Table Of ContentstnemegdelwonkcA
This book si na expanded and revised version of our earlier volume entitled "Natural Analogue seidutS
ni eht lacigoloeG Disposal of evitcaoidaR "setsaW which was published by Elsevier in 1994. nI the six
years which have elapsed since that book was written, the application of natural analogues to
radioactive waste disposal sah matured and it si encouraging to ees more discussion in safety
assessment documents acknowledging that observations from nature and archaeology nac be used to
increase our confidence in the geological disposal of radioactive wastes. eW hope this trend will
continue. Also, in the last six years, a number of large-scale analogue studies have been completed and
a few new ones undertaken. A relatively recent new esu of analogues si their application in other
environmental and waste issues. eW hope that this book adequately reflects these developments.
nI writing this book, the authors have drawn on their experience of many natural analogue studies over
the last two decades, both large and small. These studies have involved researchers and data users
from a wide range of scientific disciplines, and the authors wish to express their thanks to all their
colleagues in many countries for fruitful, demanding and protracted discussion sessions in meeting
rooms and watering holes around the world. Without these interactions the opinions expressed here
would never have been developed or tested.
The writing of this book was funded by the following six organisations from around the world who,
collectively, have been responsible for the promotion of many natural analogue studies: Enresa, Spain;
Environment Agency, ;KU JNC, Japan; Nagra, Switzerland; Posiva, Finland; ,BKS Sweden.
",llllu",,..
TNEMNORIVNE JNC na g ra 11,,,
eW thank all of these organisations for their support and tolerance in bringing this book to press.
Chapter :1
The issue of radioactive
waste disposal
Throughout history, people have disposed of most them indefinitely on the surface. Several
types of solid wastes by either burning them or repositories around the world have already been
burying them. All too often this sah resulted ni a built, or era under construction, to contain wastes
hasty and convenient shallow grave for all kinds of with low levels of radioactivity. Repositories for
environmentally unfriendly materials. sA a wastes with the highest levels of radioactivity era
consequence, the perception of waste burial si still in the design stages, although sites for the
often of dirty, old-fashioned landfill sites, strewn first of these are currently being identified, and
with garbage, and of contaminated lakes and construction si likely to begin within the decade.
rivers. ,oS when people hear of plans to bury An example design si shown in Figure 1.1.
radioactive wastes underground, they are
The location of a repository, its design and the
understandably concerned for the safety of local
depth of burial depend very much on the type of
inhabitants and for the environment.
waste it si intended to contain, ni terms of its level
However, the reality of radioactive waste disposal of radioactivity and physical and chemical
si os far removed from the images of common properties. The waste materials, and the
waste tips sa to bear no comparison. Indeed, engineered barriers which initially contain them
during the last two decades, the concept of within the repository, are expected eventually to
underground radioactive waste disposal using degrade and it si anticipated that some residual
purpose-built, engineered facil'ities has been waste radionuclides might return to the surface ni
developed to a degree far ni advance of any other very low concentrations at some time in the
disposal practice adopted ni any other industry, distant future sa part of the natural processes of
reflecting the high standards of safety which the groundwater movement and environmental
nuclear industry si expected and legally required change. enO of the challenges facing the nuclear
to achieve. industry si to demonstrate confidently that a
repository will contain wastes for so long that any
Most industrialised countries have some
releases that might take place in the future will
radioactive wastes which require disposal,
pose no significant health or environmental risk. nI
although the volumes and types of these wastes
this regard, the very fact that these wastes era
varies considerably from country to country.
radioactive can be considered helpful because
However, ni almost all cases, these countries have
natural radioactive decay will reduce their
opted to dispose of their wastes underground, in
radioactivity down to levels similar to those of the
radioactive waste repositories, rather than to store
The geological disposal of radioactive wastes and natural analogues
surrounding rocks or of natural ore deposits, years. nI contrast, many other types of wastes
Ultimately, radioactive decay will convert the which also present na immediate environmental
wastes to stable, non-radioactive materials. The risk in most industrialised countries, such sa toxic
time required for this conversion si defined by the chemicals and poisonous metals (e.g. arsenic and
half-lives of the particular radionuclides in the cadmium) will remain hazardous for ever. It si an
waste and, for most radioactive wastes, will range irony then, that the same safety standards applied
from a few hundred years to many thousands of to radioactive wastes are generally not applied to
these other dangerous
wastes types.
