ML20151V835

for Comment Issue of Reg Guide 1.111,Rev 1, Methods for Estimating Atmospheric Transport & Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors

ML20151V835
Person / Time
Issue date:	07/31/1977
From:	NRC OFFICE OF STANDARDS DEVELOPMENT
To:
References
REGGD-01.111, REGGD-1.111, NUDOCS 8808230018
Download: ML20151V835 (32)

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• REGULATORY GUIDE OFFICE OF STANDARDS DEVELOPMENT REGULATORY G 4 P METHODS FOR EST TMOSPHERIC TRANSPORT AND DISPER GASEOUS EFFLUENTS IN ROUTINE RELEASES FR I WATER-COOLED REACTORS I

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TABLE OF CONTENTS 1.111 5 A. INTRODUCTION... . ...............................................................

1.111 5 B. O!5CU55!0't.................................. ........................ ............

1.111-5

1. 01ffusion Models..............................................................

a. Variable Trajectory Models.................................................

1.111 6 1.111 6

b. Cons ta nt Mea n Wi nd Di rec ti on Model s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1.111-6

2. Release Mode..................................................................

1.111-7

3. R emo v a l Me c h a n i s in s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.................. 1.111-7 C. REGULATORY P051T!0N............................................

A tmo s p he ri c T ra n s po rt a nd Di f f u s i on Model s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-7 1.

a. Particle in Cell (PIC) Mode 1.............................................. 1.111-7 1.111-8

b. Plume Element Models...................................................... 1.111 9

c. Constant Mean Wind Direction Models..........................

Source Configuration Considerations...........................................

1.111-10 2.

1.111 10

a. Elevated Releases.................................... .................... 1.111 11

b. Rele a se s O the r T ha n El e v a t ed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Building Nake Correction.................................................. 1.111-11 c.

Removal Mechanism Considerations..............................................

1.111 12 3.

I 1,111-12

a. Radioactive Decay.........................................................

b. D r y De po s i t i o n . . . . . . . . . . . . . *. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111-12

c. 1.111 12 Wet Deposition............................................................

d. Deposition Over Water..................................................... 1.111-13 1,111-13 4 Meteorological Data for Models................................................

1.111 14 D. IMPLEMENTATION....................................................................

REFERENCES.............................................................................

1.111-15

e LIST OF FIGURES f.!1Ei f821

1. Vertical Standard Deviation of Katerial in a P1ume. . . . . . . . . . . . . . . . . . . . . . . . . . 1,111 16 l

2. Pl ure Depl eti on E f fec t f or Ground. Level Relea s es. . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 17

3. P l ume De pl e t i on E f f ec t f or 30.m Re l e a s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 18 1

i 4. Pl ume Depl e t i on ( f f ec t f or 60.m Re l e a s es . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 19

5. Pl ume Depl e tion E f f ec t f or I DO.m Rel e a s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 20

6. Rela tive Depositi on f or Ground. Level Relea s es. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . 1.111 21

7. Rel a ti ve De pos i t i on for 30-m Rel e a s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 22

8. Rel a ti ve Deposi ti on for 60-m Rel ea s e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.111 23

9. Relative Ceposition for IDO.m Releases....................................... 1.111 24 4

l 1.111 4 e l l

A. INTRODUCTION D Section 20.106, "Radioactivity in Effluents to Urrestricted 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.l(c) of 10 CFR Part 20 states that licensees should, in addition to complying with the limits set forth in that part. Nke avery reasonable ef fort 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 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 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 45 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 elfluent control, installation and mintenance of effluent control equiprent, and reporting of actual releases.

Appandix I, "Numerical Guides for Design Objectives and Limiting Conditions for Operation to Meet the Criterion 'As low As !$ 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 I, the NRC staf f 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 calculational models and assumptions fSr the estimation of atmospheric transport and dispersion of gaseous effluents in routine relettes from land-based light water cooled reactors.

The procedures 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 eteting the require-ments of Appendix !. As a result of such review, it is expected that alternative acceptable methods for calculation will be made available to applicants and that calculational procedures found to be unnecessary will tre eliminated.

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 has been withdrawn (see 41 FR 11891, 3/22/76). l' .

B. D!$CU55!0N The transport and dilution of radioactive materials in the fonn of aerosols, vapor $ or gases released into the atnosphere 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 ef fluents themselves. For a routine airborne release, the concentration of radioactive material in the surrounding region depends on the amount of effluent released; the height of the release; the mcnentum and buoyancy of the emitted plunet the windspeed, atnospheric stability, and airflow patterns of the site; and various effluent renoval mechanisms. Geographic features such as hills, valleys, and large bodies of water greatly influence dispersion and airflow pa t terns. Surface roughness, including vegetative cover, affects the degree of turbulent mixing.

