ML20128L580
| ML20128L580 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/12/1993 |
| From: | Zeringue O TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9302190300 | |
| Download: ML20128L580 (6) | |
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Tenrm,ec veey Authontf Post 04. Boam oxa wr.ama 3%co FEB 12 l993 u
O J.*lko*Zonngue v.ce hwdent. awa ren owems U.S. Nuclear Regulatory Commission ATTH: Document Control Desk Washington, D.C.
20555 centlemens In the Matter of
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Docket Nos. 50-259-l Tennessee Valley Authority
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50-260 50-296 References NRC, letter to TVA, dated October 29, 1992, HPC Inspection Report No. 50-259/92-36, 50-260/92-36, and 50-296/92-36 BROWNS FERRY NUCLEAR PLisNT (BFN) - COMHINED ZONE SECONDARY CONTAINMENT-BREACH HARGIN This letter notifies NRC of TVA's successful completion of the Secondary i
Containment survell?.anen Requirement 4 7.C.l.a in the combined zone configuration. The background and resolution of this issue is described in the Enclosure to this letter.
TVA and NRC met on September 29, 1992 to discuss the calculation of Secondary Containment breach margin based on a combined-zone configuration.
In that meeting and ac reflected in the referenced letter, TVA verbally committed to "ae only seventy five parcent of the calculated combined zone secondary containme,t until the Surveillance Instruction could be performed in.the combined zene configuration..-In-subsequent-discussions, TVA agreed to use only half the calculated allowable breach-
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TVA has successfully completed the Secondary Containment surveillance requirement in the combined zone configuration.
It' demonstrated a larger-acceptable secondary containment breach margin in the combined zone configuration than the breach margin displayed during the prc.vious performance of the surveillance in a zonal configuration.- Henceforth, TVA will utilize the' full-calculated allowable breach margin.in accordance with the norme.1 plant procedures governing secondary containment.
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There are no commitments contained in this letter.
If you have any questions, please contact G. D. Pierce, Interim Manager of Site Licensing, at (205) 729-7566.
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Sincerely, r
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Enclosure cc (Enclosure):
NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35611 Mr. Thierry H. Ross, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North l
11555 Rockville Pike Rockville, Maryland 20852 Hr. D. A. Wilson, Project Chiaf U.S. Nuclear kegulatory Commission Region II i
101 Marietta Street, NW,- Suite 2900 Atlanta, Cecrgia 30323
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ENCLOSURE BROWNS FERRY NUCLEAR PLANT (BFN)
COMBINED ZONE SECONDARY CONTAINMENT BREACH MARGIN DACKGROUND:
I Section 5.3.3 of the BFN Finul Safety Analysis Report (FSAR) defines the Secondary containment System as the Reactor Building exterior walls, roof, floor, and penttrattons.
The pre lous four zone secondary containment configuration is shown in Figure 1.
The Standby Gas Treatment System (SGTS) has the ability to me.intain a negative k inch of pressure in each zone even'if 1
cach zone has additional areas (breaches) opened to the outdoors. The
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secondary containment is tested as a total envelope (Units 1, 2, and 3 reactor l
zones and the refueling ficor). The total allowable breach margin (calculated using 0-SI-4.7.C and TI 237) was based on conservative calculations using the value of the allowable secondary containment flow (12000 cfm) minus the measured secondary containment flow during the test.
The allowable breach margin for each zone was then based on a ratio of the flow rates measured at the individual SGTS suctions for each tone.
Browns Ferry Reactor Building (Side view)
Figure 1 v4444444444444444444444444444444444444444 v
Refueling Floor v
-v 9444444444ege44g4444444444444444444444444 v Unit 1 Unit 2 Unit 3 Y Reactor Reactor Reactor v
Eone Zone Zone SGTS 44444444 I
Legend The evaluated cecondary containment boundary.
The penetrations of these walls, floors, and ceilings have not been evaluated or modified to ensure an analyzed post-design basis earthquake inleakage.
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l ENCLOSURE
!"I' 2 d' BROWNS FERRY NUCLEAR PLANT (BFN)
COMBINED ZONE SECONDARY CONTAINMENT BREACH MARGIN (CONTINUED) tiew penetrations are required through secondary containment due to the Unit 3 recovery work.
The Unit 3 secondary containment area that can be breached in the previous configuration (14 square inches) was not adequate to support the required work.
