ML20083Q501

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Rev 1A to Nuclear Guide 1.111, Methods for Estimating Atmospheric Transport & Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors
ML20083Q501
Person / Time
Site: Oconee, Mcguire, Catawba, McGuire, 05000000
Issue date: 01/06/1983
From: Edmonds R
DUKE POWER CO.
To:
Shared Package
ML20083Q427 List:
References
1.111, NUDOCS 8302250417
Download: ML20083Q501 (49)
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Text

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. FORM NG-1 REV 0

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DUKE POWER CDMPANY  : Page 1 of 26 Nuclear Guide 1.111 NUCLEAR GUIDE I Effective Date 1/6/83 Revisinn lA  ;

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2 Methods for Estimating Atmospheric Transport and Dispersion of

Title:

Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors 3

Reference NRC Regulatory Guide Number 1.111 Revision 1 4 Disposition

  • of Current Disposition of Previous RG Revisions Plants Affected This RG Revision Revision Number Disposition
  • O oconee .

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E McGuire Rewritten 1 Rewritten E Catawba Rewritten 1 Rewritten E Project 81 Rewritten 1 Rewritten i O

  • Disposition is either " Adopted", " Partial Compliance", or "Not Applicable".

If " Partial Compliance" is indicated, attached From NG-1A.

5 Originated By: Coordination With: 6 Reviewed By:

Name 7 ,, h - STA M[ RFE tRH Dept .h n h 1 -r: -

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4 FORM NG-1A REV 0 ,

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( 1 DUKE POWER COMPANY Page 2 of 26 Nuclear Guide 1.111 .

f NUCLEAR GUIDE Revision lA 2

Sumary of Alternatives taken to Reculatory Guide Refer to pages 3-25 of Nuclear Guide for complete rewrite of July,1977 Regulatory Guide. Rewrite based on March,1976 version of Regulatory Guide.

4 3

Alternatives (Rewrite the affected Regulatory Guide Section below. Continue on additional sheets as necessary. Position statements should directly correspond to the affected Reg Guide section or be a continuation of the Reg Guide format.)

!' Refer to pages 3-25 of Nuclear Guide for complete rewrite of current Regulatory G'uide. Rewrite based on March,1976 version of Regulatory Guide.

4 Justification (Must be sufficiently detailed to permit evaluation by Department

, heads and NRC)

The present Duke Nuclear Guide incorporates certain aspects of the NRC Regulatory Guide 1.111, Revision 1. dated July,1977.

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TABLE OF CONTENTS ~

_Pjygg A. INTRODUCTION........................................................ 1.111-5 B. DISCUSSION.......................................................... 1.111-5

1. Diffusion Mode 1s................................................ 1.111-5
a. Variable Trajectory Models.................................. 1.111-6
b. Straight-Line Trajectory Model s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-6

, 2. Release Mode.................................................... 1.111-6

3. Removal Mec hani sms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 -7 C. REGULATORY P0SITION................................................. 1.111-7
1. Atmospheri c Transport and Diffusion Model s . . . . . . . . . . . . . . . . . . . . . . 1.111-7
a. Parti cl e-i n-Cel l (PIC) Mode 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 -7
b. Puff Advecti on Mode 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 -8
c. Strai ght-Li ne Ai rfl ow Mode 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-9
2. Source Configuration Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-11 1 .
a. El ev a ted Rel ea s es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-11
b. Rel eases Other Than El evated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-12
c. Building Wake Correction..................................... 1.111-12
3. Removal Mecha ni sm Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-13
a. Radioactive Decay............................................ 1.111-13 i b. Dry Deposition............................................... 1.111-13 i
c. Wet Deposition............................................... 1.111-14
d. Depo s i ti on ov e r Wa te r. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-14
4. Meteo rol ogi cal Data for Model s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-14 D. IMPLEMENTATION....................................................... 1.111 REFERENCES............................................................... 1.111-16 f

1.111-3

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LIST OF FIGURES

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Figure Page

1. Open Terrain Correction Factor................................. 1.111-17
2. Verti cal Standard Devi ati on of Material i n Pl ume. . . . . . . . . . . . . . . 1.111-18
3. Pl ume Depl etion Effect for Ground Level Rel eases. . . . . . . . . . . . . . . 1.111-19
4. Plume Depletion Effect for 30m Releases. . . . . . . . . . . . . . . . . . . . . . . . 1.111-20
5. Pl ume Depletion Effect for 60m Releases. . . . . . . . . . . . . . . . . . . . . . . . 1.111-21
6. Plume Depletion Effect for 100m Releases. . . . . . . . . . . . . . . . . . . . . . . 1.111-22
7. Relative Deposition for Ground Level Releases. . . . . . . . . . . . . . . . . . 1.111-23
8. Relative Deposition for 30m Rel eases. . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-24
9. Relative Deposition for 60m Releases........................... 1.111-25
10. Relative Deposition for 100m Rel eases. . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-26 i

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A. INTRODUCTION Sectior. 20.106. " Radioactivity in Effluents to Unrestricted Areas." of 10 CFR Part 20 .

" Standards for Protection Against Radiation." establishes limits on concentrations of radio-active material in effluents to unrestricted areas. Paragraph 20.1(c) of 10 CFR Part 20 states that licensees should, in addition to complying with the limits set forth in that part, make every reasonable effort to maintain radiation exposures, and releases of radioactive materials in effluents to unrestricted areas, as far below the limits specified in that part as is

, reasonably achievable.

Section 50.34e. " Design Objectives for Equipment to Control Releases of Radioactive Material in Effluents - Nuclear Power Reactors." of 10 CFR Part 50. " Licensing of Production and Utiliza-tion Facilities." sets forth design objectives for equipment to control releases of radioactive material in effluents from nuclear power reactors. Section 50.36a. " Technical Specifications on Effluents from Nuclear Power Reactors." of 10 CFR Part 50 further provides that in order to

  • keep power reactor effluent releases as low as is reasonably achievable, each license authorizing operation of such a facility will include technical specifications that require establishment of operating procedures for effluent control, installation and maintenance of effluent control equipment and reporting of actual releases.

' Appendix 1. " Numerical Guides for Design Objectives and Limiting Conditions for Operation to Meet the Criterion 'As Low As Is Reasonably Achievable' for Radioactive Material in Light-

  • Water-Cooled Nuclear Power Reactor Effluents." to 10 CFR Part 50 provides numerical guidance for those design objectives and limiting conditions for operation for light-water-cooled

, nuclear power plants. To implement Appendix 1. the NRC staff has developed a series of guides providing acceptable methods for the calculation of effluent releases, dispersion of the effluent in the atmosphere and water bodies, and associated radiation doses to man. This guide describes basic features of calcu14tional models and assumptions for the estimation of atmospheric transport and dispersion of gasecus effluents in routine releases from land-based light-water-cooled reactors.

j The procedures and models provided in this guide will be subject to continuing review by t

the staff with the aim of providing greater flexibility to the applicant in meeting the require-

, ments of Appendix 1. As a result of such review, it is expected that alternative acceptable l methods for calculation will be made available to applicants and that calculational procedures t

found to be unnecessary will be eliminated.

i This guide supersedes portions of Regulatory Guide 1.42. Revision 1. " Interim Licensing Policy on as Low as Practicable for Gaseous Radiciodine Releases from Light-Water-Cooled Nuclear Power Reactors." which is being withdrawn.

8. DISCUSSION The transport and dilution of radioactive materials in the form of aerosols vapors, or gases released into the atmosphere from a nuclear power station are a function of the state of the atmosphere along the plume path, the topography of the region, and the characteristics of

, the effluents themselves. For a routine airborne release, the concentration of radioactive l material in the surrounding region depends on the amount of effluent released; the height of the release; the momentum and buoyancy of the emitted plume; the windspeed, atmospheric stability, and airflow patterns of the site; and various effluent removal mechanisms. Geographic features such as hills, valleys, and large bodies of water greatly influence dispersion and airflow l patterns. Surface roughness, including vegetative cover, affects the degree of turbulent mixing.

I Sites with similar topographical and climatological features can have similar dispersion and airflow patterns. but detailed dispersion patterns are usually unique for each site.

l Most gaseous effluents are released from nuclear power plants through tall stacks or vents I

near the tops of buildings. Certain plant designs can result in other release pathways. For example, auxiliary equipment and major components such as turbines may be housed outside build- '

ings; releases from these components could occur near orou W level.

