Geological Disposal: Upstream Optioneering - Overview … · Windscale Advanced Gas-cooled Reactor...

Geological Disposal

Upstream OptioneeringOverview and uses of the 6 cubic metreconcrete box

NDA Technical Note no. 18959097

March 2013

Geological Disposal

NDA Technical Note no. 18959097

Upstream OptioneeringOverview and uses of the 6 cubic metreconcrete box

March 2013

ii

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 2013. All rights reserved.

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 our Communications department 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 Radioactive Waste Management Directorate Nuclear Decommissioning Authority Building 587 Curie Avenue Harwell Oxford Didcot OX11 0RH UK

email [email protected]

iii

Executive summary

The Upstream Optioneering project was created to support the development and implementation of significant opportunities to optimise activities across all the phases of the higher activity waste (HAW) management lifecycle (i.e. retrieval, characterisation, conditioning, packaging, storage, transport and disposal). The objective of the Upstream Optioneering project is to work in conjunction with other functions within the Radioactive Waste Management Directorate (RWMD) and the waste producers to identify and deliver solutions to optimise the management of HAW, including collaboration with the Nuclear Decommissioning Authority (NDA) Strategy and Delivery (via National Programmes) functions.

This report has been produced in support of the Upstream Optioneering project and presents, at a high level, the benefits, potential risks and mitigating factors to the nuclear industry of using the 6 cubic metre concrete box1 to package intermediate level waste (ILW).

The 6 cubic metre concrete box is a standard shielded ILW container for the packaging of ILW that has been used for the packaging of decommissioning wastes generated from the Windscale Advanced Gas-cooled Reactor (WAGR) and its associated facilities. It is a Type IP-2 transport container and can therefore be transported to the geological disposal facility (GDF) concept without the need for a separate transport container. Site License Companies (SLCs) are considering the use of this container for a much broader range of wastes than previously endorsed by the disposability process.

The 6 cubic metre box was originally designed to be used for the packaging of Low Specific Activity (LSA) materials and Surface Contaminated Objects (SCO) which places limits on the quantity of fissile material in the wasteform and includes a requirement for the fissile material to be distributed homogeneously throughout the wasteform. In addition, waste packages made using the 6 cubic metre box waste container will be required to be capable of exception from the requirements in the IAEA Transport Regulations (2009 Edition as enabled into UK law) for waste packages containing fissile material. Where wastes challenge the defined limits and ethos of the transport regulations the use of an alternative container may be more appropriate.

There are a range of technical and regulatory risks that may require mitigation and management for the 6 cubic metre concrete box. The most significant risks are:

Failure to comply with the LSA and fissile excepted requirements;

Management of non-compliant packages;

Competent authority approval for transport following the interim storage period.

The potential cost of addressing these risks should be considered and accounted for when identifying a suitable container for waste streams. In some instances, the combined capital and development cost for a 6 cubic metre concrete box strategy may exceed that for an alternative package.

In summary, the 6 cubic metre concrete box provides an additional shielded ILW container option that may be cost effective for wastes that are comparable to those packaged from the WAGR facility. Other wastes could be packaged within a 6 cubic metre concrete box; however, waste producers should be cognisant that there may be an additional cost burden associated with Research and Development (R&D) to gain approvals.

1 Also referred to as the Reinforced Concrete Box

v

List of Contents

Executive summary iii

List of acronyms vii

1 Introduction 1

1.1 Objectives and scope 1

1.2 Disposability context 2

1.3 Guidance document context 2

2 Overview of 6 cubic metre concrete box 4

2.1 History of the 6 cubic metre concrete box 4

2.2 Technical overview 5

2.3 Uses for WAGR decommissioning wastes 6

2.4 Industry waste package proposals 7

3 Comparable waste containers 8

3.1 2 metre and 4 metre boxes 8

3.2 Type VI DCIC 9

3.3 Croft 2m Safstore 10

4 Technical considerations and comparisons 11

4.1 Waste type constraints 11

4.2 Waste with high external dose rate 13

4.3 Costs 14

4.4 Corrosion 15

4.5 Permeability 16

4.6 Superplasticisers 17

5 High level operational considerations 19

5.1 Non-fixed surface contamination limits 19

5.2 Waste characterisation 20

5.3 Limitations with on- and off-site movements 21

5.4 Shielding of waste 21

5.5 Management of reactive metals 22

5.6 Waste emplacement within the package 22

vi

6 Storage requirements 23

6.1 Environmental conditions 23

6.2 Operational considerations during storage 24

6.3 Monitoring and inspection 24

7 Transport requirements 25

7.1 General requirements for a Type IP package 25

7.2 Summary of specific transport considerations for the 6 cubic metre concrete box 27

8 Challenges and mitigations 29

8.1 Potential improvements 29

8.2 Risks 29

8.3 Ultimate mitigations 31

8.4 Other considerations 31

9 Conclusions 32

Appendix 1: Summary of container properties A1

Appendix 2: Transport regulation requirements A2

Appendix 3: A précis of INS report: “WAGR box Design Authority clarification and document review” A5

References A7

vii

List of acronyms

Acronym Definition

ALARP as low as reasonably practicable

CEM I formerly ordinary Portland cement

CFD computational fluid dynamics

DA Design Authority

DCIC ductile cast iron container

DSS Disposal System Specification

DSSC Disposal System Safety Case

FA fuel ash, formerly pulverised fuel ash

GDF geological disposal facility

GGBS ground granulated blastfurnace slag, formerly blast furnace slag

HAW higher activity waste

HD high density

HVAC heating, ventilation and air conditioning

IAEA International Atomic Energy Authority

ILW intermediate level waste

INS International Nuclear Services

IP-2 Industrial Package Type 2

IPR intellectual property rights

ISO Intermodal (Shipping) Container

IWM integrated waste management

LLW low level waste

LoC Letter of Compliance

LSA low specific activity

Magnox Magnesium non-oxidising

ND normal density

NDA Nuclear Decommissioning Authority

NIREX Nuclear Industry Radioactive Waste Executive

ONR-RMT Office for Nuclear Regulation – Radioactive Materials Transport

PCM plutonium contaminated material

PCP polycarboxylate comb polymer

PDSR Package Design Safety Report

viii

Acronym Definition

PIE post-irradiation examination

R&D research and development

RHPC rapid hardening portland cement

RSC robust shielded container

RSRL Research Sites Restoration Limited

RWMD Radioactive Waste Management Directorate

SCO Surface Contaminated Object

SILW shielded intermediate level waste

SLC Site Licence Company

SNF sulphonated naphthalene formaldehyde

SSS site strategic specifications

SWTC standard waste transport container

WAGR Windscale Advanced Gas-cooled Reactor

WPS Waste Package Specification

WPSGD Waste Package Specification and Guidance Documentation

UCM uranium contaminated material

UILW unshielded intermediate level waste

1

1 Introduction

The mission of the Nuclear Decommissioning Authority (NDA) is “to deliver safe, sustainable and publically acceptable solutions to the challenge of managing the UK’s civil nuclear liability, driving changes to improve delivery by enhancing innovation and improving the process of clean-up” [1]. To meet this mission, six strategic themes were created in the NDA Strategy (2011): Site Restoration; Spent Fuels, Nuclear Materials; Integrated Waste Management; Business Optimisation; and Critical Enablers.

The integrated waste management (IWM) Strategy considers how the NDA manages all forms of waste arising from operating and decommissioning of nuclear licensed sites that are owned by NDA and operated by Site Licence Companies (SLCs), including waste retrieved from legacy facilities. It also incorporates the wider work of the Radioactive Waste Management Directorate (RWMD) on implementing geological disposal. The objective of the IWM Strategy is to ensure that wastes are managed in a manner that protects people and the environment, now and in the future, and in ways that comply with Government policies and provide value for money. Underpinning the IWM Strategy are the strategies for low-level waste (LLW) [2] and higher activity waste (HAW) [3]. The latter aims to convert the HAW inventory into a form that can be safely and securely stored for many decades.

The Upstream Optioneering Project was created to support the development and implementation of significant opportunities to optimise activities across all the phases of the HAW management lifecycle (i.e. retrieval, characterisation, conditioning, packaging, storage, transport and disposal). The objective of the Upstream Optioneering project is to work in conjunction with other functions within RWMD and the waste producers to identify and deliver solutions to optimise the management of HAW, including collaboration with NDA Strategy and NDA Delivery (via National Programmes).

1.1 Objectives and scope

This report has been produced in support of RWMD’s Upstream Optioneering work programme and presents, at a high level, the benefits, potential risks and mitigating factors to the nuclear industry of using the 6 cubic metre concrete box to package intermediate level waste (ILW). These considerations are largely dependent on the physical, chemical and radiological properties of the waste streams to be packaged, and for certain wastes the 6 cubic metre concrete box may not be the optimum package. As such, this document:

Provides an overview of the 6 cubic metre concrete box;

Outlines comparable waste packages;

Highlights technical considerations and contrasts with the comparable packages;

Provides guidance on the storage and transport of 6 cubic metre concrete boxes; and

Identifies benefits, risks and mitigations of using the 6 cubic metre concrete box.

The standard design of the 6 cubic metre concrete box has been used as a waste package for the Windscale Advanced Gas-cooled Reactor (WAGR) waste streams, and will form the basis for this study. Potential changes to the design and its transport certification have been acknowledged, within Appendix 3, but are not specifically considered within this document.

2

Unlike the Waste Package Specification (WPS), this document contains a technical discussion on the use of a 6 cubic metre concrete box which is advisory rather than prescriptive.

1.2 Disposability context

The implementation of a geological disposal facility (GDF) for higher activity radioactive wastes requires demonstration that such a facility would be safe, during both the operational period and after it has been sealed and closed. As part of that process a Disposal System Safety Case (DSSC) has been produced, the prime purpose of which is to demonstrate that a GDF can be implemented in a safe manner and in such a way that would meet all regulatory requirements. To ensure waste packages fit within the safety envelope defined within the DSSC, waste producers should gain agreement on packaging proposals with RWMD through the disposability assessment process [4].

RWMD has defined the packaging standards and specifications for waste packages containing higher activity waste, and other radioactive materials that may be declared as waste, within a Level 1 Generic Waste Package Specification (GWPS) [5]. The packaging requirements for all waste packages containing ILW are provided in the Level 2 Generic Specification for waste packages containing low heat generated waste [6].

The Level 2 Generic Specification is supported by the Waste Package Specification and Guidance Documentation (WPSGD), a suite of documentation primarily aimed at those with the responsibility for developing proposals to package waste. The WPSGD comprises a range of Level 3 Waste Package Specifications (WPSs) which apply the requirements of the Level 2 Generic Specifications to waste packages manufactured using standardised designs of waste container, including the 6 cubic metre concrete box [7].

This document is intended to be used alongside the Level 2 and Level 3 WPS and supporting Guidance to aid SLCs in their waste package strategy determination; enabling the potential risks and benefits of the 6 cubic metre concrete box, and their cost impacts, to be appropriately accounted for in the decision making process.

1.3 Guidance document context

This document has been divided into the following sections to provide:

Overview of the 6 cubic metre concrete box:

o Background to the waste containers, its design and its operational history.

Comparable waste containers:

o Introduction of the waste containers considered to be comparable to the 6 cubic metre concrete box.

