ML003740205

Regulatory Guide 1.145, Revision 1 Atmospheric Dispersion for Potential Accident Consequence Assessments at Nuclear Power Plants

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Issue date:	02/28/1983
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RG-1.145, Rev 1
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Revision 1 U.S. NUCLEAR REGULATORY COMMISSION November 1982 REGULATORY GUIDE OFFICE OF NUCLEAR REGULATORY RESEARCH (Reissued February 1983 to correct page 1.145-7)

REGULATORY GUIDE 1.145 ATMOSPHERIC DISPERSION MODELS FOR POTENTIAL ACCIDENT CONSEQUENCE ASSESSMENTS AT NUCLEAR POWER PLANTS A. INTRODUCTION Reactors," and Regulatory Guide 1.4, "Assumptions Used for Evaluating the Potential Radiological Consequences of a Section 100.10 of 10 CFR Part 100, "Reactor Site Loss of Coolant Accident for Pressurized Water Reactors."

Criteria," states that meteorological conditions at the site A number of other regulatory guides also include recom-and surrounding area should be considered in determining mendations for or references to radiological analyses of the acceptability of a site for a power reactor. Section potential accidents. The applicability of the specific criteria 50.34 of 10 CFR Part 50, "Domestic Licensing of Produc- discussed herein to these other analyses will be considered tion and Utilization Facilities," requires that each applicant on a case-by-case basis. Until such time as generic guidelines for a construction permit or operating license provide an are developed for such analyses, the methodology provided analysis and evaluation of the design and performance of in this guide is acceptable to the NRC staff.

structures, systems, and components of the facility with the objective of assessing the risk to public health and safety The Advisory Committee on Reactor Safeguards has 1*

resulting from the operation of the facility. Section 50.34 been consulted concerning this guide and has concurred in of 10 CFR Part 50 also states that special attention should the regulatory position.

be directed to the site evaluation factors identified in 10 CFR Part 100 in the assessment of the site. B. DISCUSSION The regulatory positions presented in this guide repre- The atmospheric diffusion 2 models described in this sent a substantial change from procedures previously used guide reflect review of recent experimental data on diffu-to determine relative concentrations for assessing the sion from releases at ground level at open sites and from potential offsite radiological consequences for a range of releases at various locations on reactor facility buildings postulated accidental releases of radioactive material to the during stable atmospheric conditions with low windspeeds atmosphere. These procedures now include consideration of (Refs. I through 6). These tests confirm the existence of plume meander, directional dependence of dispersion effluent plume "meander" during low windspeed condi-conditions, and wind frequencies for various locations tions and neutral (D) and stable (E, F, and G) atmospheric around actual exclusion area and low population zone stability conditions (as defined by the temperature differ-(LPZ) boundaries 3 ence (AT) criteria in Regulatory Guide 1.23, "Onsite Meteorological Programs," and provide bases for quantify-The direction-dependent approach provides an improved ing the effects of plume meander on effluent concentra-basis for relating the Part 100-related review of a proposed tions. Effluent concentrations measured over a period of reactor to specific site considerations. Accordingly, this I hour under such conditions have been shown to be guide provides an acceptable methodology for deter- substantially lower than would be predicted using the mining site-specific relative concentrations (X/Q) and traditional curves (Ref. 7) of lateral and vertical plume should be used in determining xJQ values for the evalua- spread.

tions discussed in Regulatory Guide 1.3, "Assumptions Used for Evaluating the Potential Radiological Conse- Lines indicate substantive changes from previous issue.

quences of a Loss of Coolant Accident for Boiling Water 2 1n discussions throughout this regulatory guide, atmospheric dispersion will be considered as consisting of two components:

atmospheric transportdue to organized or mean airflow within the atmosphere and amospheric diffusion due to disorganized or I For additional information concerning the bases for the regula- random air motions. Plume depletion and surface deposition of tory positions presented in this guide, see NUREG/CR-2260, airborne materials are not included in the dispersion models "Technical Basis for Regulatory Guide 1.145." descibed in this guide.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555, Regulatory Guides are issued to describe and make available to the Attention: Docketing and Service Branch.

public methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate tech- The guides are issued in the following ten broad divisions:

niques used by the staff in evaluating specific problems or postu-lated accidents or to provide guidance to applicants. Regulatory 1. Power Reactors 6. Products Guides are not substitutes for regulations, and compliance with 2. Research and Test Reactors 7. Transportation them is not required. Methods and solutions different from those set 3. Fuels and Materials Facilities 8. Occupational Health out in the guides will be acceptable if they provide a basis for the 4. Environmental and Siting 9. Antitrust and Financial Review findings requisite to the issuance or continuance of a permit or 5. Materials and Plant Protection 10. General license by the Commission.

