ML20059A514
| ML20059A514 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 08/16/1990 |
| From: | Wallace E TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| IEB-88-008, IEB-88-8, NUDOCS 9008230090 | |
| Download: ML20059A514 (4) | |
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 374o1 5N 157B Lookout Place r
AUG 161990 U.S. Nuclear Regulatory Conunission ATTN Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
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Docket Nos. 50-259 Tennessee Valley Authority
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50-260 l
50-296 BROWNS FERRY NUCLEAR PLANT (BFN) - RESPONSE TO BULLETIN 88-08, SUPPLEMENT 3 -
THERMAL STRESSES IN PIPING CONNECTED TO REACTOR COOLANT SYSTEMS BFN provided the response to Bulletin 88-08, including Supplements 1 and 2 by letter dated October 24, 1988. This letter provides TVA's response to Supplernent 3 of the Bulletin.
In summary, BFN does not anticipate thermal cyclic fatigue induced piping failure, as described in Supplement 3 of the Bulletin, to occur at BfW. TVA's evaluation is discussed in detail in.
There are no conunitments contained in this letter.
If you have any questions, please contact Patrick P. Carier, Manager of Site Licensing, at (205) 729-3566.
Very truly yours, TENNESSEE VALLEY AUTHORITY t
a b E. G. Wallace, Maneger Nuclear Licensing i.nd Regulatory Affalrs Enclosure cca See page 2 b
O N 900816 Q.
OCK 05000259 flik PDC t
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An Equal Opportunity Employer
U.S. Nuclear Regulatory Commission AUS 161990 cc (Enclosure):
Ms. S. C. Black, Deputy Director Project Directorate II-4 U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike, Rockville, Maryland 20852 t
NRC Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35609-2000 Thierry M. Ross, Project Manager I). S. Nuclear Regulatory Connission One White Flint, North 11555 Rockville Pike Rockville Maryland 208 Mr. B. A. Wilson, Project Chief U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 i
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ENCLOSURE -
BROWNS FERRY NUCLEAR PLANT RESPONSE TO BULLETIN 88-08, SUPPLEMENT 3 BACKGROUND Bulletin 88-08,. Supplement 3 notified licensees of a concern regarding thermal fatigue in unisolable sections of Reactor, Coolant System (RCS) piping. The thermal stresses occurred because a normally closed.
motor-operated wedge type gate valve developed a' leak from the RCS (upstream) side, through the packing gland, and out of the system via the leak-off piping. The leakage drew hot fluid'from the hot leg. The hot fluid layer-rode on the cool fluid upstream of-the valve and resulted in thermal stratification.. Subsequently, tne hot fluid resulted in thernal expansion-which stopped the leakage. Then, the fluid upstream of the valve cooled due to heat loss to the environment. The process was repeated continuously and resulted in fatigue failure due to thermal stratification.
EVALUATION The scope of Bulletin 88-08, Supplement 3, includes only unisolable sections of piping connected to the,RCS. At BFN, the RCS is considered to extend out to and include the outermost containment isolation valve in the main steam and fcedwater piping.
Since Supplement 3 dealt with failure of piping containing stagnant RCS fluid, only-systems with piping that interface with the RCS below the normal reactor water level were reviewed. The scenario described in Supplement 3 involves leakage past the-packing of a normally closed wedge type gate valve. The RCS interfaces at BFN which are below the normal reactor water level and-contain a normally closed valve are the injection lines for High Pressure Coolant Injection (HPCI), Reactor Cork Isolation Cooling (RCIC), Residual Heat Removal (RRR) in the Low Pressure Coolant Injection (LPC1) mode, Core Spray (CS), Control Rod Drive (CRD),'and the suction line for RHR shutdown cooling.
The injection lines for HPCI, RCIC, RHR-(LPCI), CS, and CRD each have normally closed wedge type gate valves. However, each of these valves.are.
i outboard of isolation check valves which are periodically tested for leak tightness in accordance with the Browns Ferry 10CFR50, Appendix J program.
In order for these lines to be subjected to the cyclic thermal stresses discussed in Supplement 3, a failure of the check valve would have to occur prior to the development of a leak tnrough the' packing of the gate. valve.
Multiple failures of this type are not considered credible and-therefore, these lines are not considered to be subject to cyclic thermal stress failure
.ts described in Supplement 3.
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o Enclosure
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'The piping on the inboard side of the isolation valve on the RHR shutdown f
cooling suction line has a similar configuration to the piping discussed in I
Supplerient 3.-
Cyclic thermal stresses'similar to those. described in Supplement-3 are not expected to occur in this piping for the following reasonst
.j The closure of the valve employs a torque switch which provides E
consistent seat' tightness whenever the valve is closed.
The valve disk is a flexible. wedge type gate which is designed to
.f flex as the valve closes or as-the valve expands or contracts to a
provide a continuously tight seal.
potential for thermal stratification and cyclic fatigue as described in Bulletin 88-08, Supplement.3. Based upon the evaluation described above it has been concluded that the thermal cyclic fatigue induced piping failure, as described in Supplement 3, is not anticipated to occur at BFN.
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