M. Buckley, B. Handy and Z.K. Hillis

Transcription

1 Literature Review of the Potential Application of Metal Melting in the UK Nuclear Sector by M. Buckley, B. Handy and Z.K. Hillis 11426/TR/001 Issue 04 November 2004

2 The work described in this report was carried out by NNC Ltd under contract to the Health and Safety Executive (HSE). Any views expressed have not been adopted or in any way approved by the HSE and should not be relied upon as a statement of the HSE s views All rights reserved. No part of this document, or any information or descriptive material within it may be disclosed, loaned, reproduced, copied, photocopied, translated or reduced to any electronic medium or machine readable form or used for any purpose without the written permission of the Company

3 Table of Contents List of Tables...ii List of Figures...iii Summary...iv Acronyms...vi Note on Definitions...viii 1 Introduction Waste Issues UK Market Potential Recycling of Metals Outside the Nuclear Industry (Public Domain) Recycling Within The Nuclear Sector Melting as Part of a Disposal Strategy Summary - Waste Issues Melting Technology Introduction Overview of the Process Of Melting Radioactively Contaminated Metals Proven Technology Used For Melting Radioactively Contaminated Metals Current Non-Nuclear Technologies Developing and Emerging Nuclear Melting Technologies Summary - Melting Technology Policy & Regulatory Control Introduction International Policy with Regard to Clearance UK Policy and its Implications for Melting Implications of Recent UK Decommissioning Policy Developments Summary Policy Constraints on the Implementation of UK Melting Facilities Regulatory Controls Stakeholder Issues Summary Constraining Issues Conclusions Recommendations References...49 Issue 04 Page (i)

4 List of Tables Table 1 Industrial scale melting facilities Table 2 Chemical components in LLW from all sources (Electrowatt-Ekono, 2002) Table 3 Chemical components in ILW from all sources (Electrowatt-Ekono, 2002) Table 4 Metal Wastes at UK sites (Electrowatt-Ekono, 2002) Table 5 Status of UK sites ( Table 6 Requirements for drums, boxes, reinforcement, grouts in UK disposal facilities currently in operation (European Commission, 1998a) Table 7 Partitioning factors for BOFs and EAFs (NCRP, 2002: Cheng et al, 2000; Nieves et al, 1995; NRC, 1999) Table 8 Summary of issues and recommendations Issue 04 Page (ii)

5 List of Figures Figure 1 Radioactively contaminated metal arisings in the UK Figure 2 Estimate of Metal Arisings from UK decommissioning Figure 3 Scrap metal for steel-making (NCRP, 2002) Figure 4 GERTA (Siempelkamp, 2004) Figure 5 Blast Furnace Basic Oxygen Furnace ( Figure 6 Plasma Arc Furnace (Fentiman et al.) Figure 7 IET Plasma Enhanced Melter Issue 04 Page (iii)

6 Summary Large quantities of radioactively contaminated waste metal are currently, and will continue to be, generated during decommissioning of nuclear facilities in the UK. The waste producers currently manage these wastes generally on a project, or on occasion, a site-wide basis. There is currently no UK-wide strategy for coordinating or integrating management of contaminated metallic wastes, other than for disposal at Drigg. Other countries, including France, Germany and Sweden, have developed more integrated strategies for managing radioactively contaminated metal wastes through the operation of central metal melting facilities. These strategies take advantage of economies of scale to process a wide range of metallic waste streams, which produce either metals cleared for unrestricted use in the scrap metal market, for recycling within the nuclear industry or material for disposal. This review examines the opportunities for developing similar integrated strategies in the UK for managing contaminated metal wastes arising from across UK nuclear sites, and compares with the experience of operating facilities internationally. It considers: A review of the UK waste market -UK arisings of radioactively contaminated metal waste -Review of the available metal reuse market A review of melting technologies -Proven metal melting technology in the nuclear market -Proven metal melting technology in the non-nuclear market -Developing and emerging nuclear melting technologies Review of Regulatory Policies and Principles Review of Barriers to implementing integrated melting technologies in the UK, including stakeholder issues. The conclusions of the review are as follows. 1 In the UK there is a significant inventory of unconditioned waste radioactive metals (70,000 tonne of ILW and 383,000 tonne of LLW), which will require management. 2 There are a number of proven technologies for melting radioactively contaminated metals operating in a number of countries including France, Germany and Sweden. These facilities manage a number of different radioactive waste streams arising from a range of nuclear sites. 3 Induction melting is the chosen technology for existing industrial radioactive metal melting facilities. Further developing technologies are also emerging, such as cold crucible and plasma arc technology. 4 Metal melting can be used to achieve three aims: Size or volume reduction of waste Segregation or separation of contaminants Issue 04 Page (iv)