Copies of Issued guides may be purchased at the current Government This guide was issued after consideration of comments received from Printing Office price. A subscription service for future guides in spe-the public. Comments and suggestions for improvements in these cific divisions is available through the Government Printing Office.

guides are encouraged at all times, and guides will be revised, as Information on the subscription service and current GPO prices may appropriate, to accommodate comments and to reflect new informa- be obtained by writing the U.S. Nuclear Regulatory Commission, tion or experience. Washington, D.C. 20555, Attention: Publications Sales Manager.

The procedures in this guide also recognize that atmos- conservative evaluation of calms, taking into account the pheric dispersion conditions and wind frequencies are limitations of the windspeed measurement system, will be usually directionally dependent; that is, certain airflow necessary. Wind directions during calm conditions should directions can exhibit substantially more or less favorable be assigned in proportion to the directional distribution of diffusion conditions than others, and the wind can trans- noncalm winds with speeds less than 1.5 meters persecond. 3 port effluents in certain directions more frequently than in others. The procedures also allow evaluations of atmos- 1.2 Determination of Distances for X/Q Calculations pheric dispersion for directionally variable distances such as a noncircular exclusion area boundary. For each wind direction sector, XJQ values for each significant release point should be calculated at an appro-C. REGULATORY POSITION priate exclusion area boundary distance and outer low population zone (LPZ) boundary distance. The following This section identifies acceptable methods for (1) procedure should be used to determine these distances. The calculating atmospheric relative concentration (xJQ) values, procedure takes into consideration the possibility of curved (2) determining X/Q values on a directional basis, (3) deter- airflow trajectories, plume segmentation (particularly in mining XJQ values on an overall site basis, and (4) choosing low wind, stable conditions), and the potential for wind-X/Q values to be used in evaluations of the types of events speed and wind direction frequency shifts from year to described in Regulatory Guides 1.3 and 1.4. year.

Selection of conservative, less detailed site parameters For each of the 16 sectors, the distance for exclusion for the evaluation may be sufficient to establish compliance area boundary or outer LPZ boundary X/Q calculation with regulatory guidelines. should be the minimum distance from the stack or, in the case of releases through vents or building penetrations, the

1. CALCULATION OF ATMOSPHERIC RELATIVE CON- nearest point on the building to the exclusion area bound-CENTRATION (X/Q) VALUES ary or outer LPZ boundary within a 45-degree sector centered on the compass direction of interest.

Equations and parameters presented in this section should be used unless unusual siting, meteorological, or For stack releases, the maximum ground-level concentra-terrain conditions dictate the use of other models or tion in a sector may occur beyond the exclusion area considerations. Site-specific atmospheric diffusion tests boundary distance or outer LPZ boundary distance. There-covering a full range of conditions may be used as a basis fore, for stack releases, X/Q calculations should be made in for modifying the equations and parameters. each sector at each minimum boundary distance and at various distances beyond the exclusion area boundary 1.1 Meteorological Data Input distance to determine the maximum relative concentration for consideration in subsequent calculations.

The meteorological data needed for X/Q calculations include windspeed, wind direction, and a measure of atmos- 1.3 Calculation of X/Q Values at Exclusion Area Bound-pheric stability. These data should represent hourly averages ary Distances as defined in Regulatory Guide 1.23.

Relative concentrations that can be assumed to apply at Wind direction should be classed into 16 compass direc- the exclusion area boundary for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> immediately tions (22.5-degree sectors centered on true north, north- following an accident should be determined. 4 Calculations northeast, etc.). based on meteorological data representing a 1-hour average should be assumed to apply for the entire 2-hour period.

