ML18100A577

LER 93-014-01:on 930722,concern Raised Re 4 Kv Vital Bus Second Level Undervoltage Protection Dropout Setpoint Due to Design,Mfg,Const/Installation.Analysis of Event Continuing. Suppl LER Will Be Submitted

ML18100A577
Person / Time
Site:	Salem
Issue date:	08/27/1993
From:	Pastva M Public Service Enterprise Group
To:
Shared Package
ML18100A576	List: ML18100A575 ML18100A577
References
LER-93-014-01, LER-93-14-1, NUDOCS 9309030259
Download: ML18100A577 (5)

Text

NRC FORM 366 (6-89) U.S. NUCLEAR REGULATORY COMMISSION APPROVEO OMB NO. 3150-0104 LICENSEE EVENT REPORT (LER) FACILITY NAME 111 Salem Generating Station -Unit 1 TITLE 141 EXPIRES: 4/30/92 ESTIMATED BUROEN PER RESPONSE TO COMPLY WTH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARO COMMENTS REGAROING BUROEN ESTIMATE TO THE RECOR OS ANO REPORTS MANAGEMENT BRANCH (P-530), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, QC 20555, ANO TO THE PAPERWORK REOUCTION PROJECT 13150-0104).

OFFICE OF MANAGEMENT ANO BUOGET, WASHINGTON, QC 20503. I OOCKET NUMBER (2) I PAGE 131 01s101010121112 1!0F01S 4KV Vital .Bus Second Level Undervoltage Protection Dropout Setpoint Concern (both Units). EVENT .DATE (5) LER NUMBER 16) REPORT DATE (71 OTHER FACILITIES INVOLVED (Bl MONTH DAY YEAR YEAR :ff tt MONTH DAY YEAR FACILITY NAMES DOCKET NUMBERISI Salem Unit 2 o 15 Io Io I o 13 11 I 1 ol 1 2 I 2 c 3 913 -o I 114 -ol 1 o I s *2 I 1 9 I 3 OPERATING MODE (9) THIS REPORT IS SUBMITTED PURSUANT TO THE Rl.QUIREMENTS OF 10 CFR §: (Chock on* or moro of th* following}

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73.71(bl 73.71(c) OTHER in Abstroct b1tow 1nd in T..,ct. NRC Form 366A} . TELEPHONE NUMBER M. J. Pastva. Jr. LER Coordinator 6 I 0 I 9 3 I 3 I 9 1-I 5 11 16 I 5 COMPLETE ONE LINE FOR EACH C.OMPONENT FAILURE DESCRIBED IN THIS REPORT (131 . CAUSE SYSTEM COMPONENT I I I I I I I I MANUFAC* TUR ER I I I I I I SUPPLEMENTAL REPORT EXPECTED (14) --;ci YES (If v*i. compl.r* EXPECTED SUBMISSION DATE} ABSTRACT (Limit to 1400 spac6s, i.e., approximately fifteen single-space ty,nwrittan lines} (161

• I I I I I I I I MANUFAC* TUR ER I I I I I I EXPECTED SUBMISSION DATE 115l MONTH DAY YEAR 1 10 2 15 9 I 3 On 7/22/93, it was determined that the present 91.6% dropout setpoint for second level undervoltage (UV) protection of the 4 kilovolt .(KV) vital buses (both Salem Units), may not fully protect motors should the bus voltage degrade to less than 93.2% but greater than 91.6%. This is contrary to Branch Technical Position (BTP)-PSB-1 and the Updated Final Safety Analysis Report (UFSAR). However, engineering calculation shows, given the postulated worst case design basis event, vital bus recovery voltage will not degrade to less than 93.2%. The 91.6% dropout setpoint was based on the lowest voltage the 4.16 KV motors could be allowed to operate (i.e. 90%) due to voltage drops in the motors' cables and relay inaccuracy considerations.

The revised recovery voltage of 93.2% will now maintain all motors operable under degraded voltage conditions.