1 Diffusion Models Atmospheric diffusion modeling has developed along two basic approaches: gradient-transport theory and statistical theory. Gradient-transport theory holds that diffusion at a fixed point

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in the atmosphere is proportional to the local c:ncentration gradient; this theory attempts to determi.ie momentum or material fluxes at fixed peints. The statistical (e.g., Gaussian) approach attempts to determine the histories of individual particles and the statistical properties necessary to represent diffusion. Input data for models based on either approach include wind-( speed, atmospheric stability, and airflow patterns in the region of interest. Several basic models have been developed using these approaches. These models vary according to their treat-ment of the spatial changes of input data and the consideration of either a variable or a straight-line trajectory model,

a. Variable Trajectory Models Variable trajectory models allow conditions to vary spatially over the region of interest; thus, they require regional data. The number of sampling locations needed to approxi-mate the regional airflow depends on the meteorological and topographical characteristics of that region.

The particle-in-cell model is a variable trajectory model based on the gradient-transport approach. In this model " particles" representing the effluent mass are released in groups over the time period of interest. The particles move at the effective transport velocity of the windficw field into which the effluent is released. The effective velocity is determined l

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'. by the mean and turbulent windflows within the field. The number of particles located at any given time in each cell (volume) of a fixed coordinate grid determines the effluent concen-tration. Concentration averages are determined from the total number of particles that pass through a cell during the time of interest.

The puff advection model is another variable trajectory model but is based on the statistical approach to diffusion. This model approximates a continuous release by dividing a plume into a sufficient number of p1 me segments (puffs). These puffs are released at specified f intervals and are trackeJ over the region of interest. The advective transport of puff centers I and the diffusion of effluent puffs about their individual centers cause the dispersion of the I plume effluent. Concentration averages are calculated by detemining the contribution each puf' makes to the grid of points over which it passes.

b. $traiet-line Trajectory Models Straight-line trajectory models assume that the airflow transports and diffuses effluents along a straight line through the entire region of interest in the airflow direction

[ at the release point. A comonly used version of this model is the Gaussian straight-line t

trajectory model. In this model, the windspeed and atmospheric stability at the release point

' are assmed to determine the atmospheric dispersion characteristics in the direction of airflod.

These basic models can be modified to account for various modes of effluent release and for effluent removal mechanisms.

2. Release Mode At ground-level locations beyond several miles from the plant, the annual average concen-trations of effluents are essentially independent of the release mode; however. for ground-level concentrations within a few miles. the release mode is very important.

For a typical nuclear plant gaseous effluents released from tall stacks generally produce

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i I peak ground level air concentrations near or beyond the site boundary; near-ground-level releases usually produce concentrations that monotonically decrease from the release point to all locations downwind. Some releases tend to produce intermediate concentrations. Under certain conditions.

l the effluent plume may become entrained in the aerodynamic wake of the building and mix rapidly down to ground level; under other conditions the full effect of the elevation of the release

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may be realized.

l Methods have been developed to estimate the effective release height for calculations of effluent concentrations at all downwind locations. The important parameters in these methods l include the initial release height. the location of the release point in relation to obstruc-l tions, size and shape of the release point, the initial vertical velocity of the effluent the heat content of the effluent, ambient windspeed and temperature, and atwspheric stability.

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For those effluents that are entraired into the aerodynamic wake of a building, mixing of the effluent into the wake is usually 6:.sumed. This mixing 2cne can constitute a plume with an

  • f 4] initial cross section of one-half or mort of the cross-sectional area of the building.
3. Removal Mechanisms As the effluent travels from its release point, several mechanisms can work to reduce its concentration beyond that achieved by diffusion alone. Such removal mechanisms include radio. "

active decay and dry and wet deposition.

nadioactive decay is dependent on the half-life and the travel time of the radioactive effluent. All effluents can undergo dry deposition by sorption onto the ground surface however, the dry deposition rate for noble gases, tritium, carbon-14. and nonelemental radio-iodines is 50 slow that depletion is negligible within 50 miles of the release point. Elemental radiofodines and other particulates are much more readily deposited. The transfer of elemental radiciodines and particulates to a surface can be quantified as a transfer velocity (where con-

  • centration x transfer velocity = deposition rate). There is evidence that the transfer velocity is directly proportional to windspeed and, as a consequence, th2 rate of deposition is independent of windspeed since concentration in air is inversely proportional to windspeed.

At most sites precipitation occurs during a small portion of the year; therefore, for long-term averages, dose calculations considering only dry deposition are not significantly changed by the consideration of wet deposition. However, wet deposition can be an important factor in dose calculations at sites where a well-defined rainy s,eason corresponds to the local grazing season.

Deposition of radionuclides over large bodies of water is not considered in this guide.

Such deposition should be analyzed on a case-by-case basis.

C. REGULATORY N SITION This sectien identifies types of atmospheric transport and diffusio, 1els, source config-uration and removal mechanism modifications, and input data that are acceptable to the NRC staff

, for use in providing assessments of potential annual radiation doses to the public resulting from routine releases of radioactive materials in gaseous effluents.

Models proposed by the applicant and accepted by the NRC staff will be used by the staff in

.4 determining environmental technical specifications.

( 1. Atmospheric Transport and Diffusion Models The following types of atmospheric transport and diffusion mocels can be modified for elevated sources and for effective area sources created when effluent is trapped in the building i wake cavity in accordance with the source configuration considerations presented in regulatory position 2. Plume rise due to momentum or buoyancy effects can also be incorporated into the calculations. Radiological decay and dry and wet deposition consistent with the guidelines presented in regulatory position 3. should also be cor.sidered.

, a. Particle-in-Cell (PIC) Model The basic equation for each " particle" group in this variable tra,jectory model, modified from Sklarew (Ref.1), is:

6(D/6t + v.V(D = 0 (1) i where i

t is the travel time; Y is the velocity vector for effective mean wind transport. which includes the mean flow component. Y, and the turbulent flow component. V' such that V = Y+V'; and (D is the average atmospheric concentration produced by a group of particles.

, Concentration averages for long time intervals are obtained by suming all " particles" passing through each grid cell during the period of interest.

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The PIC model incorporates spatial and temporal variations of wind direction,

( windspeed, atmospheric stability, and topography to define airflow and atmos-pheric diffusion rates. The representativeness of the input data determines -

the accuracy of estimates (i.e., fewer data acquisition locations tend to increase the uncertainty of the estimates); therefore, detailed discussion of the applice.bility and accuracy of the model and input data used should be provided.

b. Puff Advection In this model, the transport of a puff is determined from a horizontal wind field which can vary in time or in space. The diffusion of each puff can be determined from the Gaussian diffusion model below, according to Start and Wendell (Ref. 2):

2 2 x/Q=2[(2x)3/2"Hz] exp[-1/2(r 7,2 + h 7,2)] (2) where r 2 = (x - ut) +y and o

H " 'y " 'x and where h, is the effective release height; Q is the effluent emission over the time interval; t is the travel time; u is the mean windspeed at the height of the release point; x is the dirtar. e from center cipuff along the direction of flow; y is the distance from center of puff in the crossflow direction; e

x is the plume spread along the direction of flow;  !

o y is the lateral plume spread; o

g is the vertical plume spread; and

! x is the atmospheric concentration of effluent in a puff at l ground level and at distance x from the puff center.

Concentration averages for long time intervals should be calculated by suming the concentrations of individual puffs for the grid of points over which they pass.

The number of puffs and the plume spread parameters (o , o , and o ) should be selected such that the resulting concentration estimate isY represefitative of the concentration from a continuous point source release. Puffs should be followed in the computational scheme until they are beyond the region of interest or until

["- their peak concentration falls below a specified value.

The puff advection model incorporates spatial and temporal variations of wind direction, windspeed, and atmospheric stability to define the transport and 1.111 8

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e diffusion rate of each puff. The effectiveness of the meteorological input data in defining atmospheric transport and diffusion conditions is dependent

, on the representadveness of these data and t.N complexity of the topography in the site region; therefore, a detailed discussion of the applicability and accuracy of the model and input data used should be provided. ,

c. Straight-Line Airflow Model Sector Average:

The equation for this model, as presented by Sagerdorf (Ref. 3), is:

2 (x/Q')D = 2.032.{j 93[NXu n rj gj(X)]~Iexp[-h/20j(X)] (3) z where h, is the effective release height (see regulatory position 2);

n is the length of time (hours of valid data) weather conditions 93 are observed to be at a given wind direction, windspeed class, i, and atompsheric stability class, j; N is the total hours of valid data; ug is the midpoint of windspeed class, 1, at a height representative of release; oj(X) z is the vertical plume spread without volumetric correction at distance, X, for stability class, j (See Figure 1);

! I zj(X) is the vertical plume spread with a volumetric correction (see l regulatory position 2.c) for a release within the building wake cavity, at a distance, X, for stability class, j; othemise I,3(X)= zj(X);

(x/Q3D is the average effluent concentration, x, normalized by source strength,Q1, at distance, X, in a given downwind direction, D; and 2.032 is(2[w)l/2 divided by the width in radians of a 22.5* sector.

