ML18037B017

Forwards Description of Util Methods for Evaluating Potential Release Paths & Determining Release Specific Atmospheric Dispersion Coefficients,In Response to NRC 940429 RAI Re BFN Meteorological Data

ML18037B017
Person / Time
Site:	Browns Ferry
Issue date:	08/10/1994
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-M83330, TAC-M83348, TAC-M83349, NUDOCS 9408170221
Download: ML18037B017 (67)

Text

RID RI "EY PACCELERATED RIDS PROCESSING)

REGULATC, INFORMATION DISTRIBUTION ESTEM (RIDS) I ACCESSION NBR:9408170221 DOC.DATE: 94/08/10 NOTARIZED: NO DOCKET FACIAL:50-259 Browns Ferry Nuclear Power Station, Unit 1, Tennessee 05000259 50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee 05000260 50-296 Browns Ferry Nuclear Power Station, Unit 3, Tennessee 05000296 AUTH. NAME AUTHOR AFFILIATION SALAS,P. Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control De'sk)

SUBJECT:

Forwards description of util methods for evaluating potential release paths & determining release specific atmospheric dispersion coefficients, in response to NRC 940429 RAI re BFN meteorological data.

DISTRIBUTION CODE: D030D TITLE: TVA Facilities COPIES RECEIVED:LTR Routine Correspondence g ENCL f SIZE: $0 NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-4 1 1 TRIMBLE,D 1 1 WILLIAMS,J. 1 1 INTERNAL: ACRS 6 6 NRR/DSSA 1 1 OC/LFDCB 1 0 OGC/HDS3 1 0 EG~W 01 1 1 RES/DE/SSEB/SES 1 1 NSIC LE'XTERNAL:

NRC PDR 1 1 1 1 NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2083 ) TO ELIM!NATE YOUR NAME FROM DISTRIBUTION LISTS I'OR DOCUMEiVTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 16 ENCL 14

II

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Tennessee Valley Authority. Post Office Box 2000, Decatur, Afabarna 35609 AUG 1 0 1994 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of Docket Nos. 50-259 Tennessee Valley Authority 50-260 50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING THE CONTROL ROOM EMERGENCY VENTILATION SYSTEM (CREVS) [TAC NOS. M83348, M83349, AND M83350]

On April 29, 1994, NRC requested additional information regarding BFN meteorological data and other parameters necessary for an independent analysis of meteorological data.

The requested information is being provided as part of the enclosure to this letter. In addition, TVA has included a description of TVA's methods for evaluating the potential release paths and determining the release specific atmospheric dispersion coefficients (X/Qs). TVA's modeling of the atmospheric transport of effluents used conservative methods and modern atmospheric transport solutions to demonstrate the doses to the control room operator would be below General Design Criterion 19 limits.

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)y6 9408170221 940810 PDR ADOCK 05000259 F PDR

U.S. Nuclear Regulatory Commission Page 3 AUG XO msC cc (Enclosure):

Mark S. Lesser, Section Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35611 Mr. J. F. Williams, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. D. C. Trimble, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852

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U.S. Nuclear Regulatory Commission Page 2 AUG iO 199<

Due to the complexity of the X/Q calculations, TVA requests a meeting at the staff's earliest convenience to review this information. There are no commitments contained in this letter. If you have any questions, contact telephone me at (205) 729-2636.

Sincer ly, Pedro Salas Manager of Site Licensing Enclosure cc: see page 3

ENCLOSURE TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT (BFN)

UNITS 1, 2, AND 3 CONTROL ROOM EMERGENCY VENTILATION SYSTEM (CREVS)

DETERMINATION OF PLANT SPECIFIC DISPERSION COEFFICIENTS (X/Qs)

INDEX I. BACKGROUND . . . . . . . . . . . . . . . . E-3 II. MODELING OF RELEASE PATHS . . . . . . . . E-5 III. DERIVATION OF DISPERSION E-7 COEFFICIENTS (X/Qs) . . . . . . . . . .

IV. RESPONSE TO SPECIFIC NRC REQUESTS . . . . E-22 V. CONCLUSION . . . . . . . . . . . . . . . . E-32 VI. REFERENCES . . . . . . . . . . . . . . . . E-33

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TABLES Table Page Inputs Used to Determine Turbine E-34 Building Roof Vent Dispersion Coefficients Maximum Annual Average Dispersion E-35 Coefficients from a Turbine Building Release Maximum Dispersion Coefficients E-36 from a Turbine Building Release FIGURES Figure Page Location of Intakes for CREVS E-37 General Plant Layout E-40 Plant Stack E-41 Cross-Section of the Base of the E-42 Plant Stack Transverse Section of the E-44 Reactor, Control, and Turbine Buildings Turbine Building Roof Vent E-45 Lateral Plume Spreading E-46 Wind Effects on Turbine Building E-47 Release E-2

I. BACKGROUND The Control Room Emergency Ventilation System (CREVS) was originally designed to maintain the main control room at a positive pressure using 500 CFM of processed outside air. The positive pressure was to ensure that all leakage should be outleakage. The air intakes for these original units were located on the North face of the Reactor Building, at plant Elevation 635', in the Units l and 3 ventilation towers.

During the Unit 2 Cycle 5 outage, an employee concern identified a specific condition that could impact the ability of the CREVS to provide an environment suitable for personnel occupancy. Ductwork, which supplies outside air to other areas of the Control Building, transverses the main control bay habitability zone (CBHZ). Ventilation fans, located in the ventilation towers, are used to pressurize this supply ductwork. These fans operate during the accident recovery period (30 days) to supply necessary cooling for essential equipment. The Control Building air supply ducts were not designed or fabricated to be leak tight.

Unfiltered outside air could leak from the seams/joints of the supply air ducts that traverse the control bay habitability zone. This duct leakage could result in make-up air bypassing the CREVS and introduce potentially contaminated and unfiltered outside air into the CBHZ.

As part of the early design basis for the CREVS, TVA postulated winds from the South-South-East (SSE), South (S), or South-South-West (SSW) sectors at speeds greater than thirty six miles per hour. These winds could offset the negative pressure maintained in the secondary containment (Reactor Building) by the standby gas treatment system (SGTS). Following a postulated Loss of Coolant Accident (LOCA), these high winds could produce ez-filtration from the reactor building. Effluents released into the reactor building could then be transported to the control room air intakes in the ventilation towers.

The duct leakage was not accounted for in the previous control room dose calculations. This was determined to be an unanalyze'd condition and a condition adverse to quality report was initiated. A survey of the ducts that pass through the habitability zone was completed and the ducts that contributed to the unfiltered inleakage were identified.

