ML20044G115

Forwards Suppl to 920731 & 930301 Ltrs Containing Proposed Resolution of Previously Identified Deficiencies W/Crevs, Consisting of Comparison Between Previous CREVS & Current CREVS & Latest Surveillance Test Results

ML20044G115
Person / Time
Site:	Browns Ferry
Issue date:	05/18/1993
From:	Salas P TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
TAC-M83348, TAC-M83349, TAC-M83350, NUDOCS 9306020044
Download: ML20044G115 (11)

Text

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MAY 181993 i

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U.S. 1:uclear 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

i BROWNS FERRY NUCLEAR PLANT (BFN) - CONTROL ROOM EMERGENCY. 4 VENTILATION SYSTEM (CREVS) CORRECTIVE ACTIONSL(TAC NOS. '

M83348, M83349, AND M83350)

References:

1) TVA letter to NRC, dated July 31, 1992, Resolution of Control Room Emergency -

Ventilation System (CREVS) Issues .;

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

t In References 1 and 2, TVA provided its proposed resoluticn for the previously1 identified deficiencies with'the CREVS. In response-to a-verbal request for additional-information, the-- .

enclosure to this letter contains a. comparison.between'the  !

-previous CREVS and current CREVS-and a summary of:the latest ,

surveillance test results. >

E 250041 9306020044 930518-PDR- ADOCK 05000259, a

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U. S. Nuclear Regulatory Commission MRf 181993 There are no additional commitments contained in this letter.

If you have any questions, please telephone me at (205) 729-2636.

Sincerel , e l

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.r /y f Pedro Salas Manager of Site Licensing ,

Enclosure cc (Enclosure):

NRC Resident Inspector Browns Ferry Nuclear Plant Athens $1bma 35611 ,

Mr. Thierry M. Ross, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900

• Atlanta, Georgia 30323 t

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U.S. Nuclear Regulatory Commission  ;

M$Y 18 DN GMM:SMK -

Enclosure cc (Enclosure):

R. R. Baron, PSB 1K-BFN D. L. Brannen, C18 ATH3-BFN i M. J. Burzynski, LP 5B-C ,

E. S. Christenbury, ET 11H-K W. R. Cobean, Jr., LP 3B-C L. M. Cuoco, LP 5B-C R. M. Eytchison, LP 3B-C M. J. Fecht, LP 5B-C R. W. Huston, Rockville Licensing Office T. J. McGrath, LP 3B-C  !

G. R. Mullee, BR SD-C D. E. Nunn, LP 3B-C J. R. Rupert, MOD 2C-BFN J. .A..Scalice, POB 2C-BFN O. J. Zeringue, PAB 1E-BFN 4 RIMS, MR 2F-C i

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ENCLOSURE BROWNS FERRY NUCLEAR PLANT (BFN)

CONTROL ROOM EMEAGENCY VPITILATION SYSTEM (CREVS)

BACKGROUND:  :

The previous Control Room Emergency Ventilation System (CREVS) was designed to protect the control room operators by automatically starting upon receipt of a control room isolation signal and pressurizing the main control bay habitability.

zone (CBHZ) with filtered outdoor air during accident conditions thhc could result in radioactive releases. The CREVS uses '

charcoal adsorbers to assure the removal of radioactive iodine l from the air and high efficiency particulate absolute (HEPA)'

filters for removing radioactive particulate matter. i 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. The '

Control Building air supply ducts are 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 outside air bypassing the CREVS and introducing potentially contaminated and unfiltered outside air into the control bay habitability zone.

In References 1 and 2, TVA provided its proposed resolution for the identified deficiencies with the'CREVS. In response to a i verbal request for additional information, the enclosure to this .,

letter contains a comparison between the previous CREVS and '

current CkEVS and a summary of the latest surveillance test l results.  !

