ML17313A355
| ML17313A355 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 04/20/1998 |
| From: | Ide W ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9804240337 | |
| Download: ML17313A355 (10) | |
Text
CATEGORY REGULA Y INFORMATION DISTRIBUTIO SYSTEM (RXDS) l jg ACCESSION NBR:980 FACIL:STN-50-528 SPN-5P-529 STN-50-530 AUTH.
NAME'DE,W.E.
RECIP.NAME 4240337 DOC.DATE: 98/04/20 NOTAR1ZED:
NO DOCKET Palo Verde Nuclear Station, Unit 1, Arizona Publi 05000528 Palo Verde Nuclear Station, Unit 2, Arizona Publi 05000529 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTHOR AFFILIATION Arizona Public Service Co.
(formerly Arizona Nuclear Power RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)
DXSTRIBUTXON CODE: A001D COPIES RECEIVED:LTR l ENCL SIZE:
TITLE: OR Submittal: General Distribution
SUBJECT:
Requests that Palo Verde submit info re double sequencing auxiliary feedwater to NRC.Info discussed in 971211 phone conversation attacged.Ltr does not make any commitments to NRC.
E NOTES: STANDARDXZED PLANT Standardized plant.
Standardized plant.
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Palo Verde Nuclear Generating Station WilliamE. Ide Vice President Nuclear Engineering TEL 602/3936116 FAX 602/3936077 Mail Station 7605
'.O.
Box 52034 Phoenix, AZ65072-2034 U. S. Nuclear Regulatory Commission ATlN: Document Control Desk Mail Station P1-37 Washington, DC 20555-0001 102-04115-WEI/SAB/RKR April20, 1998
Dear Sirs:
Subject:
Palo Verde Nuclear Generating Station (PVNGS)
Units 1, 2, and 3 Docket Nos. STN 50-528/529/530 Phone Call Regarding Double Sequencing and AuxiliaryFeedwater In a December 11, 1997 phone conversation, the Palo Verde and NRC staffs discussed additional questions that the NRC staff had regarding the August 31, 1997 submittal (102-04004) on double sequencing and auxiliary feedwater.
In a subsequent phone call the NRC staff requested that Palo Verde submit the information discussed in the phone conversation to the NRC.
Attached is the information discussed in the December 11, 1997 phone conversation.
Please contact Mr. Scott Bauer at (602) 393-5978 ifyou have any questions or would like additional information regarding this matte'r.
This letter does not make any commitments to the NRC.
Sincerely, Attachment WEI/SAB/RKR/rlh cc:
E. W. Merschoff K. E. Perkins M. B. Fields J. H. Moorman
'tt804240337
'tt80420 PDR ADQCK 05000528 P
ATTACHMENT Phone Call Regarding Double Sequencing and AuxiliaryFeedwater
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SUMMARY
OF December 11 1997 PHONE< CALLWITHTHKNRC RE<GARDING DOUBLE SK UKNCINGANDAFW In a December 13, 1996 letter summarizing a meeting between the NRC and Palo Verde, the NRC included a request for additional information (RAI)regarding double sequencing and associated issues regarding the auxiliary feedwater (AFW) system.
Palo Verde responded to the RAI in an August 31, 1997 letter (102-04004).
The purpose of the December 11, 1997 phone call was to discuss the RAI response.
A scenario where an emergency diesel generator (EDG) failure could result in a complete loss ofAC power to the B train was discussed.
The initiating event for this scenario is a feedwater line break with a concurrent loss ofoffsite power (LOP). Ifthe EDG failure happened at just the right time [i.e., after both AFAS actuations had occurred, but prior to receiving a differential pressure (DP) lockout], automatic isolation ofthe affected SG followingthe DP lockout would not occur. This would result in AFWflowbeing diverted from the intact steam generator (SG) to the affected SG.
Based on a review ofthe Palo Verde licensing basis and the single failures assumed in the Updated Final Safety Analysis Report (UFSAR), it was determined that the failure sequence discussed above was not valid for Palo Verde. Section 15.0 ofboth the Combustion Engineering Standard Safety Analysis Report (CESSAR) and UFSAR listed the single failures assumed.
For the failure ofan EDG, the assumed failure was a failure to start, run, or load. Therefore, for the Palo Verde licensing basis, the EDG would never assume any loads.
Based on this, the isolation valves to the intact SG would never open because the LOP and EDG failure would occur prior to AFAS and the flowpath would not be available.
Even though this event was not possible based on a review ofthe Palo Verde licensing basis, this event was reviewed to ensure that itwas not an event that should be of concern. APRA evaluation ofthis event determined that the probability ofthis event was SE-12 per year. Therefore, based on risk, this was not an event ofconcern.
This event was also evaluated for impact on the Palo Verde safety analysis. Itwas determined that this event was bounded by the chapter 15 events.
This event is an undercooling event. The undercooling events analyzed in the UFSAR would result in higher peak RCS pressures than this event. This event could also effect long term cooling. Areview ofother scenarios showed that conservatively there were 20 to 30 minutes to take operator action before there would be a loss ofsecondary cooling.
Approximately 45,000 gallons ofcooling water would be used during the first 30 minutes (with almost 300,000 gallons available from the CST). Therefore, there is sufficient time for operator action and there is sufficient cooling water to mitigate the event.
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The analysis for the feedwater line break does not take credit for any cooling from the
'affected steam generator.
However, there would be some cooling provided by the AFW fiowto the affected SG, further increasing the time for operator action. The NRC asked ifthat would be true for a double-ended, guillotine break. For a large FW line break (greater than 0.4 sq. ft.) this event woul'd not occur, since the larger the break size, the quicker the affected SG willdepressurize, resulting in a simultaneous AFAS and DP lockout.
During the discussion, the NRC staff referred the answer to the second question in the August 31, 1997 submittal, where itwas stated that the AC valves were powered from separate MCCs and concluded that a single active failure associated with the AC bus would not prevent isolation ofthe affected SG. The NRC staff questioned the response assuming a failure ofthe 4160 volt bus. The Palo Verde staff referred to the response to the third question, which states that "APS has reviewed AFW and loss ofpower scenarios described in the Palo Verde licensing basis. This review did not identify any events, other than degraded voltage, where a failure and a loss ofpower would result in uncontrolled flowto either an intact or faulted steam generator."
The NRC staffpointed out that this same vulnerability to loss ofAFW flowexists for selected application ofthe timing ofthe loss ofoffsite power. For example, ifthe EDG is out ofservice for maintenance, and the accident occurs, then the LOP occurs during the window between the second AFAS and the S/G delta-P lockout, the same result is achieved. Itwas pointed out that since the EDG is out ofservice and in an action statement, single failure requirements are not considered.
Therefore, when in the action time, it is not a requirement to assume a single failure ofthe EDG.
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