Regulatory Guide 1.111

Methods for Estimating Atmospheric Transport and Dispersion of Gaseous Effluents in Routing Releases from Light-Water-Cooled Reactors

ML13038A087
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Issue date:	03/31/1976
From:	Office of Nuclear Regulatory Research
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RG-1.111
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U.S. NUCLEAR REGULATORY COMMISSION MREGULATORY GUIDEOFFICE OF STANDARDS DEVELOPMENTREGULATORY býGUID.E 1, 11METHODS FOR E.tTIMAI\ING ATMOSPHERICTRANSPORT ANDI&ISRE$RSIOJ9) OF GASEOUS EFFLUENTSIN ROUTINE' RELEAE'S FROM'25IGHT-WATER-COOLED REACTORSarch 1976At13/4AUSNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, U.S. NuclearRegulatory Guides are issued to describe and make available to the public Regulatory Commission, Washington, D.C. 20555, Attention: Docketing andmethods acceptable to the NRC staff of implementing specific parts of the Service SectionCommission's regulations, to delineate techniques used by the staff in evaeu The guides are issued in the following ten broad divisionsating specific problems or postulated accidents, or to provide guidance to applicants. Regulatory Guides are not substitutes for regulations, and compliance 1. Power Reactors 6. Productswith them is not required. Methods and solutions different from those set out in 2 Research and lest Reactors 7. Transportationthe guides will be acceptable if they provide a basis for the findings requisite to 3. Fuels and Materials Facilities 8. Occupational Healththe issuance or continuance of a permit or license by the Commission 4. Environmental and Siting 9. Antitrust ReviewComments and suggestions for improvements in these guides are encouraged S. Materials and Plant Protection 10. Generalat all times, and guides will be revised, as appropriate, to accommodate cowmeets and to reflect new information or experience. However, cuontients o Copies of published guides may be obtained by written request indicating thethis guide, if received within about two months after its issuance will fi par divisions desired to the U.S. Nuclear Regulatory Commission Washington. D.C.ticularly useful in evaluating the need for an early revision 20555. Attention: Director, Office of Standards Development TABLE OF CONTENTSPage

A. INTRODUCTION

........................................................................ 1.111-5

B. DISCUSSION

...... .............................................................. 1.111-51. Diffusion Models .......................................................... 1.111-5a. Variable Trajectory Models .. ............................................ 1.111-Eb. Straight-Line Trajectory Models............................................ 1.111-62. Release Mode............................................................... 1.111-63. Removal Mechanisms .... ........................................................ 1.111-7

C. REGULATORY POSITION

........................................................... 1.111-71. Atmospheric Transport and Diffusion Models ................................... 1.111-7a. Particle-in-Cell (PIC) Model .............................................. 1.111-7b' Puff Advection Model ...................................................... 1.111-8c. Straight-Line Airflow Model ............................................... l.lll-E2. Source Configuration Considerations ........................................... 1.111-10a. Elevated Releases ......................................................... 1 .111-10b. Releases Other Than Elevated ..............................................1.111-10c. Building Wake Correction .................................................. 1.111-113. Removal Mechanism Considerations .............................................. 1.111-11a. Radioactive Decay ......................................................... 1.111-11b. Dry Deposition ............................................................ 1.111-11c. Wet Deposition ............................................................ 1.111-12d. Deposition over Water .................................................... 1.111-124. Meteorological Data for Models ................................................ 1.111-12

D. IMPLEMENTATION

.................................................................... 1.111-13REFERENCES ............................................................................. 1.111-141.111I-3 LIST OF FIGURESFigure Page1. Vertical Standard Deviation of Material in a Plume .......................... 1.111-152. Open Terrain Correction Factor .............................................. 1.111-163. Plume Depletion Effect for Ground Level Releases ............................ 1.111-174. Plume Depletion Effect for 3Dm Releases ..................................... 1.111-185. Plume Depletion Effect for 60m Releases.... ............................1.111-196. Plume Depletion Effect for lOOm Releases .................................... 1.111-207. Relative Deposition for Ground Level Releases ............................... 1.111-218. Relative Deposition for 30m Releases .................................1.111-229. Relative Deposition for 60m Releases ........................... ............ 1.111-2310. Relative Deposition for lOOm Releases ....................................... 1.111-241.111-4

