A report prepared by Quintessa for and on behalf the Low Level Waste Repository Site Licence Company.

Transcription

1 Low Level Waste Repository LLWR Environmental Safety Case Assessment of Potential Implications of Waste Treatment and Packaging Innovations on Long-term Safety A report prepared by Quintessa for and on behalf the Low Level Waste Repository Site Licence Company. Copyright in this document belongs to the Nuclear Decommissioning Authority QRS 1443H R2 Version 1.0 (Plus Goldsim Error Note) Date: Subsequent to the issue of this report, an error has been found in the assessment calculations undertaken for release in groundwater, using the program GoldSim. The error, which is described in more detail in LLWR/ESC/MeM(09)058, means that the flux of any sorbing radionuclides from the repository and the corresponding radiological impact may have been overestimated. The results provided in this report for sorbing radionuclides should not be used. Any related enquiries should be made to the LLWR ESC Project Manager

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3 LLWR ESC Technical Support Framework Assessment of Potential Implications of Waste Treatment and Packaging Innovations on Long-term Safety Alan Paulley George Towler James Penfold Laura Limer James Wilson QRS-1443H-R2 Version 1.0 June 2009

4 Document History Title: Subtitle: Client: LLWR ESC Technical Support Framework Assessment of Potential Implications of Waste Treatment and Packaging Innovations on Long-term Safety LLWR Ltd Document Number: QRS-1443H-R2 Version Number: Version 1.0 (Draft for Client Comment) Date: June 2009 Notes: Prepared by: Reviewed by: Submitted to LLWR Ltd for comment. Alan Paulley, George Towler, James Penfold, Laura Limer, James Wilson. Mike Egan Version Number: Version 1.0 Date: June 2009 Notes: Prepared by: Reviewed by: Approved by: Issue incorporating updates in response to client comments. Alan Paulley, George Towler, James Penfold, Laura Limer, James Wilson. Mike Egan Alan Paulley Quintessa Limited Dalton House Tel: +44 (0) Newtown Road Fax: +44 (0) Henley-on-Thames Oxfordshire RG9 1HG United Kingdom

5 QRS-1443H-R2, Version 1.0 Summary This study is part of a programme of work, being undertaken by the Low Level Waste Repository (LLWR), to produce an Environmental Safety Case (ESC) for submission to the Environment Agency by May The LLWR is also supporting the Nuclear Decommissioning Authority (NDA) in the development of a National Strategy for Low Level Waste (LLW) management, one aspect of which concerns plans for innovations that could have implications for the nature of wastes to be disposed to the LLWR. The purpose of this study is to evaluate the potential impact of these innovations on repository performance. Innovations Considered The innovations considered in this report are: VLLW diversion for disposal elsewhere; surface metal decontamination and metal melting; supercompaction and/or incineration of combustible wastes; use of disposal containers other than half-height ISO containers; and reduction in the quantities of grout used. The innovations would be part of a strategy to reduce the volume of waste for disposal and ensure the most effective use of available disposal capacity at the LLWR. They will have implications for the overall inventories of materials and radionuclides, and thus for the system geochemical conditions that are relevant to long-term safety. For example, reduced levels of grout will tend to reduce the overall system ph, with implications for radionuclide solubility, sorption and carbonation processes. Reduced metal and cellulose-containing waste volumes will tend to lead to more oxidising conditions, which will also influence solubility and sorption. Estimated Inventories of Materials and Radionuclides for Disposal to the future Vaults Estimates of the disposal inventory in future Vaults were undertaken, taking account of different innovations, and based on the 2007 National Inventory. These estimates confirm the scope for extending the disposal lifetime of the future Vaults (assuming that disposals are restricted to what was the consented area for planning purposes) iii

6 QRS-1443H-R2, Version 1.0 until around Consistent with existing LLWR estimates, application of VLLW diversion alone would extend the lifetime from around 2020 by up to a decade; the application of metal treatment would extend this to around ; adoption of incineration may add up to a further decade. The calculations indicate that incineration would need to be adopted at an early time to make a significant contribution to extending the disposal lifetime, as a significant proportion of the wastes that could be treated through incineration are predicted to arise pre Taking account of revised inventory estimates in the 2007 National Inventory, inventories for most of the key radionuclides associated with long-term environmental impacts are likely to be reduced compared with previous assessments. This builds confidence that the impacts to be calculated for the future Environmental Safety Case (ESC) may be reduced compared to previous estimates. Exceptions are the estimated inventories for Tc-99 and Ra-226, which have increased. However, these inventories are associated with a small numbers of specific waste streams, and are subject to uncertainty. Application of the waste treatment and packaging innovations will have limited impacts on the inventories of the key radionuclides. This is principally due to the fact that the major arisings of the key radionuclides that contribute significantly to radiological impact occur either before 2030 or after The pre-2030 arisings contribute to the assessed inventory in all cases; post-2090 arisings are not included in the inventories assessed because in all cases the future Vaults will have reached capacity by that time. This profile is due to the changing nature of LLW arisings from operational and early decommissioning wastes pre-2030, to general decommissioning wastes and, finally, late decommissioning wastes including graphite post However, these conclusions may need to be revisited if there are any further significant changes to the profile of future LLW arisings or if the available disposal volume were to be increased. Implications of Innovations for Long-term Safety A systematic assessment approach was used to explore the potential impacts of the innovations on long-term safety. An analysis of the features, events and processes (FEPs) that are important in this context was undertaken. As a result of this analysis, existing conceptual models were developed to incorporate estimates of the extent of carbonation that can be expected for different proportions of grout, and congruent release models for C-14 and Cl-36 from concrete, metals and graphite were developed. Uranium solubilities and sorption coefficients were identified that correspond with the different geochemical environments that may arise. In undertaking these assessments, a number of assumptions have been made and it may be necessary to undertake iv