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

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, ausiliary equipnent and major components such as turbines may be housed outside build-ings; releases from these cceponents could occur near ground level.

1. Dif fusion 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

' Lines indicate substantive changes from previous issue.

1.111-5

in the atmosphere is proportional to the local concentration gradient; this theory attempts to detemine mmentum or material fluxes at fixed points. The statistical (e.g., Gaussian) approach attempts to detemine the histories of individual particles and the statistical properties necessary to r(present diffusion. Input data fcr models based on either approach include wind-speed, atmspheric stability, and airflow patterns in the region of interest. Several basic models have been developed using these approaches. These mdels vary according to their treat.

ment of the spatial changes of input data and the consideration of either a variable trajectery model or a constant mean wind direction model,

a. Variable Trajectory Models Variable trajectory models allow conditions to vary spatially and terporally over the region of interesti thus, they require regional data. The number of sampling locations needed to approximate the regional airflow depends on the meteorological and topographical character-1stics 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 field into which the effluent is released. The effective velocity is detemined 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 detemines 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 plume element models, another class of variable trajectory models, are based on the statistical approach to diffusion. These mdels 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 detemining the contribJtion each element makes to the grid of points over which it passes.

b. Constant Mean Wind Direction Models Constant mean wind direction models assume that a constant mean wind transports and diffuses effluents, within the entire region of interest. in the direction of airflow at the release point. A corrionly used version of this model is the Gaussian straight line trajectory model. In this model, the windspeed and atmospheric stability at the release point are assumed to detemine the atmospheric dispersion characteristics in the direction of the mean wind at all distances.

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

2. Rolease Mode At ground-level locations beyond several miles from the plant, the annual average concen-trations of effluents are essentially independent of the release moden 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 levelt under l

other conditions. tne full effect of the elevation of the releast may be realized.

l 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 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 wake of a building, mixing of the effluent into the wake is usually assumed. This mixing rone can constitute a plume with an initial cross section of one half or more of the cross sectional area of the building.

1.111 6

3. Re mval_ % clanisn D As the effluent travels fr r its release point several rechanises can work to reduce its concentration beyond that achieved by dif fusien alone. Such removal mechanis's include radio-active decay ar'd dry and wet deposition.

Radiosctive 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; ho.ever, the dry deposition rate for noble gases, tritium, carbon 14. and nonelemental radio-icdires is so slow that depletion is negligible within 50 miles of the release point. Elemental radiciodines and other particulates are much more readily deposited. The transfer of elemental radiciodires and particulates to a surface can be quantified 45 a transfer velocity (where con-centration x transfer velocity = deposition rate). There is evidence that the transfer velocity is directly proportional to wir.dspeed and, as a consequence, the rate of deposition is independ-ent of windsceed since concentration in air is inversely proportional to windspeed.

Dry deposition is a continuous process .hile wet deposition only occurs during periods of precipitation. Vowever, 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 50 that, despite the areater ef ficiency of the wet removal process. dose c81culations for long term averages considering 2nly dry deposition should not be significantly changed by the con-sideraticn of wet deposition. However, wet deposition can be a significant factor in dose calculations for releases from stacks at sites where a well defined rainy season corresponds to the local grazing season.

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

Such deposition will te analyzed on a case by-case basis.

C. REGULATORY pC5! TION This secticn ideatifies types of atmospheric transport and dif fusion models, source config-uration and remoal rechanism modifications and input data that are acceptable to the NRC staf f for use in providing assessments of potential annual radiation ooses to the public result-ing from routire releases of radioactive materials in gaseous effluents.

The listing of the atmospheric transport and diffusion ec<dels below 15 presented in order of decreasing model complexity .ind should not be construed as indicating the preference of any one type of model over another. The preferred model is that which best simulates atmospheric transport and dif fusien in the region of interest from source to the receptor location consider-ing the rieteorolegical 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 application.

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

1 AtmosJheric Tragort and Dif fusion Models The following types of atmospheric transport 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. P'ume rise dse 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 tf Considered.

a. particle-in-Cell (P!C) Model The basic equation for each "particle" group in this variable trajectory model, rodified from Sklarew (Ref. 1), is:

!(D/f t + UV(I) = 0 (1) where t is the travel timei j V is the velocity vector for ef fective mear, wind transport, which includes the rean flow cornponent. V. and the turbulent flow cceponent. V'. such that V

• V+V'; and 1.111 7

P (i) is the average atmoseberic concentration prodaced by a group of particles.

