(DRAFT)
SAFETY-RELATED ISSUES FOR THE
DISPOSAL OF INTERMEDIATE LEVEL WASTE
(ILW)
Drafted at
Consultants’ Meeting to draft a technical document on disposal facilities
for intermediate level waste
22-26 April 2013, Vienna, Austria
Contributors to drafting
Consultants’ Meeting to draft a technical document on disposal facilities for ILW
22-26 April 2013, Vienna, Austria
Don Howard (Canada) : Chair
Jean-Michel Hoorelbeke (France)
Juergen Wollrath (Germany)
Fredrik Vahlund (Sweden)
Yumiko Kumano (IAEA)
Contents
1
Scope ............................................................................................................................................... 4
2
Current IAEA definitions on ILW ...................................................................................................... 4
3
Issues related to ILW disposal ......................................................................................................... 5
3.1
Waste characteristics .............................................................................................................. 5
3.1.1
Half-life and activity......................................................................................................... 5
3.1.2
Chemotoxicity .................................................................................................................. 5
3.1.3
Waste volume.................................................................................................................. 5
3.1.4
Waste form properties and waste conditioning ............................................................. 6
3.1.5
Properties related to the operational safety ................................................................... 6
3.2
Depth-related characteristics .................................................................................................. 7
3.2.1
Geological properties ...................................................................................................... 7
3.2.2
Permafrost and glaciation ............................................................................................... 7
3.2.3
Erosion ............................................................................................................................. 7
3.2.4
Human intrusion .............................................................................................................. 7
3.2.5
Redox ............................................................................................................................... 7
3.2.6
Other depth related properties ....................................................................................... 7
3.3
Design consideration for long-term isolation.......................................................................... 7
3.4
Operational issues ................................................................................................................... 8
4
Time scales ...................................................................................................................................... 8
5
Radionuclide migration ................................................................................................................... 9
6
Institutional control and human intrusion .................................................................................... 10
7
Waste packaging............................................................................................................................ 11
8
Characteristics of the disposal facility ........................................................................................... 12
9
Waste acceptance criteria ............................................................................................................. 13
10
Facilities for ILW – examples ..................................................................................................... 14
11
Summary.................................................................................................................................... 14
12
Conclusions/Recommendations ................................................................................................ 15
13
References ................................................................................................................................. 16
1
Scope
This document is to provide a reference for the disposal of intermediate-level waste (ILW) which is
not considered either low-level that can be disposed of in a near surface facility or high-level waste
that must be disposed in a deep geological formation. An IAEA safety guide currently exists for
geological disposal for high-level waste (IAEA Safety Guide SSG-14) and an IAEA safety guide for
near surface disposal of low-level waste is under development (draft IAEA Safety Guide DS 356). The
IAEA has published other documents for these two types of wastes and relating disposal facilities.
This document is intended to be used as supplemental technical document for the existing IAEA
Safety Standards by examining a number of issues to determine appropriate disposal options for the
ILW and for factors that may contribute to the safety case.
2
Current IAEA definitions on ILW
Intermediate level waste is defined in IAEA Safety Guide GSG-1 as:
Intermediate level waste is defined as waste that contains long lived radionuclides in
quantities that need a greater degree of containment and isolation from the biosphere
than is provided by near surface disposal. Disposal in a facility at a depth of between a
few tens and a few hundreds of metres is indicated for ILW. Disposal at such depths has
the potential to provide a long period of isolation from the accessible environment if
both the natural barriers and the engineered barriers of the disposal system are
selected properly. In particular, there is generally no detrimental effect of erosion at
such depths in the short to medium term. Another important advantage of disposal at
intermediate depths is that, in comparison to near surface disposal facilities suitable for
LLW, the likelihood of inadvertent human intrusion is greatly reduced. Consequently,
long term safety for disposal facilities at such intermediate depths will not depend on
the application of institutional controls.
This definition does not take radiological properties into consideration but focus on the design of the
disposal facility and waste acceptance criteria. Also in the IAEA safety glossary, the difference
between low- and intermediate-level waste is defined as:


low and intermediate level waste (LILW). Radioactive waste with radiological
characteristics between those of exempt waste and high level waste. This may be long
lived waste (LILW-LL) or short lived waste(LILW-SL).
Typical characteristics of low and intermediate level waste are activity levels above
clearance levels and thermal power below about 2 kW/m3 [....].
Many States subdivide this class in other ways, for example into low level waste (LLW)
and intermediate level waste (ILW) or medium level waste (MLW), often on the basis of
waste acceptance requirements for near surface repositories. These terms should not be
used in IAEA publications unless explicit definitions are given for the purposes of the
publication in question.
