.5 （Region III）

Bentonite buffer
Na-bentonite(Dry density of 1600 Mg/m3, Sand mixture of 30 wt%）

Bentonite pore water
Locally equilibration
Smecite dissolution
Smectite cation exchange
Accessory minerals dissolution(Calcite, chalcedony, pyrite)
Secondary minerals pricipitation/dissolution
Guideline(1)

Guideline(2)

Guideline(3)

Bentonite pore water
Solution- pH buffered
Locally equilibration
Solid phases- Intact bentonite-Ca-exchanged benonite- Secondary minerals

Distance

Fig.1 Schematic of scenarios for the analysis of pore waterevolution during cement-bentonite alteration

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NUMO-TR-04-05

bentonite involving each sequence of reactions in accordance with the guidelines.
- Calculation using Geochemical Modeling CodeThe scoping calculations using the geochemical modeling code, PHREEQC [20] were
performed according to the scenarios outlined above.

Chemical Modeling of Cement Pore water
Following Berner’s method [21], the mineralogical composition of hydrated cement paste(W/C=70) was determined based on the chemical composition of Ordinary Portland Cement.
The CSH-gel was modeled as a series of calcium silicate hydrate minerals in which theequilibrium constant is varied by Ca/Si ratio, following Atkinson’s model [22]. The
compositions of cement pore water of region I, II and III were calculated with the mixing tankmodel in which the equilibration between the fresh-type model groundwater [23] and theminerals of hydrated cement paste was repeated many times with the remaining solid phases.
The thermodynamic data set for minerals of hydrated cement paste [24] was used.
Chemical Modeling of Bentonite Pore water
The dissolution and precipitation reactions of minerals and cation exchange reactions on
smectite were taken into account in the scoping analysis. The bentonite buffer (dry density=1600 [Mg m-3]) contains 30% of silica sand. The mineralogy of the bentonite buffer and thecation exchange constants on smectite were assumed to be the same as in the previous PA
report [1]. Equilibrium constants were taken from Hatches, ver.14 [25] for all species andmineral hydrolysis reactions other than for the minerals CASH,CAH, clinoptilolite [26],mordenite [27] and phillipsite [28]. Unfortunately, few reliable thermodynamic data for
CASH and CAH currently exist. In our calculations, gehlenite and katoite [24] were used as
proxies for CASH minerals and phillipsite was excluded because of the large uncertainties inpublished data. Muscovite was used as a proxy for mixed-layer silicate.
The results of analysis

The results of scoping calculations are summarized in Fig.2. The layout of data in Fig.2
represents the concept of this analysis in accordance with the scenarios. The precipitation ofzeolites, especially analcime,※ Bentonite Porewater III
CementBentonite Porewater I Na-mont↑
Porewater
Na-mont↑ pH 12.0
Na-mont↑ pH 10.6
Na-clino ↓ pH 9
readily neutralized the pH of
Na-mont↑
Na-mont↑
Na-mont↑
Na-clino↓pH
8.7
Analcime↓pH
7bentonite pore water for all
CSH-gel ↓ pH 11.8
I. pH 13.5
Na-mont↑
Na-mont↑
cement leachates of region I,
Ns-mont ↑Analcime ↓ pH 7
K-feldspar↓pH 7
Illite ↓pH 12.0
II and III. The neutralization
Na-mont↑
Na-mont↑
Na-mont↑
K-feldspar ↓ pH 9.8
II. pH 12.5
Na-clino↑
Na-clino↓ pH 9.6
may inhibit the dissolution of
III (Ca-exchanges)
Analcime↓pH 8
Ca-mont↑
Na-mont↑
smectite. Once stable zeolite
Na-clino ↑Lanmontite↓ pH 10.5
Analcime ↓ pH 8
Analcime↓ pH 9.7
precipitated,theresultantCa-mont↑
III. pH 11.2
Na-mont↑
Ca-clino ↓ pH 9.7
Muscovite↓
K-feldsper ↓ pH 11.9
changes
in
pore
water
Analcime↑ pH 8.2
Ca-mont↑
Ca-clino ↓ pH 9.7
K-feldspar↓
Bentonite Porewater II
composition became minor.
Analcime↑ pH 8.2
Laumontite↑
Na-mont↑ pH 11.5
Ca-clino↓ pH 10.7
The pH neutralizing trends with
Na-mont↑
II (Ca-exchanged)
Ca-mont↑pH 9.7
CSH-gel ↓ pH 11.3
Ca-mont↑
the precipitation of CSH,
Ca-mont↑
Na-mont↑
Ca-clino ↑ pH 10.4 Ca-clino↓ pH 9.7
Laumontite↓pH 11.3
Na-clino↓ pH 9
CASH minerals, mica group
Ca-clino ↑Na-mont↑
Ca-mont↑
Laumontite↓ pH 11.3
and K-feldspar were weak, so
Analcime ↓ pH 7
Ca-clino↓ pH 10.5
Ca-mont↑
Na-mont↑※
Laumontite↓ pH 10.5
that the inhibition effect of
K-feldsper↓ pH 11.5 Ca-mont↑
K-feldspar↓ pH 11.5
Ca-clino ↓ pH 10.5
thesereactionsonthedissolutionofsmectite,Fig.2 Summary of the results of scoping calculations
therefore, is considered to be
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NUMO-TR-04-05

weak. The pH variation of bentonite pore water through the Na-type smectite alteration
process is larger than that in the presence of Ca-exchanged smectite.
Summary and Conclusions

An analysis of the mineralogical-chemical evolution in the engineered barrier was performed.
To estimate the range of probable chemical evolution, scoping calculations of spatiochronological variation of mineralogy and pore water chemistry were examined byconsidering local equilibrium with the bentonite alteration scenarios. The guidelines wereconsidered to identify the probable scenarios on the basis of the information of experimental
results and observations of natural systems. The results of this analysis showed that theestimated bentonite pore water evolution depends on sequences of secondary mineraloccurrence. It is suggested that the pore water may allow for a greater degree of local pH
buffering when the alteration from smectite to zeolites only partially occurs, thus providing
preferable conditions for smectite retention in the whole bentonite buffer region.
This work suggests that the results are helpful for the simulation of the evolution ofprobable hydraulic conditions due to cement-bentonite interaction.
References[1] JNC TY1400 2000-001, TRU TR-2000-01[2] Huertas, F.J., et. al., 2001; Kinetics of montmorillonite dissolution in granitic solutions,Applied Geochemistry, 16, pp.397-407.
[3] Eberl, D.D., Velde, B., and McCormick, T., 1993, Synthesis of illite-smectite fromsmectite at earth surface temperatures and high pH: Clay Minerals, v. 28, p. 49-60.
[4] Bauer, A. and Velde, B., 1999; Smectite transformation in high molar KOH solutions,
Clay Minerals, 34, pp.259-273.
[5] Drief, A., Mattinez-Ruiz, F. and Velilla Sanchez, N., 2002; Transmission electron
microscopy evidence for ezperimental illitization of smectite in K-rich seawater solution at
50C and basic pH, Clays Clay Mins., 50(6), 746-756.
[6] Vigil de la Villa, R., Cuevas, J., Ramirez, S. and Leguey, S.,2001; Zeolite formation
during the alkaline reaction of bentonite, Eur. J. Mineral., 13, pp.635-644.
[7] Kim, S.Y., Experimental investigations of the effect of alkali fluids on montmorillonite,
albite and quartz, JNC YN8400 2001-008 (in Japanese)[8] Iriya, K., et al., 1998, Study on degradation of engineered barrier in radioactive
repositories, JNC TJ8400 98-003 (in Japanese).
[9] Mariner, R.H., and Surdam, R.C., 1970, Alkalinity and formation of zeolites in saline,
alkaline lakes: Science, v. 170, p. 977-980.
[10] Savage, D., 1996, Zeolite occurrence, stability and behaviour: a contribution to Phase IIIof the Jordan Analogue Project: London, U.K. Department of the Environment.
[11] Adler, M., Mader, U.K. and Waber, H.N., 1999; High-pH alteration of argillaceous
rocks: an experimental study, SCHWEIZ. MINERAL. PETROGR. MITT. 79, pp.445-454.
[12] Boles, J.R., 1977, Zeolites in deep-sea sediments, in Mineralogy and Geology of Natural
Zeolites, Mineralogical Society of America, p. 137-163.

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NUMO-TR-04-05[13] Barrer, R.M., 1982; Hydrothermal chemistry of zeolite. Acad. Press, London.
[14] Huang et al., 1993; An experimentally derived kinetic model for smectite-illite
conversion and its use as a geothermometer, Clay Clay Minerals, 41, pp.162-177.
[15]. Hay, R.L.(1966);Zeolites and zeolite reactions in sedimentary tocks, Geol. Soc. Am.,
Spec. Paper, 85, 130.
[16] Akai, J., et al.,1995; Science of minerals, Tokai Univ. Press, Japan.
[17] Stumm and Morgan, 1996; Aquatic chemistry 3rd ed., John Wiley & Sons, New York,
p.807[18] Dibble, W.A., and Tiller, 1981, Kinetic model of zeolite paragenesis in tuffaceous
sediments: Clays and Clay Minerals, v. 29, p. 323-330.
[19] Brudbury, M.H. and Sarott, F.A., 1995; Sorption database for the cementitious near-fieldof a L/ILW repository for performance assessment, PSI Report, PSI Bericht Nr.95-06.
[20] Parkhurst, D.L. and Appelo, C.A.J.,1999; User’s guide to PHREEQC (version 2) –A
computer program for speciation, batch-reaction, one-dimensional transport, and inverse
geochemical calculations, Water-Resources
Investigations Report 99-4259.
[21] U. Berner, 1992; Evolution of pore water chemistry during degradation of cement in aradioactive waste repository environment. Waste Management, 12, 201-219.
[22] Atkins, A., et al.,1987; Aqueous chemistry and thermodynamic modelling of CaO-SiO2H2O gels. UK Atomic Energy Authority Report AERE-R12548.
[23] Yui, M., et al., 1999; JNC TN8400 99-030.
[24] Glasser et al.,1998;The chemistry of blended cements and backfills intended for use inradioactive waste disposal, R&D Tech. Report P98, Environment Agency.
[25] Cross, J.E., et. al.,1987; Thermodynamic modelling with application to nuclear waste
processing and disposal, HATCHES.
[26] S.Yang, A.Navrotsky and R.Wilkin; American Mineralogist, Vol.86, pp.438-447,2001[27] L.Benning, R.Wilkin and H.L.Barnes; American Mineralogist, Vol.85, pp.495-508,2000[28] Chipera, S.J. and Bish, D.L., 1997; Thermodynamic modeling of natural zeolite stability,
Proceedings of the 11th international clay conference, Otawa, Canada.