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 statesthat licensees should, in addition to complying with the limits set forth in that part, makeevery reasonable effort to maintain radiation exposures, and releases of radioactive materialsin effluents to unrestricted areas, as far below the limits specified in that part as isreasonably achievable.Section 50.34a, "Design Objectives for Equipment to Control Releases of Radioactive Materialin 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 radioactivematerial in effluents from nuclear power reactors. Section 50.36a, "Technical Specifications onEffluents from Nuclear Power Reactors," of 10 CFR Part 50 further provides that, in order tokeep power reactor effluent releases as low as is reasonably achievable, each license authorizingoperation of such a facility will include technical specifications that require establishment ofoperating procedures for effluent control, installation and maintenance of effluent controlequipment, and reporting of actual releases.Appendix I, "Numerical Guides for Design Objectives and Limiting Conditions for Operationto 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 guidancefor those design objectives and limiting conditions for operation for light-water-coolednuclear power plants. To implement Appendix I, the NRC staff has developed a series of guidesproviding acceptable methods for the calculation of effluent releases, dispersion of theeffluent in the atmosphere and water bodies, and associated radiation doses to man. Thisguide describes basic features of calculational models and assumptions for the estimation ofatmospheric transport and dispersion of gaseous effluents in routine releases from land-basedlight-water-cooled reactors.The procedures andmodels provided in this guide will be subject to continuing review bythe staff with the aim of providing greater flexibility to the applicant in meeting the require-ments of Appendix I. As a result of such review, it is expected that alternative acceptable.. methods for calculation will be made available to applicants and that calculational proceduresfound to be unnecessary will be eliminated.This guide supersedes portions of Regulatory Guide 1.42, Revision 1, "Interim LicensingPolicy on as Low as Practicable for Gaseous Radioiodine Releases from Light-Water-CooledNuclear Power Reactors," which is being withdrawn.

B. DISCUSSION

The transport and dilution of radioactive materials in the form of aerosols, v.apors, orgases released into the atmosphere from a nuclear power station are a function of the state ofthe atmosphere along the plume path, the topography of the region, and the characteristics ofthe effluents themselves. For a routine airborne release, the concentration of radioactivematerial in the surrounding region depends on the amount of effluent released; the height of therelease; the momentum and buoyancy of the emitted plume; the windspeed, atmospheric stability,and airflow patterns of the site; and various effluent removal mechanisms. Geographic featuressuch as hills, valleys, and large bodies of water greatly influence dispersion and airflowpatterns. Surface roughness, including vegetative cover, affects the degree of turbulent mixing.Sites with similar topographical and climatological features can have similar dispersion andairflow patterns, but detailed dispersion patterns are usually unique for each site.Most gaseous effluents are released from nuclear power plants through tall stacks or ventsnear the tops of buildings. Certain plant designs can result in other release pathways. Forexample, auxiliary equipment and major components such as turbines may be housed outside build-ings; releases from these components could occur near around level.1. Diffusion ModelsAtmospheric diffusion modeling has developed along two basic approaches: gradient-transporttheory and statistical theory. Gradient-transport theory holds that diffusion at a fixed point1.111-5 in the atmosphere is proportional to the local concentration gradient; this theory attempts todetermine momentum or material fluxes at fixed points. The statistical (e.g., Gaussian) approachattempts to determine the histories of individual particles and the statistical propertiesnecessary 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 