7 QRS-1443H-R2, Version 1.0 further underpinning work in relation to some of these in order to provide a robust basis for the 2011 ESC. Assessment calculations were undertaken to consider the impacts of different material volumes, inventories and chemical conditions (including higher and lower ph and reducing and oxidising conditions) for the future Vaults. The results show variations in these conditions have a limited impact on peak risks for the well pathway, which are dominated by Tc-99, C-14 and Cl-36. Use of congruent release models leads to a slight reduction in peak C-14 and Cl-36 impacts. Adoption of a cautious Tc-99 solubility value leads to a more significant reduction in peak risk. Longer-term well pathway impacts are associated with uranium disposals, and, although those risks are below the peak short-term risks, they are not insignificant. There is significant variation in the impacts associated with uranium series radionuclides according to the prevailing geochemical conditions in the Vaults. Results for the groundwater and coastal erosion, human intrusion and gas pathways together indicate that the application of innovations such as VLLW diversion, metal treatment, incineration and the use of alternative disposal containers has limited impact on calculated peak risks. Note, however, that Ra-226 and Tc-99 impacts are higher than for previous assessments due to the predicted increases in disposed inventories. Conclusion Overall this study has not identified any impacts suggesting that implementation of any of the innovations would be inconsistent with the development of a satisfactory ESC. v

8 QRS-1443H-R2, Version 1.0 Contents 1 Introduction 9 2 Study Aims and Process Objective Audience System to be Assessed Priority Radionuclides and Pathways Timeframes Assumptions and Uncertainties 15 3 Inventory of Wastes Planned for Treatment and Disposal to the LLWR Raw Volumes and Material Composition of Wastes Key Radionuclides Baseline Inventory 25 4 Waste Packaging and Treatment Options Options under Consideration Implications of Treatment and Packaging Options FEPs Relevant to the Assessment of the Implications of Treatment and Packaging Options 36 5 LLWR Conceptual and Assessment Model Updates Conceptualised Release Pathways Considered in Existing Assessments Key FEPs Relevant to Contaminant Release Existing Assessment Models Impacts of Treatment and Packaging Options on the Repository Environment and Contaminant Release 45 6 Updated Processes and Data Required for this Study Overview Congruent Release Models C Cl Tc U234 / U Uranium Solubility Model Groundwater Compositions Consideration of Solubility Limited Phases Calculated Solubility Limits Summary 75 vi

9 QRS-1443H-R2, Version Tc Solubility Distribution Coefficients Grouted Waste Soil Ungrouted Waste Corrosion Products Inventory for Each Representative Treatment Strategy Base Case ( As Present Practice plus Sorting and Segregation for VLLW Diversion) Metal Treatment Maximum Volume Reduction Calculation Cases Waste Treatment and Packaging Strategy Options for Consideration Identification of Calculation Cases Identification of Key Assumptions Calculations Groundwater Pathway Description of Option Switches Implementation of Congruent Release Models Summary of Data used in the Groundwater Pathway Models Gas Radionuclide Concentrations Human Intrusion Calculation Approach Radionuclide Concentrations Coastal Erosion Calculation Approach Comparison of Radionuclide Inventories Calculation Results Overview Implications of Inventory Studies Groundwater Pathway Calculations Gas Pathway Human Intrusion Coastal Erosion Summary and Conclusions 165 References 168 Appendix A : Summary of the Expert Workshop Held at Greengarth on 29 th March vii

10 QRS-1443H-R2, Version 1.0 Appendix B : 2007 National Inventory Waste Streams Excluded from This Study 184 Appendix C : Audit of FEP Representations in This Study 186 Appendix D : Waste Streams and Waste Forms for Key Radionuclides 190 viii

11 QRS-1443H-R2, Version Introduction The Low Level Waste Repository (LLWR) is undertaking a programme of work to produce an Environmental Safety Case (ESC) for submission to the Environment Agency by May The LLWR is also supporting the Nuclear Decommissioning Authority (NDA) in the development of a National Strategy for low-level radioactive waste (LLW) management, one aspect of which concerns plans for innovations that could have implications for the nature of wastes to be disposed to the LLWR in the future. The LLWR is also working with consignors to deliver innovations in the disposed wasteform. Waste treatment and packaging options could include the following: segregation at source to allow VLLW to be disposed elsewhere, and/or as a precursor to additional waste treatment; mechanical or chemical surface metal decontamination; metal melting; thermal treatments, in particular incineration, for wastes containing organic materials; compaction / supercompaction of compressible wastes; the use of smaller volumes of non-radioactive bulk materials (e.g. metal containers and cementitious grouts) in disposals; and changes to the composition of relevant materials, e.g. cementitious grout. The study reported here aims to support the options evaluation process by providing an initial assessment of the likely effects of different treatment options for disposals to the future Vaults in terms of their implications for the LLWR ESC. The emphasis is on a preliminary evaluation of options rather than the production of a detailed post-closure safety assessment; as such, a number of simplifying assumptions have been made compared with previous iterations of the assessment (e.g. Sumerling, 2008, BNFL, 2002a) and will be required for the 2011 ESC (Baker et al, 2008). Nonetheless, the assessment provides a broad indication of the likely overall implications of different LLW treatment and packaging options, together with identification of potential areas for further work. The report is structured as follows: 9