7 Homogenisation of contaminants within the bulk metal. 5 Following processing in these melting facilities, the metals can follow one of three paths: I. Release outside the nuclear sector (clearance) II. Reuse within the nuclear sector III. Disposal, having achieved a reduction in disposal volume and activity concentration. 6 The establishment of melting facilities for radioactive waste metals is consistent with UK government decommissioning policy and the principles of: Waste minimisation Reuse and recycle Sustainability Environmental impact & resource management 7 There are a number of drivers for reviewing the need for melting facilities: Economic o Reducing waste disposal costs o Recovering costs through reuse and recycling o Conserving natural resources o Conserving the UK s LLW disposal resources Policy To comply with government policy, guidance and principles including: Waste minimisation Reuse and recycle Sustainability Environmental impact & resource management Strategic To review application of a proven technology for radioactive waste metals on a national rather than project or site basis. 8 There are significant stakeholder issues that must be considered and managed in order to implement an integrated metallic waste management strategy. These include: Public and (non-nuclear) metal industry unease with regards to reuse of previously radioactively contaminated metals and Public concern over the transport of radioactive waste Concern over new waste or radioactive management facilities involving heat treatment Issue 04 Page (v)

8 Acronyms AC AEAT AISI BAT BF-BOF BMRA BNFL BREF Note BSS CEA CSSIN DC Alternating Current AEA Technology (UK) American Iron and Steel Institute (USA) Best Availa ble Technique Blast Furnace Basic Oxygen Furnace British Metals Recycling Association British Nuclear Fuels plc (UK) Best Available Technique Reference Note Basic Safety Standards Commissariat à l'énergie atomique / Atomic Energy Commission (France) Nuclear Information and Safety Council (France) Direct Current DRIRE Direction régionale de l'industrie, de la recherche et de l'environnement / Regional directorate of industry, of research and of the environment (France) DSIN DTI EA EAF ENRESA EPA EU EUROFER HLW HPICCM HSE Direction de la sûreté des installations nucléaires / Nuclear installation safety directorate (France) Department of Trade and Industry (UK) Environment Agency (England & Wales) Electric Arc Furnace Empresa Nacional de Residuos Radiactivos SA (Spain) Environment Protection Act (UK) European Union European Confederation of Iron and Steel Making Industries High Level Waste Hybrid Plasma Induction Cold Crucible Melter Health & Safety Executive (UK) Issue 04 Page (vi)

9 IAEA IET ILW IPPC International Atomic Energy Agency Integrated Environmental Technologies Intermediate Level Waste Integrated Pollution & Prevention Control (UK) IRR99 Ionising Radiations Regulations 1999 JPDR LLRC LLW LSA MIRC NCRP NDA NEA NII NORM OCNS OECD OPRI PET PICCM RBMK R&D RSA93 SCS SCO SEPA SOCODEI Issue 04 Japanese Power Demonstration Reactor Low Level Radioactivity Campaign (UK) Low Level Waste Low Specific Activity Metals Industry Recycling Coalition (USA) National Council on Radiation Protection and Measurements (USA) Nuclear Decommissioning Authority (UK) Nuclear Energy Agency (part of the OECD) Nuclear Installations Inspectorate (UK) Naturally Occurring Radioactive Material Office of Civil Nuclear Security (UK) Organisation for Economic Co-operation and Development Office de protection contre les rayonnements ionisants / Office for protection against ionizing radiation (France) Plasma Enhanced Melter Plasmatron with Induction Cold Crucible Melter Large Power Boiling Reactor of Soviet Union design Research and Development Radioactive Substances Act 1993 (UK) Site Condition Survey Surface Contaminated Objects Scottish Environment Protection Agency Société pour le conditionnement des déchets industriels / Company for the conditioning of the industrial waste Page (vii)

10 conditioning of the industrial waste SoLA Radioactive Substances (Substances of Low Activity) Exemption Order 1986 UKAEA US DOE UK Atomic Energy Authority Department of Energy (USA) Note on Definitions In the literature both terms smelting and melting are used in relation to metal furnaces. The term smelting is most correctly reserved for the extraction of metals from their ores. This report focuses upon the recycling of scrap metal and so the term melting is used as the furnaces are being used to convert metal into the liquid phase as opposed to metal extraction and refinement. For the purpose of this study, contamination refers to radioactive contamination. Issue 04 Page (viii)

11 1 Introduction Overview of Report Large quantities of radioactively contaminated waste metal are currently and will continue to be, generated during decommissioning of nuclear facilities in the UK. The waste producers currently manage these wastes generally on a project, or on occasion, a site-wide basis. There is currently no UK-wide strategy for coordinating or integrating the treatment of contaminated metallic wastes, other than for ultimate disposal at Drigg. Other countries, including France, Germany and Sweden, have developed more integrated strategies for managing radioactively contaminated metal wastes through the provision of proven, operating central metal melting facilities. These strategies take advantage of economies of scale to process a wide range of metallic waste streams which produce either metals cleared for unrestricted use in the scrap metal market, for recycling within the nuclear industry or material for disposal. A summary of operating metal melting facilities is shown in Table 1. There are a number of drivers for a review of UK radioactive metal waste management: Economic Policy Strategic - In order to review the most cost effective strategy for UK management of radioactive waste metal liabilities. - To comply with government policy, guidance and principles of waste minimisation and sustainability. - To review the application of proven technology of waste radioactive metals on a national rather than project or site basis. This review examines the opportunities for developing similar integrated strategies for managing contaminated metal wastes arising from across all UK nuclear sites, and compares with the experience of operating facilities internationally. It considers: A review of the UK waste market -UK arisings of radioactively contaminated metal waste -Review of the available metal reuse market A review of melting technologies -Proven metal melting technology in the nuclear market -Proven metal melting technology in the non-nuclear market -Developing and emerging nuclear melting technologies Review of regulatory policies and principles Review of the constraints to implementing melting technologies for contaminated metals in the UK, including stakeholder issues. Conclusions and Recommendations. Issue 04 Page 1