Technical considerations and comparisons:

o Consideration of waste applicability, the manufacture of the 6 cubic metre concrete boxes, high level through-life costs.

High level operational considerations:

o On-site operational considerations such as characterisation, waste emplacement, on-site movements, high dose rate wastes.

Storage considerations:

o Type of environmental conditions and monitoring required for a concrete package.

3

Transport considerations:

o Review of the 6 cubic metre concrete box transport certification status, constraints associated with a Type IP-2 package and of the 6 cubic metre concrete box.

Challenges and mitigations:

o The key challenges, their mitigations and the ultimate mitigations that could be deployed by waste producers intending to use the 6 cubic metre concrete boxes.

It is important to note the following definitions of terms used within this guidance document, which correspond to the 2009 Edition of the IAEA Regulations for the Safe Transport of Radioactive Material [8], known as the IAEA Transport Regulations, and is enabled into UK law. The IAEA Transport Regulations has recently been revised and issued [2012 Edition, 9] and is likely to be enabled into UK law by 2015; Appendix 2 provides a brief introduction to the main fissile exception changes.

Term Definition

Fissile excepted Packages containing fissile material that complies with specified limits on package size, fissile content and distribution. These packages are therefore always sub-critical.

(A detailed definition can be found in Paragraph 417 of the IAEA transport regulations [8]).

LSA Low specific activity.

Radioactive material which by its nature has a limited specific activity, or radioactive material for which limits of estimated average specific activity apply.

Type IP-2 Industrial Package Type 2.

A package that can be transported in its own right.

Packages where the hazard posed by their contents is relatively low. The contents must be classified as either “Low Specific Activity” or as “Surface Contaminated Object(s)”.

(A detailed definition can be found in Paragraph 622 of the IAEA transport regulations [8]).

Type IF A Package that meets the requirements of both an Industrial Package and Fissile Package as specified in the IAEA Transport Regulations and requires multi-lateral Competent Authority approval.

SCO Surface contaminated objects.

Solid objects which are not intrinsically radioactive but which have radioactive material distributed on their surfaces.

4

2 Overview of 6 cubic metre concrete box

The 6 cubic metre concrete box (Figure 1), is one of a limited range of standardised designs for ILW waste packages that have been demonstrated to be compatible with the GDF.

Figure 1 6 cubic metre concrete box (formerly known as the WAGR Box)

2.1 History of the 6 cubic metre concrete box

The container was originally developed for the disposal of wastes arising from the decommissioning of the WAGR. The conceptual design was undertaken in the 1970’s for use as a sea disposal package but following the “London Convention”2, the concept of sea disposal was abandoned and final design of the box as a container for surface storage / disposal was completed in the 1980’s.

The original container design was a steel clad rectangular reinforced concrete box; the design was refined and a patent obtained in 1985. A wholly reinforced concrete (i.e. unclad) container design was also investigated. It was believed that such a container could satisfy the requirements of WAGR ILW disposal whilst being more economical to manufacture. After successful analysis and testing, the unclad design was adopted.

Two versions of the WAGR box were developed; a standard density concrete version and a high density version to permit the packaging of wastes with higher activity.

The 6 cubic metre concrete box has features that are identical to that of a WAGR box. The name of the container has been changed from the WAGR box to the 6 cubic metre concrete box as it can be used for waste streams other than those associated with WAGR and its associated facility. Within this document, the term WAGR box will be used when discussing the containers used for WAGR wastes and the term 6 cubic metre concrete box will be used for all other potential waste streams.

2 Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972

5

2.2 Technical overview

The 6 cubic metre concrete box (Figure 2), is anticipated to be manufactured from reinforced concrete. It is anticipated that the 6 cubic metre concrete box will be deployed for a limited range of decommissioning wastes, which are of low activity and where that activity is uniformly distributed throughout the wasteform. Such wastes would be placed inside the waste container, backfilled with a cementitious grout and the waste package finished by the in situ casting of a “lid”. RWMD provides general guidance on the requirements for encapsulated ILW wasteforms that would result from such an approach to packaging and the means of their achievement [10].

Figure 2 6 cubic metre concrete box waste package

The 6 cubic metre concrete box is classified as a “shielded waste package”; relatively thick concrete walls provide radiation shielding of the radionuclide contents and thereby permits the handling of the waste package without the need for remote handling techniques.

2.2.1 Transport certification

As well as being suitable for disposal in a GDF, 6 cubic metre concrete box waste packages are specified as an Industrial Package – Type 2 (Type IP-2) transport package (as defined by the IAEA Regulations for the Safe Transport of Radioactive Material [8]) in their own right. This permits them to be transported through the public domain without the need for an overpack to provide additional radiation shielding and / or containment of their contents, provided that the package meets the requirements of the relevant version of the transport regulations at the point of transport.

Regulatory transport approval for the 6 cubic metre concrete box has lapsed; a review has been undertaken which has determined that sufficient information is available to enable the appointment of a design authority and subsequent transport licence application [11].

Direct limits are placed on all Type IP packages by defining two permissible types of material: Low Specific Activity (LSA) materials and Surface Contaminated Objects (SCO). As an IP package, the quantities of fissile material, neutron moderators and reflectors within the generated waste package are controlled to enable exception from the IAEA Transport Regulations [8]; such packages are referred to as “fissile excepted”.

6

The two categories of LSA suitable for geological disposal are LSA-II and LSA-III. These are fully defined within Appendix 2; however, both LSA categories require the activity in a package to be distributed throughout the wasteform. This is a key requirement for SLCs considering the use of the 6 cubic metre box.

Two categories of SCO are defined based on whether the objects have fixed and / or non-fixed contamination; these are described fully within Appendix 2.

SCOs are solid objects which are not intrinsically radioactive but which have radioactive material distributed on their surfaces. This description excludes bulk radioactive material (e.g. uranium metal) and materials such as metals and graphite which have become radioactive as a result of neutron irradiation.

Guidance is available from RWMD on the application of the IAEA Transport Regulations to “fissile excepted” packages [12] and the application of the LSA material criteria [13].

2.2.2 Box and grout formulation

Two types of 6 cubic metre concrete box and two grout formulations were produced for the WAGR wastes: a normal density (ND) box (2,350 kg/m3) and grout formulation and a high density (HD) box (3,800 kg/m3) and grout formulation. These allowed for the packaging of higher activity wastes whilst providing a suitable level of shielding without unnecessarily reducing the payload volume of the container. The two 6 cubic metre concrete box types and grout formulations enable a “mix and match” process to be used that optimises waste packaging whilst maintaining dose limits to acceptable levels, both for operator safety and to meet the requirements in the transport regulations.

The “ND box” uses a conventional aggregate reinforced concrete with the infill grout being a normal density fuel ash (FA) / rapid hardening portland cement (RHPC) mix with a water to solids ratio of 0.43.

The “HD box” uses a high density magnetite aggregate reinforced concrete to provide greater shielding. The concrete formulation used RHPC, magnetite and Sikament 10, a superplasticiser, which is an aqueous solution of a salt of a sulphonated vinyl copolymer [14].

The infilling grout formulation is a 3:1 fine iron oxide and RHPC with a water to solids ratio of 1.41. The WAGR project used RHPC produced in line with the BS 12:1996 and then BS EN 197-1 standards, these being for CEM-I cement class 52.5N. This has the same chemistry as a CEM I Portland Cement, but the powder is more finely ground to achieve higher early strengths [15]. To provide fluidity, the infilling grout contained a superplasticiser (Cellaid 500); however, this additive is no longer manufactured and an alternative product would require sourcing, testing and agreement with RWMD should a HD version of the 6 cubic metre concrete box be required.

2.3 Uses for WAGR decommissioning wastes

As discussed in Section 2.1, the 6 cubic metre concrete box was developed to support the decommissioning of the WAGR; endorsement of the packaging of ILW from WAGR and its associated post-irradiation examination (PIE) facility was provided by RWMD, and its predecessor Nirex, through the LoC3 process. The limited range of wastes packaged, or where endorsement has been gained, are:

Activated metals, such as stainless steels, mild steel, aluminium;

Activated other materials, such as concrete (bioshield);

3 The Nirex process was termed Letter of Comfort; this is now Letter of Compliance.

7

Contaminated metals;

Contaminated other materials;

Graphite ILW; and

Mixed wastes.

The wastes arising from WAGR contain a small amount of fissile material, less than 15 g per package, enabling generated packages to be fissile excepted in line with the transport regulations for a Type IP-2; further detail on the transport regulations are provided within Section 7 and Appendix 2.

The packaged wastes were typically solid, dry items; any swarf or fines generated from the decommissioning and dismantling activities, such as graphite powder and steel swarf, were immobilised in sacrificial containers before packaging. An LoC was issued to endorse the proposed disposal of wastes immobilised in sacrificial containers, however the work has not been undertaken [16]. Alternative processes such as mixing fines or swarf (corrosion products, degraded PVC and plastics, metal fines but excluding Zircaloy4) with bentonite clay and compacting, as undertaken by Research Sites Restoration Limited (RSRL) at their Harwell site [17], or immobilising with a polymer based encapsulant in sacrificial cans, could also be employed.

2.4 Industry waste package proposals

Several SLCs are exploring the potential use of 6 cubic metre concrete boxes for a range of wastes. Formal waste packaging proposals have been received by RWMD for the packaging of Magnox Swarf Storage Silo’s Miscellaneous Beta Gamma Waste and for Dounreay Shaft and Silo wastes. These wastes include ferrous metals, graphite, aluminium, organic materials, other materials, uranium (natural and enriched), Magnox, sludges, isotope cartridges and sealed sources. Some of these wastes have not been packaged previously in 6 cubic metre concrete boxes and could prove challenging to meet transport and disposal requirements.

RSRL is also considering the use of 6 cubic metre concrete boxes as an alternative to the use of the 2 metre box for reactor decommissioning wastes; these wastes are predominantly ferrous metals, aluminium, concrete and graphite.

4 An alloy of zirconium and other metals; typically 95wt% zirconium to improve mechanical properties and

corrosion resistance.

8

3 Comparable waste containers

RWMD has defined a range of standardised containers for the packaging of ILW [5]. Three broad categories of containers are available:

Unshielded ILW (UILW) containers (e.g. stainless steel 500 litre drums and 3 m3 boxes/drums);

Shielded ILW (SILW) containers (concrete boxes , or thin-walled metal boxes with integral concrete shielding); and

Robust shielded containers (RSC) (thick-walled boxes or casks with integral metal shielding).

The 6 cubic metre concrete box is a SILW container.

Waste producers should consider the category of container that is most appropriate to the characteristics of the waste stream under consideration. The following containers have been or are being considered for use in the UK for ILW. It is also anticipated that all Type IP-2 containers are suitable for LSA wastes and are likely to meet the Type IP-2 requirements [8].

6 cubic metre concrete box;

2 metre box;

4 metre box;

Type VI Ductile Cast Iron Container (DCIC); and

Croft 2m Safstore, rectangular box (a 2m half-height and a 4m Safstore are also available).

A succinct description of the 2 metre and 4 metre boxes, DCIC Type VI and Croft 2m Safstore is provided in the following sections with a comparison table provided within Appendix 1. Further detailed guidance is available within the WPSGD suite or from the Packaging Assessment Team within RWMD.