During the next refueling outage on each Unit, design changes will be implemented to change the relay setpoint to meet the requirements of BTP-PSB-1.

In the interim, administrative controls are being implemented.

Technical Specifications and the UFSAR will be reviewed and revised as appropriate.

Analysis of this event is continuing.

Upon completion of this effort, a supplement to this LER will be submitted.

9309030259 930827 I PDR ADOCK 05000272 S * *.PDR NRC Form 366 (6-89) _*-1 . i SUPPLEMENTAL LICENSEE EVENT REPORT (LER} TEXT CONTINUATION Salem Generating Station *unit 1 DOCKET NUMBER 5000272 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse

-Pressurized Reactor LER NUMBER 93-014-01 PAGE 2 of 5 Energy Industry Identification System (EIIS} codes are identified in the text as {xx} IDENTIFICATION OF OCCURRENCE:

4 KV Vitai Bus Second Level Undervoltage Protection Dropout Setpoint Concern (both Salem Units} Event Discovery Date: 7/22/93 Supplement Report Date: 8/27/93 This report was initiated by Incident Report No.93-320. This event is reportable per 10CFR50.73(a}

(2} (ii} (B} and 10CFR50.73(a}

(2} (v} (D}. CONDITIONS PRIOR TO OCCURRENCE:

Unit 1: Mode 1 Reactor Power 80% -Unit Load 815 MWe Unit 2: Mode 1 Reactor Power 100% -Unit Load 1140 MWe DESCRIPTION OF OCCURRENCE:

On July 22, 1993, it was determined that the present 91.6% dropout setpoint for second level undervoltage (UV} protection of the 4 kilovolt (KV} vital buses {VJ} (both Salem Units}, will not fully protect motors at the 230 and 460 volt level should the 4KV bus voltage degrade to less than 93.2% but greater than 91.6%. This is contrary to Branch Technical Position (BTP.}-PSB-1 and the Updated Final Safety Analysis.Report (UFSAR}. However, engineering calculation shows, given the postulated worst case design basis event, vital bus recovery voltage will not degrade to less than 93.2%. The Nuclear Regulatory Commission was notified of this event per Code of Federal Regulations 10CFR50.72(b}

(1) (ii) (B). ANALYSIS OF OCCURRENCE:

Availability of minimum redundant alternating current (A.C.) power sources and distribution systems ensures sufficient power will be available to safety-related equipment for safe shutdown of the facility and the mitigation and control of accident conditions within the facility, as required by General Design Criteria 17 of Appendix "A" to lOCFR Part 50. Per BTP-PSB-1, the plant.licensing basis requires a second level of undervoltage protection for 4KV vital buses to ensure minimum motor terminal voltage for all safety-related

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.. . SUPPLEMENTAL LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit.1 DOCKET NUMBER 5000272 ANALYSIS OF OCCURRENCE: (cont'd) LER NUMBER 93-014-01 PAGE 3 of 5 motors. At Salem, when vital bus voltage drops below the dropout setpoint for relays providing this protection for greater than 13 seconds, vital bus loads are automatically transferred to their respective emergency diesel generators.

• As part of the self-initiated Electrical Engineering Self-Assessment Program, electrical calculations are being reviewed to ensure guidelines of BTP-PSB-1 are met. On July 1, 1993, review of Revision 1 of ES-15.00S(Q), "Salem Units 1 and 2 Degraded Grid study" identified a potential concern with the 91.6% dropout setpoint of the Units' 4KV vital buses (lA, lB, lC, 2A, 2B, and 2C). on

• July 22, 1993, further analysis of this concern determined the recovery vital bus voltage is 93.2% of 4.16KV following transfer of the Auxiliary Power Transformers (APTs) to the Station Power

• Transformers (SPTs). This voltage could result should a group bus transfer to the SPTs occur coincident with a Loss-of-Coolant Accident (LOCA) and the unaffected unit in startup or shutdown.

