ML18100A557

LER 93-014-00:on 930722,concern Raised Re 4 Kv Vital Bus Second Level Undervoltage Protection Dropout Setpoint (Both Units).Caused by Design,Mfg,Const/Installation,Per NUREG-1022.Design Changes Will Be implemented.W/930820 Ltr

ML18100A557
Person / Time
Site:	Salem
Issue date:	08/20/1993
From:	Pastva M, Vondra C Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RTR-NUREG-1022 LER-93-014, LER-93-14, NUDOCS 9308300327
Download: ML18100A557 (6)

Text

Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station August 20, 1993 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-70 DOCKET NO. 50-272 UNIT NO. 1 LICENSEE EVENT REPORT 93-014-00 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulations lOCFR 50.73(a) (2) (ii) (B). This report is required to be issued within thirty (30) days of event discovery.

Sincerely yours, C. A Vondra General Manager -

Salem Operations MJPJ:pc Distribution

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The EnerQY People 9308300321 930820 95-2189 ( 10M) 12-89 PDR ADOC~ 05000272 S PDR

NRC F0RM 366 U.S. NUCLEAR REGULATORY COMMISSION (6-89) APPROVED OMB NO. 3150-0104 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD LICENSEE EVENT REPORT (LERI COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH IP-530). U.S. NUCLEAR REGULATORY COMMISSION. WASHINGTON. DC 20555. AND TO THE PAPERWORK REDUCTION PROJECT (3150-0104). OFFICE OF MANAGEMENT AND BUDGET. WASHINGTON. DC 20503.

FACILITY NAME 11) DOCKET NUMBER 12) I PAGE 13}

Salem TITLE 141 Generatin~ Station - Unit 1 I01s101010121712 1joFOl5 4KV Vital Bus Second Level Undervoltage Protection Dropout Setpoint Concern (both Units).

EVENT OATE (5) LER NUMBER (6) REPORT DATE 17) OTHER FACILITIES INVOLVED IB)

MONTH DAY YEAR YEAR rt SE~~~~~~AL j( ~~~~~~ MONTH DAY YEAR FACILITY NAMES OOCKET NUMBERISl Salem Unit 2 o 1s1 o Io Io 13 1111 o I1 I 2 2 9 3 9 I3 - a I 1 .14 - a Io oIs 21 a 9 I3 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE Rl:QUIREMENTS OF 10 CFR §: (Ch*ck on* or mor* of th* following) 111)

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LICENSEE CONTACT FOR THIS LER 112) 50.73lall2HvlllHBI 50.73lall2Hxl NAME TELEPHONE NUMBER AREA CODE M. J. Pastva. Jr. - LER Coordinator b 1019* 313*19 1-1511 1615 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 113)

CAUSE SYSTEM COMPONENT I I I I I I I I I I I I I I I I I I I I I I I I I I I I SUPPLEMENTAL REPORT EXPECTED 114) MONTH DAY YEAR EXPECTED SUBMISSION r:-i YES (If y*s, com~lot* EXPECTED SUBMISSION DATE)

DATE (151

• 110 ?1'1 ql':l ABSTRACT (Limit to 1400 spaces, i.e .* approKimtJtely fifteen single-space typewritten lines) (16)

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. Conditions necessary for the design concern coincident with a prerequisite plant transient have not occurred. As such, the health and safety of the public has not been affected by this concern. Analysis of this event is continuing. Upon completion of this effort, a supplement to this LER will be submitted.

NRC Form 366 (6-89)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 93-014-00

• 2 of 5 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse - Pressurized Water Reactor Energy Industry Identification System (EIIS) codes are identified in the text as {xx}

IDENTIFICATION OF OCCURRENCE:

4 KV Vital Bus Second Level Undervoltage Protection Dropout Setpoint Concern (both Salem Units)

Event Discovery Date: 7/22/93 Report Date: 8/20/93 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 lOCFR50.72(b) (1) (ii) (B).

ANALYSIS OF OCCURRENCE:

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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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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 93-014-00 3 of 5 ANALYSIS OF OCCURRENCE: (cont'd) 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. JKV will be. *r:'::*

adjusted between 4.JKV 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.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating station DOCKET NUMBER LER NUMBER PAGE tinit 1 .- - 5000272' 93:...014-00 4 of s APPARENT CAUSE OF OCCURRENCE:

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 relay 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.i6KV 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.SKV.

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2. Only two vital buses may be energized from their operating .,.

transformer if both the-corresponding gro~p buses are on -

their respective APT.

3a. Three.vital buses may be energized from the operatingtransf armer if one of the corresponding group ** *

• buses is transferred to the operating SPT or

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 93-014-00 5 Of 5 CORRECTIVE ACTION: (cont'd) 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.

General Manager -

Salem Operations MJPJ:pc SORC Mtg.93-077

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