Guide 1.145, "Atmospheric Dispersion

NUREG/CR-2260
NUS-3854
RB, R6
Technical Basis for Regulatory
Guide 1.145, "Atmospheric Dispersion
Models for Potential Accident
Consequence Assessments at
Nuclear Power Plants"
Manuscript Completed: July 1981
Date Published: October1981
Prepared by
W. G. Snell, R. W. Jubach
NUS Corporation
4 Research Place
Rockville, MD 20850
Prepared for
Division of Health, Siting and Waste Management
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, D.C. 20555
NRC FIN B7116
NOTICE
This report was sponsored by the Division of Health,
ing,
and Waste Management,
Research,
No.
Office of Nuclear Regulatory
U.S. Nuclear Regulatory Commission under
NRC-01-81-009.
Sit-
P.O.
NUS Corporation was not involved in
the generation of the original data or procedures for the
analyses discussed herein.
This report represents only a
compilation of data and procedures as obtained,
from the NRC staff.
unmodified,
TECHNICAL BASIS FOR REGULATORY GUIDE 1.145,
ATMOSPHERIC DISPERSION
MODELS FOR POTENTIAL ACCIDENT CONSEQUENCE ASSESSMENTS
AT NUCLEAR POWER PLANTS
W. G. Snell and R. W. Jubach
ABSTRACT
Regulatory Guide 1.145,
Atmospheric
Dispersion
Models for Potential Accident
Consequence Assessments at Nuclear Power Plants,
changes
in the
previous methodology
cribed in Regulatory Guides
Regulatory Guide
concentrations
spheric
that
1.145
atmospheric
dispersion
result of these developments,
study
to examine
licensing
and
This
des-
discussed in
in estimated ground-level
during the occurrence
are
substantial
analyses
new methodology
light wind speeds,
conditions
and
of stable atmo-
2)
directionally
the recognition
dependent.
As
a
the NRC Meteorology Staff conducted a parametric
the consequences
activities.
This
1) the reduction
due to plume meandering
stability conditions
several
of atmospheric dispersion
1.3 and 1.4.
includes,
presents
of these
parametric
changes
study was
on
previous
instrumental
and future
in the deter-
mination of appropriate probability levels for the risk assessment methodology
discussed in the guide.
The technical basis for the new methodology and the
results of the parametric study are documented in this NUREG.
This documenta-
tion includes the relationship of the new approach to the previous methodology.
i ii
TABLE OF CONTENTS
Title
Page
Abstract
iii
Table of Contents
v
List of Figures
vi
List of Tables
vii
I.
I-2
II.
Introduction
A.
Purpose
B.
Background
I-i
I-2
Determination of Plume Meander Methodology
A.
Introduction
B.
Test Data
C.
Development of Meander Factors
II-1.
11-2
11-3
III.
Basis and Use of the Equations for Ground Level Releases
III-I
IV.
Parametric Study Results
IV-1
IV-1
IV-1
IV-2
IV-2
A.
Purpose
B.
Data Used
C.
Study Result
1. Effect of Sector Dependency
2.
Effect of Meander
3.
Selection of Sector Probability Level
IV-6
IV-9
4.
Overall Impact of Regulatory Guide 1.145 Methodology
IV-10
5.
Conclusions
IV-13
IV-15
References
v
LIST OF FIGURES
Figure No.
Title
Page
Measured Values of Sigma y for Rancho Seco (X) and
II-'
EOCR*
(0)
for Stability Class A.
11-4
Measured Values of Sigma y for Rancho Seco (X) and
11-2
EOCR (0) for Stability Class D.
11-5
Measured Values of Sigma y for Rancho Seco (X) and
11-3
EOCR (0) for Stability Class E.
11-6
Measured Values of Sigma y for Rancho Seco (X) and
11-4
EOCR (0) for Stability Class F.
11-7
Measured Values of Sigma y for Rancho Seco (X) and
11-5
EOCR (0) for Stability Class G.
11-8
Meander Factors for Correction of Pasquill-Gifford
11-6
Sigma y Values by Atmospheric Stability Class.
IV-1
I1-11
Number of Hours the 5 Percent Relative Concentration
is Exceeded in the Worst-Sector Using the R.G. 1.145
Methodology With a Variable Site Boundary and No Meander.
r
*EOCR = Experimental Organic Cooled Reactor.
vi
IV-11
LIST OF TABLES
Title No.
Title
IV-1
Parametric Study Site Characterization.
IV-2
Number of Hours the 5 Percent X/Q Value is Equalled
Page
IV-3
or Exceeded in Each Sector Considering a Constant
Boundary and No Meander.
IV-3
IV-5
Number of Hours the 5 Percent X/Q Value is Equalled
or Exceeded in Each Sector Considering the Actual
Exclusion Area Boundaries and No Meander.
IV-4
IV-7
Number of Hours the 5 Percent X/Q Value is Equalled
or Exceeded in Each Sector Considering a Constant
Site Boundary and Meander Included.
IV-5
Comparison Between the Past and Regulatory Guide
1.145 Methodology.
IV-6
IV-8
IV-12
Percent of the Time the X/Q Calculated by the
Indicated Methodology is Exceeded Over the Actual
Exclusion Area Boundary.
IV-14
vii
i.
INTRODUCTION
A.
Purpose
The development
Potential
of Regulatory Guide 1.145,
Atmospheric Disperison Models for
Accident Consequence Assessments
at Nuclear Power Plants
(Ref.
1),
was initiated in order to modify the methodology in Regulatory Guides 1.3 and
1.4 (Refs.
2 & 3) for accident assessments to reflect the recent developments
in atmospheric dispersion modeling and more realistic considerations of sitespecific meteorology.
The
methodology
in Regulatory
Guide
1.145
allows
for
consideration
directional variability of wind flow and diffusion conditions
of the
at a site,
and
also permits consideration of directional
variability of Exclusion Area Boun-
dary (EAB)
distances.
and Low Population Zone
incorporates
the
results
of recent
under certain atmospheric conditions,
(LPZ)
field
tracer
In
tests
addition,
which
horizontal dispersion
the guide
indicate
that
is enhanced due to
lateral plume spreading (i.e., meander effects).
Because the methodology described in the guide represents a substantial change
from the approach described in Regulatory Guides 1.3 and 1.4,
ology staff conducted
examine
the
activities.
fications
consequences
of these
study in the summer
and fall
changes
and
on
previous
of 1978
future
licensing
including a parametric study that examines these changes.
based
to
This NUREG discusses the basis for and development of these modi-
pose of this NUREG is
is
a parametric
the NRC meteor-
The pur-
to present information on which Regulatory Guide 1.145
and not to provide an indepth analysis of the scientific basis for
any of the methodology proposed by the guide.