Also in the IAEA safety glossary, the terms short lived and long lived waste is introduced:
short lived waste. Radioactive waste that does not contain significant
levels of radionuclides with a half-life greater than 30 years
long lived waste. Radioactive waste that contains significant levels of
radionuclides with a half-life greater than 30 years
The above quotations highlight part of the issues defining ILW and relating disposal facilities. By
defining ILW as a waste that requires a higher degree of containment than LLW, an ILW disposal
facility may need a specific design. The ILW disposal facility may be interpreted as a facility that is
not a near surface facility but not as deep as a geologic disposal facility. Nevertheless, it is not
recommended to discuss an ILW disposal facility in terms of depth only, but rather by considering
many influencing properties that can provide an acceptable degree of containment and isolation.
3
3.1
Issues related to ILW disposal
Waste characteristics
A number of IAEA documents identify waste characteristics that need to be taken into account to
define disposal options and to perform relating safety case. This section is based on the IAEA
documents: Nuclear Energy Series No.NW-T-1.20: “Disposal Approaches for Long Lived Low and
Intermediate Level Radioactive Waste” and to Specific Safety Guide No. SSG-14: “Geological
Disposal Facilities for Radioactive Waste”. The following sections point out some waste
characteristics issues especially raised by ILW as introduced in sections 1 and 2.
3.1.1
Half-life and activity
The half-life of radionuclides in the waste and the evolution of waste residual activity with time are
important attributes in determining the duration of the minimum containment period during which
waste must be isolated from the environment. Near surface repositories for low level waste are
generally suitable for radionuclides with a short half-life and/or for waste with a low residual activity
after some hundreds years. HLW to be disposed of in deep geological formations have in most cases a
high content of long-lived radionuclides. ILW may be roughly categorized into two main groups. One
group of ILW contains a relatively high activity, but a low content of long lived radionuclides whereas
the other group has a relatively high content of long lived radionuclides, but with low to moderate
activity. The first group has often been co-disposed with low level and short lived waste. In some
countries the disposal of part or the entire second group is planned to be co-located with HLW
disposal.
The content in fissile material may require provision with regard to criticality. This is a major issue in
the design of disposal packages and facilities for spent fuel. For some ILW it can also be an issue to be
taken into account in the design and the safety case for waste with significant amount of uranium or
plutonium.
Waste with short lived or long-lived radionuclides such as cobalt-60, strontium-90, cesium-127,
americium-241, or silver-108m generate heat during periods of time between decades and thousands
of years as a function of their respective content in the waste. HLW generally produce significant heat
during the first few thousand years which requires sizing the disposal facility with respect to heat
dissipation. For low level short lived waste, heat is typically not an issue in the safety case, however
short-lived heat generating radionuclides may need to be taken into account in some particular cases.
For some ILW heat generation can be an issue in the sizing of disposal cells as a function of their
content in heat generating radionuclides and of the volume of waste to dispose of.
3.1.2
Chemotoxicity
Along with the radiological impact of radionuclides, the safety case for a disposal facility should take
into account the consequences arising from the potential presence of toxic or chemically hazardous
substances in the waste packages. It is generally not an issue for HLW disposed of deep underground
but it may be a significant aspect of the safety case for low level waste in particular for near surface
disposal. Depending on groundwater protection regulation, the chemotoxicity of low level waste may
also be an issue in case of deeper disposal. A similar situation can be expected for ILW.
3.1.3
Waste volume
The amount of waste and the external volume and total number of waste packages is another important
factor to be considered when choosing an appropriate disposal option. They are determinant of the
disposal facility volume along with the above-mentioned thermal output for HLW. HLW constitute a
relatively low volume of waste. On the contrary low level wastes that can be disposed of near surface
generally represent a high part of the total radioactive waste volume. The volume of ILW is usually
more significant than HLW and needs to be treated as a separate waste stream(s).
3.1.4
Waste form properties and waste conditioning
Waste form properties, including non-radiological properties, are relevant to the assessment of waste
disposal options. Factors to be considered include: the potential for mobilization of radionuclides and
the chemical compatibility with the disposal environment. Radionuclides contained in the waste can be
mobilized by water and, less often, may migrate via gaseous pathways ( 14C, Rn). With respect to the
groundwater pathway, the tendency of a radionuclide to be dissolved and transported depends on:
-
The resistance of the waste form to bio/radio/hydro degradation processes;
-
The physical and chemical forms of released radionuclides;
-
The chemical characteristics of the disposal environment (pH; redox; complexing ligands,
colloids or corrosive species initially present or progressively induced by material
degradation);
-
The sorption characteristics of dissolved radionuclides on the adjacent engineered and natural
materials.
Gases can be generated by microbial degradation of organic components of the waste (cellulose,
hydrocarbons), metal corrosion in particular under anoxic conditions, formation of radon, and
radiolysis. Particular attention needs to be paid to radiolysis induced gas build up during the
operational phase while this is generally a secondary factor after closure compared to the other gas
sources.
