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Re: Iodine in a plume as a gas
I just reviewed the Users Guide for the model at
http://www.epa.gov/scram001/userg/regmod/isc3v1.pdf
and an actual effluent report to the NRC from a BWR. I do not believe that
valid long term exposure estimates can be derived from the model by using
the annual I-131 emissions data reported to the NRC. That conclusion is
based on the above-described reviews and my personal experience reviewing
more detailed gaseous effluent data as it was recorded in HP logs.
To even begin to approach minimally accurate estimates of long term
exposure, hourly emission rates and hourly plant meteorological data must be
input to the model. The model does not appear to be designed to accept
plant meteorological data. The hourly plant emission data is important
because the I-131 emission rate can change from hour to hour. For example,
a steam leak may begin at 10:15 am and be isolated at 11:30. In addition
the size and number of leaks will vary with time. Another example would
involve a maintenance shutdown of the plant. That would involve a power
reduction, bypassing the off-gas treatment system for a short period
(increasing the emission rate by a factor of about 100), than having minimal
emissions while the plant is in cold shut down (no steam pressure). Another
example would involve the initiation, growth and suppression of a fuel leak.
A simple annual report of total I-131 emissions for an entire year could not
correlate the actual emissions with actual meteorological conditions.
Section 3.3.8 of the User's Guide describes how to input hourly emission
rates.
Here is an actual example of the variation in quarterly I-131 emissions for
a BWR:
1st quarter 1.24E-2 Ci
2nd quarter 7.49E-3 Ci
3rd quarter 5.51E-3 Ci
4th quarter 1.87E-3 Ci
Please note the variation between the 1st and 4th quarters.
For this particular plant the total annual airborne iodine and particulate
dose to the thyroid to the "maximum individual" was calculated to be 1.41
mrem. This "maximum individual" was a hypothetical person who was at the
site boundary all year (24/7/365) and moved about the boundary continually
so as to always be in the release plume.
Getting back to the dispersion model, it identifies concentration of a
pollutant at chosen "receptor locations". Those locations are fixed points
on a map, they are not people. The dose delivered to a person at a receptor
location would only apply to a person imprisioned outdoors at that location
for the entire multiyear period. The model makes no provision for the way
people actually live. For example, some people who live nine miles from the
facility could spend half or more of their time more than ten miles from the
facility.
Many nuclear power plants use the Meteorological Information Dose Assessment
System (MIDAS) to integrate their on-site meteorological data real time.
Often the system prints out information in the control room. I believe this
system may also be linked to emission data. It appears that the on-site
meteorological data cannot be input to ISCST3.
Don Kosloff dkosloff1@msn.com
2910 Main Street, Perry OH 44081
----- Original Message -----
From: "Gerald Nicholls" <GNICHOLL@DEP.STATE.NJ.US>
To: <radsafe@list.vanderbilt.edu>
Sent: Thursday, January 17, 2002 9:59 AM
Subject: Iodine in a plume as a gas
> We are reviewing an air dispersion model of effluent from the stack of a
BWR. The authors of the study used the Industrial Source Complex model
Short Term Version (ISCST3) to estimate long term (years) exposure to
iodine-131, using I-131 emissions data reported to the NRC. They indicate
that this is an EPA approved model.
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