ML20084H709
| ML20084H709 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/30/1976 |
| From: | Gilleland J TENNESSEE VALLEY AUTHORITY |
| To: | Jennifer Davis NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML20084H694 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8305040773 | |
| Download: ML20084H709 (7) | |
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'/.i916 78 March 30, 1976 9-Mr. John G. Davis, Acting Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Comission Washington, DC 20555
Dear Mr. Davis:
BROWNS FERRY NUCLEAR PLANT UNITS 2 AND 3 - POTENTIAL DESIGN DEFICIENCY IN VALVE YOKE TO MOTOR MOUNT WELD Initial report of the subject potential deficiency was made on May 14, 1974, and was followed by our June 14, July 15, August 12, September 13, 1974, January 15, 1975, March 3, and March 17, 1975, letters, J. E. Gilleland to Donald F.
Knuth. Because the yoke to motor base welds of FCV-74-58 in unit 1 failed, similar valves (FCV's 74-58 and 74-72) in units 2 and 3 may be subject to the same type of failure.
The enclosed eighth interim report (Enclosure 1) summarizes the Southwest Research Institute technical report (Enclosure 2) referred to in the fifth interim report. identifies the fix to be used to alleviate the vibrations which were studied.
A final report will be prepared and submitted shortly after eval-uation of test results.
Very truly yours, s
J. E. Gilleland Assistant Manager of Power Enclosures CC (Enclosures):
Mr. Norman C. Moseley, Director Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Region II - Suite 818 230 Peachtree Street, NW.
Atlanta, Georgia 30303 740913 gl%??c??ea?J s
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ENCLOSURE 1 S FERRY NUCLEAR PLANT UNITS 4 AND 3 POTENTIAL FOR FAILURE OF THE WELD BEIWEEN THE YOKE AND MOTOR MOUNTING i
PLATE FOR FLOW CONTROL VALVES (FCV'S) 74-58 AND 74-72
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DDN 191 EIGHTH INTERIM REPORT c
On May 14, 1974, an initial report regarding the subject deficiency was made by
'telecon to W. S. Little, AEC-DRO Inspector, Region II.
He report was made by L. D. Weber and J. A. Raulston in compliance with paragraph 50.55(e) of 10CFR50.
w j-here have been seven-interim reports previ.ous to this report. Rese were dated ij'
-June 14, 1974; July 15, 1974; August 12, 1974; September 13, 1974; January 15,
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1975; March 3,1975; and March 17, 1975. The initial report was made because the weld between the yoke and motor mounting plate of FCV 74-58 (4-inch globe valve) in the RHR test return line torus spray connection failed in Unit 1.
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Since the Unit i failure appeared to be vibration related, the corresponding i
i valves and valves in close proximity, such as FCV 74-59 (12-inch globe valve),
in Units 2 and 3 were assumed to be subject to a similar type of potential failure.
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Southwest Research Institute (SwRI), under contract to TVA, was retained to f
investigate this problem.
It has completed and reported on the initial phase 4:
of testing and evaluation of the RRR system test return lines for potential vibration induced component failures.
The SwRI report (Enclosure 2) also includes i
the results of a field evaluation of the core spray (CS) system test return line.
i The CS evaluation was conducted as a result of undesirable vibrations observed i
during operation of the system, for the CS system test return line, SwRI recommended the optimum solution of a self-drag valve in lieu of the' 10-inch globe valve FCV 75-22 (and FCV,75-5'0).
However, an alternate solution was developed using a downstream orifice plate installed inside the torus and increasing tihe diameter of the existing upstream orifice.
The objective is'to take most of the system pressure
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, drop at a point wh o the cavitation energy can be dissipsted in the suppression pool instead of in the piping. The orifice also provides a significant br.ek pressure on the 10-inch globe valve which helps to reduce the cavitation and associated vibration to an acceptable level.
This alternate' solution was found acceptable (see SwRI report, pages 23 through
- 25) and has been fanplemented on all units.
For the RHR system test return lines, SwRI recommended' the installation of self-drag valves in lieu of Fcy 74-59 and FCV 74-73 (12-inch globe valves).
An alternate solution similar to that developed for the core spray test return line was thought to be unsatisfactory since the flow objective of 20,000 gpm could not be attained. Test results indicated that the large pressure drop associated with the 12-inch globe valve in the 18-inch line precluded any reasonable chance of making the core spray type of fix work. Unit 3 testing confirmed that the RER system is capable of delivering very large flows with.the 22-inch globe valve removed and the upstream gate valve used for throttling (see SwRI report, page 25).
TVA performed two additional RHR system tests on Unit 3 in an effort to find an acceptable alternate solution. The additional tests confirmed that the 32-inch globe valve has an abnormally high pressure drop even with under-the-seat flow (which is the manufacturer's normal flow direction). The abnormal pressure drop 'is believed to be due to excessive turbulence and a large unrecovered velocity head downstream of the valve.
The testing did show that-improving flow conditions downstreem of the 12-inch globe ' valve through the addition of a flow. orifice in the torus did reduce the pressure O
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drop across tha t t.
Iha results of these addi al tcsts are includ:d u
for your information.
'At the request of TVA, the General Electric Company re-evaluated the RHR pump fl'orr requirements in the containment cooling mode of operation.
- 1he analysis confirmed that a reduction of RHR pump flow from 10,000 gpm to 8,000 gpm (per pump) would not affect' the temperature response of the contain-ment from that reported in the FSAR. This reduction in flow rate will allow the addition of a downstream orifice inside the tohs similar to that used to fix the core spray test return line. This alternate solution is now being implemented on all units. Confirmatory testing will be conducted and evaluated upon completion of the modification.
The results will be included in a final report.
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Facess DATE OP DOCUttENT, DATE RECEIVES NO.8 '
9/13/74 9/I8/74 41935 TENNESSEE VALLEY AUTHORITY
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