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

Obtaining air concentrations

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

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(superseded by ERICA Tool)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

Using R&D 128

Ensure macros are enabled in Excel

Input screen

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

Press F1 to bring up the control panel

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