Presented by : Dr S J Palethorpe

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(No Transcript)
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Sellafield Site Challenges

• R D Support to Waste Management

Presented by Dr S J Palethorpe
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Contents

• Introduction Sellafields changing focus
• Radwaste Issues
• HLW
• Pu residues
• LLW
• Operational ILW
• Historical ILW
• Effluents
• Product longevity
• Monitoring Inspection
• Summary

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Sellafield
The nature of the Sellafield site is changing
from being primarily a fuel reprocessing
operation to also being the major radioactive
waste treatment centre in the UK.

• Over-arching criteria
• Safety in ongoing operations
• Reducing hazards from redundant facilities
• Progressive reduction in liabilities
• Value for money

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Radwaste Issues
Historical ILW
Operational ILW
LLW
HLW
Effluents
Pu
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High Level Waste Plants Issues

• Remaining life of current evaporators Highly
  Active Storage Tanks
• Corrosion
• Safety case
• Regulator requirements for HA liquor stocks
  reduction
• Improving the performance of Waste Vitrification
  Plant
• Increase throughput
• Equipment performance
• Blockages in process lines

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Maintaining plant availability

• Complexity of Pipework, makes inspection
  difficult.
• Deployment of inspection equipment needs to be
  demonstrated inactively.

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Vitrification Improvements

• Full scale, inactive replica of Sellafield
  vitrification process
• Allows rapid implementation of process
  improvements
• In-depth technical support
• Cradle to grave philosophy, including on-plant
  implementation support
• Complementary to installation of equipment
  operational practice improvements

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Pu residues

• Pu containing residues
• Ongoing liability which requires constant
  monitoring
• Heterogeneous Contain Pu and other actinides
• Uneconomic to recover but Pu content too high to
  be designated PCM
• Immobilise material for long term passive storage
  disposal
• Requires a high performance wasteform
• Low effluent process
• Choice of wasteform
• Glass ceramic formulation identified for Pu
  residues
• Full ceramic formulation identified for purer
  Pu wastes and MOx residues

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Hot Isostatic Pressing (HIP) chosen

• Study of a range of technologies
• Flexibility, widest processing window
• Minimal secondary wastes, reduced volatile loss
• Insensitive to physical, electrical and thermal
  properties of waste form.
• Batch process simplifies accountancy control
• Highly uniform product.
• Can be located outside of the glovebox.

Nexia Solutions off-site facility _at_Workington
used to house full scale inactive facility
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Opportunities outside current scope

• Metal encapsulation miscellaneous sized streams
  swarf, fuel fragments
• Uranium stocks
• consolidation only
• glass/ceramic
• Clino/IX HIP without additives
• Sludges
• Re work HIP of cemented wasteforms
• Can we rework existing cemented product thru HIP
• Design for grout now/HIP later

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Grouting support to LLW Repository 1

• DGF were observing segregation of the grout, and
  were signicantly reducing to the water added to
  avoid bleed.
• Trials showed segregation was due overdosing
  grout with superplasticiser. By using less
  superplasticiser and increasing the water a
  non-segregating, high quality grout could be
  produced. Consequently

• Improved grout quality and performance
• DGF saved money by using less superplasticiser
  and increased grout volume for same amount of
  powders.

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Grouting support to LLW Repository 2

• DGF have been challenged to review the supply of
  superplasticiser to the plant.
• Nexia Solutions tested superplasticisers from a
  number of suppliers to assess performance. Three
  possible replacements where identified.

• The latest superplasticisers offer higher levels
  of performance without an increase in volume cost
  and therefore saving can be made by using less
  superplasticiser in each mix.
• The superplasticisers need to be tested on plant,
  however early indications show potential savings
  of up to 50K per year may be possible.

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Operational Intermediate Level Wastes

• Encapsulation plants availability is critical to
  continued reprocessing operations
• Magnox Encapsulation Plant (Magnox swarf)
• Waste Encapsulation Plant (Hulls, sludge)
• Waste Packaging Encapsulation Plant (floc)
• Waste Treatment Complex (supercompaction of PCM)
• Minimise production of non conforming packages.
• Accommodating powder changes

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Maximising asset use/value

• Clinoptilolite In-Drum Mixing
• SIXEP Waste Processing are investigating the
  possibility of routing waste arisings from SIXEP
  (sand and Clinoptilolite) through the Waste
  Encapsulation Plant.

