Re: Iodine in a plume as a gas

[NeilKeeney@AOL.COM]

In a message dated 1/17/02 9:58:47 AM Central Standard Time, 

GNICHOLL@DEP.STATE.NJ.US writes:



<< 1. We have not used the ISCST3 model for modeling nuclear power plant 

emissions and would like to know if anyone in the nuclear industry is using 

this model.  If so, are there any particular strengths and weaknesses of the 

ISCST3 model for estimating I-131 exposures?

_______________________

I personally am unfamiliar with that particular model.  However, before you 

make a decision I would ask the question of what problem are you trying to 

resolve?  Do you want something that's very realistic or do you need 

something to play the ingestion pathway exercise game.  There's probably two 

orders of magnitude (if not much more) difference between the standard 

gaussian dispersion model utilized by most utilities (and the EPA, and the 

NRC).  The standard gaussian dispersion models don't typically take into 

account partitioning factors or chemical reactions in the release path and 

out to deposition.



Utilities typically have a couple of models they utilize; one is for the 

plume exposure pathway where civil authorities may be force to implement 

protective actions within a couple hours depending on the scenario.   On the 

plume exposure (external) side of things, the iodine component would be 

negligible relative to the Krypton - Xenon component and that's what I'd be 

looking at for the plume exposure pathway.



For the ingestion pathway model, the deposition is initially plotted based on 

the plume exposure release but is corrected for nuclide content/ratios based 

on effluent path sample analysis from the release point and/or post accident 

sampling points.



My recommendation would be to consult with the utility for which this model 

would be utilized, just for more insight into the designs involved if nothing 

else.  If you're looking for something realistic for use in protective action 

decision-making, the standard gaussian model works fine for the plume 

exposure pathway although it is considered to be very conservative.  You 

should ensure whatever model you select permits you to input key variables 

such as post accident sample analysis data to adjust deposition and to permit 

you to make a public dose estimate since you are required to do just that 

following such a release...

___________________________________________

 

 2. Does I-131 behave as a gas at distances of up to 10 miles from the plant? 

 Our specific concern is that plate out on surfaces and adsorption of iodine 

on air particulates would be limiting factors in accurately assessing 

exposures

____________________________

Ruth Weiner answered this one for you... I would add that it depends also on 

your utility for the model.  Is it for projecting the ingestion pathway dose? 

 If so, you should go with the conservative modeling and let this be your 

guide to vectoring field sampling teams to winnow-out the areas projected to 

be above the milk-thyroid threshold of 0.013 uCi/sq. meter.

 

 3. Is there a "standard" model for the nuclear industry that is generally 

used to assess downwind exposures to I-131.

_________________________

My experience in this area has been with MIDAS Meteorological Information and 

Dose Assessment System.   A standard gausian dispersion model.  There are 

several generations of this; one of the more advanced versions portrays the 

deposition of, I think, 22 nuclides of interest out to 50 miles.  As an 

aside, many of these are designed to be compatible with EPA Guidelines for 

the ingestion pathway.  In order to build in conservatism plate-out or any 

other chemical reactions are not incorporated into the modeling.  As such, my 

belief is that you're probably looking at two orders of magnitude (minimally) 

of conservatism built into the modeling relative to what would actually 

manifest... I've done core damage assessments and dispersion modeling for 

years and it's remarkable what partitioning factors are built in that are not 

credited.  For example the Primary containment ring headers designed for 

collapsing the steam from a primary containment LOCA would, in all 

likelyhood, scrub the bulk of the halogens into the recirc solution.



Hope this helps.



G. Neil Keeney

RRPT

_____________________________________________________ 

 Any relevant thoughts and comments would be appreciated.  Thanks in advance!

  >>

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