Regulatory Guide 1.194

Atmospheric Relative Concentrations for Control Room Radiological Habitability Assessments at Nuclear Power Plants
	ML031530505
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Issue date:	06/01/2003
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	DG-1111 RG-1.194
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Regulatory guides are issued to describe and make available to the public such information as methods acceptable to the NRC staff for implementing specific parts of the NRC's regulations, techniques used by the staff in evaluating specific problems or postulated accidents, and data needed by the NRC staff in its review of applications for permits and licenses. Regulatory guides are not substitutes for regulations, and compliance with them is not require Methods and solutions different from those set out in the guides will be acceptable ifthey provide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission.This guide was issued after consideration of comments received from the publi Comments and suggestions for improvements in these guides are encouraged at all times, and guideswill be revised, as appropriate, to accommodate comments and to reflect new information or experienc Written comments may be submitted to the Rules and Directives Branch,ADM, U.S. Nuclear Regulatory Commission, Washington, DC 20555-000 Regulatory guides are issued in ten broad divisions: 1, Power Reactors; 2, Research and Test Reactors; 3, Fuels and Materials Facilities; 4, Environmental and Siting; 5, Materials andPlant Protection; 6, Products; 7, Transportation; 8, Occupational Health; 9, Antitrust and Financial Review; and 10, General. Single copies of regulatory guides (which may be reproduced) may be obtained free of charge by writing the Distribution Services Section, U.S. Nuclear Regulatory Commission,Washington, DC 20555-0001, or by fax to (301)415-2289, or by email to DISTRIBUTION@NRC.GO Electronic copies of this guide and other recently issued guides are availableat NRC's home page at <WWW.NRC.GOV> through the Electronic Reading Room, Accession Number ML031530505.U.S. NUCLEAR REGULATORY COMMISSION June 2003REGULATORY GUIDEOFFICE OF NUCLEAR REGULATORY RESEARCHREGULATORY GUIDE 1.194(Draft guide was issued as DG-1111)ATMOSPHERIC RELATIVE CONCENTRATIONS FORCONTROL ROOM RADIOLOGICAL HABITABILITYASSESSMENTS AT NUCLEAR POWER PLANTS TABLE OF CONTENTSA.INTRODUCTION.......................................................1B.DISCUSSION.........................................................2 C.REGULATORY POSITION...............................................3 1.DEFINITIONS.........................................................3 2.GENERAL CONSIDERATIONS...........................................43.CALCULATION OF /Q USING ARCON96.................................53.1Meteorological Data Input...........................................53.2Determination of Release Point (Source) Characteristics...................6 3.3Determination of Control Room Intakes (Receptors).....................113.4Determination of Source-Receptor Distances and Directions...............144.ALTERNATIVE PROCEDURES FOR GROUND LEVEL RELEASES...........154.1Point Source-Point Receptor........................................154.2Diffuse Source-Point Receptor......................................154.3Point or Diffuse Source with Two Alternative Receptors..................164.4Determination of /Q Values for Other Time Intervals....................165.INSTANTANEOUS PUFF RELEASES.....................................18 6.PLUME RISE........................................................20 7.USE OF SITE-SPECIFIC EXPERIMENTAL DATA...........................22 D.IMPLEMENTATION...................................................22 REFERENCES APPENDICES A.ARCON96 METEOROLOGICAL DATA SET STRUCTURE...................31 1 This guide will be useful to applicants for construction permits or operating licenses under Part 50; applicants for designcertifications under Part 52, "Early Site Permits; Standard Design Certifications; and Combined Licenses for Nuclear PowerPlants"; and applicants for combined licenses under Part 52 who do not reference a standard design certificatio See theImplementation section of this guide.1.194-1 INTRODUCTIONThis guide provides guidance on determining atmospheric relative concentration (/Q)values in support of design basis control room radiological habitability assessments at nuclear power plant This guide describes methods acceptable to the NRC staff for determining /Qvalues that will be used in control room radiological habitability assessments performed in support of applications for licenses1 and license amendment requests.In 10 CFR Part 50, "Domestic Licensing of Production and Utilization Facilities," Section50.34, "Contents of Applications; Technical Information," requires that each applicant for aconstruction permit or operating license provide an analysis and evaluation of the design and performance of structures, systems, and components of the facility with the objective of assessing the risk to public health and safety resulting from the operation of the facilit Appendix A,

"General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50 establishes minimumrequirements for the principal design criteria for water-cooled nuclear power plant General Design Criterion 19 (GDC-19), "Control Room," of Appendix A establishes minimumrequirements for the facility control roo Included is the requirement that adequate radiation protection be provided to permit access and occupancy of the control room for the duration of accident condition Similar criteria are provided in 10 CFR Part 50.67(b)(2)(iii) for plants that use alternative source term Atmospheric relative concentrations are significant inputs in assessments performed to demonstrate compliance with these regulation Many of the regulatory positions presented in this guide represent substantial changes fromprocedures previously used to determine atmospheric relative concentrations for assessing the potential control room radiological consequences for a range of postulated accidental releases of radioactive material to the atmospher These revised procedures are largely based on the NRC-

sponsored computer code, ARCON96 (Ref. 1). This code implements an improved building wake dispersion algorithm; assessment of ground level, building vent, elevated, and diffuse source release modes; use of hour-by-hour meteorological observations; sector averaging; and directional dependence of dispersion condition This guide also provides procedures for addressing some aspects of control room /Q determinations not currently implemented in the ARCON96 code.The information collections contained in this draft regulatory guide are covered by therequirements of 10 CFR Part 50, which were approved by the Office of Management and Budget (OMB), approval number 3150-301 The NRC may not conduct or sponsor, and a person is not required to respond to, a request for information or an information collection requirement unless the requesting document displays a currently valid OMB control numbe .194-2 DISCUSSIONIn licensing proceedings for currently operating nuclear power plants, the applicants andthe NRC staff have used various models for determining atmospheric relative concentration values (/Q) for control room habitability evaluatio The primary NRC models were those documentedin the control room habitability assessment procedure developed by Murphy and Campe (Ref. 2).

The Murphy-Campe procedure provided models addressing three different ground-level source- receptor geometrie Elevated releases were not addresse The first model was a straight-line Gaussian model for the case of a point source and point receptor geometry with a difference in elevation less than 30 percent of the containment building heigh This model included a fixed- value building wake correctio The second model was a straight-line Gaussian model appropriate for three geometries: a point source and point receptor with a difference in elevation greater than 30 percent of the containment building height, a diffuse source and point receptor, and a point source and a volume recepto The third Murphy-Campe model was used for point or diffuse sources when there were alternative receptor Section 6.4, "Control Room Habitability System,"of the Standard Review Plan (Ref. 3) references the Murphy-Campe models.In the 1980s, the NRC sponsored studies to evaluate the existing (e.g., Murphy-Campe)models against experimental testing in the environment and in wind tunnels and to develop alternative approache The results of these studies were published in 1988 in NUREG/CR-5055,