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General Design Criterion (GDC) 19 Control Room, limits control room operator doses to 5 rem whole body, or its equivalent to any part of the body (30 rem thyroid).

When TVA postulated a LOCA, coupled with the unfiltered inleakage, the high winds from a specific 'direction, and no compensatory actions, the resulting thyroid doses were in excess of GDC 19 limits.

During Unit 2 Operating Cycle 6, TVA temporarily modified the operability requirements for the CREVS in the Units 1, 2, and 3 Technical Specifications. This change involved annotating the applicable limiting conditions for operation (LCOs) 3.7.E.1, 3.7.E.3, and 3.7.E.4 by an asterisk and defining the CREVS as being inoperable because it did not meet its design basis for essentially The Technical Specification zero unfiltered inleakage.

Bases 3.7.E/4.7.E were also revised to reflect this change. Operation of Unit 2 during Cycle 6 was approved based upon the low probability of a postulated LOCA coupled with the high wind condition and the compensatory actions instituted by BFN. The compensatory actions included:

1. The operation of all three trains of the SGTS following an accident to maximize the negative pressure inside secondary containment, and

2. The monitoring of plant radiological conditions to provide an early indication that the control room habitability zone may become degraded. Upon determination that there was a possibility that the iodine uptake dose to the thyroid could exceed 10 rem, potassium iodide tablets would be distributed to control room and Technical Support Center personnel.

During Cycle 6, CREVS was maintained functional by performing all applicable surveillances.

On July 31, 1992 (Reference 1), TVA described its resolution for the identified deficiencies with the CREVS. This included the implementation of the following corrective actions:

~ The air intakes for the CREVS were relocated to the northwest and southeast sides of the turbine building (Figure 1) to reduce the concentration of effluents being introduced into the CBHZ.

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I~ ~

~ The leak tightness of the CBHZ was increased. This involved sealing penetrations, building expansion joints, and sealing other sources of outleakage.

~ Procedures were established and periodic testing was implemented to ensure the ability to maintain a positive pressure in the CBHZ.

~ The two existing 500 cfm redundant CREVS trains were upgraded to 3000 cfm of capacity for each train.

~ The extreme wind conditions, which were originally assumed to produce ex-filtration from the Reactor Building, were determined to have a probability of occurrence below 10 'nd were no longer considered a credible event.

On January 29, 1993, NRC requested additional information (Reference 2). On March 1, 1993 (Reference 3), TVA responded to this request for additional information and on May 18, 1993 (Reference 4), TVA responded to a verbal NRC request for additional information.

On April 29, 1994 (Reference 5), NRC requested additional information regarding BFN meteorological data and other parameters necessary for an independent evaluation of meteorological data. The requested information is being provided as part of this enclosure. In addition, included is a description of TVA's methods for evaluating the potential release paths and determining the plant specific atmospheric dispersion coefficients (X/Qs). In order to demonstrate the doses to the control room operator would be below GDC 19 limits, the methods utilized at BFN went beyond the required design basis assumptions. In addition, the modeling of the atmospheric transport of effluents used conservative methods and modern atmospheric transport solutions.

II. MODELING OF RELEASE PATHS""

A diagram depicting the general plant layout is provided in BFN Updated Final Safety Analysis Report (UFSAR)

Figure 12.2-52 (Figure 2). The primary containment was assumed to leak to the secondary containment (Reactor Building) at a rate of two percent per day. This is the maximum allowable leakage rate specified by Technical Specification 3.7.A.2.b. This leakage is processed by the Standby Gas Treatment System and routed to the stack E-5

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for release. There were two release points modeled for the plant stack (chimney), the top and the bottom.

In addition to the leakage from the primary containment to the secondary containment, the main steam isolation valves (MSIVs) were assumed to leak at a rate of 11.5 scfh. This is the maximum leakage rate allowed by Technical Specification 4.7.A.2.i. The MSIV leakage will be exhausted through non-safety related ventilators mounted on the Turbine Building roof. It should be noted that the consideration of MSIV leakage in control room operator dose calculations has not previously been part of TVA's licensing or design basis. TVA voluntarily included the dose contribution from MSIV leakage in its submitted assessment of control room operator doses.

Therefore, there were three release points modeled in evaluating control room operator doses. The release points are the top of the plant stack, the base of the plant stack, and the roof of the turbine building.

Details of the modeling of each release path is provided below:

The reinforced concrete Seismic Class I plant stack is shown in UFSAR Figure 12.2-52. An excerpt is provided as Figure 3. The stack is 600 feet tall.

The base of the stack is located at plant Elevation 568. The top of the stack is located at plant Elevation 1168.

B. Base of Stack The remote manually operated isolation dampers previously used to isolate potential ground level release paths from the stack were considered safety related. They were seismically qualified, redundant, had qualified power supplies, and were bubble tight.

A 30 minute time frame was conservatively assumed in the control room habitability dose calculation for the closure of these dampers. The previously submitted calculated operator doses assumed this significant 30 minute ground level release path.

Cross-sections of the base of the stack are shown in Figure 4.

However, during the Unit 2 Cycle 6 outage, TVA replaced these remote manually operated isolation dampers with safety related dampers that E-6

automatically close to prevent a backdraft through the ductwork. This modification reduced the overall dose to the control room operators and significantly reduced the ground level release at the base of the stack during the first 30 minutes of the accident.

C. Turbine Buildin Roof Vents There are four main steam lines from the reactor to the MSIVs. The average length is 141 feet and the inside diameter is 23.65 inches. The primary containment leakage was assumed to flow through the MSIVs, to the low pressure turbines and condensers, out the low pressure turbine seals, and through the Turbine Building roof vents. The average pipe length from the MSIVs to the Turbine Stop Valve Pipe Compartment is 189 feet and the inside diameter is 21.56 inches. The drain lines from the main steam lines to the condenser were assumed to remain open.

The free volume of the Turbine Building associated with each unit was 2,100,000 cubic feet. This value was used as the mixing volume in assessing the doses to the control room operators. A transverse section of the Reactor, Control, and Turbine Buildings, including the Turbine Building vents, is provided in Figure 5. The flow rate from the Turbine Building vents was 8, 640,000 cfh. A Turbine Building roof plan, showing the relative location of the Turbine Building roof vents to the intakes for the CREVS is also shown in Figure 1. A typical detail of the Turbine Building roof vents is shown in Figure 6.

