WasteLLW - PowerPoint PPT Presentation

Title: WasteLLW


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Waste-LLW
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Treatment options for metallic Low Level Waste
(LLW)

• A review of technical options for treatment

BPO Workshops 20th and 21st November 2007
Waste-LLW
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Waste metals
Estimated metal disposal arisings in m3 for
Sellafield site for the next 100 years

• The bulk of the metal arises from
  decommissioning.
• Much can be sent for reuse or recycling as exempt
  waste
• For todays workshop we will be focussing on the
  low level contaminated metals.

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Objective for treatment of metal LLW

• It is believed that most metallic LLW suitable
  for treatment will be radioactively contaminated
  to an extent that it is in the lower activity
  range for LLW but with an activity content still
  higher than Very LLW and therefore not suitable
  for exemption under the Substances Of Low
  Activity (SOLA) exemption order.

400 kBq/te All nuclides
12 GBq/te Beta Gamma 4 GBq/te Alpha
Decontamination
Release
LLW
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What we want from our treatment of metal LLW

• It is the objective to treat metallic LLW so
  that
• It may be exempted and released for recycle/
  reuse.
• If unsuitable for exemption the actual volume of
  waste disposed of to the LLW Repository is
  minimised.

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Radioactive Contamination or Radioactive
Activation

• Contamination arises by virtue of radioactive
  substances coating the metal surfaces.
• Activation arises when radiation irradiates some
  of the naturally occurring elements in the metal
  which then become radioactive themselves. These
  elements remain integrated into the matrix of the
  metal.

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Radioactive Contamination or Radioactive
Activation

• Contamination can be removed from the surface of
  metals, the ease of decontamination will depend
  upon several factors e.g. shape of the metal,
  nature of the contaminant, physical attributes of
  the contaminated surface, etc.
• Activation products cannot be easily removed
  because they are integrated into the matrix of
  the metal. However certain activation products
  will radioactively decay in a relatively short
  period of time.
• Iron 55 (Fe55) and Cobalt 60 (Co60), activation
  products found in steel have half lives of 2.7
  and 5.2 years respectively, where as Nickel 63
  (Ni63) found in stainless steel has a half life
  of 100 years.

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What to do with the waste
Likely overall waste treatment process
Volume reduction
Decontamination
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Treatment options for metallic LLW
Decay storage
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Physical techniques - abrasion

• There are many abrasion techniques in use for the
  decontamination of metals, the selection is
  dependant upon the application.
• Typical examples include shot and grit blasting
  as used in the Sellafield Ltd Wheel abrator
  facilities.
• Others include sand, dry ice, water.
• Mature technology used extensively across the
  nuclear industry.

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Typical abrasion process
Metal Characterised
Size reduction/ dismantling
Abrasion
Metal for recycle
LLW
Spent abrasive
Dust from filters
Removed contaminated material
LLW Repository
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Chemical technique - decontamination

• A range of techniques available, almost all
  consist of some form of acid dissolution of metal
  surfaces to remove contamination.
• Phadec (phosphoric acid) used in Germany.
• Medoc (sulphuric acid and cerium) used in France.
• DFD DFDX (dilute Flouroboric acid).
• Well established techniques with many
  applications.
• Application techniques have developed such as the
  simple applications of liquids or gels through to
  the pumping of foams inside plant items.

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Typical chemical technique
Metal Characterised
Size reduction/ dismantling
Chemical treatment
Metal for recycle
Contamination
LLW
Treatment of chemical to remove contamination
and/ or fix in a solid form and possible recycle
of chemicals
LLW Repository
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Thermal smelting

• The principle is to smelt the waste metal and
  remove the contamination in the slag. This leaves
  the bulk of the metal free from radioactivity in
  a billet suitable for recycling.
• Well established and mature technique.
• Used for the treatment of radioactively
  contaminated metal in the US and at least 2
  European countries.

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Thermal smelting
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Typical thermal smelting
Metal Characterised
Size reduction/ dismantling
Possible Abrasion
Metal for recycle
Smelting
LLW
Removed contaminated Material in the form of
process slag
Removed contaminated material
Dust from filters
Dust from filters
Spent abrasive
LLW Repository
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Thermal melting

• Melting differs from smelting in that the
  contamination is not removed from the metal.
• Melting offers a method of changing the physical
  shape of contaminated metals so that they occupy
  less volume within product containers consigned
  to the LLW repository.