Outside the UK, a range of shielded packages are in regular use for packaging ILW, these are not discussed within this document.

3.1 2 metre and 4 metre boxes

The 2 metre and 4 metre boxes, shown in Figure 3, can be used as freight containers that can, if required, incorporate annular shielding in the form of a concrete liner of up to 300 mm thickness for the 4 metre box and up to 200 mm thickness for the 2 metre box. They are intended to be used for the packaging of wastes arising from the decommissioning of nuclear facilities. Depending on the physical and chemical properties of the waste and the nature of the radionuclides associated with them, such wastes may be encapsulated using, for example, a cementitious grout, or left unencapsulated. The 2 metre box may be preferred when the available space for loading is limited, or when the option for rail transport does not exist for the packaging site and a 30 te limit for transport by road is imposed.

9

Figure 3 The 2 (left) and 4 (right) metre box waste containers

3.2 Type VI DCIC

The Type VI DCIC is a robust shielded container, used in Germany and which, has been identified and proposed by Magnox Ltd for the packaging of relatively low specific activity ILW such as sludges and ion-exchange resins. A Type II DCIC is available for higher specific activity ILW. The container, shown in Figure 4, is manufactured from ductile cast iron (DCI) with an internal volume of 2.83 m3. Shielding is provided by 0.15 m cast iron and unloaded the container weighs 18.3 te.

The Magnox Ltd proposals are for an unencapsulated package to be produced with residual water remaining in those packages containing dewatered wastes [18]. Further, EdF Energy Nuclear Generation Ltd have proposed the use of a DCIC for spent ion exchange resins generated at Sizewell B [19].

10

Figure 4 Type VI DCIC

3.3 Croft 2m Safstore

The Croft 2m Safstore is an IP-2 rated waste package that is manufactured from either steel with a concrete liner or DCI and is designed to accommodate ILW that requires shielding. The 2m Safstore is available in two heights [20], 2.2 m or 1.1 m, and a range of three thicknesses, 50 mm, 75 mm and 120 mm to economically accommodate the shielding requirements of the specific waste to be packaged.

Figure 5 Croft 2m Safstore

11

4 Technical considerations and comparisons

Waste packaging proposals are formally assessed through the LoC disposability assessment process [4]; however, there are a range of technical considerations that waste producers should be cognisant of when exploring the use of 6 cubic metre concrete boxes, including:

Waste type, including whether the waste in a 6 cubic metre box would meet LSA or fissile-exception requirements;

External dose rates (shielded and unshielded);

Comparative costs;

Corrosion issues;

Permeability of concrete waste package materials; and

Use of superplasticisers.

For each technical aspect considered, a comparison against the 2 metre and 4 metre boxes, the Croft 2m Safstore and the Type VI DCIC is included.

4.1 Waste type constraints

As previously detailed the 6 cubic metre concrete box is designed to meet the conditions of a fissile excepted Type IP-2 container. This imposes constraints that require waste producers to carefully consider the waste types in order that the Type IP-2 conditions are met. It has previously been used for several waste streams which originate from the same source, or associated facilities. The range of waste types packaged to date is limited.

Accounting for these constraints, the waste types classification scheme, adopted in the HAW Credible Options paper [21], has been used to provide an indication of the types of waste that could be packaged within the 6 cubic metre concrete box package and is presented in Table 1.

Table 1 Assessment of suitable waste types for the 6 cubic metre concrete box

Graphite Solid/ immobile Wet/ potentially mobile

Fuel element debris Activated metals Desiccant and catalysts

Bulk reactor graphite Activated other materials Flocculants

Graphite sleeves Concrete Fuel debris

Contaminated metals Inorganic ion exchange materials

Contaminated other materials

Legacy fuels and uranium residues

Miscellaneous scrap Organic ion exchange resins

Plutonium contaminated materials

Magnox swarf / fuel cladding

Radioactive Sources Raffinates

Thorium and uranium contaminated materials

Sludges

(Others – mixed wastes) Plutonium contaminated materials

12

Graphite Solid/ immobile Wet/ potentially mobile

Thorium and uranium contaminated materials

Oils and solvents

Soils, sand and gravel

Others – mixed wastes, orphans, filters, cakes and slurries

KEY:

Waste groups that are unlikely to be appropriate for packaging in 6 cubic metre concrete boxes

Waste groups that may require significant supporting evidence to be considered appropriate for 6 cubic metre concrete boxes

Waste groups for which 6 cubic metre concrete boxes have already been used

The logic that underpins the assessment presented in Table 1 is provided below:

Wet wastes such as sludges, flocculants, ion exchange resins, cakes and slurries typically contain mobile nuclides that can leach through the concrete walls of the 6 cubic metre concrete box; further, these types of wastes typically require in-container mixing to produce a good monolithic product using a cementitious infill which the 6 cubic metre concrete box cannot accommodate.

Fissile wastes such as legacy metallic fuels, plutonium contaminated materials (PCM), uranium contaminated materials (UCM), fuel element debris, could result in a significant challenge to the transport of the 6 cubic metre concrete box waste packages as a fissile excepted Type IP-2 transport packages.

Sources may challenge the homogeneity of activity within the package as required by the Type IP-2 rating due to their high specific activity, (see section 7.1 for LSA definition).

Oils and solvents present challenges due to their ability to leach from cement based systems.

There are specific characteristics amongst dry waste types that will require management. An example is reactive metals where cementitious encapsulation can result in expansive corrosion, hydrogen generation and the potential for temperature excursion. These characteristics would require assessment at the package and wasteform selection stage and prior to any formal waste package proposal submission to RWMD. Waste producers should also consider fissile contamination of reactor decommissioning wastes due to fuel failure during operations. Fuel contamination could challenge the ability of a package to meet the fissile exception requirements.

4.1.1 Benefits, risks and potential mitigations of 6 cubic metre concrete box

Benefits: Known performance for solid / immobile wastes

Risks: Meeting the LSA and fissile excepted requirements

Potential mitigations: Selectively packaging similar activity wastes together, good characterisation of waste (including knowledge of operational history)

13

4.1.2 Comparison to analogous container

Any wastes that challenge the Type IP-2 rating of the 6 cubic metre concrete box will provoke a similar challenge with the analogous packages under consideration. The 2 metre and 4 metre boxes may be more tolerant of mobile radionuclides such as caesium-137 due to their steel construction, but have similar constraints for wet wastes as the 6 cubic metre concrete box. Submissions have been made by Magnox Ltd to package dewatered ion exchange resins and sludges in DCI containers, including the Type VI DCIC [18]. RWMD considered the generated packages to be disposable and therefore the Type VI DCIC may be more suitable for wastes that contain residual water or potentially mobile wastes than the 6 cubic metre concrete box. The Croft Safstore 2m box can be manufactured from ductile cast iron or concrete and therefore has similar waste type constraints as the Type VI DCIC or the 2 metre / 4 metre boxes.

4.2 Waste with high external dose rate

Most container types provide additional shielding to reduce the external dose rate by inserting shielding material (concrete or metal slabs) within the container void. Where the 6 cubic metre concrete box differs is that the package is endorsed and has received a Certificate of Approval for transport of a high density grout (for the matrix infill) and high density concrete (for the container walls) to reduce the external shielded dose rate without reducing the usable waste volume.

The transport regulations also restricts the quantity of LSA material (or SCO) in a single Type IP-2 transport package so that the external dose rate of a waste package does not exceed 2 mSvh-1 at the surface and 0.1 mSvh-1 at 1 m from the external surface of the transport package.5 In addition, for unshielded material, the external radiation level at 3 m from the source should not exceed 10 mSvh-1. This limit can prove more bounding on the total quantity of activity in a package than the specific activity limits for LSA or SCO. Further, if localised shielding is introduced to manage high dose rate items, the point at which the unshielded dose rate is measured from may be significantly reduced with minimal benefit received from any infill material.


Benefits: 6 cubic metre concrete box HD grout offers good levels of shielding for high dose rate wastes or items

Risks: Transport dose rate requirements may be breached

Potential Mitigations: Selection of low specific activity waste streams that do not challenge the unshielded material requirements; selection of the best encapsulation media for the wastes (e.g. high density grout)

4.2.2 Comparison to analogous containers

The 2 metre and 4 metre boxes and the Croft 2m Safstore provide a level of flexible shielding provision through the use of variable thickness concrete (2 metre and 4 metre boxes) or by varying the thickness of the concrete shielding cast iron walls (Croft 2m Safstore). The Type VI DCIC does not have the potential to increase shielding; however, the existing design includes 0.15 m of DCI. The transport requirement for the unshielded dose rate applies to all containers discussed.

5 These limits are those specified in the IAEA Transport Regulations for the transport of packages under conditions of ‘non-exclusive use’. Less stringent dose rate limits may be applicable to a transport package if it is transported under conditions of ‘exclusive use’, however, if a significant number of packages were to be transported in such a manner, an ALARP assessment would be required.

14

4.3 Costs

As a reinforced concrete structure (Figure 6), the material costs of a 6 cubic metre concrete box may be lower than those of a steel or cast iron based waste container.

Figure 6 6 cubic metre concrete box reinforcement

In 2002, the WAGR project purchased a number of normal density and high density boxes for WAGR ILW. Escalating these costs to 2012 provides an estimated cost of between £10,000 and £20,000 per 6 cubic metre concrete box depending on the box density and the quantity of boxes required. This excludes any costs associated with initiating the contract, design and manufacture of the mould and any required modifications to the original WAGR design.

As with all of the packages considered within this document, the 6 cubic metre concrete boxes may be suitable for interim storage in an unshielded facility; these typically have lower design, build and maintenance costs than shielded stores. The required environmental conditions and monitoring requirements for the 6 cubic metre concrete boxes during interim storage is discussed within Section 6.


Benefits: Cost effective package where no design changes are required

Risks: Design improvements may increase capital cost of the container, R&D requirements for alternative additives increases cost

Potential Mitigations: Selection of waste streams that are compatible with the container


The 6 cubic metre concrete box has a low cost per container compared to the 2 metre, 4 metre and Type VI DCI containers. The payload of each container differs, resulting in a range of cost per payload data; this will be further changed by the level of shielding

15

required for different waste streams. The 6 cubic metre concrete box has the benefit of a high density box option to provide shielding whilst not reducing payload; however, the use of high density shielding or infill grouts could also be considered for the 2 metre and 4 metre boxes.

Based on existing designs, the 2 metre and 4 metre boxes are around two to three times more costly, on a cost per payload basis, than the 6 cubic metre concrete box with the Type VI DCIC being significantly higher again. Indicative costs per container and payload volume are provided in Table 2.

Table 2 Indicative costs of considered waste packages

6 cubic metre concrete box

2 metre box 4 metre

box Croft 2m Safstore

Type VI DCIC

Indicative cost per container (Note 1) (£)

15,000 40,000 60,000 High

(Note 2) High

(Note 2)

Shielding thickness (m)

0.24 concrete 0.2 concrete 0.2 concrete 0.12

cast iron (Note 3)

0.15 cast iron

Payload volume (m3)

5.8 4.9 10.9 7.5 2.8

Payload volume as % of disposal volume

49 46 51 71 51

Cost per payload volume (£/m3)

2,590 8,160 5,500 - -

Note 1: All provided costs are indicative and will be dependent on the quantity of containers ordered and the material and depth of shielding.