12 Table 1 Industrial scale melting facilities Sources: (NEA, 1999) [1], (Byrd Davis, 2003) [2], (Powell, 1999) [3], (Worchester et al, 1995) [4], (MSC, 2004) [5], (Byrd Davis, 2004) [6], (Greppo et al, 1998) [7], (Faugieres J., 2000) [8]. Facility INFANTE Plant, Marcoule, France (start 1992 now shutdown) [1], [2] STUDSVIK Melting Facility, Sweden (start 1987) [1] CARLA Plant, Siempelkamp, Germany (start 1989) [1] SEG Plant, Oak Ridge, USA (start 1992) [1] Capenhurst Melting Facility, UK (start 1994) [3] MSC, Oak Ridge, USA (start 1996) [4], [5] Centraco, France (start 1999) [6], [7], [8] Furnace type Electric arc melting furnace Induction for steel, small electric arc for aluminium Induction Induction Induction Reverberator y Induction Induction Types of metal treated Carbon steel, stainless steel Carbon steel, Stainless steel, Aluminium Carbon steel, stainless steel, aluminium, copper, lead (R & D) Carbon steel, stainless steel, aluminium, (planning to melt copper and titanium) Aluminium, (brass, copper,) steel Charge size (t) Products 12 Ingots, shield blocks, waste containers Radiologica l limitations Max. 250 Bq/g for Co-60, other limits for other nuclides 3 Ingots No specified limits 3.2 Ingots, shield blocks, waste containers 20 Ingots and shield blocks at present, waste containers and reinforcing steel after 1994 Max 200 Bq/g for betagamma nuclides, Max 100 Bq/g for alpha nuclides, separate limits for uranium Normally < 2 msv/hr, greater dose rates with prior review and approval Quantity of scrap melted (t) In excess of 5000t Recycled/released Stored/recycling in nuclear industry t released, remaining stored for decay (or disposal) t recycled in nuclear industry, 50 t free release 2000 Recycling in the nuclear industry 4 ingots 7000 For unrestricted use MSC's manufacturing plant is a fully integrated manufacturing facility with the capacity to melt, cast, roll or machine products from many specialty metals such as steel, aluminium, uranium, tantalum, and niobium. The company's facilities and equipment are ideally suited for small and medium batch sizes that are uneconomical for large metal producers to process. One of its key services is the recycling of depleted uranium. Stainless steel, carbon steel and to the lesser extent nonferrous metals 4 Ingots and tubes 370 Bq/g alpha, 20,000 Bq/g beta/gamma 1366 (in 2000) For restricted use: manufacture of storage drums or biological shield materials. Page 2 Issue 04

13 2 Waste Issues This section describes the potential market in the UK for melting of metals from the nuclear industry. It covers: UK Market Potential; Recycling of the metals outside of the nuclear industry (public domain); Recycling within the nuclear industry and, Melting as part of a disposal strategy. 2.1 UK Market Potential Quantities of Contaminated Metals Melting technology is most readily applicable to metal wastes. In the UK over 90% of the radioactively contaminated metal waste is ferrous, with lead, Magnox, aluminium and copper comprising most of the remainder. 85% of this metallic radioactive waste in the UK is categorised as low-level waste (LLW) with the remaining 15% being intermediate level waste (ILW). Some High Level Waste (HLW) also includes scrap plant items from vitrification plant maintenance that have been contaminated. The sources of radioactively contaminated metals are not confined to licensed nuclear operations; the oil and gas industry also routinely generate Naturally Occurring Radioactive Material (NORM) contaminated material (Electrowatt-Ekono, 2002). The extent of potential source material for a radioactively contaminated metal melter is outlined in Figure 1. Figure 1 Radioactively contaminated metal arisings in the UK (Derived from Electrowatt-Ekono, 2002) Metallic Radioactive Waste Quantity awaiting conditioning: LLW (85%) t ILW (15%) t Source: Decommissioning (D) / Operational (O) (O) t (D) t (O) t (D) t More detailed information as to the breakdown by individual metals is provided in Table 2 and Table 3. Issue 04 Page 3