As part of under-
standing how a radio-
active waste repository
will behave over many
thousands of years, it
is useful to look at
processes which oper-
ate in nature and
to draw appropriate
parallels between geo-
logical systems and the
repository. For ex-
ample, there are many
radioactive materials
which occur naturally
and which can be
found in. common
rocks, sediments and
waters around the
world. Uranium, which
si the principle radio-
active component in
the fuel used in nuclear
power stations, is a
naturally-occurring
element which can be
found in trace amounts
in the soils in most
peoples' gardens. By
careful examination of
Figure 1.1: An example of geological deep a repository design ot contain highly
radioactive wastes. nI this case, eht design si from Switzerland. Radioactive the distribution of
waste would eb packaged in massive metal canisters and placed in eht uranium in the natural
horizontal tunnels, which would typically eb between 500 and 1000 m below environment and by
ground, sa discussed in Chapter .2 Such purpose-built repositories are far in learning about the
advance of eht facilities used for eht disposal of any other waste type and
tce9ler eht high standards of safety which eht nuclear industry si detcepxe and processes which con-
legally required to achieve. Illustration courtesy of Nagra.
ehT issue of radioactive waste disposal
trol the movement of uranium in rocks and analogues are the slow degradation of materials
groundwaters, we nac begin to understand how it and radionuclide containment in deep rock.
and other radionuclides might behave in a Suitably chosen analogue examples nac relay
repository. Learning from nature ni this way si immediate visual impact and understanding
using nature sa na analogue for the processes (however qualitative) and relate to objects and
which will determine the behaviour of a processes which people are familiar with, even if
radioactive waste repository and which, therefore, the quantitative similarity to the repository
will control its safety. Natural analogue studies era environment si sometimes limited. yB providing
what this book si all about. some of these illustrations, it si hoped that this
book will help advance understanding of the
enO aim of this book si to review and summarise
issues associated with radioactive waste disposal
the natural analogue studies which have been
and allay some of the fears.
undertaken to date around the world, and to
highlight how natural analogue information nac eb
used to increase the scientific understanding of 1.1 The nature of radioactive
repository evolution and, thus, to make better wastes
technical predictions for repository safety.
However, a second aim of this book si to consider The majority of the radioactive wastes created
how natural analogues nac best be used for around the world era the unwanted by-products of
presenting the concept of geological disposal to electricity generation using nuclear power, and of
various interested audiences in a simple, coherent military activities. However, there si also a large
and scientifically legitimate manner. number of industrial, medical and scientific
research activities which esu radioactive materials
Anxiety about radioactive waste disposal si
and create radioactive wastes, albeit ni relatively
entirely understandable if people lack facts
small amounts. These last uses of radioactive
concerning the real risks presented by radioactive
materials mean that many more countries than
wastes and a repository. Reducing anxiety si a
just those with nuclear power have a waste
difficult problem and nac only eb achieved if
problem to address, although the magnitude of
repository developers era perceived to be making
the problem si much smaller in countries without
a serious effort to provide their scientific peers,
a nuclear power programme.
decision-makers and the public with
demonstrations of repository safety which nac eb Most radioactive wastes exist in solid form (or are
readily understood. Complex mathematical solidified) but a small proportion, by waste and by
demonstrations of safety era required by law radioactivity, arise ni liquid or gaseous waste
before na operating licence for a repository will eb streams and may eb discharged to the environ-
granted but these are not easily comprehended by ment. Tightening of environmental controls and
non-technical readers. nI addition to their regulations over the last few decades sah meant
mathematical basis, the definitions of words such that the released proportion sah been constantly
sa safe and risk used ni these formal safety shrinking sa improved methods of waste
demonstrations era hard to evaluate and to put treatment have been employed, such sa better
into context with other normal, every-day uses of filtering of gaseous effluents.