basicmodels--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 astraight-line trajectory model.a. Variable Trajectory ModelsVariable trajectory models allow conditions to vary spatially over the region ofinterest; thus, they require regional data. The number of sampling locations needed to approxi-mate the regional airflow depends on the meteorological and topographical characteristics ofthat 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 ingroup.s over the time period of interest. The particles move at the effective transport velocityof the windflow field into which the effluent is released. The effective velocity is determinedby the mean and turbulent windflows within the field. The number of particles located at anygiven 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 passthrough a cell during the time of interest.The puff advection model is another variable trajectory model but is based on thestatistical approach to diffusion. This model approximates a continuous release by dividing aplume into a sufficient number of plume segments (puffs). These puffs are released at specifiedintervals and are tracked over the region of interest. The advective transport of puff centersand the diffusion of effluent puffs about their individual centers cause the dispersion of theplume effluent. Concentration averages are calculated by determining the contribution each puffmakes to the grid of points over which it passes.b. Straight-Line Trajectory ModelsStraight-line trajectory models assume that the airflow transports and diffuseseffluents along a straight line through the entire region of interest in the airflow directionat the release point. A commonly used version of this model is the Gaussian straight-linetrajectory model. In this model, the windspeed and atmospheric stability at the release pointare assumed to determine the atmospheric dispersion characteristics in the direction of airflow.These basic models can be modified to account for various modes of effluent release and foreffluent removal mechanisms.2. Release ModeAt 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-levelconcentrations within a few miles, the release mode is very important.For a typical- nuclear plant, gaseous effluents released from tall stacks generally producepeak ground-level air concentrations near or beyond the site boundary; near-ground-level releasesusually produce concentrations that monotonically decrease from the release point to all locationsdownwind. Some releases tend to produce intermediate concentrations. Under certain conditions,the effluent plume may become entrained in the aerodynamic wake of the building and mix rapidlydown to ground level; under other conditions, the full effect of the elevation of the releasemay be realized.Methods have been developed to estimate the effective release height for calculations ofeffluent concentrations at all downwind locations. The important parameters in these methodsinclude the initial release height, the location of the release point in relation to obstruc-tions, size and shape of the release point, the initial vertical velocity of the effluent, theheat content of the effluent, ambient windspeed and temperature, and atmospheric stability.1.111-6 For those effluents that are entrained into the aerodynamic wake of a building, mixing ofthe effluent into the wake is usually assumed. This mixing zone can constitute a plume with aninitial cross section of one-half or more of the cross-sectional area of the building.3.. Removal MechanismsAs the effluent travels from its release point, several mechanisms can work to reduce itsconcentration 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 radioactiveeffluent. 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 so slow that depletion is negligible within 50 miles of the release point. Elementalradioiodines and other particulates are much more readily deposited. The transfer of elementalradioiodines 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 velocityis directly proportional to windspeed and, as a consequence, the rate of deposition is independentof 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 bythe consideration of wet deposition. However, wet deposition can be an important factor in dosecalculations 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 should be analyzed on a case-by-case basis.