Time Series:

l The equations for this model are:

For the ground release portion:

.F y

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+

] 3 (X/Q)g = 2" I"'y z + CA)

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For the elevated release portion: q,. T F -y 1 -H 2 (X/Q), = u wo **P l (

2 yz _ (2oy 3

)+**P g 2cz " 1 (3b) l (X/Q)9 and (X/Q) are the normalized average concentration frora plumes at ground leve1 and elevatId levels, respectively, 1.111-9

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F and F are the fractions of the plume which are ground level and elevated, rEspectiIely. .

u2 and u are the low level and high level average wind speeds, respectively (m/sec.)2 A minimum value of .447 m/sec is assumed.

CA is the mixing zone for the aerodynamically entrained effluent. It is one-half the cross-sectio.'.al area of the adjacent containment structure nonnal to the wind.

Yi and Y2 are the lateral distances of the receptor from the wind direction vectors u3 and uz , respectively, i H is the plume height considering all corrections as discussed above (m).

oy and az are the crosswind and vertical plume standard deviations (m) which

are functions of atomspheric stability and distance downwind. Stability categories are determined by vertical temperature gradient according to Regulatory Guide 1.23. Standard deviation values are consistent with D. B. Turner (Ref. 3).

l The factor (wo og + CA) is a measure of plume spread. This factor is restricted tobenogreat5rthan(3noo)* j z l Since the straight-line flow model does not consider the effects of spatial -

l and temporal variations in airflow in the region of the site, appropriate adjustments to the calculated (x/Q')n values should be made to account for these effects. There are three basic categories of regional airflow characteristics l that are related to topography:

! (1) Inland in open terrain, including gently rolling hills, with airflow I

dominated almost entirely by large-scale weather patterns.

s (2) In pronounced river valleys, with airflow patterns largely dominated by terrain, and (3) Along and near coasts of large bodies of water, with considerable land-water boundary layer effects on airflow patterns.

Adjustments, based on specific data and studies that characterize regional air-flow patterns, should be made in Equations (3), (3a), and (3b) to account for these topographical effects. Alternatively, the following adjustments and considerations may be used for open terrain and river valley site locations.

l These factors are based on a conservative assessment of preliminary comparisons l between variable and straight-line trajectory models.

(1) Sites in o)en terrain. The right side of Equations (3), (3a) and (3b) should be multiplied >y the correction factors shown in Figure A.

(2) Sites in river valleys. For downvalley airflow, the right side of Equations

. (3), (3a), (3b) should be multiplied by 5 for distances less than 20 miles. For upvalley airflow, the right side of Equations (3), (3a), and (3b) should be multiplied by 1.5 for all distances. For downvalley airflow beyond 20 miles and crossvalley

{- flow, no correction should be applied. For meandering valleys, additional adjus -

ments should be made on a case-by-case basis to ensure that individual doses and popluation doses at locations of interest are not underestimated.

1.111-10

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For coastal sites, specific correction factors should be developed and applied for each site and release point. Some factors that should be considered are -

the characteristics of sea or lake breezes, the variation of the mixing layer height with time and distance from shore, and the effects of shoreline bluffs or dunes. These factors should be considered in relation to the locations of the meteorological towers, plant structures, and release points with respect to the land-water boundary layer.

For all sites, a detailed discussion of the applicability and accuracy of the model and input data should be provided.

2. Source Configuration Considerations The actual height above ground of the gaseous effluent plume should be con-sidert.d in making estimates of average effluent concentrations downwind from the release points. An acceptable method to determine the effective plume height is described below,
a. Elevated Releases For effluents exhausted from release points that are higher than twice the height of adjacent solid structures, the effective release height (h,) is detemined (Refs. 2,13) from:

h, = h s +h pp +h pr -c

, -htR-c>h _ s 2

(4) j where c is the correction for low relative exit velocity (see below);

h, is the effective release height; h is the rise of the plume above the release point, according pr to Sagendorf (Ref. 3), whose treatment is based on Briggs

(Ref.4);

h is the physical height of the release point (the elevation s of the stack base should be assumed to be zero); and h

t is the height of the highest terrain feature in the vicinity b of the receptor (h t[ ..must be greater than or equal to zero).

A When the vertical exit velocit is less than 1.5 times the horizontal windspeed, a correction for downwash is natracted from Equation (4), according to Gifford (Ref.5):

c = 3(1.5 - W,/ii)d (5) where c is the downwash correction; d is the inside diameter of the stack or other release point; li is the mean windspeed at the height of release; W, is the vertical exit velocity of the plume.

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.' b. Releases Other Than Elevated For effluents released from points less than or equal to the height of adjacent .

solid structures, a ground-level release should be assumed (h, = 0).

For effluents released from vents or other points above adjacent solid structures, i but lower than elevated release points, the effluent plume should be considered as an elevated release whenever the vertical xexit velocity of the plume, W is at least five times the horizontal windspeed, u, at the height of release;,i.e.,

, as modified from Johnson et al. (Ref. 6):

W,6 3, 5.0 (6)

In this case, the release should be evaluated as described in regulatory position 2.a.

If W 6 is less than 1.0 or unknown, a ground-level release should be assumed (h,9 0).

l For cases where the ratio of plume exit velocity to horizontal windspeed is between one and five, a mixed release mode should be assumed, in which the plume is considered as an elevated release during a part of the time and as a ground-level release (h = 0) during the remainder of the time. An entrain-ment coefficient, E , modTfied from Reference 6, is determined for those cases inwhichW,6isbekweenoneandfive:

( Et = 2.58 - 1.58(W,6)for 1 < W,61 1 5 (7) and Et = 0.3 - 0.06(W,6) for 1.5 < W,61 5.0 (8)

The release should be considred to occur as an elevated release 100(1-Et) percent of the time and as a ground release 100Et Percent of the time.

Each of these cases should then be evaluated separately and the concentration calculated according to the fraction of time each type of release occurs. Wind-speeds representative of conditions at the actual release heights should be used for the times when the release is considered to be elevated. Windspeeds measured at the 10-meter level should be used for those times when the effluent plume is considered to be a ground release. If Equation (3) is used, the l adjustment described in regulatory position 2.c may be made for the ground release portion of the calculation.

c. Building Wake Correction For (3) thatground-level takes into releases only (h' initial mixing of the effluent plume within= 0), an consideration the building wake. This adjustment, according to Yanskey et al. (Ref. 7)should be in the fom of:

I,3(X) = (az j (X) + 0.5 D,2 7 ,)1/2 < k3(X) (9)

, .where

( D z

is the maximum adjacent building height either up- or downwind from the release point; X is the distance from the release point to the receptor, measured from the lee edge of the complex of adjacent buildings; 1.111-12

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oj(X) z is the vertical standard deviation of the materials in the

( plume at distance, X, for atmospheric stability class, j; and .

I,3(X) is the vertical standard deviation of plume material as above, with the correction for additional dispersion within the building wake cavity, restricted by the condition that I,)(X) 4 ,3(X) when (az j(X) + 0.5D2 /*)

  • zj(X).

Equation (3a) is appropriate for time series ground-level release calculations.

3. Removal Mechanism Considerations Radioactive decay and dry and wet deposition should be considered in radiological impact evaluations. Acceptable m thods of considering these removal mechanisms are described below.
a. Radioactive Decay For conservative estimates of radioactive decay, an overall half-life of 2.26 days is acceptable for short-lived . noble gases and of eight days for all iodines released to the atmosphere. Alternatively, the actual half-life of each radionuclide may be used. The decay time used should be the calculated time of travel between the source and receptor based on the air flow model used.
b. Dry Deposition ,

Dry deposition of elemental radioiodines and other particulates and attendant plume depletion should be considered for all releases. ,

Acceptable plume depletion correction factors and relative deposition rates are presented in Figures 2 through 9. These figures are based on the discussion of deposition in References 8 and 9.

l l Figures 2 through 5 illustrate an acceptable method for considering plume depletion effects for all distances from the source and atmospheric stability l

classes for ground and elevated release modes. After a given concentration is calculated using the models in regulatory position 1, the concentration should be corrected by multiplying by the fraction remaining in the plume, as deter-mined from these figures. In the time series approach, time averaged con-centrations are averaged by sector before the depletion correction is made.

Figures 6 through 9 show acceptable values of relative deposition rate (meters' )

i as a function of distance from the source and atmospheric stability for ground l .and elevated release modes. The relative de sition rate is the deposition rate

, per unit downwind distance (Ci/sec per meter divided by the source strength

( .(C1/sec).

