David Copplestone (University of Stirling). Whats the issue? Obtaining air concentrations for noble...
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Transcript of David Copplestone (University of Stirling). Whats the issue? Obtaining air concentrations for noble...
David Copplestone
(University of Stirling)
How to model atmospheric noble
gas releases
(and estimate doses to wildlife)
www.ceh.ac.uk/PROTECT
Overview
What’s the issue? Obtaining air concentrations for noble gases Estimating doses to wildlife from noble
gases
www.ceh.ac.uk/PROTECT
What’s the issue? Nuclear power plants
~ 85% of the total activity released is in the form of noble gases (Ar-41, Kr-85)
Except for one model, none of the available tools estimate doses to wildlife from noble gases
Most analogue radionuclides that could be used will massively over predict the dose rate
www.ceh.ac.uk/PROTECT
e.g. Environment Agency Habitat Assessments
Initially, during screening, used Cs-137 as analogue
Essentially any release containing Ar-41 or Kr-85 exceeded the screening value
Very conservative Lead to refining of modelling approach
www.ceh.ac.uk/PROTECT
Obtaining air concentrations
Various tools for atmospheric modelling (see Jordi’s presentation)
Essentially need to predict the air concentration at the point of interest (i.e. where biota are) following release
Simple models likely to be sufficient (dose rates are typically very small) SRS-19 or R91 should be adequate
www.ceh.ac.uk/PROTECT
Atmospheric modelling
Need the distance to receptor Release height Wind speed Time wind blows in the direction of the
receptor Duration of discharge Buildings nearby? Deposition coefficients (wet and dry) Etc.
www.ceh.ac.uk/PROTECT
Points to note Noble gases have a small but finite solubility in
water and body fluids Dose contribution is negligible (CRs therefore set to 0)
Noble gases are not deposited to soil (so no plant uptake etc)
Will be exchange within the air pore volume of surface soil (but small component) So assumes pore air concentration = ground level air
concentration Other factors as default in dose assessment tool
(e.g. occupancy factors)
England & Wales Environment Agency ‘R&D 128’
Initially produced back in 2001
Updated a couple of times No further development work
(superseded by ERICA Tool)
Freely available (documented) spreadsheet model for coastal, freshwater and terrestrial ecosystems
Limited radionuclide list and transfer parameter database
www.ceh.ac.uk/PROTECT
Using R&D 128
Ensure macros are enabled in Excel
www.ceh.ac.uk/PROTECT
Input screen
Enter 1 Bq/m3 in each Ar-41, Kr-85
www.ceh.ac.uk/PROTECT
Press F1 to bring up the control panel
www.ceh.ac.uk/PROTECT
www.ceh.ac.uk/PROTECT
Combining information from R&D128 with other tools
For similar reference organisms then it is possible to add the dose rate from Ar-41 and Kr-85 to the dose rates predicted by other tools (gives total dose rate)
Generally negligible dose rates but addresses perception issues and is more realistic than using analogues