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Development of MACBECE: Mechanical Analysis system considering
Chemical transition of BEntonite-based and CEment-based materials
Hiroyuki ITO, Morihiro MIHARA and Takao OHIJapan Nuclear Cycle Development Institute, Tokai, Ibaraki 319-1194, Japan
1. Introduction
TRU wastes in Japan are being considered for emplacement in large underground cavities
utilizing cementitious materials as fillers and structural materials, surrounded by a bentonite
buffer according to the current disposal concept [1]. The performance assessment for thisconcept pointed out that I-129 and Cl-36, contained in some of these wastes, are regarded as
the predominant nuclides in dose evaluation. Since these nuclides are soluble and poorly
sorbed, groundwater flow in the near-field has a significant effect on the transport of these
nuclides.
It is expected that the groundwater flow in the repository will be restricted by a multiengineered barrier system (EBS). However, the porosity of cement-based material increases
due to leaching of hydrates. Subsequently, bentonite properties tend to change as a result of
the influence of high pH leachate from the cementitious material. In addition, changes in themechanical properties affect the deformation behavior of the repository. Groundwater flow isrelated to volumetric change, which subsequently has an effect on chemical evolution (see Fig.
1). Therefore, a deterioration of material properties and the resultant effects on EBS
deformation need to be understood to evaluate hydraulic conditions. An analytical system has
been developed to calculate near-field groundwater flow with chronological variation inalteration and deformation over a long period.
The principal aim of this work is the development of a mechanical analysis system, which
can calculate the deformation of cement-based and bentonite-based material in the repository
environment. In this study, flow-through tests of cement paste were conducted in order toinvestigate the changes in mechanical/hydraulic properties reflected by chemical alterations.
Various laboratory tests of bentonite were performed to examine the effect of cation exchangeon these properties. The test results were also applied to the modeling of mechanical behavior.
Finally, a mechanical analysis system, Mechanical Analysis system considering Chemicaltransition of BEntonite-based and CEment-based materials (MACBECE), was developed
together with these relationship and modeling. The long-term deformation and the change ofpermeability distribution in the near-field were preliminary evaluated based on the assumed
chemical evolution.
2. Mechanical properties of hydrated cement during deterioration(1) Laboratory tests with cement paste
Coupled processes during degradation of the chemical, mechanical and hydraulic (C-M-H)
properties of concrete have been studied [e.g. 2,3]. A flow-through test is used to directly
measure a series of C-M-H data for samples with higher porosities. Using a batch test makes
it easier to handle samples with a wide range of porosities and to estimate their mechanicalproperties from hardness measured in a small, degraded area.
In this study, flow-through tests and batch tests were systematically conducted to obtain CM-H processes for the wide range of porosities possible in the repository environment.
Hardened paste specimens of Ordinary Portland Cement (OPC) were mixed in the same batchand subjected to the tests. The porosity and elements distribution in both solid and aqueous

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NUMO-TR-04-05

phases were measured simultaneously. A comparison of the tests and their relativeadvantages/disadvantages is shown in Table 1.
(2) Test results and modelingHydraulic conductivity, K, and compressive strength, σc, of the specimens, which had been
degraded by distilled water (DW) and a 1M-NaNO3 solution percolation, are shown withporosities, p, in Fig. 2 and Fig. 3, respectively. It is clear that both properties are strongly
dependent on the porosities. Relationships between porosity and each property were
empirically fitted by suggested equations. The fitted lines indicate good agreement to thevalues of unaltered specimens through a wide range of porosities. These results suggest thatmechanical and hydraulic properties of cement paste could be evaluated by the degree ofdegradation.
To analyze deformation of cementitious material, a stress-strain relationship is required. A
bi-linear relationship composed of a compressive strength and an elastic modulus was taken
into account. Furthermore, in the long-term, the cement-based material in the repository will
shrink due to both the deterioration of mechanical properties as well as the swelling pressureof the bentonite buffer thereby resulting in strain-softening material behavior (see Fig. 4). An
analytical iterative procedure [4] was applied to the representation of the stress-strain curve
indicating both peak strength and residual strength.
3. Mechanical properties of Ca-bentonite(1) Laboratory tests with consideration of calciumization
Various laboratory tests were conducted to investigate the effect of both (a) cationexchange of Na-bentonite for calcium ions (termed “calciumization” in this paper) and (b) theswelling behavior of bentonite on its mechanical and hydraulic properties. The test results
were applied to the extension of an elasto-plastic constitutive model of bentonite. A
constitutive model is required to determine the volumetric change. Several constitutive
models, such as proposed by Sekiguchi and Ohta [5], have been developed to evaluate themechanical behavior of natural sedimentary clay. However, the models cannot sufficiently
illustrate the volumetric change of bentonite due to swelling.
Several laboratory tests, which were divided into consolidation and shear behaviors, wereconducted with the intent of investigating the effect of modifying parameters that
corresponded to the Sekiguchi-Ohta model for clayey materials. A matrix of the tests issummarized in Table 2.
Bentonite specimens with calciumization ratios (CR) of 0% (equivalent to natural Nabentonite, KUNIGEL V1®), 50% and 100% were prepared for the tests. In the cases of
CR=50 and 100%, half and all, respectively, of the intercalated cations of the KUNIGEL V1®
were artificially exchanged by calcium ions using a calcium chloride solution. The dried,
powdered bentonite was compacted with various initial void ratios. The void ratios employedin the tests corresponded to a swelling of 0-40%, where the 0% swelling corresponded to abentonite dry density of 1.6 Mg/m3. After compaction and prior to the laboratory tests, thebentonite specimens were saturated without volumetric change.
(2) Experimental results and modeling- Consolidation behavior
The typical relationships between void ratio, e, and the logarithm of consolidation stress, p’,(e-logp’) measured in the consolidation tests are shown in Fig. 6 and Fig. 7. The normal
consolidation (NC) line of the bentonite is independent of the calciumization ratio. The
gradient of the NC line (compression index, Cc) is approximately 0.3-0.4. The non-linearity ofthe swelling behavior of the bentonite becomes more pronounced with decreasing CR. The

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gradient (swelling index, Cs) becomes larger with increasing over-consolidation ratio (OCR),
where OCR = po ' p ' , po ' is the mean effective stress at the pre-consolidation state and p ' isthe mean effective stress at the current state.
Maximum swelling deformation and equilibrium swelling pressure were measured inswelling deformation/pressure test. The results plotted in the e-logp’ plane are close to the elogp’ relationships obtained from the consolidation tests. They could be estimated from the elogp’ relationship, when the initial void ratio and pressure are measured.
The swelling behavior of bentonite, which is different from that of natural sedimentary clay,
was modeled [6]. It was initially assumed that the variation in void ratio due to swelling could
be separated into mechanical effects due to unloading, e&m , and ionic effects due to seepage, e&s ,where the symbol ‘・ ’ indicates the material time derivative. The es -lnp’ relation normalized
by po ' , in other words the es -ln(OCR) relationship, could be empirically represented with an
exponential equation of a material constant, ξ (see Fig. 5). The equation has the advantagethat only a single additional parameter is involved and the derivation of the model issimplified. The model of the swelling behavior can therefore be written as~ 3 1 − 2ν ' ~ ,
κ
~
(1)
K
K=
K, G=
2 1 +ν 'ξ (OCR ) exp{ξ (OCR − 1)} + κ%
where K is bulk modulus considering the volumetric change of bentonite due to seepage, K is

the bulk modulus, κ (= 0.434C s ) is the swelling index defined in the e-lnp’ relationship, G~ isthe shear modulus and ν ' is the effective Poisson’s ratio. By substituting Eq. (1) into
generalized Hooke’s law, the non-linear elastic component, expanded to express the swelling
behavior of bentonite, was obtained. The expanded model describes the non-linear swelling
behavior of bentonite by varying the material parameter ξ .
- Shear behavior
The effective stress paths and the relationship between deviatoric stress and axial strain
were obtained from the tri-axial CU tests as shown in Fig. 8 and Fig. 9. The critical stateparameter, M , which determines the shape of the yield surface, is important for investigating
the elasto-plastic behavior of bentonite. Its value is independent of calciumization and theconfining pressure related to initial void ratio. In addition, the values agree to previous studies[7,8]. It could be treated as a material property (approximately 0.4-0.5).
Fig. 9 shows that the bentonite with CR=100 indicates a peak strength similar to an overconsolidated clay even when confining pressure was 5MPa. On the other hand, the stressstrain profile with CR=0 is analogous to a normally consolidated clay at the same confiningpressure of 5MPa. However, the stress path of each bentonite is comparable in shape. There isa possibility that the effect of calciumization can be described as being similar to increasing
the pre-consolidation pressure. At the beginning of shearing, in the cases of CR=0 and 50%,
the bentonite behaves as an elastic material even when the confining pressure is 5MPa (below
the O-A lines in Fig. 8). The elastic behavior can be interpreted theoretically if the O-A line isequivalent to the K0-line.
- Permeability
For modeling the effects of volumetric change on the permeability, the relationship between
permeability and void ratio are shown in Fig. 10. The permeability obtained fromconsolidation tests and previous studies [7,9] is also plotted in the figure. The permeability
becomes larger in accordance with increasing CR.
4.