To obtain the relative deposition per unit area (meters 2) at a given point in a given sector, the relative deposition rate must be (1) multiplied by the fraction of the release transported into the sector, determined according to 1.111- 13

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i~

the distribution of wind direction and (2) divided by an appropriate crosswind distance (meters), as discussed below.

Figures 6 through 9 are based on the assumption that the effluent concentration in a given sector is unifom across the sector at a given distance. Therefore, for the straightline airflow model, or for any model that assumes unifom concentration across the sector at a.given distance, the relative deposition rate should be divided by the arc length of the sector at the point being considered. In addition, for the straight-line airflow model, the relative deposition rate should be multiplied by the appropriate correction factor discussed in regulatory position 1.c.

c. Wet Deposition For long-tem averages, dose calculations considering dry deposition only are not usually changed significantly by the consideration of wet deposition.

However, the effects of wet deposition and attendant plume depletion should be considered for plants with predominantly elevated releases and at sites that have a well-defined rainy season corresponding to the grazing season.

Consideration of wet deposition effects should include examination of total precipitation, number of hours of precipitation, rainfall rate distributions, and the precipitation wind rose. If the precipitation data indicate that wet deposition may be significant, washout rates and attendant plume depletion should be calculated in accordance with the relationships identified by Engelmann (Ref.10).

I d. Deposition over Water For dispersion over small bodies of water, deposition may be assumed to occur at the same rate as over land. For calculations involving radionuclide trans-port over large bodies of water, deposition should be considered on a case-by-case basis.

4. Meteorological Data for Models Sufficient meteorological infomation should be obtained to characterize transport processes (i.e., airficw trajector, diffusion conditions, deposition characteristics, etc.) out to a distance of 50 miles (approximately 30,000 meters) from the plant. The primary source of meteorological information should be the onsite meteorological program (see Regulatory Guide 1.23, Ref.11).

Other sources should include nearby National Weather Service (NWS) stations, other well-maintenance meteorological facilities (e.g., other nuclear facilities, universities, or private meteorological programs), and satellite facilities.

Adequate characterization of transport processes within 50 miles of the plant may include examination of meteorological data from stations further than 50 miles when this infomation can provide additional clarification of the mesoscale transport process. To augment the_ assessment of atmospheric transport to distances of 50 miles from the plant, the following regional meteorological data, based on periods of record specified in Regulatory Guide 4.2 (Ref.12),

from as many relevant stations as practicable should be used:

( a. Windspeed

b. Wind direction
c. Atmospheric stability
d. Mixing height
e. Precipitation 1.111-14

3

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For. input to variable trajectory atmospheric transport models, measured hourly values of windspeed should be used. Calms (defined as hourly average wind- -

speeds below the starting speed of the anemometer) should be assigned a wind-speed of one-half of the starting speed of the anemometer. Hourly wind directions should be classed into at least the 16 compass ~ point sectors (i.e., 22.5 degree sectors, centered on true north, north-northeast, etc.) according to measured values averaged over the time interval.

For in as (1)put to the hourly straight-line measured valuesairflow model, windspeed or (2) windspeed data should classes divided be presented in accordance-with the Beaufort wind scale or other suitable calss division (e.g., a greater number of light windspeed classes should be used for sites with high frequencies oflightwinds). Wind directions should be divided into the 16 compass directions (22.5-degree sectors, centered on true north, north-northeast, etc.). If joint frequency distributions of wind direction and speed by atmospheric stability class, rather than hourly values, are used in this model, calms (defined as hourly average windspeeds below the starting speed of the vane or anemometer, whichever is higher) should be assigned to wind directions in proportion to the directional distribution within an etmospheric stability class of the lowest noncalm windspeed class. If hourly data are used, calms should be assigned to the recorded wind direction averaged over the time interval. The windspeed to be assumed for calms is one-half of the starting speed of the anemometer.

! Atmospheric stability should be detennined by vertical temperature difference l , (AT) between the release point and the 10-meter level, or by other well-documented parameters that have been substantiated by diffusion data. Accept-

, able stability classes are given in Reference 11.

Appropriate time periods for meteorological data utilization should be based

, on constancy of the source term (rate of release) and potential availability L of the receptor (i.e., man or cow). If emissions are frequent or continuous, annual data suninaries should be used. Other data time periods and atmospheric dispersion models should be used if emissions are infrequent and of short duration. These infrequent releases should be evaluated on a case-by-case basis unless such releases are restricted by technical specifications to periods when atmospheric conditions are more favorable than the average for the site. If such technical specifications are planned or exist, annual average data and annual average dispersion models may be used. For calculations of doses through the milk pathway, meteorological data for the cow grazing season only should be used.

D. Implementation The purpose of this section is to provide infomation to license applicants and licensees regarding the NRC staff's plans for implementing this regulatory 9uide.

This guide reflects current Nuclear Regulatory Commission practice. Therefore, except in those cases in which the license applicant or licensee proposes an acceptable alternative method, the method described herein for complying with

, specified portions of the Consnission's regulations is being and will continue

( to be used in the evaluation of submittals for operating license or construction pennit applications until tMs guide is revised as a result of suggestions from the public or additional staff review.

1.111-15

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REFERENCES

1. R. C. Sklarew, A. J. Fabrick, and J. E. Prager, "A Praticle-in-Cell Method for Numerical Solution of the Atmospheric Diffusion Equation and Applications to Air Pollution Problems," Final Report 3SR-844, Vol. 1. EPA Contract 68-02-0006,1971.
2. G. E. Start and L. L. Wendell, " Regional Effluent Dispersion Calculations Considering Spatial and Temporal Meteorological Variations," NQAA Tech Memo ERL-ARL-44, 1974.
3. J. F. Sagendorf, "A Program for Evaluating Atmospheric Dispersion from a Nuclear Power Station," NQAA Tech Memo ERL-ARL-42,1974.

4.- G. A. Briggs, " Plume Rise," AEC Critical Review Series, T.0-25075,1969.

5. F. A. Gifford, " Atmospheric Transport and Dispersion Over Cities,"

Nuclear Safety, Vol. 13, pp. 391-402, Sept.-Oct. 1972.

6. W. B. Johnson, E. Shelar, R. E. Ruff, H. B. Singh, and L. Salas, " Gas Tracer Study of Roof-Vent Effluent Diffusion at Millstone Nuclear Power Station," AIF/NESP-007b, Atomic Industrial Forum, Inc. ,1975.
7. G. R. Yanskey, E. M. Markee, Jr. , and A. P. Richter, "Climatography

( of National Reactor Testing Station," Idaho Operations Office, USAEC, ID0-12048, 1966.

8. E. H. Markee, Jr., "A Parametric Study of Gaseous Plume Depletion by Ground Surface Adsorption," in Proceedings of USAEC Meteorological Infomation Meeting, C. A. Mawson, Editor, AECL-2787, pp. 602-613,1967.
9. C. A. Pelletier and J. D. Zimbrick, " Kinetics of Environmental Radioiodine Transport Through the Milk-Food Chain," in Environmental Surveillance in the Vicinity of Nuclear Facilities, W. C. Reinig, Editor, Charles C. Thomas l

Publishers, Springfield, Ill.,1970.

10. R. J. Englemann, "The Calculation of Precipitation Scavenging," in Meteorology and Atomic Energy,1968, D. H. Slade Editor, USAEC TID-24190, pp. 208-221, 1968.

l "Onsite Meteorological Programs,"

l 11. Regulatory Guide 1.23 (Safety Guide 23).

! U. S. Nuclear Regulatory Commission, Washington, DC.

! 12. Regulatory Guide 4.2, " Preparation of Environmental Reports for Nuclear

! Power Stations," U. S. Nuclear Regulatory Commission, Washington, D.C.

13. B. A. Egan, " Turbulent Diffusion in Complex Terrain," Lectures on Air Pollution and Environmental Impact Analysis, American Meteorological Society, 1975.

1.111-16

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TABLE OF CONTENTS Pa9t A. INTn00uCTION...................................................................... _

1.111-5

8. DISCU5510N........................................................................ 1.111-5
1. Diffusion Models.............................................................. 1.111-5 a . Va ri a bl e Traj ectory Mode 1 s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-6
b. Cons ta nt Mea n Wi nd D i rec ti on Model s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-6
2. Release Mode.................................................................. 1.111-6
3. R emov a l Mec ha n i sms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-7 C. REGULATORY P051 TION............................................................... 1.111-7
1. Atmospheric Trans port a nd Di f fusion Model s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-7
a. Particle-in-Cell (PIC) Mode 1.............................................. 1.111-7
b. Plume Element Models...................................................... 1.111 8
c. Constant Mean Wind Direction Models....................................... 1.111-9 (f \ 2. Source Configura tion Considera tions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-10 l a. Elevated Releases......................................................... 1.111-10
b. Re l ea ses Other T han E1 eva ted. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-11
c. Butiding Wake Correction.................................................. 1.111-11
3. Remova l Mec ha ni sm Cons i ders ti c s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-12
a. Radioactive Decay..................................................:...... 1.111-12
b. Dry Deposition............... 1.111-12
c. Wet Deposition...............,.............................................

