ML18033A864
| ML18033A864 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 08/07/1989 |
| From: | Michael Ray TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-00459, TAC-459, NUDOCS 8908100136 | |
| Download: ML18033A864 (13) | |
Text
AC CELE RATED Dl+6BU'nON DE MONSTJTION SYSTEM 0 ~
'EGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
SUBJECT:
Responds to NRC 890606 ltr re NFPA code deviations in relation to cable spreading room sprinklers.
DISTRIBUTION CODE:
D030D COPIES RECEIVED:LTR L ENCL TITLE: TVA Facilities Routine Correspondence SIZE:
NOTES:1 Copy each to: S.Black,D.M.Crutchfield,B.D.Liaw, R.Pierson,B.Wilson ACCESSION NBR:8908100136 DOC.DATE: 89/08/07 NOTARIZED: NO FACIL:50-260 Browns Ferry Nuclear Power Station, Unit 2, Tennessee AUTH.NAME AUTHOR AFFILIATION RAY,M.J.
Tennessee Valley Authority RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
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TENNESSEE VALLEYAVTHORITY CHATTANOOGA. TENNESSEE 37401 5N 157B Lookout Place AUB 0I'88 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Hashington, D.C; 20555 Gentlemen:
Docket No. 50-260 In the Matter of
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Tennessee Valley Authority
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BROHNS FERRY NUCLEAR PLANT (BFN) NFPA CODE DEVIATIONS IN RELATION TO CABLE SPREADING ROOM SPRINKLERS (TAC 00459)
The purpose of this letter is to respond to the NRC request made in the letter dated June 6,
1989.
In that letter NRC stated it considers that an upgraded suppression system would provide additional margin for control of fires which are still confined to a single cable tray and the staff would like TVA to consider the following modifications:
1.
Providing manual and/or automatic control of the heating, ventilating and air conditioning system to include separate control. of the intake. and exhaust for smoke control.
2.
Replacement of existing sprinkler heads with quick response heads.
Supporting analyses should include a calculation showing the relative response times of quick response heads and the existing heads.
3.
Extending the riser nipples on the upright heads to achieve the code required distance from the ceiling and providing additional anchoring so as to not invalidate the existing seismic analysis of the sprinkler system.
For item 2 above TVA will replace the existing ceiling level sprinkler heads in Cable Spreading Room A with quick response sprinkler heads prior to restart.
For items 1
and 3, TVA does not intend to pursue a modification.
These positions along with the informal results supporting the positions were discussed with the NRC Appendix R inspection team during the July 17-21, 1989 BFN Appendix R inspection and again over the telephone with Mr. Rex Hescott of NRC on August 3, 1989.
Enclosure 1 to this letter states the TVA position for each of the modifications as requested by NRC.
Enclosure 2 discusses the computer code methodology.
Enclosure 3 lists the commitment contained in this letter.
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8908100186 890807 PDR ADOCK 05000260 PDC An Equal Opportunity ErnpIoyer
U.S. Nuclear Regulatory Commission If you have any questions, please telephone Patrick P. Carier, BFN, Site Licensing at (205) 729-3570.
Very truly yours, TENNESSEE VALLEY AUTHORITY Enclosures cc (Enclosures):
Ms.
S.
C. Black, Assistant Director for Projects TVA Projects Division U.S. Nuclear Regulatory Commission One Nhite Flint, North 11555 Rockville Pike Rockvi lie, Maryland 20852 Mr. B. A. Hilson, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NN, Suite 2900 Atlanta, Georgia 30323 NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637
- Athens, Alabama 35609-2000 Mana er, Nucl Licensing and Regulatory Affairs
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ENCLOSURE 1
BRONNS FERRY NUCLEAR PLANT (BFN)
NFPA CODE DEVIATIONS IN RELATION TO CABLE SPREADING ROOM SPRINKLERS Introduction In a letter dated June 6,
1989, the NRC requested TVA to consider three modifications to the cable spreading room sprinklers.
This enclosure presents TVA's position in relation to each modification.
Position 1.
Control of the HVAC S stem in Cable S readin Room A for Smoke Control Manual control of the supply and exhaust fans that serve the cable spreading room is available by operating the hand switches that are located on panel 25-165, elevation 617.0.
An interlock with the carbon dioxide suppression system that deenergizes both the supply and exhaust fans and closes the dampers in the exhaust ducts is provided to assist in maintaining the carbon dioxide concentration during the soak time.
This interlock with the carbon dioxide system can be overridden by manual actions.
