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{{#Wiki_filter:}} | {{#Wiki_filter:*' j_ .. 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 91-024-00 July 15, 1991 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulations lOCFR 50.73(a} (2) (iv) and 50.73(a) (2) (i) (B}. This report is required to be issued within thirty (30) days of event discovery. | |||
MJP:pc Distribution . :: -: : c* *-' . Sincerely yours, C. A Vondra General Manager -Salem Operations r / / 95* 2189 I 1 OM I 12-ec NRC F.ORM 366 -U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3150-0104 (6.ari EXPIRES: 4/30/92 ESTIMATED BURDEN PEA RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD 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 (1) I DOCKET NUMBER (2) I PAGE (31 Salem Generating Station -Unit 1 015101010121 71 2 1 OF 018 TITLE (41 Reactor Trip From 100% Power Due To Lightning Strike EVENT DATE 151 LER NUMBER 161 REPORT DATE (7) OTl;tER FACILITIES INVOLVED 18) MONTH DAY YEAR YEAR SEQUENTIAL | |||
\\ REVISION MONTH DAY YEAR FAC1 LITY NAMES DOCKET NUMBERIS) | |||
NUMBER NUMBER Salem Unit 2 o I 5 Io Io I o I 31l11 o I 6 ii 911 -oi 21 4 -olo ol 7 ii 911 0151010101 I I 6 9 1 5 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE RloQUl_REMENTS OF 10 CFR §:(Chock one or more of th* following} | |||
(111 MODE (8) 1 20.402(b) 20.405(c) x 50.731*112Hivl 73.71(b) ,_ -POWER I 110 10 20 . .C05(o)(1 | |||
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LICENSEE CONTACT FOR THIS LER (12) NAME TELEPHONE NUMBER AREA CODE M. J. Pollack -LER Coordinator 6 I 019 I 3 19 t-I 2 I 0 I 2 12 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT 113) ::::::::::::: | |||
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:;:::::: 1:-::*:-SUPPLEMENTAL REPORT EXPECTED (14) MONTH DAY YEAR EXPECTED SUBMISSION | |||
_ n YES (If yes, comp/ere EXPECTED SUBMISSION DATE! DATE 1151 I I I NO ABSTRACT (Limit ro 1400 spaces, i.e., soproximately fifreen single-space typewritten lines) 1161 On June 16, 1991, at 1940 hours, during normal full power operation, Salem Unit 1 experienced a Reactor Trip/Turbine Trip. The first out overhead annunciation was "4KV Group Bus Undervoltage". | |||
At the time of the event a severe thunderstorm was in progress. | |||
Investigation revealed that lightning had struck in the vicinity of the phase B Generator Step-Up (GSU) transformer | |||
{EL} | |||
* Evidence of the lightning strike included carbonization of the high voltage bushing, damage to the corona rings and lightning arrestor and eyewitness accounts. | |||
The root cause of the reactor trip event is attributed to an act of nature; i | |||
* e *I a lightning strike in the vicinity of the phase B GSU transformer, resulted in a 4KV Group Bus Undervoltage and subsequent reactor trip. Lightning protection was assessed by engineering and found to be appropriate. | |||
The damage to the Phase B GSU transf orrner was repaired. | |||
Subsequently, on June 24, 1991r the Unit 1 was returned to service. Also as a result of the lightning strike, 500 KV breaker flashover protection was initiated due to sufficient current through the transformer neutral. This resulted in the loss of the No. 2 Station Power Transformer and subsequent de-energization of the 1F and lG Group Busses. An engineering review has been initiated to prevent flashover protection actuation from a coasting generator. | |||
Design changes will be implemented as appropriate. | |||
NRC Form 366 (6.891 | |||
.. LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE | |||
______________ | |||
____ | |||
____ =2--'0.of 8 PLANT AND SYSTEM IDENTIFICATION: | |||
Westinghouse | |||
-Pressurized Water Reactor Energy Industry Identification System (EIIS) codes are identified in the text as {xxl IDENTIFICATION OF OCCURRENCE: | |||
Reactor Trip from 100% power due to lightning strike Event Date: 6/16/91 Report Date: 7/15/91 This report was initiated by Incident Report Nos. 91-441, 91-442, 91-443, 91-444, and 91-479. CONDITIONS PRIOR TO OCCURRENCE: | |||
--------------------------- | |||
Mode 1 Reactor Power 100% -Unit Load 1142 MWe DESCRIPTION OF OCCURRENCE: | |||
------**--- | |||
-----On June 16, 1991 at 1940 hours, during normal full power operation, Salem Unit 1 experienced a Reactor Trip/Turbine Trip. The first out overhead annunciation was "4KV G:roup Bus Undervoltage". | |||