"Atmospheric Diffusion for Control Room Habitability Assessments" (Ref. 4). These resultsindicated that the existing dispersion models did not reliably predict and typically overestimated the concentrations in the vicinity of building NUREG/CR-5055 presented a statistical model that made significantly more reliable predictions in building wake Developmental work continued (Ref. 5, 6, 7). A formal peer review was conducted by the NRC in 1994 and the earlier model was revised in response to this peer review and was included in the ARCON95 cod Slight modifications were made to the code and it was re-issued as ARCON9 The code is documented in Revision 1 of NUREG/CR-6331, "Atmospheric Relative Concentrations in Building Wakes"(Ref. 1).ARCON96 is a general code for assessing atmospheric relative concentrations in buildingwakes under a wide range of situation As such, the ARCON96 code provides some user options that are not considered appropriate for use in design basis evaluations for control room habitability assessment Although the model implemented in ARCON96 was structured to address short-term atmospheric dispersion in typical reactor site building complexes, there may be atmospheric dispersion scenarios and source-receptor geometries for which the model would be inappropriate, e.g., extremely short duration releases, receptor distances shorter than about 10 meters, or control room outside air intakes located close to the base of tall elevated stack This guide provides guidance on the use of ARCON96 for determining atmosphericrelative concentrations to be used in design basis evaluations of control room radiological habitability and provides alternative methods for situations in which the modeling in ARCON96 or the application of ARCON96 is considered insufficien NUREG/CR-6331 (Ref. 1) is a contractor report that provides a user's guide to the ARCON96 code and provides several illustrativeexamples to facilitate user understandin Analysts are cautioned that the information in 2 Revision 1 to Regulatory Guide 1.78 provides for the use of ARCON96 in cases where the dispersion of the released gas isconsistent with the Pasquill-Gifford straight-line Gaussian models in ARCON96.1.194-3NUREG/CR-6331 does not constitute a regulatory position and may not be acceptable in aparticular licensing proceedin Analysts should not assume that the use of the ARCON96 code as described in this guide isacceptable for purposes other than control room radiological habitability assessment In particular, regulatory positions on atmospheric relative concentrations for toxic gas dispersion are provided in Regulatory Guide 1.78, "Assumptions for Evaluating the Habitability of a NuclearPower Plant Control Room During a Postulated Hazardous Chemical Release" (Ref. 8).2 Regulatory positions on atmospheric relative concentrations for offsite accident radiological consequence assessments are provided in Regulatory Guide 1.145, "Atmospheric DispersionModels for Potential Accident Consequence Assessments at Nuclear Power Plants" (Ref. 9). Regulatory positions on atmospheric relative concentrations for routine effluent release assessments are provided in Regulatory Guide 1.111, "Methods for Estimating AtmosphericTransport and Dispersion of Gaseous Effluents in Routine Releases from Light-Water-Cooled Reactors" (Ref. 10). Although this guide does not address toxic gas dispersion, analysts may findthat such considerations need to be reflected in the design and operation of control room outside air intake REGULATORY POSITION1.DEFINITIONSThe following definitions are used within the context of this regulatory guide.95th-percentile /Q value: The /Q value that is not exceeded by more than 5.0 percent ofthe /Q values generated with the meteorological observations in the data se Unless otherwisestated, all /Q values referred to in this guide are 95th-percentile values. Control Room: The plant area, defined in the facility licensing basis, in which actions canbe taken to operate the plant safely under normal conditions and to maintain the reactor in a safe condition during accident situation It encompasses the instrumentation and controls necessary for a safe shutdown of the plant and typically includes the critical document reference file, the computer room (if used as an integral part of the emergency response plan), shift supervisor'soffice, the operator wash room and kitchen, and other critical areas to which frequent personnel access or continuous occupancy may be necessary in the event of an accident. Control Room Envelope (CRE): The plant area, defined in the facility licensing basis, thatin the event of an emergency can be isolated from the plant areas and the environment external to the CR This area is served by an emergency ventilation system, with the intent of maintaining the habitability of the control roo This area encompasses the control room, and may encompass 3 If (1) the previously approved values are based on a misapplication of a methodology, (2) calculational errors are identified inthe values, or (3) changes are deemed necessary to ensure adequate protection of the health and safety of the public, the NRCstaff will pursue necessary corrections with the licensee or applicant.1.194-4other non-critical areas to which frequent personnel access or continuous occupancy is notnecessary in the event of an acciden Control Room Intake: The location at which the released radioactive material enters theCR Includes intentional ventilation system outside air intakes and other locations of significant infiltration into the CRE.Freestanding Stack: A stack located outside the zone of influence of structures in thevicinity of the stac (See Regulatory Position C.3.2.2)Infiltration (or Inleakage): The transport of released radioactive materials into the CREvia interstices in the structures, systems, and components that comprise the CR Such a transport is driven by pressure differentials between the CRE and areas external to the CRE.Slant Path: The shortest line-of-sight distance from the release point to the control roomintake, based on the differences in elevation and the horizontal intervening distance; calculated and used as the source-to-receptor distance by ARCON9 .GENERAL CONSIDERATIONSThe May 9, 1997, version of the ARCON96 code as described in Revision 1 ofNUREG/CR-6331 (Ref. 1) is an acceptable methodology for assessing control room /Q values foruse in design basis accident (DBA) radiological analyses, subject to the positions in this guide, unless unusual siting, building arrangement, release characterization, source-receptor configuration, meteorological regimes, or terrain conditions indicate otherwis These latter situations need to be addressed on a case-by-case basis.Although the ARCON96 code, when used as described in this guide, can provide animproved basis for determining site-specific /Q values, holders of operating licenses maycontinue to use /Q values determined with methodologies previously approved by the NRC staffand documented in the facility's final safety analysis report (FSAR) to the extent that these valuesare appropriate for the application in which they are being use Licensees may also continue touse the licensing basis methodology for determining /Q values for newly identified source-receptor combinations or re-generating the approved /Q values using more recently collectedmeteorological data set The ARCON96 code and the other models addressed in this guide may be used voluntarily, subject to the guidance herein, as a replacement for the existing licensing basis methodology for determining /Q values for design basis control room radiological habitability. Since the existing licensing basis methodology remains valid, a licensee may use the ARCON96 code and the other models addressed in this guide on a selective basis, that is, it is not necessarythat existing /Q values be update The NRC staff does expect that the methodologies will beapplied consistently in any particular accident assessmen .194-5For each of the source-to-receptor combinations, the 95th percentile /Q should bedetermine Values for parameters used as input to the /Q assessment should be selectedconsistent with achieving this confidence leve Selection of conservative, bounding source-to-receptor combinations and less detailed site parameters for the /Q evaluation may be sufficient toestablish compliance with regulatory guidelines.Control room /Q values are generally determined for each of the following averagingperiods: 0-8 hours (or 0-2 hours and 2-8 hours), 8-24 hours, 24-96 hours,96-720 hour The period of the most adverse release of radioactive materials to the environment should be assumed to occur coincident with the period of most unfavorable atmospheric dispersio If the 0-2 hour/Q is calculated, this value should be used coincident with the limiting portion of the release tothe environmen The 2-8 hour /Q value is used for the remaining 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months of the first 8-hour timeperio Part of this 6-hour interval may occur before or after the limiting 2-hour perio The 8-24, 24-96, and 96-720 hour /Q values should similarly be used for the remainder of the releaseduratio For facilities using the traditional TID-14844 (Ref. 11) source term, the 2-hour period will generally coincide with the start of the even For facilities with design basis analyses that include an alternative source term, the 2-hour period is often the onset of the in-vessel release phas In any case, the start of this period should be determined as a part of the analyses for each facility.3.CALCULATION OF /Q USING ARCON96This section addresses the use of the ARCON96 code for calculating /Q values for designbasis control room radiological habitability assessment The ARCON96 code should be obtained and maintained under an appropriate software quality assurance program that complies with the applicable criteria of Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and FuelReprocessing Plants," to 10 CFR Part 50 and applicable industry consensus standards to which thelicensee has committed.3.1Meteorological Data InputThe meteorological data needed for /Q calculations include wind speed, wind direction,and a measure of atmospheric stabilit These data should be obtained from an onsite meteorological measurement program based on the guidance of Safety Guide 23, "OnsiteMeteorological Programs" (Ref. 12), that includes quality assurance provisions consistent withAppendix B to 10 CFR Part 5 The meteorological data set used in these assessments should represent hourly averages as defined in Safety Guide 2 Data should be representative of the overall site conditions and be free from local effects such as building and cooling tower wakes, brush and vegetation, or terrai Collected data should be reviewed to identify instrumentation problems and missing or anomalous observations (see Ref. 13). The size of the data set used inthe /Q assessments should be sufficiently large such that it is representative of long-termmeteorological trends at the sit The NRC staff considers 5 years of hourly observations to be representative of long-term trends at most site With sufficient justification of its 1.194-6representativeness, however, the minimum meteorological data set is one complete year (includingall four seasons) of hourly observation Wind direction should be expressed as the direction from which the wind is blowing (i.e.,the upwind direction from the center of the site) referenced from true nort Atmospheric stability should be determined by the vertical temperature difference (T)measured over the difference in height appropriate for the projected release height (includingplume rise as applicable). A table of T values in units of degrees Centigrade per 100 meters(C/100m) versus stability class is given in Safety Guide 23 (Ref. 12). If other well-documentedmethodologies are used to estimate atmospheric stability (with appropriate justification), the models described in this guide may require modificatio A well-documented methodology is one that is substantiated by diffusion data for conditions similar to those at the nuclear power plant site involved.Appendix A provides information on the structure and content of the meteorological dataset and input parameters used by the ARCON96 code.3.2Determination of Release Point (Source) CharacteristicsA 95th-percentile /Q value should be determined for each identified source-receptorcombinatio However, it may be possible to identify bounding combinations in order to reduce the needed calculational effor In determining the bounding combinations it will be necessary to consider the distance, direction, release mode, and height of the various release points to the environment in relation to the various control room intake Additional parameters, such as those used in establishing plume rise, may need to be considered in determining the bounding combinatio For cases involving two or more release pathways associated with a single release source, acalculated composite value of /Q may be considered on a case-by-case basis if the licensee candemonstrate an acceptable modeling approach and justify the conservatism of any assumed weighting factors.Changes in associated parameters that could occur as a result of differences betweennormal operation and accident conditions, differences between accidents, differences that occur over the duration of the accident, single failure considerations, and considerations of loss of offsite power, consistent with accident sequences and descriptions, must all be considered in the characterization of the release points.The ARCON96 code provides options that allow an analyst to model ground-level,elevated stack, and vent-point source release In addition, the analyst can model diffuse area sources as a sub mode of the ground-level release typ These modes and limitations on their use are discussed in the positions that follo The plume rise may not be added to the physical height of the stack for the purpose of meeting the 2-1/2 times height criterion.1.194-73.2.1Ground-Level ReleasesThe ground-level release mode is appropriate for the majority of control room /Qassessment If the release type is ground level, ARCON96 ignores all user inputs related to release velocity and radiu Release height is used to establish the plume slant path.3.2.2Elevated (Stack) ReleasesThe stack release mode is appropriate for releases from a freestanding, vertical, uncappedstack that is outside the directionally dependent zone of influence of adjacent structure Such a stack should be more than 2-1/2 times the height of the adjacent structures or be locatedmore than 5L downwind of the trailing edge of upwind buildings, and more than 2L upwind of the leading edge of downwind buildings, andmore than 0.5L crosswind of the closest edge of crosswind buildingswhere L is the lesser of the height or width of the building creating the downwind, upwind, orcrosswind wak Since L will be dependent on wind direction for most building clusters, it will generally be necessary to assess the zone of influence for all directions within the 90 winddirection sector centered on the line of sight between the stack and the control room intak If multiple intakes are involved such that upwind, downwind, and crosswind orientations are confounded, 5L could be used for each orientatio See Figure Plume rise from buoyancy or mechanical jet effects are not calculated by ARCON9 The analyst may determine plume rise and add the amount of rise to the physical height of the stack to obtain an effective plume height as described in Regulatory Position 6 of this guid Although ARCON96 does not determine plumerise, the input values of stack flow, radius, and vertical velocity are used by ARCON96 to assessdownwash and to estimate a limiting /Q value.If the control room intake is located close to the base of a tall stack, the elevated releasemodel in ARCON96 generates negligibly low /Q value Although perhaps numerically correct,these model results may not be sufficiently conservative for a design basis assessment since themodel does not adequately address meteorological conditions that could result in higher /Qvalue Although the staff has previously suggested that licensees model fumigation as a mechanism to address this situation, the fumigation model did not appear to adequately estimate the effluent concentrations at the bases of industrial stack Concentrations greater than those predicted by ARCON96 could result from diurnal wind direction changes, meander, or stagnatio Therefore, the following procedure should be used to assess whether a particular stack-intakeconfiguration is subject to this concern and to determine the appropriate /Q values. In addition to running ARCON96 to determine the elevated stack /Q values for thecontrol room assessment, the analyst should calculate the maximum elevated stack /Q value(non-fumigation) using the methodology of Regulatory Guide 1.145 (Ref. 9) to determine themaximum /Q value at ground level for the 0-2 hour interval and for the 24-96 and 96-720 hour 1.194-8interval The NRC-sponsored code, PAVAN (Ref. 14), is acceptable to the staff for thisassessmen For this assessment, the input parameters should be adjusted such that the effective release height is measured from the elevation of the control room outside air intake rather than plant grad The same release point characterization and meteorological data sets used inARCON96 should be used to determine the /Q values for several distances in each wind directionsector with the objective of identifying the maximum /Q valu Figure A.4 of Reference 15 maybe useful in this regar The maximum /Q value obtained for the 0-2 hour interval should becompared to the corresponding /Q value generated by ARCON96 and the higher value used inhabitability assessment The /Q values generated by ARCON96 for the 2-8 and the 8-24 hourintervals may be used without adjustmen For the 24-96 hour and 96-720 hour intervals, the following expressions may be used todetermine the effective / This determinstic approach assumes that the stack plume reversesdirection for 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months of each day for the duration of the even The plume is assumed to fold over itself such that the ground level concentration is at its maximum value at the control room intak (1)24Q23Q1Q96ARCONhr9624PAVANhr9624hr9624(2)24Q23Q1Q96ARCONhr72096PAVANhr72096hr720963. Vent ReleasesThe ARCON96 calculation of vent releases includes an algorithm to model mixed-modereleases as described in Regulatory Guide 1.111 (Ref. 10), which addresses /Q values used in theassessment of routine effluent release The development of this algorithm was based in part on limited field experiment Given the limited experiment set, the results obtained with this algorithm may not be sufficiently conservative for accident evaluation For this reason, the vent release mode should not be used in design basis assessment This position is consistent with the guidance of Regulatory Guide 1.145 (Ref. 9) for offsite /Q value These releases should betreated as a ground level release (Section 3.2.1) or as an elevated release (Section 3.2.2).3.2.4Diffuse Area SourcesThe diffusion models in ARCON96 are based on point-source formulation However,some release sources may be better characterized as area source Examples of possible area sources are postulated releases from the surface of a reactor or a secondary containment buildin Typical assessments for loss-of-coolant accidents (LOCAs) have conservatively assumed that the containment structure could leak anywhere on the exposed surfac As such, these assessments typically used the shortest distance between the building surface and the control room intake and 5 Penetrations that are enclosed within safety-related structures need not be considered in this evaluation if the release would becaptured and released via a plant ventilation system, as ventilation system releases should have already been addressed as aseparate release point.6 See Regulatory Position 7 regarding the use of site-specific empirical measurements.1.194-9have treated the building as a point sourc This approach may be unnecessarily conservativ Amore reasonable approach, while still maintaining adequate conservatism, would be to model the building surface as a vertical planar area sourc This approach is not intended to address dispersion resulting from building-induced turbulenc Treatment of a release as a diffuse source will be acceptable for design basis calculations if the guidance herein is followe The staff may consider deviations from this guidance on a case-by-case basis.3.2. Diffuse source modeling should be used only for those situations in which theactivity being released is homogeneously distributed throughout the building and when the assumed release rate from the building surface would be reasonably constant over the surface of the buildin For example, steam releases within a turbine building with roof ventilators or louvered walls would generally not be suitable for modeling as a diffuse sourc (See Regulatory Positions 3.2.4.7 and 3.2.4.8.)3.2. Since leakage is more likely to occur at a penetration, analysts must consider thepotential impact of building penetrations exposed to the environment5 within this modeled are Ifthe penetration release would be more limiting, the diffuse area source model should not be use Releases from personnel air locks and equipment hatches exposed to the environment, or containment purge releases prior to containment isolation, may need to be treated differentl Itmay be necessary to consider several cases to ensure that the /Q value for the most limitinglocation is identified.3.2. The total release rate (e.g., Ci*s-1) from the building atmosphere is to be used inconjunction with the diffuse area source /Q in assessment This release rate is assumed to beequally distributed over the entire diffuse source area from which the radioactivity release can enter the environmen For freestanding containments, this would be the entire periphery above grade or above a building that surrounds the lower elevations of the containmen When a licensee can justify assuming collection of a portion of the release from the containment within the surrounding building, the total release from the containment may be apportioned between the exposed and enclosed building surface Similarly, if the building atmosphere release is modeled through more than one simultaneous pathway (e.g., drywell leakage and main steam safety valve leakage in a BWR), only that portion of the total release released through the building surfaceshould be used with the diffuse area / The release rate should not be averaged or otherwiseapportioned over the surface area of the buildin For example, reducing the release rate by 50 percent because only 50 percent of the surface faces the control room intake would be inappropriate.3.2. ARCON96 uses two initial diffusion coefficients entered by the user to representthe area sourc There are insufficient field measurements to mechanistically model these initial diffusion coefficient The following deterministic equations should be used in the absence of site-specific empirical dat The degree of significance will depend on the radius or width of the assumed area and the proximity of the vent cluster to thecontrol room intak As the radius decreases or the distance from the cluster to the control room intake increases, the lesssignificance the position of any one vent has.1.194-10(3)6WidthsourceareaYo(4)6eightHsourceareaZo3.2. The height and width of the area source (e.g., the building surface) are taken asthe maximum vertical and horizontal dimensions of the above-grade building cross-sectional area perpendicular to the line of sight from the building center to the control room intake (see Figure 2).