Only the calculations
of 0-2
hour relative concentrations are discussed.
Section
B of
the
Introduction
discusses
the
dispersion methodology for accident assessments
background
the development
the guide.
of the meander
The parametric
factor
study provides
I -1
the
atmospheric
in order to compare the Regu-
latory Guide 1.145 approach with the past methodology.
discuss
of
Sections
II
and III
and the equations utilized in
insight to changes
in methodology
and the resultant effects on relative concentration calculations.
of the parametric
discussed
study were
utilized
in
determining
in Section 2.1 of Regulatory Guide 1.145.
The results
the probability
level
This study is discussed
in Section IV.
B.
Background
The pre-Regulatory Guide 1.145 (hereafter "direction-independent")
methodology
to characterize atmospheric dispersion conditions for licensing and siting of
nuclear power plants had been developed through a series of changes to a simple model used in the 1950's and early 1960's.
in TID-14844 (Ref.
ological
The simple model
4) and referenced in 10 CFR Part 100 (Ref.
is described
5).
The meteor-
conditions assumed in TID-14844 were a very stable atmosphere
light wind
speed
corresponding
Regulatory Guide 1.23,
sification),
Ref.
closely to Pasquill
Type "F"
and a
stability
(see
6, for a discussion of atmospheric stability clas-
and a 1 meter/second wind speed.
This stability and wind speed
combination
represents
situation.
During the 1960's these assumptions were changed to reflect more
reasonable atmospheric
speed,
an infrequent
dispersion conditions
atmospheric
dispersion
allowing for variations
in wind
atmospheric stability, and wind direction.
Safety Guides 3 and 4 (now.Regulatory
in 1970,
Guides 1.3 and 1.4),
originally issued
recommended the use of Pasquill Type "F" stability, a wind speed of 1
meter/second,
sion
and conservative
and an invariant wind direction to represent atmospheric disper-
conditions for time periods less than 8 hours.
The selection
of these
atmospheric dispersion conditions was based on examination of available meteorological
data from a small
topographical
coastal).
The
number
and meteorological
examination
of reactor sites
regimes
indicated
(i.e.,
that
representing
inland,
the short-term
river
(0-2
different
valley,
hour)
and
atmos-
pheric dispersion conditions represented by Pasquill Type "F" stability associated with a wind speed equal
to 1 meter/second,
tion,
of about 5 percent of the total
were exceeded
hourly basis.
orological
ability
Subsequently,
conditions,
level
an average
independent of wind directime
on
an
to acknowledge site-to-site variability in mete-
the "5-percentile criterion" was selected as the prob-
of the atmospheric dispersion
condition
to be considered
in a
calculation to demonstrate compliance with the dose objectives specified in 10
CFR Part 100.
I - .2
A relative
concentration
(X/Q)
value which would not
ceeded more than 5 percent of the time on an annual
radial
distance
be expected to be exbasis
at
a minimum EAB
and at the minimum distance to the outer boundary of the LPZ
was used in this calculation.
These
X/Q values
are functions of wind speed,
atmospheric stability, distance from the effluent source to a potential receptor and lateral and vertical distance from the center of an airborne effluent
plume.
The distribution of the effluent plume about the plume centerline
assumed to be Gaussian,
is
but with additional spreading of the plume in the wake
of plant structures due to mechanical mixing of the atmosphere induced by air
flows over and around these obstructions.
Using
the
direction-independent
first calculating
occurrences)
atmospheric
at a distance equal
and the exclusion
X/Q
values
are
determined
by
X/Q values for hourly pairs (or joint frequency
of wind speed and
of direction,
reactor
individual
methodology,
stability conditions,
independent
to the shortest radial distance between the
area boundary or outer boundary of the LPZ.
These
individual X/Q values are then ranked from highest to lowest and their associated frequencies
are summed to generate
a.cumulative probability distribution
of X/Q
From this probability
distribution,
values.
the X/Q
value
that
is
exceeded 5 percent of the time around the entire circumference (exclusion area
or LPZ)
cal
is selected as appropriate for the Part 100 evaluation.
assumption
was
that
this
value
was
to
be
The theoreti-
equalled
or
approximately 5 percent of the total time or 438 hours per year
exceeded
(5% x 8760
hours per year).
However,
the frequency of occurrence
of this X/Q value at any specific
loca-
tion on the exclusion area boundary is expected to be substantially less than
5 percent of the time annually,
the
entire circumference
considers
because the particular location is
of the appropriate
a segment of a circular
boundary.
For example,
frequency
of the
X/Q value
if
one
exclusion area boundary which extends only
one fifth of the way around the circumference of the boundary,
pected
less than
then the ex-
in that segment would be one fifth of 5
I -3
percent or 1 percent
ple,
of course,
(approximately 88 hours)
of the total time.
does not consider any directional
cal conditions or variable distances
variability of meteorologi-
to the boundary.
considerations might cause the frequency in the example
the 1 percent level,
is evident then,
consistent
that
but it
if
This exam-
The inclusion of such
sector to vary about
would be very unlikely to approach 5 percent.
an evaluation
with past practice
is to be made on a directional
for specified
locations
on a boundary,
It
basis
an ap-
propriate percentile level for each direction segment which is much less than
5 percent must be selected.
I -4
II.
A.
DETERMINATION OF PLUME MEANDER METHODOLOGY
Introduction
The basic atmospheric dispersion model and methodology discussed in Section
I.B have been developed for calculating relative concentrations (X/Q) to be
used in assessments of the consequence of accidental releases from nuclear
power plants (see Ref. 7).
This model assumes that the plume spread has a
Gaussian distribution in both the horizontal and vertical and, therefore,
utilizes the standard deviations of plume concentration distribution in the
horizontal (a ) and vertical (az).
Applications of this model normally
utilize the traditional Pasquill-Gifford curves for a and o (Ref. 7) for
estimating concentrations for release periods of nominally one hour.
For
ground-level releases the model calculates the highest effluent concentrations
under low wind speed and stable atmospheric conditions.
The Pasquill-Gifford
dispersion coefficients,
(ay and a z) are selected independent of wind
speed and are based on diffusion test data for release periods of much less
than one hour.
Quantitative
atmospheric
tracer
studies
representing
ground
level
releases
without the effects of buildings have been performed at the River Bend, Three
Mile Island and Clinch River power reactor sites (Refs. 8-10).
These tests
have shown that during stable (E, F, and G) atmospheric conditions, as defined
by AT criteria in Regulatory Guide 1.23, when the wind speed is light, measured effluent concentrations are usually substantially lower than those predicted by the use of the traditional Pasquill-Gifford prediction curves of
lateral and vertical plume spread.