System development to evaluate long-term deformation in the repository
The finite element analytical code MACBECE is being developed to evaluate long-term
deformation in the repository. The system includes the effects of chemical alteration. An

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analytical flow chart of the system is shown in Fig. 11. The initial conditions of the chemistry
and the corresponding mechanical properties are set. An incremental deformation of the EBS
is then calculated using the non-linear elastic model for the strain-softening of thecementitious material and the extended constitutive model for the bentonite. Permeability ismodeled based on volumetric strain and calciumization. The current chemical module cansimulate only calciumization of the bentonite-based materials and calcium leaching of thecement-based materials, which are assumed to occur in the repository. After a revision of thechemical profiles, the calculation cycle loops and the above-mentioned C-M-H procedures are
re-calculated.
Using MACBECE, a preliminary analysis of the long-term deformation and the change inpermeability distribution in the TRU repository was performed based on the assumed change
in chemical profiles. The analytical results obtained from the present prototype system
indicate that both the deformation of the EBS as well as the influence of the deformation on
permeability are limited.
In the future, the chemical module will be replaced by an analytical code. The mechanicalproperties of the concrete and the buffer will also be refined based on current studies of theinfluence of the aggregates used in the concrete and of the sand used in the buffer material.
The completed system will calculate deformation and its effect on permeability under various
cases of chemical alteration, which will enhance the robustness in determining the hydrauliccondition in nuclide transport analysis.
References[1] JNC and FEPC (2000). “Progress Report on Disposal Concept for TRU Waste in Japan”, JNC TY1400
2000-002, TRU TR-2000-02.
[2] Haga, K. et al. (2002). “Alteration of Cement Hydrate by Dissolution, (I) Alteration Test of Hydrate Cement
Paste by Water-permeation Using Centrifugal Force”, J. AESJ, Vol.1, No.1, pp.20-29. (in Japanese)[3] Yokozeki, K. et al. (2003). “Prediction of Changes in Physical Properties due to Leaching of Hydration
Products from Concrete”, J. Advanced Concrete Technology, Vol.1, No.2, pp.161-171.
[4] Motojima, M. et al. (1981). “The Stability of Rock Foundation with Considering Strain-Softening Material”,
CRIEPI 380036. (in Japanese)[5] Sekiguchi, H. and Ohta, H. (1977). “Induced anisotropy and time dependency in clays”, Proc. Specialty
Session 9, 9th ICSMFE, Tokyo, pp.229-239.
[6] Sasakura, T. et al. (2004). “Studies on the mechanical behavior of bentonite for development of an elastoplastic constitutive model”, Proc. DisTec2004, Berlin, pp.498-507.
[7] JNC (2000). “H12: Project to Establish the Scientific and Technical Basis for HLW Disposal in Japan –Supporting report 2”, JNC TN1400 2000-003.
[8] Maeda, M. et al. (1997). “Triaxial CU（consolidated-undrained） compression tests on Ca exchanged
bentonite”, PNC TN8410 97-314. (in Japanese)[9] Maeda, M. et al. (1998). “Mechanical properties of the Ca exchanged and Ca bentonite”, PNC TN8410 98021. (in Japanese)

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Table 1 Comparison between flow-through and batch tests
W/C of samples
Dissolution behavior
Items measured
Permeability during degradation
Compressive strength and elastic
modulus after degradation
Experimental condition in thisstudy

Flow-through test
Preferable with high W/C (-)
Accelerated
Easier to prepare larger degraded sample(+)

Batch test
Applicable to wide range of W/C (+)
Similar to repository environment (+)
A large gradient of degrading degree
within a sample (-)

Directly measurable (+)
Directly measurable (+)

Estimated from porosity (-)
Estimated from Vickers hardness
measurable in a small area (-)- Size : φ30mm - h10mm- W/C : 40%, 55%, 70%, 85%, 105%
- Preserved in regularly renewed DW*- Surrounded by Ar gas, 20˚C

- Size : φ40mm - h40mm- W/C: 85%, 105%- Percolated by DW* or 1M-NaNO3- Surrounded by Ar gas, 20˚C
DW*: deionized and de-gassed water(+): advantages (-): disadvantages

Table 2 Laboratory test matrix for modelingCharacteristics

Tests

Consolidation test
Consolidation
Soil skeleton
Swelling pressure/
deformation test

Tri-axial CU test

Migration

Permeability test

Modeling
Elasto-plastic behavior
Effects of calciumization on e - lnp’ relations
Elastic behavior
Non-linearity of swelling behavior
Elasto-plastic behavior
Equilibrium swelling pressure andmaximum swelling deformation in e
- ln p’ relations
Elasto-plastic behavior
Effects of calciumization on
critical state parameter
Effects of calciumization on e - krelations

Bentonite-based material

Leaching ion

Pore water

Shearing

Parameters
mean effective stress p’
void ratio ecompression index Cc
mean effective stress p’
void ratio eswelling index Cs
mean effective stress p’
void ratio ecompression index Cc
swelling index Cs
critical state parameter M
mean effective stress p’deviatoric stress q
permeability coefficient k
void ratio e

Chemical evolution

Mechanical properties- cation exchange- mineralogical change- consolidation and swelling- shearGoverning equations

Void ratio - Permeability
Groundwater
flow(Constitutive model)
Nuclidetransport

Deformation

Cement-based material

Porosity - Permeability

Governing equations

Chemical evolution

Mechanical properties(Stress-Strain relation)- elastic modulus- strength- dissolution of cement hydrate

Fig. 1 Interactions of Chemical, Mechanical and Hydraulic processes in cement andbentonite system

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NUMO-TR-04-05

1.E-06

Comp. strength, σc (MPa)Permeability, K (m/s)

60

K = 4.34×10-9p3(1-p)-2

1.E-07
1.E-08
1.E-09
1.E-10DW percolation
Kozeny-Carman Eq.
NaNO3 percolation
No percolation*
No percolation**
No percolation***

1.E-11
1.E-12
1.E-13
1.E-14
0

0.2

0.4

0.6

0.8

DW percolation
Knudsen's Eq.
NaNO3 percolation
No percolation (OPC40,55,70)

50
40
30
20
10

σc = 234.75exp(-7.22p)

0

1

0

Porosity, p (-)
*

0.2

0.4

0.6

0.8

1

Porosity, p (-)

back-calculated on F=1.0 from Powers, T.C. (1958)** back-calculated on F=0.8 from Powers, T.C. (1958)*** Day and Konecny (1989)

Fig. 3 Relationship between strength and porosity

Fig. 2 Relationship between permeability and porosity
e& = e&s + e&meFresh concrete

B

Stress, σ

(b)
(a)

(c)

Degraded concreteEemNormalized by p0’

A
κ

O
p0

σc : compressive strength
E : elastic modulus

1.0

swelling ratio=0%

2.0
CR=0% (Na)CR=50%
CR=100%NC-line0.1
1
10
consolodation stress log p' (MPa)

CR=0% (Na)CR=50%
CR=100%

1.5

pc

0.5

0.0
0.01

A
ln(OC

Bentonite swells along O-B, while other popular clay swells along O-A.

void ratio evoid ratio

1.5

0

Fig. 5 NC line and swelling behavior in the e-lnp’ relation

Fig. 4 Conceptual model of concrete deformation

swelling ratio=40%pc

ln

es: swelling due to seepage
em: swelling due to mechanical unloading

compression due to self-weight and swelling pressurecompression due to deterioration of E
compression due to deterioration of σc and E

2.0

B

λ

es

Strain, ε

(a)
(b)
(c)

e s = exp{ξ (OCR − 1)} −

es

σc

1.0

p’0

Cc

0.5

100

0.0
0.01

Fig. 6 Normal consolidation line of bentonite
with various CR (swelling ratio = 0, 40%)

Cs max.

Cs at initial

0.1
1
10
consolidation stress log p' (MPa)100

Fig. 7 Swelling behavior of bentonite with various CR(swelling ratio=40%)

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A

M=0.49

1

3

0

2

1
2
3
4
5
effective mean stress p' (MPa)6

CR=50%

M

A

1
0
1
2
3
4
5
effective mean stress p' (MPa)6M

CR=100%2

M=0.50

1
0

0

1

2

3

4

CR=0% (Na)

2
1
0

0

5

3

M=0.440

3

deviatoric stressq (MPa)03
deviatoric stressq (MPa)M

CR=0% (Na)2deviatoric stressq (MPa)3

deviatoric stressq (MPa)deviatoric stressq (MPa)deviatoric stressq (MPa)NUMO-TR-04-05

5

6

10
15
axial strain εa (%)
CR=50%

2
1
0

0

5

3

CR=100%

2
1
0

0

5

mean
effective
stressp’ (MPa)
effectivemean
stressp' (MPa)

Permeabilityk (m/sec)
coefficientof permeabilityk (m/sec)

10
15
axial strain εa (%)

10
15
axial strain εa (%)

Fig. 8 Effective stress paths with CR

Fig. 9 Relationship between deviatoric stress and(swelling ratio = 0%)

axial strain (swelling ratio = 0%)

CR=0% (permeability test)
CR=50% (permeability test)
CR=100% (permeability test)
CR=0% (consolidation test)
CR=50% (consolidation test)
CR=100% (consolidation test)
CR=0% (existing research)[5],[7][7],[9
CR=100% (existing research)[5],[7][7],[9

1E-7
k=AeB

1E-9
k=AeB

k=Ae

1E-11

CR
0
50
100

1E-13

1E-15

B

0

1

2

3

4
5
6
void ratio eA
3.91E-13
6.31E-13
1.07E-11
7

8

9

B
2.788
4.211
5.170

Input data:
Boundary condition, geometry

Chemical profiles(CR of bent., Ca leaching of cement)

Initial properties in EBS

Chemical vsmechanicalCalc. stress after re-saturation(caused by self-weight andswelling pressure)
Changed properties andboundary condition

Mechanical properties corresponding
to chemical profiles and stress
Incremental deformation by non-linear
elastic model of strain-softening,extended constitutive model for swelling
Deformation, stress, strain
Pore/chemical
vs permeability

Chemical analysis

stepwise10

Permeability
outputFig. 10 Relationship between permeability and void ratio

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Fig. 11 Analytical flow of the system

NUMO-TR-04-05

Modelling diffusion of an alkaline plume in two types of clayey systems
Corresponding author: Eric Gaucher (BRGM France) e.gaucher@brgm.fr

1. Introduction
Concrete will be used extensively in the ANDRA design to construct the disposal
chambers in the host formation (Callovian-Oxfordian argillite COX), and also as waste
containment material. The large excavated chambers that will hold the containers ofradioactive waste are constructed with concrete and will be separated from therepository access galleries by bentonite plugs, several metres thick. The volume of
concrete is likely to be much higher than that of the bentonite plugs. After being sealed,
the repository will become saturated with interstitial waters from the CallovianOxfordian argillite, which will produce high pH solutions through interaction with theconcrete. The aggressiveness of these alkaline solutions, when in contact with thebentonite, may weaken the clay’s confinement properties (bentonite and argillite) withrespect to long-lived radionuclides by change of the mineralogy. The dominanttransport mechanism in these impermeable formations is assumed to be diffusion. The
aim of this study is to determine, firstly, the critical processes affecting the two clayey
media (bentonite and argillite) during the diffusion of an alkaline plume and secondly,
the extension of the perturbation in space and time. We test also our numerical
capacities to model such phenomena in a complex geochemical system.
The calculations were carried out in two steps: first, definition of the more complete
mineralogy as possible for the initial systems in equilibrium with the interstitial porewater of the Callovian-Oxfordian argillite, then diffusion of the alkaline plume from theconcrete through the clayey media. Calculations were carried out over a simulated
period of 100,000 years using PHREEQC.
The experimental work made in the European Ecoclay II project allows a selection ofreaction paths and of new phases for the thermodynamic database used in thecalculations.

