ML20010G612
| ML20010G612 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 09/08/1981 |
| 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, NUDOCS 8109220308 | |
| Download: ML20010G612 (3) | |
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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 374ot 400 Chestnut Street Tower II September 8, 1981 SQRD-50-328/81-35 ap"fj 2
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1 Mr. James P. O'Reilly, Director
+7 SEP2 2198N g' Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission vs. % u,,,,a,
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Region II - Suite 3100 101 Marietta Street g
Atlanta, Georgia 30303 Min sV Y::
Dear Mr. O'Reilly:
SEQUOYAH NUCLEAR PLANT U.IIT 2 - PORV OPERATING TIME - SQRD-50-328/81-35
- REVISED FINAL REPORT, SUPPLEMENT 1 The subjtect deficiency was initially reported to NRC-0IE Inspector R. V. Crlenjak on April 24, 1981 fn accordance with 10 CFh 50.55(e) as NCR SQN NEB 8122. An interim report was submitted on May 26, 1981. Our final report was submitted on June 15, 1981. Enclosed is our revised final report as discussed with R. V. Celenjak on September 4, 1981. We expect to submit additional information concerning our corrective actions by December 29, 1981. We consider 10 CFR 21 applicable to this deficiency.
If you have any questions, please get in touch with D. L. Lambert at FTS 857-2581.
Very truly yours, TENNESSEE VA Y AUTHORITY N
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py L. M. Mills, Manager Nuclear Regulation and Safety Enclosure oc:
Mr. Victor Stello; Director (Enclosure)
Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission g g3 ~7 Washington, DC 20555 k
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8109220308 8109 PDR ADOCK 05000a29 S
pg An Equal Opportunity Employer
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ENCLOSURE SEQUOYAH NUCLEAR PLANT UNIT 2 PORV OPERATING TIME SQRD-50-328/81-35 10 CFR 50.55(e)
REVISED FINAL REPORT, SUPPLEMENT 1 Des ription of Deficiency The opera'ional time requirement for the pressurizer PORY (manufactured by c
Copes-Vulcan) is two seconds maximum. The PORV's are being used as the pressure relieving devices in the RCS low temperature Overpressurization Mitigation System (OMS). The operating time of the PORV's at normal system pressure meets tae design requipement of two seconds. As the system pressure decreasas to 500 lb/in g, the operating time of the PORV's increases to between five and six seconds. This operating time for low pressures is unacceptable because the Westinghouse cold overpressurization setpoint analysis assumed an operating time of two seconds as stated in the FSAR (section 5.E.2.4.2).
The reason for the increased operating time is~
that, as system pressure decreases, lees system force is being exerted on the valve plug which assists the operator to open the valve. The present air supply to the valve operator is insufficient to open the valve in the required time.
The PORV's at Sequoyah unit 1 are Masoneilan valves and the PORV's at Watts Bar units 1 and 2 are Fisher valves. Therefore, this condition applies only to Sequoyah unit 2.
Safety Implications Had this condition re=ained uncorrected, the cold overpressurization system would not operate as assumed in the 3equoyah FSAR.
Ine cold overpressurization system could not have adequately mitigated the effects of all low temperature overpressure transients. Events could have occurred where the 10CFR50 Appendix G reactor vessel nil ductility transition temperature (NDT) limits could have been exceeder. Such events could have occurred only when the plant was in a water sol 2J cold shutdown condition.
Corrective Action The air supply to the valve operator solenoid was modified by replacing the 3/8-inch air supply line from the air headers to the PORV's with a 1-inch air cupply line. This changt was approved by Westinghouse.
The valves have been retested and the results have been evaluated by TVA and Westinghouse. It is our judgement that these modifications with the present OMS setpoints will not produce the required PORV response characteristics.
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Therefore, we propose to delay full implementation of the RCS Low Temperature Overpressure ~ Protection System until the first unit-2 refueling outage. The deferral of this system does not represent a reduation in available plant safety margins for the following reasons:
l 1.
For Sequoya'a unit 1, a special alarm was added to notify the operator in.the main control rgom of water solid conditions when RCS pressure exceeds 380 lb/in g.
The overpressure protection circuitry presently installed in unit 2 provides the same alarm capability. It should be noted that unlike~the unit 1 alarm, the RCS pressure algrm for unit 2 actuates when the pressure rises to within 20 lb/in of the programmed setpoint (which varies as a function of temperature) of the PORV's.
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. Operator training and administrative procedure changes are the same for units 1 and 2 and have been implemented.
l 3.
The NRC staff, in Supplement No. 2 of the Sequoyah Safet)
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Evaluation Report (SER), concluded that since no credible overpecssure transient could damage the reactor vessel during the first operating cycle (based on expected minimal neutron damage to the vessel), full implementation of the RCS Low Temperature Overpressure Protection System could be deferred until the first refueling outage. We believe that the same technical justifications can be applied to unit 2.
NRC-NRR staff has been requested to ccndition the unit 2 full power
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operating license to require complete implementation of the RCS Low i
Te=perature Overpressurication Protection System during the first scheduled refueling outage. We will provide more details regarding the final corrective action in our next report.
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