Atmospheric stability should be determined by vertical This assumption is reasonably conservative considering the AT between the release height and the 10-meter level. small variation of xIQ values with averaging time (Ref. 8).

Acceptable stability classes are given in Regulatory Guide If releases associated with a postulated event are estimated 1.23. If other well-documented parameters are used to to occur in a period of less than 20 minutes, the applicabil-determine plume dispersion (with appropriate justification), ity of these models should be evaluated on a case-by-case the models described in this guide may require modifica- basis.

tion. A well-documented parameter is one that is substan-tiated by diffusion data collected in terrain conditions Procedures for calculating "2-hour" X/Q values depend similar to those at the nuclear power plant site being on the mode of release. The procedures are described considered. below.

Calms should be defined as hourly average windspeeds below the vane or anemometer starting speed, whichever is higher (to reflect limitations in instrumentation). If the instrumentation program conforms to the regulatory 3 Staff experience has shown that noncalm windspeeds below 1.5 position in Regulatory Guide 1.23, calms should be assigned meters per second provide a reasonable range for defining the a windspeed equal to the vane or anemometer starting distribution of wind direction during light winds.

4 speed, whichever is higher. Otherwise, consideration of a See § 100.11 of 10 CFR Part 100.

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1.3.1 Releases Through Vents or Other Building X/Q values should be calculated using Equations 1, 2, Penetrations and 3. The values from Equations I and 2 should be com-pared and the higher value selected. This value should be This class of release modes includes all release points or compared with the value from Equation 3, and the lower areas that are effectively lower than two and one-half times value of these two should then be selected as the appro-the height of adjacent solid structures (Ref. 9). Within this priate xJQ value. Examples and a detailed explanation of class, two sets of meteorological conditions are treated the rationale for determining the controlling conditions are differently, as follows: given in Appendix A to this guide.

a. During neutral (D) or stable (E, F, or G) atmos-pheric stability conditions when the windspeed at the b. During all other meteorological conditions, plume 10-meter level is less than 6 meters per second, horizontal meander should not be considered. The appropriate X/Q plume meander may be considered. xIQ values may be value for these conditions is the higher value calculated determined through selective use of the following set of from Equation 1 or 2.

equations for ground-level relative concentrations at the plume centerline: 1.3.2 Stack Releases This class of release modes includes all release points at Ul 0 (irayaz + A/2) ( 1) levels that are two and one-half times the height of adjacent XIQ = I solid structures or higher (Ref. 9). Nonfumigation condi-tions are treated separately.

U1 0 (37r=a ) (2)

a. For nonfumigation conditions, the equation for ground-level relative concentration at the plume center-line for stack releases is:

X/ Q= U. Ui17TIl_,a yCz 3 2 (3) 1 Uhe IX/Q = l7hyzexpj7 ] (4) where X/Q is relative concentration, in sec/m 3 , where Ir is 3.14159. Uh is windspeed representing conditions at the release height, in m/sec, U1 0 is windspeed at 10 meters above plant grade, 5 in m/sec, he is effective stack height, in m: he = h5 - ht, ay is lateral plume spread, in mn, a function of atmos- hs is the initial height of the plume (usually the pheric stability and distance (see Fig. 1), stack height) above plant grade, in m, and Uz is vertical plume spread, in m, a function of ht is the maximum terrain height above plant atmospheric stability and distance (see Fig. 2), grade between the release point and the point for which the calculation is made, in m. If Ty is lateral plume spread with meander and building ht is greater than h5 , then he = 0.

wake effects, in m, a function of atmospheric stability, windspeed U, and distance [for For those cases in which the applicant can demon-distances of. 800 meters or less, Z = May, where strate that the vertical velocity of effluent plumes from the M is determined from Fig. 3; for Lstances greater plant (because of either buoyancy or mechanical jet effects) than 800 meters, Zy = (M - 1) uy800m + ay], and will be maintained during the course of the accident, this additional velocity may be considered in the determination A is the smallest vertical-plane cross-sectional area of of the effective stack height (he) using the same procedures the reactor building, in m2 . (Other structures described in regulatory position 2.a of Regulatory Guide or a directional consideration may be justified 1.1 11, "Methods for Estimating Atmospheric Transport when appropriate.) and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors."