These dimensions are projected onto a vertical plane perpendicular to the line of sight and located at the closest point on the building surface to the control room intak The release height is set at the vertical center of the projected plan The source-to-receptor distance (slant path) is measured from this point to the control room intake. 3.2.

Intent

ional releases from a secondary containment (e.g., standby gas treatmentsystems (SGTS) at BWR reactors) or annulus ventilation systems in dual containment structures should be treated as a ground-level release or an elevated stack release, as appropriate. The diffuse area source model may be appropriate for time intervals for which the secondary containment or annulus ventilation system is not capable of maintaining the requisite negative pressure differential specified in technical specifications or in the FSA Secondary containment bypass leakage (i.e.,

leakage from the primary containment that bypasses the secondary containment and is not collected by the SGTS) should be treated as a ground-level release or an elevated stack release, as appropriate.3.2. A second possible application of the diffuse area source model is determining a/Q value for multiple (i.e., 3 or more) roof vent This treatment would be appropriate forconfigurations in which (1) the vents are in a close arrangement, (2) no individual vent is significantly7 closer to the control room intake than the center of the area source, (3) the releaserate from each vent is approximately the same, and (4) no credit is taken for plume ris The distance to the receptor is measured from the closest point on the perimeter of the assumed area sourc For assumed areas that are not circular, the area width is measured perpendicular to the line of sight from the center of the assumed source to the control room intak The initial diffusioncoefficient Yo is found by Equation 3; Zo is assumed to be 0.0. 3.2. A third possible application of the diffuse area source model is determining a /Qvalue for large louvered panels or large openings (e.g., railway doors on BWR Mark I plants) on vertical wall This treatment would be appropriate for a louvered panel or opening when (1) the release rate from the building interior is essentially equally dispersed over the entire surface of the panel or opening and (2) assumptions of mixing, dilution, and transport within the building necessary to meet condition 1 are supported by the interior building arrangemen The staff has traditionally not allowed credit for mixing and holdup in turbine buildings because of the buoyant 1.194-11nature of steam releases and the typical presence of high volume roof exhaust ventilator Thedistance to the receptor and the release height is measured from the center of the louvered panel or openin Initial diffusion coefficients are found using Equations 3 and 4 assuming the width and height is that of the panel or opening rather than that of the buildin If the area source and the intake are on the same building surface such that wind flows along the building surface would transport the release to the intake, the initial dispersion coefficient will need to be adjuste If the included angle between the source-receptor line of sight and the vertical axis of the assumedsource is less than 45 degrees, Yo should be set to If the included angle between the source-receptor line of sight and the horizontal axis of the assumed source is less than 45 degrees,Zo should be set to .3Determination of Control Room Intakes (Receptors)This section of the guide provides guidance to the meteorological analyst in applyingmodels for determining /Q values that are appropriate for the as-built configuration of controlroom intake Radioactive materials released during an accident can enter the control room envelope via several potential pathway These pathways may be intentional (e.g., ventilation system outside air intakes) and unintentional infiltration paths (e.g., doorways, envelope penetrations, leakage in ventilation system components). The applicable pathways will vary from site to site depending on the arrangement of the control room envelope in relation to other site buildings, the pressure differentials between these buildings and the control room, the configuration of control room ventilation systems, and the classification of the control room dose control (e.g., zone isolation with filtered pressurization, zone isolation with no pressurization). Itmay be necessary to determine /Q values for each potential pathwa However, the selection ofone or more bounding intakes for the /Q evaluation may be sufficient to establish compliancewith regulatory guidelines.3. Ventilation System Outside Air IntakesAll control room ventilation systems draw makeup air from the environment during normaloperations and many draw air from the environment for the purpose of supplying filtered pressurization ai The configuration of these systems may change between normal and emergency mode In some configurations, normal ventilation outside air intakes isolate and different intakes open to supply pressurization ai Some intake dampers may have failure modes related to loss of ac power or single failure These considerations should be evaluated in identifying the controlroom outside air intakes for which /Q values should be calculated.3. Dual Ventilation Outside Air IntakesThis section applies to control room ventilation system configurations that have twooutside air intakes, each of which meets applicable design criteria of an engineered safeguards feature (ESF), including single-failure criterion, missile protection, seismic criteria, and operability under loss-of-offsite AC power condition Operability requirements should be provided in technical specification The outside air intakes should be located with the intent of providing a low contamination intake regardless of wind directio The assurance of a low contamination outside air intake depends on release point configuration, building wake effects, terrain, and the possibility of wind stagnation or wind direction reversal The two intakes should not be within the same wind direction window, defined as a wedge centered on the line of sight between the 1.194-12source and the receptor with the vertex located on the release poin If ARCON96 is used, thewedge angle is 90 (i.e., 45 degrees on either side of the line of sight). If the methods ofRegulatory Position 4 are used, the size of the wedge is as given in Table Figure 3 illustrates four examples of the interplay between control room intakes, release points, and wind directionwindow In addition, the analyst should consider /Q values for infiltration pathways asdiscussed in Regulatory Position 3.3.3.The methods of this regulatory position involve identification of the limiting and favorableintakes with regard to their /Q valu Because of the interplay of building wake, plume rise, winddirection frequency, intake flow rate, and other parameters, it may not be possible to identify thelimiting or favorable intake by observatio In these situations, /Q values should be calculatedfor each release point-intake combination and the limiting and favorable intakes identified on the basis of these values. 3.3. If both of the dual intakes are located within the same wind direction window,both intakes could be contaminated (See Figure 3(a)). In this case, the /Q values for each airintake should be calculated using ARCON96 as described in other sections of this guide and aneffective /Q value calculate Equation 5a should be used if the intake flow rates are equa Ifthe intake flow rates are not equal, but the imbalance does not shift between intakes, Equation 5b should be use If the flow rate imbalance can shift between intakes, Equation 5c should be use This calculation is repeated for each averaging time interval.(5a)21Q/Q/21Q/(5b)212211FFQ/FQ/FQ/(5c)2121212121FFQ/,Q/min)F,Fmin(Q/,Q/max)F,Fmax(Q/Where:=Effective /Q, s*m-3/Q(/Q)1, (/Q)2=/Q value for outside air intakes 1 and 2, s*m-3F1, F2=Flow rate for outside air intakes 1 and 2, cfm3.3. If the dual outside air intakes are not in the same wind direction window butcannot be isolated by design, the /Q values for the limiting outside air intake should be calculatedfor each time interval as described elsewhere in this guid Equation 6a should be used if theintake flow rates are equa If the intake flow rates are not equal, but the imbalance does not shift between intakes, Equation 6b should be use If the flow rate imbalance can shift between intakes, Equation 6c should be used.(6a)21Q/,Q/max21Q/

8 The adjustment protocol and the numeric factors of this section are deterministic in nature and are expected to be conservativefor most site Different factors may be considered on a case-by-case basis with sufficient justification.1.194-13(6b)212211FFQ/F,Q/FmaxQ/(6c)212121FFQ/,Q/max)F,Fmax(Q/3.3. If the ventilation system design allows the operator to manually select the leastcontaminated outside air intake as a source of outside air makeup and close the other intake, the/Q values for each of the outside air intakes should be calculated for each time interval asdescribed elsewhere in this guid The /Q value for the limiting intake should be used for thetime interval prior to intake isolatio This /Q value may be reduced by a factor of 2 to accountfor dilution by the flow from the other intake (see Equation 6a).8 The /Q values for the favorableintake are used for the subsequent time interval The /Q values for the favorable intake may bereduced by a factor of 4 to account for the dual inlet and the expectation that the operator will make the proper intake selectio This protocol should be used only if the dual intakes are in different wind direction windows and if there are redundant, ESF-grade radiation monitors within each intake, with control room indication and alarm, to monitor the intake The requisite steps to select the least contaminated outside air intake, and provisions for monitoring to ensure the least contaminated intake is in use throughout the event, should be addressed in procedures and in operator training.A conservative delay time should be assumed for the operator to complete the necessaryaction This delay period should consider: (1) the time for the operator to recognize the radiation monitor alarm and determine its validity (as provided for in the alarm response procedure),

