1. Page 1Nuclear Familiarisation - Reprocessing and Recycling PDW FAMILIARISATION WITH NUCLEAR TECHNOLOGY REPROCESSING AND RECYCLING Peter D. Wilson DURATION ABOUT 40 MINUTES

2. Page 2Nuclear Familiarisation - Reprocessing and Recycling PDW WHY REPROCESS? Originally – To obtain plutonium for military use Currently – To ease storage problems especially Magnox - cladding corrodes easily – To concentrate high-level waste – To recover clean plutonium and uranium – As a business opportunity

3. Page 3Nuclear Familiarisation - Reprocessing and Recycling PDW DISCHARGED FUEL HAS - Diminished reactivity owing to – substantially reduced fissile content much of initial enrichment consumed not entirely compensated by new plutonium – neutron-absorbing fission products Somewhat weakened structure Possible pressurisation by fission gases Nearly all original fertile content (U-238) Minor actinide content (Np, Am, Cm) super-proportional to irradiation Continuing heat release from decay of fission products & minor actinides Potential for much greater energy generation than already realised (by up to 2 orders of magnitude) Reasons for discharge

4. Page 4Nuclear Familiarisation - Reprocessing and Recycling PDW MANAGEMENT OPTIONS (after decay storage) Direct Disposal Minimises operations and cost Minimises immediate risk of illicit diversion, but Leaves Pu content intact with gradually rising quality and decaying radioactive defence - “plutonium mine” Minimises secondary wastes Abandons all remaining energy potential after at best ca. 1% utilisation of mined uranium (including enrichment tails) Reprocessing Major industrial operations Recovers fissile and fertile materials for further use In principle permits near-elimination of fissile content Minimises HLW volume, but Generates more ILW & LLW Operational radiation exposure Permits recycling – potentially 50 - 100% utilisation – but without fast reactors only ~15-30% improvement over once- though

5. Page 5Nuclear Familiarisation - Reprocessing and Recycling PDW PROCEDURE - CLOSED CYCLE Local storage for decay of heat release Transport to reprocessing site Further decay storage to limit radiation Reprocessing – separation of uranium & plutonium from each other and from fission products – finishing U & Pu products purification and conversion to form for use or storage – conditioning wastes for disposal Refabrication of U and Pu into new fuel

6. Page 6Nuclear Familiarisation - Reprocessing and Recycling PDW DELAY STORAGE Wet Water provides cooling and shielding Permits direct sight and manipulation Requires strong structure Needs continual purification and leak monitoring Tends to cause corrosion Liable to create uncomfortably humid working environment - needs good ventilation Dry Avoids corrosion especially of Magnox Avoids need for water purification Allows tighter packing – less risk of criticality Remote manipulation Needs more complex building and equipment Requires guided convection or forced-air cooling

7. Page 7Nuclear Familiarisation - Reprocessing and Recycling PDW TRANSPORT FLASK REQUIREMENTS Shielding appropriate to radioactive content (gamma, neutron) Heat dispersion adequate for maximum thermal load With customary water coolant, robust containment of activated corrosion products Structural integrity maintained against worst credible impact or fire Photo copyright BNFL (?)

8. Page 8Nuclear Familiarisation - Reprocessing and Recycling PDW PROCESS REQUIREMENTS Operational and environmental safety – nuclear (avoiding criticality) – against radiation & contamination Product quality - decontamination by10 6 - 10 8 Manageable wastes

9. Page 9Nuclear Familiarisation - Reprocessing and Recycling PDW BASIS OF SEPARATION PROCESS Uranium and plutonium in their most stable chemical states are readily soluble in both nitric acid and certain organic solvents immiscible with it Fission products generally are at most very much less so. – iodine (a major exception) is largely boiled off during dissolution Equilibrium distribution depends on e.g. acidity Uranium and plutonium can therefore be extracted from a fuel solution and then taken back into clean dilute acid

10. Page 10Nuclear Familiarisation - Reprocessing and Recycling PDW Separation of fuel from cladding Dissolution of fuel substance Extraction of uranium and plutonium into solvent – 1 st Sellafield plant Butex, since 1964 tributyl phosphate (TBP) diluted with e.g kerosene Separate backwashing of plutonium and uranium – plutonium backwash assisted by chemical reduction Concentration and storage of wastes (fission products etc) Waste conditioning for eventual disposal REPROCESSING STAGES Magnox, peel & dissolve; Oxide, chop & leach