these words and measures of risks. Solid radioactive wastes may eb categorised in
Natural analogues provide a sensible means of many different ways, for example by the manner
conveying the fundamental principles of a in which they were created, their physical or
repository and its safety to wider audiences, chemical form and their potential for reprocessing
Among the concepts which nac eb presented using or recycling. However, the most commonly used
ehT geological disposal of radioactive wastes and natural analogues
categorisation si by level of radioactivity because 1.2 The concept of geological
it si this feature which sets radioactive wastes disposal
apart from any other form of waste. The different
Many different options for the disposal of
types of radioactive wastes and their origins are
radioactive wastes have been proposed, several
discussed in more detail in Chapter 2.
have been investigated in detail, and a few have
At the present time, the majority of wastes with been practiced to some extent in the past. The
high levels of radioactivity are held in surface most commonly discussed alternatives include:
stores at the nuclear facilities which created them
storage until activity levels decay to below
(such sa nuclear power stations) and are kept safe
exemption limits;
and separated from people and the environment
by active institutional controls. Containment of the (cid:12)9 disposal into space;
wastes in these stores depends on constant
(cid:12)9 disposal in the polar icecaps;
surveillance and maintenance which cannot be
ensured indefinitely. Stored wastes could present a (cid:12)9 disposal on or beneath the seabed;
hazard if institutional controls were to fail through (cid:12)9 nuclear transmutation;
civil unrest or natural disaster, or if they became
(cid:12)9 shallow land burial; and
the target of deliberate military or terrorist activity.
As a consequence, it si generally believed that a (cid:12)9 deep geological disposal.
more permanent disposal option si required which
When dealing with radioactive wastes, storage
can ensure these wastes are safely isolated from
generally refers to a system which requires further
people (and from malicious tampering) and which
management action before institutional control
does not, necessarily, depend upon long-term
over the waste si given up, whereas disposal does
institutional control.
not. nI this regard, the first option si often
The duration of the required isolation period si promoted by individuals and environmental
defined largely by the level of radioactivity of the groups opposed in principle to the disposal of
waste and the half-lives of the component radioactive wastes by any means. However,
radionuclides. nI simple terms, the wastes with the consideration of the very long half-lives of some
highest activity and longest half-lives are radionuclides means that institutionally-controlled
considered to be potentially most dangerous and storage si not a practical option for the longer-
will therefore need to be disposed of in robust lived wastes because control cannot be
facilities designed to last for many thousands of guaranteed for the required very long (thousands
years or longer. Lower activity wastes with shorter of years) isolation period. nI this case, there si no
half-lives will require less robust facilities capable alternative to disposal. Institutional control can be
of isolating the waste for up to a few hundred predicted with confidence only for wastes with
years, short-lived isotopes (IAEA, 1992).
The very lowest activity waste may not require any Neither disposal to space nor to the icecaps has
special treatment if its activity si below designated been investigated in any great detail: for a
exemption (radiation)levels. These exemption discussion on space disposal ees Rice and Priest
levels vary from country to country but are (1981) and for a discussion on icecap disposal ees
roughly equivalent to the levels of radiation found EODSU (1980). nI contrast, disposal on the seabed
in many natural materials such sa soils and rocks. sah been carried out in the past in deep waters
under international agreement. Furthermore,
comprehensive international research prog-
rammes to develop and assess methods for
ehT issue of radioactive waste disposal
disposal under the seabed (sub-seabed disposal) (Rybalchenko, 1998). However, these sites era
were undertaken ni the 1970s and 1980s (e.g. planned to eb decommissioned in the next decade
,AEN 1988; Mobbs et al., 1988). However, seabed and no new injection facilities are planned. Ultra-
disposal by any method si now prohibited by deep boreholes for solid waste disposal have been
international agreement (Sjoeblom and Linsley, designed on paper (e.g. SKB, 1992: Gibb, 1999)
1994), although the International Atomic Energy but never put into practice because the latter two
Agency (IAEA) sah been investigating seabed options, shallow and deep burial in repositories,
disposals made outside the international have generally found favour in most countries.
agreement by the former Soviet Union (Linsley and Shallow land burial si already practiced for low
Sjoeblom, 1994). It si interesting to note, however, activity wastes and deep burial si planned for the
that several studies have shown that sub-seabed higher activity wastes. For a comprehensive
disposal may actually ,eb in radiological terms, a description of the background to geological
very safe option (de Marsily et al., 1988). disposal of radioactive wastes, ees Chapman and
McKinley (1987) and Savage (1995).