C. REGULATORY POSITION

This section identifies types of atmospheric transport and diffusion models, source config-uration and removal mechanism modifications, and input data that are acceptable to the NRC stafffor use in providing assessments of potential annual radiation doses to the public resulting fromroutine releases of radioactive materials in gaseous effluents.Models proposed by the applicant and accepted by the NRC staff will be used by the staff indetermining environmental technical specifications.1. Atmospheric Transport and Diffusion ModelsThe following types of atmospheric transport and diffusion models can be modified forelevated sources and for effective area sources created when effluent is trapped in the buildingwake cavity in accordance with the source configuration considerations presented in regulatoryposition 2. Plume rise due to momentum or buoyancy effects can also be incorporated into thecalculations. Radiological decay and dry and wet deposition, consistent with the guidelinespresented in regulatory position 3, should also be considered.a. Particle-in-Cell (PIC) ModelThe basic equation for each "particle" group in this variable trajectory model,modified from Sklarew (Ref. 1), is:6(T)/6t + = 0 (1)wheret is the travel time;V is the velocity vector for effective mean wind transport, which includes themean flow component, V, and the turbulent flow component, V, such thatV = V+V'; and(_) 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.1.111-7 The PIC model incorporates spatial and temporal variations of wind direction, windspeed,atmospheric stability, and topography to define airflow and atmospheric diffusion rates. Therepresentativeness of the input data determines the accuracy of estimates (i.e., fewer dataacquisition locations tend to increase the uncertainty of the estimates); therefore, detaileddiscussion of the applicability and accuracy of the model and input data used should be provided.b. Puff Advection ModelIn this model, the transport of a puff is determined from a horizontal wind fieldwhich can vary in time or in space. The diffusion of each puff can be determined from theGaussian diffusion model below, according to Start and Wendell (Ref. 2):= 3/2 2 1 2 2 2 2x/Q 2[(2r) a3a/ I-exp[-i/2(r /oH + h2/a (2)where2 2 2r (x -Ut) +y andaH =y a xand wherehe 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 distance from center of puff along the direction of flow;y is the distance from center of puff in the crossflow direction;a is the plume spread along the direction of flow;xUy is the lateral plume spread; ' ==Sz is the vertical plume spread; andx is the atmospheric concentration of effluent in a puff at ground level andat distance x from the puff center.Concentration averages for long time intervals should be calculated by summing theconcentrations of individual puffs for the grid of points over which they pass.The number of puffs and the plume spread parameters (o x, 0y, and az) should be selectedsuch that the resulting concentration estimate is representative of the concentration from acontinuous point source release. Puffs should be followed in the computational scheme until theyare beyond the region of interest or until their peak concentration falls below a specifiedvalue.The puff advection model incorporates spatial and temporal variations of wind direc-tion, windspeed, and atmospheric stability to define the transport and diffusion rate of eachpuff. The effectiveness of the meteorological input data in defining atmospheric transport anddiffusion conditions is dependent on the representativeness of these data and the complexity ofthe topography in the site region; therefore, a detailed discussion of the applicability andaccuracy of the model and input data used should be provided.c. Straight-Line Airflow ModelThe equation for this model, as presented by Sagendorf (Ref. 3), is:(x/Q)D = 2.032 n. n[NXui .Z(X)-1 exp[-h2/2o2zMI (3)S)j i zj ezj1.111-8 wherehe is the effective release height (see regulatory position 2);nij is the length of time (hours of valid data) weather conditions are observedto be at a given wind direction, windspeed class, i, and atmosphericstability class, j;N is the total hours of valid data;ui is the midpoint of windspeed class, i, at a height representative ofrelease;M ( is the vertical plume spread without volumetric correction at distance, X,z( for stability class, j (see Figure 1);Zz (X) is the vertical plume spread with a volumetric correction (see regulatoryposition 2.c) for a release within the building wake cavity, at a distance,X, for stability class, j; otherwise z(X) M ;zj zJ(x-/Q)D is the average effluent concentration, x, normalized by source strength,Q', at distance, X, in a given downwind direction, 0; and2.032 is (2/10)112 divided by the width in radians of a 22.5' sector.Since the straight-line flow model does not consider the effects of spatial andtemporal variations in airflow in the region of the site, appropriate adjustments to thecalculated (x/Q)D values should be made to account for these effects. There are three basiccategories of regional airflow characteristics that are related to topography:(1) Inland in open terrain, including gently rolling hills, with airflow dominatedalmost entirely by large-scale weather patterns,(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-waterboundary layer effects on airflow patterns.Adjustments, based on specific data and studies that characterize regional airflowpatterns, should be made in Equation (3) to account for these topographical effects. Alterna-tively, the following adjustments and considerations may be used for open terrain and rivervalley site locations. These factors are based on a conservative assessment of preliminarycomparisons between variables and straight-line trajectory models.(1) Sites in open terrain. The right side of Equation (3) should be multiplied bythe correction factors shown in Figure 2.(2) Sites in river valleys. For downvalley airflow, the right side of Equation (3)should be multiplied by 5 for distances less than 20 miles. For upvalley airflow, the rightside of Equation (3) should be multiplied by 1.5 for all distances. For downvalley airflowbeyond 20 miles and crossvalley flow, no correction should be applied. For meandering valleys,additional adjustments should be made on a case-by-case basis to ensure that individual dosesand population doses at locations of interest are not underestimated.For coastal sites, specific correction factors should be developed and applied foreach site and release point. Some factors that should be considered are the characteristics ofsea or lake breezes, the variation of the mixing layer height with time and distance fromshore, and the effects of shoreline bluffs or dunes. These factors should be considered inrelation to the locations of the meteorological towers, plant structures, and release pointswith respect to the land-water boundary layer.For all sites, a detailed discussion of the applicability and accuracy of the modeland input data should be provided.1.111-9

