Preservation of Samples for RETS, REMP and RW

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Preservation of Samples forRETS, REMP and RW

• Bob Litman
• Radiochemistry Laboratory Basics
• Presented in coordination with
• GEL Laboratories, LLC

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Abstract

• Nuclear Power Plants have special radioanalytical
  needs for several different classes of samples
  required by their operating licenses. The
  general sample categories can be characterized by
  the amount and type of radionuclides they
  contain. In order from highest to lowest activity
  they are radioactive waste (and associated
  characterization samples), routine liquid and
  gaseous effluent samples, and radiological
  environmental monitoring samples. Each step in
  the overall chain of information from sampling
  plan to final results is important. One of the
  elements that is often taken for granted is
  sample preservation. In order to provide
  assurance that the radionuclide of interest is
  not compromised during sampling, storage and
  transport of the sample the proper preservation
  must be performed for each radionuclide in each
  particular matrix. The preservation requirements
  for radionuclides (in particular 14C, iodines,
  tritium, 55Fe, TRUs and 90Sr) most commonly
  analyzed for the three general categories of
  samples and the different matrices that comprise
  these categories will be discussed.

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What is Preservation?

• A physical or chemical process that minimizes the
  potential for loss of the analyte (in this case a
  radionuclide) during the time period from
  sampling to aliquanting for analysis

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What is a Holding Time?

• Can be defined in two different ways (both are
  correct and apply to radionuclides)
• Time period during which the preserved sample
  will have negligible loss of analyte
  (radionuclide)
• Time period during which the radionuclide
  (analyte) will retain enough activity so that
  detection limits can be achieved (also referred
  to as radiological holding time)

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Loss Mechanisms

• Precipitation
• Adsorption
• Volatilization
• Chemical reaction producing one of the first
  three
• Decay

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Preservation Categories

• Radionuclides fall into three categories
• Metals
• Volatiles
• Non-metals
• The chemical forms of each radionuclide are
  important when deciding preservation technique

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Matrices Considered

• Liquids
• Waste liquids
• Surface water
• Well water
• Air Particulate Filters
• Glass fiber
• Polymeric
• Solids
• Soils
• Resins
• Vegetation

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Who Decides How Samples Should Be Preserved?

• The project team (i.e., you!)
• Know the standard preservation techniques
• Communicate
• the technique chosen should be coordinated with
  the laboratory, before collection

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Liquids

• Filtered or not filtered?
• Do you want the lab to filter?
• What micron size filter?
• Analyze residual matter on the filter?
• Whose decision is all this?

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Liquids

• Radionuclide masses can be VERY small,
• 1µCi/mL of 58Co 3.19x10-5 ppm
• 0.03 micrograms of material in one liter!
• At the same activity concentration, mass
  concentration decreases linearly with half life
• Thus for TRUs the mass is much, much smaller

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Liquids

• The available ionic surface Area within a 1-liter
  container is large (it isnt just Apdh).
• Why?
• Thus the potential for loss on surfaces is
  substantial

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Liquids

• Samples containing metals are commonly preserved
  by adding acid to pH lt 2.0
• Prevents precipitation of hydroxides
• Fills sites on sample bottle surfaces with H
• Site-M H ? M Site-H
• Check the sample stream to ensure that pH is in
  the range you want it before you send it!
• Tell the lab which acid was added (usually nitric
  or hydrochloric)
• Any container material has sites. In some
  cases it may be advisable to pre-treat the sample
  container.

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Liquids-Iodines

• Iodine has 6 different oxidation states and each
  one is different chemical form
• I-, I2, I3-, IO-, IO3-, IO4-
• But,
• Dont Add Acid!
• O2 2H2O 4I- ? 2I2 4OH-
• If necessary, preserve with S4O62-, SO32-, or
  HSO3- (add NaI as Carrier?)

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Liquids - Carbon

• What is the chemical form of 14C in the RCS?
• Formed from 17O(n, a)14C,
• In the presence of lots of H?,
• 14CH4? 14C2H6?
• What about other samples like groundwater?
• Oxidized (bacterially) to HCO31-

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Liquids - Carbon

• Preservative for 14C?
• Dont add acid!
• HCO3- H ? 14CO2 H2O
• Consult with laboratory on method.
• If necessary, use NH3 or NaOH to pH 9
• Refrigeration can help minimize volatility

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Liquids 55Fe and 90Sr

• Preservation with either nitric or hydrochloric
  acid is most effective
• Ensure pH is lt 2.0
• Waste liquids have combinations of plant liquid
  wastes and may be buffered basic
• Most waste liquids have some native iron
  content. Fe(OH)3 can precipitate even in acidic
  solutions
• Prevents carbon dioxide absorption and
  precipitation of SrCO3

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Liquids - TRU

• Nitric acid preservation is recommended
• Ensure pH is lt 2.0
• Carrier addition is recommended
• La, Ce, Nd
• Do not delay transport as the mass concentration
  is far less than that of the activation products

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Liquids - Tritium

• Preservation Required?
• What is the chemical form?

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Liquids General

• Preserve
• As soon as practicable after collection
• If compositing samples, preserve at the beginning
  not at the end
• If storing prior to analysis for extended period
  of time consider adding tracers/carriers (tell
  the lab!)

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Summary - Liquids
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Solids - Soils

• In order to assess how to preserve, you first
  need to know
• Will the entire sample be used?
• Will the sample be homogenized at the lab?
• Should miscellaneous detritus (sticks, stones,
  worms) be removed?

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Solids - Soils

• Depending on the radionuclide needed
• Should the sample be frozen?
• Shipped under nitrogen?
• Freeze or refrigerate?
• Wet weight or dry weight for results?
• Drying temperature?
• Freeze drying acceptable?
• Total digestion or leaching to be used?

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Solids - Soils

• What about the following?
• 129,125,131I
• 3H
• 14C
• Anything special required?

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Solids - Resins

• Think estimate
• Think non-homogeneous
• Whole Sample?
• Preserve dry, wet or semi-wet?
• If stored before shipment, under inert
  atmosphere?
• Dont freeze
• especially when analysis is on 10CFR61
  radionuclides

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Solids - Vegetation

• Critical factors
• Moisture content is high (75-98)
• Material changes quickly (hours to days)
• Distinguish surface from internal contamination?
• Refrigerate or freeze?

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Solids- Summary

• No universal preservation techniques
• Specified by Project
• If frozen, care needs to be taken to ensure
  sub-sampling is representative
• Wet or dry weight?
• Will determine preservation
• Project specific
• Volatiles are a concern with solids as well

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Particulate Filters

• Fold filter in half (sample on itself)
• Slide filter into glassine-style envelope
• Ship between two blank filters (could be
  polymeric, or glass fiber) in Petri-style
  container

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Particulate Filters

• Avoid situations which can induce a static charge
  on the sample
• Avoid adhering to another medium for shipment as
  the adhesive may affect the analysis

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Summary

• Choose a preservation technique that ensures
  minimal loss of radionuclide
• Identify requirements to laboratory (holding
  times, preservation techniques used, carriers
  added, etc.)
• Several aliquants of the sample may be required
  as different radionuclides require different
  preservation