Screening tier comparisons

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Screening tier comparisons

• ERICA, RESRAD-BIOTA EA RD128
• Follow-up actions from Vienna workshop

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Vienna scenario

• Comparison of the three openly available models
  RESRAD-BIOTA, ERICA-Tool EA RD128
• River receiving mixed radionuclide discharges
  from multiple sources

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Results

• ERICA highest dose rate (circa E3 µGy/h)
  predicted for insect larvae dominated by 234Th
• RD128 highest dose rate (circa E3 µGy/h)
  predicted for amphibian dominated by 239Pu
• RESRAD-BIOTA 137Cs was the only nuclide to
  result in a risk quotient (RQ) in excess of 1
  (for riparian animal)

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• Decision to further compare the screening tiers
  of the three models 1 Bq per unit media model
  runs
• Associated request can PROTECT establish the
  degree of conservatism ?

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• Screening tiers similarities/differences(where
  we think the conservatism is)
• Comparison of outputs

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ERICA-Tool - Tier 1

• Recommends enter maximum media activity
  concentration
• 95th percentile environmental media concentration
  limits (EMCLs) predicted using default transfer
  parameters pdfs (conservative habitat assumption)
• 10 µGy h-1
• 40 µGy h-1 terrestrial animals / 400 µGy h-1
  plants and all aquatic organisms
• Risk quotients reported for most limiting
  organism (and media) for each radionuclide and
  for ecosystem

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ERICA-Tool Tier 1 result
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ERICA EMCLs
Freshwater EMCLs Cd-109 Sediment 2.61E4
Bq/kg Water 51 Bq/l Cs-137 Sediment 8000
Bq/kg Water 5.1E-2 Bq/l
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ERICA EMCLs
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ERICA Tier 2

• Organism specific dose rates and RQs (from total
  predicted dose rate) reported
• Best estimate
• Conservative estimate
• Conservative dose estimated by applying
  uncertainty factor (UF) to the best estimate,
  where
• UF 3 95th percentile prediction
• UF 5 99th percentile prediction

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ERICA Tier 2
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ERICA Tier 2

• In theory conservative estimate with UF3 should
  approximate to Tier 1 result with same input
  and Tier 3 95th percentile prediction
• Generally works some case where it does not for
  aquatic ecosystems if input to sediment

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A thought on UF 3
Cs-137 BWG Chernobyl
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RESAD-BIOTA (USDOE) Tier 1

• Recommend enter maximum media activity
  concentration
• Media activity concentrations compared to biota
  concentration guidelines (BCG)
• Infinitely large/small geometries assumed
• 100 in soil sediment-water interface
• Conservative CR (BiV) values (not kd)
• 1 mGy/d (40 µGy h-1) terrestrial riparian
  animals / 10 mGy/d (400 µGy h-1 ) terrestrial
  plants aquatic animals
• More limited range of organisms considered than
  ERICA (which includes e.g. planktons, lichen
  which tend to have high exposure estimates)

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RESRAD-BIOTA Tier 1 CRs

• Aquatic animals maximum
• Predominantly taken from Till Meyer 1983
  maximum of the 84th ile from collated data for
  fish, mollusc or crustacean
• Terrestrial plants maximums
• Predominantly taken from Till Meyer 1983
  considers food crops, forage grass
• Terrestrial/Riparian animals most derived using
  kinetic-allometric approach 95th ile

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BGCs

• Terrestrial - Soil water
• Aquatic Riparian - Sediment water

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BGCs

• Aquatic animals
• Sediment - External exposure from sediment
• Water Internal external exposure from water
• Riparian animals
• Sediment Internal external exposure from
  sediment
• Water Internal external exposure from water
• Terrestrial animals
• Soil - Internal external exposure from soil
• Water - Internal external exposure from water
• Terrestrial plants
• Soil - Internal external exposure from soil
• Water - External exposure from water

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EA RD128 - screening

• As applied maximum inputs
• Compares results to 5 µGy h-1 for screening (40
  µGy h-1 action level)
• Default transfer parameters used
• Some transfer values are highly conservative

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Screening tier predictions

• Assuming 1 Bq soil/water/sediment
• Against 40/400 µGy h-1
• Terrestrial freshwater only RESRAD-BIOTA does
  not consider marine
• Radionuclides common to RESRAD-BIOTA ERICA-Tool
• Not H-3 C-14 for terrestrial RESRAD-BCGs for
  soil ERICA EMCL for air
• Compared as RQs

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Terrestrial
RESRAD-BIOTA ERICA-Tool EA RD128
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Terrestrial EA 5 µGy h-1
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RQ Min/Max gt 10
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Freshwater input to water
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RQ Min/Max gt 10
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Freshwater input to sediment
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RQ Min/Max gt 10
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Comment

• Used in basic screening assessments (their
  envisaged main use) the readily available models
  can give widely differing results
• (yet again) predominantly explained by transfer
  elements