Waste Residue Processing

Waste and Residue Processing at the National Nuclear Laboratory

Overview

  • Sentence stored materials to established processing routes where practicable
  • Develop and implement processing routes for more difficult to treat wastes and residues
  • Preserving capacity at the Low Level Waste Repository (LLWR)

Phase 1

Desktop Study

Study available information regarding:

  • known history
  • storage
  • physical properties
  • chemical properties
  • radioisotope content
  • radiological properties
  • Previous processing routes

Outcome

  • Process via an established route
  • Phase 1A assessment required
  • Phase 3 ad hoc process development

Phase 2

Testing Suitability for existing process

Largely concerned with testing for processing via nitric acid based leaching/dissolution-filtration-solvent extraction processes:

  • segregation (tramp and oil removal)
  • size reduction if required
  • leaching in nitric acid under typical plant conditions
  • leaching in nitric acid under modified plant conditions
  • observe: ‘tippability’, reactivity, solids suspension, corrosivity, filtration characteristics
  • analysis of leachates, processability by SX
  • analysis of residual undissolved solids to determine disposal options-including environmental leach testing

Outcome: thousands of Phase 2 tests completed:

  • Process via an established route
  • Phase 3 ad hoc process development

Phase 3

Development of ad hoc process

  • standard leaching yields residual undissolved solids with high uranium contents in terms of disposal to landfill-also where other radioisotopes are present at problematic levels
  • a residue is not physically or chemically suitable for treatment in nitric acid, at least in standard plant
  • where a residue yields a leachate not suitable for normal solvent extraction (due to high radioisotope and/or heavy metal content)

Phase 4

Full Scale Processing in NNL facilities

  • Generally used where processing is complex with close chemical control required
  • Modular plant easily reconfigured for different uses
  • Residue plant cleared to 100 g 235U/100g U (various criticality control methodologies)
  • Heated/stirred dissolvers and leach vessels (some PVDF lined etc); “SABRE” characteristics,  0.1-10 m3 capacity-also useful as precipitators
  • Filtration/Centrifugation
  • PVDF solvent extraction equipment
  • Furnace Treatment
  • Washing Machines (HNO3 compatible) for soft wastes
  • Oil/Solvent washing equipment
  • Ancillaries: acid/ammonia gas scrubber, effluent treatment, storage, total enclosure
  • Storage

Waste Disposal routes

  • Aqueous and gaseous discharge authorisations
  • Solid waste landfill/LLWR
  • Organic liquids to free release

Examples of residues to which this methodology has been applied

  • Process sludges (filter cakes, alkaline precipitates, high U dissolver cakes)
  • Contaminated oils, solvents, oily residues and solvent extraction cruds
  • Decommissioning residues (concrete, bricks, timber, metals, plastics, glass)
  • Uranium metal and alloys (generally unusual forms)
  • Uranic powders (UO2, U3O8, UO3, UF4) – often unusual fingerprint
  • Sintered pellets (UO2, UC)
  • HEPA and pre-filters
  • Contaminated soft wastes (paper, plastic, clothing, gloves, mops)
  • Hex cylinder washings
  • Contaminated graphite
  • Incinerator ash and other vitrified uranic slags
  • High U resinous floor coverings

Track record of success

  • Over 40,000 drums categorised via Phase 1 Assessment
  • Over 15,000 drums cleared for processing in customers’ own plants
  • Over 2,500 drums of highly intractable wastes and residues processed via the NNL flexible Pilot Plant
  • 100’s m3 oil and solvent cleaned to free release levels
  • c. £12M of uranium value recovered via NNL processing of residues as well as discharging liabilities for direct disposal costs

Residual solids typically sentenced as Very Low Level Waste Aqueous effluent disposed of via Site Authorisation