Modelling noble gases Radiation Protection of the Environment (Environment Agency Course, July 2015)

 What’s the issue?  Obtaining air concentrations for noble gases  Estimating doses to wildlife from noble gases Overview

 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 What is the issue?

 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 Environment Agency Habitat Assessments

 Various tools for atmospheric modelling (see dispersion 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

 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)

 Initially produced back in 2001  Updated a couple of times  No further development work (superseded by ERICA Tool)  Freely available (documented) spreadsheet model for coastal, freshwater and terrestrial ecosystems  Limited radionuclide list and transfer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

Ensure macros are enabled in Excel

Enter 1 Bq/m3 in each Ar-41, Kr-85

Press F1 to bring up the control panel

 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