DERIVATION OF DISPERSION COEFFICIENTS (Z/Qs)

Details regarding the calculation of specific X/Qs from each of the three release points (top of stack, base of stack, and turbine building) are provided below:

A. Releases from the Top of Stack

1. Fumi ation Conditions The X/Q value for fumigation conditions for the first 30 minutes of the accident, which are released from the top of the stack to the nearest control room air intake, was developed utilizing the Regulatory Guide 1.145 methodology. This methodology was expanded to include enhanced E-7

lateral plume spread under fumigation conditions when the plume is emitted from a tall stack.

Regulatory Guide 1.145, specifies that fumigation conditions should be assumed for X/Q calculations for the first 30 minutes following the onset of the accident. The fumigation formula is specified as Equation 5 of the Regulatory Guide:

X 1 A~ ) 0 0 (z~)'~ v~ o where:

U = wind speed representative of the fumigation layer of depth h, in m/sec, o~ = the lateral plume spread, in m, that is representative of the layer at a given distance, and h, = the effective stack height in m.

Regulatory Guide 1.145 states that, in lieu of information to the contrary, the NRC staff considers a value of 2 m/sec as a reasonably conservative assumption for U of about 100 meters. Therefore, 2 m/sec was assumed in the BFN calculations.

The distance between the nearest air intake to the stack is 165 meters. Stability Class F was assumed for the calculation, as the Regulatory Guide suggests, and the resulting value of o is 7.4 m at 165 m from the stack (Regulatory Guide 1.145, Figure 1).

The top of the stack is located at plant Elevation 1168. The CREVS air intakes are located at plant Elevation 634. An effective stack height, h of 534 feet (-165 m) was used.

This equation fails to account for enhanced later'al spreading of the plume that occurs during fumigation, especially when a plume is emitted from a tall stack. Referring to Figure 7, let the outer edge of the stable plume aloft be used as a reference point. If two lines were drawn from E-8

that point, one perpendicular to the surface below and the other to the outer edge of the fumigated plume at surface level. The angle I formed by the lines is a measure of the increased lateral spread. The incremental spread can then be translated into a distance by the expression h,tan g. Bierly and Hewson (Reference 6) concluded that a fumigating plume spreads outward by an additional 15'y the time it reaches the surface. Thomas, et al. (Reference 7), examined data collected at five sites and did not find an instance in which the increase was less than 11'.

The average was about 25'nd the maximum approached 40'. To account for the lateral spread of a fumigating plume from a tall stack, Equation 1 was revised as follows:

(2) 0 (2m) U~ (a + h, tang) h, where:

n = the incremental lateral spread of the plume, in degrees. The value of I was conservatively chosen to be 10'.

Therefore, the X/Q value for fumigation conditions from the top of the stack for the first 30 minutes of the accident was:

[ (2) (3 14159) ]

~

'2. 0) [7. 4+ (165) (0. 176327) ] (165)

(3) 3.31 x 10 sec/m'.

Nonfumi ation Conditions In accordance with the guidance provided by Regulatory Guide 1.145, Section 2.2.1, General Method, average X/Q values for time periods greater than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> can be approximated by a logarithmic interpolation between the 2-hour sector X/Q and the annual average (8760-hour) X/Q for the same sector. Calculation of the 2-hour sector X/Q was performed using the general method given in Regulatory Position 2.1 and the corresponding annual average X/Q was determined as described in Regulatory Position 1.4.

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Two-Hour Sector X/Q The nonfumigation equation (2-hour sector X/Q) for stack releases is specified as Equation 4 of Regulatory Guide 1.145:

X g

1 mU~a o, exp [

-A~

2~z

]

where:

the wind speed representing conditions at the release height, in m/sec, the lateral plume spread, in m, that is representative of the layer at a given distance, o, = the vertical plume spread, in m, that is representative of the layer at a given distance,

h. = the effective stack height in m, The value of U was conservatively assumed to be 0.3 m/sec, since this is the starting speed of the anemometer.

The horizontal dispersion coefficient, o~,

was 36.8 m at 165 m and Pasquill Stability Class A (Regulatory Guide 1.145, Figure 1).

The vertical dispersion coefficient, o was 22.56 m at 165 m and Stability Class A (Regulatory Guide 1.145, Figure 2).

Stability Class A is a conservative condition for such an elevated release.

The effective stack height was based on the elevation difference between the stack and control room air intake elevations, without any consideration of plume rise from the stack. An effective stack height, h of 163 m was used in this calculation. This differs from the approximate stack height (165 m) that was used in the calculation for the fumigation X/Q for the top of stack release.

Thus, X 1 (163) 2

(

g (3. 14) (0 3) (36. 8) (22. 56)

~ 2 (22 562)

~

5.90 x 10 sec/m

b. Annual Average Sector X/Q Meteorological data for BFN, from the five year period from January 1, 1987 to December 31, 1991, was used for the calculation of the annual average sector X/Q values. The parameters used were the wind speed at the 90 m elevation, the wind direction, and the difference in temperature between the 10 and 90 m elevations (for stability classification purposes).

Annual average sector X/Qs were calculated for a continuous gaseous release in accordance with Equation 3 of Regulatory Guide 1.111:

D g( NXu~ Z~ (X) 2 g2 (X) where:

h, = the effective release height (163 m),

ng) the length of time (hours of valid data) weather conditions are observed to be at a given wind direction, wind speed class, i, and atmospheric stability class, j, N = the total hours of valid data, ug the midpoint of wind speed class, i, at a height representative of the release, the distance downwind of the source (165 m),

o,) (X) the vertical plume spread without volumetric correction at distance, X, for stability class, j

~ ~

~ ~

~

Z,) (X) the vertical plume spread with a volumetric correction for a release within the building wake cavity, at a distance, X, for stability class, j; otherwise Z,> (X) = o,> (X)

X/Q'~ = the average effluent concentration, normalized by source strength, Q', at a distance, X, in a given downwind direction, D, and 2.032 = ('/,)" divided by the width in radians of a 22.5'ector.

The vertical plume spread (o,>) was determined based on wind direction and Stability Class in accordance with Regulatory Guide 1.145, Figure 2. The open terrain correction factor (Q) from Figure 2 of Regulatory Guide 1.111, Revision 0, was also applied.

Annual average X/Qs were calculated for each of the sixteen 22.5'ompass sectors. Only the maximum annual average X/Qs for the four source to receptor compass sectors (upwind directions 236' 326') were used for determining the intermediate X/Q values.

These four wind directional sectors were considered to be those that would transport effluents from the plant stack to the intakes for the CREVS.

The annual average X/Q was calculated using a Stone and Webster Engineering Corporation (SWEC) proprietary computer code, EN113, Atmospheric Dispersion Factors, Version 6, Level 8. This computer code has not been submitted for NRC approval.