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

The PIC model uses spatial and terporal variations of wind direction, windipeed, atmospheric stability, and topography as input parareters 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 te provided,

b. 91ury Element Models In these types of models the transport and dispersion of an effluent plume are deter-mined by using a horizontal wind field that can vary in time and space. The diffusion of individual plume eierents, according to Gifford (Ref. ?). can be determined frcn the general Gaussian diffusion model. Comenly used plume segment ele ents are vertical "disk" serents 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 spread in the lateral direction, the "disk segment" and ' puff" verstor.s of this model would be expected to yield similar results.

An equation for a "puf f" version of a fluctuating plume model, as presented by Start and Wendel (Ref. 3). 15:

2 2 t/Q = 2[(2') I2 2cs,)*Iexp(-1/2(r/o g + h fg2)) (2) where r2 = (x - ut)2 , y2 ,nq H * 'y

• 8 x and where h, is the effective release height; Q is the effluent emission over ths time intervals t is the travel time; 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; e, is the plume spread along the direction of flow; o it the lateral plume spread; f

e, is the vertical plume spread; and x is the atmospheric crancentration of effluent in a puff at ground level and at distance x fren the puff center.

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

The number of elements and the plume spread parameters (e, e j . and o,) should be selected such that the resulting concentration estimate is representative of the concentration from a continuous point source relea:e. Elements should be followed in the computational schene untti they are beyond the region of interest or until their pe4k concentratio9 falls below a specified value.

1.111 8

The pire serent model uses spatial and teeporal variations of wind direction, windspeed. and atmospheric stability as input para M ters to define the transport and diffusion rate of each elemfit. The effectiveness of the meteorological input data in defining atmospheric 4 transport and diffv51on 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 rodel and input data used should be provided.

c. Constant Mean Wind Ofrection Models The equation for this model, as presented by Sagendorf (Ref. 4), 15:

me),.2.032gn,pe,,(ini.g.h:m;pn e m where h, is the effective release height (see regulatory position 2);

n gd is the length of time (hours of valid data) weather conditions are observed to be at a iven wind direction, windspeed class.1. and atmospheric stability c ass, j; N is the total hours of valid data; 74 is the midpoint of windspeed class.1. at a height representative of release; X is the distance downwiN of the source; j e,)(X) is the vertical plume spread without volunetric correction at distance. I, for stability class, j (see Figure 1);

I,)(X) is the vertical plume spread with a volumetric correction (see regulatory position 2.c) for a release within the builJing wate cavity at a distance.

X. for stability class, j; otherwise I,)(X) = c,)(X);

} (il7)0 is the average effluent concentration x normalized by source strength, d Q' at distance. I, in a given downwind direction. D; and 2.032 is (2/,)l/2 divided by the width in radians of a 22.5* sector.

Effects of spatial and terrporal variations in airflow in the region of the site are not described by the constant mean wind direction model. Unlike the variable trajectory models, the constant mean wind direction model can only use etteorological 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 from the site. There"ore, if the -

constant mean wind direction model is to be used, airflew characteristics in the vicinity of any site should be examined to determine the spatial and temporal variations of atmospheric transpert and dif fusion conditions and the applicability of single station meteorological data to represent:

(1) Conditions tetween the site and the nearest receptors (generally within 5 miles)

(2) Conditions out to a distance of 50 miles from the site.

Exa mles of spatial and tem;cral 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, re:trculation 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, rettrictions to lateral and vertical spread of the effluent plune. and the diurnal distributions of downvalley and upvalley circulation, with particular attention to the period of flow reversal; and (3) At sites along and near coasts of large bodies of water, with si nificant land-water boundary layer effects on airflow, sea (or lake) land breere circulation including I

1.111 9

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

Therefore, adjustrants to Equation (3) may be necessary to prevent misrepresentation of actual atnospheric transport and diffusion characteristics that could result in substantial underestirates of actual esposure to an individual or population. Adjustments to Equation (3) snould be based on data (e.g., ccrparison to other sites in the region) or studies that character.

ire 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 rodel and input data should be provided. Use of Equation (3) wfll be acceptable only if a well-documented and substantiated discussion of the effects of tpatial and terporal variations in airflow in the region of the site out to a distance of 50 miles is provided.

2. Source Configuration Considerations The actual height above ground of the gaseous effluent plume should be considered in making estimates of averagt effluent concentrations downwind from the release points. An acceptable method to detemine the effective pire height is described below. In addition, for effluent plumes traversing irregular terrain under stable or neutral atmospheric conditions, the model described by Egan (Ref. 5) may be used. On the otter hand, the model described by Burc (Ref. 6) may be used when stable atmospheric conditions exist.

