Generic Waste Package Specification

NDA Report no. NDA/RWMD/067

Geological Disposal Generic Waste Package Specification March 2012

NDA Report no. NDA/RWMD/067

Geological Disposal Generic Waste Package Specification March 2012

NDA/RWMD/067

Conditions of Publication This report is made available under the NDA Transparency Policy. In line with this policy, the NDA is seeking to make information on its activities readily available, and to enable interested parties to have access to and influence on its future programmes. The report may be freely used for non-commercial purposes. However, all commercial uses, including copying and re-publication, require permission from the NDA. All copyright, database rights and other intellectual property rights reside with the NDA. Applications for permission to use the report commercially should be made to the NDA Information Manager. Although great care has been taken to ensure the accuracy and completeness of the information contained in this publication, the NDA can not assume any responsibility for consequences that may arise from its use by other parties. © Nuclear Decommissioning Authority 2012. All rights reserved. ISBN 978-1-84029-451-4

Bibliography If you would like to see other reports available from NDA, a complete listing can be viewed at our website www.nda.gov.uk, or please write to the Library at the address below.

Feedback Readers are invited to provide feedback to the NDA on the contents, clarity and presentation of this report and on the means of improving the range of NDA reports published. Feedback should be addressed to: Dr Elizabeth Atherton, Head of Stakeholder Engagement and Communications, Nuclear Decommissioning Authority (Radioactive Waste Management Directorate), Curie Avenue, Harwell Oxford, Didcot, Oxon, OX11 0RH, UK

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Executive Summary We, the Nuclear Decommissioning Authority (NDA), have been charged with implementing Government policy for the long-term management of higher activity radioactive waste, as defined by the Managing Radioactive Waste Safely (MRWS) White Paper, by planning, building and operating a geological disposal facility (GDF) in the UK. A GDF is an engineered facility for the disposal of radioactive waste. It will be located at a depth of between 200m and 1,000m below ground, in a geology that provides long-term isolation of the wastes from the human environment. The wastes destined for disposal in a GDF comprise those not considered suitable for near surface disposal (i.e. high level waste, intermediate level waste and some types of low level waste). There are also other nuclear materials that have not been declared as wastes by the Government (because they are still considered to be of potential use), but which might be the subject of geological disposal in the future, namely spent nuclear fuel, separated plutonium and uranium. A key aspect of the MRWS White Paper is that it envisages that the Radioactive Waste Management Directorate (RWMD) of the NDA will evolve into the organisation responsible for the delivery of a GDF. As implementer and future operator of a GDF, and therefore as the ultimate receiver of waste for disposal, RWMD will be responsible for the production of waste acceptance criteria (WAC) for the facility. While plans for the construction of a GDF remain at an early stage, the information necessary to define WAC is not available. In the meantime, and as a precursor to the final WAC, we produce generic specifications for packaged waste, the primary purpose of which are to provide a baseline against which the suitability of plans to package waste for disposal can be judged. By providing such a baseline we assist the holders of radioactive waste in the development and implementation of such plans by providing confidence that the resulting waste packages would be compatible with the anticipated needs for transport to and disposal in a GDF. The purpose of this Generic Waste Package Specification is to define high-level generic requirements for waste packages containing all categories of higher activity waste which will be subject to geological disposal. It represents the highest level document in a hierarchy of packaging specifications which have been produced to satisfy the needs of all who have an interest in geological disposal in general and the packaging of waste in particular.

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List of Contents Executive Summary

iii

1

Introduction

1

1.1

Structure of this document

2

2

The need for waste package specifications

3

2.1

Specifications for packaged waste

4

2.2

Application of the packaging specifications

5

3

The definition of packaging specifications

7

3.1

The Disposal System Specification

7

3.2

The Disposal System Safety Case

8

3.3

The form of the RWMD packaging specifications

9

4

The definition of waste package safety functions

11

4.1

Guidance on the role of the waste package

11

4.2

The identification of waste package safety functions

12

4.3

The identification of packaging criteria

14

4.4

Linking the packaging criteria to the waste package safety functions

16

5

High-level requirements for waste packages

17

5.1

Requirements for waste containers

17

5.2

Requirements for wasteforms

18

5.3

Requirements for waste packages

18

5.4

Requirements for the manufacture and storage of waste packages

19

6

Summary

21

Appendix A

Glossary of terms used in this document

References

23 27

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Abbreviation and acronyms used in this document CoRWM

Committee on Radioactive Waste Management

DSS

Disposal System Specification

DSFS

Disposal System Functional Specification

DSSC

Disposal System Safety Case

DSTS

Disposal System Technical Specification

EBS

engineered barrier system

GDF

geological disposal facility

GWPS

Generic Waste Package Specification (this document)