Mechanical interactions between the waste packages and the other engineered and natural components
of the disposal facility may result from:
-
The void volume within waste packages; the importance of this issue depends on the number
of waste packages in a disposal cell and on the void volume in each waste package;
-
The potential swelling properties of waste under water re-saturation or radiolysis effects.
Consequently important issues related to waste form properties and conditioning are:
-
The containment capacity of the waste form: leach-ability of the waste; additional matrix:
glass, cement, bitumen, ceramics, etc.
-
The materials present in the waste packages: organic material with regard to the formation of
complexing agents and gases; cement with regard to pH; nitrates with regard to redox etc.
-
The residual voids in waste package.
HLW are generally characterized by the high containment capacity of the waste packages and no or
few chemical interactions. In some cases, gas production due to corrosion and residual voids needs to
be taken into account.
Low level waste packages generally have a lower containment capacity. A significant part of them
may cause chemical and mechanical disturbances as well as gas generation.
The properties of ILW are generally closer to low level waste characteristics than to HLW
characteristics. Therefore, often the same processes or mechanisms as for low level waste have to be
taken into account in the safety case.
3.1.5
Properties related to the operational safety
Other waste package characteristics that need to be taken into account for the operational safety of
disposal facilities are:
-
surface dose rate, which may require additional shielding or remote handling;
-
potential surface contamination;
-
resistance of waste packages to operational hazards (drop, fire, etc).
In general, provision in the design regarding these factors may need to be graded to the activity level
of the waste.
3.2
Depth-related characteristics
The depth of a disposal facility is dependent on the geology and the characteristics of the waste. The
following geologic properties should be considered in determining the depth of the disposal facility.
The depth of the disposal facility should not be determined based on a single property.
3.2.1
Geological properties
In the early part of a siting process, a suitable disposal site is normally determined by using existing
geological information. This information needs to be improved throughout the site investigation
process. The depth of the disposal facility can then be determined based on favourable geologic
conditions.
3.2.2
Permafrost and glaciation
Materials used during the construction of the disposal facility may be impacted by permafrost. When
determining the depth of the disposal facility, this needs to be considered. Options may include a
permafrost free environment as a function of the half-lives and toxicity of the radionuclides in the
waste. However these processes need to be considered in the safety case. In the case of a permafrost
free depth, the changing boundary conditions caused by the permafrost need to be considered.
3.2.3
Erosion
At some locations, erosion is an important consideration in the long term properties of a disposal
facility. Shallow depth repositories may be susceptible to natural erosion mechanism.
3.2.4
Human intrusion
The type of human intrusion scenarios will be determined by the depth and the location of the disposal
facility.
3.2.5
Redox
The redox condition may determine corrosion rate of metallic components, solubility and sorption
capacity for different radionuclides. This could be considered when choosing a depth for the disposal
facility.
3.2.6
Other depth related properties
The above-listed properties have a role in determining the depth of the disposal facility. However there
are depth related properties that changes less dramatic with depth. For example, the radionuclide
migration, taking into consideration the waste properties, may be important for some cases. Shortlived ILW may be suitable for shallower depths whereas long-lived ILW would be better
accommodated by deeper depths (without regards to other geological features).
3.3
Design consideration for long-term isolation
The design considerations for an ILW disposal facility are typically no different than for other types of
disposal facilities, i.e. Geological Disposal Facilities for Radioactive Waste (IAEA Safety Guide SSG14). The objective of any disposal facility should be to provide containment and isolation of the
radionuclides in the waste from the biosphere.
The safety case and supporting safety assessment for a particular waste type of ILW will provide the
required demonstration for the containment capability of the disposal system. A long containment
period provided by durable waste packages may not be practicable or necessary for lower activity
long-lived waste.
The multi-barrier concept should form the foundation of the design considerations. The design
considerations need to take into consideration the waste type and form. Design considerations needs
to address disposal facility access-ways, shaft layout, cage and hoisting system, facility layout and
development sequence, ventilation system, room and tunnel configurations, waste package handling
system, waste rock management and finally shaft seal system.
#MUST BE EXPANDED TO INCLUDE LONG-TERM EFFECTS OF ISSUES LIKE GAS
GENERATION ETC……..#
3.4
Operational issues
One main difference between a disposal facility for HLW and one for ILW is the larger variety of
waste types that need to be managed in an ILW disposal facility. This larger variety of waste types
may also exist in the characterization of LLW in a near-surface disposal facility. In particular there
may be a desire to dispose of larger components which is not the case for HLW-only disposal facility.
