Questions & Answers

On this page we try to provide answers to the questions you have asked (to ask a question select the Ask a question form). Also feel free to use the form to comment on the questions or answers provided.

Posted: 05/08/2010

Topic:

Question about dose rate to flying animals

From:
Susan Schneider
Serco
UK

Question:

Please can you clarify about contaminated air.

Box 4.1 in The D-ERICA :Integrated Approach report, mentions chronic atmospheric releases of H, C, P and S, and in the report R+D 128, Sec 5.6, dose rates for these are calculated from concentrations in air.

Has this dependence on air concentration been removed in this more recent version of ERICA (I had previously used the prototype version, in Dec 2006)? Is the chronic atmospheric release only relevant when using the transport models?

Answer:

For H, C, S and P air concentrations are the input rather than soil concentrations. ERICA uses a specific activity approach to then estimate biota concentrations of C&H (there's an article by Galeriu et al describing this). This is in-line with approaches taken for human assessment (e.g. see IAEA 2010 TRS472). Honest answer to S and P is that ERICA adopted parameters from R&D128.

Note that the air concentrations are used to estimate activity concentrations in biota they are not used to estimate external dose rates from air. External dose rates for H, C, S and P are assumed to be zero in the ERICA Tool anyway (most models assume zero or very low external dose rates - see Vives i Batlle et al 2007.)

Answered by Nick Beresford 05/08/2010

Posted: 05/08/2010

Topic:

Question about terrestrial occupancies in ERICA

From:
Susan Schneider
Serco
UK

Question:

My question is about terrestrial occupancies in ERICA, which I would like to clarify for a report I am writing. In the database, terrestrial DCCs are provided for three habitats, in-air, in-soil and  on-soil. However in the ERICA Help, only two terrestrial habitats are defined in Figure 5. Habitat 6 must be In-soil, but is habitat 5 On-soil or In-air?  Is it assumed that air-borne contamination is insignificant?  (I am using media concentrations, not the transport models provided in ERICA).  Surely the In-air habitat would need to be included for eg birds and flying insects?

Answer:

You are correct in saying that Figure 5 shows only two habitats for terrestrial ecosystems - Habitat 5 is 'on-soil'. However, you are able to consider flying organisms and a fraction of time in-air can be defined in Tiers 2 and 3 for some organism types - 'Occupancy Factors and Radiation Weighting Factors' screen. There are some limitations on sizes of organisms for which in air dose conversion coefficients can be calcuculated using the create organism wizard (see Table 10 of the Help file).  Note the dose rate estimated to a flying animals is that from contaminated soil and not contaminated air. There is no consideration of external dose rates from contaminated air in the ERICA Tool (nor is it considered in either R&D128 (exception being noble gases) or RESRAD-BIOTA). The in-air habitat is not shown on Figure 5 as this presents the habitats consider during the estimation of the Environmental Media Concentration Limits used in Tier 1; these only consider the scenarios likely to give the highest dose rate.

Answered by Nick Beresford 05/08/2010

Posted: 28/07/2010

Topic:
Use of the 'IAEA SRS-19 estuarine dispersion model' within the ERICA Tool

From:
Corynne McGuire
University of Strathclyde
UK

Question:
When using the estuarine model should I be using the estuary width and depth at the point of discharge or should it be the maximum width and maximum depth?

Answer:
Good question ... we may have added - should it be the assessment site or should it be the average values for the estuary between the point of discharge and the assessment site to your options. We would probably not suggest using the maximum values for the estuary although the minimum values should result in a conservative assessment it that is your aim. Unfortunately there appears to be no guidance on this in the IAEA SRS-19 document (http:www-pub.iaea.org/MTCD/publications/PDF/Pub1103_scr.pdf).

For flow rate the SRS-19 text on estuarine model (see Section 4.2.2) states that the flow rate for the river upstream of tidal limit should be used.

Answered by Nick Beresford with input from Justin Brown (Norwegian Radiation Protection Authority) 05/08/2010

Posted: 28/07/2010

Topic:
Choice of analogue radionuclides to represent radionuclides that are not included in the ERICA Tool

From:
Corynne McGuire
University of Strathclyde
UK

Question:
I was wondering if you can offer advice on what to do when chosing analogues to represent radionuclides that are not included in the ERICA Tool or when the radionuclide is unknown and in a vague category such as other non-alpha radionuclide? I have attached an excel document with the list of radionuclides and vague categories that I will need to assess with suggested analogues.