............................................. 1.111-12

d. De pa s i t i on Ov e r Wa t er. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-13
4. Me teo rol ogi ca l Da ts for Model s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-13 D. IMPLEMENTATION.................................................................... 1.111-14 REFERENCES...................................'.......................................... 1.111-15 e

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1.111-3

D f .t  :--

i LIST OF FIGURES Fleure h

1. Vertical Standard Deviation of Material in a P1ume.......................... 1.111-16
2. Plume Depletion Effect for Ground-Level Releases............................ 1.111-17
3. Pl ume Depletion E f fect for 30-m Relea ses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-18
4. Plume Depletion Effect for 60-m Releases..................................... 1.111-19
5. Plume Depletion Ef fect for 100-m Releases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-20
6. Rel a tt 4e WMsi tion for Ground-Level Releases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-21
7. Rela ti ve Depos i tion for 30-m Releases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-22
8. Relative Deposition for 60-m Releases........................................ 1.111-23
9. Rela tive Deposi tion for 100-m Relea ses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-24 l

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A. INTRODUCTION Section 20.106, " Radioactivity in Effluents to Unrestricted Areas." of 10 CFR Part 20

" Standards for Protection Against Radiation," establishes limits on concentrations of radio-active material in effluents to unrestricted areas. Paragraph 20.1(c) of 10 CFR Part 20 states that licensees should, in addition to complying with the limits set forth in that part, make every reasonable e* fort to maintain radiation exposures, and releases of radioactive materials in effluents to unrestricted areas, as far below the limits spetified in that part as is reason-ably achievable.

Section 50.34a. " Design Objectives for Equipment to Control Releases of Radioactive Material in Effluents - Nuclear Power Reactors " of 10 CFR Part 50 " Licensing of Production and Utillas-tion Facilities.* sets forth design objectives for equipment to control releases of radioactive material in effluents from nuclear power reactors. Section 50.36a, " Technical'5pecifications on Effluents from Nuclear Power Reactors," of 10 CFR Part 50 further provides that, in order to keep power reactor effluent releases as low as is reasonably achievable, each license author-izing operation of such a facility will include technical specifications that require establish-ment of operating procedures for effluent control, installation and maintenance of effluent control equipment, and reporting of actual releases.

Appendix I, " Numerical Guides for Design Objectives and Limiting Conditions for Operation to Meet the Criterion 'As Low As Is Reasonably Achievable' for Radioactive Material in Light-Water-Cooled Nuclear Power Reactor Effluents," to 10 CFR Part 50 provides numerical guidance for those design objecthes and limiting conditions for operation for light-water-cooled nuclear

, power plants. To implement Appendix I, the NRC staff has developed a series of guides providing acceptable methods for the calculation of ' effluent releases, dispersion of the effluent in the 4

atmosphere and water bodies, and associated radiation doses to man. This guide describes basic

. features of calculational models and assumptions for the estimation of atmospheric transport and

! dispersion of gastous effluents in routine releases from land-based light-water-cooled reactors.

The procedurcs and models provided in this guide will be subject to continuing review by the staff with the aim of providing greater flexibility to the applicant in meeting the require-4 ments of Appendix I. A: a result of such review, it is expected that alternative acceptable methods for calculation will be made available to applicants and that calculational procedures 3

found to be unnecessary will be eliminated.

This guide supersedes portions of Regulatory Guide 1.42. Revision 1. " Interim Licenshig Policy on As Low As Practicable for Gaseous Radiciodine Releases from Light-Water-Cooled Nuclear Power Reactors " which has been withdrawn (see 41 FR 11891, 3/22/76).

l*

B. 015CU5510N l

The transport and dilution of radioactive materials in the fom of aerosols, vapors, or gases released into the atmosphere from a nuclear power station are a function of the state of the atmosphere along the plume path, the topography of the region, and the characteristics of i the effluents themselves. For a routine airborne release, the concentration of radioactive i material in the surrounding region depends on the amount of effluent released; the height of the

release; the momentum and buoyancy of the emitted plume; the windspeed, atmospheric stability, and airflow patterns of the site; and various effluent removal mechanisms. Geographic features

! such as hills, valleys, and large bodies of water greatly influeace dispersion and airflow l patterns. Surface roughness, including vegetative cover, affects the degree of turbulent mixing.

Sites with sistlar topographical and climatological features can have similar dispersion and airflow patterns, but detailed dispersion patterns are usually unique for each site.

l Most gaseous effluents are released from nuclear power plants through tall stacks or vents near the tops of buildings. Certain plant designs can result in other release pathways. For example, auxiliary equipment and major components such as turbines may be housed outside build-ings; releases from these components could occur near ground level.

1. Diffusion Models

[t '? Atmospheric diffusion modeling has developed along two basic approaches: gradient-transport theory and statistical theory. Gradient-transport theory holds that diffusion at a fixed point

! M ines indicate substantive changes from previous issue.

. 1.111-5 l

,.-,,a--. - ,

..:.e.

_ Z..Ls.-.:...-.  :.---.-...-

~~

-= ---- . .1.-. .

I t'

f.

in the atmosphere is proportional to the local concentration gradient; this theory attempts to

  • detemine moments or material fluxes at fixed points. The statistical (e.g., Gaussian) approach
  • attempts to determine the histories of individual particles and the statistical properties necessary to represent diffusion. Input data for models based on either approach include wind-speed atmospheric stability, and airflow patterns in the region of interest. Several basic models have been developed using these approaches. These models very according to their treat-ment of the spatial changes of input data and the consideration of either a verfable trajectory model or a constant mean wind direction model.
4. Variable Tra.iectory Models Verfable trajectory models allow conditions to va y spa'tially and temporally over the region of interest; thus they require regional data. The number of sampling locations needed to approximate the regional airflow depends on the meteorological and topographical character-istics of that region.

The particle-in-cell model is a variable trajectory model based on the gradient-transport approach. In this model. " particles" representing the effluent mass are released in groups over the time period of interest. The particles move at the effective transport velocity of the windflow fleid into which the effluent is released. The effective velocity is determined

~ by the mean and turbulent windflows within the field. The n u ber of particles located at any i

t given time in each cell (volume) of a fixed coordinate grid determines the effluent concen-

' tration. Concentration averages are determined from the total number of particles that pass through a cell during the time of interest.

i The plume element models, another class of variable trajectory models, are based on the statistical approach to diffusion. These models approximate a continuous release by dividing a plume into a sufficient number of plume elements to represent a continuous plume. These elements are released at specified intervals and are tracked over the region of interest. The advective transport of these elements and the diffusion of the elements about their individual centers cause the dispersion of the plume effluent. Concentration averages are calculated by determining the contribution each element makes to the grid of points over which it passes.

( b. Constant Mean Wind Direction Models sd. '-

Constant mean wind direction models* assume that a constant mean wind transports and j diffuses effluents, within the entire region of interest, in the direction of airflow at the l release point. A commonly used version of this model is the Gaussian straight-line trajectory I model. In this model, the windspeed and atmospheric stability at the release point are assumed to determine the atmospheric dispersion characteristics in the direction of the mean wind at

all distances.

These basic models can be modified to account for various modes of effluent release and for effluent removal mechanisms.

2. Release Mode At ground-level locations beyond several miles from the plant, the annual average concen-trations of effluents are essentially independent of the release mode; however, for ground-level concentrations within a few miles, the release mode is very important.

For a typical nuclear power plant, gaseous effluents released from tall stacks generally produce peak ground-level air concentrations near or beyond the site boundary; near. ground-level releases usually produce concentrations that monotonically decrease from the release point to all locations downwind. Under certain conditions, the effluent plume may become entrained in the aerodynamic wake of the building and mix rapidly down to ground level; under other ccaditions, the full effect of the elevation of the release may be realfred.

Methods have been developed to estimate the effective release height'for calculations of

, effluent concentrations at all downwind locations. The important parameters in these methods l' include the initial release height the location of the release point in relation to obstruc-tions, the size and shape of the release point, the initial vertical velocity of the effluent, the heat content of the effluent, ambient windspeed and temperature, and atmospheric stability.

For those effluents that are entrained into the aerodynamic woke of a building, mixing of the_ effluent into the wake is usually assumed. This mixing zone can constitute a plume with an -

initial cross section of one-half or more of the cmss-sectional area of the building.

1.111-6 .

