HLWP

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HLWP
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The HLW challenges at Sellafield

• Presentation to RWIN meeting

Date 16/1/08
HLWP
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Outline

• Background on where the waste has come from the
  active content of the glass
• Chemistry of the waste formulation how various
  feeds are accommodated vs. limits on composition
• Notes on the types of production problems
  experienced
• Outline of the development programme objectives

Site or Business area
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HA raffinate is generated from reprocessing

• When a uranium fuel rod is placed in a nuclear
  reactor
• Uranium fission gives fission products (Cs,
  Mo, Sr, Zr, Ba, etc).
• Neutron capture gives other actinides (Pu, Am,
  Cm, etc).
• Solvent extraction (THORP/B205) recovers the U
  and Pu.
• Fission products and other actinides to HA
  effluent.
• 5 to 50 kg from each tonne of reprocessed fuel.
• 5 to 10 m3 of liquid HA raffinates for each
  tonne reprocessed.
• Chemicals added during reprocessing
• Fuel cladding assembly materials (Mg,
  stainless steel, Fe, Gd).
• Gd, ammonium, phosphates, plant corrosion
  products.

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HA Raffinates
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HA raffinate is concentrated by evaporation

• Evaporation factors of 20x to 100x.
• Magnox batches typically contain 140-180 teU of
  raffinates.
• Oxide batches typically contain 40-80 teU of
  raffinates.

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HA concentrate storage

• WVP is projected to immobilise 6x1019 Bq over
  its lifetime

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HA concentrate feed to WVP

• HA concentrate is a nitric acid solution of metal
  nitrates

Solid phases include
Barium nitrate
Zirconium molybdate
Caesium phosphomolybdate
Other nitrates (Mg lanthanide nitrate)
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Differences between Oxide and Magnox HAL

• Oxide HAL has
• No Magnesium or Aluminium
• Much increased level of Gadolinium
• Increased fission products and actinide levels in
  Oxide HAL
• Increased level of suspended solids
• Increased density of liquor
• Higher heat output over longer term
• Oxide HAL is fed as a blend with Magnox to
  maximise incorporation

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Description of Vitrification Process
Image source BNFL
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Calcination

• Inclined rotating kiln furnace
• 4 pairs of radiant heaters (half shells)
• Evaporation in Zones 1 2 (water nitric acid)
• Partial de-nitration occurs in Zones 3 4
  (75)
• Calciner is operated under 10 to 12 mbag vacuum
• Rabble bar prevents accumulation and breaks up
  calcine to desired particle size distribution
• LiNO3 added to HAL binds calcine together
  reduces dust lost to off-gas by 75.
• Sugar added to calciner reduces Ru minimises
  volatalisation

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Calciner
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Vitrification

• Glass frit added to melter via lower end of
  calciner
• SiO2 63.4, B2O3 22.5, Na2O 11.4, Li2O 2.7 wt
• Batch process, 190kg glass calcine fed over 8h
• Cold cap sits on melt surface
• Induction heated melter heats up glass and
  calcine
• Residual nitrates driven off
• Calcine reaction with glass (endothermic process)
• Internal air sparge to aid mixing
• Most metals react and become part of matrix

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Melter melter stack (VTR)
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Ru phases
Fe/Cr/Ni Ce/Zr
Mo phases
Mo (opal.) Zr (white sq.) Mg (trans plates)
Ce/Zr
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Problem elements

• Molybdenum
• Corrosion elements, particularly chromium
• Ruthenium
• Technetium
• Caesium
• Zirconium

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WVP issues

• The WVP plant is complex and high technology
• Remote operation and maintenance, shielding
  containment
• Process and mechanical handling operations
• High temperature machinery complex process
  chemistry
• 3 lines, each operating for about 4000 hours
  before re-build.
• Throughput is limited by line availability as
  well as by process flowsheet.

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WVP operating problems

• Calciner issues
• Rabble bar deformation and fracture
• Seals wear Bearing life
• Dust and Ru losses to Primary off Gas
• Melter issues
• Corrosion, Deformation failure
• Heel accumulation pour nozzle blockage
• Mass balance
• Cooling water supplies
• Other issues
• Glass frit feed system reliability
• Dust scrubber performance

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Development programme

• Corrosion materials science
• Inconel melter corrosion deformation
• Integrity of civil structures
• Glass chemistry development
• Calcine chemistry
• Phase equilibria dissolution kinetics
• Product behaviour in a disposal environment
• Process engineering development (VTR)
• Product quality for increased throughput and
  incorporation
• Making best use of the operational time.
• Reduce numbers of containers for storage /
  disposal.
• To secure and underpin the knowledge base for the
  operating life of WVP.

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Vitrification Test Rig
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Summary

• HA raffinate is a complex mixture of
  radioisotopes metal nitrates from reprocessing
• This is concentrated stored prior to
  vitrification
• Development work is focussed on key issues for
  WVP
• Increasing incorporation in glass
• Improving equipment reliability throughput
• Product quality behaviour in storage disposal