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(superseded by ERICA Tool)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