ML20113H906

Confirms Results of Discussions W/Nrc on 920727,requesting NRR Temporary Waiver of Compliance from 4,160 Volt Safeguards Bus Surveillance Test Requirements of Spec Section 4.6.A.3.b.1

ML20113H906
Person / Time
Site:	Prairie Island
Issue date:	07/29/1992
From:	Parker T NORTHERN STATES POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9208060135
Download: ML20113H906 (6)

Text

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. . Northem States Power Company 414 N; collet Mall Minneapotes. Minnesota $54011927 Telephone (612) 330 5500 July 29, 1992 U S Nuclear Regulatory Commission Attn: Document Control Desk Vashington, DC 20$55 PRAIR1E IS1AND NUCLEAR GENERATING PiANT Docket Nos. 50 282 1.feense Nos. DPR 42 50 306 DTR 60 Request for URR Temporary Waiver c' Compliance to Technical Specification Surveillance Reauirements_

The purpose of this letter is to confirm the results of discussions batveen Northern States Pouer Company and the NRC Staff on July 27, 1992, in which Northern States Power requested a NRR Valver of Compliance from the 4160V safectards bus surveillance test requirements of Prairie Island Technical Spe nfication Section 4.6.A.3.b.1. An NRR Waiver of Compliance was verbally issued by the NRC Staff at 2025 on July 27, 1992.

As a result of not completing all of the individual surveillance test requirements specified in Section 4.6.A.3.b.1, and the associated bases for Section 4.6, Unit 14160V safeguards bus 16 was declared inoperable at 1600 on July 27, 1992. Unit 2 4160V bus 26 will exceed its 18 month surveillance interval plus 25% on August 5, 1992. Northern States Power requests a M ay in the completion of the surveillance test requirements and operability verification for 4160V safeguards buses a* specified in Spccification 4.6. A.3.b.1 and the basis for Section 4.6 untti an Emergency License A mendment can be submitted and approved. That License Amendment will request authorization to delay the performance of the incomplete portion of the surveillance testinr on buses 46 and 26 until completion of the electrical system upgrade modh ications of the station blackout project during the two unit outage scheduled to begin in October 1992.

Requirements for Vhich Relief in Recuested Section .6..A.3.b.1 of the Prairie Island Technical Specifications requires verification that the simulation of a loss of offsite power in conjunction with a safety injection signal will result in the de energization of the emergency buses and load shedding from the emergency buses. The bases for Section 4,6 state that this test will detronstrate that the emergency power system and the control systems for the engineered safeguards equipment will function automatically in the event of loss of all other sources of a-c power, and that the diesel generators will start automatically in the event of a loss-of-cooltnt accident. The bases further state that this test will  !

demonstrate proper tripping of motor fen Nr breakers, main s'aply and tie i

breakers on the affected bus, and seg .1 starting of enr o tial equipment,

! as well as the operability of the diens generatore. A

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'USNilC July 29, 1992 Northern States Power Company Page 2 Circumstances Leadinr to Reauest and Need for Prompt Action As a result of a detailed exatnination of the Emergency Power System Technical Specifications conducted during the Operating Experience Assessments of Kewaunee Licensee Event Report 92 n11 and NRC Information Notice 92 40,

" Inadequate Testing of Ernergency Bus Undervoltage Logic circuitry", it was identified on July 27, 1992 that a portion of the surveillarice testing described in the bases for Section 4.6.A.3.b.1 had not been completed within the required tirne fratne. Since a portion of the required surveillance testing for Unit 1 4160V bus 16 was not completed within the required survellL tce interval plus 25%, Unit 1 4160V safsguards bus 16 was declared inoperable at 1600 on July 27, 1992. boit 2 4160V bus 26 will exceed its 18 month surveillance interval plus 25% on August 5, 1992.

During each refueling outaga. the integrated safety injection test has been used to fulfill the requirements of Technical Specification 4.6. A.3.b.1. The integrated Si test simulates a loss of off site power by directing an operator to manually open the supply breaker to the safeguards bus. This method of tripping the source breakers from the safeguairds buses was used in the pre-operational test of the diesel generators and during each subJequent integrated SI test, llowever, the integrated SI test does not demonstrate the full capability of the undervoltage trip feature to automatically de attergize the safeguarus buses upon a loss of powet. The testing perfortned during the integrated SI test does not demonstrate proper tripping of the main supply and tie breakers on the affected 4160V safeguards bus. All other requirements of 4.6.A.3.b.1 are fulfilled by the integrated SI tent.