This may need consideration of other design requirements. Furthermore in an ILW disposal facility
both operational and decommissioning waste may need to be considered. There is a higher possibility
to standardise operational waste than there is for decommissioning waste. The waste for an ILW
disposal facility may, for instance, consist of large components (i.e. pumps, steam generators, pipes)
that, in order to minimise dose to workers, need to be disposed of intact.
The disposal of large components, for example those resulting from decommissioning operations, may
create operational issues, both logistically and radiologically. Some ILW waste including large
components may need to be delivered at the disposal facility at a time when it is suitable for the waste
producers. Therefore temporary accommodation of the waste may need to be considered at the
disposal site prior to emplacement. The other issue that needs to be considered is the radiological issue
during the operational phase. These large components may need additional shielding and workers may
have to operate close to the component. Large components may also put other requirements on the
disposal system, such as the installation of a ramp as opposed to a shaft.
The large variety and the composition of the ILW needs to consider various issues that are not
associated with HLW such as chemical interactions between different waste types as well as between
the waste and the engineering system.
4
Time scales
The time-scale of a safety case needs to be consistent with the depth of the disposal facilities and the
local geodynamic conditions. Natural evolutions may occur on the surface at much faster time scales
than deep underground. This includes erosion induced by wind, rain water and potential land uplift,
subsidence and post glaciation rebound as well as climate induced processes like glaciation or
permafrost. These phenomena may change the future boundary conditions of the system, for example
hydrographic system and hydrogeology. They possibly will progressively reduce the thickness or
performance of containment barriers interposed between the waste and the environment. In an extreme
situation the disposal facilities and waste packages may be destroyed in the long term, leading to loss
of containment, direct access to waste and dispersion of residual activity. The affected depth with time
and the velocity of these mechanisms are site dependent.
For near surface disposal facilities, limited time scales are generally considered in safety cases. IAEA
Safety Guide on the Safety Assessment for Near Surface Disposal No. WS-G-1.1 provides that:
“Assessments may therefore need to project the behaviour of the site and facility for time periods of
the order of hundreds or even thousands of years.” In the IAEA Safety glossary, short-lived
radionuclides are defined as radionuclides with half-lives less than 30 years. The inventory of those
radionuclides will decrease substantially during the time period when institutional control period can
be relied on (see Chapter 6). The long term geodynamic evolution has been scarcely addressed in near
surface disposal.
On the other hand, deep geological disposal makes it possible in principle to consider very long timescales as necessary with respect to the half-life of radionuclides in the waste. An ICRP draft report on
the Radiological Protection in Geological Disposal of Long-Lived Solid Radioactive Waste indicates
that
“the goal of a geological disposal facility is to achieve the isolation end containment of
the waste and to protect humans and the environment for time-scales that are
comparable with geological changes. At great distance from the surface, such changes
are particularly slow (…)”.
However provisions are to be made in siting geological disposal facilities to avoid excessive
geodynamic disturbances that could affect the underground facilities, the host rock and the long term
safety functions. IAEA Specific Safety Guide on Geological Disposal Facilities for Radioactive Waste
No. SSG-14 provides that
“The site should be located in a geological and geographical setting where these
geodynamic processes or events will not be likely to lead to unacceptable releases of
radionuclides. (…) Geodynamic effects such as ground motion associated with
earthquakes, land subsidence and uplift, volcanism and diapirism may also induce
changes in crustal conditions and processes. Such types of event, which in some cases
can be interrelated, may affect the overall disposal system through disturbances in the
site integrity or modifications of groundwater fluxes and pathways.”
Reasonable margins are to be taken into account between the scientific capacity to predict the
evolution of a site and the time-scale of the safety case. It is generally recognized that a safety case for
deep geological disposal is limited to about one million years. Geologists can extrapolate the geologic
evolution of deep underground facilities in well-chosen sites for millions of years but uncertainties
increase with time.
Regardless of the type of waste and the repository depth, the safety case has to define an appropriate
time-scale. It must be consistent with the natural evolution of the site and the considered depth on the
one hand, and with the characteristics of the waste, in particular the reduction of activity with time as a
function of the half-life of radionuclides.
With regard to geodynamic evolution, shallower depth disposal facility compared with geological
disposal facilities might be typically associated with an intermediate timescale between 10,000 years
and 100,000 years which is a representative timescale for a glaciation cycle. At such a timescale, some
radionuclides with intermediate half-lives such as C14, Ra226, and Am241 will have been
substantially decreased.
The radiological exposure of man has to be acceptable at all times. Therefore one has to take into
account loss of containment and potential dispersion of waste at the end of the considered time-scale.
As a consequence, the acceptable content of long lived radionuclides is a function of the applicable
time scale.
5
Radionuclide migration
The main purpose of a disposal facility is to isolate the waste from the biosphere. When considering a
disposal facility, the capability to isolate the waste must be considered and this capability should not
be related to the depth itself but to depth related properties.