IAEA

International Atomic Energy Agency

LoC

Letter of Compliance

MRWS

Managing Radioactive Waste Safely

NDA

Nuclear Decommissioning Authority

RWMD

Radioactive Waste Management Directorate

WAC

waste acceptance criteria

WPS

Waste Package Specification

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1

Introduction

In 2001 the UK Government initiated the Managing Radioactive Waste Safely (MRWS) programme with the aim of finding a practicable solution for the long-term management of the UK’s higher activity radioactive wastes. Underpinning this aim was a need to achieve long-term protection of people and the environment in an open and transparent way that was based on sound science and that made effective use of public monies. In June 2008, in response to recommendations from the Committee on Radioactive Waste Management (CoRWM) [1], the UK Government published the MRWS White Paper [2]. The White Paper confirmed the Government’s acceptance of CoRWM’s recommendation that geological disposal is the best available approach for the long-term management of higher activity radioactive wastes 1 and other radioactive materials 2. It also sets down the framework by which the geological disposal option is to be implemented. A key aspect of the MRWS White Paper is that it envisages that the Radioactive Waste Management Directorate (RWMD) of the Nuclear Decommissioning Authority (NDA) will evolve into the organisation responsible for the delivery of a geological disposal facility (GDF). As implementer and future operator of a GDF, and therefore as the ultimate receiver of waste for disposal, RWMD will be responsible for the production of waste acceptance criteria (WAC) for the facility. While plans for the construction of a GDF remain at an early stage, the information necessary to define final WAC is not available. In the meantime, and as a precursor to the final WAC, we produce generic specifications for packaged waste. A key purpose of the publication of these ‘packaging specifications’ is to provide a baseline against which the suitability of plans to package waste for disposal can be judged. By providing such a baseline we assist the holders of radioactive waste in the development and implementation of such plans, by providing confidence that the resulting waste packages would be compatible with the anticipated needs for transport to and disposal in a GDF. The purpose of this Generic Waste Package Specification (GWPS) is to define high-level requirements for all designs of waste package, containing any type of radioactive waste, which will be subject to geological disposal. It is aimed at a wide range of stakeholders, but primarily at those who have a interest in the principles that underlie our approach to the packaging of radioactive waste for geological disposal, and who are not directly involved in such packaging. The generic packaging requirements defined herein are drawn from a number of key documents notably the generic Disposal System Specification (DSS) and the generic Disposal System Safety Case (DSSC). They form a basis from which more detailed packaging specifications, for waste packages containing the different types of waste and for specific designs of waste packages, are developed.

1

These comprise radioactive wastes not deemed suitable for disposal in a near surface facility; i.e. high level waste, intermediate level waste and certain types of low level waste.

2

The MRWS White Paper identifies these materials, which may be declared as waste in the future, as spent fuel from UK nuclear reactors, plutonium produced by the reprocessing of such fuel and uranium arising from a range of fuel manufacture and reprocessing activities.

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1.1

Structure of this document

The remainder of this document is structured in the following manner: •

Section 2 introduces the role played by packaging specifications in the preparation of radioactive waste for geological disposal.

•

Section 3 sets out the basis for the definition of the packaging specifications by reference to the primary sources; the generic DSS and the generic DSSC. This Section also outlines the hierarchy of packaging specifications and the role they play in assessing the disposability of waste packages.

•

By reference to UK regulatory guidance, international precedent and guidance, and the DSS and DSSC, Section 4 defines waste package safety functions which are used as the basis for the identification of a series of packaging criteria.

•

In Section 5 the packaging criteria are set out as a series of high level qualitative packaging requirements.

•

The document is summarised in Section 6.

•

A glossary of important terms and phrases is presented in Appendix A.

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2

The need for waste package specifications

The MRWS White Paper sets out the Government’s framework for the long-term management of the UK’s higher activity waste 3, a key aspect of which is the ‘geological disposal, coupled with safe and secure interim storage’ of such waste. Whilst the precise manner in which geological disposal would be implemented in the UK is not yet defined, we envisage that any such approach to the long-term management of higher activity waste in this manner would comprise a number of distinct stages. These could include: •

the manufacture of passively safe and disposable waste packages;

•

a period of interim surface storage, usually at the site of waste arising or packaging;

•

transport of the waste packages to a GDF;

•

transfer of waste packages underground and emplacement in the disposal facility;

•

backfilling of the disposal areas; and

• eventual sealing and closure of the facility. The exact nature, timing and duration of each stage would depend on a number of criteria, including the geographical location and host geology of a GDF, as well as the disposal concept selected for implementation for each distinct type of waste. The key aim of all of the geological disposal systems implemented or under development worldwide is the containment and isolation of radionuclides and other hazardous materials associated with the waste, the former being achieved by the use of multiple barriers. The barriers provided by a geological disposal system are illustrated schematically in Figure 1 and can include those provided by: •

the engineered barrier system (EBS) comprising: o

•

the waste package consisting of: ƒ

the contents of the waste package, or wasteform 4; and

ƒ

the waste container.

o

any engineered buffer/backfill placed around the waste package;

o

mass backfill in the rest of the underground excavations, and;

o

sealing materials.

the surrounding geology, consisting of: o

host rocks;

o

overlying strata.

3

The use of the description ‘higher activity waste’ from hereon encompasses all radioactive wastes and other radioactive materials identified in the MRWS White Paper as being potentially destined for geological disposal.

4

A wasteform may comprise waste which has been immobilised (e.g. by the use of an encapsulant) or that which has received more limited treatment prior to packaging (e.g. size reduction or drying).

3

NDA/RWMD/067 The effectiveness of the disposal system relies on these barriers working together to ensure that radionuclides and other hazardous materials associated with the waste will not return to the surface at levels that could cause harm to people or the environment.

Figure 1

Schematic representation of the multiple barrier concept for geological disposal

As shown in Figure 1 the barrier provided by the waste package can be considered to comprise two components, these being provided by the waste container and the wasteform. The relative contributions of each of these two components will depend on the physical and chemical nature of the waste, the manner in which it has been prepared for disposal and the design of the waste container.

2.1

Specifications for packaged waste

Much of the waste destined for geological disposal does not arise in a form that is immediately suitable for such disposal. It must therefore be treated or ‘conditioned’ and packaged in such a way as to render it: •

passively safe, such that it can be managed safely with the minimum need for active safety systems, monitoring or prompt human intervention;

•

capable of safe handling during interim storage 5, transport to and emplacement in a GDF; and

•

‘disposable’, in that it can be shown to be compliant with all the relevant regulations and safety cases for transport to and disposal in a GDF. In order that wastes can be converted into passively safe and disposable forms, as soon as is reasonably practicable, we produce generic packaging specifications. These specifications define the standard features and performance requirements for waste

5

It is expected that many waste packages will need to be stored, either at their site of manufacture or elsewhere, pending the availability of a GDF.

4

NDA/RWMD/067 packages which are compatible with the anticipated systems and safety cases for transport to and disposal in a GDF. We produce packaging specifications with a number of specific purposes in mind: •

To support the development of our plans for the implementation of geological disposal for higher activity radioactive waste;

•

To provide the UK nuclear industry and regulators with a clear definition of the requirements for packaged waste in advance of the construction of a GDF;

•

To provide a basis for the assessment of the suitability of plans to package waste to produce disposable waste packages and thereby permit the early packaging of waste; and

•

To permit scrutiny of this aspect of our plans to implement geological disposal for higher activity waste in the UK. In this way they play an important part in determining the disposability of waste packages (see Section 2.2.1) and may therefore be considered as the preliminary WAC for a future GDF. This approach to the definition of packaging specifications in lieu of WAC is consistent with that outlined in guidance produced by the International Atomic Energy Agency (IAEA) [3] and adopted in a number of countries worldwide.