12 QRS-1443H-R2, Version 1.0 Section 2 summarises the aims of the work and the process followed in its execution; Section 3 provides an overview of the anticipated inventory of waste materials and radionuclides from future disposals to the LLWR; Section 4 describes the range of waste treatment and packaging strategy options that have been assessed; Section 5 discusses key assumptions that are required to underpin assessment modelling of the future Vault system and its environs for this study, summarises the potential impacts of the wasteform changes on system behaviour, and provides an overview of modelling approaches adopted in recent long-term environmental safety assessments; Section 6 discusses the additional data and process modelling needed to support an assessment of the implications of wasteform innovations; Section 7 describes the calculation cases that have been defined to explore the potential impacts of different waste treatment and packaging strategies; Section 8 explains how the computational models used in previous assessments have been adapted to implement the calculation cases addressed in the current study; Section 9 presents the results of the assessment calculations; and Section 10 summarises the overall conclusions from the study. A schematic representation of the report structure is presented below. 10

13 QRS-1443H-R2, Version 1.0 Figure 1: Report Structure Aims and Process Section 2 Overview of Future Planned Disposals Section 3 Identification of Waste Treatment and Packaging Strategic Options Section 4 Conceptual and Mathematical Models Section 5 Updated Process Models and Data Section 6 Calculation Cases, Computational Models and Calculation Results Sections 7 to 9 Summary and Conclusions Section 10 Three appendices provide additional supporting information: Appendix A provides a record of a workshop held at Greengarth on 26th March 2009 to agree a representative range of treatment strategy options and the key Features, Events and Processes (FEPs) relevant to assessing their implications for safety performance; Appendix B summarises VLLW/LLW waste streams noted in the 2007 UK National Inventory not considered in the current study; Appendix C provides an overview and audit of the high-level FEPs considered in this study; and Appendix A provides additional details of the underpinning inventory-related calculations undertaken. 11

14 QRS-1443H-R2, Version Study Aims and Process 2.1 Objective An important component of the National LLW Strategy concerns the development of plans for waste treatment and packaging innovations in LLW management. Such innovations could have implications for the nature of the wastes to be disposed to the LLWR in the future. For example, in future the specific activity of disposed wastes could be increased, or the physical or chemical characteristics of the wasteform might change. In addition to delivering benefits to the National Strategy in terms of volume reduction and more efficient use of available capacity at LLWR, such changes could have an impact on the long-term safety performance of the repository. It is therefore necessary to explore the extent to which such safety considerations might constrain the range of innovations that could be implemented. The primary aim of the present study is to evaluate possible innovations, through identification of their key characteristics and assessment of their implications for the post-closure safety of disposals to the planned future Vaults at the LLWR. This is achieved through assessment calculations for key radionuclides and potential pathways of release. The calculations are not intended to provide a comprehensive assessment sufficient to underpin the overall safety case, but instead provide a simple evaluation of the main trade-offs that might be associated with alternative approaches to waste treatment and packaging. A range of supporting calculations is also described. Particularly relevant are analyses showing how the material and radionuclide inventories vary depending upon the innovations that might be applied. The inventory studies focus on the different proportions of materials that would be present once disposals are complete, and the radionuclide activities that would be associated with those materials. The inventory analyses also indicate the timescales upon which the future Vaults will reach capacity depending upon the innovations implemented. For the purposes of this study it is assumed that the volumetric capacity of the Vaults does not vary across the options considered, although it is noted that, subject to planning permission and Authorisation controls, it may be possible to extend the proposed footprint of the future Vaults should it be considered beneficial to do so. The main output of the study is based on an analysis of the results of assessment calculations, taking into account the uncertainties that apply to those analyses as well as other relevant lines of reasoning. This is summarised to present a set of arguments, 12

