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What to look for when interpreting an assessment

Nick Beresford (CEH). What to look for when interpreting an assessment. Objective. Give an overview of what may impact on assessment results using the available approaches In part based on things we know are being done

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What to look for when interpreting an assessment

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  1. Nick Beresford (CEH) What to look for when interpreting an assessment

  2. Objective • Give an overview of what may impact on assessment results using the available approaches • In part based on things we know are being done • Consider chronology of development, misuse of default values, double accounting, screening tier application • Not considering dispersion modelling and sampling strategies www.ceh.ac.uk/PROTECT

  3. Chronology • Environmental Radiological assessment approaches have developed rapidly over the last 10 y • A number of approaches have been made freely available • Some of these have been superseded • But they are still available & are being used www.ceh.ac.uk/PROTECT

  4. Chronology • UK • Environment Agency R&D128 - 2001 • Spreadsheet model for limited number of radionuclides • Comparatively limited review to derive CR values • Dosimetry methods similar to later approaches • Environment Agency Sp1a – 2003 • Supports R&D128 including derivation of complete CR data sets using a ‘guidance approach’ (can be extremely conservative) www.ceh.ac.uk/PROTECT

  5. Chronology • Europe • FASSET (EC) 2001-2004 • Establish a framework for radiological environmental protection from source characterisation – interpretation, including: • Tabulated CR and DCC values for: • radionuclides of 20 elements • circa 30 reference organism in 7 ecosystems • Developed the on-line FASSET Radiation Effects Database www.ceh.ac.uk/PROTECT

  6. Chronology • Europe • EPIC (EC) 2000-2003 • Establish a framework for radiological environmental protection for the Arctic • Ran concurrent to FASSET and shared CR database • Although presented differently and for only 12 radionuclides • DCCs derived by a different method • Allowed participation of Russian institutes leading to EPIC effects database www.ceh.ac.uk/PROTECT

  7. Chronology • Europe • ERICA (EC) 2004-2007 • Developed the CR and effects (FREDERICA) databases from FASSET & EPIC • Developed FASSETdosimetry methodology • Adapted ‘guidance’ for selecting missing CRs from EA SP1a • Output - the ERICA Tool implementing the ERICA Integrated Approach • More generic ecosystem types (because of lack of data) than FASSET and adapted reference organism list (to encapsulate European protect species & remove some unjustified sub-categories) • Derived 10 µGy/h screening dose rate (by SSD) • Being maintained and updated www.ceh.ac.uk/PROTECT

  8. Chronology • Europe • ERICA (EC) 2004-2007 • Developed the CR and effects (FREDERICA) databases from FASSET & EPIC • Developed FASSETdosimetry methodology • Adapted ‘guidance’ for selecting missing CRs from EA SP1a • Output - the ERICA Tool implementing the ERICA integrated approach • More generic ecosystem types (because of lack of data) than FASSET and adapted reference organism list (to encapsulate European protect species & remove some unjustified sub-categories) • Being maintained and updated ERICAsupersedes both FASSET and EPIC outputs & EA state intention to move to ERICA (parameters) rather than develop R&D128 EC PROTECT supported the 10µGy/h screening dose rate – using additional data and improved data selection www.ceh.ac.uk/PROTECT

  9. Chronology • International • IAEA (2009-) • Developing wildlife transfer parameter handbook and associated on-line database • Database will be maintained and updates released annually www.ceh.ac.uk/PROTECT

  10. Chronology • International • IAEA (2009-) • Developing wildlife transfer parameter handbook and associated on-line database • Database will be maintained and updates released annually • ICRP Committee 5 (2005-) • Developing a framework (ICRP-108) • Currently provided tabulated DCC values (using ERICA methodology) and summarised effects information • Draft report presenting CR values for RAPs currently with main Commission Will be used to update the ERICA Tool CR values (and recalculate EMCLs) www.ceh.ac.uk/PROTECT

  11. Chronology • USA • USDOE Graded Approach (2002) • Initially supported by BCG-Calculator spreadsheet model. Still available – but replaced by: • RESRAD-BIOTA • Limited and conservative CR values for generic organisms • RESRAD-BIOTA v1.5 (2009) includes values from the ERICA CR database in supporting documentation for application in uncertainty analysis www.ceh.ac.uk/PROTECT

  12. So don’t ...... • Use out of date approaches unless you can justify why they have been used, e.g.: • OK to use R&D128 for noble gases • Not OK to use FASSET CR values because they offer more refined reference organism list/ecosystem range (there’s a reason these were not included in ERICA) www.ceh.ac.uk/PROTECT