2.2

Application of the packaging specifications

The production of packaging specifications plays an important role in ensuring the safe and efficient preparation of waste for geological disposal. In particular they provide a baseline against which the suitability of proposed waste packages for geological disposal can be judged.

2.2.1 Assessing the disposability of waste packages We have established a Disposability Assessment Process which we use to support the UK nuclear industry’s ongoing work on the conditioning and packaging of higher activity wastes for eventual disposal in a GDF. The process also supports our work to develop safety cases and enables us to test and populate them with information from real waste packages. The process is designed to evaluate the properties of proposed waste packages and to assess their safety performance, to determine whether they are likely to be disposable. This process tests whether the proposed waste packages comply with our packaging specifications, and thereby with the disposal concepts identified in the DSS, the safety cases for transport and disposal and are in line with regulatory expectations for the long term management of the waste [4]. The compliance of proposed waste packages with all of these requirements is signified by the issue of a Letter of Compliance (LoC) which indicates our endorsement of the disposability of that specific design of waste package. The process also serves to identify wastes that could challenge the disposal concepts that we have identified as being suitable for the geological disposal of the different types of higher activity waste. This permits early consideration of the changes that may be required to these concepts to permit these wastes to be accommodated in the GDF, and whether a case exists to justify such changes.

2.2.2 Disposability Assessment Policy and Principles The philosophy that underpins our approach to the assessment of the disposability of waste packages is set out in our Disposability Assessment Policy and Principles (DAPPs), which have been produced with the objectives of: •

providing a succinct policy statement to summarise the purpose of our work in support of waste packaging and disposability assessment;

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NDA/RWMD/067 •

setting down the underlying principles governing the provision of disposability assessments and the issue of LoCs; and

•

setting down the conditions under which a LoC can be issued, and the status of that LoC, at each stage of the assessment process. The DAPPs, which are applicable to the packaging of all types of waste that may be the subject of geological disposal, are defined in such a manner as to align with Government policy 6 and regulatory guidance [4]. They also reflect the NDA mission statement to adopt a safe and cost effective approach to the management of waste and the reduction of the hazard posed by such waste.

6

As defined in the MRWS White Paper [2].

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3

The definition of packaging specifications

In order for packaging specifications to play an effective role in assessing the disposability of waste packages they must reflect all of the relevant aspects of the disposal system. Specifically waste packages must be physically compatible (i.e. by virtue of their dimensions, weight and handling features) with the handling systems anticipated for transport and disposal. It will also be necessary that their contents and performance can be shown to be compliant with the assumptions underpinning the safety cases for the geological disposal system. Our process for the development of the geological disposal system is illustrated in Figure 2, which shows how the packaging specifications, in their role as preliminary WAC, are outputs of the process. As such they are founded on the DSS, the generic designs of the transport and disposal systems, and the safety assessments that comprise the DSSC.

Figure 2

3.1

Iterative development of the geological disposal system

The Disposal System Specification

As part of our programme for the implementation of geological disposal in the UK and to set out a clear definition of the requirements of the disposal system we have developed the generic DSS. These requirements include regulatory and stakeholder requirements, as well as a consideration of the nature, characteristics and quantities of the wastes that are destined for disposal. As shown in Figure 2 the development of the DSS, and the associated disposal system designs, is an iterative process supported by assessments of safety, environmental effects and cost. Accordingly the DSS will be periodically updated, as appropriate, to take into

7

NDA/RWMD/067 account the results from work on the waste inventory, engineering design, site investigations, safety, environmental and sustainability assessments, consideration of security and safeguards issues, R&D, and public and stakeholder engagement. The DSS comprises two documents: •

The Disposal System Functional Specification (DSFS) [5], the purpose of which is to identify and document the overall objectives and constraints of the disposal system. It describes the high-level requirements for the disposal system and is in a form suitable for a wide range of stakeholders;

•

The Disposal System Technical Specification (DSTS) [6], which underpins and develops the high-level DSFS by describing in more detail and justifying the requirements for and constraints on the disposal system. It defines the scope and bounds of the engineering design work and provides the designers of the disposal system with the requirements that must be satisfied. The DSTS is a starting point for the development of geological disposal system designs, which are detailed in the following documents: •

The Generic Disposal Facility Designs report [7] which provides information on the potential designs for the GDF systems for the different types of waste that could be used in a GDF constructed in a range of geological environments; and

•

The Generic Transport System Designs report [8] which sets out the designs of the systems that will be required to transport waste packages containing the different types of waste to a GDF.

3.2

The Disposal System Safety Case

As a means of presenting the methods, evidence and arguments by which we demonstrate the safety of our plans for geological disposal we have developed the generic DSSC [9]. As shown in Figure 2 the DSSC is founded on the generic DSS and the designs of the systems assumed for the transport and disposal of waste packages. The DSSC comprises a suite of documents (Figure 3) which consider the safety of all relevant aspects of the long-term management of the waste following its export from interim storage. This includes: •

the transport of waste packages to a GDF;

•

the construction, operation, decommissioning and closure of the disposal facility; and

•

the safety of the disposal facility in the very long term, after it has been sealed and closed 7. The DSSC also includes documents which summarise the current status of the underlying science base in key areas of relevance to geological disposal, such as waste package longevity, radionuclide behaviour and criticality safety.

7

This period being generally referred to as the ‘post-closure period’.

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Figure 3

3.3

Main components of the generic DSSC

The form of the RWMD packaging specifications

The purpose of this GWPS is to define high-level generic requirements for waste packages containing any type of radioactive waste which could be subject to geological disposal. It is the highest level document in a hierarchy of packaging specifications illustrated in Figure 4.