At the time of the event a severe thunderstorm was in progress. | |||
Investigation revealed that lightning had struck in the vicinity of the phase B Generator Step-Up (GSU) transformer | |||
{EL}. Evidence of the lightning strike included carbonization of the high voltage bushing, damage to the corona rings and lightning arrestor and eyewitness accounts. | |||
The Nuclear Regulatory Commission (NRC) was notified of the actuation of the Reactor Protection System (RPS) {JC} at 2037 hours on June 16, 1991 in accordance with Code of Federal Regulations lOCFR 50. 72 (b) (2) (ii). APPARENT CAUSE OF OCCURRENCE: | |||
The root cause of the Salem Unit 1 June 16, 1991 reactor trip event is attributed to an act of nature. At 1940 hours, a lightning strike in the vicinity of the phase B GSU transformer, resulted in a 4KV Group Bus Undervoltage and subsequent reactor trip. Lightning protection was assessed by engineering and was found to be appropriate. | |||
Refer to the attached schematic, for additional details, when reviewing this section and the Analysis of Occurrence section. | |||
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 SEQUENCE OF EVENTS: (cont'd) Date/Time Event DOCKET NUMBER 5000272 LER NUMBER 91-024-00 PAGE 3 of 8 7-16/1940 Lightning strike in vicinity of Phase B of the Main Power Transformer (i.e., GST} Electrical fault on 500 KV Main Power Transformer Unit 1 Generator Differential Regular and Backup Trip Relays actuate 500 KV Breakers open (lOX and 12X); Generator Field Breaker opens and Turbine Trip signal initiated 4KV Group Busses transfer initiates; from the Auxiliary Power Transformer to the Nos. 11 and 12 Station Power Transformers Rx Trip Breakers open 4KV Group Bus transfer complete and Bus voltage returns to normal Flashover protection relays and alarms (Salem Units 1 and 2) actuate (to + 4 seconds) 12 and 22 Station Power Transformers trip 18 Vital Bus Transfers.to 11 SPT 2B Vital Bus Transfers to 21 SPT lF and lG Group Busses deenergize and alarm in Control Room ANALYSIS OF OCCURRENCE: | |||
Following the GSU transformer lightning strike, the resultant phase to ground fault operated the generator differential regular and backup instantaneous trip relays on Phases B and C GSU transformers opening the lOX and 12X 500 KV breakers, opening the generator field breaker and causing a Unit 1 turbine trip (Unit Isolation Trip). The Unit Isolation Trip subsequently initiated a Group Bus transfer (i.e., fast transfer scheme) from the Auxiliary Power Transformer to the Nos. 11 and 12 Station Power Transformers, respectively. | |||
It is not uncommon, when you have single phase to ground faults, for only two (2) of the three (3) phases to pick-up the instantaneous relays initiating the Unit Isolation Trip (i.e., Phase A instantaneous relays did not pick-up) . At the time of the Phase B phase to ground fault, voltages on the LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 ANALYSIS OF OCCURRENCE: | |||
DOCKET NUMBER 5000272 (cont'd) LER NUMBER 91-024-00 PAGE 4 of 8 electric distribution system for the four (4) 4KV Group Busses and the three (3) 4KV Vital Busses decayed. All 4KV Vital Bus voltages recovered within 4 cycles while the Group Bus voltages recovered after completion of the fast transfer (in approximately 12 cycles). This degraded Group Bus voltage (below 70% rated voltage) lasted sufficiently long to initiate a Reactor Trip signal via the Group Bus undervoltage relays. Also as a result of the lightning strike, 500 KV breaker (lOX and 12X) flashover protection initiated due to sufficient current through the transformer neu"tral. | |||
The flashover protection occurred four (4) seconds following the fault, on the phase B GSU transformer, causing: 1) all adjacent 500 KV breakers to open; 2) loss of half of the 13 KV ring bus (13 KV 4-5 and 3-4 breakers opened); 3) lockout of the Unit 3 (Gas Turbine) 13 KV breaker; 4) the New Freedom Line was remote tripped to the New Freedom Substation; and 5) of the Salem New Freedom Line from Section 2 (of the 500 KV Switchyard) . Flashover protection actuation should have occurred approximately 13 cycles after fault occurrence. | |||
It could not be determined why flashover protection was delayed; however, the delay did not have an impact on this event. Testing was performed but the circuits timed correctly and the event could not be duplicated. | |||