14 Table 2 Chemical components in LLW from all sources (Electrowatt-Ekono, 2002) Weight (tonnes) (2) (3) Material (1) Stocks at Stocks and arisings Operational Decommissioning Total Operational Decommissioning Total METALS: Ferrous metals 2,171 2,400 4,571 52, , ,144 Aluminium 61 2,423 2,484 1,531 4,853 6,384 Copper ,578 4,166 5,744 Lead ,236 3,944 10,180 Zinc Magnox/Magnesium Zircaloy/Zirconium Boral Brass ,022 Bronze Dural Inconel Monel Nimonic Stellite Others ,776 1,829 STABLE ELEMENTS: Nickel ,051 5,600 7,650 Tin Niobium Selenium Molybdenum INORGANIC ANIONS: Fluorides ,326 1,347 Chlorides ,325 1,341 Iodides ,325 1,337 Cyanides Carbonates ,652 2,706 Nitrates ,325 1,341 Phosphates ,325 1,340 Sulphates ,649 2,664 Sulphides ,325 1,337 Other anions ORGANICS: Cellulosics ,501 8,422 94,923 Halogenated plastics ,607 8,437 19,044 Non-halogenated plastics ,142 5,623 13,765 Ion exchange materials Rubbers ,450 3,240 11,690 Other organics , ,852 COMPLEXING AGENTS TOXIC METALS AND COMPOUNDS: Cadmium Lead ,233 3,819 10,052 Mercury Beryllium Other toxic metals OTHER HAZARDOUS MATERIALS: Combustible metals Low flash point liquids Explosive materials Phosphorus Hydrides Materials reactive with water Strong oxidising agents Pyrophoric materials Generating or evolving toxic gases Putrescible wastes Biological, pathogenic materials Asbestos ,103 1,212 Free aqueous liquids (4) Free non-aqueous liquids (4) Powder (4) Notes: (1) The materials listed do not include all components of the wastes, e.g. soil. (2) Note that care needs to be taken if summing material weight as certain materials appear in more than one category (3) Only waste streams with a quantified material concentration contribute to this table. (4) Potentially hazardous for the process of supercompaction Page 4 Issue 04

15 Table 3 Chemical components in ILW from all sources (Electrowatt-Ekono, 2002) Weight (tonnes) (2) (3) Material (1) Stocks at Stocks and arisings Operational Decommissioning Total Operational Decommissioning Total METALS: Ferrous metals 19,659 1,694 21,353 29,826 30,318 60,144 Aluminium ,236 Copper Lead Zinc Magnox/Magnesium 5, ,300 7, ,079 Zircaloy/Zirconium , ,351 Boral Brass Bronze Dural Inconel Monel Nimonic Stellite Others ,038 STABLE ELEMENTS: Nickel 1, ,448 2, ,102 Tin Niobium Selenium Molybdenum INORGANIC ANIONS: Fluorides Chlorides Iodides Cyanides Carbonates Nitrates 1, ,232 1, ,373 Phosphates Sulphates Sulphides Other anions ORGANICS: Cellulosics 1, ,089 1, ,655 Halogenated plastics 2, ,096 2, ,258 Non-halogenated plastics 1, ,068 1, ,576 Ion exchange materials Rubbers ,143 Other organics COMPLEXING AGENTS TOXIC METALS AND COMPOUNDS: Cadmium Lead Mercury Beryllium Other toxic metals OTHER HAZARDOUS MATERIALS: Combustible metals 4, ,222 6, ,431 Low flash point liquids Explosive materials Phosphorus Hydrides Materials reactive with water 3, ,586 4, ,258 Strong oxidising agents 1, ,239 1, ,250 Pyrophoric materials Generating or evolving toxic gases 1, ,239 1, ,250 Putrescible wastes Biological, pathogenic materials Asbestos Free aqueous liquids (4) 12, ,410 14, ,876 Free non-aqueous liquids (4) Powder (4) Notes: (1) The materials listed do not include al components of the wastes, e.g. graphite. (2) Note that care needs to be taken if summing material weight as certain materials appear in more than one category (3) Only waste streams with a quantified material concentration contribute to this table. (4) Potentially hazardous for the process of supercompaction Issue 04 Page 5

16 Table 4, derived from (Electrowatt-Ekono, 2002) shows predicted arisings of radioactive metal waste from the major nuclear operators. The evaluation of the application of metal melting technologies should therefore consider the timescales and policy governing these arisings. Table 5 produced by the Department of Trade and Industry (DTI) shows the status of UK nuclear sites and it can be seen that of the 20 sites listed, 13 are currently undergoing some form of decommissioning. The geographical location of the arisings will be a consideration for melting operators and waste owners for the siting of any proposed melting facility. Table 4 Metal Wastes at UK sites (Electrowatt-Ekono, 2002) Weight of Metals Stocks and Arisings (Tonnes) Operator Site BNFL BNFL Magnox British Energy Generation Ltd UKAEA Ministry of Defence Amersham Plc Capenhurst Sellafield Springfields Calder Hall Chapecross Berkeley Bradwell Dungeness A Hinkley Point A Oldbury Sizewell A Trawsfynydd Wylfa Hunterston A Berekeley Centre Dungeness B Hartlepool Heysham 1 Heysham 2 Hinkley point B Sizewell B Hunterston B Torness Dounreay Harwell Windscale Winfrith Culham Aldermaston Devonport Rosyth Royal Dockyard HMNB Clyde Rosyth and Devonport Eskmeals DSTL Fort Halstead DSDC North Defence Estates Organisation NRTE Vulcan Amersham Cardiff Harwell Capenhurst (Also minor producers) ILW LLW Operational Decommissioning Operational Decommissioning 26,077 6,505 44,624 80,855 4,008 6, ,679 1,711 6,209 1,401 65,109 7,282 6,126 4,043 96, ,166 2,872 8, Page 6 Issue 04