15 QRS-1443H-R2, Version 1.0 issues and suggestions for consideration in the future development of National Strategy and the LLWR ESC. 2.2 Audience The target readership for this report is technical and management staff within LLWR Ltd, although the report may also provide a basis for material to be presented to regulators and other stakeholders. 2.3 System to be Assessed Detailed analyses of the radiological and non-radiological impacts of the LLWR have been made in studies undertaken over more than two decades. As a result of these assessments, understanding has been developed of the facility and its environmental setting, the projected performance of the disposal system over time, and associated major areas of uncertainty. The system has been described in terms of key FEPs, their interactions, and changes with time. A comprehensive description of the LLWR system is provided by Baker (2008), Randall (2008) and Shevelan (2008); Sumerling (2008) presents an analysis of the system and its representation in long-term performance assessment, providing the most recent reference base case description of the system. System understanding has, however, developed since the work reported by Sumerling (2008). In particular, estimates of the likely future inventory of waste to be disposed to the LLWR (and any successor facilities and VLLW disposal routes) have been updated in the latest National Inventory (NDA and Defra, 2008). A range of other studies have provided further information on the likely status of the future Vaults at the time of facility closure (e.g. Small et al., 2009, Wilson and Metcalfe, 2009). It is therefore important to define an updated base case description that considers the outcomes of recent work. This is provided in Section 5 below. Any innovations in waste treatment and packaging will not be applied retrospectively to past disposals to the LLWR. Hence the analysis presented in this study centres on the consequences of possible changes in waste characteristics in so far as they relate to the future disposal Vaults at the LLWR. The review and development of assessment models for the purposes of the current study therefore focus on modifications to the FEPs that describe the characteristics and evolution of the future Vaults. 2.4 Priority Radionuclides and Pathways As the aim is not to undertake a full-scale long-term environmental safety assessment, but to gain understanding of potentially important impacts on safety performance 13

16 QRS-1443H-R2, Version 1.0 associated with a range of possible wasteform innovations, it is appropriate to prioritise assessment effort based on the outcomes of previous studies. Drawing on past experience, the following priorities were agreed at a workshop held at Greengarth on 29 th March 2009 (see Appendix A). Key radionuclides for consideration are: C-14, Cl-36, Tc-99, Ra-226, Np-237, U- 234, U-238, Pu-239, Pu-240, and Am Key pathways for release from the Vaults are: o groundwater - in particular the implications of well-water abstraction; o human intrusion; o gas generation and migration; and o site disruption through coastal erosion. It was also agreed that calculated impacts should be presented in terms of indicative doses and risks, in line with the results presented in Sumerling (2008) and underpinning documents (e.g. Paksy and Henderson, 2008). The approach to assessment for the above radionuclides and release pathways was agreed at a further meeting held at Greengarth on 8 th May Details are provided in Section Timeframes As a basis for this study, it is envisaged that the LLWR will continue to operate until it reaches capacity. Unless innovations to make more efficient use of this capacity are implemented, this may be around (NDA and LLWR, 2009; see also Section 3) However, if disposal volumes can be significantly reduced, the operational lifetime may be extended by a number of decades. The reference strategy involves closing the facility using appropriate engineering measures and then maintaining institutional control. The period for which this will be implemented is not yet defined, but could be of the order of some 300 years. After this 1 Note however that recent estimates of the inventory, based upon the 2007 National Inventory, suggest that disposed Np-237 activities will be small (Solente, 2009). 14

17 QRS-1443H-R2, Version 1.0 time, it is not anticipated that direct control over the site will be maintained, although it is likely that records will persist and might limit the use that is made of the site. Assessments of safety performance in support of the 2011 ESC need to consider a timeframe that is sufficiently long to capture the period in which the highest impacts on people and the environment could occur. This implies a need to undertake assessments over periods of tens of thousands of years. However, the present best estimates of the impacts of coastal erosion and sea-level rise (Baker, 2008; Thorne and Kane, 2007) suggest that gross disruption of the site could occur with a timeframe of a few thousand years. Existing studies, such as Sumerling (2008), provide an analysis of the important safety-relevant issues for the relevant timeframes. It is recognised that the uncertainties in the results of assessment modelling studies may be substantial over extended timescales. Due consideration therefore needs to be given to such uncertainties when evaluating the results and differentiating between the long-term safety implications of alternative wasteforms. This is discussed further in Section 2.6, below. For the purposes of the present study, calculated impacts are presented for a period of up to 2,500 years after facility closure. This period is judged sufficient to encompass the likely timescales for site disruption by coastal erosion and sea-level rise. 2.6 Assumptions and Uncertainties Many aspects of the long-term performance assessment (PA) for the future Vaults will be subject to uncertainty. Uncertainties arise from natural variability in system characteristics, limitations in knowledge of key processes or data, and alternative interpretations of system behaviour and evolution. It is necessary to manage the treatment of these uncertainties in such a way that their significance for the conclusions that can be drawn from the study is understood. A range of assumptions are made and sources of uncertainty identified in the assessments described in subsequent sections of this report. They range from, for example, uncertainties associated with future inventory predictions, to the magnitude of radionuclide solubilities under the geochemical conditions of interest. Note that a key aim of some of the assumptions made (e.g. regarding the potential for congruent rather than instantaneous availability release of certain radionuclides) is to consider some of the cautions assumptions made in previous assessment, and to identify opportunities for more realistic representations that may assist comparisons between options. 15

18 QRS-1443H-R2, Version 1.0 These issues are managed as follows. An analysis of the FEPs that are key to this study provides a framework for the identification of important assumptions and uncertainties and indicates how they are to be addressed (see Section 4). Subsequent sections of the report details how the assumptions made and how uncertainties are managed throughout the assessment, consistent with the scope of this study. This is summarised in Section 7. The calculations presented provide a quantitative indication of the likely impacts of some of the most important uncertainties. This is supplemented by qualitative arguments in considering the implications of uncertainty for analysis of the results (see Sections 9 and 10). 16