(2) delays associated with other accident response actions competing for the operator's attention,(3) the time needed to complete the actions, and (4) diesel generator sequencing time, if applicabl If actions are required outside the control room, delays associated with transit to the local control stations (including those delays caused by worker radiological protection controls associated with accident dose rates), and the availability of personnel should be considered.3.3. If the ventilation system design provides for automatic selection of the leastcontaminated outside air intake, the /Q values for the favorable intake should be calculated foreach time interval as described elsewhere in this guid The /Q values may be reduced by afactor of 10 to account for the ability to automatically select a "clean" intak This protocol should be used only if the dual intakes are in different wind direction windows, there are redundant ESF-

grade radiation monitors within each intake, and an ESF-grade control logic and actuation circuitry is provided for the automatic selection of a clean intake throughout the even . Infiltration PathwaysInfiltration of contaminated air to a control room can be minimized by proper design andmaintenance of the control room envelope (CRE). However, infiltration is always a possibilityand the location and significance of these leakage pathways may warrant determination of /Qvalue An unfiltered inleakage path of 100 cfm can admit the same quantity of radioactive material as a pressurization air intake having a flow of 2000 cfm through a 95 percent efficient 9 The site meteorological tower wind direction sensors are generally calibrated with reference to true north (360 degrees). Analystsshould use caution in measuring directions on site engineering drawings since these drawings typically incorporate a plant grid anda plant "north" that may not align with true nort The source-to-receptor directions input to ARCON96 must use the same northreference as the wind direction observations.1.194-14filte The situation can be further compounded if the /Q for the unfiltered pathway is morelimiting than that for the control room outside air intak The infiltration paths actually applicable to a particular facility will be identified viainleakage testing or CRE inspections and surveillance Refer to Table H-1, "Determination of Vulnerability Suspectability," of NEI 99-03, "Control Room Habitability Guidance" (Ref. 16), for further guidance on infiltration pathways.A 95th-percentile /Q value should be determined for each time interval for any infiltrationpath that could result in a significant intake of contaminated air into the CR Because of the interplay of source-to-receptor distance and direction, infiltration path flow rate, whether the path is filtered or unfiltered, and other considerations, it may not be possible to identify the potentialimpact of an infiltration path by observatio In these situations, /Q values should be calculatedfor each pathway and the limiting /Q value(s) identifie If there is sufficient margin available, itmay be possible to calculate /Q values assuming the shortest distance between the release pointand any identified point of infiltration on the outside of the CR .4Determination of Source-Receptor Distances and DirectionsWhen the combinations of release points and intakes have been identified, the direction anddistance between the release point and the intake should be determine Wind direction data are recorded as the direction from which the wind blows (e.g., a north wind blows from the north, a wind blowing out of the west is recorded with a direction of 270 degrees). The direction input to ARCON96 is the wind direction that would carry the plume from the release point to the intake.9 For example, an analyst standing at the intake facing west to the release point, would enter 270 degrees; an analyst facing north, would enter 360 degrees, etc.The source-to-receptor distance is the shortest horizontal distance between the release pointand the intak ARCON96 will use this distance and the elevations of the source and receptor to calculate the slant pat For an area source such as building surface, the shortest horizontal distance from the building surface to the control room intake is used as the source-to-receptor distanc For releases within building complexes, the shortest horizontal distance between the release point and the intake could be through intervening building In these cases, it is acceptable to take the length of the shortest path (e.g., "taut string length") around or over the intervening building as the source-to-receptor distanc If the distance to the receptor is less than about 10 meters, the ARCON96 code and the procedures in Regulatory Position 4 should not be used toassess /Q value These situations will need to be addressed on a case-by-case basi The Murphy-Campe document identified this as the 5th-percentile /Q value.1.194-154.ALTERNATIVE PROCEDURES FOR GROUND-LEVEL RELEASESThis regulatory position addresses alternative methods for determining /Q values forcontrol room radiological habitability assessment The methods in Regulatory Positions 4.1 to 4.3 are based on Murphy-Campe (Ref. 2) and the Standard Review Plan Chapter 6.4 (Ref. 3).4.1Point Source-Point ReceptorThe 0-8 hour 95th-percentile10 /Q value for a single point source on the surface of thecontainment or other building and a single point receptor with a difference in elevation less than 30 percent of the building height may be estimated using Equation (7)zyU31QWhere:/Q=Relative concentration at plume centerline for time interval 0-8 hours, s*m-33=Wake factorU=Wind speed at 10 meters, m*s-1y, z=Standard deviation, in meters, of the gas concentration in the horizontal andvertical cross wind directions evaluated at distance x and by stability class4.2Diffuse Source-Point ReceptorEquation 8 may be used when the activity is assumed to leak from many points on the surface of abuilding such as the containment in conjunction with a single point recepto This equation is also appropriate for point source-point receptors where the difference in elevation between the source and the receptor is greater than 30 percent of the height of the upwind building, typically the containment, which creates the most significant building wake impac The equation is also applicable to a point source and volume receptor (e.g., an isolated control room with infiltration occurring at many locations). (8)QUAKyz21Where:/Q=Relative concentration at plume centerline for time interval 0-8 hours, s*m-3U=Wind speed at 10 meters, m*s-1y, z=Standard deviation, in meters, of the gas concentration in the horizontal andvertical cross wind directions evaluated at distance x and by stability classK=4.1)d/s(3 11 Previous guidance also provided for including a factor to account for personnel occupancy factor Since typical radiologicalanalysis codes provide the capability to enter these factors separately, the staff recommends that the factors not be included in the/Q value to avoid inadvertent double crediting. 1.194-16s=Shortest distance between building surface and receptor location, md=Diameter or width of building, mA=Cross-section area of building, m2The reference to "building" in the definitions of s, d, and A is to the diffuse source (e.g.,containment). If the equation is used with a point source, the reference is to the building that has the greatest impact on the building wak The values of the parameters y, z and U should be determined onthe basis of the values of the site meteorological dat Some early analyses may have been based on generic meteorology conditions (e.g., F stability with wind speeds of 1.0 m*s-1). If these early analyses areto be updated, the staff recommends that the ARCON96 code be use If the ARCON96 code is not used,site-specific hourly meteorological data should be used to determine the 95th-percentile /Q value. Figures 4 and 5 provide sigma values by stability category for distances greater than 10 meter The data on these graphs should not be extrapolated for distances less than 10 meters.4.3Point or Diffuse Source with Two Alternative ReceptorsEquations 7 and 8 of this guide may be used in conjunction with the procedures in RegulatoryPosition 3.3.2 to determine /Q values for control room designs having two or more control room outsideair intakes, each of which meets the requirements of an engineered safety feature (ESF) including, as applicable, single-failure criteria for active components, seismic criteria, and missile criteri If Equation 8 of this guide is used, the parameter K should be set to In a change from previous practice, the staff no longer finds Equation 7 of Reference 2 to be acceptable for use in new applications.4.4Determination of /Q Values for Other Time IntervalsEquations 7 and 8 are used to determine /Q values for the first time interval of 0-8 hour The/Q values for other time intervals are obtained by adjusting for long-term meteorological averaging ofwind speed and wind direction.11 This is accomplished by multiplying the 0-8 hour time interval /Q valueby a correction factor for wind speed and a correction factor for wind direction.4. /Q Correction for Wind Speed Averaging This correction is defined as the ratio of the wind speed used to determine the 0-8 hour /Q valueto the wind speed appropriate for each of the other time interval Column 2 of Table 1 tabulates the wind speed percentiles that correspond to each of these interval The hourly data should be arranged in order of increasing wind speed and the wind speed percentiles determined (i.e., the lowest wind speeds associated with the lowest percentiles). Include only the wind speed data associated with wind directions from sectors that result in receptor contaminatio Table 2 tabulates the size of the minimum wind direction window to be use From this ranking, identify the wind speed value for each interval that is not exceeded more than the stated percentage of the tim Divide this wind speed value into the 5th-percentile windspeed used to determine the 0-8 hour /Q to obtain the /Q correction factor for wind spee The valuesshown in Column 1 of Table 1 are representative correction factors that may be used if hourly observation meteorological data are not available.Table 1 12 Centered on the source-to-receptor direction.1.194-17/Q Correction for Wind Speed AveragingColumn 1Column 2RepresentativeCorrespondingTime Interval/Q FactorsWind Speed Percentile0-8 hours1.058-24 hours0.6710 1-4 days0.5020 4-30 days0.3340Table 2Wind Direction Sectorss/d RatioMinimum Window12>2.5681.25 - 2.590~ !"! " ! #! ~~ The s/d is defined as:(9)m building, of Widthor Diameter m location, receptor and surface building between distance ShortestdsThe reference to "building" in Equation 9 is to the diffuse source (e.g., containment). If theequation is used with a point source, the reference is to the building that has the greatest impact on the building wak . /Q Correction for Wind Direction Averaging The average wind direction frequency F is obtained by summing the annual average wind directionfrequencies within the minimum windo Table 2 tabulates the size of the minimum wind directionwindow to be use Column 2 of Table 3 is used to determine the /Q correction factor for wind directionfor each time interva Column 1 is used when F has not been determined.Table 3Wind Direction Averaging CorrectionColumn 1Column 2RepresentativeEquations for 1.194-18Time Interval/Q Factors/Q Factors0-8 hours1.01.08-24 hours0.880.75 + F/4 1-4 days0.750.50 + F/2 4-30 days0.5F5.INSTANTANEOUS PUFF RELEASESThe alternative method in this section may be used to model the release to the environment as aninstantaneous puff releas One hundred percent of the radionuclides must be released directly to the environment over a period no longer than about 1 minute for a release to qualify as a puff releas Releases to enclosed buildings, intermittent releases that occur over a period longer than about 1 minute (e.g., releases from relief valves, atmospheric dumps), and releases that occur over a period longer than about 1 minute should be treated as continuous point source release The diffusion equation for an instantaneous puff ground level release, with no puff rise and no crosswind offset (i.e., center of puff is assumed to pass over control room intake), integrated over the duration of the puff passage is:$$T0T02I2z22I2y,x22I2y,x23212I2zdt)t(Fdt)t(F))k,x((h))k,x(()tux(21exp))k,x(()2())k,x((2),h,k,u,x(Q(10)Where:=Effective puff relative concentration, s*m-3)h,k,u,x(Q=Integrated concentration at control room intake, Ci*m-3*s-1Q i=Release quantity, for nuclide i, Cix=Release point to receptor distance, mu=Wind speed, m/se Assume 1.0 m*s-1k=Stability Clas Assume F.h=Difference in elevation between the physical release point and the control roomintake, If the control room intakes is at a higher elevation than the release point and the puff is buoyant, assume h = 0.T=Time for trailing edge of puff to pass control room intake, sec.=u)k,x(3xIy,xF=Control room total intake flow rate, cf (If the control room intake flow rate isconstant over the period 0 to T seconds, the F(t) terms can be omitted from Equation 10.)