Electrical preventive maintenance is perfo,w d on one of the two 4160 V safeguards buses during each refueling outage, while the refueling cavity is flooded. Prior to restoring the bus, a separete. surveillance procedure is performed to ft.nettonally check the voltage testoration scheine. During this test, the ti typing of the source breakers (main supply and tio breakers) is verified during a bus undervoltage. This surveillance test was performed as part of post maintenance testing prior to bus rectoration and was not intended to meet Technical Specification requirements (as interpreted at the time),

llowever, it provices sufficient overlap vith the integrated safety injection test to meet the Technical Specification requirements in Section 4.6.A.3.b.1 and its bases. This test is ;- dormed every other refueling outage, rather than the each r fueling outage (or 18 month) frequency in TS 4.6.A.3.h.1.

Testing on Unit 1 4160 V bus 16 was last performed on February 20, 1990.

Testing on Unit 2 4160 V bus 26 was last performed on September 20, 1990.

The requested Temporary Waiver of Cotopliance is necessary to avoid the initiation of a shutdown of Unit 1 at 2400 on July 27, 1992 and a shutdown of 3 Unit 2'on August 5, 1992.

Due to the natura of this event, it was not possible to foresce its occurrence and take ineasures to avoid it. Therefore, it was not possible to avoid the 4 submittal of this request for a Temporary Waiver of Compliance.

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'USNRC July 29, 1992 Northern States Power Company Page 3 Evaluation of Safety Sirnificance and Potential Connavery Portions of the load reject / voltage restoration scheme are tested frequently.

The undervoltage and degraded voltage relay setpoint calibration la verified on a monthly basis. Also on a monthly basis, under a separate surveillance, the emergency diesel generators are started, synchronized to the safeguards bus and the load sequencing portion of the scheme is tested. This normal monthly surveillance testing verifies operability of the majority of the load reject / voltage restoration scheme components.

Further, no probletas affecting operability have been identified with the-voltage restoration logic during the perfortaance of the preventative maintenance described above. This preventative snaintenance program has been in place since 1977.

This testing and maintenance demonstrates the reliability of the voltage restoration logic and provides a high degree of assurance-that it will remain operabic until the two unit outage scheduled to begin in October 1992.

Even though Unit 14160V bus 16 was declared inoperable at 1600 on July- 27, k 1992, the bus is energized and its related controls remain available and capable of responding to any plant transient. Based on the results of past testing a high degree of confidence extsta that all electrical functions are

. fully operable.

• It is overly conservative to assume that systems or components are inoperable when a surveillance requirement has not been perfortoed at its required frequency. The opposite is in fact the case; t!.e vast. majority of surveillances demonstrate that systems or componento in fact are operable.

When a surveillance har not been completed, it is primarily a question of operability that has not been verified by the perforna.nce of the required surveillance.

Assuming that the incomplete surveillance testing results in inoperable voltage restoration logic, only 4160V buses 16 and 26 would be affected.

4160V buses 15 and 25 are still within the required surveillance test interval and remain operable. Therefore, consistent with the plant accident analysis, at least one train of safeguards components would remain

• arable on each unit.

Therefore, safety significance and potential consequences of this event are

, minimal.

Discussion o ' Compensatory Actions

' Even though Unit 14160V bus 16 was declared inoperable at 1600 on July 27, 1992, the bus is etiergized and-its related controls remein available and capable of responding to any plant transient. Based on the-results of past testing a high degree of confidence exists that all electrical functions are fully opecable.

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USNRC July 29, 1992 Northem States Power Company Page 4 Even though there is a high degree of confidence that the voltage restoration logic for buses 16 and 26 will function as designed, the following compensatory actions are being put in place:

1. The monthly safeguards bus undervoltage testing and emergency diesel generator surveillance will continue.

2. The relays associated with the 4160V safeguards bus undervoltage restoration scheme will be visually inspected monthly.

3. Should unforeseen degradation, not the result of pre planned testing or maintenance, occur on the onsite electrical supply system (including the switchyard), discussion will be initiated with the NRC Staff for the verbal re confirmation of the acceptability of. the Temporary Waiver of Compliance.

4. All control room operators will review the emergency operating and abnormal operating procedores related to safeguards bus voltage restoration.

5. A procedure to complete the delinquent portions of the Specification 4.6.A.3.b.1 testing requirements, at a mode other than cold shutdown, will be evaluated.