These reduced concentrations are due primarily to enhanced horizontal spreading of the plume as it meanders over a
large area which occasionally may exceed a 180 degree arc. This meandering of
the plume produces ay values that are much larger than have been assumed for
these conditions.
Since these tracer studies represented only near ground level, point source
releases without the effects of release elevation and building influences, and
were carried out in terrain exhibiting characteristics unique to each site,
they were not considered appropriate for generic application to all nuclear
power reactor sites.
II - 1
To obtain data representative of releases at constructed nuclear power plants,
the NRC and NOAA jointly funded atmospheric
1975
duffusion tests
in the fall
at the Rancho Seco nuclear facility in California (Ref.
11).
of
Data from
these tests, along with consideration of the results already generated by past
diffusion
tests,
were used
to determine
building wake on values of X/Q.
the combined effects of meander
Analyses of these tests,
ation of the results already generated
and
along with consider-
by past diffusion tests,
provide the
meander factors discussed later in this section applicable during light wind,
relatively stable atmospheric stability conditions.
For releases through vents or other building penetrations,
the meander factor
allows credit for the combined effects of plume meander and building wake.
the
effects
of meander
diminish
stability,
the effects
releases,
the dispersion
with
increasing
wind
of building wake become more
assessment
remains
speed
and
As
decreasing
dominant.
For elevated
because
the data col-
unchanged
lected to date does not confirm the existence of meander at elevations greater
than 60m.
Because enhanced plume dispersion due to meandering appears
to be
most prevalent during periods of low wind speed and stable atmospheric conditions, which are the same conditions that give the highest concentrations for
ground-level
releases,
the NRC has incorporated plume meander into the model
in an effort to provide more realistic assessments of atmospheric dispersion.
B.
Test Data
A quantitative
assessment
power plant site was made,
of
effects
of plume meander
at an
actual
nuclear
utilizing data from the Rancho Seco tests.
Atmos-
pheric stability during these tests was determined from the NRC AT classification scheme (Ref.
6).
stability classes.
No test data were available for the B or C atmospheric
Samplers were located in arcs with radii of 100,
and 800 meters from the reactor containment vessel.
able tests were utilized in the analysis.
200,
400,
Data from all the avail-
More detail on the field program is
provided in Reference 11.
In addition to the tests conducted at Rancho Seco,
similar tests were jointly
funded by NOAA and the NRC and performed at the Experimental
Reactor (EOCR)
Organic
Cooled
test reactor building complex at the Idaho National Engineering
Laboratory in Idaho
in 1975
and 1976
(Ref.
EOCR
II - 2
12).
Although
data from of the
Lests were not available to be included
meander,
in the original
assessment
of plume
they have since become available and have been plotted with the Ran-
cho Seco data (Figures II-i through 11-5).
The results of the EOCR tests were
very similar to those of Rancho Seco.
The NRC analysis of the results of the Rancho Seco tests focused on the measured
values
of the
the vertical
of
horizontal
dispersion
dispersion coefficient,
a y from
the
tests
that
were
using the second moment method.
az,
used
An
coefficient,
were not made.
in the
NRC
important
Measurements
ay*
The measured
analysis
were
consideration
of
values
calculated
was that
atmos-
pheric stability was based on the NRC AT classification scheme as per Regulatory Guide 1.23.
Use of other classification schemes may not provide similar
results in analysis of these data relative to NRC assessments.
C.
Development of the Meander Factors
The
values
of ay that
were
are shown by atmospheric
shown
obtained
from the Rancho Seco and EOCR
stability class in Figures
are the Pasquill-Gifford ay curves for
II-i through
studies
11-5.
each stability class
Also
and a ay
curve enhanced by an appropriate multiplier to give a lower envelope to the
test
results.
Because
the
results
of this
evaluation
were
to
be used
in
safety assessments of nuclear power plant design and in siting evaluations for
sites located in various topographical and meteorological regimes, a lower
envelope of this measured test data was selected as a reasonably conservative
approach
for
estimating
increased
horizontal
lower envelope curve was subjective.
dispersion.
Various
whole
examined and the curve which most appropriately,
determining
lower
these meander
envelope
multiplier
factors,
to
the meander factor applicable
As
indicated
in Figure
the
enveloped
Selection
number
multipliers
the
were
considering the objective
the
Pasquill-Gifford
data
was
aY was
to the appropriate atmospheric
II-i,
of
selected.
then
selected
in
This
as
stability class.
no increase in the Pasquill-Gifford aY value is
applicable for A stability because the a curve is consistent with the lower
Y
envelope.
II - 3
A -STABILITY
1000
500
200
mL
Uo
UY
W
V-
100
CD
C')
50
20
10
200
100
500
DISTANCE
FIGURE
II-i.
(METERS)
Measured Values of Sigma y for
Rancho Seco (X) and EOCR (0)
for Stability Class A.
II-4
1000
D
STABILITY
1000
500
200
U-)
I
77
100
200
500
DISTANCE
(METERS)
FIGURE 11-2. Measured Values of Sigma y for
Ranoho Seco (X) and EOCR (0)
for Stability Class D.
11-5
1000
E
STABILITY
1000
500
200
U)
100
LOJ
50
20
10
100
500
200
DISTANCE
1000
(METERS)
FIGURE 11-3. Measured Values of Sigma y for
Ranoho Seco
For Stability
11-6
(X) and EOCR
Class E.
(0)
F
STABILITY
1000.
500
200
U)
100
U)
50
20
-
10100
200
500
DISTANCE
FIGURE 11-4.
(METERS)
Measured Values of Sigma y for
Rancho Seco (X) and EOCR (0)
for Stability Class F.
11-7
1000
G
STABILITY
1000
500
200
Ui)
Lii
100
CD-.
03
U)
50
20
10
100
500
200
DISTAN\CE
FIGURE 11-5.
(METERS)
Measured Values of Sigma y for
Rancho Seco (X) and EOCR (0)
for Stability Closs G.
II-8
1000
The
NRC analysis
of the Rancho
Regulatory Guide 1.145
power
plants.
Seco
data was
and application
Application
of
the
to
accomplished
the design
meander
factors
and
specifically for
siting of
developed
nuclear
by the NRC
to
other assessments should not be accomplished without a thorough examination of
all test data provided in References 11 and 12.
At this
point two limiting criteria were
meander
factors.
Since
the Rancho
imposed
on
the application
Seco measurements
tance of 800m from the release point,
it
any values for distances beyond this.