This computer model calculated both the vertical and horizontal stability classes based on the temperature difference between the two instrument heights on the meteorological tower. Sector averaging, the discarding of the portion of the area under the Gaussian curve outside of the was not performed. Dispersion22.5'urve, coefficients were calculated by a subroutine that generated Gifford's dispersion

coefficient curves. No correction was applied for plume rise. However, a building wake meander correction was utilized and a plain terrain adjustment factor selected (Regulatory Guide 1.111, March 1976, Page 9).

Using the methodology discussed above, the annual average X/Q from the top" of the stack was determined to be 4.27 x 10 sec/m'.

C. Intermediate Value X/Q The X/Q values for the periods greater than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> were determined graphically using the logarithmic interpolation technique discussed in Regulatory Guide 1.145. The maximum "

nonfumigation X/Q value (i.e., 5.90 x 10 sec/m3) was plotted at 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> on logarithmic X/Q versus time coordinates. The corresponding maximum annual" average sector X/Q value (i.e., 4.27 x 10 sec/m') was plotted at 8, 760 hours0.0088 days <br />0.211 hours <br />0.00126 weeks <br />2.8918e-4 months <br />. Logarithmic interpolation was used to determine the X/Q values corresponding to the 2 to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, 8 to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, 1 to 4 day, and 4 to 30 day X/Qs.

Xn summary, the following fumigation and non-fumigation X/Q values for the applicable time periods were utilized for determining the resultant radiological doses for an elevated release from the top of the BFN stack:

Release Path Time Period X/Q (sec/m')

Top of Stack 0 30 min. 3.31 x 10 5 30 min. 2 hrs. 5 90 x 10->>

2 8 hrs. 3.80 x 10 >>

8 hrs. 1 day 02 x 10 1s 1 4 days 1.90 x 10->>

4 30 days 9.60 x 10" Fumigation conditions B. Release from the Base of the Stack The X/Q dilution factors for the release from the base of the stack to 0he nearest control room air intake were determined using a bivariate normal, or

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Gaussian diffusion model (Regulatory Guide 1.145, Revision 1) modified for source configuration and lateral meander under neutral and stable conditions.

1. Short-Term (2-Hour) X/Q Regulatory Guide 1.145, specifies the formulas for short-term (2-hour) ground level releases in Equations 1, 2, and 3 of the Regulatory Guide:

Reg. Guide. Eq. 1 X 1 Reg. Guide. Eq. 2 X 1 g v(3~ o o.)

Reg. Guide. Eq. 3 X 1 10 7T yoz where:

Uzo wind speed at 10 meters above plant grade, in m/sec, the lateral plume spread, in m, a function of atmospheric stability and distance, the vertical plume spread, in m, a function of atmospheric stability and distance, the lateral plume spread with meander and building wake effects, in m. For distances of 800 meters or less, Z~ =

Mo, where M is determined from Figure 3 of Regulatory Guide 1.145, and the smallest vertical-plane cross-sectional area of the reactor building, in m'Other structures or a directional consideration may be justified, where appropriate). In this case, the diameter of the ceiling of the room at the base of the stack is

~ wo 57 feet and the height of the room is 31.5 feet. Therefore, A was conservatively taken to be 168 m'.

The lateral and vertical plume spread (a~ and o,)

was determined based on wind direction and Stability Class in accordance with Regulatory Guide 1.145, Figures 1 and 2.

In accordance with Regulatory Guide 1.145, the X/Q values were calculated using Regulatory Guide 1.145 Equations 1, 2, and 3, above. The values from Equations 1 and 2 were compared and the higher value selected. This value was then compared with the value from Equation 3, and the lower value of these two selected as the appropriate X/Q value.

A meteorological database was compiled using the valid BFN meteorological data from the five year period from January 1, 1987 to December 31, 1991.

A data-point was considered valid ifmeter the wind speed, wind direction, and 10 90 differential temperature for that hour was recorded. For the hours that calm winds were recorded, a wind speed of 0.6 mph (0.27 m/sec) was assigned. The wind directions during these calm conditions were assigned in proportion to the directional distribution of the non-calm through 1.5 m/sec wind speed conditions.

Only those meteorological parameters that occurred in the influencing directional sectors (WSW, W, WNW, and NW) were kept in the database. The other sectors were set to zero. However, the total number of good observations was based on the number of valid data-points for all sixteen directional sectors.

The short term accident X/Q values were calculated for the influencing directional sectors using SWEC proprietary computer code, EN113, Atmospheric Dispersion Factors, Version 6, Level 8. The modeling used in the computer program was as previously discussed.

The X/Q values were then ranked in descending order. As a result, the five percent overall value was selected as the controlling 0 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> X/Q. Using the program and methodology discussed

a~o above, the short-term (2-hour) X/Q was determined to be 8.89 x 10 sec/m'.

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2. Lon -Term (Annual Avera e) X/Q Following the methodology described in Section III.A.2.b for the top of stack release, the maximum annual average sector (8760-hour) X/Q was then calculated for the base of stack release.

The elevated release model was used to determine the annual average X/Q. The elevation difference between the base of the stack and the elevated CREVS intakes was used as the effective release height.

As in Section III.A.2.b, meteorological data for BFN, from the five year period from January 1, 1987 to December 31, 1991, was used for the calculation of the annual average X/Q values and only the maximum annual average X/Qs for the four source to receptor compass sectors (upwind directions 236' 326') were used for determining the intermediate X/Q values.

The annual average X/Q is represented by Equation 3 in Regulatory Guide 1.111:

(10) where:

hB the effective release height, n,> = the length of time (hours of valid data) weather conditions are observed to be at a given wind direction, wind speed class, i, and atmospheric stability class, j, N = the total hours of valid data, ui = the midpoint of wind speed class, i, at a height representative of the release, X = the distance downwind of the source (165 m),

o,>(X) = the vertical plume spread without volumetric correction at distance, X, for stability class, j Z,>(X) = the vertical plum spread with a volumetric correction for a release within the building wake cavity, at a distance, X, for stability class, j; otherwise Z,> (X) = o,> (X) the average effluent concentration, normalized by source strength, Q', at a distance, X, in a given downwind direction, D, and 2.032 = ('/)" divided by the width in radians of a 22.5'ector.

The CREVS air intakes are located at plant Elevation 634. The base of the stack is located at plant Elevation 568. Thus, the effective stack height (h,) is 66 feet (20 meters).

The annual average X/Q was then calculated using SWEC proprietary computer code, EN113, Atmospheric Dispersion Factors, Version 6, Level 8. Using this methodology, the annual average X/Q from the base of the stack was determined to be 2.75 x 10 4 sec/m'.