UFSAR Section 8.3.1.2 describes the setpoint as being determined using the 90% minimum motor terminal voltage as the starting point. Since 93.2% bus voltage is required to ensure the minimum motor terminal voltage, the existing 91. 6% dropout setpoint is not in compliance with the UFSAR or the BTP. However, because ES-15.00S(Q) calculations also show that vital bus recovery voltage will not degrade to a level at which actual motor degradation could occur, the intent of the UFSAR and BTP is still met. These calculations take credit for operation, prior to the event, of the load tap changers which are set to maintain a minimum initial bus.voltage of 4.3KV. Following

• event discovery, an evaluation to justify continued operation of both Salem Units, concluded the present dropout setpoint of the relays does not meet the intent of the BTP. However, Revision 1 of Engineering Calculation ES-15.00S(Q) determined there is not a significant safety concern with the present dropout setpoint provided the 4.16KV vital buses are maintained at 4.3KV or greater. Design changes will be implemented during the next refueling outage on each Unit to change the dropout setpoint to meet the intent of the BTP. For the interim, 4.16KV vital bus voltages are being monitored to assure load tap changers are operating properly to maintain a minimum bus voltage of 4.3KV. In addition, bus voltages below 4.3KV will be adjusted between 4.3KV and 4.5KV and restrictions concerning vital bus lineup will be in effect (see "CORRECTIVE ACTIONS:" section).

Analysis of this event is continuing..

Included will be a historical assessment of the effect of the revised assumptions at vital bus levels below 4KV. Upon completion of this effort, a supplement to this LER will be submitted.

SUPPLEMENTAL LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 APPARENT CAUSE OF OCCURRENCE:

DOCKET NUMBER 5000272 LER NUMBER 93-014-01 PAGE 4 of 5 The cause of this event is."Design, Manufacturing, Construction/Installation", per NUREG-1022

• -The 91. 6% dropout setpoint was based on the lowest voltage the 4.16 KV motors could be allowed to operate (i.e. 90%) due to voltage drops in the motors' cables and relay inaccuracy considerations.

The revised dropout setpoint, based upon the revised recovery voltage of 93.2%, will now maintain all motors operable under degraded voltage conditions.

PRIOR SIMILAR OCCURRENCES:

No prior similar occurrences of this event were identified.

SAFETY SIGNIFICANCE:

Engineering is currently completing its evaluation of the safety significance of past operation with the non-conservative second level UV setpoint.

With the current interim controls, the health and safety of the public.is not affected by this event. Upon completion of this evaluation this LER will be supplemented.

CORRECTIVE ACTION: Design changes will be implemented to change the.relay setpoint on both Units to meet the requirements of BTP-PSB-1 and be in accordance with the plant design basis. This will be done during the upcoming Unit 1 refueling outage and the next Unit 2 refueling outage. A License Change Request will be implemented to revise Technical Specifications in accordance with the second level UV reiay setpoint concern. The UFSAR will be reviewed and revised as appropriate.

Administrative controls are being implemented to ensure the following restrictions are employed as interim action until implementation of design changes: 1.

• 4.16KV vital bus voltages will be logged hourly to assure a minimum vital bus voltage of 4.3KV. Bus voltages less than 4.3KV will be adjusted to between 4.3KV and 4.5KV. 2. Only two vital buses may be energized from their operating transformer if both the corresponding group buses are on their respective APT. 3a. Three vital*buses may be energized from the operatingtransf ormer if one of the corresponding group buses is transferred to the operating SPT or l

• SUPPLEMENTAL LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating station Unit 1 CORRECTIVE ACTION: (cont'd) DOCKET NUMBER 5000272 LER NUMBER 93-014-01 PAGE 5 of 5 3b. Three vital buses may be energized from the operating transformer if the load which can be transferred from the APTs is reduced by 5 mega volt amps. MJPJ:pc SORC Mtg.93-077 General Manager -Salem Operations