Therefore,
of the
were limited to a dis-
was not deemed appropriate to apply
credit for additional
plume
spread from meander would only be applied to a downwind distance of 800m from
the
release
However,
point.
any credit
Beyond
800m,
additional
credit
would
not
received up to 800m would be retained.
To
be
allowed.
account for
this, the following equations were adopted.
Xy = Ma for distances less than or equal to 800 m
yy
y =(M-1)OySO0m] + cy for distances greater than 800 m
where:
XIy
is
lateral
a
effects, meters,
is
lateral,
plume
plume spread with meander
spread
based
and building wake
on
Pasquill-Gifford,
meters,
Analysis
ay8wOm
is ay at a distance of 800m, meters,
M
is the meander factor, dimensionless.
of the Rancho
Seco and other
prevalent during D, E, F,
tests indicated
and G stability conditions
and
that meander
accompanied
is
most
by low wind
speeds.
full
A wind speed of 2.0 meters/second was selected as a limit below which
meander credit could be received and a speed of 6.0 meters/second was
selected as a limit above which no additional
tween these
two
values
the meander
factor
credit could be received.
varies
logarithmically
credit at 2.0 meters/second to no credit at 6.0 meters/second.
of these wind speeds was based on the many different
II - 9
Be-
from full
The selection
atmospheric dispersion
studies
performed
over the
past
several
decades
(e.g.,
Prairie Grass
(Ref.
A graph of the
and others mentioned previously).
meander factors developed from this analysis versus wind speed can be found in
13),
Green Glow (Ref.
14),
Figure 11-6.
II - 10
10
6
4
ICD,
ILL
3
CD
2
1
1
2
3
WINDSPEED
FIGURE 11-6.
4
5
6
10
(M/SEC)
Meander Factors for Correction of
Pasquill-Gifford Sigma y Values by
Atmospheric Stability Class.
II-11
Ill.
BASIS AND USE OF THE EQUATIONS FOR GROUND-LEVEL RELEASES
Regulatory Guide 1.145
calculating
incorporated the use of three principal
ground-level
These equations,
relative
concentrations
referred to in the guide
at
the
as Equations
equations for
plume center
1, 2
and 3,
line.
are
as
follows:
1
X/Q =
(1)
ulO(1ay az+A/2)
X/Q =
1
(2)
ulO0 3 T a y az
X/Q =
1
u10
(3)
ITIy
where
X/Q
is relative concentration,
is 3.14159,
7T
ulO
is windspeed at 10 meters above plant grade,
ay
A
sec/m 3 ,
is lateral plume spread,
and distance, meters,
a function
of atmospheric stability
a function of atmospheric stability
z
is vertical plume spread,
and distance, meters,
iy
is lateral plume spread with meander
fects, (see Section II.C), meters, and,
is
the
smallest
m/sec,
vertical-plane
and
building wake ef-
cross-sectional
area
of
the
reactor building, square meters.
The bases for Equations 1 and 2 can be found in Meteorology and Atomic Energy1968,
(Ref.
7) and Regulatory Guides 1.3 and 1.4 (Refs.
2 and 3).
The factor
A/2 in Equation 1 and the factor 3 in Equation 2 are included to give additional
credit for turbulent mixing
The A/2 term in Equation 1 is
in the wake of buildings
and structures.
better known as the cA term with c being con-
servatively assigned a value of 0.5.
The factor of 3 in Equation 2 is used as
III - 1
upper limit to the amount of credit that can be obtained from the building
wake effect.
tions 1 and 2.
This
is the basis for choosing the higher value between
Credit
Equa-
is given for building wake effects based on Equation 1
until it reaches the upper limit determined by Equation 2,
then the value from
Equation 2 is used.
based on
Equation 3 was formulated
cluded credit for
inclusion of the meander factor which in(See
building influences.
Section
II.)
By comparing the
higher value derived from Equations 1 and 2 with the value from Equation 3 and
picking the lower of the two values,
enhanced
plume spreading under
additional
low wind
credit may be received
speed and
tions as well as for building wake effects.
for
stable atmospheric condi-
For further information, Appendix
A of Regulatory Guide 1.145 contains several examples of the selective use of
Equations 1, 2 and 3 under various wind speed and stability conditions.
The
dispersion
equations
in the guide for elevated releases
are essentially
the same as discussed in Meteorology and Atomic Energy and Regulatory Guide
1.3.
Since these equations
or their use does not entail significant changes
from past practice (except for the direction dependent applications),
not discussed here.
For further information,
III - 2
they are
refer to Regulatory Guide 1.145.
IV.
A.
PARAMETRIC STUDY RESULTS
Purpose
As discussed
in the Introduction
of this report,
the parametric
study was
accomplished in order to examine the effects of the Regulatory Guide 1.145
accident analysis dispersion methodology relative to the direction-independent
The Regulatory Guide 1.145 methodology utilizes the critical
methodology.
sector relative concentration (X/Q) approach in which the effects of the directional dependence of boundary distances, wind direction frequencies, and
The guide
frequencies of atmospheric stability conditions are considered.
also incorporates credit for horizontal diffusion by considering the effects
The critical sector refers to the selection of X/Q values
of plume meander.
for the determination of compliance with the dose guidelines contained in
Regulatory Guide 1.145 should be referred to for additional
1OCFR Part 100.
Because this approach is a marked departure from the directionguidance.
independent method, the effects of each of the three features of the model
(i.e., direction-dependent consideration, a variable exclusion distance as a
function of direction, and meander), as well as the complete Regulatory Guide
1.145 approach, were examined in the parametric study. The basis for all the
analyses in the parametric study was to determine the effect on the directionindependent 5 percent X/Q value used for accident consequence assessments.
This approach puts the effect of the Regulatory Guide 1.145 methodology
perspective relative to the direction-independent method.
B.
in
Data Used
Data that were used for the parametric study were the
meteorological data from 18* nuclear power plant sites
tive of the meteorological and topographical regimes
various licensing activities. All sites utilized had
most recently available
which were representaencountered during the
meteorological programs
*Initially, 18 sites were examined in detail while three additional sites were
evaluated later. The three additional sites were not studied to the extent of
the original 18; most figures and tables provided in this NUREG are discussed
or based on 18 sites.
IV - I
consistent with the 1972 version of Regulatory Guide 1.23 Onsite Meteorological Programs.
The data were obtained in the form of joint frequencies of wind
wind speed, and atmospheric stability as provided on the plant
direction,
docket with the NRC.
differential
inal
(AT)
Atmospheric stability was based on vertical
and wind speed and wind direction were collected
height of 10 meters.