Figure 4

Hierarchy of the RWMD packaging specifications

The hierarchy comprises three ‘levels’ of packaging specifications in which each successive level represents an increasing degree of specificity, both to the nature of the waste and the design of the waste package. Each of the levels in the hierarchy satisfies a specific function and is produced for a particular audience: •

The Generic Waste Package Specification: Defines high-level requirements for all waste packages destined for disposal in a GDF. It is aimed at industry regulators and stakeholders who are not directly involved with the packaging of waste.

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NDA/RWMD/067 •

Generic Specifications: Define generic requirements for all waste packages that will be disposed of in accordance with a specified concept or range of concepts, and which will encompass waste packages containing wastes with similar radiological characteristics. They are produced for industry regulators and for use by waste packagers involved in the development of new or innovative packaging proposals.

•

Waste Package Specifications (WPS): Define, where applicable, quantitative requirements for waste packages containing a specific type of waste and using a standardised design of waste container8. They are produced for use by waste packagers intending to use such a waste container for the packaging of waste. The definition of the packaging requirements by the successive levels of the hierarchy will in general become more specific to the waste type and waste package design. For example, in the case of the requirements for waste package identification: •

GWPS: ‘The waste package shall enable unique identification until the end of the GDF operational period’

•

Generic Specification 9: ‘The waste package shall be marked at multiple defined locations with a unique alpha-numeric identifier. The waste package shall remain identifiable by automated systems for a period of 150 years following manufacture.’

•

WPS 10: ‘The identifier shall be marked in four positions, spaced at 90º around the circumference, on the vertical surface of the waste container lifting feature. The identifier shall comprise ten OCR-A characters between 6mm and 10mm high…’

8

These are designs which have been shown to be suitable for the manufacture of waste packages which are compatible with the anticipated needs of transport and disposal.

9

For waste packages containing low heat generating waste.

10

For 500 litre drum waste packages containing low heat generating waste

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4

The definition of waste package safety functions

In this Section we identify the safety functions that waste packages must deliver by considering the fundamental role that they will play in the delivery of a safe and effective geological disposal system. We do this by reference to UK regulatory guidance and to international standards and guidance, which outline the high level requirements for the safety of geological disposal in general and how those requirements apply to waste packages in particular.

4.1

Guidance on the role of the waste package

The IAEA Specific Safety Guide for geological disposal facilities [10] states that: ‘The objective of geological disposal of radioactive waste is to provide containment and isolation of the radionuclides in the waste from the biosphere.’ The most immediate barriers that provide containment of radionuclides in a GDF are those provided by the waste package. This is epitomised by the IAEA Specific Safety Requirements for the Disposal of Radioactive Waste [11] in which Requirement 8 (Containment of radioactive waste) states that: ‘The engineered barriers, including the waste form and packaging, shall be designed, and the host environment shall be selected, so as to provide containment of the radionuclides associated with the waste.’ This also highlights the dual nature of the barrier provided by the waste package, which can be considered to comprise two distinct components, each of which can act as a barrier in its own right: •

the waste container, which provides a physical barrier and also enables the waste package to be handled safely; and

•

the wasteform, which may provide a significant degree of physical and/or chemical containment of the radionuclides in the waste. A key aspect in the packaging of waste for geological disposal is the achievement of passive safety by waste packages. Requirement 5 of the IAEA Specific Safety Requirements [11] states that: ‘The operator shall evaluate the site and shall design, construct, operate and close the disposal facility in such a way that safety is ensured by passive means to the fullest extent possible…’ As a key component in the safety of a disposal facility, this requirement encompasses the waste packages that are disposed there and their design should include features that ensure that they will be passively safe for an appropriate period. The joint regulatory guidance on waste conditioning and the disposability of packaged waste [12] states that: ‘Waste conditioning should yield waste packages that are: •

passively safe and suitably robust physically, so as to ensure containment and safe handling…

•

suitable for safe transport …; and

•

disposable, such that the nature and properties of the conditioned waste product are compatible with the anticipated standards for eventual disposal e.g. WAC of an appropriate disposal facility.’

11

NDA/RWMD/067 With regard to the definition of WAC, for which our packaging specifications are intended to be forerunners, Requirement 13 the UK regulators’ Guidance on Requirements for Authorisation for geological disposal facilities [13] includes a requirement for the developer/operator of such a facility to: ‘…establish waste acceptance criteria consistent with the assumptions made in the environmental safety case and with the requirements for transport and handling, and demonstrate that these can be applied during operations at the facility.’ In this context the ‘requirements for transport’ are those implemented into UK law, notably the IAEA Regulations for the Safe Transport of Radioactive Material [14]. To provide a basis for the identification of the full range of safety functions that are required of waste packages we define a high-level safety function for all waste packages which encompasses both aspects of their long-term management following export from interim storage (i.e. transport and disposal): Waste packages shall be compatible with safe transport to and disposal in a GDF.

4.2

The identification of waste package safety functions

The various components of a multiple barrier geological disposal system each contribute to the achievement of the safety objectives in different ways over different timescales. During the production of the DSS and the DSSC we developed an approach which defined safety functions for each of the various components of the multiple barrier system, including that provided by the waste package. This approach is intended to provide a means of setting out what each barrier should achieve to ensure the overall safety of the disposal system. It is similar to that adopted by other national programmes and aligns with UK regulatory guidance [4].

4.2.1 Safety functions that apply to transport and GDF operations The barriers provided by the waste package will play key roles in achieving the required degree of safety during transport and will continue to do so during the operational period 11 of a GDF. For the purpose of defining high-level packaging requirements we use the DSSC [15] and the regulatory joint guidance [12] to identify five operational safety functions that are required of waste packages during transport and the GDF operational period. These require that waste packages are able to: •

Provide containment of radionuclides and other hazardous materials during normal operations and under accident conditions;

•

Limit radiation dose 12 to workers and members of the public;

•

Preclude criticality;

•

Provide the means of safe handling; and

• Withstand internal and external loads. The period for which these safety functions will be required to persist will depend on the disposal concept selected for each specific type of waste and specifically on the timescale defined for the operational period (it being assumed that, by comparison, the transport operation will be relatively short-term). Their persistence for such a time will also give

11

The operational period is assumed to extend until the time when the GDF is backfilled and closed.