19 QRS-1443H-R2, Version Inventory of Wastes Planned for Treatment and Disposal to the LLWR A fundamental baseline for the study is the overall inventory of materials and radionuclides that is anticipated to require treatment and disposal to the LLWR or any successor facility. The primary source of inventory information used for this study is the WIDRAM database (Solente, 2009), maintained by the LLWR Site Licence Company, which was populated with data as it was being gathered for the 2007 National Inventory (Defra and NDA, 2008). The database contains 954 waste streams that are identified as either LLW or VLLW. For each waste stream, information if provided on the generic disposal route, material composition and projected raw volume for waste arising each year between 2007 and LLWR team members have identified separately those VLLW/LLW streams that are considered likely to be disposed of at the LLWR (or any successor facility) in the future, those that are possibly destined for eventual LLWR disposal, and those that are unlikely to be disposed to the LLWR (including, for example, large volume VLLW waste streams) (Solente, 2009). These designations have been used to inform the identification and definition of inventories for the assessment calculations. Some of the waste streams have been excluded from consideration given the objectives of the current study: All Dounreay waste streams (both LLW and VLLW), as it is expected that these will be disposed to a dedicated facility constructed on the Dounreay site (211 waste streams). All non-dounreay VLLW (14 waste streams). It is noted that waste streams specifically identified as VLLW was not excluded in recent studies supporting development of the LLWR ESC (Baker, 2008; Wareing e al., 2008). Note that a significant number of the waste streams declared as LLW will also contain significant volumes of VLLW and thus enhanced sorting and segregation could lead further efficiencies in terms of VLLW diversion for disposal elsewhere. LLW waste streams identified as requiring disposal to a geological disposal facility (17 waste streams). Waste streams identified as requiring special precautions burial (1 waste stream). 17

20 QRS-1443H-R2, Version 1.0 This leaves 711 waste streams to be taken into account in the current study. The full list of the excluded waste streams and a list of the remaining waste streams are provided in Appendix B. Studies undertaken by and on behalf of the LLWR (e.g. Wareing 2009a, b) have noted inconsistencies and uncertainties in estimates of future LLW and VLLW arisings that are currently planned for disposal at the LLWR. Uncertainties are always present when making projections of future waste arisings over long time-periods, particularly when those inventories principally relate to decommissioning wastes with uncertain volumes and activities. In addition, however, a number of potentially important errors and omissions have been identified for some of the Sellafield waste streams (Khan et al., 2009) and waste streams containing significant quantities of Ra-226 (discussed further in Appendix D). The scale and significance of these and other problems in inventory assignment will be examined in ongoing inventory reviews being undertaken for the LLWR. So far as has been practicable, any errors and omissions in Solente (2009) identified by cross checking with Wareing et al. (2009a, b) and Khan et al. (2009) have been resolved in the preparation of the inventories presented in this report. Particular issues for relevant waste streams/radionuclides are identified in subsequent sections. Nevertheless, in considering the study outcomes, it is important to recognise that significant future changes to inventory may occur. 3.1 Raw Volumes and Material Composition of Wastes A summary of the projected total raw waste volume (m 3 ) requiring disposal to the LLWR or a successor facility is shown in Figure 2. The estimated contribution to total waste volume from different types of waste material on the same timescales is shown in Figure 3. For comparison, the estimated remaining disposal capacity for packaged waste at the LLWR is approximately 700,000 m 3 (NDA and LLWR, 2008). Diversion of VLLW to alternative disposal routes would mean that the site s lifetime could be extended from circa 2020 to circa 2030, once packaging has been accounted for. Waste treatments that serve to reduce the volume prior to packaging, and potentially the volume of packaging required, would further extend the lifetime of the site. The effect of packaging is discussed further in Sections 4 and

21 QRS-1443H-R2, Version 1.0 Figure 2: Cumulative Total Raw Volume of LLW Waste arising (m 3 ) 1.20E E+06 Unlikely to go to LLWR/LLWR2 Possible to go to LLWR/LLWR2 Likely to go to LLWR/LLWR2 Cumulative Raw Waste Volume (m3) 8.00E E E E E+00 Upto Figure 3: Estimated Contribution to Cumulative Raw Volume of LLW from different Waste Materials (m 3 ) Cumulative Raw Volume by Material (m 3 ) 1.2E E E E E E+05 Unknown Oil Wood Plastic / Rubble Metals Other Graphite Soft Organics Soil / Rubble Total Raw Volume 0.0E+00 Up to

22 QRS-1443H-R2, Version Key Radionuclides This section lists the key radionuclides that need to be considered in assessment calculations based on the interim safety assessment calculations undertaken by Sumerling (2008) and discussions held at the workshop in Greengarth on 29 th March 2009 (Appendix A). Groundwater Pathway: C-14 Cl-36 Tc-99 U-234 / U-238 Human Intrusion and Gas: C-14 Cl-36 Cs-137 Pu-239 Np-237 Rn-222 from Ra-226 and U-234/238 Coastal Erosion: Ra-226 Th-232 Pu-239 Pu-240 Am-241 Five key radionuclides (C-14, Cl-36, Tc-99, U-234 and U-238) are therefore identified as being significant to evaluation of the effects of waste treatment and packaging innovations on the groundwater and gas release pathways. In addition, six further 20