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Dismantling cutting

• This requires selective surgery of plant and
  equipment to remove the radioactive components.
• Well established and deployed technique at
  Sellafield and other nuclear facilities.
• Removed radioactive components are then either
  consigned to the LLW Repository or sent for
  decontamination prior to exemption.

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Decay storage

• Metals containing activation products that have
  short half lives may be stored until they have
  radioactively decayed to a level that is
  acceptable for exemption. Factors associated
  with decay storage are
• Country specific acceptable levels of
  radioactivity for exemption.
• Period of time required to decay store.
• Control of material ensuring that metals are not
  released for reuse too early.
• Quality of analysis of the metal itself to gain
  an accurate measure of the isotopes present and
  the time required for them to decay to levels of
  radioactivity which would permit the metal to be
  released.

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Nuclide destinations summary
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Indicative Costings

• Abrasion a typical cost per tonne ferrous metal
  for blasting is around 1,000. Estimated
  process set up cost will be 2.5 3M.
• Chemical a typical cost per tonne metal for a
  chemical process is 1,000. Estimated process set
  up cost will be 1.5M capital, 500K operational
  cost and 200K decommissioning.
• Thermal typical smelting costs approximately
  3,000 - 5,000 per tonne. Estimated process set
  up cost will be 2.5M 5M capital.
• Note the above are cost estimates for
  establishing facilities on a current nuclear
  licensed site.

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Review

• It is the objective to treat metallic LLW so
  that
• It may be exempted and released for recycle/
  reuse.
• If unsuitable for exemption the actual volume of
  waste disposed of to the LLW Repository is
  minimised.

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Low Level Waste Metals BPO

• Questions

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Technical information

• The following slides provide additional technical
  information on the topic of treating low level
  radioactive waste metals.
• Additional general information
• Flow diagram for a couple of the chemical
  treatment processes
• Illustration of the recovery of clean metal
  from the processes
• Some of the pros and cons of the treatment
  processes

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Additional metal specific issues

• Activated stainless steel would probably be
  unsuitable for decay storage owing to the Ni63
  content.
• Lead processing will require extra precautions
  associated with lead toxicity.
• Aluminium processing has a high hazard with
  respect to the explosive nature of any dust.
• Copper waste will most likely be in the form of
  electrical cable and will require the removal of
  the insulated sheath.

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Example Chemical technique - Phadec

• Phadec Phosphoric acid decontamination

Metal Characterised
Size reduction/ dismantling
Chemical treatment
Metal for recycle
Phosphoric acid recycle
Caustic dip
Acid dip
Iron oxalate precipitated
Iron oxide produced
Water rinse
Oxalic acid addition
LLW
LLW Repository
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Example Chemical technique DFD DFDX

• DFD Dilute fluoroboric acid decontamination

Metal Characterised
Size reduction/ dismantling
Chemical treatment
Metal for recycle
Flouroboric acid regeneration
Dilute Acid Bath
Ion exchange
Spent IX media
Electrolysis
Precipitated metal
LLW Repository
LLW
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Examples of performance of treatment processes

• Thermal Smelting
• 90 -95 of metal recovered from process.
• For the 5-10 waste
• 99 of contaminants will be deposited in the
  process slag
• The remaining 1 is captured in filters or
  discharged via the process off gases.
• Typical nuclides captured in filter dust will be
  Caesium (Cs137).
• Typical nuclides discharged through the off gas
  system will be Tritium (H3) in water vapour and
  Carbon (C14) in carbon dioxide.

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Examples of performance of treatment processes

• Abrasion
• The quantity of waste generated by an abrasion
  process will vary dependent upon the thickness of
  any contaminated coatings on the metal and the
  quantity of abrasive required to remove it.
  Experience with the shot blasting process at
  Sellafield is that for decontamination after all
  coatings are removed approximately 40 microns of
  the metal itself is removed.
• In abrasion techniques there is no separation of
  nuclides, 100 of the contamination will be
  captured as dust in the filters or collected
  separately sometimes with the spent abrasive.

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Examples of performance of treatment processes

• Chemical Phadec
• 98 of the metal is recovered from the process.
• For the waste.
• The remaining 2 metal is found in the solid
  waste precipitate.
• There will also be a proportion of spent
  chemicals requiring disposal.

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Decontamination methods pros and cons

• Abrasion

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Decontamination methods pros and cons

• Chemical

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Decontamination methods pros and cons

• Thermal