• One of the main issues is overcoming high
  start-up torques when mixing high waste loadings
  of settled waste.
• investigations have been carried out on paddle
  design and introduction of a soft-start method.
• Desk-top study and practical trials proved the
  feasibility of routing the waste through WEP and
  significantly increased the possible waste
  loadings.

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Historical - Intermediate Level Wastes
Dry silo
Wet silo
Ponds
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Legacy Ponds Silos The Problem

• Wastes from the earliest days of the UK Nuclear
  Programme. Stored either under water or dry in
  facilities dating back to _at_1948.
• All facilities contain reactive metals
  (Magnesium, Aluminium and Uranium).
• Material was not sorted prior to filling silos
  etc.
• Facilities not designed for emptying.

Facilities are past original design life, current
improvements keep them safe but they can not go
on indefinitely.
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Waste Science

• Waste characterisation techniques legacy ponds,
  silos and tanks to support retrieval operations,
  processing waste product formulations.
• Sludge and liquor sampling techniques
• Gas monitoring techniques sensors
• Remote in-situ measurements eg. physical
  characteristics- settling, particle size
  distribution and rheology.

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Sludge Effluents

• A considerable inventory of sludge and fuel
  debris is stored in a range of facilities across
  Sellafield (BSTs, Ponds Silo).
• Sludge beds consolidate over time results in
  localised conditions that differs from the
  pond/silo liquor.
• Retrieval disturbs sludge, releasing trapped pore
  water and shearing sludge - this changes liquor
  chemistry thus leading to activity release and
  suspended particles.
• Hence sludge movements need
• Settling and/or filtration of re-suspended/sheared
  solids.
• Appropriate abatement for soluble activity.
• Management of gas generation.

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In-situ Experiments
Camera
Motor
Bell Jar Developed to assess the amount of
activity transferred from ILW sludge to the bulk
liquor phase upon sludge disturbance.
Liquor sample tube
Mixing chamber
Sludge Sampler
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Effluents

• Soluble abatement
• Feed stream characterisation and simulant
  formulation
• IX material selection and active performance
  testing
• Modelling of feedstreams and abatement
  performance
• Filtration
• Assessment of particulate challenge
• Assessments on the performance of sand bed ,
  cross flow filtration and Filter performance
• Modelling of filtration performance
• Knowledge of wastes
• Sampling and characterisation of pondwater and
  sludges
• Assessment of release of soluble activity from
  sludges (fundamental investigations with
  simulants)
• Assessment on the role of colloids on the
  transport of radioactivity and their abatement
  (PhD)
• Modelling of feed stream and sludge speciation
  using environmental codes

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Responding to the Silo challenge

• Magnox swarf pieces corrode ultimately producing
  a magnesium hydroxide sludge that can display
  clay-like consistency
• Solids/sludge/water, high activity, large size
  range metallic and non-metallic debris, graphite
  and fissile material.

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Silos Direct Encapsulation Plant

• Simple solution tumble mixing of mixed waste,
  minimum segregation and allow grout to self
  regulate water content.

• Expected that wasteform might struggle to meet
  disposal requirements.
• Multi-barrier response annulus box, each part
  of the waste package contributes to overall
  performance

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Product Longevity

• Practical trials and modelling underpins concept.
  Global and localised expansion studied.
• Some scenarios helpful e.g For Mx only, evolution
  of packages at 20C not enough Mx or water to
  split box.
• Timing of annulus fill i.e. product finishing not
  rework.
• Implications for other streams opportunities
  with alternative matrices

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Monitoring Inspection

• Large packages difficult to inspect.

• X-rays shown to image 800mm cemented ILW.
• Very high energy expensive, shielding.
• 3D images, resolution lt1mm. Proven over more
  than 10 years.
• How much thicker? Must be near limit.

• Acoustic emission.
• Both drum and contents emit noise if corroding.
  Identify suspect drums. Need means to instrument
  every drum.

• Capacitive imaging.
• Very new, relatively untested. Could offer
  similar abilities to X-ray whilst being safer
  cheaper.

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Summary

• The presentation has briefly covered a variety of
  current RD issues over the full spectrum of
  waste management.
• Some key themes are
• Dealing with ageing plant / corrosion/ hazard
  reduction
• Meeting Regulator requirements/demands
• Understanding effluent challenge satisfying
  environmental discharge reduction
• Innovating ways for processing legacy wastes
• Wastes reduction process optimisation
• Maintaining credibility with the
  stakeholders/public
• Remaining economic
• Much achieved but much more to do!