Depth related properties should be considered in order to impede or minimize radionuclide migration.
Over time containment of the radionuclides cannot be assured, therefore isolation from the biosphere
needs to be considered. The biosphere is defined in the glossary as:
Biosphere That part of the environment normally inhabited by living organisms.
 In practice, the biosphere is not usually defined with great precision, but is
generally taken to include the atmosphere and the Earth’s surface, including
the soil and surface water bodies, seas and oceans and their sediments. There
is no generally accepted definition of the depth below the surface at which soil
or sediment ceases to be part of the biosphere, but this might typically be taken
to be the depth affected by basic human actions, in particular farming.
 In waste safety in particular, the biosphere is normally distinguished from the
geosphere.
Measures for the protection of the biosphere may include means other than depth itself, such as:
impermeability to water, dissolution, leach rate and solubility; retention of radionuclides; and
retardation of radionuclide migration. Some of these properties are related to the geosphere and may
be depth related and may be used to impede and minimise the transport of radionuclides to the
biosphere. Over time the migration of longer lived radionuclides in a disposal facility may be
inevitable. The use of geological conditions at certain depths will assist in impeding the migration of
the radionuclides but the bulk of the geosphere may be sufficient to provide isolation.
The required performance concerning radionuclide migration can be graded to the activity level of the
waste with respect to the long-term protection of man and environment.
6
Institutional control and human intrusion
Specific Safety Requirements No. SSR-5 provide that
“after its closure, the safety of the disposal facility is provided for by means of passive
features inherent in the characteristics of the site and the facility and the characteristics
of the waste packages, together with certain institutional controls, particularly for near
surface facilities. Such institutional controls are put in place to prevent intrusion into
facilities and to confirm that the disposal system is performing as expected by means of
monitoring and surveillance.”
IAEA Specific Safety Requirements No. SSR-5 points out differences between near surface and
geological disposal with regard to the institutional control:
-
“For near surface facilities, isolation has to be provided by the location and the design of
the disposal facility and by operational and institutional controls. (…) Near surface
disposal facilities are generally designed on the assumption that institutional control has
to remain in force for a period of time. (…) The waste acceptance criteria will limit any
consequences of human intrusion to within the specified criteria, even if control over the
site is lost.”
-
“For geological disposal of radioactive waste, isolation is provided primarily by the host
geological formation as a consequence of the depth of disposal. (…) Geological disposal
facilities have not to be dependent on long term institutional control after closure as a
safety measure. Nevertheless, institutional controls may contribute to safety by preventing
or reducing the likelihood of human actions that could inadvertently interfere with the
waste or degrade the safety features of the geological disposal system.”
The maximum duration of the institutional control period that may be applied to a specific disposal
facility should be equal to or less than the maximum duration of the societal capability to control the
land use with time. This maximum duration is generally considered as restricted to a few hundred
years. For instance a 500 years limit is considered in France in their national safety guides. For any
repository project, an institutional control period after closure should be defined consistently with the
half-life and activity level of the disposed waste and with the type of repository. Specific Safety
Requirements No. SSR-5 indicates that for short lived waste disposed of in near surface disposal
facilities, “the period [of the institutional control] will have to be several tens to hundreds of years
following closure.” IAEA safety standards do not impose any minimum duration for the institutional
control of geological disposal after closure.
For remote sites, the need to take active measures to avoid human intrusion may be different for sites
located near people provided a limited timescale for the safety case is appropriate.
Regardless of the waste type and the depth of the disposal facility, the safety case cannot rely on
institutional periods longer than several hundred years. Human intrusion scenarios must be considered
in the safety case after the end of the institutional control period. The type of intrusion scenario is
depth dependent. For very low depths civil works are to be considered such as tunnel boring. For
higher depths human intrusion can be by drilling. Additionally site characteristics may lead to
potential mining or the construction of underground storage facilities. It is generally considered that
the deeper the disposal facility, the likelihood of human intrusion decreases.
Taking into account human intrusion scenarios in the safety case leads to identify limits for the
acceptable residual activity within the waste after the institutional control period. Consistently this also
justifies the duration of the institutional control which should be implemented as necessary.
Because of its maximum duration restricted to several hundred years, the institutional control has an
influence only on the initial amount of short lived radionuclides in the waste. The acceptable content
in long lived radionuclides is a function of the type of intrusion scenarios to be considered and
therefore a function of repository depth.
7
Waste packaging
Packaging is required to provide safe containment of the waste during handling, storage, transportation
and disposal. Waste packages shall meet the waste acceptance requirements of the individual storage
and/or disposal facilities. They can vary widely in their design complexity [IAEA Tecdoc 1572 with
modifications]
ILW waste may consist of metallic waste, concrete rubble, liquid waste, sludge, filters, ion exchange
and dry active waste. Most of these waste streams need to be appropriately conditioned and packaged
for storage, transportation and disposal. Desirable characteristics of waste packages include the
following:
 Limiting of the gross mass (important for both handling and stacking in
engineered structures).