23 QRS-1443H-R2, Version 1.0 radionuclides (Cs-137, Ra-226, Th-232, Pu-239, Pu-240 and Am-241) require attention in the context of assessing potential releases arising from human intrusion and coastal erosion. The waste materials and packaged waste forms associated with key radionuclides for the groundwater and gas pathways need to be considered in some detail in order to develop appropriate release models that reflect the impact of specific waste treatment options. Specifically, these models may provide insight as to the performance of treatment options in terms of the containment of radionuclides (e.g. the release of C-14 and Cl-36 from scrubbers following metal melting treatment versus the release of C-14 and Cl-36 from untreated metal). For each key radionuclide it is therefore important to identify those waste streams which contain the highest inventory, their material composition (which affects applicable treatment options) and the years in which they are projected to arise. The focus of the human intrusion calculations was on radiological impacts associated with radon gas exposure (i.e. though decay chains involving Ra-226 and thus Rn-222) because previous assessments have indicated that the most likely human intrusion exposure route is associated with the building of a house on top of the repository followed by exposure of the occupant to Rn-222 gas. Figure 4 and Figure 5 present the cumulative inventory of all identified key radionuclides, based upon the projected figures for raw waste arisings given in Solente (2009), with notable exceptions for Ra-226, C-14 and some Sellafield waste streams. Wareing (2009a) highlighted a significant difference in the volume of key waste streams associated with Ra-226 as presented on the Waste Stream Description Sheet (WSDS) and the data provided in Solente (2009); the revised data is what is used. Wareing (2009b) presented uncertainties associated with the C-14 inventory; this used different assumptions for whether waste streams were considered likely to go to the LLWR (or a successor plant) to Solente (2009). Khan et al. (2009) presented revised volumetric and specific activity data for some of the Sellafield waste streams; it is this revised data that has been used. Given the baseline assumption that VLLW is diverted to other disposal routes, then the majority of the total inventory of Tc-99, U-234, U-238, Ra-226 and Np-237 (in terms of raw waste volume) is expected to arise prior to The total disposed inventory of these radionuclides is not therefore expected to increase significantly in response to waste treatment and packaging options that increase the volume of raw waste that can be disposed to the LLWR. However, the wasteform and near-field mobility of these key radionuclides will be affected by any associated changes to near-field biogeochemistry. 21

24 QRS-1443H-R2, Version 1.0 For both C-14 and Cl-36, a substantial fraction of the inventory is expected to arise after 2070 (Figure 4 and Figure 5. Over 50% of the Cs-137 inventory is projected to arise after 2030; the majority of the Cs-137 inventory is associated with specific Sellafield wastes (more details are given in Appendix D). Although the future Vault inventories of these radionuclides will be increased if the site s operational lifetime is extended beyond 2070, the impact of waste treatment options on wasteform and near-field biogeochemistry is likely to have a greater effect on site impacts than the additional radionuclide inventory. The materials associated with each radionuclide are given in Table 1. A more detailed discussion of the waste streams and waste forms associated with each key radionuclide are given in Appendix D. Figure 4 : Cumulative inventory (TBq) based upon raw waste volumes for disposal to the future Vault: Radionuclides whose total projected inventory is less than 4 TBq 4.5E E+00 Am-241 Cl-36 Np-237 Pu-240 Ra-226 Th-232 U-234 U E+00 Radionuclide Inventory (TBq) 3.0E E E E E E E+00 Up to

25 QRS-1443H-R2, Version 1.0 Figure 5 : Cumulative inventory (TBq) based upon raw waste volumes for disposal to the future Vault: Rradionuclides whose total projected inventory is more than 4 TBq 7.0E E+01 C14 Tc-99 Cs-137 Pu-239 Radionuclide Inventory (TBq) 5.0E E E E E E+00 Up to

26 QRS-1443H-R2, Version 1.0 Waste Material Table 1: Projected Radionuclide Inventory (TBq) by Waste Material Total Radionuclide Inventory (TBq) projected to arise by 2129 Am-241 C14 Cl-36 Cs-137 Np-237 Pu-239 Pu-240 Ra-226 Tc-99 Th-232 U-234 U-238 Graphite 3.9E E E E E E E E E E E E+08 Metals 8.1E E E E E E E E E E E E+12 Oil 3.3E E E E E E E E E E E E+05 Other 1.5E E E E E E E E E E E E+10 Plastic / Rubber 1.5E E E E E E E E E E E E+10 Soft Organics 2.4E E E E E E E E E E E E+10 Soil / Rubble 1.2E E E E E E E E E E E E+10 Wood 6.7E E E E E E E E E E E E+10 Unknown Material 8.1E E E E E E E E E E E E+09 24