3. Intermediate X/Q Values The X/Q values for the periods greater than 2 hours were determined graphically using the logarithmic interpolation technique discussed in Regulatory Guide 1.145. The maximum nonfumigation X/Q value (i.e., 8.89 x 10 sec/m') was plotted at 4

2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> on logarithmic X/Q versus time coordinates. The corresponding maximum annual average sector X/Q value (i.e., 2.75 x 10 'ec/m')

was plotted at 8,760 hours0.0088 days <br />0.211 hours <br />0.00126 weeks <br />2.8918e-4 months <br />. Logarithmic interpolation was used to determine the X/Q values for the time periods corresponding to the 2 to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />, 8 to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, 1 to 4 day, and 4 to 30 days.

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In summary, the following X/Q values were utilized for the base of stack release:

Release Path Time Period X/Q (sec/m')

Base of Stack 0 2 hrs. 8.89 x 10 4 2 - 8 hrs. 7.30 x 10 4 8 hrs. 1 day 6.60 x 10 1 4 days x 10 '.40 4 30 days x 10 4

'.00 C. Turbine Buildin The X/Q values for the MSIV release from the Turbine Building were determined by a methodology that accounted for the release from the roof vents and the effect of building downwash.

The air intakes for the CREVS are located on the northwest and southeast sides of the turbine building. Intakes in this position are in the building downwash region, commonly referred to as the "cavity" for winds coming out of the northwest or southeast sectors. The cavity is characterized by strong turbulence and reversed flows. With the method described herein to analyze the releases from the turbine building roof vents, the precise location of the intakes is immaterial.

This first modeling assumption is that the vertical layer of air next to the side of the building is uniformly mixed with the effluent throughout a volume having cross-sectional dimensions equal to the height and projected width of the building and the downwind dimension is equal to the numerical value of the wind speed.

Thus, X 1 (11) g CHWu E-18

~~ ~

where:

C = a constant of proportionality, H = height of the building (m),

W = projected width of the building (m), and u = wind speed (m/sec).

Values of C, which depend on the building configuration, are generally cited in the range of 0.5 s C s 1.5. To be conservative, a value of 0.5 was assumed for the BFN calculations.

The Turbine Building roof is at plant Elevation 682.

Grade Elevation is 565. Therefore H is equal to 117 ft. (35.6 m).

Wind speeds (u) were assumed to vary between 2 and 22 meters per second in 2 meter per second intervals.

The above equation normally applies to a "free standing" structure, i.e., there are no nearby structures or terrain features to influence the aerodynamic patterns. The turbine building would be such a structure, were it not for the presence of the reactor, radwaste, service bay, and office buildings.

In the free-standing case, the projected width of the turbine building would be the projection of the entire building onto a line perpendicular to the wind direction. For example, where wind was blowing from one corner toward the diagonal corner, the projected width would be the length of the perpendicular diagonal of the building (Figure 8). Because the reactor building is taller than the turbine building, it blocks flows from the northeast sector and prevents effluent from spreading along the entire projected width of both buildings. When wind is blowing toward a side on which an air intake is located, the model compensates for the blockage by projecting only that side and not the entire length of the turbine building. The overall effect is to conservatively reduce the cross-sectional area of the building and thus reduce the estimate of the volume in which the effluent is mixed.

Two other assumptions are noteworthy. First, it is assumed that when the wind is blowing toward the southwest (so that the turbine building is upwind of

the reactor building) or toward the northeast (so that the turbine building is downwind of the reactor building), the side mounted air intakes are not influenced by effluent from the roof vents. In the first case, the effluent is transported into or above the canyon between the turbine and reactor buildings and subsequently flushed out downwind. In the second case, the effluent is transported over the northeast end of the turbine building and past the point where the air intakes are located. The second assumption is that the presence of the radwaste building, service bay, etc., on the northwest side of the turbine building induce additional turbulence and support the assumption of a uniform distribution of effluent within the cavity region of the turbine building.

To adapt the model to allow for multiple wind directions, the following modifications were made:

X +(z) +(r) (12) g CHV(>> ~)u where:

r = the number of the roof vent, D = the wind direction, A, and B) are factors depending on the location of source r, and W(,o) is a factor depending on the location of source r and on the wind direction D. It is the effective width of the volume in which the effluent from source r is mixed.

A, is the fraction of the effluent emitted by source r that contributes to the dispersion factor at an air intake. For this scenario, it is assumed that if the effluent from a source is transported to the side of the turbine building, all the effluent mixes in the lee of the building, i.e., A, = 1.0 for each source r.

B, is the fraction of the effluent emitted by the entire turbine building that is being exhausted E-20

through source r. It is assumed that each of the nine sources emits at an equal rate. Hence, for each source r, B~,~ = 1/9.

W<, z is the effective width of the volume in which the effluent from source r is mixed. Figure 8 shows a source on the roof of the turbine building and the four sectors into which it could be transported. If the wind transports the effluent toward the sides where the air intakes are located, they are affected.

When the wind is blowing toward a side where an air intake is located, the value of W( p) is taken to be the projected width of the side. It is assumed the air intake on a given side is affected by a release if thepointwindalong direction transports the release toward the side. This assumption may not any hold for all wind directions and air intake placements, but is made to maintain a conservative posture for the calculation. Figure 8 shows the projected width of the northwest side of the turbine building for a specific wind direction.

A computer program, called SideIntake, was written to apply the model to the Browns Ferry situation. For each wind direction, the program calculated the impact at, the air intakes for a series of wind speeds (2, 4, 6, ... 22 meter per second). Each impact is the sum of the individual impacts of releases from a row of roof vents. The inputs to the model are listed in Table 1. The maximum 0 30 minute X/Qs were identified for each case and the highest value was used in the dose calculations: 3.48 x 10

'ec/m'. The program SideIntake was also used to obtain annual average X/Qs for 14 years (Table 2). A log interpolation was used on the maximum 0 to 30 minute X/Q and the maximum annual averages to obtain the maximum X/Qs for the intermediate averaging times. These results are listed in the other rows of Table 3.

E-21

In summary, the following X over Q values were utilized for the MSIV leakage from the Turbine Building release:

Release Path Time Period X/Q (sec/m')

MSIV Turbine 0 30 minutes 3.48 x 10' Building 30 min. 2 hrs. 3.48 104 2 8 hrs. 2.94 x 104 8 hrs. 1 day 2.53 x 104 1 4 days 2.01 x 104 4 30 days 1.44 x 10'V.

RESPONSE TO SPECIFIC NRC REQUESTS A. NRC Request Provide a description of buildings with the locations of vents and control room intakes identified.

Include relative elevations.