2. Construction of the model
Clayey systems
The two clayey systems were defined by their mineralogy (% of phases). Taken into
account a porosity of 10% for the bentonite (MX80) and 4.6% for the COX, input data
were converted to molar scale. The molar concentrations of exchange sites were 6.47
eq/kgw for the MX80 and 4.38 eq/kgw for the COX. The partial pressure of CO2 was not
imposed in the simulations of reference, it was considered that a complex mineralogy
with carbonaceous minerals is able to fix this parameter.

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Database and Calculation
Aqueous species and mineral solubility products were taken from the LLNL Phreeqc
Database. We had added the thermodynamical properties of 15 “cement” phases. 50
phases were presented or susceptible of precipitation in the model. The exchange
constants (Gaines-Thomas convention) were from Fletcher and Sposito [Clay Minerals,1989] for the MX80 and were determined especially for the COX in our laboratory.
Considering the very long time of interaction between minerals and solution due to thelow diffusion coefficient, all calculations were made at the thermodynamical
equilibrium. No kinetics was taken into account.
Cement porewater
A cement porewater was calculated by Andra to simulate an evolved (OPC) cement
porewater (table 1).
Table 1

Chemical composition (mol/kgw) for the concrete pore water.
pHpe
Na (mol/kgw)
K (mol/kgw)
Ca (mol/kgw)
Si (mol/kgw)
S (mol/kgw)

12.50
-8.6
8.02 10-3
2.21 10-2
2.19 10-2
3.01 10-5
1.20 10-4

The mineralogical and chemical evolution of the concrete was not taken into
consideration in this study for several reasons. First, this evolution is not documented
over a long period of time and, second, the huge volume of concrete relative to thevolume of bentonite expected in the repository, allowed us to assume the concrete
medium was infinite. Nevertheless, it is clear that the chemistry of the concrete will
evolve with time. The selection of a solution of pH 12.5, can represent a “moderately
evolved” concrete pore water.
Transport and MeshIn simulating the alkaline plume, the transport of solutes into the clay barrier wasconsidered to be a pure diffusion process in a saturated medium with interconnectedporosity. The boundary conditions were those of a semi-infinite medium for the clay
barrier, and constant, fixed fluid concentrations, in the concrete. The mesh of thebarrier was not linear with 10 small cells of 2.5cm near the interface with the concrete,followed by 10 cells of 5cm and 75 cells of 10cm. The high number of small cells near
the concrete allows a fine description of the interface. The simulation covered a periodof 100,000 years in 10,000-year steps. Based on the diffusion coefficient obtained by
the CEA in this project, 3 orders of magnitude were tested: 10-9 m2/s, 10-10 m2/s, 1011
m2/s.

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NUMO-TR-04-05

13

10 000 years

12

100 000 years

pH

11
10
9
8
7
0

1

2

3

4

5

6

7

8

Distance from concrete (m)Figure 1 MX80 Change in the pH of the barrier pore water. Diffusion coefficient
10-11 m²/s.

10000

MX80
after 100 000 years
Reaction path :1- Montmorillonite -> Clinoptilolite-K
Calcite dissolution
Cristobalite dissolution
2- Montmorillonite -> Illite
3- Illite -> Zeolites
4- Zeolites -> Cement phases
Calcite precipitation
4'- Illite -> Saponite -> Clinochlore

9000

Volume (cm3)

8000
7000
6000
5000
4000

Montmor-Na
Saponite-Na
Nontronite-Na
IlliteCalciteGypsumEttringite
Gismondine
KatoiteAfwillite

3000

Montmor-Ca
Saponite-Ca
Nontronite-Ca
Clinochlore
Cristobalite
PyriteClinoptilolite-K
Gyrolite
Hydrotalcite
Tobermorite

1

2000
1000

4

0

4'

0.00

0.10

2

3
0.20

0.30

0.40

0.50

0.60

0.70

Distance from concrete (m)Figure 2 MX80, Mineralogical composition of the barrier after 100,000 years,
diffusion coefficient 10-11 m²/s.

3. Results
MX80. One of the most expectable chemical changes in the barrier would be theincrease of the pore water pH (Figure 1). However, at 100,000 years, a very strong
buffering of the pH is observed and the pH front does not evolve much from 10,000 to
100,000 years. The pCO2 is not externally imposed in all our calculations. Carbon
dioxide is thus produced by the mineral assemblage itself. This indicates that themineralogical assemblage is rich enough to fix internally the pCO2, which act as animportant acid buffer. Another major buffer effect is the consequence of the dissolutionof the minerals, which consumes the hydroxide ions.

Important change involved the dissolution/precipitation of mineral phases (Figure 2)
after a diffusion period of time of 100,000 years:
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NUMO-TR-04-05

Between 0.40 and 0.70 m from the interface, the dissolved potassium concentration
increases because the concrete porewater is more potassic than the host water and theprecipitation of K-clinoptilolite is favoured at the expense of Na-montmorillonite andcristobalite. Partial dissolution of montmorillonite provides magnesium that isincorporated in Na-saponite. Within this zone, Na-montmorillonite is progressively
replaced by Ca montmorillonite since concrete porewater is slightly richer in calcium.
Between 0.10 and 0.40 m, both Ca and Na-montmorillonite are illitized. Zeolites
become the predominant phases and replace illite, which is entirely dissolved at 0.10 mfrom the concrete. Mg released by illite dissolution is included in Na and Ca-saponite.
Between 0.00 and 0.10 m, cement phases (Afwillite, Tobermorite, Katoite andHydrotalcite) precipitate in replacement of zeolite phases. The increase in pH favours
the precipitation of calcite. The strong increase of the total molar volume (9000cm3)
near the interface can be considered as a closure of the porosity. This phenomenon willdiminish the extent of the perturbation.
COX. As the COX is a more complex rock than the MX80, the buffer effect on the pH
is stronger and no instability in pH is observed near the interface. Some differences areobserved in the mineralogical evolution of the barrier, however the major reaction paths
are conserved.
An empirical relation has been calculated given the extension of mineralogicaltransformation in function of both diffusion coefficient (D, m²/s) and time (t, year). The
best-fitting expression for the empirical relation has the following form:
P = A ⋅ t ⋅ D with A = 498 for COX and 555 for MX80.

4. Conclusion
The simulation of the effects of an alkaline perturbation on some complex mineralogicalsystems including surface reactions is possible with the actual numerical means.
The simulation of the diffusion of an alkaline plume from concrete through two types ofclayey barriers shows:•a strong pH buffering effect close to the clayey/concrete interface (< 2m for D=109 2
m /s and 100,000 years)•

an important mineralogical transformation of the barrier close to the concreteinterface
These modelling meet several limits: (i) the use of one single diffusion coefficient, (ii)the diffusion coefficient do not change when the total molar volume of the mineralschanges. Our modelling do not take into account (iii) the effect of inhomogeneous
diffusion in the matrix as observed at Mol URL and (iv) a pre-oxidised zone resulting
from the introduction of O2 in the galleries of the disposal. However, compare tonatural analogues, the results seems realistic. They can been exploited for safety
analyses
and
for
the
scenariosofevolutionofthedisposal.

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Potential complications in the development of a thermodynamic databasefor hyperalkaline, argillaceous systems
Randy Arthur1, Hiroshi Sasamoto2 and Mikazu Yui2
1
Monitor Scientific, LLC, Denver, Colorado, USA
2
Japan Nuclear Cycle Development Institute, Tokai mura, Japan
Background

Geological disposal concepts for radioactive wastes generally call for a bentonite buffer
and/or bentonite-containing backfill to be emplaced between the host rock and othercomponents of the engineered-barrier system (EBS; including the waste form, metallic
containers and cementitious materials used for encapsulation, structural support andbackfilling purposes). When fully water-saturated at high compaction densities, bentonite is
an ideal barrier material due to its favorable physical and rheological properties under suchconditions. These properties include:•

an extremely low hydraulic conductivity, which ensures that a diffusional transportbarrier will exist between the host rock and EBS;•a permeability to gas flow that is high enough to allow any gases generated bycorrosion of metallic components of the EBS to pass through the barrier without
forming permanent permeable channels or cavities;•

a swelling pressure that is sufficiently high to establish and sustain good contact withthe host rock and EBS, but not so high as to deform individual components of the
EBS, or fracture the rock;•a deformability that is high enough to absorb rock movements, but not so high as tocause the position of EBS components to shift in their deposition holes or drifts;•

a filtration capacity that effectively stops the migration of colloidal-sized particles;
and•a thermal conductivity that is sufficiently high to ensure rapid dissipation ofradiogenic heat.

These properties arise from the unique mineralogical characteristics of bentonite. Bentonites
contain dioctahedral smectite clays (montmorillonites, and possibly also nontronites and/or
beidellites) along with lesser amounts of quartz, feldspars, zeolites, carbonates and sulfides.
The clay minerals have a characteristic 2:1 lattice structure consisting of one octahedrally
coordinated layer between two tetrahedrally coordinated sheets. Isomorphous substitutions in
the octahedral and tetrahedral layers result in a low interlayer charge, which allows the
crystalline lattice to expand rapidly and reversibly as hydrated cations are exchanged for lesshydrated cations in interlayer positions. The expandable nature of the smectite clays controls
the swelling pressure of bentonite as a function of water content, water chemistry andcompaction density. The swelling pressure in turn directly affects the hydraulic conductivity,
gas permeability, deformability and filtration properties of this barrier material.

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Given the importance of mineralogy in controlling the physical and rheological properties ofbentonite, the question arises whether plausible conditions in a repository environment could
adversely affect the long-term stability of bentonite minerals. The potential for such alteration
by hyperalkaline fluids, which are likely to be produced by the interaction of cementitious
materials in the repository with groundwater (e.g., Berner, 1992), is a matter of some concern
because the expandable clay minerals may not be stable in the presence of high-pH solutions(e.g., Savage et al., 2002). Resultant reactions could lead to irreversible changes inmineralogy, and thus to undesirable changes in the physical, chemical and rheologicalproperties of bentonite barriers.
Literature review

Experimental, natural-system and modeling studies dealing with the alteration of clay-bearing
materials by high-pH solutions were reviewed in the present study. The objective of this work
is to identify minerals, aqueous species and reactions that should be included in athermodynamic database that can be used with appropriate geochemical models to asses thelong-term stability of bentonite barriers in geologic repositories for nuclear wastes. Ourreview covers the period from 1999 to the present. The older literature is summarized by
Savage et al. (2002).
Batch experiments at relatively high temperatures (≈ 50° – 200°C), along with a limited
number of open-system experiments, modeling studies and field studies of natural high-pH
systems, all demonstrate that clay-bearing materials can be strongly altered by contact withhyperalkaline fluids containing high concentrations of Na or K. Details concerning the extent
of alteration and associated changes in mineralogy are not completely consistent among thesestudies. In general, however, alteration appears to involve the following sequence ofreactions:•partial rearrangement of the stacking sequence of smectite layers, and possible
amorphization of clay particles;•

dissolution of discrete smectite, or selective dissolution of smectite in mixed-layer
clays, with possible neoformation of different smectite types (e.g., beidellites,
saponites) by direct precipitation from aqueous solution or by isomorphous
substitution on octahedral or tetrahedral sites;•

formation of illite from smectite via a layer-by-layer replacement process or by adissolution-recrystallization process;•precipitation of zeolites (often including Na-, K-phillipsites and analcime); and•precipitation of K-feldspar and quartz.