COMPARISON:

i 1

Attached are simplified diagrams of the previous CREVS (Figure 1) I and current CREVS (Figure 2). Also listed below is a comparison of major design aspects of the previous CREVS and the current CREVS: '

PREVIOUS CREVS CURRENT CREVS  !

Two 500 cfm CREVS trains and Two 3,000 cfm CREVS trains and units. units.

Each train power by a Same.

separate, diesel backed, electrical division.

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1 ENCLOSURE ros,2,rs BROWNS FERRY NUCLEAR PLANT (BFN)

CONTROL ROOM EMERGENCY VENTILATION SYSTEM (CREVS)

(CONTINUED)

PREVIOUS CPEVS CURRENT CREVS Each train contained a fan Both trains share a common unit, drawer type charcoal upstream HEPA filter. Each adsorber, and down stream HEPA CREVS unit contains a relative filter. humidity heater, fan unit, drawer type charcoal adsorber, and an after-filter.

Each CREVS train took supply Each CREVS train tak2s suction air from separate portions of from separate building intake ductwork that serve the ducts that are located on the electric board rooms located East and West sides of the in the Reactor Building. This Turbine Building. This new supply ductwork transverses ductwork is fabricated from the CBHZ. three-sixteenth inch plate (Correction from TVA's March 1, 1993 letter, which stated it was a three-eighth inch plate), which is heavier than the normal requirements for three nsi ductwork. The ducts serving CREVS become a common header at the Unit 2 vent tower.

Supply ductwork in the control The supply ductwork serving bay vent towers was not CREVS is not tornado missile tornado missile protected. protected.

Both CREVS trains Only one of the CREVS trains automatically started upon starts upon receipt of a receipt of a control room control room isolation signal.

isolation signal.

Each CREVS train was designed A single CREVS train will to maintain the CBHZ at a assist other sources of slight positive pressure and pressurization.in maintaining to ensure essentially zero the CBHZ at a half inch water unfiltered inleakage. gauge positive pressure.

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4 ENCLOSURE  !**' ' 'f '

BROWNS FERRY NUCLEAR PL. ANT (BFN)

CONTROL ROOM EMERGENCY VENTILATION SYSTEM (CREVS)

(CONTINUED)

TEST RESULTS:

The control bay habitability zone (CBHZ) is located on the top floor of the Control Building. The CBHZ contains the Units 1, 2, and 3 control rooms, equipment rooms, relay room, lunch room, rest rooms, and office spaces. The Control Bay ventilation towers, located on the north wall of the reactor building, provide the outside air for the Control Building supply ductwork.

Ventilation supply fans, which are located in the ventilation towers, pressurize this supply ductwork, including the'ductwork that traverses the main control bay' habitability zone. Some of the fans operate during the accident recovery period (30 days) to supply necessary cooling for essential equipment. In addition, the cable spreading room ventilation system, while not required to operate after an accident, is not prohibited from functioning after an accident. This could also contribute to the unfiltered inleakage into the habitability zone.

Surveillance Instruction 0-SI-4.7.E.7, Control Bay Habitability Zone Leakage Rate Test, was conducted on May 16, 1993 to determine the unfiltered inleakage rate into the CBHZ. This surveillance 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 (door mounted fan).

TVA determined the amount'of-flow necessary to maintain the CBHZ at various positive pressures. Readings were taken from an average CBHZ pressure of 0.09 inches water gauge to 0.41 inches water gauge, using a single door fan. Two test fans were used to bring the CBHZ pressure up to a half inch water gauge. However, the data with two test fans in operation was determined not to be credible. Hence, an extrapolation of the previous test data was used to determine the unfiltered inleakage rate at a CBHZ pressure of a half inch water gauge (Figure 3).