2. Source Conficuration ConsiderationsThe actual height above ground of the gaseous effluent plume should be considered inmaking estimates of average effluent concentrations downwind from the release points. Anacceptable method to determine the effective plume height is described below.a. Elevated ReleasesFor effluents exhausted from release points that are higher than twice the height ofadjacent solid structures, the effective release height (h e) is determined (Ref. 3) from:h =h + h -h -c (4)e s pr twherec is the correction for low relative exit velocity (see below);h is the effective release height;eh is the rise of the plume above the release point, according to Sagendorfpr (Ref. 3), whose treatment is based on Briggs (Ref. 4);hs is the physical height of the release point (the elevation of the stackbase should be assumed to be zero); andht is the maximum terrain height (above the stack base) between the releasepoint and the point for which the calculation is made (ht must be greaterthan or equal to zero).Note that the effective release height is a function of the distance between therelease point and the location where the concentration is being calculated.When the vertical exit velocity is less than 1.5 times the horizontal windspeed, acorrection for downwash is subtracted from Equation (4), according to Gifford (Ref. 5):c : 3(1.5 -W /U)d (5) 0wherec is the downwash correction;d is the inside diameter of the stack or other release point;-is the mean windspeed at the height of release; andWo is the vertical exit velocity of the plume.b. Releases Other Than ElevatedFor effluents released from points less than or equal to the height of adjacent solidstructures, a ground-level release should be assumed (he = 0).For effluents released from vents or other points above adjacent solid structures,but lower than elevated release points, the effluent plume should be considered as an elevatedrelease whenever the vertical exit velocity of the plume, W0, is at least five times the hori-zontal windspeed, u, at the height of release; i.e., as modified from Johnson et al. (Ref. 6):Wo/5 > 5.0 (6)0In this case, the release should be evaluated as described in regulatory position 2.a.If W /T is less than 1.0 or unknown, a ground-level release should be assumed (he = 0).For cases where the ratio of plume exit velocity to horizontal windspeed is betweenone and five, a mixed release mode should be assumed, in which the plume is considered as anelevated release during a part of the time and as a ground-level release (h = 0) during thee1.111-10

remainder of the time. An entrainment coefficient, Et, modified from Reference 6, is deter-mined for those cases in which W /u is between one and five:0Et = 2.58 -1.58(W /-U) for 1 < Wo/ T< 1.5 (7)t0 0andEt 0.3 -0.06(Wo0 ) for 1.5 < Wo//<U 5.0 (8)The release should be considered to occur as an elevated release 100(1 -Et) percentof the time and as a ground release lOOEt percent of the time. Each of these cases should thenbe evaluated separately and the concentration calculated according to the fraction of time eachtype of release occurs. Windspeeds representative of conditions at the actual release heightsshould be used for the times when the release is considered to be elevated. Windspeeds measuredat the 10-meter level should be used for those times when the effluent plume is considered tobe a ground release. If Equation (3) is used, the adjustment described in regulatory position2.c may be made for the ground release portion of the calculation.c. Building Wake CorrectionFor ground-level releases only (he = 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. 7), should be in the form of:Mzj(X) = (a 2 (X) + 0.5 D2/)I/2 <va_ (X) (9)whereD is the maximum adjacent building height either up- or downwind from thez release point;X is the distance from the release point to the receptor, measured from thelee edge of the complex of adjacent buildings;a .(X) is the vertical standard deviation of the materials in the plume atzj distance, X, for atmospheric stability class, j; andEz (X) is the vertical standard deviation of plume material as above, with thecorrection for additional dispersion within the building wake cavity,restricted by the condition thatzj (X) : /a zj(X)when2 (X) + 5D2/r)112 > o'jaxW.3. Removal Mechanism ConsiderationsRadioactive decay and dry and wet deposition should be considered in radiological impactevaluations. Acceptable methods of considering these removal mechanisms are described below.a, Radioactive DecayFor conservative estimates of radioactive decay, an overall half-life of 2.26 daysis acceptable for short-lived noble gases and of eight days for all iodines released to theatmosphere. Alternatively, the actual half-life of each radionuclide may be used. The decay timeused should be the calculated time of travel between the source and receptor based on the airflowmodel used.b. Dry DepositionDry deposition of elemental radioiodines and other particulates and attendant plumedepletion should be considered for all releases.I .111-II