17 Table 5 Status of UK sites ( / w w w.dti.gov.uk/ nuclearcleanup/ tl.htm) RESPONSIBLE ORGANISATIONS SITE BNFL UKAEA Magnox Sellafield Capenhurst Works Springfield Works Drigg Disposal Site Dounreay Windscale Harwell Winfrith Culham Wylfa Oldbury Sizewell A Dungeness A Hinkley Point A Bradwell Hunterson A Trawsfynydd Berkeley STATUS Operational and decommissioning - fuel reprocessing and storage and management of nuclear wastes and materials Decommissioning/waste management and storage Operational and Decommissioning - fuel manufacture, nuclear services and decommissioning of redundant historic facilities Operational - low level waste disposal Decommissioning Decommissioning Decommissioning Decommissioning Operational Operational Operational Operational Operational Defuelling & Decommissioning Defuelling & Decommissioning Decommissioning Decommissioning Decommissioning Chapelcross Operational (will shut down by March 2005) Calder Hall Defuelling & Decommissioning Issue 04 Page 7

18 2.1.2 Nature of the Radioactive Contamination Metal contamination can be of two forms, either bulk or surface contamination. Bulk contamination usually arises from neutron activation of nuclides during the service life of the component. These components will usually be in-core components i.e. will have experienced high neutron fluxes. The main activation products will be Co-58, which arises from the nickel content of the metal (Inconel alloys and stainless steel), and Co-60, which arises from cobalt impurity. Other activation products of shorter half-life include Cr-51, Fe-55 and Mn-54. Surface activity can be loose contamination arising from deposition of nuclides from the interfacing medium, i.e. aqueous phase or gas phase during service. The deposited nuclides will depend on the environment of the component during service. Surface contamination can also be tightly bound, and this usually arises from the adsorption of deposited nuclides into the oxide layer formed on the metal. These require more aggressive decontamination techniques to remove such as melting. Much of the metallic waste arising during decommissioning is only surface contaminated rather than activated. As melting causes a homogenisation of the radionuclides mentioned above, the removal of surface contamination should be actively considered by waste owners and melt operators prior to melting if the aim is to reduce activity of the waste to as low as is possible. As will be later described in Section 3, melting redistributes radioactivity between the slag, the metal and off-gases depending on the radionuclides present. The radionuclides generally present within the radioactively contaminated scrap metal are Co-58, Cr-51, Fe-59, Ni-58, Zn-65 and Mn-54. These appear in combination with the main fission products Cs-134 and Cs137. The more volatile nuclides such as strontium and caesium leave the melt and are essentially transferred to the slag and the fumes. These are then retained by special filter systems. Other radionuclides such as cobalt, nickel, chromium, iron, zinc and manganese remain within the melt with only a small transfer to the slag (European Commission, 1998a). 2.2 Recycling of Metals Outside the Nuclear Industry (Public Domain) In order for material from the nuclear sector to enter the public domain it must be released from regulatory control i.e. it must be cleared. In the UK this is by means of the Radioactive Substances (Substances of Low Activity) Exemption Order. In addition to demonstrating compliance with these objective regulatory criteria, there are a number of subjective obstacles that must first be overcome. These include for example, the concerns of the scrap metal industry and the general public over radioactivity in the environment. These issues are discussed in more detail in Section 5. Assuming the barriers to recycling of radioactively contaminated material and its later use in the non-nuclear market can be addressed, there are two main options for release into the general scrap market: 1. Surface contamination is removed. The metal is authorised for release from the nuclear site to a commercial non-nuclear metal melting facility for Page 8 Issue 04

19 recycling along with normal scrap metal. After melting the ingots are free to be sold on the open market. This follows the route of specific or conditional clearance foreseen in RP 89 (see European Commission, 1998b). 2. Surface contamination is removed and the metal is melted at a designated/separate melting facility specifically for radioactive scrap metal. The resulting ingots are then cleared for the open market Specific Clearance The advantage of using existing operational (non-nuclear) melting facilities where radioactive waste metal is mixed with normal metal is that the expense of construction is avoided. In addition there are savings in efficiency as the plant will be able to operate at near-full capacity. There will be a dilution effect from the mixture of charges, as a result of mixing contaminated material from the nuclear industry with non-nuclear sourced scrap in the melting load. However, all waste metals would have to meet stringent specific clearance levels such as those recommended by the European Commission in RP 89 before release from a nuclear site could be authorised. RP 89 gives clearance levels for surface contamination in Bq/cm 2 as well as Bq/g limits. These specific clearance levels are radionuclide specific. They were derived on the basis of radiological assessments that assumed only a fraction of the scrap in the furnace came from cleared scrap (European Commission, 1998b). Specific or conditional clearance is where the material is released for a specific purpose e.g. for melting. In the case of general or unconditional clearance material is released from regulatory control without any future controls or restrictions. In UK legislation there are no specific clearance levels. Traceability and controls to ensure the material reached its defined destination, i.e. the melting facility, would have to be in place. Agreements also would have to be reached with furnace operators to accept the waste. Finding a commercial melting facility willing to melt material meeting the specific clearance standards is likely to prove difficult. In Germany there has been a reluctance from the non-nuclear steel industry to accept material from nuclear facilities even when the material is below the more restrictive general clearance criteria (European Commission, 1998a). In France a programme of recycling ran into problems due to the commercial steelm aker partner not wishing to be associated with the nuclear industry. The details of the French example are that the Atomic Energy Commission (CEA) set up a pilot program for recycling decontaminated scrap metal using a commercial steelworks. The key aspects of the system included: the choice of operators, the identification of objects, traceability with regard to operations and operators, the contractual basis of the services provided, the contracts between the owner of the containers, the decontamination contractor and the steelmaker, documentary control of operations, verification inspections and measurements, second-level supervision, auditing of operators, Issue 04 Page 9