ENCLOSURE ras' # #8 BROWNS FERRY NUCLEAR PLANT (BFN)

CONTROL ROOM EMERGENCY VENTILATION SYSTEM (CREVS)

(CONTINUED)

The maximum unfiltered inleakage into the CBHZ was assumed.to be ,

the flow rate required to maintain the CBHZ at a half inch water gauge. The control room operator dose was calculated using this ,

extrapolated unfiltered inleakage rate and this calculation is  !

considered to be conservative. The CREVS units and the special test fan were not running simultaneously. 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 relatively higher pressure compared to adjacent areas, all other leakage would be out of the habitability zone.

The major parameters / data from the CBHZ surveillance test are shown in the attached table. The results of the test were:

• The outleakage is linear with respect to CBHZ boundary pressure. This was concluded from a linear plot of the log of the CBHZ pressure versus the log of the pressurizing flow rate.

• An extrapolation of the log-log plot showed an unfiltered inleakage rate of 3835 cfm at a CBHZ pressure of-0.51 inches water gauge. This compared favorably to an estimated value of 3717 cfm at a pressure of 0.50 inches. water gauge as discussed in Reference 1. The resulting thyroid dose to the control room operator is less than the 18.0 REM stated in TVA's March 1, 1993 letter to NRC since, during the current Unit 2 Cycle 6 outage, TVA replaced the manually operated stack isolation dampers with automatically closing backdraft dampers. This modification lessened the amount of ground level release from the base of the stack, and hence, lowered the overall dose.

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Pagefef8 ENCLOSURE BROWNS FERRY NUCLEAR PLANT (BFN)

TABLE CONTROL BAY HABITABILITY ZONE SURVElLLANCE TEST RESULTS Unit 1/2 Meet:.

Fan Flow Fan Flow Average Average Unit 1 Unit 3 Equipment Roots Rate Rate Pressure Pressure Door Fan Manometer Manometer Manometer (cim) (M'/S) .(inches w.g.) ( P. ) (inches w.g.) (inches w.g.) (inches w.g.) { inches w.g.)

1,639 0.77 0.09 22 0.05 0.10 0.08 0.12 1,919 0.91 0.13 33 0.10 0.15 0.12 0.15 2,256 1.07 0.18 45 0.15 0.20 0.17 0.20 2,571 1.21 0.23 58 0.20 0.24 0.22 0.25 2,764 1.30 0.27 68 0.25 0.29 0.26 0.29 2,958 1.40 0.32 80 0.31 0.33 0.30 0.33 3,191 1.51 0.35 88 0.35 0.36 0.33 0.37 3,469 1.64 0.41 103 0.40 .0.41 0.39 0.42 3,835" 1.81 0.51 128 0.51- 0.52 0.48 0.52 3,189* -

-0.34 - -

0.35 0.30 0.36-Footnotes

- Value extrapointed from log-log plot of.the data.

" - Values-with CREVS running in lieu of the tect fan.

Page 6 cf 8 ENCLOSURE BROWNS FERRY NUCLEAR PLANT (BFN)

FIGURE 1 PREVIOUS CREVS CONFIGURATION Ur411 3 SHUTDOWiJ UtJI T I UtJIT 3 yy SHUTDOWtJ UrJI T I EMERGEtJCY BOARD ROOM EMERGEtJCY SHUTDOWIJ SUPPLY T AtJ- SHUTDOWIJ BOARD ROOM

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/ BOARD ROOM SUPPLY fAtl SUPPL Y F AtJ -

O O O O r IJORMAL UtJI T l/2 tJORMAL UtJIT 3$

,_.,'x ) COfJT ROL COtJTROL ROOM L 7 ROOM MAkE-UP MAkE-UP X LOW LEAKAGE LOW LEAKAGE ISOL AT IOtJ DAMPERS ISOLATIOf4 DAMPERS 500 CFM FAtJ (g

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. Page 7 of 8 ENCLOSURE BROWNS FERRY NUCLEAR PLANT (BFN) 1 FIGURE 2 CURRENT CREVS CONFIGURATION Util l 3 U DItJG ItJT AKE I i: I l

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