Note 2: Waste producers should directly contact commercial providers to obtain cost data to inform their decision making process.

Note 3: The Croft 2m Safstore is available with other thicknesses of cast iron shielding as an integral part of the container.

4.4 Corrosion

The 6 cubic metre concrete box incorporates steel reinforcing bars into the concrete walls which are essential for container strength. There is potential for atmospheric chloride-induced localised corrosion of the reinforcement to occur which could result in damage to the container walls. To minimise the risk of corrosion occurring, the box should be protected from adverse conditions such as condensation and extreme temperature variations. Chloride concentrations on the box surface should be kept as low as possible during packaging, interim storage and transportation. Environmental conditions within the store are discussed in Section 6.

The greatest risk of chloride contamination / deposition is during transport of the waste packages to the GDF; the 6 cubic metre concrete box could be protected by use of an appropriate overwrap or a protective surface coating.

Corrosion of the packaged waste is also a concern for package longevity, due to the relative inability of concrete to withstand tensile forces, particularly if expansive corrosion of the wasteform occurs. In addition, reactive metals such as aluminium and Magnox have the potential to generate significant volumes of hydrogen that could challenge the integrity of the box. The volume of hydrogen generated is dependent on the surface area and

16

volume of metal packaged. Waste producers should therefore assess the likely volumes of hydrogen evolved within the acute phase during grouting and curing, which may discharge through the wasteform, and the chronic phase, where the permeation rate of hydrogen through the box structure is the concern.


Benefits: Not applicable

Risks: Ingress of chloride resulting in corrosion of the reinforcement bar; container failure due to expansive corrosion of wasteform

Potential Mitigations: Control of environmental conditions during packaging, transport and storage; Use of protective overwrap or surface coating; selection of compatible wastes and encapsulant for use with the 6 cubic metre concrete box

4.4.2 Comparison with analogous containers

The 2 metre and 4 metre boxes are constructed from stainless steel; corrosion is therefore a concern with these packages requiring a significant level of contamination / deposition control. The benefit of these packages is that the stainless steel structure has a greater ability to withstand tensile forces from expansive corrosion. The Croft 2m Safstore (cast iron type) and Type VI DCICs have good corrosion properties due to their construction from DCI which is not as prone to localised corrosion processes as stainless steels are. DCI has a much greater tensile strength than stainless steel and concrete, and can therefore better tolerate expansive forces. The Type VI DCIC is unvented and sealed; any gases generated by the packaged waste largely remain in the package.

4.5 Permeability

The 6 cubic metre concrete box is constructed from concrete; therefore it is gas permeable and can be considered as self-venting. Due to this, the package can accommodate some gas generation from radiolysis, microbial degradation or radioactive decay of the waste. The ability for the package to self-vent is dependent on the rate of gas generation and this should be reviewed when considering potential waste streams for packaging.

A disadvantage of the package’s permeability is the potential migration of radionuclides from the waste matrix through the wall to the external surfaces during the interim storage and GDF operational period. The waste strategy proposals produced by SLCs should consider this risk and identify mitigations to reduce the level of migration and recovery processes should migration occur. These mitigations should then be assessed against the requirements for the container to be gas permeable.

The WAGR waste streams did experience migration of caesium-137, and resolved this by the application of a sealant coating, Sika Top Seal 107, to the internal surfaces of the box. Sika Top Seal 107 is a two part polymer modified cementitious waterproof mortar slurry comprising of a liquid polymer and a Portland cement based mix incorporating admixtures [22]. As with the grout and box additives, it is recommended that discussions are held with RWMD to agree the composition of any sealants prior to a formal Letter of Compliance submission.

An alternative approach to retaining caesium, or other mobile nuclides such as tritium, may be the inclusion of an impermeable liner. This would represent a change to the endorsed position of the 6 cubic metre concrete box as monolithic and potentially introduces a shear plane. As such, the inclusion of an impermeable liner would need to consider how the design change could affect the certification of the 6 cubic metre concrete box and the level of additional works to gain approval of the revised design by RWMD, through the disposability assessment process.

17

SLCs proposing to use the 6 cubic metre concrete box should consider the impact of mobile nuclides on their interim storage regime and the ability of the box to be transported to and accepted at the GDF.


Benefits: Self-venting of gases

Risks: Migration of mobile nuclides to external surface of the container

Potential Mitigations: Minimise packaging of wastes with mobile nuclides, application of sealant coating to internal surfaces, incorporation of impermeable liner


The 2 metre and 4 metre boxes and the Croft 2m Safstore have engineered vents to enable off-gassing but retain particulate; these packages may enable a greater level of off-gassing than the 6 cubic metre concrete box. The Type VI DCIC is a sealed unvented package and therefore robust technical underpinning may be required to demonstrate that the package can withstand any internal pressure from waste degradation.

Caesium-137 is unable to migrate through steels and ductile cast iron therefore the external build-up of caesium-137 on external surfaces of the analogous packages is not an issue. Other mobile nuclides, such as tritium, may provide a greater challenge than caesium-137 due to its diffusion properties.

4.6 Superplasticisers

Superplasticiser chemicals have the potential to form complexes that enhance the solubility of many radionuclides, including actinide species that could prejudice the safety performance of the GDF [23]. As previously stated, the WAGR box HD concrete and HD grout formulations used superplasticisers which are no longer available. An alternative additive to Cellaid 500 would therefore need to be considered for the manufacture of a 6 cubic metre concrete box and the impact on other wastes disposed of within the GDF, particular any enhanced solubility effects, would require assessment. The composition of any additives proposed for a 6 cubic metre concrete box or its infill should be agreed with RWMD.

R&D work has been undertaken on comb superplasticisers, including ADVA Cast 551 [24] which indicate that polycarboxylate comb polymer (PCP) superplasticisers may be preferable to sulphonated naphthalene formaldehyde (SNF) superplasticisers. Further R&D [25] has demonstrated that the enhancement of nuclide solubility is dependent on the environmental conditions, the irradiation of the superplasticisers and is nuclide specific. As such, waste producers should carefully consider the physical and radiochemical inventory of their wastes, the effects of superplasticisers for long-term performance within the GDF concept and the development programme required to underpin their proposed wasteform [26].

As with other cement products, the nuclear sector is a small user of cement powders and admixtures with the prime user being the construction sector. Manufacturers regularly update their product range or may change the composition of their products resulting in an approved or promising product no longer being available for use. This is the case with ADVA Cast 551 and, as noted above, Cellaid 500. Typically a specific formulation of superplasticiser has a limited availability of around 10 years and this may present a technical and commercial risk if the use of superplasticisers forms a key component of a developing or developed waste formulation. Specific guidance from RWMD on the status of superplasticisers is available and should be consulted [26].

18


Benefits: Allows manufacture of HD packages

Risks: Security of supply, potential negative impacts on the safety performance of the GDF

Potential Mitigations: Undertake R&D on fully characterised superplasticisers, secure fixed formulations for NDA estate wide future use

4.6.2 Comparison of analogous packages

The 2 metre and 4 metre box designs do not require the use of superplasticisers in their manufacture and typical waste packaging proposals have used FA or GGBS grout formulations which have a good fluidity without superplasticisers. The Type VI DCIC and the Croft 2m Safstore are manufactured from DCI and therefore the use of superplasticisers is not required.

19

5 High level operational considerations

The compatibility of the waste package with the GDF is only one aspect of the disposal process; the packaging, interim storage and transport of the 6 cubic metre concrete box should also be considered as part of the waste package selection process. Operational considerations to bear in mind when exploring the use of 6 cubic metre concrete boxes include:

Non-fixed surface contamination limits;

Waste characterisation requirements;

Construction of waste packages and movement restrictions;

Waste shielding requirements;

Management of reactive metals;

Alternative methods of waste emplacement within the package.

5.1 Non-fixed surface contamination limits

Transport regulations state that the limits of non-fixed contamination on the surface of a package must be a maximum of 4.0 Bq/cm2 for beta and gamma emitters and low toxicity alpha emitters, and 0.4 Bq/cm2 for all other alpha emitters.

For 6 cubic metre concrete boxes, this condition becomes more significant because of the concrete container walls. Should the container become contaminated from external sources (for example, from airborne contamination, in-store condensation, rainwater etc) such that non-fixed contamination is above the transport limits or would prove challenging to container integrity then removal from the concrete surfaces would be difficult.

Compliance monitoring, undertaken prior to transport or as part of a package monitoring regime, is not simple on a concrete surface. For example, swabs can easily be taken from smooth metal surfaces, with standard assumptions on the pickup factor, or dose measurements. However, it is difficult to detect contamination that has ingressed the pores of a concrete surface when performing reassurance monitoring. Therefore, other operational procedures (e.g. sacrificial covers) may be beneficial to ensure contamination limits are met. Any measures taken to reduce external contamination would require an appropriate assessment of secondary risks such as gas generation, secondary waste generation etc.

The potential migration of radionuclides, such as caesium-137 or tritium, through the container wall may also lead to difficulties in remaining within external contamination limits. Decontamination of the external surfaces may prove difficult and an external transport cover could be a pragmatic way forward. As discussed within Section 4.5, an impermeable barrier may be an appropriate mitigation if the secondary risks are assessed and appropriately managed.



Risks: Non-compliant with transport regulations; difficulty associated with conducting reassurance monitoring

Mitigations: Minimise packaging of wastes with mobile nuclides; high levels of contamination control during packaging, storage and transport; use of protective

20

covers; use of an impermeable liner; use of a transport container for transfer to the GDF

5.2 Waste characterisation

To ensure that the waste package meets transport regulations for a Type IP-2 container, not only does the total package need to meet a limit for an average specific activity (e.g. LSA-II being 10E-4 A2/g and LSA-III being 2 x 10E-3 A2/g), but the activity within the waste must be ‘distributed throughout’. In practice this may require characterisation of several individual sections of the waste. If the waste arriving at the packaging plant is variable, the plant may need to consider the option of several different packages being available at the same time, to allow waste to be packed with similar type waste. Alternatively, a sacrificial box could be used to package similar wastes together; these could be stored within a buffer area until sufficient boxes have been filled to allow the packaging and grouting of a 6 cubic metre concrete box. The WAGR and Pile Decommissioning Projects [27] both considered the use of sacrificial boxes, known as box liners, for their decommissioning activities.

To date, the 6 cubic metre concrete box has been certificated as a fissile excepted package where a high level of confidence that fissile limits are not exceeded is required. Unless this confidence can be achieved by using known provenance, reassurance measurements may be required. If reassurance measurements are required, it is not likely to be practical to perform them after the waste has been placed inside the package. Standard non destructive assay techniques rely on the detection of radiation from the waste. Since these packages are shielded, radiation levels from the waste will be greatly attenuated, and therefore measurements from the outside of the package are not likely to be adequate to quantify the amount of fissile material present. Another consideration is the volume of waste being measured at one time. With any non destructive assay technique, the greater the sample volume, the greater the measurement uncertainty. To prove that the package meets the criteria for a fissile excepted package, it is very likely that measurements would need to be performed on smaller samples of waste, before the waste is finally packaged.