27 QRS-1443H-R2, Version Baseline Inventory The derivation of alternative inventories to represent the influence of potential waste treatment and packaging innovations is described in Section 6.6. A baseline inventory is presented here in advance of those discussions in order to provide context for subsequent analysis. As noted previously, the baseline inventory to underpin the calculations undertaken in this study is derived from the data presented in Solente (2009), modified to address the key issues noted in recent inventory reviews (Wareing 2009a, b; Khan et al., 2009). The calculated inventory incorporates the assumption that all VLLW waste streams classified as unlikely to go to LLWR will be diverted for disposal elsewhere, with the remaining wastes being subject to existing waste management practices. It is also assumed that the material compositions of each of the waste streams do not vary with time 2. Treatment of raw waste Current waste management practices at the LLWR include the segregation of compactable wastes and oils. Adopting the terminology of Solente (2009), the impacts of enhanced waste segregation can be described in terms of: a Segregation Factor (SF) - the maximum fraction of material that can be segregated across all waste streams, noting that for some waste streams it is not practicable to separate materials that comprise a minor component of the waste stream; and the Segregation Efficiency (SE) - the percentage of the Segregation Factor that is actually achieved at a particular time. Estimated segregation factors and efficiencies relating to present day LLWR operations are given in Table 2 (reproduced from Solente, 2009). 2 Note that for some waste streams the material composition may change in the future, e.g. 2D109 for which Sellafield is the consignor (Wareing, 2009) 25

28 QRS-1443H-R2, Version 1.0 Table 2: Updated Base Case Assumptions for Segregation Factors (SF) and Current (2008) Segregation Efficiencies (SE) Waste Treatment Route Compaction Waste Materials Plastic/Rubber, Soft Organics, Wood Segregation Factor 75% 50% Oil Oil 100% 100% 2008 Segregation Efficiency Compaction is currently utilised at the LLWR. The estimated overall waste volume reduction (WR) factors presently achieved by compaction are detailed in Table 3. A volume reduction factor of 1:3 means that the treated waste is one third of the volume of the raw waste. Note that oils are diverted from the LLWR for interim storage and it is assumed that no secondary wastes from the future treatment of oils will be disposed of to the LLWR (Solente, 2009). However, in this study we conservatively assume no volume reduction of oil as a result of any treatment prior to packaging, and no loss of radionuclide inventory associated with oil. However this assumption is of limited consequence due to the comparatively small volumes of oils for disposal. Table 3: Current Assumptions for Waste Volume Reduction Factors (WR) Waste Treatment Route Waste Volume Reduction Factor Compaction 1:3 Non-compactable 1:1 Following segregation and compaction, the waste must be packaged before it can be emplaced in the LLWR disposal facility. This is accounted for using a packaging factor (PF), which describes the ratio between packaged waste volume 3 and the treated waste volume. The packaging factors for the various waste treatment routes assuming current practice are given in Table 4. 3 This includes grout and/or ISO freights. 26

29 QRS-1443H-R2, Version 1.0 Table 4: Updated Base Case Assumptions for Packaging Factors (PF k) Waste Treatment Route Compaction Waste (Pucks) Waste Materials (if ideal segregation was achieved) 18.75% of Plastic/Rubber, Soft Organics, Wood Non-compactable N/A 1.56 Packaging Factor Determination of Packaged Volume Given the above information it is possible to calculate the packaged waste volume of each waste type, k, for each waste stream, x. Equation (1) below shows how the packaged volume is calculated (Solente, 2009): x x ( Packaged Volume) SF ( % Material) ( Raw Volume) k = k k i= years WR k PF k x, i SE k, i (1) The implications of segregation on both the packaged volume and radionuclide inventory for the base case are given in Section The values for the volume reduction factor and packaging factors for supercompaction are taken from Solente (2009). Higher values could also be conceived as being reasonable, but calculation suggest that applications of factors as high as 1.5 would have only minor implications for the overall packaged volume, and so this value has been retained. 27

30 QRS-1443H-R2, Version Waste Packaging and Treatment Options 4.1 Options under Consideration Approach to the Identification of Options LLWR is presently considering a number of waste treatment and packaging innovations that could be applied to disposals to the future Vaults. These innovation technologies were considered alongside the list of material types to be disposed to the LLWR in order to derive a prioritised set of technologies for consideration as part of an overall volume reduction strategy. Technologies were then combined into candidate waste packaging and treatment strategy options to be taken forward within the present study. The options were discussed and agreed at an expert workshop held at Greengarth on 29 th March 2009 (see Appendix A). The focus of this process was not to provide a complete catalogue of all potentially feasible strategies, but to identify an appropriate range of options sufficient to underpin an exploration of the implications of possible innovations in waste treatment and packaging. The illustrative strategies described are here are therefore not intended to represent specifications of real options for potential future implementation. Overview of Future Waste Volumes In order to consider how the potential waste treatment options identified might be employed to optimise the future Vaults wasteform, it is useful to consider the relative proportions of materials that may be disposed to the Vaults in the future. According to Solente (2009), approximately 3 million cubic metres of raw LLW and VLLW wastes are planned to arise for disposal to the LLWR or alternative facilities as a result of the NDA decommissioning programme. The wastes are likely to comprise the following material types: > 10% of total raw volume - Rubble (51%), Metals (30%); 3 10% - Plastic/Rubber (7%), Other (5%), Soft Organics (5%); and < 3% - Wood (2%), Unknown (1%), Graphite (0.5%). Existing estimates of the proportion of VLLW to LLW in raw wastes suggest that the total volume of VLLW could exceed that of LLW if it were efficiently segregated (approx 1.8 million m 3 compared with 1.2 million m 3 ) (NDA and LLWR, 2009). 28