12

In this context radiation dose is that which could result from exposure to direct radiation from the surface of the waste package.

12

NDA/RWMD/067 confidence that the waste packages will enter the post-closure period in an appropriate condition. The actual timescale for which the operational safety functions may need to be maintained will also depend on the period during which retrieval of the waste package is required. The MRWS White Paper states that the length of such a period will be decided at a later date in consultation with the independent regulators and local communities. In the meantime, planning for a GDF, including the packaging of waste for disposal, should be carried out in such a way that the option of retrievability is not excluded.

4.2.2 Safety functions that apply to the post-closure period During the GDF post-closure period the role the waste packages play in the multiple barrier disposal system will change. It is assumed in the post-closure safety case that waste packages will enter that period possessing properties that will enable them to continue to provide a barrier to the release of radionuclides. It is also acknowledged that over time, evolution of waste packages in the disposal environment will result in the eventual loss of those properties, following which the containment provided by the other barriers will act to maintain the overall safety of the geological disposal system. It is noted that waste packages could have a potential impact on the effectiveness of the other barriers that make up the geological disposal system, notably the other components of the EBS. For example, the chemical barrier provided by the backfill in some disposal concepts could be subject to challenges derived from waste packages, including exposure to heat, ionising radiation and/or the chemical products of waste package evolution 13. Each of these has the capability to cause localised chemical changes in the backfill, which could result in it no longer fulfilling its intended purpose. The DSTS [6] identifies the safety functions that will need to be provided by each of the barriers during the post-closure period, including those by the waste package. For the purpose of defining high-level packaging requirements we use these to identify four postclosure safety functions which require waste packages to: •

Provide containment of radionuclides and other hazardous materials;

•

Contribute to the overall performance of the EBS;

•

Contribute to ensuring that, following GDF closure, a criticality event is not a significant concern; and

• Withstand internal and external loads. The durations of the periods for which each of these safety functions will be required to persist will, as was the case for the operational safety functions, depend on the disposal concept selected for each specific type of waste. It will also depend to a significant degree on the nature of the contents of waste packages, notably the quantities of radionuclides and their half lives. For many radionuclides, the waste package can provide total containment until they and their daughters decay to insignificant levels. However, the barriers provided by the waste package will degrade progressively over time and will eventually gradually lose their ability to provide containment of longer-lived radionuclides. Further containment of radionuclides will however be provided by the other components of the EBS, and the geological barrier, which will act to delay the movement of any remaining quantities of these longer-lived radionuclides as they are released from the waste package. The isolation provided by the geological disposal system will also contribute to containment in that locating the geological disposal facility in a suitably deep and stable environment 13

These could include chemicals resulting from corrosion of the waste container and/or those released from the waste package (i.e. from the waste and/or conditioning materials).

13

NDA/RWMD/067 protects the engineered barriers, helping them to preserve their containment functions for longer periods.

4.3

The identification of packaging criteria

Following identification of the waste package safety functions, we now define the requirements for waste packages in the form of a series of packaging criteria which can be used to show that all of the necessary waste package safety functions can be achieved in practice. To aid in the identification of these packaging criteria we have used IAEA guidance on the properties of waste containers [16 14]and of waste packages and their contents [17], which have significance for their transport and disposal. Also of relevance in this process is IAEA guidance of the development of specifications for packaged waste [3], studies of the potential form of WAC for a UK GDF [18], and a consideration of the WAC produced for disposal facilities worldwide [19]. For waste containers the following criteria are identified [16]: •

Handling: shape, dimensions, lifting arrangements, gross package weight, stackability, impact resistance and gas build-up/venting systems.

•

Radiological protection: surface contamination and surface dose rate.

•

Container durability: container material, container closure and degradation of the material.

• Waste package identification. Similarly the following criteria are identified for waste packages and wasteforms [17]: •

Properties related to radioactivity: total activity, radionuclide composition, criticality safety, heat output, radiation stability, homogeneity, surface dose rate;

•

Chemical properties: chemical stability, composition, pyrophoricity, ignitability, reactivity, corrosivity, explosiveness, chemical compatibility, gas generation, toxicity, decomposition of organics.

•

Physical properties: permeability, porosity, homogeneity, density, voidage.

•

Mechanical properties: load resistance, dimensional stability, impact resistance.

•

Thermal properties: fire resistance, thermal conductivity, freeze/thaw stability.

• Biological properties: biological degradation, decomposition of organic wastes. These criteria have been used as the basis for the identification of the 14 packaging criteria which we will use throughout our packaging specifications, in the manner illustrated in Figure 5.

14

Whilst this guidance is primarily aimed at containers for use with ILW the general principles it contains are also generally applicable to waste containers that could be used for the packaging of all categories of higher activity waste.

14

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Figure 5

Derivation of packaging criteria from IAEA guidance

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4.4

Linking the packaging criteria to the waste package safety functions

The purpose of defining packaging criteria is to identify a list of waste package properties for which qualitative and/or quantitative requirements can be defined such that the waste package safety functions can be shown to be achieved in practice. The method by which each of the packaging criteria identified above are linked to the achievement of the waste package safety functions identified in Section 4.2 is illustrated in 4.4. This shows how each safety function is linked to at least one of the packaging criteria. As a result, demonstration of each safety function will be addressed by one or more of the requirements that make up the packaging specifications.

