ML20115G685
| ML20115G685 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 10/22/1992 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 92-687, NUDOCS 9210260298 | |
| Download: ML20115G685 (4) | |
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'v VIRGINIA ELECTitIC AND Powen COhfPANY lllCIIMOND VlltOINI A 23001 October 22, 1992 l
1 U.S. Nuclear Regulatory Commission Serial No.92-687 Attention: Document Control Desk NAPS /JHL:JDH:R3 Washington, D.C. 20555 Docket No.
50-338 License No.
NPF-4 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION UNIT 1 TEMPORARY WAIVER OF COMPLIANCE AUXILIARY FEEDWATER PUMP RELAY RESPONSE TIME TESTING This letter requests a one tima temporary waiver of compliance for North Anna Unit 1 from a Technical Specification surveillance requirement involving an engineered safety feature (ESF) response time.
The need for the waiver was identified during our programmatic review of Technical Specification surveillance requirements as described in a letter to you dated September 8,1p?? (Serial No.92-482). A discussion of the affected surveillance requirement and plant systems, basis and duration of the temporary waiver, requested aporoval riate, safety impact and potential consequences of the proposed action, significant hazards considerations, and environmental consequences are discussed in the following paragraphs.
DISCUSSION Technical Specification surveillance requirement 4.3.2.1.3, Table 3.3 5, item 11 requires Engineered Safety Feature (ESF) response time testing of the auxiliary feedwater (AFW) pump circuit as a result of a " main feedwater pump trip"(i.e., loss of main feedwater). The test is required at least once per 18 months. On October 21,1992 at 1245 hours0.0144 days <br />0.346 hours <br />0.00206 weeks <br />4.737225e-4 months <br /> it was determined that this requirement had not been met for North Anna Unit 1. (North Anna Unit 2 is in full compliance with the surveillance requirement.) The requirements of Technical-Specification 4.0.3 were immediately invoked which permits conducting the required surveillance test within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> following discovery of the missed surveillance. The 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> interval ends at 1245 hours0.0144 days <br />0.346 hours <br />0.00206 weeks <br />4.737225e-4 months <br /> on Thursday, October 22,1992.
While prepari' g a test procedure to conduct the required surveillance, it was determined that the actuation of two relays in the AFW pump start circuit (Relays 3-CK~l-1FWSA05 and 3-CKT 1FWSB05) due to a loss of main feedwater would cause a turbine trip. Lifting a lead to prevent relay actuation is possible, however, an error or an arc on the contacts could ceuse the relays to actuate and cause a turbine trip / reactor trip. This surveillance test is usually performed while the unit is in a shutdown condition. Unit 1 is currently in coastdown operation at approximately 70% power and near the end of its cycle prior to its 1993 Steam Generator Replacement Outage which is scheduled to begin January 2,1993.
Due to the r >tential for a turbine trip / reactor trip if an error or arc occurs when the survelilence.est is conducted, and the possibility of a subsequent plant transient, it is
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requested that a temporary waiver of compliance be granted for the remainder of the Unit 1 operating cycle. Specifically, it is requested that response time testing of the two relays within the AFW pump start circuit that actuate due to a trip of ail main feedwater pumps be excluded from the response time test requirement in Technical Specification surveillance requirement 4.3.2.1.3, Table 3.3-5, item 11 for the remainder of the operating cycle. Unit 1 is scheduled to shut down on January 2,1993. NRC approval of this temporary waiver of compliance is requested by 1245 hours0.0144 days <br />0.346 hours <br />0.00206 weeks <br />4.737225e-4 months <br /> on October 22,1992.
To better understand the basis for the waiver, a description of the affected ESF features is necessary. There are four events that automatically start the AFW pumps. These are: 1) safety injection,2) steam generator low-low water level, 3) loss of offsite power, and 4) main feedwater pump trip. Response time testing is required to provide assurance that the protective and ESF actuation functions are completed within the time limits assumed in the accident analyses. However, the main feedwater pump signal is an anticipatory trip and no credit is taken in any safety analysis for that event. Technical Specification 4.3.2.1.3, Table 3.3-5, item 11 requires the initiation of the AFW pumps within 60 seconds of a loss of main feedweler.
The basis for waiving the response time test requirement for the two relays in the AFW pump start circuit for the remainder of the operating cycle involves several factors. First, the relays have repeatedly been demonstrated to perform as expected during periodic functional testing as required by the Technical Specifications. (The only aspect not specifically addressed during the functional test has been the relay response time. The funct;onality of the system has been repeatedly demonstrated.) Second, no credit is taken in the safety analysis for an AFW pump start on trip of a main feedwater pump. Third, the affected relays are HFA relays, which are used throughout the plant. Response time testing of those relays in other instNied configurations has consistently demonstrated a response time, typically much less than 0.1 seconds, well within that assumed in the response tima acceptance criterion that forms the basis for the Technical Specification requirement.
In addition, in August 1991, a safety injection occurred on Unit 1. The sequence of events recorder during that event documented that the required relay function occurred well withir the < 'ecification requiiement. Similar information is documented for an August 1992 safety injection on North Anna Unit 2.
