ML18100A721

LER 93-016-00:on 931021,ESF Actuation Occurred Due to Electrical Short within 4 Kv Switchgear.Caused by Personnel Error Associated W/Ongoing Relay Maint Activities.Imposed Vital Bus & Switchyard Work standdown.W/931122 Ltr

ML18100A721
Person / Time
Site:	Salem
Issue date:	11/22/1993
From:	Pastva M, Vondra C Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-016, LER-93-16, NUDOCS 9312020421
Download: ML18100A721 (6)

Text

e Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station 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 93-016-00 November 22, 1993 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulation 10CFR50.73(a)

(2) (iv). This report is required to be issued within thirty (30) days of event discovery.

MJPJ:pc Distribution

• l' ..A -' ') ( :; ... " '.* *:.i: 9312020421 931122 S PDR ADOCK 05000272 PDR TI1e b in vuur hands. ' . Sincerely yours, c. A. Vondra General Manager -Salem Operations 95-2189 REV 7-92 NRC FORM 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 LICENSEE EVENT REPORT (LEA) INFORMATION COLLECTION REQUEST: 50_0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (P-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 (1) lDOCKET NUMBER (2) I PAGE 3J Salem Generating Station -Unit 1 o I 5 I o I o I o 12 I 7 12 I 1 OF 0 J'.i TITLE (4) ESF Actuation; Diesel Generator Blackout Signal Loading of lA & lC 4KV Vital Bus. EVENT DATE (51 LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (8) MONTH DAY YEAR YEAR t< SEQUENTIAL Ht REVISION MONTH DAY YEAR FACILITY NAMES DOCKET NUMBER(SI NUMBER NUMBER 01s1010101 I I ii 0 21 913 -o l 1 I 6 -ol o 1 11 212 9 I 3 1 9 3 o 1 s1010 1 0 1 I I OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE OF 10 CFR §: (Check one or more of the following)

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I I I I I I I -:*: *:*: *:*:*: -:*:-:* I I I I I I I """" .. }(){( ;.; .. ;.; ;.:-:*: *:.;:*:* ........ -.... -:-:-: SUPPLEMENTAL REPORT EXPECTED (14) MONTH DAY YEAR bi NO EXPECTED SUBMISSION (If yes, complete EXPECTED SUBMISSION DATE/ DATE (151 I I I ABSTRACT (Limit to 1400 spaces, i.e .. approximately fifttum single-space typewritten lines} '161 On 10/21/93, at 1525 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.802625e-4 months <br />, the inf eed breakers to lA and lC 4 Kilo-Volt (KV) buses tripped on an undervoltage (UV) signal, resulting in automatic starting and "blackout signal" loading of the buses from lA and lC Diesel Generators (D/Gs) . At approximately 2030 hours0.0235 days <br />0.564 hours <br />0.00336 weeks <br />7.72415e-4 months <br /> (same day), inf eed power to the buses from 12 station Power Transformer (SPT) was restored and the D/Gs were secured and returned to standby. The root cause of this event is electrical shorting within the 4KV switchgear, due to personnel error associated with ongoing relay maintenance activities.

The electrical shorting most probably occurred between adjacent terminals on the 12 SPT undervoltage (UV) relay circuit within the B vital bus 12BSD breaker cubicle. As a result of this event, work associated with SP Ts and 4KV vital switchgear was reevaluated to ensure minimized plant safety risk. Increased coordination of activities and the importance of exercising caution in the vicinity of 4KV switchgear and protective relays was emphasized with key supervisory personnel and workers. A vital bus and switchyard work standdown was imposed by the station General Manager, to allow review of remaining outage-related activities.

Station outage management will review scheduling of similar activities to ensure incorporation of lessons learned into future outage schedules.

NRC Form 366 (6-89)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse

-Pressurized Water Reactor LER NUMBER 93-016-00 PAGE 2 of 5 Energy Industry Identification System (EIIS) codes are identified in the text as {xx} IDENTIFICATION OF OCCURRENCE:

Engineered Safety Feature Actuation; Diesel Generator Blackout Signal Loading of 1A and 1C 4KV Vital Buses Event Date: 10/21/93 Report Date: 11/22/93 This report was initiated by Incident Report No.93-427. This event is reportable per 10CFR50.73(a)

(2) (iv) CONDITIONS PRIOR TO OCCURRENCE:

11th Refueling in progress; Reactor defueled.

1B 4 Kilo-Volt (KV) Vital Bus {EB} and 11 station Power Transformer (SPT) were cleared and tagged and 12 SPT was supplying 1A and 1C 4KV Vital buses. Maintenance testing, of 1B 4KV Vital Bus overload protection and the undervoltage and transfer circuits was in progress.

DESCRIPTION OF OCCURRENCE:

On October 21, 1993, at 1525 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.802625e-4 months <br />, the infeed breakers to lA and lC 4 KV buses tripped on an undervoltage (UV) signal resulting in automatic starting and "blackout signal" loading of the buses from their respective Diesel Generators (D/Gs) (1A and lC) {EK}. At 1709 hours0.0198 days <br />0.475 hours <br />0.00283 weeks <br />6.502745e-4 months <br /> (same day) the Nuclear Regulatory Commission (NRC) was notified of this event, in accordance with 10CFR50.72(b)

(2) (ii). At approximately 2030 hours0.0235 days <br />0.564 hours <br />0.00336 weeks <br />7.72415e-4 months <br /> (same day), infeed power to the buses from 12 SPT was restored and the D/Gs were secured and returned to standby. ANALYSIS OF OCCURRENCE:

The Salem Safeguards Systems design basis includes the requirement that the station must be safely shutdown during a loss of coolant accident (LOCA) and a coincident loss of offsite power (Blackout).