Table 1

Relevance of packaging criteria to waste package safety functions Waste package safety functions

Packaging criterion

Provide containment

Limit radiation dose

Ensure criticality safety

Provide safe handling

Withstand loads

Contribute to EBS performance

Requirements for waste containers External dimensions

9

Handling feature

9 9

Identification

9 9

Stackability Durability of integrity

9

9

9

9

Requirements for waste packages/wasteforms

9

Gross mass Surface contamination

9

Activity content

9

Gas generation

9

9 9

9

9

9

External dose rate

9

9

9

Heat output

9

Wasteform properties

9

9

9

9

Accident performance

9

9

9

9

9

9

Criticality safety

9

9

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5

High-level requirements for waste packages

In this Section we use the packaging criteria identified in Section 4 as the basis for the definition of high-level requirements for all waste packages that are to be the subject of geological disposal. The requirements defined below apply to the complete waste package as prepared for transport to and disposal in a GDF. They do not apply to any devices that may be used as part of either of those stages of geological disposal, such as overpacking containers that could be used to provide additional protection during transport, or ancillary equipment used to assist in the handling or stacking of waste packages. The consequences of the use of such devices will be included, where relevant, in the definition of packaging requirements in the Generic Specifications and the WPS. It should be noted that whilst packaging requirements are, in general, defined for the complete waste package, in practice the manner in which they are achieved will depend on a number of factors including: •

the nature of the waste container;

•

the physical, chemical and radiological properties of the waste; and

• the means by which the waste is conditioned for disposal. The requirements defined below are separated into those which are most directly related to the waste container, the wasteform, or to the waste package as a whole. In addition, a number of generic requirements are defined to be applied during the manufacture and storage of waste packages. This approach is further developed for the different specific types of waste in the Generic Specifications. In a number of the requirements defined below reference is made to waste packages meeting ‘regulatory limits’ during transport and/or the operational period of a GDF. Such limits are defined in accordance with all of the relevant UK and international regulations, as explained in our Radiological Protection Policy Manual [20], and are applied to specific designs of waste package in the relevant WPS (see Section 3.3). It should be noted that, where the words ‘shall’ and ‘should’ are used in the packaging requirements, they have the following meaning: •

‘shall’ denotes a limit which is derived from consideration of a regulatory requirement and/or from a fundamental assumption regarding the current designs of the transport or disposal facility systems;

•

‘should’ denotes a target, and from which relaxations may be possible if they can be shown not to result in any significant reduction in the overall safety of the geological disposal system.

5.1

Requirements for waste containers

5.1.1 General properties The properties of the waste container shall be such that, in conjunction with those of the wasteform, it satisfies all of the requirements for the waste package.

5.1.2 External dimensions The external dimensions of the waste package shall be compatible with the transport and GDF handling systems.

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5.1.3 Handling feature The waste package shall enable safe handling by way of the transport and GDF handling systems.

5.1.4 Stackability Where required by the transport or disposal system, the waste package shall enable safe stacking.

5.1.5 Identification The waste package shall enable unique identification until the end of the GDF operational period.

5.1.6 Durability of the integrity of the waste container The waste package shall enable safe handling by way of its handling feature until the end of the GDF operational period. The waste container shall maintain containment for as long as is required by the GDF safety case.

5.2

Requirements for wasteforms

The properties of the wasteform shall be such that, in conjunction with those of the waste container, it satisfies all of the requirements for the waste package. The properties of the wasteform shall comply with the requirements for containment within the geological disposal concept, as defined by the GDF safety case.

5.3

Requirements for waste packages

5.3.1 Activity content The activity content of the waste package shall be controlled to comply with the radionuclide related assumptions that underpin the safety cases for transport and the GDF operational period.

5.3.2 Gross mass The gross mass of the waste package shall be compatible with the transport and GDF handling systems and with the requirement for the waste package to be safely stacked.

5.3.3 External dose rate The external dose rate from the waste package shall enable safe handling of the waste package during transport and the GDF operational period, and shall comply with regulatory limits for transport.

5.3.4 Heat output The heat generated by the waste package shall be controlled to ensure that: •

thermal effects result in no significant deterioration in the performance of the waste package, or of the disposal system as a whole; and

•

regulatory limits on the surface temperature of transport packages are not exceeded.

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5.3.5 Surface contamination The non-fixed surface contamination of the waste package shall be as low as reasonably practicable and shall comply with regulatory limits for transport.

5.3.6 Gas generation The generation of bulk, radioactive and toxic gases by the waste package shall comply with the requirements for safe transport and disposal. The release of radionuclides in gaseous form from the waste package shall comply with the assumptions that underpin the safety cases for transport and the GDF operational period.

5.3.7 Criticality safety The presence of fissile material, neutron moderators and reflectors in the waste package shall be controlled to ensure that: •

criticality during transport is prevented;

•

the risk of criticality during the GDF operational period is tolerable and as low as reasonably practicable; and

•

in the GDF post-closure period both the likelihood and the consequences of a criticality are low.

5.3.8 Accident performance Under all credible accident scenarios the release of radionuclides and other hazardous materials from the waste package shall be low and predictable. The waste package should exhibit progressive release behaviour within the range of all credible accident scenarios. The impact and fire accident performance of the waste package shall comply with the assumptions that underpin the safety cases for transport and the GDF operational period. The accident performance of the waste package shall ensure that, in the event of any credible accident during the GDF operational period, the on- and off-site doses resulting from the release of radionuclides from the waste package shall be as low as reasonably practicable and should be consistent with meeting the relevant Basic Safety Levels.

5.4

Requirements for the manufacture and storage of waste packages

Adequate controls shall be established and applied to ensure that manufactured waste packages have the properties and performance required of them. Adequate controls shall be applied during any period of interim storage to ensure that waste packages retain their required properties and performance for the duration of such a period.

5.4.1 Quality management Adequate management arrangements shall be applied to all aspects of the packaging of radioactive waste, and the storage of waste packages, that affect product quality. These arrangements shall be agreed with RWMD prior to the start of the activities to which they relate.

5.4.2 Data and information recording Information shall be recorded for each waste package covering all relevant details of its manufacture and interim storage. This information shall be sufficient to enable assessment

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NDA/RWMD/067 of the characteristics and performance of the waste package against the requirements of all stages of long-term management.

5.4.3 Requirements for waste packages containing nuclear materials The management of waste packages containing nuclear material shall comply with all relevant international safeguards obligations and security requirements for their transport and disposal.