Values of relative concentrations
for the study are all for ground-level
majority of
licensing
topographical
table will
temperature
assessments.
regime of each
at a nom-
(X/Q)
calculated
releases since this represents the vast
Table
IV-1 provides
site examined.
the meteorological/
The reference
be utilized throughout this section.
numbers
Boundary distances
on
this
utilized
in various aspects of the study were actual distances for a given site.
C.
Study Results
1.
Effect of Sector Dependency
Atmospheric diffusion conditions
location,
with
are directionally dependent for a particular
some wind direction flows
others with relatively good diffusion.
associated with poor diffusion
The differences
and
in atmospheric diffu-
sion as a function of wind direction can be especially prominent at sites on
the shores of large bodies of water (e.g., lakes and oceans) and in deep river
valleys.
Knowledge of these directionally-dependent
ation of variable Exclusion Area Boundary (EAB)
or Low Population Zone (LPZ)
distances results in a more realistic evaluation.
methodology considers
boundary distances
Although
wind
by dividing
direction
direction-independent
tionally,
the
the directional
data
The Regulatory Guide 1.145
variability of diffusion conditions and
the
boundaries
are
recorded
methodology did
direction-independent
conditions plus consider-
not
into
in
consider
methodology
16
22.5-degree
22.5-degree
this
sectors.
sectors,
information.
the
Addi-
utilized circular
boundaries
with a radius equal to the minimum distance of the actual boundary,
as opposed
to the actual boundary distances.
The first part of the parametric study was
to examine the effect of the Regulatory Guide 1.145 methodology relative to
the direction-independent approach by examining the relationship of the two
methods for sector dependency.
IV - 2
TABLE IV-1
Parametric Study Site Characterization
Site
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Site Characteristics
Midwest (Flat)
Southeast (Valley)
Southeast (Rolling Hills)
Midwest (Flat)
East-Central (Valley)
South (Coastal)
Midwest (Valley)
Midwest (Flat)
East (Valley)
Southeast (Rolling Hills)
Southeast (Rolling Hills)
Southeast (Rolling Hills)
Southeast (Rolling Hills)
Northeast (Valley)
Southeast (Coastal)
Midwest (Coastal)
Northeast (Coastal)
Southeast (Coastal)
Midwest (Coastal)
East (Valley)
East (Valley)
IV-3
it atmospheric
dispersion conditions (represented
pairings) and boundary distances
direction sectors,
and if
of the 16 directions
independent
ceeded about 27
Since
100%/16 or 6.25%),
X/Q value
(see
sector
(i.e.,
dispersion
conditions
and
vary considerably from sector to sector,
X/Q value is
then the calculated direction-
Section
hours in each
atmospheric
in each of 16 22.5-degree wind
the wind direction frequencies are identical in each
(i.e.,
5 percent
are identical
by stability and wind speed
I.B)
would be equalled
5% x 8760
wind
hours per year/16).
direction
frequencies
the direction-independent
can
5 percent
equalled or exceeded a different number of hours in each sector.
The total number of hours for all
sectors
year).
direction-independent
The
or ex-
likelihood
that
the
is
still 438 (5% x 8760 hours per
5
percent
X/Q value
would be equalled or exceeded in a specified sector would be less than 5 percent,
and
usually much less
than 5 percent of the total
time,
averaging 27
hours in each sector (approximately 0.31%).
Table IV-2 shows
values
exceed the
the distribution
direction-independent
sectors for the 18 sites,
tions by direction (i.e.,
example,
number of
exceeded
of the number
an analysis
of hours per year that X/Q
5 percent
X/Q
in
each
of
16
considering only the variation of diffusion condia circular boundary).
Meander is not included.
of 18 of the sites (Table IV-2)
hours per year the direction-independent
in a specific
value
direction was 158 hours
For
shows that the maximum
5 percent
(158/8760,
X/Q value
was
1.8% of the total
time) at Site 6.
The minimum number of hours per year the directionindependent 5 percent X/Q value was exceeded in a specific direction was zero
hours also at Site 6.
those sectors
This is indicative of a very high frequency of winds in
with the maximum number
of hours and a corresponding
low fre-
quency in those sectors with the minimum number of hours.
The greater
. number of hours the 5 percent value is exceeded, the more frequently it
curs,
and consequently,
the poorer the diffusion conditions
are.
Note
the
octhat
the average per sector for each site is about 27 hours and the average around
the site is nearly 5% x 8760,
or 438 hours.
IV - 4
Number of Hours the 5 Percent X/Q Value is Equalled or Exceeded in Each Sector Considering a Constant
Boundary and No Meander.
Table IV-2.
Site
Direction
N
NN E
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
Total
Average
U,
1
2
3
4
5
44
39
37
32
31
24
27
34
45
24
15
12.
16
20
23
28
31
26
25
34
39
73
30
23
13
15
19
13
15
32
22
40
15
12
12
3
4
5
7
13
17
29
101
141
34
17
11
14
48
3
4
40
28
22
23
18
21
22
38
33
33
34
32
28
427
27
451
28
450
28
435
27
6
7
8
19
16
27
32
16
10
14
18
29
40
75
71
43
27
17
16
135
39
20
10
3
0
0
0
0
0
1
1
2
14
71
158
22
10
24
14
14
20
12
21
22
15
26
17
26
50
86
49
41
26
38
26
27
22
20
20
31
23
44
21
21
24
31
31
25
27
30
28
32
25
14
26
24
17
17
25
30
37
39
28
21
28
28
41
16
21
31
28
31
40
39
35
23
22
18
21
470
29
454
28
428
27
446
28
424
27
443
28
9
10
18
12
13
14
15
16
17
18
28
36
25
34
30
36
26
28
25
23
20
29
25
22
20
8
15
31
71
113
88
28
13
11
8
7
9
6
7
6
8
15
12
17
20
29
21
28
19
35
29
50
55
56
27
15
14
17
19
15
10
20
39
54
57
68
79
57
11
3
1
4
5
16
30
23
42
36
44
43
39
21
12
17
8
27
22
27
26
72
23
19
21
18
16
15
12
12
9
10
17
45
59
53
54
31
63
77
47
37
11
9
25
19
13
11
8
12
14
20
20
15
12
18
30
46
43
58
92
43
24
10
14
7
11
5
7
425
26
429
27
442
28
459
29
433
27
455
28
417
26
435
27
11
Average
440
27.5
Consideration of a variable EAB or LPZ as a function of direction will always
result in equal
pared
to
or lower calculated X/Q values for ground-level
the
direction-independent
methodology.
This
is
boundaries were chosen as the minimum boundary distance
releases com-
because
and any
circular
increase
in
distance to account for the actual boundary will result in lower values since,
for ground-level
fect,
the
releases,
number
of
X/Q decreases
hours
the
with distance.