20 environmental impact calculations and public information (Bordas, 2000). Despite a unanimous favourable decision from the Public Health Commission for the region which followed 3 years of reviews by the French authorities including the OPRI, DSIN, CSSIN, DRIRE, the Ministries of Health, Industry and the Environment and a public consultation, the operation has stalled due to the concerns of a key stakeholder, namely the steelmaker. A foreign owner bought the steelmaker partner, and was afraid of the consequences of adverse media publicity and refused to get involved (Bordas, 2000) General Clearance The alternative is to set-up a licensed melting facility dedicated to the melting of scrap metal from the nuclear industry. The melting would still be subject to regulatory control thus metals of higher activity could be melted. There is the opportunity to reduce the level of segregation and sorting on the basis of activity levels required in advance of melting. It may be possible also to reduce the extent of the surface decontamination and its verification. After melting, ingots could then be sorted into those that can be cleared, those that should be recycled within the nuclear industry and those that require disposal. There is no guarantee that after melting and after achieving radioactive decontamination below the general clearance levels such that the metal ingots can be sold on the open metal market that a buyer will be found. As mentioned previously, in Germany steel companies continued to be reluctant to take material from nuclear facilities even when the material is below clearance levels (European Commission, 1998a). As later described in Section 5, cleared material can set off gate alarms on the entrance to the steel facilities which steel producers procedures dictate they will reject; there is also a concern that the acceptance of cleared material into the system will have an adverse effect on the industry commercially by reducing demand for metal amongst consumers due to a nervousness regarding radiation. There have been some notable successes, including the aluminium melter at Capenhurst, UK where 7000 t of aluminium has been melted for unrestricted use (See Table 1). A matter for consideration by the melter operators in conjunction with the waste owners in this approach is achieving a cost efficient use of the facility i.e. maximising its use. 2.3 Recycling Within The Nuclear Sector Availability And Potential Usage Of The Recycled Material Within The Nuclear Sector Uses of recycled metals within the nuclear sector other than in radioactive waste disposal or storage facilities are limited, an example being in shielding blocks. A review of the amounts of waste steel, concrete, copper and aluminium generated from the decommissioning and normal operations of nuclear facilities in the EU from 1998 to 2050 was made in EUR (European Commission, 1998a). Twelve scenarios for the recycling and reuse of these materials within the controlled nuclear sector were analysed. The intended final product dictates the scrap grade that can be used. Product specifications and the inherent radioactivity must be appropriate to the intended future use. Thin cold rolled products (e.g. for waste drums) will require Page 10 Issue 04

21 higher purity steel to prevent surface defects and stress cracking during fabrication, whereas rebar and structural steel only requires lower quality steel. The report, (European Commission, 1998a), concluded that steel recycling by melting, and concrete recycling by crushing were the most likely forms of controlled release recycling that could be carried out economically. Copper and aluminium recycling within the nuclear sector was considered unfeasible. With respect to copper, refining processes are most likely to yield copper suitable for clearance. It was estimated by ENRESA and AEAT, the authors of the European Commission report, that there is insufficient copper arising as waste in the nuclear sector to run a plant dedicated to its refinement at full capacity. With respect to aluminium, recycling for unrestricted release (as demonstrated by operations at Capenhurst) would be the most likely form of recycling. Following a review of existing European radioactive waste disposal facilities by AEAT and ENRESA, the requirements for steels for rebars, boxes, drums, and concrete for boxes and grouts across Europe have been calculated (European Commission, 1998a), and the estimated UK requirements have been reproduced in Table 6. In the UK the final decommissioning of stations is delayed for around 100 years to take advantage of the decay of some radionuclides and thus reduce the amount of waste that may require final disposal in controlled facilities. Thus in the UK the large amounts of waste generated from decommissioning of nuclear power plants were outside the timescale being considered for the European Commission study. Table 6 Type of container used 500 litre drums (requires 0.13 t of stainless steel) Requirements for drums, boxes, reinforcement, grouts in UK disposal facilities currently in operation (European Commission, 1998a) UK Total/ yr Total Steel requirements (t) Timescale litre drums Concrete boxes (requires 0.62 t of carbon steel for reinforcing bars) 3m 3 boxes (requires 0.63 t of stainless steel) ISO containers (require 2.5 t steel plate) In the UK the waste container which will be in greatest demand is the 200 litre drum. The estimated annual arisings of metals are presented in Figure 2. Issue 04 Page 11

22 Figure 2 Estimate of metal arisings from UK decommissioning SOURCE DATA: European Commission, 1998a based upon figures from the 1994 United Kingdom Radioactive Waste Inventory. DOE/RAS/96.001, UK Nirex Report No Page 12 Issue 04

23 Figure 2 cont d The LLW arisings of aluminium within the UK are plotted above. Although it appears that there are significant arisings of aluminium in general it arises as only a small percentage of waste within any waste stream. As for aluminium the copper waste generally arises as a small percentage of a waste stream e.g. electrical components and cabling. Issue 04 Page 13