TVA Response A general layout of the BFN site is shown in UFSAR Figure 12.2-1 (Figure 2). It shows the relative location of the Reactor and Turbine Buildings to the plant stack. The control rooms are located on the top floor of the Control Building. The Control Building is a 3 story structure that is located between the Reactor and Turbine Buildings. A transverse section of the Reactor, Control, and Turbine Buildings is provided on UFSAR Figure 1.6-8, Sheet 2 (Figure 5).

The Control Bay habitability zone is located on the top floor of the Control Building. The habitability zone contains the Units 1, 2, and 3 control rooms, equipment rooms, relay room, lunch room, rest rooms, and office spaces. The air intakes for the CREVS are located on the northwest and southeast sides of the turbine building.

General information about the building dimensions and relevant dimensions are provided below:

Reactor Building

~

Height above plant grade: 152 feet (46.3 meters)

~

Length [North-Southj: 119 feet (36.3 meters)

E-22

~ I

~ +0

~+ ~

~

Width [East-West]: 468 feet (143 meters)

Control Building

~

Height above plant grade: 69.6 feet (21.2 meters)

~

Length [North-South]: 41 feet (12.5 meters)

~

Width [East-West]: 465 feet (142 meters)

Turbine Building Height above plant grade: 117 feet (35.7 meters)

Length [North-South]: 345 feet (105 meters)

Width [East-West]: 420 feet (128 meters)

Location of intakes for CREVS:

Height above plant grade: 69 feet (21 meters)

The Unit 1 intake is located 6.25 feet (1.91 meters) West of the Turbine Building West wall The Unit 3 intake is located 6.25 feet (1.91 meters) East of the Turbine Building East wall Location of Turbine Building Vents:

The Turbine Building vents (exhaust fans) are located in three groups.

Each group consists of 9 fans. The Unit 1 group of fans is located 97.9 feet (29.9 meters) from the West face Turbine Building wall.

The Unit 2 group of fans is located 165 feet (50.3 meters) from the West face Turbine Building wall. The Unit 3 group of fans is located 322 feet (98.1 meters) from the West face Turbine Building wall. All the fans are located 117 feet (35.7 meters) above plant grade.

Distance Between Xntakes for CREVS and Plant Stack:

Unit 1 intake is 545 feet (166 meters)

Unit 3 intake is 928 feet (283 meters)

Distance Between Nearest Turbine Building Vents and Xntakes for CREVS:

E-23

Unit 1 fan group to Unit 1 intake is 106 feet (32.3 meters)

Unit 2 fan group to Unit 1 intake is 172 feet (52.4 meters)

Unit 3 fan group to Unit 1 intake is 328 feet (100 meters)

Unit 1 fan group to Unit 3 intake is 328 feet (100 meters)

Unit 2 fan group to Unit 3 intake is 262 feet (79.8 meters)

Unit 3 fan group to Unit 3 intake is 105 feet (32.0 meters)

Plant Stack Height above plant grade: (602 feet) (183 meters)

Base outside diameter : (62.4 feet) (19.0 meters)

Top outside diameter: (6.1 feet) (1.8 meters)

B. NRC Request Provide dimensions for the turbine and reactor buildings. This information will be used to determine building surface area for atmospheric dispersion calculations.

TVA Response This information was included in response to NRC Request A.

C. NRC Request Provide turbine building vent diameters and heights above the top surface of the building. Define flow rates for normal and accident conditions. Provide estimated plume temperature as a function of season.

TVA Response There are a total of 9 Turbine Building exhaust fans per unit (27 total fans). Each fan is rated at 16,000 CFM. The fans are located at plant Elevation 682. The fans have an opening diameter of 50 in. The fans are located atop 8 in. curbs and are 32 in. high. The actual air flow release point is approximately 20 in. above the roof. The fans are non-safety related and are assumed to run E-24

~~ ~

continuously. They do not have an accident operating mode.

The release temperatures are not recorded. These temperatures are estimated to be a minimum of nine 9 degrees above the ambient air temperature. Ambient air temperature data is provided as discussed in response to Request G. During the summer months, the release temperature could reach 20 degrees above the ambient air temperature.

Provide the inside diameter at the top of the stack, with the elevation relative to the control room intakes.

TVA Response The inside diameter of the stack at the top is 3 ft.

4% in. The top of the stack is 534 ft. above the control bay air intakes.

E. NRC Request Identify all accident source term release points, and their location (distance and direction) relative to the control room intakes, release point dimensions (e.g., length, width or diameter), flow rates, stack diameters, and release temperatures.

TVA Response There were three release points modeled in evaluating control room operator doses. The release points are the top of the plant stack, the base of the plant stack, and the roof of the turbine building. Details

1. ~k of the modeling of each release path is provided below:

The reinforced concrete Seismic Class I plant stack is 600 feet tall. The top of the stack is located at plant Elevation 1168. The Units -1 and 3 CREVS air intakes are located at 83'nd from true north from the plant stack, 99'lockwise E-25

respectively. The distance between the intakes and the plant stack are provided in response to Request A. The dimensions of the top of the stack were provided in response to Request D. A flow rate from all three trains of the Standby Gas Treatment System (SGTS) of 22,000 cfm was assumed.

The release from the top of the stack was 18, 600 cfm for the first 30.5 minutes and

'1, 995 cfm for the remainder of the time. The release temperature was assumed to be at ambient.

Information on ambient temperatures is provided in response to Request G.

2. Base of Stack The base of the stack is located at plant Elevation 568. The inside diameter of the base of the stack is 61 feet and the height of the room at the base of the stack is 314 feet. The distances between the intakes and the, plant stack are provided in response to Request A. The dimensions of the top of the stack were provided in response to Request D. There was a release from the base of the stack for the first 30.5 minutes at a flow rate of 3,400 cfm. A continuous leakage of 5 cfm existed for the remainder of the accident. The release temperature was assumed to be at ambient.

Information on ambient temperatures is provided in response to Request G.

The remote manually operated isolation dampers previously used to isolate potential ground level release paths from the stack were safety related.

They were seismically qualified, redundant, had qualified power supplies, and were bubble tight.

A 30 minute time frame was conservatively assumed in the control room habitability dose calculation for the closure of these dampers. The previously submitted calculated operator doses assumed this significant 30 minute ground level release path.

However, during the Unit 2 Cycle 6 outage, TVA replaced these remote manually operated isolation dampers with safety related dampers that automatically close if there is a backdraft through the ductwork. This modification reduced the overall dose to the control room operators and significantly reduced the ground level release at the base of the stack to 5 cfm.

