Wasteform Evolution Studies Methods and Observations

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Wasteform Evolution Studies Methods and
Observations
Presented by Ed Butcher Encapsulation, Waste
Science and Analytical Team
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Overview

• Research, Development and Implementation Work
• Product Evaluation Task Force/Programme
• Longevity Studies on Full Scale Real Time Aged
  Samples
• Additional Underpinning Studies at the
  Immobilisation Science (ISL)
• Legacy Waste streams
• Ongoing and Potential Future Work

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Waste Management Life Cycle

• Encapsulation process
• Engineered Storage
• Transport and handling
• Repository Storage

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Phased Approach to PETF/PEP Encapsulation
Programmes

• Phase 1 Waste characterisation. Simulant
  definition. Evaluation of range of matrix
  options
• Phase 2 Selection of preferred encapsulation
  matrix by physical testing of most favourable
  options from phase 1 study.
• Phase 3 Practical studies to determine the
  product properties of reference encapsulated
  wastes up to 90 days curing
• Phase 3a Extension of timescales of certain Phase
  3 studies to 360 days curing.
• Phase 4 Detailed Practical studies which define a
  range of acceptable formulations (envelope)
  for encapsulating waste

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Parameters Assessed

• Physical Properties
• Fluidity, setting, working time,
• Bleed
• Strength development versus time
• Dimensional stability
• Impact and fire testing
• Generic longevity issues
• Radiation Stability
• Cement ageing
• Corrosion reactions

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Magnox
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Waste Encapsulant Interactions

• Reactive metals
• Magnox
• Acute versus chronic corrosion rates
• Temperature
• Water Content
• Swarf versus fin
• Precorrosion of magnox
• Infilling effects
• Acceptable expansion
• Loadings

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Assessment of Full Scale - Aged samples

• Objectives
• Analysis of aged inactive samples to increase the
  understanding of wasteform evolution and provide
  additional data on stability
• Products assessed
• WPEP Ferric flocs
• MEP - Magnox
• WEP - Fuel hulls and BaCO3
• WTC Compacted PCM wastes

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Available Samples

• Approximately 100 full-scale inactive samples
  stored in Cumbria.
• Representative of all plant products,
• 10 to 15 years, similar in age to plant packages,
• Samples have been stored under various conditions
  but generally at the warehouse conditions for
  last 9 years,
• Many of the samples have been sectioned,
• Few have been capped and lidded, and many do not
  have s/s drum,
• Can be considered a conservative comparison

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Sampling

• 50mm diameter diamond drilled cores
• Stored - prevent oxidation, carbonation, etc
• Wet cored to depth

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Encapsulated floc Product
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Typical Solids drum
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Testing techniques

• Physical and Chemical
• Visual
• Cracking
• Carbonation
• Acid neutralisation capacity (ANC)
• Equilibrium extraction
• Permeability / Porosity

• Instrumental
• SEM Electron Microscopy
• XRD
• TGA Thermal Analysis

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Characterisation
Initial Characterisation

• Logging of cores physical characteristics,
• Logging of bore hole to identify historic faults,
• Bulk Density, Specific Gravity, Moisture content
  for moisture density relationships - porosity,
  degree of saturation,
• pH and redox profiles through low Liquid/Solid
  ratio extraction, and carbonation profiles using
  standard indicator method, and
• ANC profiles to indicate degree and form of
  alkalinity present.

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Characterisation
Instrumental Characterisation

• Analysis of grout by SEM with elemental analysis
  using energy dispersive x-ray spectroscopy (EDS),
• Analysis of grout with x-ray diffraction (XRD)
  analysis to investigate CSH incorporation, and
• Thermogravimetric Analysis (TGA) of cores to
  confirm/refute presence of phases (e.g., Ca(OH)2).

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• Results
• A selection

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Physical characterisation

• The bulk density of wasteforms consistent
  throughout with little evidence of densification
  at depth.
• Porosity decreased over time.
• Moisture content remains consistent throughout
  wasteform generally 100 saturated - no
  significant desiccation.
• Slight carbonation of wasteforms 0-3mm, while
  lt35mm in cap.

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Physical characterisation

• Flocs - one sample contains the only internal
  cracks found - probably due to handling methods
  and removal of paddle.
• Investigated with SEM

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Scanning Electron Microscopy of cracks

• Historic fracture found -covered in ettringite
  which degrades in the presence of CO2.
• Suggests fracture is isolated from atmosphere
  cracks self sealing.

