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EMRAS Biota Working Group –Main findings

EMRAS Biota Working Group –Main findings. IAEA EMRAS Biota Working Group. Regular participants: Belgium - SCK ·CEN; Canada – AECL; France – IRSN; Japan – NIRS; Lithuania – IoP; Netherlands – NRG; Norway – NRPA; Russia – Spa-Typhoon; UK – CEH, EA, Westlakes; Ukraine – IRL; USA - ANL.

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EMRAS Biota Working Group –Main findings

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  1. EMRAS Biota Working Group –Main findings

  2. IAEA EMRAS Biota Working Group Regular participants: Belgium - SCK·CEN; Canada – AECL; France – IRSN; Japan – NIRS; Lithuania – IoP; Netherlands – NRG; Norway – NRPA; Russia – Spa-Typhoon; UK – CEH, EA, Westlakes; Ukraine – IRL; USA - ANL

  3. Activities • Two exercises to compare (i) dosimetry and (ii) transfer components of models. • Two case study scenarios (predictions v’s data): Perch Lake (Canada) and terrestrial ecosystems within Chernobyl 30 km exclusion zone.

  4. Models and approaches participating • RESRAD-BIOTA(USA) [all] • Environment Agency ‘R&D 128’(UK) [all] • ERICA (& FASSET) (European) [all] • Atomic Energy Canada Limited approach [all] • LIETDOS-BIO (Lithuania) [all] • DosDimEco (SCK·CEN approach) (Belgium)[1,2, Ch] • Dmax (UK)[PL,Ch] • EDEN-CENTEAUR(France)[1,2,PL] • LAKE(ECO) (Netherlands)[PL] • ECOMOD (Russia)[1,2,PL] • EPIC-DOSES3D (European) [all] • SÚJB approach (Czech Republic) [1,2]

  5. Exercise 1 - dosimetry comparison • Assume 1 Bq per unit media or organism • Estimate unweighted internal and external dose rates for Cs-137, Am-241, Co-60, U-238, C-14, Sr-90, H-3 • Organisms selected from list of proposed ICRP Reference Animals & Plants • Equates to comparison of dose conversion coefficients (DCCs) used within models where:

  6. Internal dose rates • Internal dose estimates generally all within 20 % of mean (of predictions) • exception being for U-238: two approaches including U-234 as daughter (resulting in 2x higher DCC)

  7. External dose rates • Considerably more variable between models – especially for β- emitters

  8. e.g. Duck on soil surface predictions for Sr-90

  9. External dose rates • More variable between models – especially for β- emitters • Especially H-3 & C-14 (e.g. external DCC for duck on soil for H-3 ranged 0 to 5E-11) • Media assumptions (density and distribution of contamination) can be seen to result in some variation • Differences in approaches that do not matter: • use of specific geometries v’s nearest default • number of emissions assumed

  10. Exercise 2 – transfer comparison • Assume 1 Bq per unit media to estimate wholebody activity concentration of range of radionuclides (241Am,14C,60Co,137Cs,131I,210Po,239Pu,226Ra, 90Sr,99Tc,232Th & 238U) in 19 terrestrial & freshwater organisms

  11. Approaches • Many use concentration ratios (CR): • But others using foodchain models, most often incorporating allometric relationships for dietary intake and radionuclide biological half-lives • Y=a∙(liveweight)b • Some have ‘guidance’ derived values in the absence of defaults

  12. Predicted activity concentrations • Considerable variation between predictions (3-orders of magnitude being common) Pu-239

  13. Predicted activity concentrations • Some variation can be understood, e.g.: • Missing value guidance approach often give comparatively high estimates (often for little studied organisms) • Site specific (and national) data • Some approaches include reindeer data in derivation of CRs leading to high predictions for mammals (especially Po-210) • Tc-99 predictions had least variation • Very few data and all using similar approach

  14. Perch Lake Case Study • H-3, Cs-137, Co-60, Sr-90 data for wide range of freshwater biota

  15. Data presentation • For each species/organism type mean prediction for each model normalised to mean measurement

  16. Cesium-137 in Aquatic Macrophytes

  17. Strontium-90 in Freshwater Fishes

  18. Cobalt-60 in Freshwater Mammals

  19. Chernobyl Case Study • Available data for Cs-137, Sr-90 Am-241, Pu-isotopes data - bias towards mammals (some birds, amphibians, invertebrate, plant, reptile). • TLD measurements for small mammals at 4 sites.

  20. Data presentation • Each prediction normalised to the data mean for a given site • Normalised predictions averaged by organism group for each model

  21. TLD reading prediction (= external Cs-137 prediction)

  22. Total unweighted dose rates • Presented as normalised to the mean prediction for each site

  23. Summary • Estimation of dose rate (DCC) adds little to variability in exposure estimates • Efforts should concentrate on transfer component • Support IAEA TRS 364 for biota • Can begin to understand some variability between predictions & improve the participating models

  24. Comparison of Exercise 2 Cs-137 predictions by DoseDimEco

  25. Summary • … But we have only completed two model-data comparisons • and overall considered a fairly limited range of radionuclides • Recommendations will contain a justification for continuing activities of BWG into EMRAS II

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