---.--2

. 3. Removal Mechanisms

' As the effluent travels from its release point, several mechanisms can work to reduce its concentration beyond that achieved by diffusion alone. Such removal mechanisms include radio-active decay and dry and wet deposition.

Radioactive decay is dependent on the half-life and the travel time of the radioactive effluent. All effluents can undergo dry deposition by sorption onto the ground surface; however, the dry deposition rate for noble gases, tritium, carbon-14. and nonelemental radio-todines is so slow that depletion is negligible within 50 miles of the release point. Elemental radiolodines and other particulates are much more readily deposited. The transfer of elemental radiciodines and particulates to a surface can be quantified as a transfer velocity (where con-centration x transfer velocity = deposition rate). There is evidirnce that the transfer velocity l 1s directly proportional to windspeed and, as a consequence the rate of deposition is independ-ont of windspeed since concentration in air is inversely proportional to windspeed.

Dry deposition is a continuous process while wet deposition only occurs during periods of precipitation. However, the dry removal process is not as efficient as the wet removal process.

At most sites, precipitation occurs during a small percentage of the hours in a year so that.

despite the greater efficiency of the wet removal process. dose calculations for long-tem averages considering only dry deposition should not be significantly changed by the con-sideration of wet deposition. However, wet deposition can ha a significant factor in dose calculations for releases from stacks at sites where a well-defined retry season corresponds to the local greatng season.

Deposition of radionuclides over large bodies of water is not considered in this guide.

Such deposition will be analy:ed on a case-by-case basis.

  • i C. REGUI.ATORY POSITION This section identifies types of atmospheric transport and diffusion models, source config-

,f uration 'and removal mechanism modifications and input data that are acceptable to the NRC staff for use in providing assessments of potential annual radiation doses to the public result-( ing from routine releases of radioactive materials in gaseous effluents.

The listing of the atmospheric transport and diffusion models below is presented in order of decreasing model complexity and should not be construed as indicating the preference cf any one type of model over another. The preferred model is that which best simulates atmospheric transport and diffusion in the region of interest from source to the receptor location, consider-ing the meteorological characteristics of the region, the topography, the characteristics of the effluent source and the effluent as well as the receptor, the availability and representative-ness of input data the distance from source to receptor, and the ease of appitcation.

Models proposed by the applicant and accepted by the NRC staff will. be used by the staff in detemining environmental technical specifications.

1. Atmospheric Transport and Diffusion Models The following types of atmospheric transpo:t and diffusion models can be modified for elevated sources and for effective area sources created when effluent is trapped in the building wake cavity in accordance with the source configuration considerations presented in regulatory position 2. Plume rise due to momentum or buoyancy effects can also be incorporated into the calculations. Radiological decay and dry and wet deposition, consistent with the guidelines presented in regulatory position 3. should also be considered.
a. Particle-in-Cell (PIC) Model The basic equation for each " particle" group in this variable trajectory model.

modified from Sklarew (Ref. 1). is:

(1) 4(D/4t + T V(D = 0 where t is the travel time;

'V is the velocity vector for effective mean wind transport, which includes I the mean flow component. Y, and the turbulent flow camponent. V'. such that l

V = Y+V'; and

- 1.111-7 m__ --__-_m*m___ - - - * - _ _ _ - - _ _ _ _ _ _ _ - m_ _p-= e- -g G 4 ---d---A-!'-- . W D -

O I (i) is the average atmospheric concentration produced by a group of particles. -

Concentration averages for long time intervals are obtained by summing all " particles" passing through each grid cell during the period of interest.

The PIC model uses spatial and temporal variations of wind direction, windspeed, atmospheric stability, and topography as input parameters to define airflow and atmospheric diffusion rates. The representativeness of the input data determines the accuracy of estimates (i.e., fewer data acquisition locations tend to increase the uncertainty of the estimates);

therefore, detailed discussion of the applicability and accuracy of the model and input data used should be provided.

b. plume Element Models
  • . In these types of models, the transport and dispersion of an effluent pipe are deter-mined by using a hort20ntal wind field that can vary in time and space. The diffusion of indivioual plume elements, according to Gifford (Ref. 2), can be determined from the general Gaussian diffusion model. Casunonly used plume segment elements are vertical " disk." segments

' and three-dimensional " puffs." In using the " puff" version, if it is assumed that the plume spread within a puff along the direction of flow is equal to the spreed in the lateral direction.

the " disk segment" and " puff" versions of this model would be espected to yield similar results.

An equation for a " puff" version of a fluctuating plume model, as presented by Start and idendel (Ref. 3) is: ,

2 x/Q=2[(23)3/2,,g)-lexp[-1/2(r/of+h,2,2)] 7 (2) where r 2 , {, , gg)2 , y2 and

'N * 'y " 's s. a h, is the effective release height; Q is the effluent emission over the time interval; t is the travel time; i u is the mean windspeed at the height of the effective release point; x is the distance from center of puff along the direction of flow; y is the distance from center of puff in the crossflow direction; l o, is the plume spread along the direction of flow; l e y is the lateral plume spread; e, is the vertical pi ne spread; and

  • x is the atmospheric concentration of effluent in a puff at ground level and at distance a from the puff center.

Concentration averages for long time intervals should be calculated by suuning the concentrations of individual elements for the grid of points over which they pass.

The number of elements and the plume spread parameters (e,.je . and og ) should be selected such that the resulting concentration estimate is representative of the concentration from a continuous point source release. Elements should be followed in the computational scheme untti they are beyond the region of interest or until their peak concentration falls below a specified value.

^

g.

. 1.111-8 1 ~

1

~

(.,

The plume seipneait model uses spatial and temporal variations of wind direction.

windspeed. and atmospheric stability as input parameters to define the transport and diffusion rate of each element. The effectiveness of the meteorological input data in defining atmospheric -

transport and diffusion conditions is dependent on the representativeness of these data and the complexity of the topography in the site region; therefore a detailed discussion of the appli-cability and accuracy of the model and input data used should be provided.

c. Constant Mean Wind Ofrection Models

. The equation for this model, as presented by Sagendorf (Ref. 4). is:

1 n gj[NXug 2j(X)T exp[-h /2o (I)] *

(i7lF)0=2.032 E (3) where h, is the effective release height'(see regulatory position 2);

n,d is the length of time (hours of valid data) weather conditions are observed to be at a given wind direction, avindspeed class.1. and atmospheric j stability class, j; L M is the total hours of valid data; I

j ug is the midpoint of windspeed class 1. at a height representative of release; X is the distance downwind of the source; l

o zj(X) is the vertical plume spread without volumetric correction at distarce. X.

for stability class, j (see Figure 1);

E2j(X) is the vertical plume spread with a volumetric correction (see regulatory position 2.c) for a release within the building wake cavity. at a distance.

., X. for stability class. j; othemise.Egj(X)=oj(X); g (i7lTr)0 is the average effluent concentration. x normalized by source strength.

Q'. at distance. I. in a given dounwind direction. 0; and

! 2.032 is(2/s)1/2 divided by the width in radians of a 22.5' sector.

l L Effects of spatial and temporal variations in airflow in the region of the site are I- not described by the constant mean wind direction model. Unitke the variable trajectory models, the constant mean wind direction model can only use meteorological data from a single station to represent diffusion conditions within the region of interest. For Appendix ! considerations.

the region of interest can extend to a distance of 50 miles frce the site. Therefore, if the constant mean wind direction model is to be used, airflow characteristics in the vicinity of any site should be examined to determine the sostial and temporal variations of atmospheric transport

and diffusion conditions and the applicability of si_ngle station meteorological data to represent

l (1) Conditions between the site and the nearest receptors (generally within 5 miles) and (2) Conditions out to a dist. ace of 50 miles from the site.

Exaspies of spatial and temporal variations of airflow to consider for three basic categories of topography are:

(1) At inland sites in open terrain. including gently rolling hills, with airflow

(' dominated almost entirely by large-scale weather patterns, recirculation of airflow and direc-tional biases during periods of prolonged atmospheric stagnation; (2) At sites in pronounced river valleys. with airflow patterns largely dominated by terrain, restrictions to lateral and vertical spread of the effluent plume, and the diurnal distributions of doynvalley and upvality circulation, with particular attention to the period of flow reversal; and (3) At sites along and near coasts of la bodies of water, with si ificant land-k water boundary layer effects on airflow, sea (or la landbreezecirculationhncluding

. 1.111-g

_  ;; _ _ = n.-___J .. ~. .u --.

. -l D

distance of penetration, vertical development, temporal variations of wind direction. and con-ditions during periods of flow reversal), variation of the mixing layer height with time and ,

distance from the shore (e.g.. fumigation and plume trapping), and the effects of shoreline bluffs and dunes.