13 As used here, 95th-percentile wind speed is that wind speed that is not exceeded more than 5 percent of the tim A 95th-percentile ambient temperature is that temperature that is not exceeded more than 5 percent of the time.1.194-19=Standard deviation, m, of the puff in the horizontal along the wind direction and)k,x(y,xcross-wind directions at the receptor locatio Use Figure 4 with the distance xand stability class k to determine at the receptor, e.g., .y,xyy,x=Standard deviation, m, of the puff in the vertical cross-wind direction at the)k,x(zreceptor locatio Use Figure 5 with the distance x and stability class k todetermine at the recepto z=Initial standard deviation, mI=3123)2(V2V=Initial puff volume (expanded to standard atmospheric conditions), m3 (The puffdimensions that would exist when the puff is at the control room intake are assumed to exist during the entire puff transit.) Equation 10 provides the effective relative concentration for the puf This value can be input todose assessment codes such as RADTRAD or HABIT as any value of /Q would be if the intake flows,release duration, and release rates are modeled consistent with the inputs to Equation 10.6.PLUME RISEAn applicant or licensee may propose adjustments to the release height for plume rise that are dueto buoyancy or mechanical jet on a case-by-case basi In order to credit these adjustments, the applicant or licensee must be able to demonstrate that the assumed buoyancy or vertical velocity of the effluent plumes will be maintained throughout the time intervals that plume rise is credite Such justifications need to consider the availability of AC power, failure modes of dampers and ductwork, time-dependent release stream temperatures and pressures, and 95th-percentile wind speeds and ambient temperatures.13 Plume rise may be considered for freestanding stacks and for vents located on plant building However, plume rise may not be used in demonstrating that a particular stack meets the 2-1/2 times the adjacent structure height criterion in Regulatory Position 3. A mixed-mode release model, such as that in Regulatory Guide 1.111 (Ref. 10), should not be used for design basis assessments.The plume rise may be determined through the use of the following set of equations (Ref. 17). Theplume rise for plant vents is determined using Equation 1 The distance x is entered as the horizontal distance between the vent and the control room outside air intak The plume rise for isolated, free-standing stacks is calculated using Equations 11, 12, and 1 Thedistance x in Equation 11 should be based on the downwind location corresponding to the maximum /Qvalu See Regulatory Position 3. The plume rises calculated using Equations 12 and 13 should be compared and the larger plume rise identifie The result of this comparison is then compared to the plume rise determined using Equation 11 and the smaller plume rise selected for us (11)3/123b212m21xUF23xUF3h%%

14 This adjustment factor and the associated velocity ratio criterion are deterministic in nature and their selection was based onsensitivity analyses performed for typical steam release points at LWR The adjustment factor should not be ratioed for differentvertical velocity ratios.1.194-20(12)3/1bUsF6.2h(13)4/1msF44.2hWhere:h=Plume rise, mFm=Momentum flux parameter, m4s-2=aooowV&1=Dimensionless entrainment constant for momentum = 0.6U=Wind speed at release height, ms-1x=Distance from release point to receptor, m (see text)Fb=Buoyancy flux parameter, m4s-3=aooaV)(g&&wo=Effluent exit velocity, ms-1Vo=Volumetric release rate, m3s-1&o=Effluent density after expansion to atmospheric pressure, kgm-3&a=Density of air, kgm-3s=0.0001 s-2 for A, B, C, and D stability; 0.00049 s-2 for E stability; 0.0013 s-2 for Fstability; 0.002 s-2 for G stabilityg=Gravitational acceleration, 9.8 ms-2Although ARCON96 processes ambient meteorological conditions on an hour-by-hour basis, thecode cannot vary the other parameters that enter into a plume rise determinatio For example, wind speed and stability class are varied hour by hour, but the density of air, the density of the effluent stream, and the vertical velocity are not varied hour-by-hou As such, the analyst should ensure that these parameters arebounding for the entire period of the /Q assessment or use individual time intervals to model the time-variant parameter An alternative approach would be to calculate the plume rise for each hour independently of ARCON96 and to select a plume rise that is exceeded more than 95 percent of the tim This rise is then added to the stack height as input to ARCON96.In lieu of mechanistically addressing the amount of buoyant plume rise associated with energeticreleases from steam relief valves or atmospheric dump valves, the ground level /Q value calculated withARCON96 (on the basis of the physical height of the release point) may be reduced14 by a factor of 5. This reduction may be taken only if (1) the release point is uncapped and vertically oriented and (2) the time-dependent vertical velocity exceeds the 95th-percentile wind speed13 (at the release point height) by afactor of .194-217.USE OF SITE-SPECIFIC EXPERIMENTAL DATAThe methods and parameters provided in this guide are acceptable for use for design basis controlroom habitability radiological assessments provided that all stated prerequisites and conditions are met. The staff believes that use of the guidance in this guide will result in /Q values that are acceptablyconservativ However, there may be circumstances in which these methods and parameters may not be advantageous for a particular plant configuration and site meteorological regimes and may lead to results that are deemed to be unnecessarily conservativ Licensees and applicants may opt to propose alternative methods and parameters such as those that are based in part on data obtained from site-specific experimental measurement Data based on wind tunnel tests should be accompanied with an evaluation of the representativeness of the experiment results to the particular plant configuration and site meteorological regime These proposed alternatives, with supporting data, will be considered by the staff on a case-by-case basi The staff recommends that licensees considering an experimental program request a meeting withthe staff in advance of starting the progra The intent of this recommendation is to allow the staff and the licensee (or applicant) to discuss the proposed program, prior to resource expenditure, and for the staff to provide a preliminary assessment of the proposa The staff's approval of the proposed alternativemethods and parameters will not be granted, however, until the licensee or applicant completes the experimental program and dockets the proposal with supporting analyses and data for formal staff review.An acceptable experimental program should incorporate the following standards:7.1The experimental program should be appropriately structured so as to provide data of appropriatequantity and quality to support data analysis and conclusions drawn from that dat The program should be developed by personnel who have educational and work experience credentials in air dispersion meteorology and modeling. 7.2The experimental program should encompass a sufficient range of meteorological conditionsapplicable to the particular site so as to ensure that the data obtained address the site-specific meteorological regimes and the site-specific release point/receptor configurations that impact the controlroom /Q value Meteorological conditions observed at the particular site with a frequency of 5 percentor greater in a year should be addresse Parameters derived from statistical analyses on the experimental data should represent the 95th-percentile confidence level.7.3The experimental program, including data reduction and analysis, should incorporate applicablequality control criteria of Appendix B to 10 CFR Part 5 The products of the experimental program should be verified and validate IMPLEMENTATIONThe purpose of this section is to provide information to licensees and applicants regarding theNRC staff's plans for using this regulatory guid No backfitting is intended or approved in connectionwith the issuance of this guide.Except when an applicant or licensee proposes an acceptable alternative method for complyingwith the specified portions of the NRC's regulations pertaining to control room habitability, the methods described in this guide will be used in the evaluation of the compliance with these regulations in (1)