11. Page 11Nuclear Familiarisation - Reprocessing and Recycling PDW PUREX PROCESS OUTLINE U, Pu, FPs U, Pu FPs Highly-active waste Pu Plutonium purification U U Uranium purification Solvent purification (alkali wash) Extraction Reductive backwash Dilute acid backwash Dissolution Aqueous Solvent

12. Page 12Nuclear Familiarisation - Reprocessing and Recycling PDW COUNTERCURRENT OPERATION Fresh solvent Aqueous feed Loaded solvent Depleted aqueous Required separation factors need many stages of equilibrium or equivalent in partial equilibrations Loaded solvent meets the most concentrated aqueous solution Fresh solvent meets depleted aqueous feed Thus extraction and loading are maximised Similar principles apply in reverse to backwashing Design challenge is to maximise local inter-phase contact without excessive longtitudinal mixing Contact between solvent and aqueous may be continuous or stagewise

13. Page 13Nuclear Familiarisation - Reprocessing and Recycling PDW MIXER-SETTLER Physical & theoretical stages very nearly equivalent Simple to design and operate – can be set up effectively with beakers and bent tubes on a bench Tolerates variable throughput BUT Large settler volume at each stage Therefore long residence time, high process inventory and solvent degradation Poor geometry for high plutonium content NEVERTHELESS Adequate for uranium and low- irradiated fuel Part of mixer-settler bank

14. Page 14Nuclear Familiarisation - Reprocessing and Recycling PDW PULSED COLUMN Multiple stage equivalence with settler volumes only at top and bottom Tall, thin profile - good for nuclear safety Gamma loss & short residence time reduce solvent degradation Therefore satisfactory for plutonium and fairly high-irradiated fuel BUT Performance depends on conditions – limited range of throughput Prediction largely empirical and approximate Needs sophisticated operational control Height requires tall buildings, seismic qualification expensive

15. Page 15Nuclear Familiarisation - Reprocessing and Recycling PDW REDUCTIVE BACKWASH Necessary for clean separation of plutonium from uranium – Pu(III) very much less extractable than Pu(IV) Magnox plant uses ferrous sulphamate – leaves salt residue (ferric sulphate) corrosive limits volume reduction - intended for discharge after decay storage, so must be kept free from major contamination – therefore U/Pu split in second cycle Thorp uses uranous nitrate – waste contains no residual salts – can be greatly concentrated by evaporation – therefore acceptable in first cycle (early split) nearly didn’t work - unexpected complications from technetium

16. Page 16Nuclear Familiarisation - Reprocessing and Recycling PDW SOLVENT DEGRADATION Combination of radiolysis and acid attack Short-term, i.e. within cycle (chiefly TBP extractant) – forms (a) dibutyl and (b) monobutyl phosphates – (a) impairs backwash – (b) forms precipitates – removed by alkaline wash Long-term (largely diluent) – forms acids, alcohols, ketones, nitro-compounds etc. – impair decontamination and settling – only partly removed by washing – require gradual or complete solvent change – waste solvent needs disposal

17. Page 17Nuclear Familiarisation - Reprocessing and Recycling PDW WASTE MANAGEMENT PRINCIPLES Absolute separation of radioactive from inactive material impossible – most fission products etc. confined to small volume – some inevitably emerge in other streams Radioactive content confined as far as practicable to eventually solid forms for disposal Some very difficult to confine reliably, e.g. iodine, krypton – very small dose to everyone preferred to risk of local accidental high dose – therefore dilution & dispersion rather than concentration

18. Page 18Nuclear Familiarisation - Reprocessing and Recycling PDW SOLID WASTE CLASSIFICATION High level (HLW) - sufficiently radioactive for heat release to be significant in storage or disposal Low level (LLW) - no more than 4 GBq alpha per tonne or 12 GBq beta/gamma per tonne Intermediate level (ILW) - higher than LLW but not significantly heat-releasing Very low level (VLWW) - disposable with ordinary rubbish bulk less than 4 GBq/m 3 beta/gamma no single item over 40 kBq beta/gamma