To examine this ef-
direction-independent
5
percent
value
equalled or exceeded by sector with a variable boundary was calculated.
is
shown
in Table
study involving
IV-3.
For this
variable
and other
boundaries,
evaluations
over-water
in
boundaries
is
This
the parametric
at coastal
sites
were assigned a distance equal to the shortest overland boundary distance,
and
actual site boundary distances were used to define the EAB boundary over land.
Table
IV-3
independent
shows
5th
that
the
percentile
decrease
in
value
equalled
is
the
number
or
of
hours
exceeded
the
direction-
(indicative
of
a
larger number of lower X/Q values in the distribution) can be significant for
some sectors
Site 3.
at
some sites.
The maximum
overall
decrease was 281
hours
at
No change occured at Site 14 because the actual boundary was defined
as circular.
On the average,
the decrease was 127 hours around the site and
7.5 hours for a sector.
This portion of the study, then,
by sector (Table IV-2),
shows the variability of diffusion conditions
with some wind directions being associated with poorer
diffusion conditions and the expected changes due to the inclusion of a variable boundary (Table IV-3).
2.
Both results are reflected in the X/Q value.
Effect of Meander
Atmospheric diffusion tests have shown that short-term X/Q values may be reduced substantially due to lateral
tests
has resulted
in the
plume meander.
The NRC analysis of these
development of conservative
reduction
X/Q values to describe the effect of meander.(See Section II).
of meander alone resulted in a decrease
factor of two,
factors for
Consideration
in the selected X/Q. value by about a
varying between about 1.5 and 2.5 for the 18 sites.
gives the number of hours that the direction-independent
IV - 6
Table IV-4
5 percent X/Q value
Table IV-3.
Number of Hours The 5 Percent X/Q Value is Equalled or Exceeded in Each Sector Considering The Actual
Exclusion Area Boundaries and No Meander.
Site
Direction
N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WMW
NW
NNW
Total
Average
1
2
3
4
5
44
34
35
30
24
21
19
29
41
21
6
6
9
15
20
29
21
21
27
34
38
73
7
4
3
5
8
5
6
12
15
27
15
13
10
1
2
2
3
9
11
3
8
34
18
8
4
13
28
0
0
40
25
20
19
15
17
18
14
13
1
19
11
20
4
5
9
9
6
4
8
12
25
36
75
60
17
10
3
4
383
24
306
19
154
10
260
16
287
18
6
7
135
1
39
0
20
1
10 14
3 14
0 17
0
3
0
7
0
9
0
3
1
9
1 14
0 26
1 35
6 43
59
3
275
17
199
12
8
9
9
10
17
8
9
10
14
18
28
21
24
16
9
9
10
4
15
26
27
28
33
24
18
14
9
8
15
4
7
8
6
23
216
14
265
17
10
19
24
17
24
10
24
13
10
11
11
14
24
15
14
18
20
268
17
11
17
21
23
22
33
22
25
22
24
22
22
30
28
24
21
19
375
23
12
6
6
17
69
113
85
20
6
5
4
3
5
3
4
4
6
356
22
13
14
11
10
12
16
5
11
6
13
2
6
31
36
15
7
14
209
13
14
16
17
17
15
72
19
30
23
1523 14
1042 10
20 36
3
39 44
4
54 42
5
57
36
10
68
20
7
79 12
9
57
17
10
11
8 17
3 26 45
1 22 59
4 26
53
5 25 54
31
63
77
47
37
11
6
21
14
10
8
6
6
11
13
20
459
29
15
424
27
395
25
381
24
18
15
12
11
30
46
43
58
92
43
17
8
12
6
11
6
7
417
26
Average
313
20.0
Table IV-4.
Number of Hours the 5 Percent XIQ Value is Equalled or Exceeded in Each Sector Considering a Constant
Site Boundary and Meander Included.
Si te
1
2
3
4
5
6
7
8
9
N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
16
13
14
15
13
9
11
12
16
8
4
4
5
6
8
10
9
8
7
10
10
21
9
7
4
4
6
4
5
10
7
11
5
5
4
1
1
5
2
6
8
13
41
56
14
7
4
6
16
0
0
10
9
7
7
6
5
3
8
4
8
3
9
6
5
8
7
4
2
4
4
9
8
16
16
12
8
3
5
11
2
2
2
0
0
o
0
o
o
0
0
0
0
5
15
9
4
12
7
7
10
5
10
28
7
13
8
13
23
46
21
0
0
1
0
1
0
1
0
1
1
4
3
2
2
1
1
11
14
12
14
11
12
9
11
12
6
7
9
13
11
14
9
4
10
10
12
5
7
10
8
9
12
11
10
6
5
5
6
Total
Average
164
10
132
8
177
11
100
6
117
7
37
2
223
14
18
1
175
11
130
8
Direction
10
12
13
14
15
16
17
18
8
12
5
13
17
16
16
11
10
10
8
7
11
10
8
7
1
2
4
8
12
10
4
2
'2
1
1
1
1
1
1
1
2
2
3
4
5
4
5
3
6
5
9
8
8
4
3
2
2
2
1
2
1
5
4
7
5
6
6
0
0
0
0
0
7
16
14
19
16
24
23
17
10
5
8
4
13
11
13
12
12
0
8
8
6
7
5
5
4
6
6
8
15
13
12
10
21
19
16
7
11
5
13
13
12
9
8
6
8
12
14
21
4
4
6
13
21
20
27
42
19
10
5
6
3
5
2
2
Average
169
11
52
3
73
5
41
3
212
13
125
8
195
12
189
12
129
8.0
11
is
exceeded
at each
of the 18 sites
due to meander
alone
boundary).
Consideration
X/Q value.
The number of hours the direction-independent
of meander
significantly
(i.e.,
decreases
a circular
the
calculated
5 percent value was
equalled or exceeded decreased from the comparable analysis in Table IV-2
an average for all
sites of 311 hours or 19.5 hours per sector.
apparent that the magnitude
of the effect of meander
is site
It
by
is also
and direction
dependent.
3.
Selection of the Sector Probability Level
To consider
the
variability
of
atmospheric
dispersion
conditions
and
wind
direction frequencies among 16 sectors from site to site in a consistent manner, the X/Q value exceeded for a specified fraction of the time in each sector should be considered.
Since the direction-independent approach utilizes a
constant probability (5 percent)
tire site,
that is equalled or exceeded around the en-
this can be used as a point of departure for selecting
a constant
level of probability for considering X/Q values in each of the 16 directional
sectors.
This would result in the determination
of 16 X/Q values (one in each
sector) which are exceeded no more than some percentage of the total time in
each
sector.