24 The data suggests that the arisings of material will always exceed the possible uses of that material identified for disposal facilities. Around 40 % of Europe-wide arisings of carbon steel could be recycled into waste containers and rebars. For stainless steel the fraction of material generated that could be recycled is smaller at around 20 % of arisings. For stainless steel it is suggested that in some cases storage of metals for later use should be considered, especially if disposal plans for the second half of the 21st century indicate that large quantities of stainless steel containers would be required for disposal or storage of ILW or spent fuel (European Commission, 1998a). The use of recycled metallic materials in the manufacture of spent fuel storage disposal containers is an attractive scenario because the activity of the final containers will be dominated by the activity of the waste contained therein rather than any residual activity in the recycled product. The review of practices in spent fuel management reveals several opportunities for the use of recycled steel for the manufacture of containers. For example, casks such as the CASTOR type used in Finland could be easily made at a plant similar to that proposed for the manufacture of cast boxes for disposal of LLW/ILW. However, Given that the plans for dealing with spent fuel are at an early stage in many countries, this gives suitable scope for examining the possibility of incorporating a controlled release strategy in this area Necessary Additional Processing Facilities One of the problems in the reuse of stainless steels that cannot be sold to the scrap market for unrestricted release is the requirement for processing of the metal into plate. Due to the high value of the material and its anti-corrosive properties, stainless steel products used in the nuclear industry are essentially formed and welded from plate. For production of containers such as a 500 litre drum used for disposal of ILW in the UK, a rolling mill would be required. If material is of an activity higher than that suitable for unrestricted release then a nuclear installation rolling mill would be required. Any facility of this nature would have to address operational complexities including maintenance of potentially contaminated equipment and the possible requirements for remotely operated machinery. Even mini-mills used in conventional industry have annual capacities of 200,000 tonne meaning that a nuclear facility of this type will be operating significantly under capacity. This raises problems in finding suitable sources of material for processing within the country of location of such a facility, and with it problems in transportation and legislation regarding movement of material across borders. The alternative of using the facility to also roll plate for unrestricted release may not be acceptable to the conventional market. Investment in such a facility for a short lifetime and the siting of a large facility may mean that this scenario may not be feasible within Europe. The alternative manufacturing process of back-extrusion instead of forming from plate, raises further possibilities for stainless steel controlled release recycling. However, further evaluation of this method of manufacture and analysis of the economics would be required (European Commission, 1998a). With respect to carbon steel used for the production of 200 litre / 220 litre drums from plate, the same problems of processing of the metal into plate would be encountered as those for stainless steel recycling. It should be noted, however, that because of the extensive use of such drums around the EU, the production of Page 14 Issue 04

25 these drums would provide a larger market for carbon steel. The requirement for drums in a single country would be much larger than for stainless steel containers, and may therefore support a facility dedicated to arisings from a single country. This would reduce problems in transportation, but those of siting of such a facility would still have to be resolved. The adoption of a strategy of recycling within the nuclear sector may require considerable collaboration between several organisations e.g. the waste owners, melter operator, disposal facilities and the regulators. In cases where the decommissioning operations, construction and placement of waste materials are carried out by the same organisation, the availability of disposal facilities (and thus options for restricted release recycling) and the arisings of materials suitable for recycling can be easily matched. Where this is not the case there is need for considerable collaboration (European Commission, 1998a) Experience Facilities in France, Sweden, Germany and the USA are currently melting material and producing waste containers and shielding. (See Table 1). 2.4 Melting as Part of a Disposal Strategy In addition to facilitating recycling as described above melting can be advantageous for disposal. SOCODEI in France has operated a contaminated scrap metal melting unit at CENTRACO since February CENTRACO has achieved volume reduction ratios from ten to one to twenty to one (Faugieres, 2000). However, this may take into account a degree of reuse of the metal for shielding blocks and packaging. A more conservative estimate of volume reduction is that Electric Arc Furnace (EAF) and induction furnaces can achieve a reduction factor of 4 6 (ISTC, 2004). The reduction in volume will be dependent on the geometry and form of the metal. It may be possible to redistribute activity of a number of ILW waste streams by combining them such that the eventual waste is a single waste stream reduced to it s maximum density with the volume of the waste reduced when compared to that of the initial separate waste streams. If the melter s purpose is purely to reduce the volume prior to disposal (i.e. there is no intention to recycle the material), there will be no requirement to decontaminate or sort the metals (other than to ensure there are no water containing vessels in the load). Melting technology can be chosen to avoid the production of slag or the slag can be added back into the melt and disposed of together. In addition to volume reduction melting provides: A homogeneous waste form which makes characterisation simpler and easier; A stabilised final waste package (Faugieres, 2000). It may be possible that once the metal is melted and formed into easily stacked ingots the need for further packaging for disposal could be avoided as the radioactivity is stabilised within the bulk metal. As a consequence of homogenisation during melting the activity concentration will fall which may affect the categorisation of the radioactive waste and thus the correct disposal facility for it. Issue 04 Page 15