b. For fumigation conditions, a "fumigation X/Q" should be calculated for each sector as follows. The equa-5 tion for ground-level relative concentration at the plume The 10-meter level is considered to be representative of the centerline for stack releases during fumigation conditions layer through which the plume is mixed when subjected to building wake effects. is:

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2. DETERMINATION OF MAXIMUM SECTOR x/Q X/Q= 'he >0 VALUES (27r) Uh, ayhe The XJQ values calculated in regulatory position 1 are used to determine "sector xJQ values" and "maximum sector XJQ values" for the exclusion area boundary and the outer LPZ boundary.

where 2.1 Exclusion Area Boundary Uhe is windspeed representative of the fumigation layer of depth he, in m/sec; in lieu of informa- 2.1.1 GeneralMethod tion to the contrary, the NRC staff considers a value of 2 meters per second as a reasonably Using the XJQ values calculated for each hour of data conservative assumption for he of about 100 according to regulatory position 1.3, a cumulative proba-meters, and bility distribution of X/Q values should be constructed for each of the 16 sectors. Each distribution should be de-Gr is the lateral plume spread, in m, that is repre- scribed in terms of probabilities of given XJQ values being sentative of the layer at a given distance; a exceeded in that sector during the total time. A plot of XJQ moderately stable (F) atmospheric stability versus probability of being exceeded should be made for condition is usually assumed. each sector, and a smooth curve should be drawn to form an upper bound of the computed points. For each of the 16 Equation 5 cannot be applied indiscriminately because curves, the XJQ value that is exceeded 0.5 percent 7 of the the X/Q values calculated, using this equation, become total number of hours in the data set should be selected unrealistically large as he becomes small (on the order of (Ref. 10). These are the sector X/Q values. The highest of 10 meters). The x/Q values calculated using Equation 5 the 16 sector values is defined as the maximum sector X/Q must therefore be limited by certain physical restrictions. value.

The highest ground-level xJQ values from elevated releases are expected to occur during stable conditions with low 2.1.2 Fumigation Conditionsfor Stack Releases windspeeds when the effluent plume impacts on a terrain obstruction (i.e., he = 0). However, elevated plumes diffuse Regulatory position 1.3.2 describes procedures for upward through the stable layer aloft as well as downward calculating a fumigation XJQ for each sector. These sector through the fumigation layer. Thus ground-level relative fumigation values, and the general (nonfumigation) sector concentrations for elevated releases under fumigation values obtained in regulatory position 2.1.1, are used conditions cannot be higher than those produced by to determine appropriate sector fumigation x/Qs. Conserva-nonfumigation, stable atmospheric conditions with he = 0. tive assumptions for fumigation conditions, which differ for For the fumigation case that assumes F stability and a inland and coastal sites, are described below. Modifications windspeed of 2 meters per second, Equation 4 should be may be appropriate for specific sites.

used instead of Equation 5 at distances greater than the distance at which the XIQ values determined using Equa- a. Inland Sites: For stack releases at sites located 3.2 tion 4 with he = 0 and Equation 5 are equal. kilometers or more from large bodies of water (e.g., oceans or Great Lakes), a fumigation condition should be assumed 1.4 Calculation of X/Q Values at Outer LPZ Boundary to exist at the time of the accident and continue for 1/2 Distances hour (Ref. 11). For each sector, if the sector fumigation X/Q exceeds the sector nonfumigation X/Q, use the fumiga-Two-hour XjQ values should also be calculated at outer tion value for the 0 to 1/2-hour time period and the non-LPZ boundary distances. The procedures described above fumigation value for the 1/2-hour to 2-hour time period.

for exclusion area boundary distances (see regulatory Otherwise, use the nonfumigation sector value for the position 1.3) should be used. entire 0 to 2-hour time period. The 16 (sets of) values thus determined should be used in dose assessments requiring An annual average (8760-hour) X/Q should be calculated time-integrated concentration considerations.