19. Page 19Nuclear Familiarisation - Reprocessing and Recycling PDW RADIOACTIVE WASTES HLW - vitrified fission products, minor actinides and corrosion products mostly from the first cycle raffinate ILW - cladding fragments, plutonium-contaminated materials, resins & sludges from effluent treatment, scrapped equipment LLW - e.g. domestic-type rubbish from active areas, mildly contaminated laboratory equipment Low-level liquid - treated effluents from ponds, condensate from evaporators, etc. Gaseous - filtered and treated ventilation air from cells and working areas

20. Page 20Nuclear Familiarisation - Reprocessing and Recycling PDW SELLAFIELD WASTE MANAGEMENT Confine as much as possible of the heat- releasing radionuclide waste to a small volume of glass - HLW Immobilise other substantially radioactive waste (without troublesome heat release) with cement - ILW Pack and encapsulate low-level solid waste in secure containers for near-surface burial Discharge hard-to-confine species e.g. iodine, krypton Otherwise discharge as little as reasonably achievable in liquid and gaseous effluents For eventual deep disposal

21. Page 21Nuclear Familiarisation - Reprocessing and Recycling PDW PRODUCT FINISHING Finishing - conversion to a form suitable for sale, use or storage – Uranium – thermal denitration to UO 3 – Plutonium – precipitation as oxalate – calcination to PuO 2

22. Page 22Nuclear Familiarisation - Reprocessing and Recycling PDW WHY RECYCLE? To make the most of a finite resource To reduce short-term need for fresh mining – Most environmentally damaging part of industry To reduce storage or disposal requirements for materials with little or no other legitimate use – e.g. over a million tonnes depleted uranium world-wide plutonium from decommissioned weapons To put fissile material out of reach of potential terrorists

23. Page 23Nuclear Familiarisation - Reprocessing and Recycling PDW Uranium – recovered from oxide still has more than natural enrichment could be used “as is” in CANDU – also has U-232 (radiation hazard from daughters) and – U-234 & U-236 (neutron absorbers) - though U-234 fertile Plutonium – contains – Pu-238 (heat & neutron emission) – Pu-240, Pu-241 (parent of Am-241 - radiation hazard) & Pu-242 – as well as desirable Pu-239 – only odd-numbered isotopes fissile Current reactors take at most a partial load of plutonium-enriched fuel; newer types designed for full load Refabricating recycled civil material more expensive than fresh but can be offset by avoiding isotopic enrichment of uranium FACTORS RELEVANT TO RECYCLING

24. Page 24Nuclear Familiarisation - Reprocessing and Recycling PDW DIFFICULTIES IN RECYCLING AS MOX Deleterious isotopes in uranium – U-236; unproductive neutron absorber – U-232; extremely energetic  -  emitting daughter Tl-208 Requirement for intimate mixing, ideally solid solution – to avoid hot spots weakening cladding – achievable but difficult in solid state – co-precipitation tends to some segregation – sol-gel process may be preferable in future Plutonium oxide very hard to dissolve in pure nitric acid – a mixed product from a future reprocessing plant would be more tractable

25. Page 25Nuclear Familiarisation - Reprocessing and Recycling PDW PRACTICAL RECYCLING Uranium – 1600 te AGR fuel produced from re-enriched recovered uranium – manufacture essentially as from fresh material – generally cheaper to use fresh - but for how long? Plutonium – used in about 2% of current fuel manufacture – ~2000 tonnes fuel so far – in UK as powder dry-blended with uranium dioxide, formed into loose aggregates, pressed into pellets, sintered, ground to size and packed into tubes – elements distinguished only by identification markings

26. Page 26Nuclear Familiarisation - Reprocessing and Recycling PDW FUTURE REPROCESSING Aim to simplify, reduce waste arisings and costs at source Single-cycle flowsheet? – increased cycle decontamination, or – reduced (more realistic) specification Intensified process equipment – continuous dissolver – centrifugal solvent-extraction contactors (essentially short-residence mixer-settlers) Different (e.g. pyrochemical) processes for special fuels Waste partitioning (e.g. for transmutation) – currently seems an unjustifiable complication

27. Page 27Nuclear Familiarisation - Reprocessing and Recycling PDW FUTURE RECYCLING Near term Reconstitution of oxide fuel for CANDU (Dupic) – possibly with minimal process to remove volatiles Sol-gel vibro-packing route Distant Molten salts – as process medium avoids large volumes of aqueous waste generally poorer separations – as fuel? – symbiosis between pyrochemical reprocessing and molten-salt reactors