As well as achieving dose rate limits on contact with the package, and at 1m, an additional constraint on Type IP transport packages is that the dose rate from the unshielded material contents must be less than 10 mSvh-1 at 3m at the time of an offsite movement. SLCs should have a high level of confidence that dose rates at the point of transport will meet the Transport Regulations, particularly where decay storage is being utilised. Confidence can be gained through accurate inventory compilation (historic records and physical characterisation) and decay calculations. Although some nuclides (such as cobalt-60) may contribute towards a large proportion of the dose at the time of packing, in the future when short lived radioisotope have decayed significantly, other longer lived isotopes may dominate the contribution to dose rate. At the time of packing, it may be difficult to directly measure longer lived isotopes in the presence of other significant gamma emitters, so other forms of analysis may be needed.

Packages generated so as to be compliant at the point of transport to the GDF may be more vulnerable to changes in the transport regulations should the interim storage period be significant. As the 6 cubic metre concrete box is likely to be licensed at the point of transport, ‘grandfather’ rights may not necessarily apply. This transport vulnerability would be increased by any loss of information or issues with waste package records.

21



Risks: Unable to meet the transport regulations at point of transport; unable to demonstrate compliance with LSA requirements for the wasteform

Potential Mitigations: Use of box liners to package similar wastes generated at different points of decommissioning; transport non-compliant packages in a Type-B transport package; detailed understanding of waste inventory and associated uncertainties

5.3 Limitations with on- and off-site movements

At present, the design of the 6 cubic metre concrete box incorporates a concrete lid that is cast in place once the package has been filled with waste and infilled with grout. The lid is an integral component of the waste package providing shielding and is required to be cast before the container can be moved. Therefore, generation of the waste packages must be completed before the lid is cast, in order, to enable movement to the interim storage location. The rate determining step would likely be the packaging, grouting and casting processes in a sequential decommissioning and waste packaging process. Multiple loading stations could be used to improve the through-put, and the containers could remain open until the containers are filled, encapsulated and the lid cast. Alternatively, the waste could be loaded into box liners, likely mild steel, which could be loaded into the containers to generate the package. This second option would require a shielded buffer storage area, but would de-link the decommissioning and package generation processes.


Benefits: None identified for the 6 cubic metre concrete box

Risks: Complex operations for packaging directly into 6 cubic metre concrete boxes; packaging and lid casting limits the decommissioning programme

Mitigations: Use of box liners and buffer storage; package 6 cubic metre concrete boxes outside of decommissioning programme

5.4 Shielding of waste

To date, two types of 6 cubic metre concrete box have been used, a version with standard concrete walls, and a version with high density concrete walls, to provide extra shielding. The high density version generally contains a superplasticiser and the formulation should be agreed with RWMD; this is discussed in Section 4.6.

It may be possible to add extra shielding inside the package to achieve the transport dose rates and to ensure the cumulative doses to workers are ALARP. However, waste packages will still need to be able to demonstrate that the wasteform is LSA material or SCO. Any changes to the standard waste container, such as the inclusion of additional shielding would constitute a change to the package design and would require re-certification for transport. Additionally, extra shielding to provide dose rate reductions may result in the package being deemed non-compliant in respect of the unshielded dose rate requirements, see Section 4.2.


Benefits: HD options provides greater shielding

Risks: Gross mass limits may be challenged; unshielded dose rate limit breached

22

Mitigations: Inventory management

5.5 Management of reactive metals

If the waste stream contains metals that may adversely react with the cementitious infilling grout (aluminium, uranium, magnesium, etc) then the issue of hydrogen formation and the expansive corrosion product when subjected to the alkaline environment of the cement pore water must be considered. The 6 cubic metre concrete box structure does not cope with the expansive forces as well as steel or DCI based containers. Potential solutions may include limiting the surface area of reactive metals packaged, or using an alternative infill such as a polymer, or geopolymer cement. Use of an alternative encapsulant may require a significant R&D programme to underpin the performance and compatibility of the proposed wasteform. This would include demonstration of the container characteristics for use within the GDF and specifically the activities associated with gaining a transport approval certificate. As with superplasticisers, security of supply should be considered due to the nuclear sector being a minor user of these materials. The issue of expansive corrosion is discussed in Section 4.4.


Benefits: None specific to 6 cubic metre concrete box

Risks: Failure of container integrity

Mitigations: Manage volume and surface area of reactive metals in packages; use of alternative encapsulants

5.6 Waste emplacement within the package

Consideration should be given to the method of placing waste into the package. For some items, package furniture may be advantageous, as it could maximise the packing density. A variety of specific furniture was developed for the WAGR boxes, such as ‘toast racks’ and ‘milk crates’; these could be used in future uses of the 6 cubic metre concrete box. Loose tipping may be an option for some types of waste, however contamination control, mentioned above, would need to be considered, as would damage to the container. The selective emplacement of some items of waste may be beneficial to enable dose rates to be optimised. However, the package must still meet the relevant transport requirements. Furniture gives some damage protection to the inside of the box during the packing process. It does utilise some space within the package, but can be designed to assist with void minimisation during the encapsulation process.


Benefits: Voidage minimisation

Risks: Container damage (loose tipping)

Mitigations: Appropriate packaging technique employed

23

6 Storage requirements

General guidance on the interim storage of ILW packages in the UK is provided by NDA [28], [29] and [30] and the regulators [31]. Currently, WAGR decommissioning wastes are stored in an unshielded store with a capacity of ~240 contact-handled reinforced concrete packages (Figure 7) [32].

Figure 7 Shielded WAGR boxes stacked inside the WAGR store at Sellafield alongside the purpose-built shielded fork lift truck used to move the boxes

6.1 Environmental conditions

Degradation of concrete waste packages, including cementitious and steel reinforcement materials, is affected by a number of environmental conditions. For example, the potential for water condensation to occur on surfaces which may facilitate penetration of aggressive ions into the concrete and influence the rate at which the concrete degrades is affected by the relative humidity and consequently the temperature of a store. Transient conditions increase the risk of condensation and therefore the risk of degradation of concrete waste packages [29]. Freeze-thaw conditions [28] have the potential to cause spallation of the cementitious materials; therefore, reinforced concrete waste packages should be kept at temperatures above 0°C.

Carbonation is a key concrete degradation mechanism which depassivates the oxide layer on steel reinforcement, making it more susceptible to corrosion [35]. A low store temperature combined with a low relative humidity will prevent initiation of reinforcing bar corrosion and reduce the risk of carbonation [35]. The risk of expansive corrosion from reactive metal wastes, which could lead to cracking of the package, may also be reduced by maintaining lower temperatures within the store. The corrosion of the steel reinforcement bars in concrete waste packages is accelerated by the presence of aggressive ions, such as chloride or sulphide [33]. Chloride-induced localised corrosion could result from deposition of chloride on packages combined with the presence of surface moisture, due to diffusive penetration. A chloride concentration of 400 ppm in pore fluids is considered to be the threshold for the onset of localised corrosion [34]. Steel

24

reinforcement bars should be at the defined depth beneath the concrete to protect the bar from corrosion and therefore mitigate the risk of concrete spallation.

Although the environmental factors discussed above are the same as those that affect stainless steel and mild steel containers [28], different degradation mechanisms are expected.

6.2 Operational considerations during storage

Prior to and during storage, consideration should be given to the promotion of good air flow (potentially using computational fluid dynamics (CFD) modelling) and the control of temperature and relative humidity to prevent stagnant environments and localised condensation events. Filtration of inlet air can be used to minimise the concentration of harmful particulates (e.g. chlorides and sulphides). The WAGR box store stacks waste packages three high, separated by spacers to improve air flow [32], as shown in Figure 7.

6.3 Monitoring and inspection

The waste packages and the store should be monitored and inspected on an appropriate frequency that enables the early identification of enhanced degradation conditions or the start of any waste package degradation. The store should be monitored for ingress of water (due to leaks), temperature and relative humidity. In the WAGR box store, temperature and relative humidity are monitored weekly. Methods to monitor and inspect reinforced concrete waste packages include:

Visual inspection; to detect staining caused by general corrosion, pitting or cracking of the concrete and degradation from interaction with aggressive or corrosive chemical agents. Digital photography could also be used to assess these package degradation indicators.

Structural integrity inspection; to provide early warning of progressive degradation mechanisms such as the depth of carbonation fronts over time. Dummy packages could be used to measure the corrosion potential or corrosion rate of the concrete and its steel reinforcement [35].

25

7 Transport requirements

The safety of transporting radioactive materials is ensured by a stringent regulatory regime, underpinned by the IAEA Transport Regulations [8]. The IAEA Transport Regulations specify criteria that must be met by each transport package. Criteria are dependent on the type of transport package, and the 6 cubic metre concrete box is a Type IP transport package as defined by the Regulations.

Compliance with the requirements of the IAEA Transport Regulations is demonstrated by the Package Design Safety Report (PDSR) which includes all the information required to demonstrate the safety of the transport package and establishes limits on key parameters that describe the package inventory. The PDSR is submitted to the national Competent Authority (CA) for approval. If the PDSR is satisfactory, the CA will issue a license for the use of the transport package. For Type B packages the competent authority in the UK is ONR-RMT. The package designer (or a suitable independent body) may act as the Competent Authority for Type IP packages.

The Certificate of Approval for the WAGR box has expired. The responsibility for producing a PDSR lies with the Design Authority, which is normally the designer. This is considered within Appendix 3.

The 6 cubic metre concrete box must meet the criteria set out in the Regulations that are specific to Type IP waste containers. Criteria relate to, for example, the type and level of waste and it’s immobilisation, the dose rate from the unshielded and shielded package, the fissile material contents, mass, heat generation, and surface contamination.

A high-level discussion on each criterion in relation to IP-2 packages in general is given below in Section 7.1 and a fuller discussion in Appendix 2. A summary of the implications for the 6 cubic metre concrete box, compared to alternative Type IP packages, is given in Section 7.2.

It should be noted that the criteria set out by the IAEA Transport Regulations are upper limits to ensure the safety of operators and the public during transport. Another less quantifiable requirement set out in the Regulations is that protection and safety shall be optimized in order that the magnitude of individual doses, the number of persons exposed, and the likelihood of incurring exposure shall be kept as low as reasonably achievable. Hence waste packagers have a responsibility to ensure risks posed by the packages are ALARP, and not just packaged within the limits. In particular, RWMD’s LoC Disposability Assessment process assesses not only that the dose of an individual package is within the limit but that the cumulative dose received by an operator from handling multiple packages is acceptable.

7.1 General requirements for a Type IP package

The criteria set out in the IAEA Transport Regulations are as follows:

1. The waste must conform to the definition of Low Specific Activity (LSA) material or Surface Contaminated Objects (SCO)

The two types of LSA material suitable for transport of HAW are:

a) LSA-II: Criteria apply to encapsulated or non-encapsulated material in which the activity is distributed throughout.

b) LSA-III: Criteria apply to encapsulated material which is relatively insoluble, in which the activity is throughout a solid is essentially uniformly distributed in a solid compact binding agent.