for each sector at the outer LPZ boundary distance for that sector, using the method described in regulatory posi- b. Coastal Sites: For stack releases at sites located less tion L.c of Regulatory Guide 1.1 11. For stack releases, he than 3.2 kilometers from large bodies of water, a furniga-should be determined as described in regulatory posi- tion condition should be assumed to exist at the exclusion tion 1.3.2 above. area boundary at the time of the accident and continue for the entire 2-hour period. For each sector, the larger of the These calculated 2-hour and annual average values are used in regulatory position 2.2 to determine sector X/Q 7 values at outer LPZ boundary distances for various inter- Selection of the 0.5 percent level is based on an equality without consideration of plume meander, between the S percen mediate time periods. 6 directionally independent evaluation of X/Q (the previous evaluatior procedure) and the 0.5 percent directionally dependent evaluation of VQ averaged over a reasonably representative number of existini 6

See § 100.11 of 10 CFR Part 100. nuclear power plant sites. See NUREG/CR-2260 for additiona information.

1.145-4

sector fumigation X/Q and the sector nonfumigation X/Q These are then the maximum sector X/Q values. However, if should be used for the 2-hour period. Of these 16 sector the highest sector X/Qs do not all occur in the same sector, values, the highest is the maximum sector X/Q value. the 16 (sets of) values will be used in dose assessments requiring time-integrated concentration considerations.

c. Modifications: These conservative assumptions do not The set of XJQ values resulting in the highest time-consider frequency and duration of fumigation conditions integrated dose within a sector should be considered the as a function of airflow direction. If information can be maximum sector X/Q values.

presented to substantiate the likely directional occurrence and duration of fumigation conditions at a site, the assump- 2.2.2 Fumigation Conditionsfor Stack Releases tions of fumigation in all directions and of duration of 1/2 hour and 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for the exclusion area boundary may be Determination of sector X/Q values for fumigation modified. Then fumigation need only be considered for conditions at the outer LPZ boundary involves the follow-airflow directions in which fumigation has been determined ing assumptions concerning the duration of fumigation for to occur and of a duration determined from the study of inland and coastal sites:

site conditions.8

a. Inland Sites: For stack releases at sites located 3.2 2.2 Outer LPZ Boundary kilometers or more from large bodies of water, a fumigation condition should be assumed to exist at the outer LPZ 2.2.1 GeneralMethod boundary at the time of the accident and continue for 1/2 hour. Sector xJQ values for fumigation should be deter-Sector X/Q values for the outer LPZ boundary should be mined as for the exclusion area boundary in regulatory determined for various time periods throughout the course position 2.1.2.

of the postulated accident.9 The time periods should represent appropriate meteorological regimes, e.g., 8 and b. Coastal Sites: For stack releases at sites located less 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> and 3 and 26 days as presented in Section 2.3.4 of than 3.2 kilometers from large bodies of water, a fumiga-Regulatory Guide 1.70, "Standard Format and Content of tion condition should be assumed to exist at the outer LPZ Safety Analysis Reports for Nuclear Power Plants-LWR boundary following the arrival of the plume and continue Edition," or other time periods appropriate to release for a 4-hour period (Ref. 11). Sector X/Q values for fumiga-durations. tion should be determined as for the exclusion area bound-ary in regulatory position 2.1.2.

For a given sector, the average X/Q values for the various time periods may be approximated by a logarithmic inter- c. The modifications discussed in regulatory posi-polation between the 2-hour 10 sector X/Q and the annual tion 2.1.2 may also be considered for the outer LPZ average (8760-hour) X/Q for the same sector. The 2-hour boundary.

sector XJQ for the outer LPZ boundary is determined using the general method given for the exclusion area boundary 3. DETERMINATION OF 5 PERCENT OVERALL SITE in regulatory position 2.1. The annual average X/Q for a given X/Q VALUE sector is determined as described in regulatory position 1.4.

The X/Q values that are exceeded no more than 5 per-The logarithmic interpolation procedure produces results cent of the total number of hours in the data set around the that are consistent with studies of variations of average exclusion area boundary and around the outer LPZ bound-concentrations with time periods up to 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> (Ref. 8). ary should be determined as follows (Ref. 10):

Alternative methods should also be consistent with these studies and should produce results that provide a mono- Using the xJQ values calculated according to regulatory tonic decrease in average X/Q with time. position 1, an overall cumulative probability distribution for all directions combined should be constructed. A plot For each time period, the highest of the 16 sector X/Q of X/Q versus probability of being exceeded should be values should be identified. In most cases, these highest made, and an upper bound curve should be drawn. The values will occur in the same sector for all time periods. 2-hour X/Q value that is exceeded 5 percent of the time should be selected from this curve as representing the dispersion condition indicative of the type of release being 8