Although the sequence of events recorder only documented the first of the two relays to actuate, it clearly showed that one relay fun':tioned as expected and had a response time well within that required.
Finally, the type of relays for which a temporary waiver is being sought are reliable and generally known to have acceptable response times.
SAFETY IMPACT AND POTENTIAL CONSEQUENCES A safety evaluation has been performed for the proposed temporary waiver of compliance.
Waiving the requirement to response time test the two relays in the AFW pump start circuit due to a trip of all main feedwater pumps for the remainder of the operating cycle does not pose a significant safety impact. The initiation signalis anticipatory. No credit is taken for it in the plant's safety analysis. Instead, the safety analysis assumes an AFW pump start on steam generator low-low level in the event of a loss of normal feedwater. The start of the auxiliary feedwater system on a main feedwater pump trip is considered anticioatory in nature and provides a diverse protection feature not credited directly in the accident analysis.
Furthermore, because the unit is in a coastdown mode with power levels currently about 70%
and decreasing daily, any plant transient would be initiated from a reduced power condition and be less severe than those that would occur starting from full power. The pctential consequences of any such reduced-power transients are well within the limits of the current safety analysis.
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COMPENSATORY MEASURES i
'Although temporarily waiving the surveillance requirement does not pose a significant safety impact, several compensatory measures have been identified that will provide additional j
assurance of safe operation during the interval until the unit completes its current operating cycle. Therefore, for the remainder of the current Unit 1 operating cycle, the following compensatory measures will be in place:
- 1) The standby main feedwater pump will not be removed from service for pre-planned maintenance. Tnis will ensure that one standby main feedwater pump will be availab:e to auto start in the event of a !oss of the other main feedwater pumps.
- 2) The Emergency Operating Procedures (EOPs) currently require the manual start of the AFW pumps in the avent that all normal feedwater flow is lost. This requirement will be reviewed with operations personnel.
- 3) Operations will review the material condition of the main feedwater pumps during each operating shift.
SIGNIFICANT HAZARDS CONSIDERATION The proposed temporary waiver of compliance for excluding response time testing of the relays in the AFW pumps start circuit due to a main feedwater pump trip, as required by Technical Specification surveillance requirement 4.3.2.1.3, Table 3.3-5, item 11, has been evaluated against the criteria in 10CFR50.92, Based on that evaluation, we have determined that no significant hazards consideration exists. A summary of our evaluation is provided below.
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- 1. The proposed waiver does not-involve a significant increase in the probability or consequences of an accident previously evaluated. No credit is taken for the AFW pump start in the event of a main feedwater pump trip in the accident analysis. The tyre of relay in question is used throughout the plant and response time testing of HFA-type relays in other applications has consistently been well within -specifications. Therefore, not response time testing the two relays in he AFW pump start circut during the interval until the unit shuts down--roughly 73 days ~-does not significantly affect the performance of the AFW system. Lastly, the surveillance test is normally conoucted when the unit is shut down. Performing the surveillance during power operation has the potential for creating an undesired transient or plant trip.
- 2. The proposed waiver does not create the possibility of a new or different kind of accident-frnm any accident previously evaluated. Since the proposed waiver of the surveillance requirement will require no hardware modification (i.e, alterations to the plant configuration), operation of the facility without those surveillance requirements does not' l
create the possibility for any new or different kind of accident which has not already been evaluated in the Updated Final Safety Analysis Report (UFSAR).
l Waiving the requirement for response time testing of the two relays will not result in any physical alteration to any plant system and there will not be a change in the method by wh ch any safety related system performs its function. The design and operation of the
AFW system, to include an automatic pump start due to a main feedwater pump trip, remains unchanged. Tha type of relays for which a temporary waiver is being sought are
' reliable and generally known to have acceptable msponse times.
- 3. The proposed waiver does not involve a significant reduction in !he margin of safety. The design and operation of the AFW system is not boir.s changed. The type of relays for which a temporary waiver is being sought are reliable and generally known to have acceptable response times. When compared to the entire circuit response time, the respense time of the relays is insignificant. Further, the margin of safety will not be reduced because the accident analysis assumptions will continue to be met,i.e., the AFW pumps will start within the required response time !nitiated by a steam generator low low level signal.
ENVIRONMENTAL CONSEQUENCES Approval of a temporary waiver as described above will not change the types of any effluents that may be released offsite, nor create a significant increase in individual or cumulative occupational radiation exposure.
The proposed waiver involves only surveillance requirements, Therefore, the consequences of accidents related to or dependent on response time testing the AFW pump start circuit due to a main feedwater pump trip remain unaffected.
This waiver request has been reviewed and approved by the Station Nuclear Safety and Operating Committee. If you have any questions or require additional information, please contact us.
Very truly yours, l
/ Q4 J
W. L. Stewart Senior Vice President - Nuclear Attachment cc:
Nucleai Regulatory Commission Region ll 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. M. S. Lesser NRC Senior Resident inspector North Anna Power Station r
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