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Wasteform Evolution Studies Methods and Observations

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

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Wasteform Evolution Studies Methods and Observations

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    1. Wasteform Evolution Studies – Methods and Observations

    2. 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

    3. Waste Management Life Cycle Encapsulation process Engineered Storage Transport and handling Repository Storage

    4. 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

    5. 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

    6. Magnox

    7. 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

    8. 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

    10. Sampling

    12. Typical Solids drum

    13. Testing techniques Physical and Chemical Visual Cracking Carbonation Acid neutralisation capacity (ANC) Equilibrium extraction Permeability / Porosity Instrumental SEM – Electron Microscopy XRD TGA – Thermal Analysis

    16. Results A selection

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

    19. Historic fracture found -covered in ettringite which degrades in the presence of CO2. Suggests fracture is isolated from atmosphere – cracks self sealing. Scanning Electron Microscopy of cracks

    20. WTC products No sign of degradation of waste No sign of corrosion of puck walls Corrosion visible occurred after slicing

    21. WTC ‘core’

    22. Detail of WTC Puck Core

    23. Physical characterisation - capping key IDM and Hulls - very good key of cap to matrix Magnox - less good keying of cap

    25. Physical characterisation summary Samples in good condition No significant desiccation Very little cracking observed - seems to be repaired Permeability / porosity reduced with ageing

    27. Acid neutralisation capacity

    28. Acid neutralisation capacity

    29. Carbonation Phenolphthalein test - purple pH>9.2 Caps - see significant carbonation up to 35mm Matrix (including PFA of flocs) < 3mm

    33. 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

    34. 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

    35. 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

    36. 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

    37. 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

    38. 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

    39. 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 >10 years of storage in pessimistic conditions. Only two cracks found, one was investigated and appeared to have resealed itself.

    40. 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.

    41. 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

    42. Options not available ! Technology Readiness Level = 0?

    43. 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

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