E-26

3. Turbine Buildin Roof Vents The MSIVs were assumed to leak at a rate of 11.5 scfh. This is the maximum leakage rate allowed by Technical Specification 4.7.A.2.i. The leakage was assumed to flow through the MSIVs, to the low pressure turbines and condensers, out the low pressure turbine seals, and through the Turbine Building roof vents. It should be noted that the consideration of MSIV leakage in control room operator dose calculations has not previously been part of TVA's licensing or design basis. TVA voluntarily included the dose contribution from MSIV leakage in its submitted assessment of control room operator doses.

There are four lines from the reactor to the MSIVs. The average length is 141 feet and the inside diameter is 23.65 inches. The average pipe length from the MSIVs to the Turbine Stop Valve Pipe Compartment is 189 feet and the inside diameter is 21.56 inches. The drain lines from the main steam lines to the condenser remain open.

Doses due to MSIV leakage, including the effects of iodine plateout and re-suspension, were calculated in accordance with NEDC-31858P, Revision 2, "BWROG Report for Increasing MSIV Leakage Rate Limits and Elimination of Leakage Control Systems".

The free volume of the Turbine Building associated with each unit was 2,100,000 cubic feet. This value was used as the mixing volume in assessing the doses to the control room operators. The flow rate from the Turbine Building vents was 8, 640, 000 cfh.

The Turbine Building release point dimensions (e.g., length, width or diameter), flow rates, and release temperatures were provided in response to Request C. The distances between the 27 Turbine Building vents and the CREVS intakes are provided in response to Request A.

E-27

r'%

F. NRC Re est Describe control room intake and exhaust flow rates and filtration systems, including drawings, if available.

TVA Response The Control Building Heating, Ventilating, and Air Conditioning (HVAC) System is depicted in BFN FSAR Figure 10.12-2a. There are two independent chilled water systems; one serving Units 1 and 2 and the other serving Unit 3. These systems provide cooling for the main control rooms, common relay room, office spaces, and safety related electrical spaces on the lower floor of the building (Elevation 593). These systems have air handling units that recirculate air within the served spaces. During normal operation, outside make-up air is provided for habitability considerations.

During accident condition, this air supply to the control room and relay room air handlers is isolated.

However, the fans that provide this air continue to operate in order to supply cooling to the various mechanical equipment spaces and make-up to the air handlers serving the lower floor. The outside air is provided by the Board Room Supply Fans located in the Units 1 and 3 vent towers. These fans have the following capacity:

Unit 1A Board Room Supply Fan 14,400 CFM Unit 1B Board Room Supply Fan 13,400 CFM Unit 3A Board Room Supply Fan 10,260 CFM Unit 3B Board Room Supply Fan 10,260 CFM The cable spreading room supply and exhaust ductwork traverses the habitability zone. The fans associated with the cable spreading room have the following capacities:

Units 1 and 2 Supply Fan 5, 000 CFM Unit 3 Supply Fan 5,000 CFM Common Exhaust Fans 10,000 CFM The exhaust system that serves the electrical equipment spaces on Elevation 593 has the following fan capacities:

Units 1 and 2 Exhaust Fans 5,700 CFM Unit 3 Exhaust Fan 1,700 CFM

There are two toilet exhaust fans for the control room areas. They have the following capacities:

Units 1 and 2 Exhaust Fans 550 CFM Unit 3 Exhaust Fan 330 CFM The shutdown board room exhaust fans, which are located in the Units 1 and 3 vent towers, have been abandoned in place and will only be used for smoke removal, if necessary.

The CREVS is activated by an accident signal or high radiation signal from the Control Building intake duct radiation monitors, the same signals also initiate the isolation of the CBHZ. The CREVS processes outside air needed to provide ventilation and pressurization for the CBHZ during isolated conditions. The two 100 percent redundant filter trains are safety-related and are powered from separate divisions of normal and emergency diesel power. Only one train operates post accident with the other train on standby.

Each train of the CREVS is designed to process 3,000 scfm of outside air for 30 days without danger of saturation.

The filtered outside air aids in pressurizing the CBHZ to greater than 1/8 in. water gauge with respect to the outdoors. Outside air for the CREVS is drawn from both of the main outside air intake ducts supplying ventilation tower 1 and ventilation tower 3. Outside air pulled from these two intakes passes through a HEPA filter bank located in ventilation tower 2.

As committed in TVA's May 5, 1992 submittal, a Special Test was conducted on May 23, 1992 to determine the amount of unfiltered inleakage into the CBHZ. This test was conducted by isolating the CBHZ, including the supply and exhaust fans and ductwork that provide ventilation air to and from the outside, isolating the CREVS, and pressurizing the CBHZ by using a test fan. The flow required to maintain the CBHZ at various pressures was recorded. This allowed TVA to:

1. Demonstrate by test, that each 3000 cfm replacement CREVS unit would be capable of pressurizing the CBHZ, and, E-29

T

~I IM

2. Calculate the bypass flow area of the CBHZ. This can be ascertained with relative certainty since the other two variables, flow rate in >>to the CBHZ (which equals flow rate out of the CBHZ) and pressure in the habitability zone, were known.

In order to determine the amount of unfiltered inleakage into the habitability zone, the door fan was disconnected and groups of vent tower fans were started. The habitability zone pressure was measured after each fan group was started. The unfiltered inleakage rate was then calculated in a manner similar to the analysis discussed above. The outleakage area and the habitability zone pressure was known. Therefore, the maximum unfiltered inleakage into the CBHZ, from the supply ductwork was calculated to be 3717 cfm.

This calculation is considered to be conservative. The CREVS units or the special test fan were not running.

Pressurization of the habitability zone from the CREVS units, which would occur during post-accident habitability zone isolation conditions, would result in a decrease in the rate of unfiltered inleakage. Since the habitability zone would be at a relative high pressure compared to adjacent areas, all other leakage would be out of the habitability zone. The analysis performed to calculate unfiltered inleakage rate was in accordance with NFPA 12A.

In order to be sensitive to the possibility of the unfiltered inleakage rate increasing over the life of the plant, TUA has implemented a Surveillance Instruction to quantify the unfiltered inleakage rate once per cycle. A substantial change in the flow rates required to maintain the habitability zone boundary pressure would indicate boundary degradation. TVA has a program in place to control penetrations of the habitability zone and a maintenance program for door seals. With these programs in place, TVA does not anticipate significant degradation of the habitability zone pressure boundary.

G. NRC Request Provide meteorological data that has been collected at the Browns Ferry site for at least 5 contiguous years. If available, provide the data on a PC-compatible 3.5-inch diskette in ASCII format.