For example, examination of site-specific information at a considered. In addition, for the outer LPZ boundary the location in a pronounced river valley may indicate that fumigation conditions occur only during the downvalley "drainage flow" maximum of the 16 annual average X/Q values should be regime and persist for durations of about 1/2 hour. Therefore, in used along with the 5 percent 2-hour X/Q value to deter-this case, airflow directions other than the downvalley directions may be excluded from consideration of fumigation conditions, and mine X/Q values for the intermediate time periods by the duration of fumigation would still be considered as 1/2 hour. logarithmic interpolation.

On the other hand, data from sites in open terrain (noncoastal) may indicate no directional preference for fumigation conditions but may indicate durations much less than 1/2 hour. In this case, fumigation should be considered for all directions, but with dura- 4. SELECTION OF X/Q VALUES TO BE USED IN tions of less than 1/2 hour. EVALUATIONS 9

See § 100.11 of 10 CFR Part 100.

1 oThe X(Qs are based on 1-hour averaged data but are assumed The X/Q value for exclusion area boundary or outer LPZ to apply for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />. boundary evaluations should be the maximum sector X/Q 1.145-5

(regulatory position 2) or the 5 percent overall site xIQ incorporating or referencing a duplicate plant design (regulatory position 3), whichever is higher. All direction- and those submitted under the replicate plant option dependent sector values should be presented for considera- of the Commission's standardization program).

tion of the appropriateness of the exclusion area and outer LPZ boundaries. Where the basic meteorological data 3. Operating license applications.

necessary for the analyses described herein substantially deviate from the regulatory position stated in Regulatory For operating reactors, the licensee may use the method Guide 1.23, consideration should be given to the resulting described in this guide or may continue to use the method uncertainties in dispersion estimates. previously contained or referenced in the FSAR for such facilities.

D. IMPLEMENTATION This guide does not apply to the following options The purpose of this section is to provide information to specified in the Commission's standardization policy under applicants regarding the NRC staff plans for using this the reference system concept:

regulatory guide.

1. Preliminary design approval applications.

Except in those cases in which an applicant proposes an acceptable alternative method for complying with specified 2. Final design approval, Type 1, applications.

portions of the Commission's regulations, the method described herein will be used in the evaluation of the 3. Final design approval, Type 2, applications.

following:

4. Manufacturing license applications.

1. For early site review applications.

The implementation date for this guide is December 30,

2. For construction permit applications (including those 1982.

1.145-6

l4 5 IiI' I_ XDA E2 B I

-3 E z

O = ZaEZ t_ _ e l _I JI IIII!-

U 0

c ) o 00

~j2 40/ i_ _ _C 11l

<0 E1 2 S 03 2 104 2 05L0 2 - - MODERATELY STNL Fiur1. Laea ifso1wtotmadrad uligwk fecs y S on 5Rf stbliy )

£0' adiioa infonaton 4100 2 5 0 2 5 14 25 1 DISTANCE FROM SOURCE (M)

Figure 1. Lateral diffusion without meander and building wake effects, ay, vs. down-wind distance from source for Pasquill's turbulence types (atmospheric stability) (Ref. 7).

The sigma values presented above are for unrestricted flow over relatively flat, uniform terrain. They may require modification before application in situations in which rough terrain or restricted flow conditions (e.g.,

within the confines of a narrow valley) must be considered or in coastal and desert areas. (See Ref. 12 for additional infonnation.)