Automatic operation of the system for smoke control would not be desirable due to the considerations regarding the carbon dioxide suppression system.
The present system is adequate and the benefits from further modifications are not substantial.
TVA does not intend to pursue this modification.
2.
Re lacement of Existin S rinkler Heads with uick"Res onse Heads To evaluate the relative response times of the existing sprinkler heads with quick response sprinklers (QRS) located approximately 24 inches below the ceiling, an informal computer program based upon the ASET and DETACT codes developed by the National Institute for Science and Technology, was utilized.
Below is a summary of the results:
a.
The HVAC system will have minimal effect upon the response times of the sprinkler heads due to the location of the exhaust duct near floor 1
eve 1 '.
b.
Replacing the existing heads with 165 F
QRS heads will reduce the response time of the suppression
- system, providing water application during an earlier stage of fire development.
For example, the probable growth fire produces a response time of six minutes and two seconds with QRS heads versus 10 minutes and 14 seconds with the existing heads.
cd The deep pockets formed by the beams in the cable spreading room will improve the response time of the suppression system in comparison to the response times expected for an unobstructed ceiling.
The methodology used to develop this program is discussed in enclosure 2.
TVA intends to replace the existing ceiling level sprinkler heads in Cable Spreading Room A with QRS heads prior to restart.
This modification will provide more effective fire control.
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Page 2 of 2 3.
Extendin Riser Ni les to Achieve Code Re uired Distance from Ceilin Extending the riser nipples is feasible on approximately 14 of the 26 branch lines in Cable Spreading Room A. It is not feasible on the other branch lines due to their routing along the ceiling support beams.
Extensive seismic analysis and additional supports would likely be required to bring those spri nklers, where possible, within code distance to the ceiling.
In addition, hydraulic reverification would have to be performed.
The effect that this modification, in conjunction with the addition of QRS heads, would have on the response time of the suppression system has been analyzed using the program noted in item 2 above.
The average difference in response times for ceiling heads in their current position as compared to heads located within nine inches of the ceiling, is less than one minute.
Therefore this modification is.not desirable due to the extensive effort it would require to obtain a marginal improvement.
TVA does not intend to pursue this modification.
ENCLOSURE 2
BROWNS FERRY NUCLEAR PLANT (BFN)
NFPA CODE DEVIATIONS IN RELATION TO CABLE SPREADING ROOM SPRINKLERS Methodolo for Develo ment of Com uter Code The program used to support the TVA positions for items 2 and 3 was developed by TVA from two NFPA approved codes.
This informal program was used to approximate the response times of thermally actuated devices that are located outside the influence of the ceiling jet generated by the fire.
The effect of mechanical ventilation on the descent of the thermal layer within the fire compartment was also evaluated.
The program is unable to calculate, due to the mixing of unvitiated air with that contained in the thermal layer, the effect that the HVAC supply air will have on the response. times of sprinklers in its zone of influence.
The effects of the supply air should be limited to the four branch lines located between columns R4 and R5 on the east side of the spreading room.
Three different fire growth rates were modeled corresponding to the fast,
- medium, and slow developing fires described in Appendix C of NFPA 72E.
Due to the lack of transient combustibles in the room and the fire retardant coating applied to the cables, a slow developing fire is the most credible and most probable for cable tray fires.
The response time index (RTI) for the existing sprinklers (Astra 212'F, 15mm orifice, pendent) is not available; therefore, a RTI of 300 sec'~'/m' was selected.
This value is consistent with the tested..RTI, value of other manufacturers link and lever fusible elements.
For'he QRS'eads a 165'F temperature rating with an RTI of 23 sec'/m' was chosen.
The sprinklers are assumed to be 24 inches below the ceiling of the cable spreading room.
The HVAC exhaust from the room during normal conditions is 6050 cfm through a grille and damper that is approximately 16 inches by 62 inches located in the wall that separates the cable spreading room from the stairwell between spreading rooms.
Fires were modeled with the HVAC system on and off.
The beams supporting the cable spreading room ceiling are approximately 33 inches in depth.
The equation utilized in the program are intended for large unobstructed ceilings, therefore in addition to the computer runs modeling the entire cable spreading
- room, each condition was modeled with the beam pocket considered as a separate compartment to provide bounding information regarding relative response times.
The results of this program are listed in the item 2 position above.
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ENCLOSURE 3
Summary of Commitments TVA wi 11 replace the existing ceiling level sprinkler heads in Cable Spreading Room A with quick response sprinkler heads prior to restart.
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