license amendments at operating reactors, (2) combined operating license applications, (3) construction permit applications, (4) operating license applications, and (5) design certification application .194-22Figure 1ZONE OF INFLUENCE FOR STACKSNote: In this example, L is taken has the height or width, whichever is less, of the building clustercross-section perpendicular to the win A stack located inside the zone should be 2.5 times (2.5X) the height of the structure that causes the building wak The zone will change with wind direction and, depending on the building arrangement, there may be overlapping zone For example, a stack located at 5L could not be considered "freestanding" if that point was within 2Lof a downwind buildin For control room applications, wind directions in the 90 degree sector centered on the line of sight between the stack and the intake should be considered when defining the cross-section and .194-23Figure 2ARCON96 DIFFUSE SOURCE MODELINGThis figure applies only to the modeling of a diffuse source in ARCON9 Only that part of the structure abovegrade or an enclosing building should be included in the building heigh However, the height need not be reduced for an adjacent building if the assumed building surface release can be reasonably transported around or over the building to the intak .194-24Turbine BldgControl BldgFuel BuildingContainmentTurbine BldgControl BldgFuel BuildingContainmentTurbine BldgControl BldgFuel BuildingContainmentTurbine BldgControl BldgFuel BuildingContainment(a)(b)(c)(d)These figures apply when using the methodology described in Regulatory Position 3.3.2Wind direction window(assuming release pointon top of containment)Figure 3ALTERNATIVE LOCATIONS FOR DUAL INTAKES These figures apply when using the methodology described in Regulatory Position 3. .194-25101234456102234456103234456104Distance from Source, m10-1234456100234456101234456102234456103Sigma-Y, Lateral Dispersion Coefficient, mCalculated using method of POLYN subroutine in PAVAN (Ref. 14); also Eimultis and Konicek (Ref. 18)ABCDEFGDO NOT extrapolate below 10 meter Figure 4LATERAL DISPERSION COEFFICIENT vs DISTANCE AND STABILITY CLASS 1.194-26101234456102234456103234456104Distance from Source, m10-1234456100234456101234456102234456103Sigma-Z, Vertical Dispersion Coefficient, mCalculated using method of POLYN subroutine in PAVAN (Ref. 14); also Eimultis and Konicek (Ref. 18)ABCDEFGDO NOT extrapolate below 10 meter Figure 5 VERTICAL DISPERSION COEFFICIENT vs DISTANCE AND STABILITY CLASS 1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328(telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road,Springfield, VA 22161; < telephone (703)487-465 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR's mailing address is USNRC PDR, Washington, DC20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV. 2 Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automaticdistribution list for single copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; email <DISTRIBUTION@NRC.GOV>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor), Rockville, MD; the PDR's mailing address is USNRC PDR,Washington, DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.1.194-27REFERENCES1.J.V. Ramsdell, Jr., and C.A. Simonen, "Atmospheric Relative Concentrations in BuildingWakes," NUREG/CR-6331, Revision 1, USNRC, May 1997.12.K.G. Murphy and K.W. Campe, "Nuclear Power Plant Control Room Ventilation SystemDesign for Meeting General Criterion 19," published in Proceedings of 13th AEC AirCleaning Conference, San Francisco, CONF 740807, U.S. Atomic Energy Commission(now USNRC), August 1974.3.USNRC, "Standard Review Plan For the Review of Safety Analysis Reports for NuclearPower Plants," Chapter 6.4, "Control Room Habitability System," NUREG-0800,USNRC, 1987.1 4.J.V. Ramsdell, Jr., "Atmospheric Diffusion for Control Room Habitability Assessments,"NUREG/CR-5055, USNRC, May 1988.15.J.V. Ramsdell, Jr., "Diffusion in Building Wakes for Ground Level Releases," AtmosphericEnvironment, 24B(3):377-388, 199 .G.A. Briggs et al., "Discussion," Atmospheric Environment, 26B(4):513-515, 1992. 7.J.V. Ramsdell, Jr., "Author's Reply," Atmospheric Environment, 26B(4):515-517, 1992. 8.USNRC, "Assumptions for Evaluating the Habitability of a Nuclear Power Plant ControlRoom During a Postulated Hazardous Chemical Release," Regulatory Guide 1.78, Revision 1, December 2001.9.USNRC, "Atmospheric Dispersion Models for Potential Accident ConsequenceAssessments at Nuclear Power Plants," Regulatory Guide 1.145, Revision 1, November1982.210.USNRC, "Methods for Estimating Atmospheric Transport and Dispersion of GaseousEffluents in Routine Releases from Light-Water-Cooled Reactors," RegulatoryGuide 1.111, Revision 1, July 197 .194-2811.J.J. DiNunno et al., "Calculation of Distance Factors for Power and Test Reactor Sites,"USAEC TID-14844, U.S. Atomic Energy Commission (now USNRC), 196 (Available through the NRC's Public Electronic Reading Room, Accession number 8202010067.) 12.USNRC, "Onsite Meteorological Programs," Safety Guide 23, February 1972.2 (N.B. maybe referred to elsewhere as Regulatory Guide 1.23.)13.W.G. Snell, "Nuclear Regulatory Commission Staff Computer Programs for Use withMeteorological Data," NUREG-0917, USNRC, July 1982.114.T.J. Bander, "PAVAN: An Atmospheric Dispersion Program for Evaluating Design BasisAccidental Releases of Radioactive Materials from Nuclear Power Stations," NUREG/CR-2858, USNRC, November 1982.115.D.H. Slade, Editor, "Meteorology and Atomic Energy," TID-24190, USNRC, 1977. (Available through the NRC's Public Electronic Reading Room at <www.nrc.gov> underAccession number 8203090377.)16.Nuclear Energy Institute, "Control Room Habitability Guidance," NEI 99-03, Revision 0,June 2001 (available through the NRC's Public Electronic Reading Room, AccessionNumber ML020600236).17.D. Randerson, Editor, "Atmospheric Science and Power Production," DOE/TIC-27601,198 (Available from National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161; telephone (800)553-6847; <http://www.ntis.gov/ordernow> , NTIS number 84005177.) 18.E.C. Eimutis and M.G. Konicek, "Derivations of Continuous Functions for the Lateral andVertical Atmospheric Dispersion Coefficients," Atmospheric Environment, Vol 6, p , Pergamon Press, 197 .194-29Appendix AARCON96 METEOROLOGICAL DATA SET STRUCTUREThe meteorological data set is input to the ARCON96 code as one or more data filescomposed of a series of records, each of which contains the data for one hourly observatio Data should be reviewed to ensure that parameter conversions or normalizations have been made properl These data should be input to ARCON96 in chronological orde ARCON96 can accept up to 10 separate meteorological data files in a single ru Each individual file may contain the data for one year, a fraction of a year, or multiple year ARCON96 will process the data in blocks of 10,000 records, spanning files as necessary, until all data are processe The file is a formatted, ASCII text data fil The format of each record is shown in Table A- Table A-2 discusses input parameters for ARCON96.Table A-1ARCON96 METEOROLOGICAL DATA SET1FieldParameterDiscussion1XOne blank spaceA4IdentifierAny four character string to identify fil Canbe used for any purpose, site name, etc.I4Calendar yearFour digit calendar year.

I3Julian date of observation1-365 or 1-366 (leap year) as an integer.