26 2.5 Summary - Waste Issues There is a large quantity of metal in the UK that could be melted. The majority of this radioactively contaminated metal is LLW. 90% of the metal is ferrous. There are three main melting strategies for these wastes: Melting for release to the open market: Melting for release to the open market will require the product to meet stringent clearance criteria. There will also be exacting controls for the verification and monitoring of the process. There also remains the issue of whether there is a market for the material due to continuing nervousness amongst the public and steel producers over radiation. Melting for reuse within the nuclear sector, Melting for reuse within the nuclear market will permit the recycling of metals which would not achieve the more stringent clearance levels required for free release. It is likely that the UK supply of contaminated metal generated within the nuclear sector would outstrip the demand for recycled materials within this sector. Melting for disposal. Melting for size reduction, would require no prior surface decontamination and very little sorting of the waste material. Melting can achieve a volume reduction factor of 4 6, thus significantly reducing the disposal cost accordingly. Melting will homogenise and stabilise the waste reducing packaging requirements. These strategies have been described as three separate approaches. There is opportunity however to integrate the strategies such that were possible material can be cleared, reused within the nuclear sector or disposed of at Drigg or Nirex depending on the activity of the product and the available markets. Whatever the strategy or approach each will require to a lesser or greater extent the co-operation and acceptance by the public and the non-nuclear steel industry: Acceptance of metal products containing recycled metal from the nuclear sector (public), Acceptance of cleared material (steel maker), Acceptance of radioactive metals/ingots for controlled melting/rolling for the nuclear sector (steel maker), Acceptance of a melting facility for radioactive material (public), Acceptance of a variation in source material at an existing melter (public and steel maker). The issues which arise for each strategy are summarised in Table 8. Page 16 Issue 04

27 3 Melting Technology 3.1 Introduction In Section 2, the extent of available radioactively contaminated metal in the UK was explored and the potential strategies for melting and their implications discussed. Section 3 concentrates upon the available technology for the achievement of those strategies. The section addresses: Overview of the process of melting radioactively contaminated metals, Proven technology used for melting radioactively contaminated metals, Current non-nuclear technologies, Developing and emerging nuclear melting technologies. 3.2 Overview of the Process Of Melting Radioactively Contaminated Metals In the 1990s, the melting of contaminated steel in purpose built plants for recycling developed as a new industry (NEA, 1999). Seven plants have been identified as having melting facilities or having melted contaminated metals on an industrial scale (see Table 1). The plants are located in France, Germany, Sweden, UK and the USA. Six out of seven of the facilities use induction melting, and the remaining plant used electric arc melting (see Section 3.3). To date, available information suggests that scrap metal has largely been recycled within the nuclear industry. A review of the feasibility of recycling and/or reuse of non-releasable components and materials arising from nuclear operations within the European Community has been undertaken by ENRESA and AEAT on behalf of the European Commission. The study concluded that the recycling of radioactive steels (carbon and stainless) is an already well researched area which requires no further development as regards the melting and refining of steel arising from nuclear facilities (European Commission, 1998a) The Treatment Process The treatment of radioactively contaminated steels will depend on whether the contamination lies within the bulk of the steel or on the surface. Surface Contamination In the case of surface contamination, the melting process will distribute the activity within the bulk. Consequently, if melting technologies are used to process steels and the aim is to maximise the reduction of activity, it is important to remove surface contamination before treatment if the reduction/removal of radioactivity is to be achieved (See Section 3.2.2). A pre-treatment, surface decontamination process will generate secondary waste arisings, which may require further treatment prior to disposal. Bulk Contamination A generic flow diagram for bulk-contaminated scrap is given in Figure 3. Prior to melting, items have to be size reduced to allow charging of the furnace through a Issue 04 Page 17

28 suitable air-lock which prevents the escape of aerosols during the loading process. The material must be sorted, for steel melting for example there must be no copper, lead or cadmium entering the melt, as this would result in an unacceptable final product for recycling. Sorting is also necessary to ensure there are no bodies containing water as this leads to formation of vapour in the melt and presents an explosion risk (European Commission, 1998a). Figure 3 Scrap metal for steel-making (NCRP, 2002) Melting The metal is melted usually either by heating by means of electrical induction heating or by electric arc in the furnace and flux potentially added, a slag phase containing the bulk of the contamination forms and floats on top of the metal phase. Fluxing agents may be added to im prove the slag separation; flux is a mixture of oxides added to the molten metal to enhance the capture of impurities (NCRP, 2002). Any combustible and volatile materials including volatile metals and metal oxides are either contained by vacuum melters and enter into the slag, or they enter an off-gas system (Garcia, 1996). Page 18 Issue 04

29 3.2.2 Distribution of Radioactive Material in the Metal-Melting Process When the aim is to maximise the reduction of activity, the first step is to remove as much surface contamination as possible. Melt refining can then be used to remove radionuclide contaminants from metals or alloys by preferential oxidation, and the oxidized contaminants are then separated from the metal. The removal of impurities can be achieved by vaporisation if they have a low boiling point. The vapours can be removed in the off-gas system or reacted with oxygen to form an oxide fume. For high boiling point impurities, they are combined with flux components and removed in the slag. The mode of removal is therefore a function of the chemistry of the furnace (acidic or basic), the thermodynamics of the system, and the chemistry of the impurities. Table 7 presents ranges of partitioning data for various radionuclides when melted in the electric arc furnace (EAF) steelmaking furnaces. Table 7 Partitioning factors for BOFs and EAFs (NCRP, 2002: Cheng et al, 2000; Nieves et al, 1995; NRC, 1999) Issue 04 Page 19