For purposes of estimating ay during extremely stable (G) atmospheric stability conditions, without plume meander or other lateral enhancement, the following approximation is appropriate:

a (G) -- (F) y 1.145-7

10 z

Uj U-02 000, X00, 1-z 0

01 2 5 10 I-- 2 5 135 l-2 E OEAEYUSAL

> 10 01 DISTANCE fROM SOURCE Am) building wake effects, Figure 2. Vertical diffusion without meander and oz. vs. downwind distance from source for Pasquill's turbulence types (atmospheric stability) (Ref. 7).

may flow over relatively flat, uniform terrain. They The sigma values presented above are for unrestricted or restricted flow conditions in which rough terrain require modification before application in situations a narrow valley) must be considered or in coastal and desert areas. (See Ref. 12 (e.g., within the confines of for additional information.)

following stable (G) atmospheric stability conditions, the For purposes of estimating cz during extremely approximation is appropriate:

a z (G) -

5_ z (F) 1.145-8

10 T 1 ,;- ---. I

-1 l J Stability I j Class I G i 6

l X:

4.

at CZ I-C)

C-3-

C-)

CC) 14 --

i I- .5 r  ; I -

2 3 4 5 6 WINDSPEED (m/sec)

Figure 3. Correction factors for ay values by atmospheric stability class (see Appendix this guide). A to 1.145-9

APPENDIX A ATMOSPHERIC DIFFUSION MODEL FOR RELEASE THROUGH VENTS AND BUILDING PENETRATIONS Rationale vertical plume meander is shown to be virtually nonexistent during light wind, stable conditions. However, the experi-The effects of building wake mixing and ambient plume mental results for both situations could not be quantified meander on atmospheric dispersion are expressed in this for general application at this time.

guide in terms of conditional use of Equations 1, 2, and 3.1 The conditional use of Equations 1, 2, and 3 is consid-Equations I and 2 are formulations that have been ered appropriate because (1) horizontal plume meander acceptable for evaluating nuclear power plant sites over a tends to dominate dispersion during light wind and stable period of many years (Ref. 7 and Regulatory Guides 1.3 or neutral conditions and (2) building wake mixing becomes and 1.4). The conditional use of Equations 1 and 2 provides more effective in dispersing effluents than meander effects an assessment of atmospheric diffusion, including only the as the windspeed increases and the atmosphere becomes less effects of building wake mixing that occur during moderate stable.

windspeed conditions (>3 m/sec). These equations have recently been found to provide estimates of ground-level Examples of Conditional Use of Diffusion Equations concentrations that are consistently too high during light wind and stable or neutral atmospheric conditions for Figures A-1, A-2, and A-3 show plots of XU10 /Q (X/Q 1-hour release durations (Refs. I through 6). multiplied by the windspeed U1 )versus downwind distance based on the conditional use (as described in regulatory Equation 3 is an empirical formulation based on NRC position 1.3.1) of Equations 1, 2, and 3 during atmos-staff analysis of atmospheric diffusion experiment results pheric stability class G. The variable M for Equation 3 (Ref. 2). The NRC staff examined values of lateral plume equals 6, 3, and 2 respectively in Figures A-1, A-2, and A-3 spread with meander and building wake effects (:y) by (M is as defined in regulatory position 1.3.1).

atmospheric stability class (based on AT), calculated from measured ground4evel concentrations from the experi- In Figure A-I, the XU, IQ from Equation 3 (M=6) is mental results. Plots of the computed Z; values by atmos- less than the higher value from Equation 1 or 2 at all pheric stability class and downwind distance were analyzed distances. Therefore, for M= 6, Equation 3 is used for all conservatively but within the scatter of the data points by distances.

virtually enveloping most test data. The resultant analysis is the basis for the correction factors applied to the a values In Figure A-2, the xU1 0/Q from Equation 3 (M = 3) is (see Fig. 3 of this guide). Thus, Equation 3 identiges con- less than the higher value from Equation 1 or 2 beyond 0.8 servatively the combined effects of increased plume meander km. Therefore, for M = 3, Equation 3 is used beyond 0.8 and building wake on diffusion in the horizontal crosswind km. For distances less than 0.8 kin, the value from Equa-direction under light wind and stable or neutral atmos- tion 3 equals that from Equation 2. Equation 2 is therefore pheric conditions, as quantified in Figure 3. These experi- used for distances less than 0.8 km.

ments also indicate that vertical building wake mixing during light wind and stable conditions is not as complete In Figure A-3, the XUIO/Q from Equation 3 (M = 2) is as during moderate wind, unstable conditions. In addition, never less than the higher value from Equation 1 or 2.

Therefore, for M = 2, Equation 3 is not used at all. Instead, Equation 2 is used up to 0.8 km, and Equation 1 is used l For additional information see NUREG/CR-2260. beyond 0.8 km.