Nuclear transmutation si a process whereby some
types of long-lived wastes are irradiated such that oT ensure adequate levels of safety, the design of
some of the longest-lived radionuclides they any shallow or deep repository for solid
contain are converted to shorter-lived nuclides, radioactive wastes must pay attention to the
Current opinion si that transmutation nac provide nature of the waste and to the geological
a solution only for reducing the quantities of some environment. oT be feasible, a repository must
particularly long-lived radionuclides and that it si meet a number of fundamental design
not a feasible proposition for the large volumes of requirements, the most basic being that the
radioactive wastes which now exist. More repository:
significantly, transmutation would not avoid the
ensures the waste will not be released to the
need for the disposal of the shorter-lived but still
surface environment in concentrations which
highly radioactive nuclides it would generate.
would represent na unacceptable hazard;
Given the current situation, the majority of effort
effectively isolates the waste from the effects
in most countries si focussed on land based
of human activities undertaken at the surface
disposal and several methods have been
and from the effects of climate change;
proposed, sa follows:
si capable of being built using available
deep >( 100 metres)injection of liquid wastes
technology and achievable at a reasonable
into porous rock formations;
cost; and
ultra-deep >( several kilometres) burial of solid
si sufficiently simple such that its future
wastes in boreholes drilled from the surface;
behaviour and safety can be assessed
shallow (few metres) burial of solid wastes in quantitatively and reliably.
surface or near-surface trenches or bunkers
nI addition, certain other requirements might eb
covered with engineered barriers; and
placed on some repository designs, such sa to
deep (50 to 1000 metres) underground burial ensure retrieval of the waste is both
of solid wastes in excavations containing na technologically and economically feasible, if os
engineered barrier system. desired by future generations.
Of these four options, the first, deep injection of Given these basic requirements, two approaches
liquid radioactive wastes, sah been carried out in to geological disposal are possible (Savage, 1995).
Russia at several locations since the 1960s The first si based on designs to contain the waste
The geological disposal of radioactive wastes and natural analogues
in one place for sa long sa possible or for sa long solidified into a stable matrix which si isolated
sa necessary to avoid unsafe radionuclide releases from the environment by a set of physical barriers.
to the environment. While this objective appears During containment, radionuclides within the
sensible, it si very difficult to demonstrate waste undergo radioactive decay os that, for all
convincingly for radioactive wastes containing nuclides, containment for a sufficient number of
very long-lived radionuclides. The second half-lives will effectively reduce their inventory to
approach si based on designs which allow some extremely low levels. roF example, a containment
progressive natural releases to the environment time period equal to 01 half-lives leads to a
and esu well-understood natural processes to reduction in inventory by around three orders of
dilute and disperse radionuclides so that magnitude.
concentrations are maintained below designated
The optimal duration for a containment period
safe levels, depends on the type of waste and its radionuclide
Both the shallow and deep land-based disposal content. For low activity wastes containing only
schemes rely on elements of both the containment small amounts of long-lived radionuclides,
and controlled release approaches. Containment containment for a period of around 300 years
generally requires that the radioactive waste si would eb sufficient to reduce the activity in the
waste to acceptably safe
levels. Assuming proper
institutional controls for this
time period, these wastes
could eb safely placed in a
near-surface facility.
Ensuring safe disposal of the
higher activity wastes
containing very long-lived
radionuclides requires more
robust repository designs.
