ML19347D246
| ML19347D246 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 03/04/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NCR-SQN-NEB-800, NUDOCS 8103110627 | |
| Download: ML19347D246 (2) | |
Text
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- 400 Chestnut Street Tower II March 4, 1981 al@M(
Mr. Jane P. O'Reilly, Director 8
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Office of Ihspection and Enforcement 4
U.S. Nuclear iegulatory Commission
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M Atlanta, Georgia 303
Dear Mr. O'Reilly:
SEQUOYAH NUCLEAR PLANT UNIT 2 - UHI HYDRAULIC ISOLATICN VALVE ACCUMULATOR WEIGHING SYSTEM - NCR SQN NEB 8007 - FINAL REPORT The subject deficiency was initially reported to NRC-0IE Inspector-If. J. Gouge cm March 25, 1980, in accordance with 10 CFR 50.55(e). Interim reports were submitted on April 24, June 18, July 23, and September 25, 1980, and January 9, 1981. Enclosed is our final report.
If you have any questions, please get in touch with D. L. Lambert at FTS 857-2581.
Very truly yours, TENNESSEE VALLEY AUTHORITY L. M. Mills, Manager Nuclear Regulation and Safety Enclosure
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cc Mr. Victor Ste11o, Director (Enclosure),V Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington, DC 20555 gio/f Suf; 810s12os,27-
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ENCLOSURE SEQUOYAH NUCLEAR PLANT UHI HYDRAULIC ISOLATION VALVE ACCUMULATOR WEIGHING SYSTEM NCR SQN NEB 8007 10 CFR 50.55(e)
FINAL REP 0RT Description of Condition The UHI hydraulic isolation valves are actuated by hydraulic fluid from an accumulator which is pressurized with nitrogen gas. The accumulator was equipped with a weighing device which was intended to
. verify proper charge of hydraulic fluid in the accumulators. The weighing device would have permitted monitoring of the hydraulia fluid availability in the main control room. The accumulators are initially charged by 2
pressurizing the internal nitrogen bladder to a pressure of 1500 lb/in g and then filling the accumujator with hydraulic fluid until the system pressure reaches 3000 Ib/in g.
A change in the weight of the accumulator would then indicate either a fluid or gas leak. Load cell readout devices were provided in the main control room so that the operator could verify proper accumulator charge. In practice, however, the weighing system is inconsistent, and it is difficult to obtain repeatability in accumulator weights.
The problem with this system is evidently caused by the stiffening of connecting hydraulic lines under pressure.
Safety Implications Had this condition gone uncorrected, it would have been possible for the operator to receive an incorrect indication of proper accumulator charge when, in fact, the accumulator could be inoperable because of leakage., Since these isolation valves are necessary to terminate UHI at the appropriate ' time, this condition could have adversely affected the safety of the plant by reducing the redundance of the safety-related accumulator isolation valves.
Cf;rrective Action TVA has decided not to implement proposed design changes to the weighing system proposed by Westinghouse, which would have required experimental and development' work. An administrative procedure which is being used at Sequoyah unit 1 will.be adopted instead. This administrative procedure (SI-2) is to monitor locally the pressure of the nitrogen gas space in the UHI hydraulic ' isolation valve accumulators to ensure proper charge of the device. A drop in nitrogen pressure will indicate a leak of
- either nitrogen or hydraulic fluid, and will be investigated by draining the accumulator and measuring the available charge. Repairs will be made
. as indicated by the investigation. The implementation of this procedure for:Sequoyah unit 2 will be accomplished before fuel loading of unit 2.
4 L.