ML14038A077

Palo Verde Nuclear Generating Station (PVNGS) Units 1, 2 and 3 - Response to Request for Additional Information - NRC Bulletin 2012-01, Design Vulnerability in Electric Power System

ML14038A077
Person / Time
Site:	Palo Verde
Issue date:	01/31/2014
From:	Mims D C Arizona Public Service Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
102-06825-DCM/RKR
Download: ML14038A077 (7)

Text

Bulletin 2012-0110 CFR 50.54(f)DWIGHT C. MIMSQ aps Senior Vice President, NuclearRegulatory

& Oversight Palo VerdeNuclear Generating StationP.O. Box 52034Phoenix, AZ 85072102-06825-DCM/RKRMa'Stin70 Mail Station 7605January 31, 2014 Tel 623 393 5403ATTN: Document Control DeskU.S. Nuclear Regulatory Commission 11555 Rockville PikeRockville, MD 20852

Subject:

Palo Verde Nuclear Generating Station (PVNGS)Units 1, 2, and 3Docket Nos. STN 50-528, 50-529, and 50-530Response to Request for Additional Information

-NRC Bulletin 2012-01, Design Vulnerability in ElectricPower SystemPursuant to 10 CFR 50.54(f),

Arizona Public Service Company (APS) letternumber 102-06610, dated October 25, 2012 provided the response to NRCBulletin 2012-01, Design Vulnerability in Electric Power System [Agencywide Document Access and Management System (ADAMS) Accession No.ML12305A361].

By letter dated December 20, 2013 (ADAMS Accession No.ML13351A314) the NRC staff requested additional information to verifycompletion of interim actions and compensatory

measures, and to obtain thestatus of long-term corrective actions.The industry established a template to guide development of plant responses to the NRC request for additional information regarding Bulletin 2012-01.APS used the established industry template as a guide in developing theresponse.

The NRC letter requested that licensees submit a written responseto the request for additional information by February 3, 2014. The enclosure to this letter provides the APS response to the NRC request for additional information regarding Bulletin 2012-01.This response is submitted in accordance with 10 CFR 50.4. APS hasreviewed the response and it does not contain any proprietary, sensitive, safeguards or classified information.

A member of the STARS (Strategic Teaming and Resource Sharing)

AllianceCallaway

-Comanche Peak -Diablo Canyon -Palo Verde -Wol.f Creek ATTN: Document Control DeskU.S. Nuclear Regulatory Commission Response to Request for Additional Information

-NRC Bulletin 2012-01, Design Vulnerability in Electric Power SystemPage 2No commitments are being made to the NRC by this letter. Should you needfurther information regarding this response, please contact Robert K.Roehler, Licensing Section Leader, at (623) 393-5241.

I declare under penalty of perjury that the foregoing is true and correct.Executed on(Date)Sincerely,

Enclosure:

APS Response to Request for Additional Information

-NRC Bulletin 2012-01,Design Vulnerability in Electric Power SystemDCM/RKR/CJS/hsc cc: M. L. DapasJ. K. RankinA. E. GeorgeM. A. BrownNRC Region IV Regional Administrator NRC NRR Project Manager (electronic

& hard copy)NRC NRR Project Manager (electronic

& hard copy)NRC Senior Resident Inspector for PVNGS ENCLOSURE APS Response to Request for Additional Information

-NRC Bulletin 2012-01, DesignVulnerability in Electric Power System Enclosure

-APS Response to Request for Additional Information

-NRC Bulletin 2012-01, Design Vulnerability inElectric Power SystemBackground Pursuant to 10 CFR 50.54(f),

Arizona Public Service Company (APS) letternumber 102-06610, dated October 25, 2012, provided the response to NRCBulletin 2012-01, Design Vulnerability in Electric Power System [Agencywide Document Access and Management System (ADAMS) Accession No.ML12305A361].

As part of the Bulletin

response, APS described the designand operating alignments at the Palo Verde Nuclear Generating Station(PVNGS).During normal plant operation, the Engineered Safety Features (ESF) busesare powered by offsite power sources (preferred source).

The safety-related equipment is divided into two load groups per unit (ESF Bus A and ESF BusB). Each Startup Transformer (SUT) supplies power to one ESF bus of twodifferent units. Either one of the ESF buses is capable of providing power forsafely shutting down the unit and/or supporting design basis accidentmitigation.

The ESF buses also supply power to certain selected non-Class loads important to plant operation, such as normal chilled water pumps andcontainment building reactor cavity normal cooling fans. These non-Class loads are tripped upon a Safety Injection Accident Signal (SIAS).A postulated single-phase open circuit condition located on the high side ofthe SUT affects only one ESF bus of two different units. A single phase opencircuit condition located on the low side of the SUT would only affect theassociated ESF bus of one unit. The unaffected redundant train is capable ofsafely shutting down the unit and supporting design basis accidentmitigation.

A potential outcome of implementing the industry open phase condition (OPC) initiative may be the installation of protection relay schemes that willautomatically separate the preferred off-site power sources from the Class 1Ebus in the event of a sensed OPC. The existing relay schemes beingimplemented at other sites are complex and the analysis techniques thatsupport the relay settings have limited operating history.