Acceptable plume depletion correction factors and relative deposition rates arepresented in Figures 3 through 10. These figures are based on the discussion of deposition inReferences 8 and 9.Figures 3 through 6 illustrate an acceptable method for considering plume depletioneffects for all distances from the source and atmospheric stability classes for ground andelevated release modes. After a given concentration is calculated using the models in regulatoryposition 1, the concentration should be corrected by multiplying by the fraction remaining in theplume, as determined from these figures.Figures 7 through 10 show acceptable values of relative deposition rate (meters-1)as a function of distance from the source and atmospheric stability for ground and elevatedrelease modes. The relative deposition rate is the deposition rate per unit downwind distance(Ci/sec per meter) divided by the source strength (Ci/sec).To obtain the relative deposition per unit area (meters-2) at a given point in agiven sector, the relative deposition rate must be (1) multiplied by the fraction of the releasetransported into the sector, determined according to the distribution of wind direction and(2) divided by an appropriate crosswind distance (meters), as discussed below.Figures 7 through 10 are based on the assumption that the effluent concentration in agiven sector is uniform across the sector at a given distance. Therefore, for the straight-line airflow model, or for any model that assumes uniform concentration across the sector at agiven distance, the relative deposition rate should be divided by the arc length of the sectorat the point being considered. In addition, for the straight-line airflow model, the relativedeposition rate should be multiplied by the appropriate correction factor discussed in regulatoryposition l.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 bythe ratio of the maximum effluent concentration in the sector at the distance being consideredto the average concentration across the sector at the same distance.c. Wet DepositionFor long-term averages, dose calculations considering dry deposition only are not ' I 'usually changed significantly by the consideration of wet deposition. However, the effects ofwet deposition and attendant plume depletion should be considered for plants with predominantlyelevated releases and at sites that have a well-defined rainy season corresponding to thegrazing season. Consideration of wet deposition effects should include examination of totalprecipitation, 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. 10).d. Deposition over WaterFor dispersion over small bodies of water, deposition may be assumed to occur at thesame rate as over land. For calculations involving radionuclide transport over large bodies ofwater, deposition should be considered on a case-by-case basis.4. Meteorological Data for ModelsSufficient meteorological information should be obtained to characterize transport pro-cesses (i.e., airflow trajectory, diffusion conditions, deposition characteristics, etc.) outto a distance of 50 miles (approximately 80,000 meters) from the plant. The primary source ofmeteorological information should be the onsite meteorological program (see Regulatory Guide1.23, Ref. 11). 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 includeexamination of meteorological data from stations further than 50 miles when this informationcan provide additional clarification of the mesoscale transport processes. To augment theassessment of atmospheric transport to distances of 50 miles from the plant, the followingregional 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:1.111-12 a. Windspeedb. Wind directionc. Atmospheric stabilityd. Mixing heighte. PrecipitationFor input to variable trajectory atmospheric transport models, measured hourly values ofwindspeed should be used. Calms (defined as hourly average windspeeds below the starting speedof the anemometer) should be assigned a windspeed of one-half of the starting speed of theanemometer. Hourly wind directions should be classed into at least the 16 compass pointsectors (i.e., 22.5-degree sectors, centered on true north, north-northeast, etc.) according tomeasured values averaged over the time interval.For input to the straight-line airflow model, windspeed data should be presented.as (1)hourly measured values or (2) windspeed classes divided in accordance with the Beaufort windscale or other suitable class division (e.g., a greater number of light windspeed classesshould be used for sites with high frequencies of light winds). Wind directions should bedivided 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 atmosphericstability class, rather than hourly values, are used in this model, calms (defined as hourlyaverage 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 anatmospheric 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. Thewindspeed to be assumed for calms is one-half of the starting speed of the vane or anemometer,whichever is higher.Atmospheric stability should be determined by vertical temperature difference (JT) betweenthe release point and the 10-meter level, or by other well-documented parameters that have beensubstantiated by diffusion data. Acceptable 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 of the receptor (i.e., man orcow). If emissions are frequent or continuous, annual data summaries should be used. Otherdata time periods and atmospheric dispersion models should be used if emissions are infrequentand of short duration. These infrequent releases should be evaluated on a case-by-case basisunless such releases are restricted by technical specifications to periods when atmosphericconditions are more favorable than the average for the site. If such technical specificationsare planned or exist, annual average data and annual average dispersion models may be used.For calculation of doses through the milk pathway, meteorological data for the cow grazingseason only should be used.