Therefore, most of the higher
activity wastes will be
emplaced in deep repositories
which utilise the multibarrier
concept, whereby the wastes
era emplaced inside a series
of nested engineered struc-
tures and natural barriers
which act ni concert to restrict
the rate of release of
Figure 1.2: Diagrammatic illustration of the multibarrier concept, in
this case for a generic repository design for wastes with intermediate radionuclides over long
levels of radioactivity. ehT waste si packaged in a drum or canister, then periods. The multibarrier
placed in a concrete overpack ot create a stable waste package. This si concept si shown diagram-
then placed in the repository disposal tunnels and surrounded by an matically in Figure 2.1 and si
envelope of suitable buffer or ll'~lkcab material. Physical containment si
assured by the solid wasteform, eht waste package, the buffer and the discussed ni more detail ni
rock. Chemical containment si assured by low groundwater swo91 in a Section 2.3.
chemically reducing environment. Other multibarrier system designs
are discussed in Chapter .2
ehT issue of radioactive waste disposal
nI a simple multibarrier repository, solidified assessment and requires detailed mathematical
wastes era packed into containers which may analysis of all aspects of the repository system and
themselves eb placed inside a thick overpack. its evolution.
Normally, both containers and overpacks are made
nI fact, performance assessment calculations will
of metal or cement and, together, they comprise
eb undertaken long before a proposed repository
the waste package. The waste packages are then
site si finally selected. Various performance
emplaced at some depth in the repository
assessments will eb undertaken throughout a
excavations. The spaces around the waste
complete repository design programme, which
package are filled with some suitable buffer
may last several decades, at different stages, e.g.
material to provide long-term structural, hydraulic
to help identify suitable host rock formations, to
and chemical stability for the package.
evaluate alternative barrier materials and to ssessa
After repository operations have been completed, the consequence of unusual, low probability
access tunnels and shafts would eb backfilled and events, such sa accidental human intrusion into
sealed to the surface. A variety of materials and the repository. Some performance assessments
mixtures, often making esu of crushed rock from may only focus on a certain aspect of the
the repository excavations, si available for repository system, such sa the behaviour of diff-
backfilling and sealing operations. The host rock erent types of multibarrier systems, and are likely
in which the repository si excavated si generally to vary ni complexity and realism. Since most of
selected to be adequately stable for the these performance assessment calculations will eb
construction and operation of the facility and, undertaken at the conceptual repository design
most importantly, to provide a stable environment stage, they will esu a variety of generic geological
where groundwater flows slowly through the and geochemical information sa input data.
repository zone, and other natural geological and
Once a final repository site sah been chosen and
geochemical processes are also slow and
characterised (see Section 1.5.1), additional
predictable.
performance assessments will eb performed ni
Demonstrating complete containment of longer- order to obtain a licence to build and to operate
lived wastes in a deep repository si considerably the repository. These performance assessments
more difficult than for the short-lived wastes due will benefit from the esu of sa much site specific
to the inevitable process of degradation of the data sa possible and will examine the repository
engineered barriers within the repository. For this systems sa a whole, from degradation of the waste
reason, repositories for higher activity wastes are through to future releases to the surface.
designed to allow for progressive release and Considerable effort sah been expended over the
dispersal, after containment failure, into the rock last couple of decades to develop reliable
without adversely affecting the surface assessment methodologies for all stages in a
environment, sa shown in Figures 3.1 and 1.4. repository development programme. nI addition,
other work sah been ongoing to define acceptable,
independent criteria against which the safety of a
1.3 Evaluating repository safety
repository nac eb judged.
Before a repository nac eb built and operated, its Formal, legally-defined safety (or licensing)criteria
safety must eb adequately evaluated and shown to are usually set nationally for specific waste and
comply with various regulatory targets associated repository types, and international organisations
with radionuclide releases or movement ni the such sa the IAEA also provide general guidelines.