Therefore, adjustments to Equation (3) may be necessary to prevent misrepresentation of actual atmospheric transport and diffusion characteristics that could result in substantial underestimates of actual exposure to an individual or population. Adjustments to Equation (3) should be based on data (e.g., comparison to other sites in the region) or studies that character-1 e airflow patterns in the region of the site out to a distance of 50 miles.

For all sites, a detailed discussion of the applicability and accuracy of the model and input data should be provided. Use of Equation (3) will be acceptable only if a well-documented and substantiated discussion of the effects of spatial and temporal variations in

, airflow in the region of the site out to a distance of 50 miles is provided.

2. Source Configuration Consic% rations The actual height above ground of the gaseous effluent pipe should be considered in making i estimates of average effluent concentrations downwind from the release points. An acceptable method to detemine the effective pipe height is described below. In addition, for effluent

. plumes traversing irregular terrain unoer stable or neutral atmospheric conditions, the model described by Egan (Ref. 5) may be used. On the other hand, the model described by Burt (Ref. 6) may be used when stable atmospheric conditions exist.

Source configuratiot e'faluations may consider the effluent release point (s) and adjacent or nearby solid structure (s) in conjunction with the individual direction sector (as described in regulatory position 4) in which the downwind receptor of interest is located.

a. Elevated Releases For effluents exhausted from release points that are higher than twice the height of adjacent solid structures, the effective release height (he ) is detemined (Ref. 4) from:

f h, = h, + ph , - ht** (*}

where c is sne correction for low relative exit velocity (see below);

h, is the effective release height; h is the rise of the plume above the release point, according to Sagendorf pr (Ref. 4), whose treatment is based on Briggs (Ref. 7);

h, is the physical height of the release point (the elevation of the stack base should be assumed to be aero); and hg is the maximum terrain height (above the stack base) between the release point and the point for wh4ch the calculation is made (hg must be g nater thanorequaltozero).

Note that the effective release height is a function of the distance between the release point and the location where the concentration is being calculated.

When the vertical exit velocity is less than 1.5 times the horizontal windspeed, a correctionfordownwashissubtractedfromEquation(4).accordingtoGifford(Ref.8):

c=3(1.5-W,6)d (5) where C is the do m wash correction; d is the inside' diameter of the stack or other release point; ii is the mean windspeed at the height of release; and

[ is the vertical exit velocity of the plume.

W,

. 1.111-10

V b. Releases Other Than Elevated For effluents released from points less than the height of adjacent solid structures. -

a ground-level release should be assumed (h,= 0).

For effluents released from vents or other points at the level of or above adjacent solid structures, but lower than elevated release points, the effluent pi ne should be considered as an elevated release whenever the vertical exit velocity of the plume. W, is at least five times the horizontal windspeed, u. at the height of release; 1.e., as modified from Johnson et al. (Ref. g):

W,/u g 5.0 .

(6)

In this case, the release should be evaluated as described in regulatory position 2.a.

If W,/7 is less than 1.0 or unknown, a ground-level release should be assumed (h, = 0)

For ct'es where the retto of plume exit velocity to horizontal windspeed is between one and five, a n.ced release mode should be assmed, in which the plume is considered as an

=0

- .remainder elevated releaseof the time. during a part of the time and as ga ground-level release (hAnisentrafsment deter- coefficient. E .

mined for those cases in which W,/u is between one and five:

Et = 2.58 - 1.58(W,M for 1 < W,6 g 1.5. (7) and Eg = 0.3 - 0.06(W,S for 1.5 < W,6 3 5.0 (8)

The release should be considered to occur as an elevated release 100(1 - E ) percent t

[ of the time and as a ground release 100Et percent of the time. Each of these cases should then

, be evaluated separately and the concentration calculated according to the fraction of time each type of release occurs. Windspeeds representative of conditions at the actual release heights

~

should tt used for the times when the release is considered to be elevated. Windspeeds measured at the 10-meter level should be used for those times when the effluent plume is considered to be a ground release. If Equation (3) is used, the adjustment described in regulatory position 2.c may be made for the ground release portion of the calculation.

c. Buildine Wake Correction

, For ground-level releases only'(h, = 0), an adjustment may be made in Equation (3)

( that takes into consideration initial mixing of the effluent plume within the building wake.

This adjustment according to Yanskey et al. (Ref.10), should be in the form of

2 2 r,)(X) = fe,3 (X) + 0.50 7,)1/2 f_ do,3(X) (g) where Og is the maximum adjacent building height either up- or downwind from the release point; I is the distance from the release point to the receptor, measured frem the lee edge of the complex of adjacent buildings; og(X) is the vertical standard deviation of the materials in the pl ee at distance. X for atmospheric stability class, j; and l 'I g(X) is the vertical standard deviation of pi p e material as above, with the correction for additional dispersion within the building wake cavity, restricted by the condition that I,j(I) = dog (X) ,

k 1.111-11 A

s

- . _ . _ , . _ -,u . . _ . . _ __ _________v

~

~

_........-...~.....:..--..:..---.. c.. :- . . ~ - - - T -:- - - ^ -

.l  :

(-

0 when O

(o,2(K)+0.k/w)1/2>do

) (X). *

3. Removal Mechanism Considerations Radioactive decay and dry and wet deposition should be considered in radiological impact evaluations. Acceptable methods of considering these removal mechanisms are described below.
4. -Radioactive Decay For conservative estimates of radioactive decay, an overall half-life of 2.26 days is i

acceptable for short-lived noble gases and of 8 days for all fodines released to the atmosphere.

' Alternatively, the actual half-life of each radionuclide may be used. The decay time used should be the calculated time of travel between the source and receptor based on the airflow model used.

b. Dry Deoosition Dry deposition of elemental radiciodines and other particulates and attendant plisme

+

depletion should be considered for all releases. .

Acceptable plume depletion correction factors and relative deposition rates are pre-sented in Figures 2 through 9. These figures are based on measurements of deposition velocity as a function of windspeed as presented in Reference 11 and on a diffusion-deposition model as presented in Reference 12.

Figures 2 through 5 illustrate an acceptable method for considering plume depletion effects for all distances from the source and atmospheric stability classes for ground and elevated release modes. After a given concentration is calculated by using the models in regulatory position 1. the concentration should be corrected by multiplying by the fraction remaining in the plume, ac determined from these figures.

Figures 6 through g show acceptable values of relative deposition rate (meters ) as a I

l function of distance from the source and atmospheric stability for ground and elevated  %.d re modes. The relative deposition rate is the deposition rete per unit downwind distance (C1/sec ner meter) divided by the source strength (C1/sec).

( To obtain the relative deposition per unit area (meters-2) at a given point in a given sector, the relative deposition rate must be (1) multiplied by the fractius of the release transported into the sector, determined according to the distribution of wind direction and (2) divided by an appropriate crosswind distance (meters) as discussed below.

l Figures 6 through g are based on the assumption that the effluent concentration in a given sector is uniform across the sector at a given distance. Therefore, for the straight-line trajectory model, or for any model that assumes uniform concentration across the sector at a given distance, the relative deposition rate should be divided by the arc length of the sector at the point being considered. In addition, for the straight-line trajectory model, the relative deposition rate should be multiplied by the appropriate correction factor discussed in regulatory position 1.c.

For models where concentration at a given distance is not uniform across the sector, the relative deposition at a given point should be calculated as above, but then multiplied by the ratio of the mximum effluent concentration in the sector at the distance being considered to the average concer wation across the sector at the same distance.

c. Wet Oeoosition l For long-term averages dose calculations considering dry deposition only are not usually changed significantly by the consideration of wet deposition. However, the effects of wet deposition and attendant plume depletion should be considered for plants with predominantly elevated releases and at sites that have a well-defined rainy season corresponding to the grazing season. Consideration of wet deposition effects should include examination of total precipitation, number of hours of precipitation, rainfall rate distributions, and the precipita-tion wind rose. If the precipitation data indicate that wet deposition may be significant, washout rates and attendant plume depletion should be calculated in accordance with the relation-ships identified by Engelmann (Ref. 13).
e
  • 4 1.111-12 I

i I 6

_.r_._. ._.. ... . - ._- .- .. _ . _ . . . . . . . . _ . - - _ .

d. Deposition Over Water -

For dispersion over small bodies of water, deposition may be assumed to occur at the same rate as over land. For calculations involving radionuclide transport over large bodies of .

. water. deposition should be considered on a case-by-case basis.