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6

Summary

The aim of this document is to define high-level requirements for all waste packages that will be the subject of geological disposal. The requirements derive directly from those defined for waste packages by the generic DSS By reference to UK regulatory guidance and international precedent and guidance we have defined a high-level safety function for all waste packages which are to be the subject of geological disposal: Waste packages shall be compatible with safe transport to and disposal in a GDF. By considering the requirements of the barriers provided by waste packages as part of a multiple barrier geological disposal system we have identified eight safety functions that must be achieved by all waste packages destined for geological disposal: •

•

During transport and the GDF operational period, waste packages are required to: o

provide containment of radionuclides and other hazardous materials during normal operations and under accident conditions;

o

limit radiation dose to workers and members of the public;

o

preclude criticality;

o

provide the means of safe handling; and

o

withstand internal and external loads.

During the GDF post-closure period, they are required to: o

provide containment of radionuclides and other hazardous materials;

o

contribute to the overall performance of the EBS;

o

contribute to ensuring that, following GDF closure, a criticality event is not a significant concern; and

o withstand internal and external loads. We have identified 14 packaging criteria by which the ability of a waste package to satisfy these safety functions can be judged and have shown the relevance of each of these criteria to the achievement of the eight waste package safety functions: External dimensions

Handling feature

Identification

Stackability

Durability of waste container integrity

Gross mass

Surface contamination

Activity content

Gas generation

External dose rate

Heat output

Wasteform properties

Criticality safety

Accident performance

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NDA/RWMD/067 We have defined high-level requirements for each of the packaging criteria in a manner that allows them to be applied to all waste packages which are to be the subject of geological disposal. These requirements will be used as the basis for the definition of Generic Specifications for waste packages containing specific types of waste, and which will in turn be used to define WPS for waste packages manufactured using standardised designs of waste container.

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Appendix A

Glossary of terms used in this document

barrier A physical or chemical means of preventing or inhibiting the movement of radionuclides. conditioning Treatment of a radioactive waste material to create, or assist in the creation of, a wasteform that has passive safety containment The engineered barriers, including the waste form and packaging, shall be so designed, and a host geological formation shall so be selected, as to provide containment of the waste during the period when waste produces heat energy in amounts that could adversely affect the containment, and when radioactive decay has not yet significantly reduced the hazard posed by the waste criticality A state in which a quantity of fissile material can maintain a self-sustaining neutron chain reaction. Criticality requires that a sufficiently large quantity of fissile material (a critical mass) be assembled into a geometry that can sustain a chain reaction; unless both of these requirements are met, no chain reaction can take place and the system is said to be sub-critical. criticality safety A methodology used to define the conditions required to ensure the continued sub-criticality of waste containing fissile material. disposability The ability of a waste package to satisfy the defined requirements for disposal. disposal In the context of solid waste, disposal is the emplacement of waste in a suitable facility without intent to retrieve it at a later date; retrieval may be possible but, if intended, the appropriate term is storage. disposal system All the aspects of the waste, the disposal facility and its surroundings that affect the radiological impact. dose A measure of the energy deposited by radiation in a target.   emplacement (of waste in a disposal facility) The placement of a waste package in a designated location for disposal, with no intent to reposition or retrieve it subsequently. engineered barrier system The combination of the man-made engineered components of a disposal facility, including the waste package, buffer, backfills and seals. fissile material Fissile material is that which undergoes fission under neutron irradiation. For regulatory purposes material containing any of the following nuclides is considered to be ‘fissile’: uranium-233, urainium-235, plutonium-239 and plutonium-241.

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NDA/RWMD/067 geological disposal A long term management option involving the emplacement of radioactive waste in an engineered underground geological disposal facility or repository, where the geology (rock structure) provides a barrier against the escape of radioactivity and there is no intention to retrieve the waste once the facility is closed. geological disposal facility (GDF) An engineered underground facility for the disposal of solid radioactive wastes. hazardous materials Materials that can endanger human health if improperly handled. As defined by the Control of Substances Hazardous to Health Regulations, 2002. higher activity radioactive waste Generally used to include the following categories of radioactive waste: low level waste not suitable for near surface disposal, intermediate level waste and high level waste. high level waste (HLW) Radioactive wastes in which the temperature may rise significantly as a result of their radioactivity, so this factor has to be taken into account in the design of storage or disposal facilities. intermediate level waste (ILW) Radioactive wastes exceeding the upper activity boundaries for LLW but which do not need heat to be taken into account in the design of storage or disposal facilities. Letter of Compliance (LoC) A document, prepared by RWMD, that indicates to a waste packager that a proposed waste package is compliant with the relevant packaging criteria and disposal safety assessments, and is therefore deemed to be compatible with the requirements for storage, transport, handling and disposal. low level waste (LLW) Defined as “radioactive waste having a radioactive content not exceeding 4 gigabecquerels per tonne (GBq/te) of alpha or 12 GBq/te of beta/gamma activity”. Managing Radioactive Waste Safely (MRWS) A phrase covering the whole process of public consultation, work by CoRWM, and subsequent actions by Government, to identify and implement the option, or combination of options, for the long term management of the UK’s higher activity radioactive waste. Nuclear Decommissioning Authority (NDA) The NDA is the implementing organisation, responsible for planning and delivering the GDF. The NDA was set up on 1 April 2005, under the Energy Act 2004. It is a nondepartmental public body with designated responsibility for managing the liabilities at specific sites. These sites are operated under contract by site licensee companies (initially British Nuclear Group Sellafield Limited, Magnox Electric Limited, Springfields Fuels Limited and UK Atomic Energy Authority). The NDA has a statutory requirement under the Energy Act 2004, to publish and consult on its Strategy and Annual Plans, which have to be agreed by the Secretary of State (currently the Secretary of State for Trade and Industry) and Scottish Ministers.