 Acceptable compressive strength and minimal void space to ensure the stability
and stackability of waste packages, and the stability of the storage/disposal
facility against subsidence.
 Absence of free liquids to prevent contamination and activity release, to
prevent damage to the containers during handling, and to prevent corrosion of
the waste packages.
 Restriction of the fissile material content to prevent nuclear criticality incidents,
particularly in the event that the packages are exposed to water during storage
or disposal.
 Management of organic substances (e.g. decontamination solvents) that exhibit
chelating or complexing behaviour.
 Physical and chemical compatibility between waste and immobilization/
encapsulation materials.
 Ability of the package to withstand various accident conditions, such as fire or
drop/impact events.
 Immobilization of radionuclides consistent with the requirements of waste
acceptance criteria for the disposal facility.
Waste containers generally contribute to waste package and repository performance by delaying the
release of radionuclides, thereby allowing short-lived radionuclides to decay prior to their
mobilization. The container lifetime is one component used in the safety case to demonstrate the risk
criteria with respect to long-term releases of radioactivity to the environment, particularly for near
surface repositories.
While LILW waste packages are primarily selected for transportation, handling and operational
purposes, their degradation may become of concern for long-term safety considerations. As a result,
the resistance of these packages to degradation is one of the principal characteristics of the waste
package. The confinement of radionuclides and structural integrity of the waste package, in other
words its durability, may contribute to reducing the risks to the public from disposal of ILW to
acceptable levels as a function of the respective role of each component of the entire containment
system.
Factors affecting the waste container’s durability during disposal need to be studied in the context of
the design life of the whole repository barrier system, and its host environment. Due to differences in
the variety of ILW wastes, the relative importance of particular mechanisms may be important. For
example, decommissioning wastes will contain much more metal than operational wastes and,
therefore, corrosion and gas generation are considered to be more important. For metallic containers,
corrosion performance is an important indicator of container integrity and lifetime. Therefore, it is
essential to establish underlying corrosion scenarios that contribute to container failure for the various
types of material. Corrosion scenarios may need to consider swelling, gas generation and loss of
integrity.
Carbonation rate, degradation due to chemical and mechanical attack, and corrosion of reinforcing
metals need to be considered in order to estimate the lifetime of concrete containers. Polymercontainer materials (HDPE), on the other hand, are not susceptible to corrosion; although creep,
embrittlement, and irradiation-induced degradation can affect their durability.
Along with containment, wastes packages should be designed with respect to the mechanical and
chemical of the other components of the natural and engineered containment system.
The waste form itself provides certain radionuclide containment. The physical-chemical properties of
the waste form, including the nature of the contaminant, and its compatibility with other engineered
barriers and specific environmental conditions, will determine the rate of radionuclide release. Once
the container degrades, giving rise to access of water to the waste, releases of radionuclides are
determined primarily by the properties of the waste form. Moreover, decommissioning may produce a
number of large components (i.e. steam generators, control rods, pumps, and motors.), for these, the
waste form in itself may be necessary to limit radionuclide releases.
#FURTHER DEVELOPMENT OF THIS SECTION TAKEN INTO CONSIDERATION.
CONSIDERATION SHOULD BE TAKEN TO SUBDIVIDE THIS SECTION INTO SECTIONS
REGARDNING OPERATIONAL ASPECTS, LONG TERM PERFORMANCE, PROTECTION OF
WORKERS ETC.#
8
Characteristics of the disposal facility
Specific Safety Requirements No. SSR-5 specify that: “the disposal facility and its engineered barriers
shall be designed to contain the waste with its associated hazard, to be physically and chemically
compatible with the host geological formation and/or surface environment, and to provide safety features
after closure that complement those features afforded by the host environment. The facility and its
engineered barriers shall be designed to provide safety during the operational period. The designs of
disposal facilities for radioactive waste may differ widely, depending on the types of waste to be disposed
of and the host geological formation and/or surface environment. In general, optimal use has to be made of
the safety features offered by the host environment. This has to be done by designing a disposal facility that
does not cause unacceptable long term disturbance of the site, is itself protected by the site and performs
safety functions that complement the natural barriers. The layout has to be designed so that waste is
emplaced in the most suitable locations.”