Source configuration evaluations may consider the effluent releasi point (s) and adjacent or nearby solid structure (s) in conjunction with the individual directen sector (as described in regulatory position 4) in which the downwind receptor of interest is Nated,

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

h, e h g +h pg - h (4) t*E wtere c is the correction for low relative emit velocity (see below);

h, is the effective release height; is the rise of the plume above the release point. se. cording to $agendorf h"P (Ref. 4) whose treatment is based on Briggs (Ref. 7);

h 8

is the physical height of the release point (the elevation of the stack l base should be ass ced to be zero); and h is the maxim.m terrain height (above the stack base) between the release t

point and the poir.t for which the calculation 15 rade (ht must te greater than or equal to zero),

hote that the effective release height is a function of the distance between the release peint and the location where the concentration is being calcu'ated.

When the vertical exit velocity is less than 1.5 times the horizontal windspeed, a correction for downwash is subtracted f rce Equation (4), according to Gifford (Ref. 8):

c = 3(1.5 - W,5)d (5) where c is the dowerwash correction; d is tw inside diameter of the stac6 or other release point; U is the mean windspeed at the height of release; and W, is the vertical edit velocity of the plume, 1.111 10

b. Releases Other Than Eleva_ted 9 For effluents released from points less than the height of 3djacent solid structures.

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

For effluents released from vents or other points at the level of or above adjacent olid struttares, but lower than elevated release points, the offluent plume should be censidered is an elevated release whenever the vertical exit velocit/ of the plume W , is at least five

'ines the horizontel windspeed, u at the height of release; i.e., as modified from Johnson al. (Ref 9):

5.0 (6)

W,/u In this case, the release sheuld be evaluated as described in regulatory position 2.a.

If Wg/E is less than 1.0 or unknown, a ground-level elease should be assumed (h, = 0)

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 ele.ated release during a part of the time and as a ground-level release (h = 0) during the remainder of the time. An entrainment coefficient, Et, modified from ReferInce 9, is deter-mined for those cases in which W /u is between one and five:

Eg = 2.58 - 1.58N,M for 1 < W,6 g 1.5 W and Et = 0.3 - 0.06(W,/J) for 1.5 < W,/7 < 5.0 (8)

The release should be considered to occur as an elevated release 100(1 - Et ) percent of the time and as a ground release 100Eg percent of the time. Each of these cases should the.1 9 be evaluated separately and the concentration calculated accordfr.g to the fraction of time each type of release occurs. Windspeeds representative of conditions at the actual release heights should be used for the times when the release is considered to be elevated. Windspeeds meas'Jred 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. Building 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 fom of:

2 2 I gj(X) = (o,j (X) + 0.5D,/v)I/2 < do,j(X)

(9) where D,

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 ouildings; is the vertical standard deviation of the materials in the plume at l

og j(X) distance, X, for atmospheric stability class, j; and I,)(X) is the vertical standard deviation of plune material as above, with the correction for additional dispersion within the building wake cavity, restricted by the condition that I gj(X) = de,)(X) 1.111-11

when (o (X) + 0.50,27 ,)l/2 >

(X). l

3. Removal Mechanism Consideratiorg Radioactive decay and dry and wet deposition shoeld be considered in radiological impact evaluations. Acceptable methods 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 8 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 bett een the source and receptor based on the airflow 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 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 c? asses for ground and elevated relea:e modes. After a given concentration is calculated by using the models in regulatory position 1, the concentration should be corrected by multiplyin; by the fraction remaining in the plume, as determined from these figures.

Figures 6 through 9 show acceptable values of relative deposition rate (meters ) as a l function of distance from the source and atmospheric stability for ground and elevated r modes. Tre relative deposition rate is the deposition rate per unit downwind distance (Ci/sec l 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 tiic sector, determined according to the distribution of wind direction and (2) divided by an appropriate crosswind distance (#neters), as discussed below.

l Figures 6 through 9 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 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 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 maxirnum effluent concentration in the sector at the distance being considered to the average concentration across the sector at the same distance,

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 incl"de 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 identif $ed by Engelmann (Ref.13).

1.111-12 1

l . .

d. Deposition Over Water For dispersion over small bodies of water, ceposition 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 Meteorological Data for Models Sufficient meteorological informtion 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 information 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 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 processes. To augment the assessment of atmospheric transport to distances oi 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: f

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 'Jsed. Calms

• should be assigned a windspeed of one-half of the appropriate starting speed, as described in the footnote, for instruments conforming to the recomendations 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.