1.145-10

1 02 10-3 Eq. II 1....I i I _ I_

A I.

,10_-4. _X ___

x EEq.

H 1

= = --- Eq. 3(M=6)

I 1Eq. 2 10 0.1 1.0 10 PLUME TRAVEL DISTANCE (km)

Figure A-1. xU1 O/Q as a function of plume travel distance for G stability condition using Equations 1, 2, and 3 (M = 6).

1.145-11

10 10 0*0 10 =q.

1.0 10 0.1 PLUME TRAVEL DISTANCE (km) condition Figure A-2. xU1 0 /Q as a function of plume travel distance for G stability using Equations 1, 2, and 3 (M = 3).

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102 4

10-5 ; i I Eq. 3 (M=2) 0.1 1.0 10 PLUME TRAVEL DISTANCE (km)

Figure A-3. xU 1j/Q as a function of plume travel distance for G stability condition using Equations 1, 2, and 3 (M = 2).

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REFERENCES

1. I. Van der Hoven, "A Survey of Field Measurements sion Experiments with SF Tracer Gas at Three Mie of Atmospheric Diffusion Under Low-Wind Speed Island Nuclear Station Under Low Wind Speec Inversion Conditions," Nuclear Safety, Vol. 17, Inversion Conditions," Final Safety Analysis Report, No.4, March-April 1976. Amendment 24, Docket Number 50-289, 1972.

2. G. E. Start et al., "Rancho Seco Building Wake 7. F. A. Gifford, Jr., "An Outline of Theories of Diffu Effects on Atmospheric Diffusion," NOAA Technical sion in the Lower Layers of the Atmosphere,'

Memorandum ERL ARL-69, Air Resources Labora- Chapter 3 in Meteorology and Atomic Energy-1960 tory, Idaho Falls, Idaho, November 1977. Available (D. H. Slade, Ed.). Available as TID-24190 from th(

from Publication Services, Environmental Research National Technical Information Service, Springfield Laboratories, National Oceanic and Atmospheric Virginia 22151.

Administration, Boulder, Colorado 80302.

8. F. Gifford, "Atmospheric Dispersion Models fo)

3. R. B. Wilson et al., "Diffusion Under Low Windspeed Environmental Pollution Applications," Lectures or Conditions Near Oak Ridge, Tennessee," NOAA Air Pollution and Environmental Impact Analyses Technical Memorandum ERL ARL-6 1, Air Resources American Meteorological Society, pp. 35-38, 1975 Laboratory, Idaho Falls, Idaho, 1976. Available from Publication Services, Environmental Research Labora- 9. W. H. Snyder and R. E. Lawson, Jr., "Determinatioi tories, National Oceanic and Atmospheric Administra- of a Necessary Height for a Stack Close to a Building tion, Boulder, Colorado 80302. A Wind Tunnel Study," Atmospheric Environment Vol. 10, pp. 683-691, Pergamon Press, 1976.

4. J. E. Sagendorf and C. R. Dickson, "Diffusion Under Low Windspeed, Inversion Conditions," NOAA 10. D. R. Muller memorandum to H. R. Denton, "Meteoro Technical Memorandum ERL ARL-52, Air Resources logical Model for Part 100 Evaluations," July 25 Laboratory, Idaho Falls, Idaho, 1974. Available from 1978, and August 2, 1978 reply.

Publication Services, Environmental Research Labora-tories, National Oceanic and Atmospheric Administra- 11. 1. Van der Hoven, "Atmospheric Transport ani tion, Boulder, Colorado 80302. Diffusion at Coastal Sites," Nuclear Safety, Vol. E pp. 490-499, 1967.

5. Gulf States Utilities Company, "Dispersion of Tracer Gas at the Proposed River Bend Nuclear Power 12. International Atomic Energy Agency, "Atmospheri Station," Preliminary Safety Analysis Report, Amend- Dispersion in Nuclear Power Plant Siting-A Safet ment 24, Docket Numbers 50-458 and 50459, 1974. Guide," Safety Series No. 50-SG-S3, Vienna, Austria 1980. Available from UNIPUB, 345 Park Avenu

6. Metropolitan Edison Company, "Atmospheric Diffu- South, New York, N.Y. 10010.

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