Carbonates, CSH and/or CASH solids/gels, and Ca-Mg hydroxides may also precipitate, andmay later dissolve, at all stages of the above reaction sequence.
These results suggest that a thermodynamic database supporting models of bentonite-cement
interactions should include properties (e.g., equilibrium constants or derived standard molal
A3-92

NUMO-TR-04-05

thermodynamic quantities) for both the dioctahedral and trioctahedral smectite clays. Similar
properties should also be included for minerals that directly or indirectly affect the stabilitiesof these clay minerals (i.e., illites, zeolites, CSH/CASH phases, carbonates, Ca- and Mghydroxides, K-feldspar and quartz). There has been little experimental investigation of theaqueous-speciation behavior of key mineral-forming elements (e.g., Si and Al) under
hyperalkaline conditions.
Conceptual uncertainties related to the thermodynamic properties of bentonite minerals

The studies considered in our literature review reveal several sources of conceptual
uncertainty that could complicate efforts to develop a reliable thermodynamic database forclay-bearing, hyperalkaline systems:•

the mineralogy, structural formulae and crystallinity of secondary solids produced by
the interaction of clay-based materials with high-pH fluids have not generally been
well characterized;•

the basic thermodynamic properties of representative clay minerals, zeolites andCSH/CASH solids/gels are poorly known in many cases;•

early mineral assemblages tend to be metastable, and may slowly transform to a seriesof progressively more stable assemblages over time scales as long as thousands tomillions of years;•

precipitates may be amorphous or poorly crystalline, and may persist metastably withrespect to their crystalline counterparts over long periods of time; and•crystalline solids are often complex solid solutions that exhibit a considerable
compositional range depending on the chemistry of the coexisting aqueous phase(especially pH, SiO2(aq) activity and cation content).

Minerals that should be represented in a thermodynamic database for such systems thus tend
to be complex, possibly metastable solids having highly variable compositions that have not,in general, been well characterized experimentally or thermodynamically. Given the highcosts and technical difficulties in conducting experimental investigations of the basic
thermodynamic properties of minerals and aqueous species, it seems unlikely that suchstudies would be able to provide all the needed data in a timely manner.
A pragmatic approach that could be used to help deal with these problems involves the use of
a consistent set of empirical methods to estimate missing thermodynamic parameters,
combined with uncertainty analyses to asses the importance of the resultant, possibly large
uncertainties on models of the alteration of clay barriers by high-pH fluids (e.g., Savage et al.,
2002; Gaucher et al. 2001). An estimation technique that is particularly useful for silicate
minerals, for example, uses a set of elemental building blocks composed of unique polyhedra
to represent a mineral’s crystalline structure, composition and coordination environment(Hazen, 1988). By summing the contributions from each polyhedron, thermodynamic
properties can be estimated for the complete mineral. This representation is useful because it
permits routine calculation of the thermodynamic properties of minerals for which
experimentally determined properties are unavailable, and calculation of ranges in property
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values that are consistent with minerals having variable compositions. The reliability of theestimated data can be checked by comparison of predicted and observed stability relations inlaboratory and natural systems, and by comparison of estimated values with their available
experimental counterparts.
Conclusions

Minerals that should be represented in a thermodynamic database supporting models ofbentonite-cement interactions include the smectite clays, as well as other minerals that
directly or indirectly affect the stabilities of these clay minerals (i.e., illites, zeolites,
CSH/CASH phases, carbonates, Ca- and Mg-hydroxides, K-feldspar and quartz).
Calorimetric, solubility and/or phase-equilibrium studies on the thermodynamic properties of
the clay minerals, zeolites and CSH/CASH phases are generally lacking. Interpretation ofsuch properties based on the limited experimental data that are available is further
complicated by solid-solution behavior and associated ranges in mineral chemistry, by acommon tendency to form metastable mineral assemblages that may persist over long periodsof time, and by variations in crystallinity. An approach that could be used to help deal withthese problems would utilize existing empirical techniques to estimate missing
thermodynamic properties (i.e., Gibbs free energies and enthalpies of formation, and standard
entropies, heat capacities and volumes) and uncertainty analyses to evaluate the importanceof associated uncertainties on models of bentonite-cement interactions. Additional
experimental work may be needed to refine the estimates for key minerals identified in theuncertainty analyses, and to better characterize the aqueous-speciation behavior of mineralforming elements in concentrated high-pH solutions.
References

Berner, U. R. 1992. Evolution of pore water chemistry during degradation of cement in aradioactive waste repository environment. Waste Management, 12, 201-219.
Gaucher, E., Blanc, P., Michau, N. and Jacquot, E. 2002. Progress in the chemical modellingof the interactions between cement porewater and clay barrier. International Meeting on
Clays in Natural and Engineered Barriers for Radioactive Waste Confinement, Dec. 9-12,
2003, Reims, France, p. 409-410.
Hazen, R. M. 1988. A useful fiction: Polyhedral modeling of mineral properties. Am. J. Sci.,
288-A, 242-269.
Savage, D., Noy, D. and Mihara, M. 2002. Modeling the interaction of bentonite withhyperalkaline
fluids.
AppliedGeochem.,
17
(3),
207
–
223.

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Nano/macro-based cation/water transport and adsorption in bentonite
Y. Ichikawa1*, S. Prayongphan1, S. Suzuki2, K. Kawamura3
1

Dept of Environmental Engineering and Architecture, Nagoya University, Nagoya 464-8601, Japan
2
Institute of Research and Innovation, Kashiwa 277-0861, Japan
3
Dept of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japane-mail: YIchikawa@nucc.cc.nagoya-u.ac.jp

Abstract Microsacle sorption characteristics of bentonite are treated together with the
diffusion mechanism under a coupled molecular dynamics (MD) simulation andhomogenization anlysis (HA). The diffusion coefficient is evaluated by MD. The sorption
caused at the edge part of clay minerals is modeled as a source term in the microscaleequation of HA (micro-sorption). A through-diffusion experiment is simulated numerically.
The calculated concentration and macroscale break-through curve are agreeable.
Key words: bentonite, clay hydrate, micro-sorption, diffusion, homogenization
INTRODUCTION

Bentonite is a candidate buffur material for high-level radioactive waste (HLW) disposal [1].
Bentonite mainly consists of micrometer scale quartz particles and nanometer scale smectite
clay minerals such as montmorillonite and beidellite. Chemical properties od the bentonite arecharacterized by the clay minerals. One clay mineral is a platelet (Fig. 1), which is called alayer, with the thickness ca.1 nm and the width ca.100×100 nm. The mineral surface isnegatively charged. Several layers cohere to form a stack, and a group of stacks constitutes anaggregate or a ped. Microscope images of Kunigel V1 of Kunimene Co. are shown in Fig. 2.

Fig. 1 Atomic structure of montmollironite

Fig. 2 High-resolution images of a bentonite
sample by confocal laser scanning microscopy

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The sorption behavior is commonly treated by evaluating the distribution factor Kd [1]. The
Kd value is determined by the batch method or by a combination of the non-steady statemethod (i.e., the in-diffusion method giving an apparent diffusivity Da) and the steady statemethod (i.e., the through-diffusion method giving an effective diffusivity De). Both are related
as
Da =

De
n + (1 − n) ρ s K dwhere n is the porosity, and ρs is the true density of solid-part of clay minerals (ca. 2.7
Mg/m3). A lot of discussions have been given on these experimental methods, since the
distribution factor Kd for each chemical species determined by these experiments is severely
scattered. In addition let us observe the following conventional diffusion equation including
retardation coefficient Rd
Rd∂c ∂ ∂c −
 De
 = 0,∂t ∂xi  ∂xi 

Rd = 1 +(1 − n) ρ s K dρw.

Here ρw is the water density, and Rd represents the sorption characteristics. We understandthat only the ratio of Rd to De can be determined in this equation. This may be physicallyunacceptable. The conventional theory must involve difficulties to simulate the true diffusion
procedure including sorption.
We here show that the diffusion/sorption behavior in compacted bentonite can be treated byconsidering adsorption at edges of clay mineral and diffusion in the interlayer spaces of clay
minerals. The sorption behavior is given as a microscale source term, and we call this amicro-sorption mechanism. For this purpose we develop a new homogenization analysis (HA)
method to explain the micro-/macro-diffusion behavior including micro-source term due toedge-sorption. The diffusion characteristics are specified by the molecular dynamics (MD)simulation.
MD SIMULATION

Crystalline structures of layered silicates, [alkaline metal]-Mg-Al-Si-H-O, such as
Muscovite
KAl2(OH)2[Si3AlO10]
Phlogopite
KMg2 (OH) 2 [Si3AlO10]
Paragonite
NaAl2 (OH) 2 [Si3AlO10]
Pyrophyllite Al2 (OH) 2 [Si4O10]
Kaolinite
Al2(OH)4[Si2O5]
Talc
Mg3(OH)2[Si4O10]
are well-known. The 2-body and 3-body interatomic potential functions for MD are
determined so that material properties of the above silicates (e.g., the lattice constants) andwater (e.g., density and dielectric constant depending on temperature) are represented well.
Details are found in [2].
The material property which we need in the subsequent HA is diffusivity in the interlayer
space of clay minerals for each chemical spcies. In our analysis we treat cesium ion Cs+, andby a MD simulation we have the diffusion coefficient 2.0x10-9 m2/s in external pore water and2.62 x10-10 m2/s in inter-layer space.
HA WITH MOCRO-SORPTION

The governing equation of mass transport is given byε∂cε∂  ε ∂cε 
ε ∂c
ε
+ vj
−
 Dij + f = 0 in Ω f .
∂t∂x j ∂xi ∂x j 

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NUMO-TR-04-05

where cε is the mass concentration (the upper script ε implies a locally rapid-changing value),vε the velocity vector, Dεij the diffusion coefficient, f ε the source term and Ωf the flow region.
We consider the adsorption at the edges of clay minerals, so f ε  consists of the true source
term γ& such as chemical reaction and the adsorption term γ& ad at the microscal edge domainΩad (Fig. 3):

Fig. 3 Micro-sorption domain at the clay edgel s (c − c)γ& = 
0,if c < c ladif c = c l.