26

In order for the waste to be classified as LSA-II or LSA-III material, the radioactivity must either be distributed throughout the wasteform (for LSA-II) or be essentially homogeneous (for LSA-III). To be considered as distributed throughout the waste, the specific activity in any tenth of the package should not be over ten times the specific activity in any other tenth of the package.

IAEA Advisory Material states that there is no need to compare the specific activity of each portion provided the estimated maximum average specific activity in any portion is below the limit. That means that if each portion of the waste would qualify as LSA-II material when taken in isolation, the waste as a whole is still LSA-II even if specific activity varies. This is particularly useful for activated steel components.

2. The dose rate from the unshielded waste form should not exceed 10 mSv/hr at 3 m

Compliance with this criterion is not dependent on the type of IP-2 waste container used.

3. The external package dose rate must not exceed 0.1 mSv/hr at 1 m from the surface and must not exceed 2 mSv/hr on the surface

The external package dose rate is dependent on the shielding provided by the waste container. Limits on the activity of each radionuclide necessary to meet this criterion are set out in the contents specification for the package type, usually available in the PDSR. If a contents specification is not available, or does not include all relevant radionuclides, the waste producer should undertake dose rate calculations based on the shielding thickness of the waste container walls to ensure this criterion can be met.

4. The amount of fissile material in a Type IP transport package must be within fissile exception limits

Fissile exception is described fully in Appendix 2. The ability to meet this criterion is not dependent on the type of waste container, but on the waste to be packaged.

5. Gross mass

Although not a specific requirement of the IAEA Transport Regulations, limits apply to the gross mass of a transport package to ensure it is transportable on the UK road or rail network.

The maximum gross mass for any load to be carried by standard HGV on the roads is 30 te, hence with a loaded mass of 50 te, the 6 cubic metre concrete box is unsuitable for road transport. Transport packages which would exceed the 30 te limit could be carried using a Special Types General Order (STGO) vehicle6 as stated in the GTSD [36] but additional provisions are required in respect to permissions and route availability e.g. strength of bridges etc. Use of STGO vehicles are typically limited to journeys between sites and a remote railhead and are subject to operational restrictions e.g. speeds and restricted turning circles.

The GTSD currently assumes the use of a four-axle wagon for the transport of ILW transport packages. The maximum permissible axle loading for most of the UK rail system is 22.5 te per axle and this leads to a maximum loaded rail wagon mass of 90 te for such a wagon. The current design of wagon for the transport of ILW has an unladen mass of ~26 te which limits the maximum transport package mass to ~64 te [37]. However, due to the stacking requirements in a GDF the gross mass of a 6 cubic metre box is further restricted to 50 te, as stated in [7].

6 Sometimes known as Special Category vehicles

27

6. The temperature on the surface of the package should be less than 50°C

Heat is generated most significantly by radiogenic heat and also by biodegradation, corrosion and other chemical reactions. Heat at the surface generated by the waste within the package is dependent on the volume of the waste package, and RWMD has set limits in accordance with this. The limit on the 6 cubic metre concrete box is 60 W at the time of transport, and for the 4 metre Box and 2 metre Box the limits are 200 W and 60 W respectively.

7. Non-fixed surface contamination

Limits for surface contamination are given in Appendix 2. Smooth, hard, corrosion resistant surfaces are best for minimising surface contamination, so as with any wholly concrete box there remains the potential for the 6 cubic metre concrete box packages to exceed the non fixed surface contamination limits. This would most likely be due to caesium-137 leaching over time.

The properties of waste container material that would influence surface contamination have been previously investigated [38]. The key means of minimising the risk of the non-fixed surface contamination of a waste package is by good practice during manufacture, storage, handling etc and by effective decontamination in the event that activity becomes attached to the external surfaces of the waste package. In the case of waste packages containing conditioned ILW, decontamination is normally achieved by the use of water jetting and/or swabbing to mechanically remove loosely attached particulate activity. However, the use of these techniques would abrade the surface of the 6 cubic metre concrete box and greater emphasis is required on the protection of the boxes from contamination.

8. Gas generation and release

There are no limits placed on gas generation rates for shielded ILW packages within the GDF. Furthermore, the permeable nature of the 6 cubic metre concrete box concrete structure would allow passage of internally generated gas, preventing internal pressure build-up provided the generation rate is lower than the capacity of the box to vent.

9. Worker dose

It is possible that transport of a large number of transport packages, each individually compliant with the dose rate criterion, could result in unacceptable doses to transport workers. RWMD’s LoC Disposability Assessment process checks for this, and a Letter of Compliance may not be issued if this cumulative dose target is challenged. An unacceptably high cumulative dose is most likely to result from a large number of transport packages, each with a relative high (albeit compliant) external dose rate. Waste producer’s should keep this in mind, and can seek advice on the matter from RWMD.

7.2 Summary of specific transport considerations for the 6 cubic metre concrete box

The ability to meet some of the above criteria is dependent on the specific Type IP package, i.e. some criteria might be easier to meet depending on whether a 6 cubic metre concrete box or another Type IP waste container is used. Specific considerations are as follows:

The dose rate from the shielded transport: This is dependent on the shielding provided by the waste container. To reduce the external package dose rate, consideration could be given to the use of a transport container. This could also be beneficial in achieving compliance with surface contamination criterion.

28

The gross mass of the waste container: The maximum allowable gross mass for road transport is 30 te; which a laden 6 cubic metre concrete box exceeds at 50 te (maximum total weight).

Surface contamination: Limits for surface contamination are given in Appendix 2. There is a potential for 6 cubic metre concrete box packages to exceed the non fixed surface contamination limits at some time in the future due to caesium-137 leaching. This could be minimised by good practice in operating procedures and also through the use of a transport container.

Package approval: The PDSR for the WAGR box has lapsed. It is understood that all historical documents relating to the design approval have now transferred to International Nuclear Services (INS) [11].

29

8 Challenges and mitigations

The 6 cubic metre concrete box has the potential to provide a cost-effective waste packaging for a limited range of wastes; there are aspects of the 6 cubic metre concrete box design that could be improved upon to enable the range of wastes to be increased or where the wasteform could be adjusted to minimise deleterious effects. There are also technical and commercial risks that SLCs should account for in their decision making process and ensure that appropriate mitigations (for example, research and development, operating procedures) are devised and implemented. These are highlighted below.

8.1 Potential improvements

A range of improvements could be made to the 6 cubic metre concrete box to enhance the containers ability to manage container integrity risks or compliance with the GDF concept. Any changes to the 6 cubic metre concrete box design would require discussion with the Design Authority and RWMD to determine re-certification and transport and disposability needs at the GDF. A programme of R&D to underpin the design changes, such as impact assessment, may also be required. These are described below:

Nuclide migration: Migration of certain mobile nuclides (Sections 4.5 and 5.1) could be managed by modifying the box design to incorporate an impermeable, positive cavity, lidless liner within the box cavity. Gases generated by the wasteform could vent through the top face of the liner and the container. Use of a sealant has previously been assessed and endorsed by RWMD.

Reinforcement corrosion: Atmospheric chloride induced corrosion (Section 4.4) of the steel reinforcement is the most significant corrosion mechanism that could lead to degradation of 6 cubic metre concrete boxes. A surface coating could provide protection from chloride deposits in addition to the management of environmental conditions during storage (both prior to and after packaging).

Expansive corrosion: An alternative grout infill could be identified to mitigate the risk of waste degradation from corrosion processes and mitigate the risk of container failure due to expansion of the wasteform (Section 4.5). LoC assessment may require the completion of R&D activities such as leach tests, revised impact modelling or to consider corrosion mechanisms between the infill grout and the wastes to be packaged. The operational implications of a revised infill encapsulant would need to be assessed; both in terms of safety (for example, the high gel temperatures of some polymer based systems) and in ease of operations. Security of supply should be considered for any alternative encapsulants.

Box liners: Both the WAGR and Piles Decommissioning Projects considered the use of box liners, a sacrificial box, to provide an initial container for packaging waste. This approach may be advantageous to SLCs as the box liners can be used to package similar activity wastes together, regardless of when they are generated in the decommissioning process. Similar box liners could then be assayed and transferred to a 6 cubic metre concrete box providing confidence that the LSA requirements are met and that a good packing fraction is achieved.

8.2 Risks

Use of the 6 cubic metre concrete box carries specific risks for the nuclear sector. These are described below:

Non-compliance with LSA or SCO requirements: Only LSA or SCO, as defined by the Transport Regulations, can be packaged within 6 cubic metre concrete boxes. SLCs should

30

be confident that the wastes they intend to package are either LSA or SCO. For LSA material, the activity must be evenly distributed throughout the package. Emplacement of waste items within the package may require additional measures to distribute the activity. SLCs may also wish to consider whether the waste will be LSA at the point of transport and whether it can still meet the evenly distributed requirement after storage due to differences in the half-life of radionuclides. SCOs are solid objects which are not intrinsically radioactive but which have radioactive material distributed on their surfaces. Objects which are radioactive themselves (e.g. activated objects) and are also contaminated cannot be classified as SCOs. If there are concerns on the nature of the wastes and the subsequent classification as LSA or SCO, an alternative waste package may be more appropriate.

Meeting fissile exemptions: One of the three fissile exceptions must applicable to the proposed waste packages in order to use the 6 cubic metre concrete box [Appendix 2]. Challenges to the exceptions may be fissile contamination. Trace impurities should also be considered when assessing activated metals. SLCs may wish to consider Type B and Type IF containers7 if there is concern on meeting the fissile exceptions.

Transport Regulations are modified: The Transport Regulations are likely to change during the interim storage period for 6 cubic metre concrete boxes. A risk is that the boxes will not meet the transport regulations at the point of transport. SLCs should consider the most appropriate method of mitigating the risk; an example is the re-packaging the 6 cubic metre concrete box into an alternative transport packaging.

Lapsed package approval: The Package Approval for the 6 cubic metre concrete box has lapsed. SLCs should discuss the re-approval of the container with the Design Authority and fully understand the programme of activities required to achieve this, prior to producing waste packages.

Change in Competent Authority: The Competent Authority is responsible for providing self-certification for packages to be transported. The 6 cubic metre concrete boxes could be interim stored on SLC sites for a significant time period, during which the original Competent Authority may be replaced. SLCs should consider the risk that the Competent Authority at the point of transport may not provide certification. The regulator should be consulted to discuss alternative arrangements for managing the transport of non-compliant packages.

Waste package integrity failure: A number of mechanisms may result in a minor, or significant, failure of the waste package integrity; these may include spalled concrete due to corrosion, expansive corrosion or damage during normal operations. Assuming that the contents meet the LSA requirements, the 6 cubic metre concrete box could be repackaged into a Type IP-2 for transport to the GDF (either whole or after sectioning). The failed waste package could also be transported to the GDF in a Type B transport container, subject to agreement with RWMD. SLCs should plan for failed or non-compliant waste packages as part of their waste management strategy.

Superplasticisers unavailable: The superplasticisers used for the WAGR box construction and infill are no longer commercially available to use for a 6 cubic metre concrete box. SLCs will need to identify a replacement superplasticiser which is underpinned by research and development. This should include engagement with RWMD on identifying the research and development needs and agreeing the composition. Typically superplasticisers have a shelf-life of around 10 years; therefore, SLCs should consider security of supply for these components.