6. Following a unit trip or the placing of either unit in hot sh.tdown, discussion will be initiated with the NRC Staff for the verbal re-confirmation of the acceptability of the Temporary Waiver of Compliance. .

I Justification of Duration of the Recuegg This request for a Temporary Waiver of Compliance requests a delay in the completion of a portion of the surveillance' test requirements and operability verification for 4160V safeguards buses as specified in Specification 4.6.A 3.b.1 and the basis for Section 4.6 until an Emergency License Amendment can be submitted and approved. That License Amendment will request authorization to delay performance of the incomplete portion of the surveillance testiny .. buses 16 and 26 until completion of the electrical system upgrade modifications of the station blackout project during the two

, . unit outage scheduled to begin in October 1992.

As discussed above, even though Unit 1 4160V bus 16 was declared inoperable at 1600 on July 27, 1992, the bus is energized and its related controls remain available and capable of responding to any plant transient. Based on the results of past testing a high degreo of confidence exists that all electrical functions are fully operable.

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4 USt@C July 29, 1992 Northern States Power Company Page 5 l

i jinnificant llazards Consideration Evaluation I

This request for Temporary Waiver of compliance has been evaluated to

determine whether it constitutes a significant hazards consideration. This analysis is provided below

1

1. The requested Temporary Vaiser of Compliance will not involve a significant i

) increase in the probability or consequences of an accident previously  !

j evaluated. )

l j Assumin6 that incomplete surveillance testing results in inoperable voltage i restoration logic, only 4160V buses'16 and 26 would be a"fected. 4160V buses 15 and 25 are still within the required surveillance test interval l

j and remain operable. Therefore, consistent with the plart accident analysis, at least one train of safeguards components would remain operable

} on each unit.

Even though Unit 14160V bus 16 was declared inoperable at 1600 on July 27 i 1992, the bus is energized and its related controls remain available and capable of responding to any olant transient. Based on the results of past

{. testing a high degree of confidence exists that all electrical functions l are fully operable.

)

l Therefore, the requested Temporary Waiver of Compliance vill not i significantly affect the probability or consequences of an accident l previously evaluated.

I '

2. The requested Temporary Waiver of Compliance will not create the

! possibility of a new or different kind of accident from any accident  ;

I previous 1v analyzed.

2 There are no new failure modes or mechanisms associated with the requested

Temporary Waiver of Compliance. The requested Temporary Waiver of  ;

j Compliance does not involve any modification of plant-equipment or changes in operational limits, it only requests the delay of a portion of the -

surveillance testing of the voltage restoration logic.;

Therefore, the requested Temporary Whiver of Compliance does not create the possibility of a new or different kind of accident from any previously evaluated, and the accident analyses. presented in the Updaced Safety -t Analysis Report will remain bounding.

3. The requested Temporary Vaiver of Compliance will not involve a significant: >

reduction in the marrin of safety, i

-Assuming that incomplete surveillance testing results in inoperable voltage restoration logic, only 4160V buses 16 and 26 would be affected. 4160V buses 15 and 25 are still within-the required aurveillance test inte rval and remain operable. Therefore, consistent with the plant accident analysis, at:1 east-one. train of safeguards components would remain operable.

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4 USJ1RC July 29, 1992 Nodhorn States Power Company Page 6 Even though Unit 14160V bus 16 was declared inoperable at 1600 on July 27, 1992, the bus is energized and its related controls remain available and capable of responding to any plant transient. Based on the results of past testing a high degree of confidence exists that all electrical functions are fully operable, Thorofore, the requested Temporary Waiver of Compliance will not result in any reduction in the plant's margin of safety.

Based on the evaluation described above, Northern States Power Company has determined that operation of the Prairie Island Nuclear Generating Plant in accordance with the requested Temporary Valver of Compliance does not involve any significant hazards considerations ao defined by NRC regulations.

Environmental Assessment The requested Temporary Waiver of Compliance does not change effluent types or total offluent amounts nor does it involve an increase it; power level.

Therefore, this change will not result in any significant environmental impact.

Operations Comt.ttee Review end Approval The Plant Operations Committee has reviewed and approved this request for a Temporaty Veiier of Compliance.

Please contact us if you have any questions related to this request for a Temporary Waiver of Compliance.

hasThomasMParker Manager Nuclear Support Services c: Regional Administrator Region III, NRC Senior Resident Inspector, NRC NRR Project Manager NRC J E Silberg 4

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