(2)Here s is the adsorption coefficient determined by the data of the site number, pH etc. [3], andcl is the limit value of concentration adsorbed at the edge domain Ωad. Note that the domainΩad is determined by the ion radius and the number of adsobed layers [3].
1. Two-scale HA We introduce a two-scale system such as x0, the global coordinates in themacro- domain Ω1, and x1, the local coodinates in the micro-domain Ω2. Then the
differentiation of (1) changes to

∂
∂
1 ∂
= 0+
.
∂xi ∂xi ε ∂xi1

(3)

The perturbation is introduced for the concentration cε(x;t) bycε ( x; t ) = c 0 ( x 0 , x1 ; t ) + ε c1 ( x 0 , x1 ; t ) + L(4)

where cα,s (α=0,1,2,…) are periodic functions. The micro-sorption term (2) is set into thesource term asf ε = ε −1 Γi ( x1 )

∂c 0
;
∂xi0

γ& ad ( x1 ; t ) = Γi ( x1 )

∂c 0
∂xi0

(5)

The reason why we intoroduce this term will be clarified later. Substituting (3), (4) and (5)into (1) and taking ε-->0, we get the following partial differential equations corresponding toeach ε-term.

ε −2 -term:∂  ε ∂c 0 
Dij 1  = 0 ⇒ c 0 ( x 0 , x1 ; t ) = c 0 ( x 0 ; t )
1 

∂xi 
∂x j 

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(6)

NUMO-TR-04-05

ε −1 -term: −∂  ε  ∂c 0 ∂c1  
∂c 0
D
+
+
Γ
=0



ij 
k
∂xi1   ∂x 0j ∂x1j  
∂xk0

(7)

Let us introduce the characteristic function N1k (x1) such thatc1 ( x 0 , x1 ; t ) = − N1k ( x1 )∂c 0 ( x 0 ; t )
∂xk0

(8)

Then (7) is reduced into the following microscale PDE:
∂N1k  ∂  ε
 Dij  δ jk − 1   − Γ k = 0∂xi1  ∂x j  (9)This can be solved unde a microscale periodic boundary condition. Now the reason why the
micro-sorption term (5) is introduced is obvious if we observe (7), (8) and (9).

ε 0 -term: ∂c 0 ∂c1  ∂   ∂c 0 ∂c1   ∂   ∂c1 ∂c 2  ∂c 0+ vεj  0 + 1  − 0  Dijε  0 + 1   − 1  Dijε  0 + 1   = 0
 ∂x ∂x  ∂x   ∂x ∂x   ∂x   ∂x ∂x  
∂t
j 
i 
j 
i 
j 
 j
 j
 j

(10)

We introduce the volume average for (10) in the micro-domain Ω1, then all the terms
concerning ∂ (⋅) / ∂xi1 are vanished due to the periodic condition. So we we have the following
macroscale PDE:
∂c 0
∂c 0 ∂  H ∂c 0 + v Hj
−
 Dij
=0
∂t
∂x 0j ∂xi0 ∂x 0j DijH =

∂N1k  1
1
ε
−
D
dx ,
δ

ik  kjk Ω1 ∫Ω1
∂
x
j



(11)

v Hj =

1vεj dx1Ω1 ∫Ω1

The first order approximation of the mass concentration can be given ascε ( x; t ) = c 0 ( x 0 ; t ) + ε c1 ( x 0 , x1 ; t ) = c 0 ( x 0 ; t ) − ε N1k ( x1 )

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∂c 0
∂xk0

(12)

NUMO-TR-04-05

2. Numerical example We simulate a through-diffusion experiment of a pure smectite clay
specimen with thickness 1 cm as shown in Fig. 4(a). In the micro-domain given in Fig. 4(b)we introduce 8 stacked clay minerals with thickness 1 nm and width 100x100 nm, which are
randomely distributed in the macro- domain. As shown in the MD analysis the diffusion
coefficient in the external pore water is calculated as 2.0x10-9 m2/s, and one in the inter-layer
space is as 2.62x10-10 m2/s. The upper stream boundary concentration cUp is given as 1.0x10-2,
1.0x10-3, and 1.0x10-4 mol/l. The microscale model involves adsorption edge parts whose
volume is determined as follows: the total edge surface is estimated as 35 m2/g by the BET
method [4] and its half is effective, so the total amount of Cs which can be adsorbed on edge
surface is mlim=6.51x10-5 mol/g. Here the ion radius r of Cs is assumed as 0.334 nm, and theshape of one clay mineral as 100x100x1 nm. The adsorption volume is set at each edge site in
the microscale model with the thickness 0.1 nm where the above amount of adsorption occurs.
That is, in the edge volume we have the condition c ≤ c l where the limit value cl is calculated
by using mlim. The calculated time- dependent change of concentrations at the points D and G
of Fig. 4(a) are given in Fig. 5 in which the cases without adsorption are shown forcomparison. Note that the unit of the vertical axis of Fig. 5 is a percentage to the upstream
concentration.

(a) Macro-domain model(b) Micro-domain modelFig. 4 Through-diffusion model

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NUMO-TR-04-05
100.00E

CONCENTRATION ( C )CONCENTRATION ( CE )100.00
80.00
60.00

Point

40.00

with sorption
without sorption

20.00
0.00
0.000

1.500

3.000

4.500

80.00
60.00

with sorption
without sorpton

20.00
0.00
0.000

6.000

Point

40.00

1.500

3.000

4.500

6.000

TIME

TIME

(a) Upstream concentration cUp=1.0x10-2 mol/l
100.00
CONCENTRATION ( CE )CONCENTRATION ( CE )100.00
80.00
60.00

Point

40.00

with sorption
without sorption

20.00
0.00
0.000

1.000

2.000

3.000

4.000

5.000

80.00
60.00

with sorption
without sorpton

20.00
0.00
0.000

6.000

Point

40.00

1.000

2.000

TIME

(b) Upstream concentration cUp=1.0x10-3 mol/l

80.00
60.00
40.00

Point
with sorption
without sorption

20.00
0.00
0.000

4.000

5.000

6.000

TIME

100.00
CONCENTRATION ( CE )CONCENTRATION ( CE )100.00

3.000

2.000

4.000

6.000

8.000

80.00
60.00

Point

40.00

with sorption
without sorpton

20.00
0.00
0.000

2.000

TIME

(c) Upstream concentration cUp=1.0x10-4 mol/l

4.000

6.000

TIME

Fig. 5 Break-through curves

Fig. 6 Distribution of mass-concentration in the micro-domain for the above case (b).
(Representing the 1/4 domain and the scale indicates the percentage
to the upstream bounbary concentration cUp=1.0x10-3 mol/l.)

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NUMO-TR-04-05

CONCLUSIONSIn existing theories the adsorption is usually treated as the the distribution factor Kd, which
gives the ratio of the mass of solid part to the mass of liquid part. Theoretically this does notcompletely give the correct chemical procedure of adsorption for the bentonite clay.We here
showed a new method to represent the microscale adsorption behavior.
Bentnite consists of nanometer scale of smectite clay minerals. The adsorption of smectite ismainly induced at the edge part of minerals, and the adsorption is treated as a microscale
source term at the edge domain under a homogenization analysis (HA) method. We call thisas the micro-sorption term. Note that the microscale diffusion property is specified by themolecylar dynamics (MD) simulation.
The calculated break-through curve (Fig. 5) is acceptable. In further development we will
extend this to a multiscale problem.
REFERENCES[1] Japan Nuclear Cycle Development Institute (JNC), H12: Project to Establish the
Scientific and Technical Basis for HLW Disposal in Japan; Supporting Report 3, JNC(1999).
[2] K. Kawamura, Y. Ichikawa, Physical properties of clay minerals and water -By means ofmolecular dynamics simulations-, Bull. Earthq. Res. Inst., Univ. Tokyo, 76 (2001), 311320.
[3] S. Kondo, T. Ishikawa, I. Abe, Science of Adsorption, 2nd ed., Maruzen (2001), in
Japanese.
[4] B. Baeyens, M. Bradbury, A mechanistic description of Ni and Zn sorption on Namontmorillonite Part I: Titration and sorption measurement, J. Contaminant Hydr., 27(1997), 199-222.

A3-101NUMO-TR-04-05

Status of Cement Modelling
Future investigations in the view of cement/bentonite interactions

Urs Berner, Paul Scherrer Institut
Contribution to an International Workshop on Bentonite – Cement Interaction in Repository
Environments, Tokyo, Japan, April 14-16, 2004

Interactions of cement with bentonite, or more generally, the interplay between high-pH
systems and clayish solids are topics that are discussed since the beginning of waste
solidification with cementitious materials. Although substantial progress was achieved inmany associated scientific areas, till this day a crucial overall break-through did not take placein the “pH-plume” topic.
This may be because a deeper understanding of this topic requires that many different
chemical and physical processes, which themselves may proceed in parallel with different
time constants, must be linked with one another. The substantial progress as mentioned above
was made in e.g., diffusion in compacted systems, in large-scale hydrological systems, in rockmechanics or in the chemistry and thermodynamics of solid phases. However, combining allthese new scientific realisations to a comprehensive picture in order to achieve the mentioned
break-through requires the definition of a waste disposal system as realistic as possible.
Unfortunately it is not sufficient to achieve progress in discrete and independent investigation
areas.
The presentation specifically considers the issue of cement modelling. From a chemical pointof view, cement represents some kind of a singularity when located in a quasi-naturalenvironment like a bentonite barrier. Large chemical gradients will establish between the
cement and its neighbourhood, thus generally inducing a material flow from the cement to thebentonite. Exceptions to this may include carbonate and magnesium, maybe also sulfate andchloride. In such environments the cement and its pore solution behave as source term. Hence,
investigations dealing with the mentioned interactions call for elementary knowledge on thethermodynamic characteristics of cement phases and wherever possible on their kinetic
behaviour.
Since about 20 years the geochemical behaviour of cement phases is described using more
and more realistic models having continuously increasing complexities [1-9]. Three distinct
stages may be differentiated when hydrated cement is degraded under ambient and natural
conditions:(i) the release of well soluble alkali hydroxides. This stage is short. It depends on the alkali
content of the cement and on corresponding transport parameters. The release of hydroxide isof crucial importance when reactions with the surrounding bentonite/clay are considered. The
hydroxide accelerates the dissolution of clays and accompanying Na+ and K+ promote theformation of secondary phases like illites or zeolites,(ii) the release of portlandite (CaOH)2 from the cement. This stage lasts for a long time.
Reactions with the clay materials produce secondary CSH-phases with smaller Ca/Si ratios in
the contact zone. Changes of the porosity need to be considered. However, the surrounding
clay buffers such reactions (as it buffers reactions under (i)). In the Swiss case where plans
foresee emplacement of cemented ILW wastes in Opalinus clay, about 1 m3 of host rock isrequired to chemically buffer 4 m3 of cemented waste matrix. This translates to only 0.5 m oftransformed Opalinus clay around an 8.5 m in diameter emplacement tunnel when 100 % of
the buffer capacity is utilized,

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NUMO-TR-04-05(iii) the release of silicates and aluminates. This phase lasts for a very long time. The chemical
gradients have almost disappeared, but the former cement and the former clay still differ instructure. Compared to stage (i), a completely altered pore space needs to be considered due
to phase transformations.
The results of a PSI long-term cement degradation experiment are used as a thread (Fig. 1),
guiding through the formerly mentioned stages. The state of ongoing (PSI) research
associated with the different stages is pointed out and summarised.