As shown in Figure 2, the original solution was to seismically analyze and modify, as required, the boundary between the Unit 3 reactor zone and (1) The Unit 2 reactor zone ar,' (2) The refuel floor.
This Reactor Building configuration is temporarily allowed by Technical Specification Amandment IJos. 187, 200 and 159.
Browns Ferry Reactor Building (Side view)
Figure 2 v.....ewee4 e.
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Refueling Floor v
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veeeeeeeeeegeeege4egee44eece v Unit 1 Unit 2 Unit 3 v Reactor Reactor Reactor v
Zone Zone Zone SGTS
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E Legend The penetrations of these walls, floors, and ceilings would be avaluated and/or modified to ensure an analyzed post-design basis earthquake inloakage.
The penetrations of these walls, floors, and ceilings have been evaluated and/or modified to ensure an analyzed post-design basis earthquake inleakage.
The pe.-
- rations of these walls, floors, and ceilings have not been evaluated or modified to ensure an analyzed post-design oasis earthquake inleakage.
The SGTS was to be isolated from the Unit 3 reactor zone and the Unit 3 reactor zone removed from secondary containment. There would be three modes of operating with the three zone as follows:
- 1) The drywell head would be on and would form the accondary containment boundary, 2) The vessel head would be on and would form the secondary containment boundary, or 3) The reactor vessel itself and attached piping up to and including the first isolation valve would f orm the secondary containment bour.dary.
This three zone plan would require approximately 1500 valves and various pipes be included in the secondary containment boundary. The seismic qualification of the pipes associated with these isolation valves would also be required to be verified and maintained.
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ENCLOSURE r.,, s of 4 BROWNS FERRY NUCLEAR PLANT (DFN)
COMBINED ZONE SECONDARY CONTAINMENT BREACH MARGIN (CONTINUED)
In order to preclude this additional work, another alternative was identified and is shown in Figure 3.
If the refueling floor to reactor zone hatches were removed from Units 2 and 3, and Unit I was opened up through the equipment hatches, it would allow free communication between the refueling floor and the Units 1, 2, and 3 reactor zones.
,'N would then effectively be in a combined zone secondary containment for the purpose of calculating the allowable area that could be breached. This alternative would not change the overall configuration of the Secondary Containment System that is required to-support Unit 2 operation and is consistent with the FSAR description of secondary containment (Reference Section 5.3.3).
However, it would allow the Unit 3 reactor zone to " share" in the SGTS breach margine of the Units 1 and 1 reactor zones and the refueling zone. The allowable breach area in a. combined zonal configuration would be the sum of the margins of the four separate zoned.
Browns Ferry Reactor Building (Side view)
Figure 3 v4 44....
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Refueling Floor v
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Zone Zone Zone SGTS
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The evaluated secondary containment boundary.
The penetrations of these walls, floors, and ceilings have not been evaluated or modified to ensure an analyzed post-design basis earthquake inleakage.
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1 ENCLOSURE
'Se' d v d BROWNS FERRY NUCLEAR PLANT (BFN)
COMBINED ZONE SECONDARY CONTAINMENT BREACH MARGIN (CONTINUED)
ISSUE RESOLUTION:
TVA and NRC met on September 29, 1992 to discuss the calculation of secondary containment breach margin based on a combined zone configuration.
In that meeting and as reflected in Inspection Report 91-36, dated october 29, 1992, TVA verbally committed to use only seventy fivo percent of the calculated combined zonc secondary containment breach margin until the surveillance Instruction could be performed in the combined zone configuration. After additional discussions, TVA revised its commitment and stated that it would not use more than 50 percent of the calculated combined zone secondary containment breach margin.
TVA performed surveillance Instruction 0-s!-4.7.c-1, combined Zone sacondary containment Integrity Test, on January 30, 1993.
In'accordance with the requirements of Technical specification 6.9.2.8, Special Reports - Secondary Containment Leak Rate Testing, TVA will provide a summary technical report of the leak rate test by April 30, 1993.
This report will include data on the wind speed, wind direction, outside and inside temperatures during the test,-
concurrent reactor building pressure and emergency ventilation sy9 tem flow rate. Thie survelliance demonstrated a larger acceptable secondary containment breach margin in the combined zone configuration than the breach margin displayed during the previous performance of the surveillance in a zonal configuration, llenceforth, TVA will utilize the full calculated allowable breach margin in accordance with the normal plant. procedures governing secondary containment.
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