D. IMPLEMENTATION

The purpose of this section is to provide information to license applicants and licenseesregarding the NRC staff's plans for implementing this regulatory guide.This guide reflects current Nuclear Regulatory Commission practice. Therefore, except inthose cases in which the license applicant or licensee proposes an acceptable alternativemethod, the method described herein for complying with specified portions of the Commission'sregulations is being and will continue to be used in the evaluation of submittals for operatinglicense or construction permit applications until this guide is revised as a result of sug-gestions from the public or additional staff review.1.111-13 REFERENCES1. R. C. Sklarew, A. J. Fabrick, and J. E. Prager, "A Particle-in-Cell Method for NumericalSolution 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 ConsideringSpatial and Temporal Meteorological Variations," NOAA Tech Memo ERL-ARL-44, 1974.3. J. F. Sagendorf, "A Program for Evaluating Atmospheric Dispersion from a Nuclear PowerStation," NOAA Tech Memo ERL-ARL-42, 1974.4. G. A. Briggs, "Plume Rise," AEC Critical Review Series, TID-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 ofRoof-Vent Effluent Diffusion at Millstone Nuclear Power Station," AIF/NESP-007b, AtomicIndustrial Forum, Inc., 1975.7. G. R. Yanskey, E. H. Markee, Jr., and A. P. Richter, "Climatography of National ReactorTesting Station," Idaho Operations Office, USAEC, IDO-12048, 1966.8. E. H. Markee, Jr., "A Parametric Study of Gaseous Plume Depletion by Ground Surface Adsorp-tion," in Proceedings of USAEC Meteorological Information Meeting, C. A. Mawson, Editor,AECL-2787, pp. 602-613, 1967.9. C. A. Pelletier and J. D. Zimbrick, "Kinetics of Environmental Radioiodine TransportThrough the Milk-Food Chain," in Environmental Surveillance in the Vicinity of NuclearFacilities, W. C. Reinig, Editor, Charles C. Thomas Publishers, Springfield, Ill., 1970.10. R. J. Englemann, "The Calculation of Precipitation Scavenging," in Meteorology and AtomicEnergy 1968, D. H. Slade, Editor, USAEC TID-24190, pp. 208-221, 1968.11. Regulatory Guide 1.23 (Safety Guide 23), "Onsite Meteorological Programs," U. S. NuclearRegulatory Commission, Washington, D.C.12. Regulatory Guide 4.2, "Preparation of Environmental Reports for Nuclear Power Stations,"U.S. Nuclear Regulatory Commission, Washington, D.C.~N(.1.111-14

1000 --fdAII-1000010-000, // -' '.10 .00 -1010PLM TRAE ITNE(IOEESFigr 1.VrialSadr Deiaio ofMtrai lmILI,(Ler D t/ I Ir C0.10 1.0 10 100i -NOTE: THESE ARE STANDARD RELATIONSHIPS AND MAY HAVE TO BEMODIFIED FOR CERTAIN TYPES OF TERRAIN AND/OR CLIMATICCONDITIONS (E.G., VALLEY, DESERT, OVER WATER).1 .111-15 w-JCLzzzLuxz0L-.o_U-1.00.90.80.70.60.50.40.30.20.1STABLE (E,F,G*) ___(A, B, C)0.11.010100PLUME TRAVEL DISTANCE (KILOMETERS)Figure 4. Plume Depletion Effect for 30m Releases (Letters Denote Pasquill Stability Class)

j". fzzz0L)LL.1.00.90.80.70.60.50.40.30.2-0.1 -0.11.0 10PLUME TRAVEL DISTANCE (KILOMETERS)Figure 5. Plume Depletion Effect for 60m Releases (Letters Denote Pasquill Stability Class)100

10-3I-lI I '71NEUTRAL (D)Z 1-5 STABLE00 N10-6U' I ---- -"-III-IIII "I 'ISTABLE (E, F,G).1.0PLUME TRAVEL DISTANCE (KILOMETERS)Figure 8. Relative Deposition for 30m Releases (Letters Denote Pasquill Stability Class)1.111-22

,10-4J-UN~TARLF fA 8 C).10-5LUwLUI-Z0wcc0-6NSAL I ICNEUTRAL (D)i : UNSTA LNEUTRAL N-f II/L i t II II 1 110-710-80.11.010100PLUME TRAVEL DISTANCE (KILOMETERS)Figure 9. Relative Deposition for 60m Releases (Letters Denote Pasquill Stability Class)1.111-23

10-4--r,,EE3IEE]EEEEEIHEIEVIIEEFEE3I--UNSTABLE- ----(A, B, C) /,NE:UT'A..1It,JFEFIEEEF3~II [1 ' 1 41,7cc.0~P:Iu.--J1o-06;-.-Il IIHSTABLE M., F*r. GT(NOiDEPLETIONiI f I II f:&108.10,11,1.010100PLUME TRAVEL DISTANCE (K(ILOMETERS)Figure 10. Relative Deposition for 100m Releases (Letters Denote Pasquill Stability Class)1.111-24