0.025
SO4 x 50

Ca x 1Al x 1000

0.020
Concentration [M]

SiO2 x 25
K & Na x 0.25

0.015
Ba x 1000

0.010
Sr x 100.005
Fe x 10'000

0.000
10 ml

100 ml1000 ml

10000 ml

Mg x 1000

100000 ml

Cumulative Volume [ml]Fig. 1: A cement disc (volume 13 ml) was leached with pure CO2-free water for morethan 3 years (about 3000 pore volumes). The strongly schematised analyses areconveniently normalised to the size of the diagram.

An initial stage is governed by the dissolution of portlandite in strongly alkaline solution.
Here, a still open problem is the distinction between the true solubility of portlandite and theformation of the complex Ca(OH)+. The question becomes particularly important whenquantitative modelling at high pH and/or the composition of thermodynamic databases
becomes an issue. In this pH-range the properties of both species belong to the essential
thermodynamic data. A sensible and consistent evaluation of thermodynamic parameters for
calcium silicates and -aluminates is hardly possible without them. However, the stabilities ofboth species just fall into that critical concentration range where activity corrections become
an important issue. As long as an independent determination of the Ca(OH)+-stability is
missing, the understanding of this simple system is crucially influenced by the choice of theactivity correction model (e.g., Davies, Extended Debye-Hückel, SIT, Pitzer). Unfortunately,
this choice will affect the entire high-pH database and has to be done very carefully.
Important progress was made in the thermodynamic description of hydrated calcium silicates(CSH). Former model concepts on the basis of phase pure CSH solids initially provided good
insights into this class of compounds, but it seems that these former models become now
outdated. Today, solid solution concepts become state-of-the-art. These alternative concepts
describe available solubility data as did former models, but they do it in a more fundamental
way and with a substantially increased flexibility in quantitative applications. It turned outthat structural aspects of the solid phases may and will become very important model
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parameters. Therefore, future investigations must give special attention to sophisticated anddifferentiated analysis of the solids structural aspects, be it by classical (e.g., microscopic,
XRD) or by all the different modern spectroscopic techniques. From my point of view two
things are important when considering B/C interactions: (i) studying the retention of alkalihydroxides by neo-formation of CSH phases with alkalis. A retarded release of (“less high”)
hydroxide concentrations may alter the vector of secondary precipitates, (ii) studying theformation of secondary CSH phases in the contact zone cement/clay, which has direct impact
on the hydraulic system parameters.
Hydrated calcium aluminates do not contribute very much to the cement’s mass balance.
However, for performance assessment this class of compounds (laminated calcium aluminates,
ettringites, hydrotalcites) is important because it has a large potential for retaining anions
within its structure. The present literature describes mainly solubilities and thermodynamic
data for ettringite, which unfortunately exhibit a very large scattering among different authors.
Data of this quality are of limited use only in quantitative applications. For the present PSI
undertakes literature reviews to investigate the hydrated calcium aluminates. As a first resultin this area, over 60 years old literature data on the solubility of hydrogarnet could smoothly
be explained with the help of a simple ideal solid solution approach.

12

Precipitation exp.
Dissolution exp.
Stable hydrogarnet

Dissolved aluminium [mmol/kg]

10

8

6

4

2

0
0

5

10

15

20

25

Dissolved calcium [mmol/kg]

Fig. 2: Literature data on the solubility of stable (green dots) and metastable (yellow
and blue dots) hydrogarnet in water [10]. A simple ideal solid solution approachproduces very satisfying results (blue curve).

The convincing results will serve as basis for further investigations including more complex
systems with additional anions such as sulfate or carbonate. Just as in the case of CSH phases,
it was recognised that constricted thermodynamic stability fields, metastability (kinetic
constraints) as well as structural aspects form important model parameters. Studies on the(solubility) behaviour of calcium aluminates in the presence of common anions are sparse andonly few data are available. Instead, much more is known about the formation of solids
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including these anions. Calcium aluminates do not have direct impact on B/C interactions, but
are very important compounds when sorption and/or retention characteristics of secondary
minerals need to be addressed. Relevant future fields of work on this topic were called.
Since the formation of secondary phases like illites, chlorites, zeolites, CASH phases,
hydrotalcites, Mg-silicates etc. is not really the topic of this presentation, it’s referred to therelevant literature, e.g., [11]. However, secondary mineral formation changes porosity andthus the hydraulic characteristics of the contact zone and its adjacent environments. From thepoint of view of cement the reaction of portlandite with the carbonate from the bentonite/claypore water is essentially of interest. The thermodynamics of this reaction are undisputed andthe precipitation of calcite is not kinetically hindered. This simple chemical system is well
suited to demonstrate the expected fundamental effects. Figure 3 shows results of a twodimensional model exercise of calcite formation after 500 and 2000 years of pure diffusion. A
cement structure simulated by Ca(OH)2 (inside of the ring-shaped region) reacts withcarbonate from the surrounding Marl pore water. Calcium from the cement diffuses into thehost rock and carbonate from the host rock into the cement. Precipitated calcite reduces
porosity to almost zero and decreases the hydraulic conductivity by orders of magnitude. A
largely non-studied, “open field” in this context is the impact of changing geometries(porosity) on the hydraulic parameters.

Fig. 3: Simulation of cement pore water reacting with carbonate groundwater,
calculated for 500 (left) and 2000 (right) years. A peripheral rim characterized bysubstantial calcite precipitation forms in the contact zone around the cement. Purediffusion system, hydraulic conductivity assumed to be K=10-12 m/s [12].

Similar effects are to be expected for all ongoing mineral conversions, but of course do not all
reactions decrease porosity. For example, Adler [11] predicts a complete clogging of the
Opalinus clay (the Swiss host rock) after few years, based on corresponding experiments. The
conclusions from these findings are self-evident: Porosity changes induced by mineraltransformations as well as the respective changes of transport parameters should get highpriorities in further investigations.
One has to note that such investigations should not be performed without simultaneously
looking at real or very close to real systems. Laboratory studies are essential and will be able
to point out general trends and maybe fundamental effects related to single, independent
systems. However, repository systems, of which B/C-interactions are just a part, are highly
integrated systems. Transport processes and chemical processes tend to affect each otherA3-105

NUMO-TR-04-05

mutually strongly, and thus investigations with real materials under close to real conditions
are indispensable as well.
Literature:
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]

Jennings, J. Am. Ceram. Soc. 69 (1986)614
Glasser et al., J. Am. Ceram. Soc. 70 (1987)481
Atkinson et al., J. Chem. Soc. Dalton Trans. (1989)2371
Berner, Waste Management 12 (1992)201
Kersten, Environ. Sci. Technol. 30 (1996)
Börjesson et al., Cem. Concr. Res. 27 (1997)1649
Stronach & Glasser, Adv. Cem. Res. 9 (1997)167
Sinitsyn et al., Mat. Res. Soc. Symp. Proc. 506 (1998)953
Kulik & Kersten, J. Am. Ceram. Soc. 84 (2001)3017
Wells et al., J. Res. Natl. Bureau of Standards 30 (1943)36
Adler, Thesis, University of Berne (2001) 120p.
Pfingsten, PSI report 01-09 (2001) 96p.

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Discussion on PA model development for bentonite barriers affected bychemical interaction with concrete: Do we have enough evidence tosupport bentonite stability?
Hiroyasu Takase** Quintessa Japan, 707 Queen’s Tower A, 2-3-1 Minato-mirai, Nishi-ku, Yokohama, 2206007 Japan
1. Introduction
In many cases designs for geological disposal facilities for radioactive wastes adopt cement
together with bentonite clay as engineered barriers. However, there are concerns that themineralogical composition of the bentonite will not be stable under the hyperalkaline pore
fluid conditions typical of cement and its properties will change over long time periods.
Use of the low pH cement may solve this potential problem but, taking into account thatvast amount of experience of using the Ordinary Portland Cement (OPC) in the similar
environment exists, it is desirable to keep OPC as an option so that flexibility in designingand constructing the facility can be guaranteed. Thence alteration of bentonite clay under
the hyperalkaline conditions remains as an issue in performance assessment.