Answer:
To represent radionuclides not included within the Tool as defaults you assuming Pu-239 for all alpha-emitters and Tc-99 for all other categories you have to assess which is as suggested by the England and Wales Environment Agency (EA) . You could argue this approach on the grounds of consistency. However, it depends upon the purpose of your assessment - do you want to be conservative?. If yes then the analogues suggested by EA may not always be the most conservative choices. However, the ERICA Tool allows you to explore alternatives as it has more fuctionality than the EA approach: 

(a) You could add some of the missing radionuclides to the ERICA Tool and generate your own EMCLs. Some of the elements (e.g.) Ce already have transfer parameters. This would involve using Tier 3 and you would then have to compare the resultant Environmental Medial Concentration Limits (EMCLs) to your media concentrations outside of the Tool as the user cannot add EMCLs (see Brown et al. 2008 for details of how to estimate EMCLs);

(b) look at the available EMCL values and pick the most conservative (i.e. lowest) available dependent upon emitter type. You can view the Tools EMCL value by selecting Database and then Parameter Database from any screen within the Tool.

There is not a  definitive 'correct' answer to this question - but you need to justify your choice.

Answered by Nick Beresford 05/08/2010

Posted: 07/06/2010

Topic:
Modelling exposure to Acacia trees (EMRAS II Little Forest Burial Ground Scenario)

From:
Marko Černe
Jožef Stefan Institute
Slovenia

Question:
Acacia has it's roots 0-2m deep in the waste (part in Zone 1 and part in Zone 2) and has also aboveground part. How to use occupancy factors in this case? The major part of the tree is above the soils, so in that case we will use on soil, but the dose from ionising radiation here is a consequence of underground direct contact and aboveground part, but according to permitted occupancies for tree reference organisms (ERICA help) we could use occupancy factor just on soil? Does this approach include also the roots? How to deal with such cases?

Answer:
This question is in regard to one of the IAEA EMRAS II programme Biota Modelling Group (WG4) scenarios - Little Forest Burial Ground, Australia. The Zone 1 referred to in the question is contamination at >1 m depth into which it is assumed the Acacia roots.

 An interesting question as you are correct in that the ERICA Tool considers plants to be on the soil surface and in the case of trees the assumed geometry is the trunk (specifically the ICRP Reference Pine Tree trunk geometry as defined in ICRP Publication 108). Therefore, the default tree reference organism within the ERICA Tool may not model this scenario very well especially with regard to external dose rates. It would be a fair criticism of the currently available models to say that perhaps the dosimetry for plants requires some further thought. However, scenarios such as this are proposed to make you think and identify problems and (hopefully) solutions. It's not the purpose of the exercise to tell participants what to do - but there are (probably) ways you could try to get around the limitations of the ERICA Tool - although you may then need to consider how to interpret the results. RESRAD-BIOTA has a default geometry which is stated as appropriate for plant roots (default geometry 1 with dimensions 0.2x0.2x0.2 cm and allows any organism type to me modelled as in soil); the Environment Agency R&D128 spreadsheet model also probably has a default geometry more analogous to plant roots. Note that the default CR values in both these models can be highly conservative - read the documentation before using.

Answered by Nick Beresford 08/06/2010

Posted: 25/05/2010

Topic:
Effect of occupancy factors on estimated wholebody activity concentrations

From:
Marko Černe
Jožef Stefan Institute
Slovenia

Question:
How does the geometry or occupancy factor within the ERICA Tool influence the CR value?

Answer:
There is no transformation of CRs according to geometry or occupancy factors - these are used by the ERICA Tool to determine dose rates only. Occupancy factors influence external dose estimates only. However, perhaps the guidance within the ERICA Help is to some extent misleading as it suggests the user can use the occupancy factors to model organims which do not spend 100 % of their time in a given ecosystem. However, if for example an occupancy factor of 0.4 is used the external dose rate would be reduced to 40 % of that if the organism was assumed to spend 100 % of its time in the ecosystem under consideration, whereas, the internal dose estimation (and wholebody activity concentration) would be the same (as if the animal spend 100 % of time in the ecosystem).Note that the Area Factor (AF) parameter in RESRAD-BIOTA is used in the estimation of internal dose rate (although the reported tissue activity concentration appears to stay the same regardless of the value of AF).

Answered by Nick Beresford 07/06/2010

If you want to model an organism as spending only a proportion of time in a contaminated environment using the ERICA Tool then perhaps the simplest approach is to use an occupancy factor of 1.0 and multiply the resultant dose rate by the fraction of time spent in the assessment area.

Added 09/08/2010