31 QRS-1443H-R2, Version 1.0 A Hierarchy of Alternative Treatment / Packaging Approaches Analysis of the waste types anticipated to be disposed to the LLWR as decommissioning accelerates confirms that the treatment and packaging innovations identified could provide important roles in any future volume reduction strategy implemented. The innovations under consideration are listed below, ranked roughly according to their potential to support volume reduction. Sorting and segregation. Disposal of VLLW-labelled waste streams to a facility other than the LLWR will lead to a significant reduction in demand for capacity at the LLWR. The baseline inventory for the current study (Section 3) and the treatment and packaging options that have been assessed all assume that VLLW diversion will take place. Further gains may be achievable if waste streams currently classified as LLW are subject to enhanced sorting and segregation. Sorting and segregation is also an essential precursor to volume reduction techniques that can only be applied on a material-specific basis. Following sorting and segregation, surface decontamination and metal melting or other size reduction techniques could further reduce the volume of metals to be disposed. The aim in this case would be to release the majority of the metal volumes for re-use and recycling, either on licensed nuclear sites or potentially elsewhere, following exemption from control as radioactive waste. It is assumed that metal decontaminated from LLW to VLLW that is not suitable for free release would not be returned for disposal to the LLWR. Similarly, incineration could dramatically reduce the volumes of wastes that contain organic materials. Supercompaction would also achieve significant volume reduction for some organic wastes. Whereas incineration leads to a significant volume reduction compared with the raw waste, if the resulting ashes are to be grouted and placed in half-height ISO-freights after treatment, the overall effective volume reduction for the two approaches will be similar (e.g. Solente, 2009). For wastes that are already sufficiently chemically stable it may be possible to reduce the volume of cementitious grout that is added on emplacement in the final waste package. The composition of the grout itself could also be altered in conjunction with this. A reduction in the volume of grout will also be a natural consequence of treatment options that give rise to an increase in overall packaging efficiency. 29

32 QRS-1443H-R2, Version 1.0 The use of alternative disposal containers (or even direct emplacement for large items) may enhance the effective waste packing efficiency compared with use of half-height ISO-freights. Combined Waste Treatment and Packaging Strategy Options to Take Forward At the project workshop (see Appendix A), representatives of Quintessa, the LLWR ESC and National Strategy teams agreed the following options to carry forward for further analysis. 1. Continuation of the current treatment and packaging strategy Enhanced sorting and segregation for VLLW diversion Option (2) + Metal treatment (i.e. surface decontamination + metal melting for re-use). 4. Option (2) + Incineration (4a) or supercompaction (4b) of suitable wastes (including metals not treated under (3)). 5. Option (2) + Direct emplacement and replacement of half-height ISO-freights with smaller boxes and simple liners/overpacks. 6. Option (2) + No or reduced grouting. The priority in defining this alternative was to identify a set of broad strategies consistent with those likely to be considered in options assessments being undertaken by the National Strategy and Consignor Support teams. The proposed calculation cases that are investigated in the assessment study (described in subsequent sections of this report) are designed to identify the ESC-relevant impacts that may apply across this range of options, rather than being directly based on the options themselves. Options 2 4 represent a hierarchy of treatment options that could in principle deliver volume benefits compared to continuation of the current treatment and packaging 5 Subsequent to the workshop this option was combined with option (2) as it was considered that it is extremely likely that VLLW diversion for disposal elsewhere will be pursued, noting the volumes of VLLW due for disposal, and so this assumption represents the true baseline for comparison. 6 This relates principally to the diversion of VLLW waste streams to an alternative facility, but additional benefits may be achieved for waste streams labelled as LLW. 30

33 QRS-1443H-R2, Version 1.0 regime (Option 1). Option 5 then examines the additional benefits that may be gained through the use of alternative waste packages or direct emplacement where possible. Option 6 then represents situations where less (or even zero) grout is used within the waste packages, a strategy that could in principle be applied alongside Options 2 5; the volume reductions achieved by those strategies would naturally lead to reduced levels of grout within the disposed waste packages. 4.2 Implications of Treatment and Packaging Options Sorting and Segregation Activity-based sorting and segregation will enable wastes to be subdivided according to radionuclide content. The primary motivation for this is to exclude from disposal to the LLWR a fraction of the raw waste volume that can be re-classified as VLLW (or even free-release, FR). It is assumed that no treatments would be applied as part of the process, and that conventional techniques (e.g. a belt-based monitoring system using gamma assay) would be used. At the simplest level of application, sorting and segregation at source (i.e. prior to shipment to LLWR) can be used to divert future waste streams already identified as VLLW to an alternative disposal facility. Implementation of such an approach is a key baseline assumption for the purposes of the current study. In addition, it is possible that an enhanced programme of sorting and segregation could lead to reclassification as VLLW of a significant proportion of future waste arisings that are currently classified as LLW within the National Inventory. The influence of this option on the wastes for emplacement at the LLWR will be determined by the distribution of activity in the raw wastes. This will, in turn, be a function of the heterogeneity of each waste stream and its source. In each case, a certain proportion of the total volume arising can be assumed to be VLLW and FR. At present there is limited information on these factors (indeed, if it were known, it is possible that the consigners might indeed perform the segregation at source). Nevertheless, it seems likely that some wastes are likely to be more homogeneous than others owing to their nature and arisings. A simple hierarchy (least scope for VLLW/FR diversion to most) might be: oils; graphite; metals; 31