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Screening tier comparisons

Screening tier comparisons. ERICA, RESRAD-BIOTA & EA R&D128 Follow-up actions from Vienna workshop. Vienna scenario. Comparison of the three openly available models – RESRAD-BIOTA, ERICA-Tool & EA R&D128 River receiving mixed radionuclide discharges from multiple sources. Results.

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Screening tier comparisons

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  1. Screening tier comparisons ERICA, RESRAD-BIOTA & EA R&D128 Follow-up actions from Vienna workshop

  2. Vienna scenario • Comparison of the three openly available models – RESRAD-BIOTA, ERICA-Tool & EA R&D128 • River receiving mixed radionuclide discharges from multiple sources

  3. Results • ERICA – highest dose rate (circa E3 µGy/h) predicted for insect larvae dominated by 234Th • R&D128 – 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)

  4. 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 ?

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

  6. 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

  7. ERICA-Tool Tier 1 result

  8. EMCL for water – takes into account external exposure from sediment (kd) or water and internal exposure estimated from water conc. using CR EMCL for sediment - takes into account external exposure from sediment or water (kd) and internal exposure estimated from water conc. (kd) using CR 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

  9. ERICA EMCLs

  10. 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

  11. ERICA Tier 2

  12. ERICA Tier 2 • In theory conservative estimate with UF=3 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

  13. A thought on UF =3 Cs-137 BWG Chernobyl

  14. 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)

  15. 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

  16. BGCs • Terrestrial - Soil & water • Aquatic & Riparian - Sediment & water

  17. 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

  18. EA R&D128 - 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

  19. 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

  20. Terrestrial RESRAD-BIOTA & ERICA-Tool + EA R&D128

  21. Terrestrial – EA 5 µGy h-1

  22. RQ Min/Max > 10

  23. Freshwater – input to water

  24. ERICA kd’s often comparatively high RQ Min/Max > 10

  25. Freshwater – input to sediment

  26. RQ Min/Max > 10

  27. 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

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