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WTC products

• No sign of degradation of waste
• No sign of corrosion of puck walls
• Corrosion visible occurred after slicing

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WTC core
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Detail of WTC Puck Core
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Physical characterisation - capping key

• IDM and Hulls - very good key of cap to matrix
• Magnox - less good keying of cap

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Centrifuge Cake Cap
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Physical characterisation summary

• Samples in good condition
• No significant desiccation
• Very little cracking observed - seems to be
  repaired
• Permeability / porosity reduced with ageing

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Chemical Characteristics

• pH generally ranging from 11.92 to 12.32, below
  Ca(OH)2 saturation for the ambient temperature,
  and ANC indicates very little free Ca(OH)2 exists
  in all PFA/OPC wasteforms.
• EH ranging from 123.5 to 316.5 mV for PFA/OPC
  blend. Indicating that oxidising conditions
  prevail through selection of the PFA blended
  grout.
• EH ranging from -100.7 to 7.0 mV for BFS/OPC
  blend. Indicating reducing conditions maintained
  through selection of BFS blended grout.

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Acid neutralisation capacity
Magnox swarf drum showing cap and matrix
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Acid neutralisation capacity
Floc drum
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Carbonation

• Phenolphthalein test - purple pHgt9.2
• Caps - see significant carbonation up to 35mm
• Matrix (including PFA of flocs) lt 3mm

Al Hulls (GR/93/44) grout/cap interface
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Summary of Results

• Wasteforms all have significant buffering
  (gt4eq/kg) to pH9. Relates to a 1 kg sample
  capable of neutralising 40,000 L of pH 4 mineral
  acid.
• Carbonation of cap lt35mm,
• Carbonation of matrix (including flocs) lt3mm

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SEM

• Normal calcium silicate hydrate field.
• Relatively dense matrices.
• Little hydration of large BFS particles in BaCO3
• Significant proportion of flyash remains
  available in WPEP wasteforms.
• Magnox samples showed little corrosion product
  except in originally water filled porosity
  adjacent to the Magnox.

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Magnox Infill
Fresh Magnox in Grout GR/91/242
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Summary of instrumental results

• XRD and TGA did not uncover any unexpected
  phases.
• Confirms carbonation observations
• Little lime present - little support for further
  pozzolanic reactivity
• BFS - little hydration of large particles in
  BaCO3
• No unexpected phases, reactants all consumed -
  product in virtual steady state

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ISL - Encapsulation of Ferric Flocs

• Utilises five flocs reflecting the range of
  materials processed in WPEP
• Assessment in three stages
• characterisation of materials
• assessment of effect of pretreatment
• effect of cementation of floc material
• Identified phases formed
• CSH, calcium hydroxide, sulphate phases plus iron
  substituted CSH, CSH with adsorbed iron
• Floc chemically immobilised with in encapsulant
  matrix

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ISL Corrosion of Metals in Composite Cements

• Assessing effect of
• metal type steel, aluminium and Magnox
• cement composition
• temperature
• time
• Identification of reaction products at
  encapsulant- metal interfaces

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ISL - Effect of BaCO3 on Cement Hydration

• Examination of a range of blended cement
  compositions
• Effect of temperature on microstructure and
  phases formed
• BaCO3 simulant for WEP wastes
• Presence of unreacted slag at 720 days
• Reactions of BaCO3 with slag and cement

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Legacy Wastes

• Multiple component waste streams
• Expected to be retrieved as highly heterogeneous
  materials
• Treatment systems will build on the knowledge of
  the behaviour of the wastes generated from
  research, development and operations
• Annulus double skinned box
• Option to fill annulus and also rework boxes
  during product finalisation stage

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Ongoing Work and Future Work

• Project support work for legacy plants
• Legacy Magnox wastes
• Ongoing uranium corrosion trials in range of
  matrices
• Alternative cement systems
• Generic Research
• Water distribution with time in grouted wastes in
  relation to product evolution

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Conclusions Aged Wasteforms

• Confirms validity of earlier work measuring
  properties over shorter timescales during the PEP
  
• Quality of products still very good, no
  significant changes observed in 10 years. More
  evidence for satisfactory longer term quality.
• No significant desiccation or carbonation even
  after gt10 years of storage in pessimistic
  conditions. Only two cracks found, one was
  investigated and appeared to have resealed itself.

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Conclusions Aged Wasteforms

• Moisture, density, porosity and degree of
  saturation very consistent, throughout wasteform
• Wasteforms have a mature, relatively porous
  matrix, with no evidence of source of lime to
  support further pozzolanic reactivity.
• Wasteform reaching / reached a steady state.

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Conclusions

• ISL based research work provides additional
  underpinning which correlates with PEP and aged
  wasteform observations
• Experience and data generated feeds into the
  legacy waste development trials

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Options not available !

• Technology Readiness Level 0?

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Acknowledgements

• Rob Caldwell
• Drs Claire Utton, Nick Collier, Anthony Setiadi
  and Neil Milestone and John Sharp at ISL
• Hugh Godfrey, Newton Bowmer, Drs Steve
  Palethorpe and Mike Angus at NNL