For input to the constant mean wir.d 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 othe" 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, calms

• should be assigned to wind directions in proportion to the directional distribution within an atmospheric 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 vane or anemometer, whichever is higher, for instrtrents conforming to the recomendations or intent of Regulatory Guide 1.23. Otherwise, the windspeed to be assumed for calms is 0.1 meter /second.

Atmospheric stability should be determined by vertical temperature difference (AT) between

he 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 as*d 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 sumaries should be used. 1: releases are inter-mittent, cons'deration should be given to frequency and duration of release. If emissions are Calms are defined as hourly average windspeeds below the starting speed of the vane or anemometer, whichever is higher.

I 1.111-13 l

, , , , J

infrequent and of short duration, atmospheric dispersion models and meteorological data applicable to the time of release should be considered. Use of annual average conditions for consideration of ir.temittent releases will be acceptable only if it is established that releases will be random in time. Otherwise the method of evaluation of intemittent releases {

should follow the methodology outlined in Section 2.3.4 of NUREG-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 D/Q for the total number of hours associated with in-termittent releases per year. Detailed infomation 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-milk pathway, meteorological data for l

only the grazing or growing season should be used.

D. IMPLEMENTATION The purpose of this section is to provide information to license applicants and licensees regarding the NRC staff's plans fer implementing this regulatory 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 partions of the Cornission'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 sugges* ions from the public or additional staff review.

l l

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1.111-14 8 i 1

i

REFERENCES I

D 1. R. C. Sklarew et al. , "A Particle-in-Cell Method f ar Numerical Solutis,a of the Atmospheric Diffusion Equation and Applications to Air Pollution Problems,"

Final Report 3SR-844, Vol. 1 EPA Contract 68-02-0006, 1971.

2. F. A. Gif ford, "Statistical Properties of a Fluctuating 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 Spatial and Temporal Meteorological Variations," NOAA Tech Memo ERL-ARL-44, 1974.

4. J. F. Sagendorf, "A Program for Evaluating Atmospheric Dispersion r am 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 Meteorology and Envi,onmental 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 C9M3D," U.S. Environmental Protection Agency Dispersion Program, available from the United States Environmental Pr>tection Agency, Of fice of' Air Quality Planning and Standards, Research Triangle Park, NC 27711, pp. 4 6.

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

8. F. A. Gifford, "Atmospheric Transport and Dispersion Over Cities," Nuclear Safety, Vol. 13, pp. 391-402, Sept. -Oc t. 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,"

D l 11.

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

E. H. Markee, Jr., "A Parametric Study of Gaseous Plume Depletinr. by Ground Surface Adsorp-tion," in Proceedings of USAEC Meteorological Infomation Meeting, C. A. Mawson, Editor, AECL-2767, pp. 602-613,1967. ,

12. C. A. Pelletier and J. D. Zimbrick, "Kinetics of Environmental Radioiodine Transpcrt Through the Milk-Food Chain," in Environmental Surveillanca in the Vicinity of Nuclear Facilities, W. C. Reinig, Editor, Charles C. Thomas Publishers, Springfield Ill.,1970.

13. 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.

14. Regulatory Guide 1.23 (Safety Guide 23), "Onsite Meteorological Programs," U. S. Nuclear Regulatory Comission, Washington, D.C.

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

U.S. Nuclear Regulatory Cornission 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 Comission, Washington, D.C.

17. J. Sagendorf and J. Goll. "X0QD0Q-Program for the Meteorological Evaluation of Routine Effluent Releases at Nuclear Power Stations," Draf t. U.S. Nuclear Regulatory Comission, Washington, D.C. ,1976, 1.111-15 9

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UNITED STATES g NUCLEAR REGULATORY COMMISSION

< o WASHINGTON, D. C. 20665 0 $

%,...../

January 1977 ERRATA Regulatory Guide 1.111, March 1976 "Methods for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors" A computer programing error that affected the depletion and deposition l curves in Figures 3 through 10 of Regulatory Guide 1.111. "Methods

% for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors," has been dis covered.

The corrected figures transmitted herewith should be used in future l assessments of potential annual radiation doses to the public resulting from routine releases of radioactive materials in gaseous l effluents. A conparison of the revised depletion and deposition curves l to the original ones has shown that, in the region where highest

! individual doses are usually calculated (i.e.,1-10 km), the relative i concentrations (X/Q), including depletion, will be about 10% higher l than before and the relative deposition values (0/Q) will be about 30% lower. Therefore, since D/Q is usually controlling, application of the new curves to plants that have already been evaluated and found to be in compliance with Appendix I will not be required l because there would be no change in the conclusion of acceptability.

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