Specific Safety Guide No. SSG-14 relating to Geological Disposal Facilities for Radioactive Waste
provides design guidelines which can be applied to disposal facilities for ILW. Draft Safety Guide DS 356
relating to Near Surface Disposal Facilities for Radioactive Waste can also be used in a complementary
way. It stipulates in particular that: “The initial design of the facility should be used to validate the
suitability of a candidate site for the disposal facility. The design of the facility, the physical characteristics
of the site, and the characteristics of the waste or inventory are mutually interdependent and need to be
managed in such a way that a set of independent and complementary safety functions can be proposed in
order to achieve the desired performance of the disposal system. The initial design of the facility should be
used to demonstrate that the site, in combination with the design of the facility and the characteristics of
the waste, will provide adequate containment and isolation of radionuclides for the necessary period of
time.”
Taking into account these existing or draft guidelines, there is no need for specific guidance for ILW.
As a function of the ILW characteristics one can use either SSG-14 or DS-356.
Taking into account the volume of ILW (section 3.1) the number of waste packages per disposal cell
or pit and its volume has to be optimized with regard to the footprint of the disposal facility whereas
the optimisation of the design of an HLW disposal facility is generally driven by heat generation.
However some ILW may generate heat which should not be neglected in the facility design. Then
provision needs to be made in the design and spacing of the disposal cells to dissipate heat to comply
with temperature limits assigned to:
- engineered and natural materials with respect to their safety functions and
- operational conditions (protection of people and operating systems).
The materials used to construct the disposal cells and pits are to be chosen with regard to their
potential impact on the degradation of the waste form and package and on the dissolution and retention
of radionuclides. The differences of the waste forms between ILW and HLW may lead to the use of
significantly different materials. For instance cement is not considered in the near-field of a HLW
disposal facility in many countries but the use of concrete is often envisaged for ILW. On the other
hand, materials used for LLW and ILW are often similar.
The engineered and natural materials in the near-field also need to be chosen taking into account
potential chemical disturbances induced by some ILW (e.g. nitrate resistant cement).
As necessary gas generated by ILW such as radiolysis induced hydrogen needs to be managed during
the operational phase to protect workers. This may include removal of gas via a ventilation system.
The facility also needs to be designed to account for gas generation during closure and beyond.
The selected depth needs to be considered in the final facility design. In particular engineered
structures need to resist hydrostatic pressures and in situ stresses at the chosen depth with respect to
the protection of workers and facility during operation and to long term safety functions. This may
affect the sizing of the disposal cells/pits, the distance between them, the dimensions of the rock
support and other engineered structures. The above considerations apply to either underground works
as for geological disposal of HLW or on open pits equipped with an engineered cover.
9
Waste acceptance criteria
As with any other disposal facility, the establishment of waste acceptance criteria is essential to ensure
the continued validity of the safety case. In the case of an ILW disposal facility, it is important to
recognize that due the large variety and complexity of the ILW waste, the waste acceptance criteria
will need to be reviewed and adjusted if required. Any changes of the waste acceptance criteria will
need to keep in mind the boundaries of the safety case.
Paragraph 6.38 in SSG-14 identifies some issues to consider in the waste acceptance criteria that are
also applicable to ILW waste.
(a) The permissible range of chemical and physical properties of the waste and
the waste form;
(b) The permissible dimensions, weight and other manufacturing specifications
of each waste package;
(c) Allowable levels of radioactivity in each package;
(d) Allowable amounts of fissile material in each package;
(e) Allowable surface dose rate and surface contamination;
(f) Requirements for accompanying documentation;
(g) Allowable decay heat generation for each package.
10
Facilities for ILW – examples
[Needs to be improved and completed by Member States]
Canada:
 Intermediate level waste disposal facility at 683m. The reason for choosing this depth is a
suitable host formation at that depth, not the depth itself. In the facility also LLW will be
disposed.
France:
 SL-ILW co-disposed with SL-LLW in a near-surface facility.
 LL-ILW planned at 500m, the reason for choosing this depth is a suitable host formation at
that depth, not the depth itself. However, regulations require a depth of more than 200m for
this kind of waste. In this facility, CIGEO, HLW will also be disposed.
 LL-LLW, disposal concept not yet decided. Siting and conceptual design is still ongoing.
Depth will at least be around 15m or more due to geological properties (hydrogeological and
chemical) at the site.
Germany:
Waste classified based on heat generation
 Heat generating waste, will probably be co-disposed with spent nuclear fuel and HLW.
 Non-heat generating waste will be disposed of in the Konrad repository at a depth between
800m and 1200m, the chosen depth is due to geology at the site.
 LLW and SL-ILW has been disposed of at the Morsleben repository at a depth of about 500m
in a former salt mine.
Sweden:
 SL-ILW is co-disposed with LLW in the SFR facility. The depth of the facility is between 70
and 120 m. The depth of the facility was selected based on the geological properties
(hydrogeological) at the site.
 LL-ILW, design of the facility is ongoing.