The
highest
of these 16
X/Q values
determining compliance with 10 CFR Part 100.
can then
be selected for
This procedure ensures that all
sites are evaluated on a consistent probabilistic basis.
Because the variable boundary distance concept,
is
like the directional
a conceptual change from the direction-independent
methodology,
concept,
both these
changes will
total
have to be considered in the selection of a "percentage of the
time" that will be used to determine the controlling X/Q value in each
sector.
However,
physical
characteristics of dispersion
since meander is credit to be given to better represent the
and not a conceptual
change,
it
is not
used for this determination.
To obtain a controlling sector percentile value consistent with the directionindependent 5 percent
value for the site,
the number of hours the 5 percent
X/Q value is exceeded in each of the 16 sectors for 18 of the sites, including
IV - 9
variable site boundaries
(Table IV-3)
was examined.
tor at each site that the direction-independent
From these data the sec-
5 percent X/Q value was ex-
ceeded the greatest number of hours was chosen as the worst sector and plotted
in Figure IV-l.
Figure IV-1 shows that,. on the average
direction-independent
(geometric mean),
the
5 percent X/Q is equalled or exceeded approximately 0.6
percent (about 53 hours) of the total time in the worst sector.
is a large spread in the data,
Because there
it was determined that the 0.5 percentile level
(about 44 hours)
in the Regulatory Guide 1.145 methodology would be reasonably
consistent
the
with
5
percent
value
in
the
direction-independent
approach
while not implying more refinement in the selection process than what existed.
This means the 0.5 percent X/Q value is selected from each of the 16 sectors,
and
the highest of these
(i.e.,
the critical
sector)
is
used
to
determine
compliance with 10 CFR Part 100.
However,
mined
in unusual
by
the
conservative.
siting situations
Regulatory
Guide
To avoid this,
1.145
it
is possible that a X/Q value deter-
methodology
may
not
be
sufficiently
a 5 percent overall site (based on total obser-
vations) X/Q value is also calculated considering variable site boundaries and
meander.
than it
4.
If this X/Q value is
is used to represent the diffusion conditions at the site.
Overall
Table
IV-5
independent
(i.e.,
greater than the 0.5 percent sector X/Q value,
Impact of the Regulatory Guide 1.145 Methodology
shows
a comparison
approach
and
the
of X/Q
complete
with direction dependency,
Regulatory Guide
1.145
approach,
based on the 0.5 percent value,
Guide 1.145 approach
produced
values
selected
Regulatory
Guide
variable boundaries,
the highest
is presented
using
1.145
direction-
methodologies
and meander).
X/Q value
in this
the
for
all
table.
For the
directions,
The Regulatory
X/Q values which were about 70% of those pro-
duced by the direction-independent
approach.
of the
decrease ranged from of a factor
average
decrease of 1.4.
For the 21 sites,
the magnitude
of 1.1 to a factor of 2.2 with an
At only one site,
crease (by about a factor of 1.3).
IV - 10
did the selected X/Q value
in-
PERCENT OF TOTAL TIME
.50
.25
I
.75
1.00
1.25
I
I
I
I
R F
RF FFF
V
R
V
C
CRVCV
Geometr
0
(53Hr-s
,r-0. 6%)
C
1.70
1.50
R
C
Mean
H-H
0
21
0! 400
30
59
50
[
60
70
80
90
10I
100
11
110
1
120
I
130
I
140
HOURS
FIGURE IV-1.
Number- of Hour-a the 5 Per-cent
Relative Concentr-ation is
Exceeded in the Wor-st SectorUsing the R.G..
145 Methodology
With a Var-iable Site Boundar-y
and No Meander-. Data ar-e
Plotted as Site Types.
Key
Site Type
C
F
R
V
Coastal
Flat
Rolling
Valley
150
Table IV-5
Comparison Between the Past and Regulatory Guide 1.145 Methodology
Exclusion Area Boundary
Past Model
Site
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
(5% X/Q)
4.2
1.6
4.3
2.6
1.5
1.4
6.2
1.8
1.1
1.2
2.2
1.4
1.4
9.9
1.7
4.2
9.6
6.6
9.6
8.2
1.9
-4*
-3
-3
-4
-3
-3
-3
-4
-3
-3
-4
-3
-3
-4
-4
-4
-4
-4
-4
-4
-3
Regulatory Guide 1.145 Model
Critical Sector X/Q
2.9
1.4
2.2
1.6
1.2
1.2
5.2
1.3
6.5
5.7
1.8
1.1
6.4
7.1
1.6
3.4
8.7
8.8
7.9
6.1
1.7
-4
-3
-3
-4
-3
-3
-3
-4
-4
-4
-4
-3
-4
-4
-4
-4
-4
-4
-4
-4
-3
Ratio (Past/R.G. 1.145)
1.4
1.1
1.9
1.6
1.2
1.2
1.2
1.4
1.7
2.1
1.2
1.3
2.2
1.4
1.1
1.2
1.1
0.7
1.2
1.3
1.1
1.4
Average
*X/Q = 4.2 x 10-4 sec/m3
IV-12
lable
IV-6
presents
independent
a comparison
of the percent of the time the direction-
approach and the Regulatory Guide 1.145
exceeded at the actual
EAB.
approach X/Q values
are
Note that the X/Q value selected by the Regula-
tory Guide 1.145 approach for each site is actually exceeded between 0.4 percent and 3.4 percent
of the time around the entire site, averaging about 1.8
percent for all 18 sites.
X/Q,
calculated at
exceeded
less
For comparison,
an assumed
than 5 percent
circular
of
the direction-independent
exclusion
the time
around
area boundary,
the actual
EAB,
5 percent
is
actually
averaging
about 3.6 percent for the 18 sites examined.
5.
Conclusions
The Regulatory Guide 1.145 approach permits consideration of the actual variations of atmospheric dispersion conditions and wind frequencies as a function
of direction from the plant, as well
of site shape.
mospheric
conditions.
as allowing for more complete utilization
This methodology also incorporates
diffusion tests
The approach
the results of recent
to better define
dispersion
is
improvement
a significant
atmospheric dispersion characteristics
at reactor sites.
during
at-
low wind speed
in the evaluation
of
The methodology also
allows for a more consistent evaluation from site to site by ensuring that the
X/Q
more
value
used for evaluating
plant design will be equalled
than 0.5 percent of the time
(44
hours/year)
exclusion area boundary for any reactor site.