  13. Misuse of default values • To serve the purpose for which they were intended RESRAD-BIOTA, R&D128(SP1a) and the ERICA Tool give a complete list of radionuclide-organism transfer parameters. • ERICA Tool and R&D128 missing values derived using ‘guidance’ approaches. These should not be blindly used in higher tier assessments nor should they be picked out for use in other models/recommendations without being clearly identified as such • RESRAD-BIOTA Biv values very generic and conservative www.ceh.ac.uk/PROTECT

  14. Misuse of default values • ERICA and R&D128 both clearly identify values which have been derived via guidance approach rather than data • But have been taken as ‘values’ www.ceh.ac.uk/PROTECT

  15. Double accounting • Some scope for ‘double accounting’ associated with daughter product half-life cut-offs • e.g. R&D128 includes all 234Th and 234U in DCCs for 238U • Entering both 234Th and 238U activity concentrations would over estimate dose rates • RESRAD-BIOTA and ERICA both offer the user the opportunity to do similar www.ceh.ac.uk/PROTECT

  16. How do screening tiers compare?

  17. Screening tier - recap • Aim - to enable sites of negligible concern to be identified and removed from need for further assessment – with a high degree of confidence • Envisaged that most sites will only need this level of assessment [i.e. ‘be screened out’] www.ceh.ac.uk/PROTECT

  18. ‘Concentration limits’ • Input media concentrations compared to predefined concentrations = media concentration giving rise to screening dose rate • ERICA: ‘environmental media concentration limits’ EMCLs • RESRAD-BIOTA: ‘biota concentration guidelines’ BCGs

  19. ERICA Tool - EMCLs Estimated assuming: • Habitat assumption to maximise exposure • Probability distributions associated with the default CR and Kd databases were used to determine 5th percentile EMCL • No conservatism applied to dosimetry • For aquatic ecosystems EMCL for water includes consideration of external dose from sediment and that for sediment includes external dose from water and biota-water transfer

  20. RESRAD-BIOTA - BCGs Estimated assuming: • Infinitely large (internal) and small (external) geometries for dose calculations • Daughter T1/2’s up to 100 y included • All terrestrial organisms 100% in soil; aquatic 100% water-sediment interface • ‘Maximum’ CR values or 95th percentile CR values predicted using a kinetic-allometric approach

  21. RESRAD-BIOTA - BCGs Estimated assuming: • Infinitely large (internal) and small (external) geometries for dose calculations • Daughter T1/2’s up to 100 y included • All terrestrial organisms 100% in soil; aquatic 100% water-sediment interface • ‘Maximum’ CR values or 95th percentile CR values predicted using a kinetic-allometric approach

  22. Screening Tier Comparison • Run RESRAD-BIOTA, ERICA Tool and EA R&D128 against 10 µGy/h screening dose rate • Data suitable for application in screening tier assessment report – maximum media activity concentrations for • Four freshwater • Three terrestrial scenarios • Taken from SENES-WNA report 2007 www.ceh.ac.uk/PROTECT

  23. Input data - freshwater

  24. Input data - terrestrial

  25. Freshwater

  26. Freshwater

  27. Freshwater

  28. Freshwater

  29. Freshwater U-238 – ERICA Tool and EA R&D128 RQ estimated from input sediment; kd value used estimates much higher water activity concentration than observed; RESRAD-BIOTA uses water and sediment inputs separately

  30. Freshwater Co-60 (& Ru-106) – ERICA Tool kdvalues >> than values in other two models

  31. Terrestrial

  32. Terrestrial

  33. Terrestrial

  34. Terrestrial H-3 – Difference in input options RESRAD-BIOTA = soil (+ groundwater) other two models = air. Soil concentrations in excess of what would be anticipated from air.

  35. Terrestrial Organism – ERICA Tool and EA R&D128 include organisms with comparatively high CR values (Lichen&Bryophytes, fungi) – not included in RESRAD-BIOTA Guidance values – Fungi U (& Ra) CR values in R&D128 are guidance values. Values used ≥10x higher than data for fungi

  36. Screening tier comparison • Can be considerable variation in screening tier results • Some of variation can be understood: • CR and kd (including if 95%’ile, maximum, best estimate used) • Organism • How sediment and water inputs used • Input options • Exposure geometry • Other Tier 1 type approaches being developed • Need to compare & understand before application www.ceh.ac.uk/PROTECT

  37. Summary • Do not use/accept out of date approaches – unless justified • Ensure no misuse of default values provided by various approaches • There are differences between approaches • Dosimetric methods tend to give similar results • Transfer parameters can add significant variation • Screening tiers www.ceh.ac.uk/PROTECT

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