In addition, alternative OPC detection alternatives are being investigated that may impactdesign decisions, particularly for the PVNGS Class 1E buses which arenormally lightly loaded. As the PVNGS electrical design and operational features make this site less vulnerable to an OPC, when compared to otherconfigurations that exist in the industry, APS plans to assess the safetybenefit of modifications with the potential safety consequences of aninadvertent separation of the preferred off-site sources.

Should emergingOPC detection alternatives be determined to be viable that would be moreconducive to plant reliability and nuclear safety than present industryinitiatives involving installation of complex protective relay schemes,additional time to finalize and demonstrate the alternative schemes maydelay modification decisions into 2015.I Enclosure

-APS Response to Request for Additional Information

-NRC Bulletin 2012-01, Design Vulnerability inElectric Power SystemNRC Request of Additional Information By letter dated December 20, 2013 (ADAMS Accesssion No. ML13351A314),

the NRC requested the following additional information to complete its reviewof responses to Bulletin 2012-01, Design Vulnerability in Electric PowerSystem:1. Provide a summary of all interim corrective actions that have beentaken since the January 30, 2012, event at Byron Station, Unit 2, toensure that plant operators can promptly diagnose and respond toopen phase conditions on the offsite power circuits for Class-lE vitalbuses until permanent corrective actions are completed.

2. Provide a status and schedule for completion of plant design changesand modifications to resolve issues with an open phase of electricpower.Response 1 -Summary of All Interim Corrective ActionsAPS has reviewed industry lessons learned from the events at Byron Stationand implemented various interim actions for PVNGS. Based on the PVNGSoffsite power configuration and electrical design details, the following actionswere taken to ensure plant operators can promptly diagnose and respond toan OPC on the offsite power circuits that supply the Class 1E vital buses untilpermanent corrective actions are completed:

• Interim Corrective Actionso Daily walk-downs of the switchyard are performed to identify OPCvulnerabilities.

Specifically, steps were added to visually verify theintegrity of high voltage connections supplying the SUTs inprocedure 40DP-90PA9, Outside Area Operator Logs.o Alarm response procedures were revised to clarify that negativesequence relays may be activated by an unbalance betweenvoltages when no under-voltage condition exists and to check forunbalance by verifying voltages locally.

The specific alarm responseprocedures revised were:* Procedure 40AL-9RKIA, Panel BOIA Alarm Responses

• Procedure 40AL-9RKIB, Panel BOIB Alarm Responses

• Procedure 40AL-9RKIC, Panel B01C Alarm Responses o The severe weather abnormal operating procedure was revised toverify the integrity of the SUT connections following a severeweather event (40AO-9ZZ21, Acts of Nature).

In addition, thesame procedure was revised to now require that APS maintenance 2

Enclosure

-APS Response to Request for Additional Information

-NRC Bulletin 2012-01, Design Vulnerability inElectric Power Systempersonnel be notified to perform thermography and/or corona scansof overhead lines feeding the SUTs, at the next available opportunity subsequent to the severe weather event, to identifysigns of fatigue or cracking that could lead to an OPC.o Thermography inspections of the SUTs are performed when theyare returned to service following maintenance.

o Training for the Byron Event was provided to both licensed andnon-licensed operators to familiarize the operating staff memberswith the event and its potential consequences.

Response 2 -Status and Schedule for Completion of Plant DesignChanges* Statuso Holders of operating licenses and combined licenses for nuclearpower reactors are investigating options being researched byseveral vendors (PSC2000, EPRI, Schweitzer, etc.) to detect OPCfaults. There is currently no generic, off-the-shelf technology thathas been proven to detect all the required open phase faultconditions for all plant and transformer designs.o Holders of operating licenses and combined licenses for nuclearpower reactors are engaged in the development of NEI 13-12,Open Phase Condition Industry Guidance

Document, as well asdevelopment of enhancements to software tools being used toanalyze OPC faults.o With the goal of ensuring accurate detection without compromising nuclear safety or increasing plant risk, new OPC detection technology will be thoroughly evaluated, tested, and fully analyzedbefore installation.

o Vulnerability studies of the OPC faults have been started forPVNGS.* Scheduleo APS has agreed to the generic schedule, provided in the industryOPC initiative

document, for PVNGS. Specifically:

• By December 31, 2014, demonstrate compliance with theindustry OPC initiative criteria through analysis or identifyappropriate actions required to demonstrate compliance.

3 Enclosure

-APS Response to Request for Additional Information

-NRC Bulletin 2012-01, Design Vulnerability inElectric Power System" By December 31, 2016, implement design changes, ifnecessary, to comply with the industry OPC initiative criteria.

The 'active' actuation

features, if installed, may remain in amonitoring mode to demonstrate reliability.

" By December 31, 2017, if a monitoring period was deemednecessary, complete any design adjustments and enable'active' actuation features needed to demonstrate compliance with the industry OPC initiative criteria.

Any relevant UFSARupdates are also to be completed by this date. If theTechnical Specifications are impacted, any licenseamendment request should be submitted by this date.Should a TSTF Traveler be developed, the licenseamendment request should be submitted within six monthsof issuance of an NRC approved Traveler.

o APS expects to meet the milestones of the generic schedule;

however, deviations may be required to accommodate outageschedules, development and demonstration of modification options,complexities discovered in modeling

analyses, software andhardware availability, manufacturer delivery capabilities, licensing delays, or similar issues.o Any deviation from the industry OPC initiative schedule will bedocumented through the deviation/exemption process described inNEI 13-12, Open Phase Condition Industry Guidance Document.

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