I2Hour of day of observationLocal time, 24-hour clock, 0-23, with midnight= 0 as an integer.2XTwo blank spacesI3Lower-level wind directionIn degrees from which wind is blowing as anintege A wind from the north is entered as 360 and a wind from the south is entered as 180.I4Lower-level wind speedIn mph, m*s-1, or knots, entered to the nearesttenth of the reporting unit2 with the decimalpoint assume For example, 5.3 m*s-1 is enteredas 53, 5 meters/second as 50, et XOne blank spaceI2Stability classAs an integer, A=1, G=7. If determined usingT, the vertical temperature difference is thatmeasured over the difference in elevation appropriate for the projected release height.32XTwo blank spacesI3Upper-level wind directionIn degrees from which wind is blowing as anintege A wind from the north is entered as 360 and a wind from the south is entered as 180.I4Upper-level wind speedIn mph, m*s-1, or knots, entered to the nearesttenth of the reporting unit2 with the decimalpoint assume For example, 5.3 m*s-1 is enteredas 53, 5 meters/second as 50, et Notes:(1)Invalid data should be represented by the field completely filled with 9 For example, "999" for aI3 field, "999" for a I4 field.(2)The analyst selects the reporting unit on an ARCON96 dialog form during the code run. ARCON96 analysts need to ensure that the measurement unit used to represent wind speed in the data set corresponds to the measurement unit selected on the dialog form.(3)The stability classification table in Safety Guide 23 assumes that T is expressed in units ofC/100 Analysts need to ensure that the site-specific values are converted to the same units usedin Safety Guide 2 .194-30For example, for 0500 on the 165th day of 2002, with a level 1 wind direction of 78, alevel 1 wind speed of 5.3 mph, a stability class of A ("1"), and a level 2 wind direction of 180,and a level 2 wind speed of 10.1 mph, the record would read (blank).TEST200216505078005311800101 1.194-31Table A-2ARCON96 INPUT PARAMETERS FOR DESIGN BASIS ASSESSMENTSParameterDiscussionAcceptable InputLower Measurement Height,metersThe value of this parameter is used byARCON96 to adjust wind speeds for differences between the heights of the instrumentation and the release.Use the actual instrumentation height when known. Otherwise, assume 10 meters.Upper Measurement Height,metersThe value of this parameter is used byARCON96 to adjust wind speeds for differences between the heights of the instrumentation and the release.Use the actual instrumentation height when known. Otherwise, use the height of the containment or the stack height, as appropriat If wind speed measurements are available at more than two elevations, the instrumentation at the height closest to the release height should be used.Wind Speed UnitsARCON96 requires that wind speed beentered as miles per hour, m*s-1, or knots.Use the wind speed units that correspond to the units ofthe wind speeds in the meteorological data file.Release Height, metersThe value of the release height is used forthree purposes in ARCON96: (1) to adjust wind speeds for differences between the heights of the instrumentation and the release, (2) to determine slant path for ground level releases, (3) to correct off-centerline data for elevated releases.Use the actual release heights whenever available. Plume rise from buoyancy and mechanical jet effects may be considered in establishing the release height if the analyst can demonstrate with reasonable assurance that the vertical velocity of the release will be maintained during the course of the accident.

If actual release height is not available, set release height equal to intake height.Building Area, meters2ARCON96 uses the value of the building areain the high speed wind speed adjustment for ground-level and vent release models.Use the actual building vertical cross-sectional areaperpendicular to the wind direction. Use default of 2000 m2 if the area is not readily available. Do not enterzero. Use 0.01 m2 if a zero entry is desired.Note: This building area is for the building(s) that hasthe largest impact on the building wake within the wind direction window. This is usually, but need not always be, the reactor containment. With regard to the diffuse area source option, the building area entered here may be different from that used to establish the diffuse source.Vertical Velocity,meters/secondIn ARCON96, the value of the verticalvelocity is used only in vent and stack release model It is used for the downwash calculatio In the vent release model the velocity is used in the mixed-mode calculation.If the vertical velocity is set to zero, themaximum downwash will be calculated and the release height will be reduced by an amount equal to six times the stack radius.Note: the vent release model should not be used forDBA accident calculations.For stack release calculations only, use the actualvertical velocity if the licensee can demonstrate with reasonable assurance that the value will be maintained during the course of the accident (e.g., addressed by technical specifications), otherwise, enter zer If the vertical velocity is set to zero, ARCON96 will reduce the stack height by 6 times the stack radius for all wind speed If this reduction is not desired, the stack radius should also be set to zer ParameterDiscussionAcceptable Input1.194-32Stack Flow, meters3/secondARCON96 uses the value of the stack flow in/Q calculations for all 3 release types toensure that the near field concentrations are no greater than the concentration at the release point. The impact diminishes with increasing distance.Use actual flow if it can be demonstrated withreasonable assurance that the value will be maintained during the course of the accident (e.g., addressed by technical specifications). Otherwise, enter zero.The flow is used in both elevated and ground-levelrelease modes to establish a maximum /Q valu Thisvalue is significant only if the flow is large and the distance from the release point to the receptor is small.Stack Radius, metersARCON96 uses the value of the stack radiusin downwash calculations in the vent and stack release modes.Use the actual stack internal radius when both the stackradius and vertical velocity are available. If the stack flow is zero, the radius should be set to zero.Distance to Receptor,metersThe value of horizontal distance to thereceptor from the release point is used in ARCON96 for calculating the slant range for ground level releases and the off-centerline correction factors for stack release models.Use the actual straight line horizontal distance betweenthe release point and the control room intake.For ground-level releases, it may be appropriate toconsider flow around an intervening building if the building is sufficiently tall that it is unrealistic to expect flow from the release point to go over the building. Note: If the distance to receptor is less than about 10meters, ARCON96 should not be used to assess relative concentrations.Intake Height, metersThe value of the intake height is used inARCON96 for calculating the slant range for ground level releases and the off-centerline correction factors for stack release models.Use the actual intake height. If the intake height is notavailable for ground level releases, assume the intake height is equal to the release height. For elevated releases, assume the height of the tallest site building.Elevation Difference, metersThe value of this parameter is used byARCON96 to normalize the release heights and the intake heights when the two heights are specified as "above grade" with different grades for the release point and intake height, or when one measurement is referenced to

"above grade" and the other to "above sea level."Use zero unless it is known that the release heights arereported relative to different grades or reference data.Direction to Source, degreesARCON96 uses the value of this parameterand the Wind Direction Window to establish which range of wind directions should beincluded in the assessment of the /Q.Use the direction FROM the intake back TO the releasepoint. (Wind directions are reported as the direction from which the wind is blowing. Thus, if the direction from the intake to the release point is north, a north wind will carry the plume from the release point to the intake.) Note: some facilities have a "plant north" shown onsite arrangement drawings that is different from "true north." The direction entered must have the same point of reference as the wind directions reported in the meteorological dat For ground-level releases, if the plume is assumed toflow around a building rather than over it, the direction may need to be modified to account for the redirectedflow. In this case, the /Q should be calculatedassuming flow around and flow over (through) the building and the higher of the two /Q s should beuse ParameterDiscussionAcceptable Input1.194-33Surface Roughness Length,metersARCON96 uses the value of this parameter inadjusting wind speeds to account for differences in meteorological instrumentation height and release height.Use a value of 0.2 in lieu of the default value of 0.1 formost sites. (Reasonable values range from 0.1 for sites with low surface vegetation to 0.5 for forest-covered sites.)Wind Direction Window,degrees Code DefaultARCON96 uses the value of this parameterand the Direction to Source to establish which range of wind directions should be included inthe assessment of the /Q.Use the default window of 90 degrees (45 degrees oneither side of line of sight from the source to the receptor).Minimum Wind Speed,meters/secondCode DefaultARCON96 uses the value of this parameter toidentify calm conditions.Use the default wind speed of 0.5 m*s-1 (regardless ofthe wind speed units entered earlier), unless there is some indication that the anemometer threshold is greater than 0.6 m*s-1.Averaging Sector WidthConstant Code DefaultARCON96 uses the value of this parameter toprevent inconsistency between the centerlineand sector average /Q s for wide plumes. Haslargest effect on ground level plumes.Although the default value is 4, a value of 4.3 ispreferred. (A future revision to ARCON96 will change the default to 4.3)Initial DiffusionCoefficients, metersARCON96 uses these parameters in modelinga diffuse source.These values will normally be set to zero. If the diffusesource option is being used, see Regulatory Position 2.2.4.Hours in AveragesCode DefaultThe values of this parameter were selected toprovide results for desired periods and toprovide a smooth /Q curve.Use the default values.Minimum Number of HoursCode DefaultThe default values of this parameter will allowprocessing with up to 10% missing data.Use the default value .194-34REGULATORY ANALYSISA separate regulatory analysis was not prepared for this regulatory guid The regulatory analysisprepared for the draft of this guide, Draft Regulatory Guide DG-1111, "Atmospheric RelativeConcentrations for Control Room Radiological Habitability Assessments at Light-Water Nuclear Power Reactors" (December 2001), provides the regulatory basis for this regulatory guide as wel DG-1111was issued for public comment as the draft of this present regulatory guid A copy of DG-1111 with the regulatory analysis is available for inspection and copying for a fee at the U.S. Nuclear Regulatory Commission Public Document Room, 11555 Rockville Pike, Rockville, MD; the PDR's mailingaddress is USNRC PDR, Washington, DC 20555; telephone (301) 415-4737 or 1-(800) 397-4209; fax (301) 415-3548; e-mail <PDR@NRC.GOV>. An electronic copy of DG-1111 with the regulatory analysis is also available in the NRC's Electronic Reading Room under ADAMS with AccessionNumber ML013130132.

Regulatory Guide 1.194

Intent

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