E-30

Z 4

TVA Response Meteorological data for BFN, from the five year period from January 1, 1987 to December 31, 1991, has been provided on a PC-compatible 3.5-inch diskette in ASCII format. The disk contains meteorologic data in the following format:

BFN Meteorological Data Format Column Descri tion 1-2 TVA Station Identified 3-4 Year 5-7 Annual Day 8-11 Time (0100 2400) 12-13 No. of Parameters 14-23 Wind Speed Average (MPH) at 91 Meters 24-33 Wind Direction (Degrees) at 91 Meters 34-43 Wind Speed Average (MPH) at 46 Meters 44-53 Wind Direction (Degrees) at 46 Meters 54-63 Wind Speed Average (MPH) at 10 Meters 64-73 Wind Directi'on (Degrees) at 10 Meters 74-83 Air Temperature at 91 Meters (Deg. F) 84-93 Air Temperature at 46 Meters (Deg. F)94-103 Air Temperature at 10 Meters (Deg. F) 104-113 Rainfall (Inches)

E-31

l

)

H. NRC Request Provide the relative location (distance and direction) of the control room intakes to the meteorological towers. Provide the instrumentation elevations on the towers.

TVA Response Collection of onsite meteorological data at the Browns Ferry Nuclear Plant commenced in February 1967 from a meteorological tower located about 0.5 mile north-northeast of the reactor building and about 25 feet above plant grade. This facility was moved in early 1970 to a new location approximately 0.7 mile north-northwest of the reactor building and about 10 feet above plant grade. In March 1973, the facility was moved to its present location.

The permanent meteorological facility is approximately 30 feet above plant grade and consists of a 300-foot tower, sensors mounted on the tower, and a data collection system in an instrument building (Environmental Data Station or EDS). The Unit 1 CREVS air intake is located approximately 3, 567 feet (1, 087 meters) at 290'lockwise from true north from the meteorological tower. The Unit 3 CREVS air intake is located approximately 3,160 feet (963 meters) at 287'lockwise from true north from meteorological tower. The data collected include:

wind speeds and directions at the 33-, 150-, and 300-foot levels (wind data collection at 150 feet began on April 23, 1976); temperatures at the 33-,

150-, and 300-foot levels (temperature data collection at four feet ended on May 24, 1979); and dewpoint temperatures at the 33-foot level (dewpoint data collection at 150 and 300 feet ended on March 6, 1978 and the 4-foot dewpoint data collection ended on November 15, 1978). Atmospheric pressure data collection ended on April 2, 1981.

V. CONCLUSION In order to demonstrate the doses to the control room operator would be below General Design Criterion (GDC) 19 limits, the methods utilized in evaluating the control room operator doses at BFN went beyond the required design basis assumptions. The modeling of the atmospheric transport of effluents used realistic methods E-32

'E and modern atmospheric transport solutions. TVA's methods for evaluating the potential release paths and determining the release specific X/Qs are technically sound and conservative.

VI . REFERENCES

1. TVA letter to NRC, dated July 31, 1992, Resolution of Control Room Emergency Ventilation System (CREVS)

Issues

2. NRC letter to TVA, dated January 29, 1993, Control Room Emergency Ventilation System Corrective Actions Browns Ferry Nuclear Plant

3. TVA letter to NRC, dated March 1, 1993, Control Room Emergency Ventilation System (CREVS) Corrective Actions

4. TVA letter to NRC, dated May 18, 1993, Control Room Emergency Ventilation System (CREVS) Corrective Actions

5. NRC letter to TVA, dated April 29, 1994, Request for Additional Information Regarding the Control Room Emergency Ventilation System for the Browns Ferry Nuclear Plant

6. E. W. Bierly and E. W. Hewson. Some Restrictive Meteorological Conditions to be Considered in the Design of Stacks, Journal of A lied Meteorolo Vol 1 3g 383 390 1962

7. F. W. Thomas, et al. Report on Full-Scale Study of Inversion Breakup at Large Power Plants, Tennessee Valley Authority, March 1970.

E-33

TABLE 1 INPUTS USED TO DETERMINE TURBINE BUILDING ROOF VENT DISPERSION COEFFICIENTS Angle of true North from assumed North: 38 degrees Coordinates of Turbine Building corners:

Corner Location X (m) Y (m)

Northeast 0.0 0.0 Northwest 127.9 0.0 Southwest 127.9 105.1 Southeast 105.1 Height of Turbine Building: 31.8 m Coordinates of Roof Vents:

X (m)

Vent Number Unit 1 Unit 2 Unit 3 Y (m) 97.9 79.4 30.0 98.9 97.9 79.4 30.0 87.4 97.9 79.4 30.0 73.8 97.9 79.4 30.0 61.2 97.9 79.4 30.0 49.6 97.9 79.4 30.0 37.9 97.9 79.4 30.0 26.2 97.9 79.4 30.0 15.1 97.9 79.4 30.0 5.0 E-34

TABLE 2 MAXIMUM ANNUAL AVERAGE DISPERSION COEFFICIENTS FROM A TURBINE BUILDING RELEASE Annual Average X/Q Values (sec/m')

Year Unit 1 2 3 77 8.66 x 7.66 x 10 5 8.28 x 10 5

'nit 'nit 10'.69 78 x 10 5 7.70 x 10 5 8.50 x 10 8.60 x 10 7.54 x 10 x 10

'.96 5

79 8.06 x 10 x 10 5 x 10

'.12 '.16 80 x 10 7.88 x 10 5 x 10 5

'.78 5

'.79 81 82 8.74 x 10 5 7.56 x 10 9.96 x 10 5 83 8.74 x 10 5 x 10 5

'.69 8.41 x 10 5 84 8.96 x 10 5 7.78 x 10 5 8.08 x 10 5 85 9.28 x 10 8.16 x 10 8.80 x 10 5 x 10

'.78 x 10 5

'.65 8.47 x 10 5 87 x 10 5

'.64 8.50 x 10 5 9.24 x 10 5 88 8.76 x 10 5 7.66 x 10 8.46 x 10 5 89 8.71 x 10 5 x 10 5

'.56 8.60 x 10 5 90 8.79 x 10 7.71 x 10 8.56 x 10

'-35

TABLE 3 MAXIMUM DISPERSION COEFFICIENTS FROM A TURBINE BUILDING RELEASE Averaging Period 0.0 (hr) 0.5 Duration (hr) 0.5 Unit 1 3.48 x 10 'nit '.92 4

2 3.02 x 10

'nit Average X/Q Values (sec/m')

3.48 x 3

10 4 2 - 8 2.94 x 10 2.56 x 10 x 10 4 8 24 16 x 10 4

'.53 2.21 x 10 4 2.50 x 10 4 24 96 72 2.10 x 10 1.76 x 10 1.97 x 10 96 -720 x 10 x 10 x 10 4

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