4. Meteorcionical Data for Models Sufficient meteorological information should be obtained to characterize transport pro-cesses (i.e., airflow trajectory, diffusion conditions, deposition characteristics) out to a

. distance of 50 miles (approximately 80.000 meters) from the plant. The primary source of meteorological infomation should be the onsite meteorological program (see Regulatory Guide 1.23. Ref.14). Other sources should include nearby National Weather Service (NWS) stations.

other well-maintained meteorological facilities (e.g., other nuclear fact 11 ties, universities, or private meteorological programs), and satellite facilities.

. Adequate characterization of transport processes within 50 miles of the plant may include examination of meteorological data from stations further than 50 miles when this information can provide additional clarification of the mesoscale transport processes. To augment the assessment of atiaspheric transport to distances of 50 miles from the plant, the following regional meteorological data, based on periods of record specified in Regulatory Guide 4.2 (Ref.15), from as many relevant stations as practicable should be used:

a. Windspeed
b. Wind direction
c. Atmospheric stability
d. Mixing height
e. Precipitation For input to variable trajectory atmospheric transport models, measured hourly values of windspeed should be used. Calms
  • should be assigned a windspeed of one-half of the appropriate h: starting speed. as described in the footnote for instruments conforming to the recommendations or intent of Regulatory Guide 1.23 (Ref.14). Otherwise, a windspeed of 0.1 meter /second should be assigned to calms. Hourly wind directions should be classed into at.least the 16 compass point sectors (i.e. 22.5-degree sectors. centered on true north, north-northeast, etc.) according to measured values averaged over the time interval.

l For input to the constant mean wind direction model. windspeed data should be presented as (1) hourly measured values or (2) windspeed classes divided in accordance with the Beaufort wind scale or other suitable class division (e.g., a greater number of light windspeed classes should be used for sites with high frequencies of light winds). Wind directions should be divided into the 16 compass directions (22.5-degree sectors, centered on true north, north-northeast etc.).

, If joint frequency distributions of wind direction and speed by atmospheric stability class.

! rather than hourly values, are used in this model, cales* should be assigned to wind directions l in proportion to the directional distribution within an atmospheric stability class of the lowest i

noncalm windspeed class. If hourly data are used, cales should be assigned to the recorded wind

~ direction averaged over the time interval. The windspeed to be assumed for calms is one-half of the starting speed of the vene or anemometer. whichever is higher. for instruments conforming to the reconnendations or intent of Regulatory Guide 1.23. Otherwise. the windspeed to be assumed for cales is 0.1 meter /second. ,

Atmospheric stability should be determined by vertical temperature difference (AT) between the release point and the 10-meter level, or by other well-documented parameters that have been substantiated by diffusion data. Acceptable stability classes are given in Reference 14.

Appropriate time periods for meteorological data utilization should be based on constancy of the source term (rate of release) and potential availability of the receptor (e.g., man or cow). If emissions are continuous, annual data summeries should be und. If releases are inter-mittent, consideration should be given to frequency and duration of re Wase. If emissions are f " Calms are defined as hourly average windspeeds below the starting speed of the vane or anemometer, whichever is higher.

1.111-13

-_- - , . . - . , , - - . - - - - - - - . _ - _ . . x ---

..._x.....

u. . n -. n _. .a -.

. . . . . _ . . ._ ... _ _ . J . _ n - --- _- . :

= .

infrequent s'wi of short duration.' atmospheric dispersion models and meteorological data

'("

appilcable to the time of release should be considered. Use of annual average conditions for .

< consideration of intermittent releases will be acceptable only if it is established that releases will be random in time. Otherwise the method of evaluation of intermittent releases -

should follow the methodology outlined in Section 2.3.4 of IRlREG-75/087 (Ref.16). This method l uses an appropriate x/Q probability level, as well as the annual average x/Q. for the direction and point of interest being evaluated to provide the basis for adjustments reflecting more adverse diffusion conditions than indicated by the annual average. These adjustments are applied to the annual average x/Q and 0/Q for the total number of hours associated with in-tenaittent releases per year. Detailed information for this calculation is given by Sagendorf and Goll (Ref.17). However, if intermittent releases are limited by technical specifications to periods when atmospheric conditions are more favorable than average for the site, annual average data and annual average dispersion models could be used. For calculations of doses through ingestion pathways, particularly through the cow-ellk pathwa'y. meteorological data for only the grazing or growing season shou.1d be used.

0. DFLDIENTATION The purpose of this section is to provide information to license applicants and licensees regarding the NRC staff's plans for implananting this ftgulatory guide.

This guide reflects current NRC staff practice. Therefore, except in those cases in which the license applicant or licensee proposes an acceptable alternative method, the method described herein for complying with specified portions of the Conudssion's regulations will continue to be used in the evaluation of submittals for operating license or construction permit applications until this guide is revised as a result of suggestions from the public or additional staff Nview.

. P .,

f

.f ' , e

(

1.111-14

  • * . we e ** gue o e . .me.-.e e .

- - - , .-pg - - - y p--,- .i- ,

yy,y -- w- ..w--- - - -

y , , - - - - - - - . - - - - - - . --p-. ,-,---r-.-- -----

t.O..

c

. s REFERENCES I

1. R. C. Skierow et al.. "A Particle-in-Cell Method for Neerical Solution of the Atmospheric Diffusion Equation and Applications to Air Pollution Problems."

Final Report 35R-444. Vol.1. EPA Contract 68-02-0006. 1971.

, 2. F. A. Gifford " Statistical Properties of a Fluc'tuating Plume Dispersion Model." in Advances in Geophysics. Vol. 6. F. N. Frankiel and P. A. Sheppard. Editors. Academic Press.

, Inc. New York, pp. 117-138, 1959.

3. G..E. Start and L. L. Wendell. " Regional Effluent Dispersion Calculations Considering Spetta1 and Temporal Meteorological Variations." NOAA Tech Memo ERL-ARL-44.1974.
4. J. F. Sagendorf "A Program for Evaluating Atmospheric Dispersion From a Nuclear Power Station. NOAA Tech Memo ERL-ARL-42,1974.

. 5. B. A. Egan. " Turbulent Diffusion in Complex Terrain" in Lectures on Air Pollution and Environmental Impact Analyses - AMS Workshop on Meteoroloay and Environmental Assessment.

Boston 1975. Dwayne Haugen. Workshop Coordinator. American Meteorological Society.

Boston. MA. pp. 123-124, 1975.

6. E. W. Burt. " Description of Valley Model-Version cgm 3D." U.S. Environmental Protection Agency Dispersion Program. available from the United States Environmental Protection Agency. Office of Air Quality Planning and Standards. Research Triangle Park. NC 27711.

pp. 4-6.

~

f ~

7. G. A. Briggs.'"P1 me Rise." AEC Critical Review Series. TID-25075, 1969.

i 8. F. A. Gifford. " Atmospheric Transport and Dispersion Over Cities." _ Nuclear Safety Vol. 13.

pp. 391-402 Sept.-Oct. 1972.

9. W. B. Johnson et al.. " Gas Tracer Study of Roof-Vent Effluent Diffusion at Millstone Nuclear Power Station.* AIF/NESP-007b. Atomic Industrial Forum. Inc.,1975.
10. G. R. Yanskey et al.. "Climatography of National Reactor Testing Station."

. Idaho Operations Office. USAEC, 100-12048,1966.

11.

E. H. Markee. Jr.. "A parametric Study of Gaseous Plume Depletion by G'round Surface Adsorp.

tion." i.. .%ceedings of USAEC Meteoroloeical Information Meetina. C. A. Mawson. Editor, j AECL-2787.' a 602-613, 1967.

12. C. A. Pelletiei e.'d J. D. Zimbrick. " Kinetics of Environmental Radiciodine Transport Through the Milk-Fuod Chain." in Environmental Surveillance in the Vicinity of Nuclear Facilities. W. C. Reinig. Editor. Charles C. Thomas Publishers. 5pringfield. Ill., 1970.
13. R. J. Englemann. "The Calculation of Precipitation Scavenging." in Meteoroloay and Atomic Enerny-1968. D. H. Slade. Editor CWC TID-24190, pp. 205-221.1965.

14 Regulatory Guide 1.23 (Safety Guide 23). *0nsite Meteorological Programs." U. 5. Nuclear Regulatory Consnission. Washingtcn. D.C.

15. Regulatory Guide 4.2. " Preparation of Environmental Reports for Nuclear Power Stations."

U.S. Nuclear Regulatory Commission. Washington, D.C.

16. " Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants."

NUREG-75/087. September 1975. Office of Nuclear Reactor Regulation. U.S. Nuclear Regulatory Commission. Washington. D.C.

17. J. Sagendorf and J. Goll. "10000Q-Program for the Meteorological Evaluation of Routine Effluent Releases at Nuclear Power Stations." Draft. U.S. Nuclear Regulatory Commission.

/ Washington. D.C. 1976.

7 t

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