Post on 24-Jan-2016
EMRAS Biota Working Group –EMRAS Biota Working Group –Main findingsMain findings
IAEA EMRAS Biota Working IAEA EMRAS Biota Working GroupGroup
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
ActivitiesActivities
• 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.
Models and approaches participatingModels 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]
Exercise 1 - dosimetry comparisonExercise 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:
)()/(
)/(
mediaororganismbodywholekgBqionconcentratActivity
hGyratedoseabsorbedunweightedDCC
Internal dose ratesInternal 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)
External dose ratesExternal dose rates• Considerably more variable between models –
especially for β- emitters
e.g. Duck on soil surface e.g. Duck on soil surface predictions for Sr-90predictions for Sr-90
1.E-11
1.E-10
1.E-09
1.E-08
1.E-07
1.E-06
1.E-05
1.E-04
1.E-03
AECL EA EDEN ERICA LIETDOS RESRAD SCK SUJB
DCC
External dose ratesExternal 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
Exercise 2 – transfer comparisonExercise 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
Terrestrial organisms Freshwater organisms
Grass/Herb Phytoplankton Pelagic fish
Shrub Zooplankton Benthic fish
Earthworm Macrophyte Fish egg
Herbivorous mammal Benthic mollusc Amphibian
Carnivorous mammal Benthic crustacean Duck
Bird egg
ApproachesApproaches• 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
)dry weight kg (Bq soilin ion concentratActivity
ht)fresh weig kg (Bqbody wholebiotain ion concentratActivity CR
1-
-1
Predicted activity concentrationsPredicted activity concentrations• Considerable variation between predictions (3-
orders of magnitude being common)
Pu-239
Predicted activity concentrationsPredicted 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
Perch Lake Case StudyPerch Lake Case Study
• H-3, Cs-137, Co-60, Sr-90 data for wide range of freshwater biota
PerchLake
Built-up Area
Chalk River Laboratories
Waste Management Area
Legend
Lake / River
Road
CRL Boundary
Stream0 1 2
kilometres
Sudbury
Ottawa
TorontoLake Ontario
Lake Erie
Lake Huron
CRL
Data presentationData presentation
• For each species/organism type mean prediction for each model normalised to mean measurement
Cesium-137 in Aquatic MacrophytesCesium-137 in Aquatic MacrophytesFreshwater Primary Producers
Model
AECL
ERICA (CEH)
EA R&D128
CASTEAURDmax
ECOMOD
LakeCo
RESRAD-BIOTA (UK)M
od
eled
-to
-Mea
sure
d 1
37C
s C
on
cen
trat
ion
0.000001
0.00001
0.0001
0.001
0.01
0.1
1
10
100
Emergent MacrophytesFree-floating MacrophytesFloat-leafed MacrophytesSubmergent MacrophytesMinimum Measured (free-floating)Maximum Measured (free-floating)Minimum Measured (floating-leafed)Maximum Measured (free-floating)
Minimum Measured (submergent)Maximum Measured (submergent)
Strontium-90 in Freshwater FishesStrontium-90 in Freshwater FishesFreshwater Fishes
Model
AECL
ERICA (CEH)
EA R&D128
ERICA (NRPA)
Dmax
ECOMOD
LakeCo
RESRAD-BIOTA (UK)
RESRAD-BIOTA (NRPA)M
od
eled
-to
-Mea
sure
d 90
Sr
Co
nce
ntr
atio
n
0.001
0.01
0.1
1
10
Brown BullheadCyprinidsPumpkinseedsMinimum Measured (bullhead)Maximum Measured (bullhead)Minimum Measured (cyprinids)Maximum Measured (cyprinids)
Minimum Measured (pumpkinseed)Maximum Measured (pumpkinseed)
Cobalt-60 in Freshwater MammalsCobalt-60 in Freshwater Mammals
Chernobyl Case StudyChernobyl 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.
Species Common name Number of predictions
(English) 90Sr 137Cs Pu 241Am Dose rates TLD
Aegithalos caudatus Long-tailed tit - - 1 - 1 -
Apodemus flavicollis Yellow necked mouse 5 5 1 - 2 2
Apodemus sylvaticus Wood mouse 1 1 - - 1 -
Canis lupus Wolf 2 2 - - 1 -
Capreolus capreolus Roe deer 7 7 - - 1 -
Clethrionomys glareolus Bank vole 7 6 2 1 2 2
Erithacus rubecula Robin 2 2 - - 1 -
Hirundo rustica Barn swallow 1 1 - - 1 -
Lactera agilis Sand Lizard 1 1 - - 1 -
Microtus arvalis Common vole 2 2 - - 1 -
Microtus oeconomus Root vole 2 3 - - 1 1
Microtus spp. Vole species 1 1 1 - 1 1
Parus major Great tit 2 2 1 - 1 -
Perdix perdix Partridge - 2 - - 1 -
Rana esculenta Edible frog - 2 - - 1 -
Rana terrestris Brown frog 2 4 - - 1 -
Sicista betulina Northern birch mouse 1 1 - - 1 -
Sorex araneus Common shrew 5 5 - - 1 -
Sturnus vulgaris Starling 1 1 - - 1 -
Sus scofa Wild boar 9 9 - - 1 -
Beetles 1 1 - - 1 -
Grassy vegetation 4 4 - - 1 -
Data presentationData presentation
• Each prediction normalised to the data mean for a given site
• Normalised predictions averaged by organism group for each model
TLD reading prediction TLD reading prediction (= external Cs-137 prediction)(= external Cs-137 prediction)
Total unweighted dose ratesTotal unweighted dose rates
• Presented as normalised to the mean prediction for each site
SummarySummary
• 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
Comparison of Exercise 2 Cs-137 predictions by DoseDimEco
SummarySummary
• … 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