All electrical equipment needed during a LOCA is powered from the vital buses, which can be powered from the standby alternating current LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 ANALYSIS OF OCCURRENCE: (cont'd) LER NUMBER 93-016-00 PAGE 3 of 5 diesel generators.

Safeguards Equipment Control (SEC) is a logic system, comprised of three control systems, that provide proper actions in response to any accident and/or blackout condition.

Each SEC (A, B, or C) is physically and electrically isolated from the other, is associated with its own DG and vital bus, and responds to accident (safety injection) and vital bus UV input signals. Based upon the combination of these signals, the respective SEC will actuate to strip the vital buses, start the D/Gs, and reload the vital buses. On October 21, 1993, at shortly before 1525 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.802625e-4 months <br />, the Unit 1 11th Refueling was in progress with the Reactor defueled.

1B 4KV Vital Bus and its associated D/G and 11 SPT were cleared and tagged for maintenance and outage-related activities and 12 SPT was supplying 1A and 1C 4KV Vital buses. In addition, maintenance testing, of 1B 4KV Vital Bus overload protection and the undervoltage and transfer circuits was in progress.

This included work within the breaker cubicle of 12BSD (4KV infeed breaker from 12 SPT to 1B Vital Bus). At 1525 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.802625e-4 months <br /> (same day), the 12 SPT UV Transfer Relays tripped 12ASD and 12CSD 4KV infeed breakers from 12 SPT to 1A and 1C Vital Buses. This normally would have initiated an automatic transfer of 1A and 1C vital buses' to the infeed breakers from 11 SPT. However, since 11 SPT was not energized (tagged out of service), the buses' 70% UV relays picked up which automatically started and loaded 1A and 1C D/Gs to their buses. The appropriate loads were automatically sequenced on by the SEC and spent fuel pit cooling was restored within approximately five minutes. At approximately 2030 hours0.0235 days <br />0.564 hours <br />0.00336 weeks <br />7.72415e-4 months <br /> (same day), following assessment of the consequences and approximate root cause of the event, infeed power to 1A and 1C Vital buses from 12 SPT was restored.

Investigation determined this event resulted from an electrical fault. This fault caused the Potential Transformer (PT) fuses for B and c phases to experience a momentary high current and blow, which caused the 12 SPT UV Transfer Relays to trip the 12 SPT inf eed breakers to the buses. This determination is based on results of testing, inspection, and examination of the blown fuses. Interviews with personnel working within the 12BSD breaker cubicle, did not reveal any connection with the blown PT fuses. However, the electrical shorting most probably occurred between adjacent terminals on the 12 SPT UV relay circuit within the B vital bus 12BSD breaker LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 ANALYSIS OF OCCURRENCE: (cont'd) cubicle. LER NUMBER 93-016-00 PAGE 4 of 5 As a result of this event the planning and scheduling of work associated with the SPTs and vital switchgear was reviewed to ensure that the potential is minimized for future similar occurrences.

Methods identified to help minimize this include increased coordination of activities in the vicinity of 4KV switchgear and protection relays, as well as reemphasizing the importance of exercising caution during these activities.

In addition, a vital bus and switchyard work standdown, for approximately 21 hours2.430556e-4 days <br />0.00583 hours <br />3.472222e-5 weeks <br />7.9905e-6 months <br />, was imposed by the station General Manager, to allow review of pending outage-related activities, including electrical work, to ensure proper planning and scheduling.

APPARENT CAUSE OF OCCURRENCE:

The root cause of this event is electrical shorting within the 4KV switchgear due to personnel error. The electrical shorting most probably occurred between adjacent terminals on the 12 SPT UV relay circuit within the B vital bus 12BSD breaker cubicle. PREVIOUS OCCURRENCES:

Previous events involving undervoltage conditions on 4KV Vital Buses which resulted in automatic starting and loading of D/Gs have been reported in LERs 311/92-013-00 and 272/93-012.

These occurrences involved personnel error due to misplacement of switches.

SAFETY SIGNIFICANCE:

This event did not affect the health and safety of the public. Equipment functioned as required during this event. As a result of this event, 11 SFPP, which is supplied from lA 460V vital bus, was automatically stripped from the bus. Within approximately five minutes of the event, the pump was then restarted to restore cooling to the Spent Fuel Pit. In addition, offsite power was available and the affected 4KV vital buses could have been restored to service from offsite power, if necessary.

CORRECTIVE ACTION: As a result of this event, work associated with SPTs and 4KV Vital switchgear was reevaluated to ensure minimized plant safety risk.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 CORRECTIVE ACTION: (cont'd) DOCKET NUMBER 5000272 LER NUMBER 93-016-00 PAGE 5 of 5 Increased coordination of activities and the importance of exercising caution in the vicinity of 4KV switchgear and protective relays was emphasized with key supervisory personnel and workers. A vital bus and switchyard work standdown was imposed by the station General Manager, to allow review of remaining outage-related activities.

station outage management will review scheduling of similar activities to ensure incorporation of lessons learned into future outage schedules.

MJPJ:pc SORC Mtg.93-102 11 L ';

G neral Manager -Salem Operations