IV - 13
at
or exceeded
any point
around
no
the
Table IV-6
Percent of the Time the X/Q Calculated by the Indicated Methodology
is Exceeded Over the Actual Exclusion Area Boundary
Past Approach
Si te
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Average
(5% X/Q)
Regulatory Guide 1.145
(0.5% maximum sector)
4.4
3.5
1.7
3.0
3.3
3.1
2.3
3.3
3.0
3.0
4.2
4.0
2.4
5.0*
4.8
4.5
4.4
4.8
2.7
1.3
1.7
2.1
1.2
0.4
1.2
1.0
2.4
3.4
2.6
0.9
2.0
1.8
2.6
1.9
2.2
1.4
3.6
1.8
*Circular Boundary
IV-14
REFERENCES
1.
Regulatory
Guide
1.145,
Dispersion
"Atmospheric
Models
for
Potential
Consequence Assessments at Nuclear Power Plants," USNRC,
Accident
Issued
for Comment, August 1979.
2.
Guide
Regulatory
"Assumptions
Rev.
Regulatory
1.4,
Guide
"Assumptions
J.J.,
et
al.,
Used
for
Evaluating
of Distance
"Calculation
Potential
Power
and
March
USAEC,
1962.
6.
Regulatory Guide 1.23,
7.
Gifford,
F.A.,
Jr.,
"Onsite Meteorological Programs," USNRC.
"An
Outline
Layers of the Atmosphere,"
1968,
of Theories
Dispersion of Tracer Gas at the Proposed
Power Station,
Preliminary Safety Analysis
Amendment 24,
Dockets 50-458 and 50-459,
Metropolitan
Edison
Gas
Inversion
50-289,
in the Lower
Chapter 3 in Meteorology and Atomic Energy -
Gulf States Utilities Company,
Tracer
of Diffusion
Slade, Ed.)
(D.H.
River Bend Nucleaer
10.
for
Information Document 14844,
"Code of Federal Regulations," Title 10-Energy, Part 100.
9.
the
Factors
5.
8.
Potential
the
2, June 1974.
Test Reactor Sites," Technical
23,
Evaluating
of a Loss of Coolant Accident for Pressurized
Consequences
Water Reactors," USNRC, Rev.
DiNunno,
for
2, June 1974.
Reactors," USNRC,
Radiological
4.
Used
Consequences of a Loss of Coolant Accident for Boiling Water
Radiological
3.
1.3,
Company,
at Three Mile
Conditions,
Final
Report,
1974.
Atmospheric
Island Nuclear
Diffusion
Station
Safety Analysis Report,
Experiments
Under
with SF6
Low Wind
Amendment 24,
Speed
Docket
1972.
Project Management
Corporation,
Clinch River Breeder Reactor Plant Envi-
ronmental Report, 1975.
IV - 15
REFERENCES (continued)
11.
et
G.E.,
Start,
Diffusion, NOAA Technical Memorandum ERL ARL-69,
12.
Start,
sion,
13.
et
G.E.,
al.,
Building Wake
H.E.,
pheric
Contaminants,"
Fuquay,
Exposures
Diffu-
November 1980.
C.L.
from
Data," J. Appl.
Proceedings
of
the First
C-33 to C-55,
pp.
National
Conference
American Meteorological
on
Society,
October 1957.
Conn.,
J.,
on Atmoshperic
"A Practical Method For Estimating the Dispersal of Atmos-
Cramer,
Hardford,
November 1977.
Effects
NOAA Technical Memorandum ERL ARL-91,
Applied Meteorology,
14.
EOCR
on Atmospheric
Effects
Seco Building Wake
Rancho
al.,
Simpson,
Sources
Near
Meteorology,
and W.T.
the
Hinds,
Ground
3(6):761-770.
IV - 16
"Predicton
Based
on
of Environmental
Hanford
Experimental
NRC
1. REPORT NUMBER (Assignedby DOC)
FORM 335
NUREG/CR-2260
U.S. NUCLEAR REGULATORY COMMISSION
(777)
NUS-3854
BIBLIOGRAPHIC DATA SHEET
4. TITLE AND SUBTITLE (Add Volume No., if
ppropriare)
Technical Basis for Regulatory Guide 1.145,
2. (Leave blank)
Atmospheric
Dispersion Models for Potential Accident Consequence
3. RECIPIENT'S ACCESSION NO.
Assessmentsat Nuclear Power Plants
5. DATE REPORT COMPLETED
7. AUTHOR(S)
YEAR
MONTH
W. G. Snell and R. W.1Jubach
.1Ql1 y
9. PERFORMING ORGANIZATION NAME AND MAILING ADDRESS (Include Zip Code)
DATE REPORT ISSUED
NUS Corporation
4 Research Place
October
Rockville, Maryland
1
YEAR
MONTH
20850
1981
6. (Leave blank)
B. (Leave blank)
12. SPONSORING ORGANIZATION NAME AND MAILING ADDRESS (Include Zip Code)
10. PROJECT:TASK'WORK UNIT NO.
Office of Nuclear Regulatory Research
Division of Health, Siting and Waste Management
11.
U.S. Nuclear Regulatory Commission
Washington, DC 20555
13. TYPE OF REPORT
CONTRACT NO.
FIN B7116
PE R I OD COV E RE D (Inclusive dares)
NUREG/CR
14. (Leave blank)
15. SUPPLEMENTARY NOTES
16. ABSTRACT 1200 words or less)
Regulatory Guide 1.145, Atmospheric Dispersion Models for Potential Accident
Consequence Assessmentsat Nuclear Power Plants, presents several substantial
changes in the previous methodology of atmospheric dispersion analyses described in
Regulatory Guides 1.3 and 1.4.
This new methodology discussed in Regulatory Guide
1.145 includes, 1) the reduction in estimated ground-level concentrations due to
plume meandering during the occurrence of stable atmospheric stability conditions and
light wind speeds, and 2) the recognition that atmospheric dispersion conditions
are directionally dependent.
As a result of these developments, the NRC Meteorology
Staff conducted a parametric study to examine the consequences of these changes on
previous and future licensing activities.
This parametric study was instrumental in
the determination of appropriate probability levels for the risk assessment
methodology discussed in the guide.
The technical basis for the new methodology and
the results of the parametric study are dOcumented in this NUREG.
This documentation
includes the relationship of the new approach to the previous methodology.
17. KEYWORDS AND DOCUMENT ANALYSIS
17a. DESCRIPTORS
17b. IDENTIFIERS/OPEN-ENDED TERMS
18. AVAILABILITY STATEMENT
19. SECURITY CLASS (This report)
Unclrifi
N
Unlimited
ORi
N PC FORM 335 (7-7 7)
prl
20. SECURITY CLASS (This page)
UncF
21. NO. OF PAGES
fi In
22. PRICE
s