environment. This formal process of evaluating It si common for licensing organisations to define
repository safety si known sa performance the post-closure safety criteria in terms of
The geological disposal of radioactive wastes and natural analogues
radiological dose or risk to humans, where risk si Most countries have adopted safety criteria similar
defined sa risk of death due to cancer arising from to these. Depending on the type of the waste,
exposure to repository releases. Other forms of quantitative assessments of dose and risk may eb
target criteria will be set for the pre-closure required to be made for some specified future
(operational) phase of repository development. post-closure time period, this might 5 , 10 be 4 10 or
Typical post-closure safety criteria for a specific 6 10 years, although some current regulations give
target individual or group of individuals are: no time limit. Many authorities now believe that,
after this time, more qualitative assessments of
a radiological dose of < 1 mSv/yr (often
safety may eb most appropriate to demonstrate
< 1.0 mSv/yr), and
the continued safe operation of the repository. nI
(cid:12)9 a risk target of < l O6/yr.
~this case, qualitative
'predictions may be re-
quired for up to one million
years or more. Again, these
time periods are indicative
and different systems may
be adopted in different
countries.
In order for a performance
assessment to be able
to calculate the expected
dose and risk for a
repository, it si necessary
to represent understanding
of the system behaviour by
a series of conceptual
models which can be
converted into simple
mathematical models for
computational purposes.
This simplification of the
real system into something
that can be dealt with in a
computer model si shown
illustratively in Figure 1.5.
At the most basic, a
performance assessment
will need to include
conceptual and mathe-
Figure 1.3: Over a long period of time eht engineered components of eht matical models for:
repository will degrade and, eventually, eht waste will eb to exposed eht
(cid:12)9 the degradation of the
groundwater and will begin ot degrade. radionuclides Some may evlossid
in eht very slow moving groundwater but their transport away from eht engineered barriers
repository will eb retarded by interactions with eht rock and eht corrosion which contain the
products of eht engineered barriers. Dilution of radionuclides in eht waste;
groundwater will also .rucco
ehT issue of radioactive waste disposal
dissolution of the solid wasteform" may be explicitly included within the performance
assessment calculations.
the solubility of the radionuclides in the
groundwater; Undertaking a performance assessment is a
complex operation which requires much more
transport of groundwaters and dissolved
than simply writing a number of computer codes.
radionuclides through the engineered barriers
From beginning to end, the development of a
and the surrounding rock formations (natural
model to examine a particular feature of a reposi-
barriers) to the surface;
tory (say, dissolution of the waste) si undertaken
various processes which may retard in a number of stages, sa indicated in Figure 1.7,
radionuclide transport in the engineered which roughly can be described :sa
barriers and the rock; and
)1 construction of a conceptual model which
radionuclide release to the surface, describes the system and includes all of the
incorporation of radionuclides into the food important processes and their couplings"
chain and eventual uptake by humans.
nI reality, a separate
model will be con- Complete containment
(corrosion-resistant canister)
structed to represent
each of these pro- emiT >
==
cesses. These will m r Additional retardation time
then be linked to- o (cid:12)9 Technical measures
gether, with the m -Buffer/backfill
output from one i (cid:12)9 Selected natural surroundings
i
model fed, sa input, gnoL- water-flow times
-High retardation (sorption/matrix diffusion)
to the next, sa shown
-Geological long-term stability
diagrammatically in
Figure 1.6. As well sa
the models in the
T Retention improved yb
formal performance
(cid:12)9 Technical measures
assessment, other -Stable wasteform
-Buffer diffusion barrier
research codes may
gnitimiL -Buffer for reducing conditions )eF(
be used during fo release
(cid:12)9 Selected natural surroundings
performance assess-
-Low water supply
ment to perform -Suitable chemistry
-Geological/climatic long-term stability
scoping calculations
to ascertain the
significance of some
Natural retention
processes. These res-
(geosphere solubility limits)
earch models are a
I I
fundamental part of 01 3 '01 01 s 01 8 '01
safety assessment. If Years after emplacement of waste
they indicate that a Figure 1.4: ehT waste canister will fail after some 01 3 to 01 4 years in the
particular process si repository after which time continued retention of radionuclides in the repository
significant for safety, will eb due to the physical behaviour of the other barriers and chemical
containment processes. While the canister is intact, the total radioactivity in the
then that process waste drops substantially due to decay of the shorter-lived radionuclides.