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NDA/RWMD/067 nuclear material Fissile material or material that can be used to produce fissile material (i.e. source material). This includes all isotopes of uranium, plutonium and thorium, together with certain isotopes of neptunium and americium. passive safety Not placing reliance on active safety systems and human intervention to ensure safety. post-closure period (of a disposal facility) The period following sealing and closure of a facility and the removal of active institutional controls. quality management system (QMS) A quality management system is the overall system by which an organisation determines, implements and ensures quality. radioactive material Material designated in national law or by a regulatory body as being subject to regulatory control because of its radioactivity. radioactive waste Any material contaminated by or incorporating radioactivity above certain thresholds defined in legislation, and for which no further use is envisaged. Radioactive Waste Management Directorate (RWMD) The NDA Directorate established to design and build an effective delivery organisation to implement a safe, sustainable, publicly acceptable geological disposal programme. It is envisaged that this directorate will become a wholly owned subsidiary company of the NDA. Ultimately, it will evolve under the NDA into the organisation responsible for the delivery of the GDF. Ownership of this organisation can then be opened up to competition, in due course, in line with other NDA sites. radioactivity Atoms undergoing spontaneous random disintegration, usually accompanied by the emission of radiation. safeguards Measures used to verify that nation states comply with their international obligations not to use nuclear materials (plutonium, uranium and thorium) for nuclear explosives purposes. Global recognition of the need for such verification is reflected in the requirements of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) for the application of safeguards by the International Atomic Energy Agency. Also, the treaty establishing the European Atomic Energy Community (the Euratom Treaty) includes requirements for the application of safeguards by the European Community. safety cases A ‘safety case’ is the written documentation demonstrating that risks associated with a site, a plant, part of a plant or a plant modification are as low as reasonably practicable and that the relevant standards have been met. Safety cases for licensable activities at nuclear sites are required as license conditions under NIA65. safety function A specific purpose that must be accomplished for safety.

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NDA/RWMD/067 spent nuclear fuel Nuclear fuel removed from a reactor following irradiation that is no longer usable in its present form because of depletion of fissile material, poison build-up or radiation damage. transport system The transport system covers the transport modes, infrastructure, design and operations. It can be divided in two main areas– the transport of construction materials, spoil and personnel associated with building a GDF and the more specialised transport of the radioactive waste to a GDF by inland waterway, sea, rail and/or road. waste acceptance criteria (WAC) Quantitative and/or qualitative criteria, specified by the operator of a disposal facility and approved by the regulator, for solid radioactive waste to be accepted for disposal. Quantitative or qualitative criteria specified by the regulatory body, or specified by an operator and approved by the regulatory body, for radioactive waste to be accepted by the operator of a repository for disposal, or by the operator of a facility for storage. waste container Any vessel used to contain a wasteform for disposal. wasteform The waste in the physical and chemical form in which it will be disposed of, including any conditioning media and container furniture (i.e. in-drum mixing devices, dewatering tubes etc) but not including the waste container itself or any added inactive capping material. waste package The product of conditioning that includes the wasteform and any container(s) and internal barriers (e.g. absorbing materials and liner), as prepared in accordance with requirements for handling, transport, storage and/ or disposal. waste packager An organisation responsible for the packaging of radioactive waste in a form suitable for transport and disposal.

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References

1

Committee on Radioactive Waste Management, Managing our Radioactive Waste Safely, CoRWM’s recommendations to Government, 2006.

2

Defra, BERR, Welsh Assembly Government, Northern Ireland Department of the Environment, Managing Radioactive Waste Safely A Framework for Implementing Geological Disposal, 2008.

3

IAEA, Development of Specifications for Radioactive Waste Packages, IAEA TECDOC-1515, 2006.

4

HSE/EA/SEPA, The management of higher activity radioactive waste on nuclear licensed sites. Joint guidance from the Health and Safety Executive, the Environment Agency and the Scottish Environment Protection Agency to nuclear licensees, 2010.

5

NDA, Geological Disposal: Disposal System Functional Specification, NDA Report No. NDA/RWMD/043, 2010.

6

NDA, Geological Disposal: Disposal System Technical Specification, NDA Report No. NDA/RWMD/044, 2010.

7

NDA, Geological Disposal: Generic Disposal Facility Designs, NDA Report No. NDA/RWMD/048, 2010.

8

NDA, Geological Disposal: Generic Transport System Designs, NDA Report No. NDA/RWMD/046, 2010.

9

NDA, Geological Disposal: The Safety of a Geological Disposal System: An Overview, NDA Report No. NDA/RWMD/010, 2010.

10

IAEA, Geological Disposal Facilities for Radioactive Waste, IAEA Specific Safety Guide No. SSG-14, 2011.

11

IAEA, Disposal of Radioactive Waste, Specific Safety Requirements SSR-5, 2011.

12

HSE/EA/SEPA, The management of higher activity radioactive waste on nuclear licensed sites. Part 3b Conditioning and disposability. Joint guidance from the Health and Safety Executive, the Environment Agency and the Scottish Environment Protection Agency to nuclear licensees, 2011.

13

EA/SEPA/NIEA, Geological Disposal Facilities on Land for Solid Radioactive Wastes Guidance on Requirements for Authorisation, February 2009.

14

IAEA, Regulations for the Safe Transport of Radioactive Material 2009 Edition, Safety Requirements No. TS-R-1, 2009.

15

NDA, Geological Disposal: Package Evolution Status Report, NDA/RWMD/031, 2010.

16

IAEA, Containers for Packaging of Solid Low and Intermediate Level Radioactive Wastes, IAEA Technical Report Series No. 355, 1993.

17

IAEA, Characterisation of Radioactive Waste Forms and Packages, IAEA Technical Report Series No.383, 1997.

18

Nirex, Initial Consideration of Waste Acceptance Criteria for the Long-term Management of certain UK Radioactive Wastes and Potential Wastes, Nirex Report No. N/118, 2004.

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19

RM Consultants, Comparison of the Nirex Waste Package Specification with Waste Acceptance Criteria for Storage and Disposal Facilities in Other Countries, RMC225, R02-229(S), 2002.

20

NDA, RWMD Radiological Protection Policy Manual, RWM02, 2010.

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