USA
 LL-ILW from defence disposed of in the WIPP disposal facility at a depth ~655 m. The reason
for choosing the depth is geological conditions at the site.
Country X…NEED TO EXPAND
11
Summary
Intermediate-level waste (ILW) is, from a disposal and safety case perspective, situated between lowlevel waste which can be disposed of in a near surface facility and high-level waste that must be
disposed in a deep geological formation. ILW may be roughly categorized into two main groups. One
group of ILW contains a relatively high activity, but a low content of long lived radionuclides whereas
the other group has a relatively high content of long lived radionuclides, but with low to moderate
activity. The volume of ILW is usually more significant than HLW. This justifies the treatment of
ILW as separate waste stream(s).
For some ILW with significant amounts of uranium or plutonium, criticality and safeguards can be an
issue. Also heat generation can be an issue for the sizing of disposal cells for some ILW. Concerning
chemtoxicity the situation of some ILW waste can be similar to LLW waste whereas it is not an issue
with HLW waste. With regard to mechanical and chemical disturbances induced by the waste
packages, the properties of ILW are generally closer to low level waste characteristics than to HLW
characteristics. Regarding dose rates, potential surface contamination and resistance of the waste
packages to operational hazards, such as fire and drop scenarios, provision in the design regarding
these factors are to be graded to the activity level of the waste.
It is not recommended to discuss an ILW disposal facility only in terms of depth but rather by
considering many influencing properties that can provide an acceptable degree of containment and
isolation. The depth of the disposal facility should be primarily determined based on a set of site
specific properties, such as site geology, permafrost and glaciation, erosion, redox, as well as waste
properties and facility design.
Whatever the type of waste and the repository depth, the safety case has to define an appropriate timescale. It must be consistent with the natural evolution of the site and the considered depth on the one
hand, and with the characteristics of the waste, in particular the reduction of activity with time as a
function of the half-life of radionuclides. An assessment timescale over 1 million years may require
disposal in a deep geological formation. An assessment timescale between 10,000 and 100,000 years
may result in disposal at a swallower depth. The acceptable content of long lived radionuclides is a
function of the applicable time scale.
The safety case cannot rely on institutional periods longer than a few hundred years. Human intrusion
scenarios must be considered in the safety case after the end of the institutional control period. The
type of intrusion scenario is depth dependent. This leads to the identification of limits for the
acceptable residual activity within the waste after the institutional control period. The institutional
control has an influence only on the initial amount of short lived radionuclides in the waste. The
acceptable content in long lived radionuclides is a function of the type of intrusion scenarios to be
considered and therefore a function of repository depth.
The design considerations for an ILW disposal facility are typically no different than for other types of
disposal facilities; however, the final design will be specific to the characteristics of the waste, for
instance the construction material used and the volume size of the cells or pits.
The large variety and the composition of the ILW waste needs to consider various issues that is not
associated with a HLW waste such as gas generation and compatibility between different waste types
as well as between the waste and the engineering system. These issues are however more related to
LLW waste.
Paragraph 6.38 in SSG-14 identifies some issues to consider in the waste acceptance criteria that are
also applicable to ILW waste.
12
Conclusions/Recommendations
1. It is recommended to revisit the definition of the ILW (GSG-1) to potentially provide more
flexibility. Consideration on long-lived LLW and short-lived ILW could be included without
imposing the types of disposal facilities in the sense of near surface or geological.
2. Historically, the depth has been associated with the class of wastes, e.g. LLW is associated
with near-surface disposal. This has resulted in confusion with respect to disposal facilities for
ILW. The depth of the disposal facility should be adapted to the characteristics of the waste
such as the half-life as well as site-specific geological and technological features.
3. Consideration should be given to one or more separate waste streams for ILW as a function of
half-life.
4. Some ILW can be characterized by intermediate half-life nuclides (radium 226, carbon 14 or
americium 241) which are compatible with an intermediate timescale that can be used in the
safety case. This timescale lies between short-lived LLW and HLW.
5. ILW has a higher diversity than HLW and different mechanisms, in particular interactions
between the waste and its environment, are to be considered in the design and safety case.
6. ILW waste streams needs development of specific disposal options which can be co-located or
not with other types of waste.
7. While developing disposal options for ILW, the existing IAEA safety guides relating to LLW
and HLW can be used as appropriate.
8. This report can constitute a first draft in the development of a TECDOC of which the purpose
is to assist in the use of existing guides for the development of ILW specific disposal facilities.
9. On this basis, existing guides could be updated to make them more efficient for ILW for
instance to take into consideration all potential characteristics of ILW and to adapt the
wording.
13
References
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IAEA Safety Guide SSG-14
draft IAEA Safety Guide DS 356
IAEA Safety Guide GSG-1
IAEA safety glossary
Nuclear Energy Series No.NW-T-1.20