7 A Type IF is a Package that meets the requirements of both an Industrial Package and Fissile Package as specified in the IAEA Transport Regulations and requires multi-lateral Competent Authority approval.

31

8.3 Ultimate mitigations

SLCs should apply an appropriate level of risk management to the development of packaging strategies for their wastes. Where the 6 cubic metre concrete box, and other Type IP-2 packages, are used, the SLC should consider the risks and improvements discussed in the previous section.

Even with careful risk management, there may be situations where risk mitigations are unable to be completed prior to the generation of waste packages; these include competent authority approval at the point of transport or changes in the transport regulations. SLCs should therefore have plans to manage these risks; these have been termed ultimate mitigations to show that these mitigations should only be deployed where no other option is available and where the risk cannot be mitigated at an earlier stage.

The resultant package should still be acceptable to the GDF, both in terms of its waste package properties and the handling and operational requirements.

Ultimate mitigations that may be appropriate for the 6 cubic metre concrete box are:

Transport within a Type B container: The 6 cubic metre concrete box could be transported to the GDF within a Type B container which may provide an effective mitigation for packages that do not meet the LSA or SCO requirements, but could still be emplaced within the GDF as it meets the WPS. It is probable that a bespoke Type B container would need to be designed and approved due to the size of the 6 cubic metre concrete box. An alternative approach may be the size reduction of the packages to enable the use of an existing Type B. This approach may require significant investment to provide facilities that could undertake the size reduction and provide worker protection.

External barriers: Packages that have external contamination could be managed through the application of an external barrier such as a sealant or a cover. Early engagement with the regulators, Design Authority and Competent Authority would be appropriate. Where a sealant is used, the composition would require agreement with RWMD and may require targeted R&D to underpin its use.

Overpacks: A bespoke overpack could be designed and deployed to transport the 6 cubic metre concrete box to the GDF. As with the Type B mitigation, this approach would require the design and approval of the overpack. The SLC would need appropriate facilities to transfer the 6 cubic metre concrete boxes into the overpack.

8.4 Other considerations

SLCs wishing to progress a 6 cubic metre concrete box strategy should engage early with RWMD and refer to the suite of WPSGD, including the waste package WPS. These contain the requirements and targets that RWMD expect waste packages to meet.

Selecting the optimum container and waste package strategy for a particular waste stream mitigates a range of risks to the SLC; the longevity of the waste package can be further protected by providing and monitoring optimum interim storage conditions. These can be summarised as:

Select an appropriate store temperature which is above 0°C;

Maintain a low relative humidity;

Enable good air flow between stacks;

Monitor store conditions regularly, including water ingress;

Monitor the waste packages regularly and consider the inclusion of dummy packages.

32

9 Conclusions

The 6 cubic metre concrete box is a standardised design of shielded waste container for the packaging of ILW that has been used for the packaging of decommissioning wastes generated from the WAGR and its associated facilities. As a shielded waste package, the container can be stored in an unshielded store and then transported to the GDF concept without the need for a separate transport container. The use of reinforced concrete means that this container is cost-effective in terms of capital expenditure in comparison with other IP-2 containers.

The use of 6 cubic metre concrete box has only previously been endorsed for the packaging of a limited range of wastes and due to its concrete structure may be most suitable for dry wastes with a limited mobile nuclide content. Proposals for other wastes, beyond those endorsed to date, may require the design and implementation of an R&D programme to underpin technical justifications for their packaging and disposal within a 6 cubic metre concrete box.

As with other IP-2 packages, the 6 cubic metre box can only be used for LSA or SCO wastes. LSA requires the packages to be homogeneous in terms of specific activity and SCO requires the waste to be non-radioactive except for surface contamination. Wastes also need to be compliant with the fissile exception requirements (typically the 15g per package exception is used). Where wastes challenge the defined limits and ethos of the transport regulations the use of an alternative container may be more appropriate.

There are a range of technical and regulatory risks that may require mitigation and management for the 6 cubic metre concrete box; the cost of these risks should be considered and accounted for when identifying a suitable container for waste streams. In some instances, the combined capital and development cost for a 6 cubic metre concrete box strategy may exceed that for an alternative package.

In summary, the 6 cubic metre concrete box provides an additional SILW container option that may be cost effective for wastes comparable to those already packaged and endorsed from the WAGR facility.

A1

Appendix 1: Summary of container properties

Waste Package Property

6 cubic metre

concrete box

2 metre box

4 metre box

Croft 2m Safstore

Type VI DCIC

Dimensional envelope (mm)

Length: 2438 1969 4013 1969 2000

Width: 2210 2438 2438 2438 1600

Height: 2200 2200 2200 2200 1700

Maximum gross mass (te)

50 40 65 65 25

Payload (m3) 5.8

Maximum with

200mm shielding =

4.9

Maximum with

200mm shielding =

10.9

Maximum with 120mm shielding =

7.5

Maximum with

150mm shielding

= 2.8

Activity content Contents must be LSA material or SCOs

Dose rate 0.1 mSv h-1 at 1m from waste package

2 mSv h-1 at surface of waste package

Surface contamination

0.4 Bq cm-2 for all other alpha emitters

4.0 Bq cm-2 for beta, gamma and low toxicity alpha emitters

A2

Appendix 2: Transport regulation requirements

This appendix corresponds to the 2009 Edition of the IAEA Regulations for the Safe Transport of Radioactive Material [8] which is enabled into UK law. The IAEA Transport Regulations has recently been revised and issued [9] and is likely to be enabled into UK law by 2015; notable changes from the 2009 Edition have been identified as appropriate. Waste producers should follow the 2009 IAEA Transport Regulations for waste to be transported in the near future and should carefully review the 2012 IAEA Transport Regulations for medium to long-term transport requirements.

Activity The IAEA Transport Regulations place direct limits on the activity levels of all Type IP packages (including the 6 cubic metre concrete box) by defining two permissible types of material: Low Specific activity (LSA) materials and Surface Contaminated Objects (SCO). Three categories of LSA are defined but only two types are suitable for geological disposal. Specifically:

LSA-II: For non-encapsulated material in which the activity is distributed throughout and the estimated average specific activity does not exceed 10-4A2 g

-1; and

LSA-III: for encapsulated material which is relatively insoluble, in which the activity is throughout a solid or is essentially uniformly distributed in a solid compact binding agent and the estimated average specific activity of the solid does not exceed 2x10-3A2 g

-1. LSA-III material is required to be in non-readily dispersible form, which explicitly excludes powders and liquids. Waste packagers will be required to conduct a leaching test in order to demonstrate sufficient solubility of the material when exposed to weather conditions such as rainfall.

SCOs are solid objects which are not intrinsically radioactive but which have radioactive material distributed on their surfaces. This description excludes bulk radioactive material (e.g. uranium metal) and materials such as metals and graphite which have become radioactive as a result of neutron irradiation.

Objects which are radioactive themselves (e.g. activated objects) and are also contaminated cannot be classified as SCOs. Such objects may be regarded as LSA material provided that the requirements in the LSA definition are complied with. In addition, some objects which could potentially be classified as an SCO may have an ‘inaccessible’ surface, which may result in difficulties in demonstrating that the object can be classed as an SCO. Inaccessible surfaces may include the inner surfaces of pipes or maintenance equipment which are closed or blanked off. Under these circumstances, the object may be classified as LSA material by demonstrating compliance with the LSA definition.

Two categories of SCOs are defined on the basis of the degree of fixed and/or non fixed surface contamination. The surface contamination limits for SCOs with the highest level of surface contamination (i.e. SCO-II) are listed below:

A3

Nature of contamination

Contamination on surfaces of object averaged over 300 cm2 (Bq cm-2)

- and -emitters and low toxicity -emitters

All other -emitters

Non-fixed contamination on accessible surfaces

400 40

Fixed contamination on accessible surfaces

8 x 105 8 x 104 Non-fixed plus fixed contamination on inaccessible surfaces

For waste containing combustible solids a further restriction of 100 A2 is placed on the total activity of LSA material or SCOs carried on a single vehicle

Dose rate The total quantity of LSA material or SCOs that can be carried in a Type IP-2 transport package is such that the ‘unshielded’ dose rate from the “unpackaged” waste itself at 3 m does not exceed 10mSv h-1. The benefits on any self-shielding by the waste itself, or that provided by any encapsulating materials, can however be taken into account when assessing the ‘unshielded’ dose rate.

Fissile material The NDA specifies that for Type IP transport (including the 6 cubic metre concrete box), the quantities of fissile material, neutron moderators and reflectors in the waste package should be controlled to ensure that they can be excepted from the requirements of the IAEA Transport Regulations for packages containing fissile material.

Three ways of gaining an exception are currently defined [8]:

i. A total consignment1 limit of 290 g of uranium-235 or 180 g of any other fissile nuclide, provided there are not more than 5 g of fissile nuclides in any 10 litre volume of material in the package;

ii. A individual transport package limit of 15 g of fissile nuclides, provided that the total consignment limit defined in (i) is not exceeded; or

iii. Transport packages containing uranium with a uranium-235 concentration of no more than 1%, provided that the fissile nuclides are distributed essentially homogeneously throughout the bulk of the materials in the package.

The 2012 IAEA transport regulations have an amended definition of fissile exceptions, which state that each package should not contain more than 2 g of fissile material, and that each consignment should not contain more than 15 g of fissile material. These changes could make a significant difference to waste packaged in the near future, which undergoes an extended interim storage period prior transport. Waste producers should therefore use an edition of the IAEA transport regulations that is appropriate to their transport timescales.

The NDA has produced guidance to assist waste packagers in the application of fissile exceptions from the requirements of the IAEA transport regulations [12].

A4

The IAEA Transport Regulations define fissile nuclides as being U-233, U-235, Pu-239 and Pu-241. Excluded from the definition of fissile material are:

a) Natural uranium or depleted uranium which is unirradiated.

b) Natural uranium or depleted uranium which has been irradiated in thermal reactors only.

Note that the 2012 IAEA Transport Regulations state two further definitions:

c) Material with fissile nuclides less than a total of 0.25 g.

d) Any combination of (a), (b) and/or (c).

The IAEA transport regulations do permit type IP packages to carry fissile material and such packages are referred to as type IF packages. IF packages are subject to additional test requirements over and above the fissile but the additional package test requirements are unlikely to be met by the large packages used for GDF disposal purposes

Mass The maximum gross mass of a 6 cubic metre concrete box waste package is 50 te. This limit allows the waste package to be transported by rail but not by conventional HGV. Payload varies according to density of the waste container:

Heat generation The heat generated by the waste package should not exceed 60 W at the time of transport.

Surface contamination Non-fixed surface contamination averaged over an area of 300 cm2 of any part of the surface of the waste package, shall not exceed:

4.0 Bq cm-2 for beta, gamma and low toxicity alpha emitters and;

0.4 Bq cm-2 for all other alpha emitters.

If these levels are exceeded, this would necessitate the requirement to overpack 6 cubic metre concrete boxes at the time of transport.

A5

Appendix 3: A précis of INS report: “WAGR box Design Authority clarification and document review”

The draft International Nuclear Services (INS) report “WAGR Box Design Authority Clarification and Document Review” TDP/029/1/1003 – Revision 1 was prepared on behalf of RWMD to:

Clarify the status of 6 cubic metre concrete box transport certification;

Investigate the possibility of increasing the fissile content.

