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|  DOE-STD-1027-92
ATTACHMENT 1
1.
The NRC use of a conservative value at 100 meters was based on the fact that most
of the commercial radionuclide handling facilities for which emergency planning was
being considered have boundaries with populated areas at or less than 100 meters.
The majority of DOE Category 2 facilities have site boundary distances much greater
than 100 meters.
2.
The calculation of values at 100 meters achieves a less accurate result from
dispersion models since building wake effects are still a predominant effect at this
distance.
3.
The use of F at 1 m/sec was considered to be overly conservative, particularly in
light of the difference in application between the DOE and NRC in the resulting
calculated quantities. DOE consequently decided to use a Pasquill stability class D
at 4.5 m/sec windspeed, a value used for comparison by NRC, as the assumed
meteorological conditions for the dispersion calculations. Using a no-buoyancy
model, which will by itself be conservative for many releases, a nominal distance for
the 1 rem evaluation would be slightly less than 300 meters. These conditions
correspond to a X/Q of approximately 1 E-4 sec/m 3, which is considered adequate
for a calculation which does not account for mitigation or size distribution of
particles.
Release Fractions
The final set of assumptions modified by DOE were the set of release fractions used by the
NRC in NUREG-1140. NRC proposed the following set of release fractions based upon
experimental data and historical observations:
1.
Noble Gases
1.0
2.
Highly Volatile/Combustible
0.5
3.
Carbon
1 E-2
4.
Semi-volatile
1 E-2
5.
Unknown form
1 E-2
6.
Nonvolatile powder
1 E-3
7.
U and Pu Metal
1 E-3
8.
Nonvolatile solids
1 E-4
9.
Nonvolatiles in flammable liquid
5 E-3
10.
Nonvolatiles in non-flammable liquid
1 E-3
DOE desired to simplify this list because some components could be combined, some of
the categories were not used by the NRC, and the regulatory framework for the list clearly
allowed lowering release fractions for regulatory calculations.
Therefore, DOE first changed the noble gas category to simply gases and moved specific
gases such as tritium from the highly volatile/combustible category into the gas category,
where the release fraction of 1.0 was retained. DOE then chose to keep the highly
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