In order to assess potential impact of the chemical alteration of the bentonite on its barrier
performance, the following key questions have to be answered:- How will the bentonite clay be altered by reactions with the hyperalkaline pore fluid?
- How much bentonite will be altered in the PA relevant time scale?
- Will the chemical alteration of bentonite lead to any significant advert effect on its barrier
performance?
In this presentation existing evidence relating to these questions is reviewed so that level ofthe current understanding can be assessed. In addition issues for further R&D are identified.
2. Processes relating to bentonite alteration
Reactions of bentonite clays with hyperalkaline fluids have been investigated in manystudies (e.g. Steefel and Lichtner, 1994; Bauer and Berger, 1998; Savage et.al, 2002;
Fujiwara et.al., 2003). Many of these studies note that short-term interactions are dominatedby ion exchange processes, whereas in the longer-term and/or at high temperatures, mineraldissolution-precipitation reactions become more important. These two groups of processes
have to be coupled together when we assess their significance since:- Ca ion in solution will be removed when secondary minerals precipitate, resulting inretardation of ion exchange processes;- Decrease in effective bentonite density due to dissolution will enhance partial loss of
swelling capability caused by ion exchange.
3. Three approaches to model bentonite dissolution
Since ion exchange is likely to take place in the entire buffer region fast enough within the
PA time scale (Fujiwara et.al., 2003), we focus on the amount of montmorillonite that will
dissolve in the time scale of interest. There are three distinct controls on total amount ofbentonite to be dissolved in the hyperalkaline pore fluid. These are namely;

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NUMO-TR-04-05- constraint by mass balance,- constraint by mass transport,- constraint by reaction kinetics.
3.1 Constraint by mass balance
Assuming that HSiO3- is the dominant silica species in solution, dissolution ofmontmorillonite in the hyperalkaline pore fluid can be formulated as follows;
Na.33Mg.33Al1.67Si4O10(OH)2 +4.68OH-+2H20= 0.33Na+ + 0.33Mg2+ + 1.67Al(OH)4+ 4HSiO3-.
This implies that dissolution of unit mole of montmorillonite consumes 4.68 moles of OH-.
Assuming further;- 8,000 moles of OH- will be produced by reaction of 1 m3 of concrete,- around 1,500 moles of montmorillonite is involved in 1m3 of buffer material,- montmorillonite is dissolved preferentially among the constituents of the buffer material,
10 cm thick OPC liner around a disposal tunnel of 2.2 m diameter filled with compacted
bentonite (dry density 1.6 g/cm3; mixture of 70% Kunigel V1 and 30% sand) can dissolve
up to 20% of the initial amount of montmorillonite. This poses a constraint on amount ofmontmorillonite that can be dissolved by reacting with concrete. In case of thicker tunnel
support and/or existence of concrete wall as in L/ILW repository, total amount ofmontmorillonite dissolution constrained by mass balance increases in proportion to theamount of concrete existing in the EBS. The constraint derived from this simple calculation,
however, is uncertain for a number of reasons. Firstly precipitation of secondary minerals
will contribute to consumption or generation of OH-. For example, precipitation of
tobermorite (Ca5Si6H21O27.5 = 5Ca2+ + 6HSiO3- + 4OH- + 5.5H2O) will enhance pH
buffering capacity and decrease the amount of montmorillonite to de dissolved, whereas
precipitation of analcite (Na.96Al.96Si2.04O6.H2O + 2.04 OH- + 0.92H2O =0.96Na+ + 0.96
Al(OH)4- + 2.04 HSiO3-) and laumontite (CaAl2Si4O12:4H2O + 4 OH- = Ca2+ + 2Al(OH)4- +4 HSiO3-) will generate OH- and increase amount of montmorillonite dissolution. If weassume that all the silica generated by montmorillonite dissolution precipitates as analcite
or laumontite, 10 cm thick OPC liner is sufficient to supply OH- ion required to dissolve all
the montmorillonite existing in the 2.2m diameter disposal tunnel. Secondly a significant
fraction of OH- generated by concrete reaction can migrate out of the EBS and react with
the near field host rock, resulting in decrease of montmorillonite dissolution. Thirdly
minerals in the buffer material other than montmorillonite, e.g., quartz and chalcedony, candissolve and consume OH-, leading to decrease of montmorillonite dissolution. In summary
it is difficult to specify a useful constraint on the amount of montmorillonite dissolution
based on consideration of mass balance unless sequence of secondary mineral precipitation,transport of OH- out of the EBS and relative time scale of dissolution of various pH
buffering minerals in the buffer material are taken into account.
3.2 Constraint by mass transport
All the OH- ion to be generated by concrete reaction may not react with bentonite sinceslow diffusive transport of OH- into the buffer material, in comparison with advective
transport around the tunnel, could limit cumulative amount of OH- reacting with thebentonite. This leads us to consider a constraint on the amount of montmorillonite
dissolution by mass transport. OH- initially existing in concrete will dissolve into solution
and react with montmorillonite and other pH buffering minerals. At this stage OH- will bein the form of HSiO3- that can be transported in and around the buffer material. Following
this step, precipitation of secondary minerals will take place. As we described above,
candidates of the secondary minerals that will precipitate under hyperalkaline conditions,A3-108

NUMO-TR-04-05

e.g., tobermorite, tend to consume OH-, whereas candidates for secondary minerals under
milder pH conditions such as analcite and laumontite will generate OH-. This implies thatOH- will be stored in the high pH product initially and gradually return into the solution as
those minerals dissolve again at lower pH. This, together with formation of OH- generating
secondary minerals, will retard the pH decrease and result in prolonged tail of hyperalkaline
plume. Dissolution of montmorillonite constrained by transport of OH- ion in and aroundthe buffer material together with its storage in and release from the sequence of secondary
minerals can be simulated by combining mass transport equations with a number of mineralreactions including montmorillonite assuming local instantaneous equilibria. Figure 1
illustrates an example of such simulations, which provides a less pessimistic constraint thanthe one derived by considering mass balance (see 3.1). We need to be careful, however,since this is constrained by mass transport through the altered bentonite region where
information that can be used to specify type of secondary minerals to form in the PA timescale is very much limited. Our estimate on the mass transport characteristics of this layerof unidentified secondary minerals thence inevitably includes significant uncertainty. Thismight be acceptable in case of the interface between the concrete structure of L/ILW
repository and the bentonite clay surrounding it since unaltered bentonite around the alteredregion will provide barrier against advective transport and a reasonable upper bound for
effective diffusion coefficient in the altered bentonite region may be assumed. On the other
hand bentonite alteration at its interface with the surrounding concrete liner may initiate
advective transport if altered bentonite exhibits greater hydraulic transmissivity, leading
potentially to “fingering” of the alteration front.
Existing experimental studies (e.g.; Jefferies et al., 1988; Fujiwara et al., 2003) suggest that
dissolution of montmorillonite coupled with precipitation of the secondary minerals canresult in net decrease in porosity, effective diffusion coefficient and hydraulic conductivity.
However it is likely that the secondary minerals observed in the experiments will be slowly
transformed into more stable minerals and it is difficult to justify assuming barrier functionof the altered bentonite region over PA time scale.
Concrete liner
Montmorillonite濃度

Buffer material

Time (y)1600

Abundance(mol/m3)濃度 [mol/m3]

1400
1200
1000
800
600
400
200
0
0.4

0.6

0.8

1

1.2

1.0E+00
3.2E+00
1.0E+01
3.2E+01
1.0E+02
3.2E+02
1.0E+03
3.2E+03
1.0E+04
3.2E+04
1.0E+05
3.2E+05
1.0E+06

位置 [m]
Distance(m)

Figure 1 Amount of montmorillonite dissolution constrained by mass transport(HLW)

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NUMO-TR-04-05

3.3 Constraint by reaction kinetics
Kinetics of montmorillonite dissolution can be regarded as a direct constraint on theamount of dissolution. A number of studies have been carried out on reaction kinetics of themontmorillonite dissolution. In many of them enhanced dissolution rate under higher pH isobserved (e.g.; Huertas et al., 2001; Fujiwara et al., 2003; Sato et al., 2002). Dependence ofdissolution rate on degree of saturation is also reported (Cama et al., 2000). Combining
these existing information, the following options for the rate expressions were proposed(Fujiwara et al., 2003);

Model 1: k.A.(aH+)n.{ 1 – exp[-a(logQ/K)6]}, a=6e-10,
Model 2: k.A.(aH+)n.(1 – Q/K),
where Log k = -17.1, n=-0.34. Dependence on the degree of saturation in Model 1 is basedon the empirical expression suggested in (Cama et al., 2000) whereas that in Model 2 isderived from the transition state theory but not necessarily consistent with the experimental
results. As depicted in Figure 2, dissolution rates derived from these two model options arevastly different. Results of reaction transport calculations taking into account kinetic
control on montmorillonite dissolution are sensitive to selection of these model options.
Figure 3 shows the result of a calculation corresponding to Model 1 where loss ofmontmorillonite due to dissolution is negligibly small whereas the result corresponding toModel 2 is almost identical to the instantaneous equilibrium model ( Figure 1).
A parametric survey using Model1 revealed that the result shown in Figure 3 is insensitive
to choice of secondary minerals (including a case without any secondary mineral),boundary conditions and variation in effective diffusion coefficient in the altered bentonite
region.

0

Log normalized dissolution rate

Model 2-1-2Model 1

-3
-4
-5
-10

-8

-6

-4

-2

0

Log Q/K

Figure 2 Model options for montmorillonite dissolution kinetics

A3-110NUMO-TR-04-05

Concrete liner
Montmorillonite濃度

Buffer material

Time (y)1600

Abundance(mol/m3)濃度 [mol/m3]

1400
1200
1000
800
600
400
200
0
0.4

0.6

0.8

1

1.2

1.0E+00
3.2E+00
1.0E+01
3.2E+01
1.0E+02
3.2E+02
1.0E+03
3.2E+03
1.0E+04
3.2E+04
1.0E+05
3.2E+05
1.0E+06

位置 (m)[m]
Distance

Figure 3 Amount of montmorillonite dissolution constrained by reaction kinetics(HLW)
4. Effects of bentonite alteration on barrier performance
Once amount of montmorillonite to be dissolved by reaction with hyperalkaline pore fluid
is estimated, its potential impact on the barrier performance need to be assessed. Although
there remains a possibility that altered bentonite region may provide good enough barrier
function against flow, diffusion resistance and colloid filtration, it is difficult to guarantee
over long time periods. Hence we need to focus on barrier function of remaining
montmorillonite that is likely to have been transformed to Ca-montmorillonite by ion
exchange. Flow test on Na-bentonite and Ca-bentonite over a range of effective bentonite
density indicates that hydraulic conductivity of Ca-bentonite is similar to that of Nabentonite if the effective bentonite density is greater than 1.5 g/cm3 and that hydraulicconductivity of Ca-bentonite increases drastically for the lower effective density (Mihara etal., 2000). Hence, by calculating effective density of remaining bentonite, potential impact
of chemical alteration on the barrier performance against flow can be assessed. In thiscalculation, loss of montmorillonite and other initial minerals in the buffer, volume ofdegraded concrete and secondary minerals need to be taken into account. In addition
expansion of corroded overpack and structural stability of concrete facility need to beconsidered in case of HLW and L/ILW repository respectively.

It needs to be noted that the flow tests in (Mihara et al., 2000) were conducted underhydraulic gradient that is several orders of magnitude greater than that is expected in therepository. In other study it was observed that hydraulic conductivity of Ca-bentonite witheffective density lower than 1.5 g/cm3 decreases as the hydraulic gradient becomes small(Fujiwara et al., 2003). In addition there was evidence suggesting that increased hydraulicconductivity of low density Ca-bentonite was due to gap between bentonite sample and theflow column possibly caused by combination of decreased swelling capacity and greater
water pressure gradient. As for the diffusion coefficient and colloid filtration, experiments
on Ca-montmorillonite with wide range of effective density are yet to be carried out.

A3-111NUMO-TR-04-05

5. Issues for further R&D
Based on the discussions in the previous sections, issues for further R&D will be identified
and presented at the workshop.

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