Status of WAGR box transport certification INS considers the current status for transport certification for the WAGR box to be as follows:

The current regulatory approval for the WAGR Box has lapsed;

For INS to act as the Design Authority (DA) for the WAGR box, a formal agreement between the NDA and INS is necessary. Regulatory approval for INS to fulfil the role can then be sought;

NDA and therefore INS have Intellectual Property Rights (IPR) for the WAGR box;

The WAGR IPR will be needed by the DA to apply for a licence;

The available certification documentation (included in the IPR) for the WAGR box is considered sufficient for a successful licence application, assuming that the lifetime records of packaged WAGR boxes are available and of adequate standard.

The risks associated with relicensing are manageable but include:

NDA, and hence INS, access to WAGR Box IPR is limited to the “Authority Field of Use.” Exclusive Exploitation Rights are owned by Babcock. It would be prudent to obtain agreement with Babcock before proceeding with relicensing.

The duration of the relicensing process can be quite protracted - approximately 2 years. Waste producers would carry a risk that the WAGR box could not be relicensed and rework would be necessary.

The WAGR box was licensed as a Type IP-2 transport package up until June 2009, when the licence expired. The licence was granted against the 2005 Edition of the Transport Regulations [39]. There have been minimal changes regarding LSA and IP-2 criteria in the 2009 and 2012 edition of the Transport Regulations, therefore risks of relicensing are low in this respect.

Possibility of increasing fissile material content RWMD currently specifies that IP packages for disposal in the GDF must be “fissile excepted”. One possibility for increasing the fissile content over and above the limits for excepted packages in the 2009 and 2012 editions of the transport regulations would be to obtain Competent Authority approval for the 6 cubic metre concrete box as a Type IF package under the existing regulations. This would include proving sub-criticality after an accident consistent with Type B test conditions. i.e. 9 m drop test, 800 °C fire test, punch test and water immersion tests.

The risk with this strategy is significant in that considerable damage to a 6 cubic metre concrete box would occur after Type B testing - possibly the complete destruction of the box. Modelling of the package accident performance, in conjunction with early consultation with the ONR, could mitigate this risk.

A6

This strategy is waste specific, possibly requiring multiple waste specific assessments. A reduction of the number of assessments may be possible by the definition of bounding cases but this may be problematic.

A7

References

1 NDA (2011), Strategy Effective from April 2011, ISBN 978-1-905985-26-5. Also available at: http://www.nda.gov.uk/documents/upload/NDA-Strategy-Effective-from-April-2011-print-friendly-version.pdf.

2 LLW Repository Ltd (2009), LLW Strategic Review, Report Number NLWS/LLWR/01, Issue 1, January 2009. Also available at: http://www.nda.gov.uk/documents/upload/LLW-Strategy-Review-Issue-1-January-2009.pdf.

3 NDA (2011), Higher Activity Waste Credible Options (Gate A), Document Number SMS/TS-D1-HAW/001A, February 2011. Also available at: https://www.nda.gov.uk/documents/upload/Higher-Activity-Waste-Credible-Options-February-2011.pdf.

4 NDA (2008), Geological Disposal: Waste Package Specification and Guidance Documentation, WPS/650: Guide to the Letter of Compliance Assessment Process, March 2008.

5 NDA (2012), Geological Disposal: Generic Waste Package Specification, Report no. NDA/RWMD/067, 2012.

6 NDA (2012), Geological Disposal: Generic Specification for Waste Packages Containing Intermediate Level Waste, Report no. NDA/RWMD/068, 2012.

7 NDA (2012), Geological Disposal: Waste Package Specification for 6 cubic metre concrete box waste packages, WPS/360/01, 2012.

8 IAEA (2009), Regulations for the Safe Transport of Radioactive Material 2009 Edition, IAEA Safety Standards Series No. TS-R-1, 2009.

9 IAEA (2012), Regulations for the Safe Transport of Radioactive Material 2012 Edition, IAEA Safety Standards Series No. SSR-6, October 2012.

10 NDA (2012), Geological Disposal: Guidance on the achievement of adequate performance for encapsulated ILW Wasteforms, WPS/501/01, 2012.

11 INS (2012), Draft WAGR Box Design Authority Clarification and Document Review, Report no. TDP/029/1/1003, Revision 1, July 2012.

12 NDA (2009), Geological Disposal: Waste Package Specification and Guidance Documentation WPS/911: Guidance on the Application of the IAEA Transport Regulations for the ‘Fissile Exception’ of Waste Packages, January 2009.

13 NDA (2009), Waste Package Specification and Guidance Documentation WPS/910: Guidance on the Application of the LSA Material Criteria to Waste Packages.

14 http://www.curtis-enterprises.com/html/Concrete%20Admixtures/MSDS%20Sheets/Readymix/Sikament%2010.pdf , accessed 5 July 2012.

15 Hanson Ltd, RHPC Technical data sheet. Available from: http://www.heidelbergcement.com/NR/rdonlyres/9921CD98-A1B0-4252-9AA5-B653D2F66E80/0/HansonRapidHardeningDataSheet.pdf Accessed 4 July 2012.

16 NDA (2010), Executive Summary of Windscale Advanced Gas-Cooled Reactor (WAGR) Stringer Steel wastes at Sellafield (Extension to Final stage), May 2010. Also available at: http://www.nda.gov.uk/documents/upload/WAGR-Stringer-Steel-wastes-at-Sellafield-extension-to-final-stage-May-2010.pdf

A8

17 Research Sites Restoration Limited (2012), Integrated Waste Strategy, NDA/038/IWS, Issue 4, March 2012. Also available at: http://www.research-sites.com/UserFiles/File/publications/general-linfo/RSRL%20Integrated%20Waste%20Strategy%20-%20Issue%204%20-%20Mar%202012.pdf , accessed 16 July 2012.

18 NDA (2010), Executive Summary of Assessment Report; Magnox Care and Maintenance Preparation Wastes in Ductile Cast Iron Containers (Conceptual stage), May 2010.

19 ONR (2011), Paper of Intent – Proposed Strategy for Long-term Management of Intermediate Level Waste Ion Exchange Resin, Report no. NP/SC 7609, ONR-SZB-PAR-11-036, October 2011.

20 http://www.croftltd.com/products/prod_sheets/4004%20-%202m%20Safstore.pdf, accessed 12 July 2012.

21 NDA (2012), An Overview of NDA Higher Activity Waste, February 2012. Also available at: http://www.nda.gov.uk/documents/upload/An-overview-of-NDA-higher-activity-waste-February-2012.pdf.

22 http://gbr.sika.com/dms/getdocument.get/96628e77-c362-31cd-b1b3-9fe86cca70e5/SikaTop%20Seal%20107%20PDS%20(CE).pdf; accessed 5 July 2012.

23 NDA (2012), Summary of Assessment Report. Assessment of the Generic Use of Comb Superplasticisers in Cement Grouts for Packaging of ILW, April 2010.

24 A.J. Young, P. Warwick, M. Felipe-Sotelo, T. Beattie and S.Williams, The effect of cement superplasticisers on the solubility and sorption of radionuclides, Department of Chemistry, Loughborough University and NDA RWMD. Available at: http://www.diamondconsortium.org/main_pubs/2010/File%2004%20-%20113%20Amy%20Young.pdf , accessed 5 July 2012.

25 NDA (2011), Effect of ADVA Cast 551 on the Solubility of Plutonium(IV) and Uranium(VI), Serco Assurance Report for NDA RWMD, Report No. SERCO/TAS/003145/001 Issue 02, March 2011. Also available at: https://www.nda.gov.uk/documents/upload/Effect-of-ADVA-Cast-551-on-the-solubility-of-plutonium-IV-and-uranium-VI-report-to-NDA-RWMD-March-2011.pdf.

26 NNL (2012), Current status paper on the potential use of Superplasticisers in a Geological Disposal Facility, July 2012.

27 NDA (2009), Executive Summary: Concrete and Metal Waste from the Windscale Pile Reactors, Summary of Assessment Report, August 2009.

28 NDA (2011), Interim Storage of Higher Activity Waste Packages – Integrated Approach, Industry Guidance, Issue 1, August 2011. Also available from: http://www.nda.gov.uk/documents/upload/Interim-Storage-of-Higher-Activity-Waste-Packages-Integrated-Approach-August-2011.pdf#.

29 NDA (2008), Waste Package Specification and Guidance Documentation: WPS/630: Guidance on Environmental Conditions during Storage of Waste Packages, Report no. 8766013, March 2008. Also available from: http://www.nda.gov.uk/documents/upload/WPS-630-Guidance-on-Environmental-Conditions-During-Storage-of-Waste-Packages-2008.pdf.

30 NDA (2008), Waste Package Specification and Guidance Documentation: WPS/640: Guidance on the Monitoring of Waste Packages during Storage, Report no. 8765291, March 2008. Also available from:

A9

http://www.nda.gov.uk/documents/upload/WPS-640-Guidance-on-Monitoring-of-Waste-Packages-During-Storage-2008.pdf.

31 SEPA, Environment Agency and ONR (2011), Joint Guidance on the Management of Higher Radioactive Waste on Nuclear Licensed Sites. Part 3c: Storage of radioactive waste, November 2011. Also available from: http://www.hse.gov.uk/nuclear/wastemanage/rwm-part3c.pdf.

32 S.M. Wickham et al. (2005), Identification and Analysis of Interim Safe Storage Conceptual Store Designs: Storage Database. Report for BNFL no. 0234-5, Version 3.

33 Breton et al. (2005), Dossier de Synthese des Etudes d’Entrepots de Longue Duree. Entreposage en surface des dechets MA-VL. CEA Rapport Technique DTEC/2005/3.

34 J. Kissel and A. Pourbaix (1996), Les effets combinés de la teneur en chlorure et de l'alcalinité des bétons sur la corrosion de l'acier. Rapports Techniques CEBELCOR, Vol.165, RT.315, 1996.

35 NDA (2010), Higher Activity Waste – Interim Store Performance and Monitoring, UKAEA and GSL Report for NDA, Report no. TSG (10) 0650, Issue 1, March 2010.

36 NDA (2010), Geological Disposal: Generic Transport Systems Design, NDA/RWMD/046.

37 INS (2010), A Review of the use of 8-axle rail wagons (Type KXA-C) on the UK rail network, November 2010.

38 Nirex (2003), Waste Container Design Requirements and Methods for Control of Surface Finish, Nirex Report N/087.

39 IAEA (2005), Regulations for the Safe Transport of Radioactive Materials, 2005 Edition, TS-R-1, IAEA Safety Standards.

Certificate No 4002929

Certificate No 4002929

Nuclear Decommissioning AuthorityRadioactive Waste Management DirectorateBuilding 587Curie AvenueHarwell OxfordDidcotOxfordshire OX11 0RH

+44 (0)1925 802820

+44 (0)1925 802932

www.nda.gov.uk

© Nuclear Decommissioning Authority 2013

t

f

w

Geological Disposal: Upstream Optioneering - Overview … · Windscale Advanced Gas-cooled Reactor...

Documents

Transcript of Geological Disposal: Upstream Optioneering - Overview … · Windscale Advanced Gas-cooled Reactor...