The loss of 500 KV power to Section 1' (of the 500 KV Switchyard) resulted in the loss of the No. 2 Station Power Transformer | |||
{SPT). With the loss of the No. 2 SPT, 13 KV power to the Nos. 12 and 22 SPTs was lost. After the loss of the No: 12 SPT, the lF and lG Group Busses de-energized (i.e., the Auxiliary Power Transformer was already de-energized due to the Unit Isolation signal) and the lB Vital Bus transferred from the No. 12 SPT to the No. 11 SPT. Due to the loss of the No. 22 SPT, the 2B Vital Bus successfully transferred from No. 22 SPT to the No. 21 SPT. An extensive analysis provided by oscillograph, digital fault recordeJ* | |||
and sequence of events recorder records indicated that the relay operations were correct for the conditions. | |||
Although the breaker flashover scheme is designed to protect against the flashover of either 500 KV generator breaker, it also operates for a fault between the 500 KV generator breakers and the main transformer when the fault current is supplied by the generator. | |||
There was no evidence, either oscillographic or physical, of the flashover of either 500 KV generator breaker. Therefore it is concluded that the flashover relay scheme was operated by the current contributed by the coasting generator. | |||
An Engineering review, along with appropriate modifications, has been initiated. | |||
After the loss of the "lF" and "lG" Group Busses, the following | |||
--LICENSEE EVENT REPORT {LER) TEXT CONTINUATION Salem Generating Station Unit 1 ANALYSIS OF OCCURRENCE: | |||
DOCKET NUMBER 5000272 (cont'd) significant equipment was LER NUMBER 91-024-00 PAGE 5 of 8 1. Nos. 13 and 14 Reactor Coolant Pumps {RCPs); The loss of No. 13 RCP resulted in limited pressurizer spray capability; however, the No. 11 RCP was available for pressurizer spray and was successfully used. 2. Control Pressurizer Heaters and pne set of Backup Pressurizer Heaters 3. Plant Vent composite sample pump; this pump is required to remain operable as per Technical Specification 3.3.3.9 Table 3.3-13. Chemistry was notified and alternate sampling was initiated. | |||
The pump was returned to service when lF Group Bus was restored {at 0041 hours on June 17, 1991) An excessive cooldown occurred following the reactor trip. This was due to Auxiliary Feedwater making up for Steam Generator shrink from the trip and loss of Nos. 13 and 14 Reactor Coolant Pumps. In accordance with the guidance provided by the EOPs, closure of the main steam isolation valves was successfully performed. | |||
Excessive cooldown is a concern identified from prior plant trips. Engineering has assessed this phenomenon and concluded that it does not pose a safety concern; however, corrective actions are being pursued (reference LER 311/91-029-00). | |||
The 11MS10 atmospheric relief valve (SB} changed operational modes from automatic to manual and then went full open while reducing its setpoint (to 1005 psig) to control Stearn Generator pressure. | |||
A work order was initiated to investigate and correct this concern. Operator actions following the automatic actuation of the reactor trip began with the NCO initiating a manual trip. Procedure EOP-TRIP-1 was then entered followed by entry into EOP-TRIP-2. | |||
Actions required by these procedures were complied with including closure of the main steam isolation valves due to Tavg excessive cooldown. | |||
Operators compensated for the inadvertent full opening of the 11MS10 valve (following its setpoint adjustment}, and subsequent lower level in No. 11 Steam Generator, by adjusting the Auxiliary Feedwater flow to the No. 11 Steam Generator. | |||
With the loss of the 1F and 1G Group Busses, the Control Pressurizer Heaters and one set of Backup Pressurizer Heaters were unavailable. | |||
Also, as stated above, the No. 13 RCP became unavailable. | |||
Using the available Backup Pressurizer Heaters and the No. 11 RCP Pressurizer spray capability Operators were abJ.e to to maintain RCS pressure control. After completing the actions required by EOP-TRIP-1 and EOP-TRIP-2, IOP-8 was entered. Using this procedure, the plant was stabilized (in Mode 3) with the twc (2) operating Reactor Coolant Pumps (i.e., Nos. 13 and 14 RCPs were not operating due to the loss of the 1F and 1G Group Busses). After stabilization of the plant, Technical Specifications were reviewed and required actions performed due to the loss of an off-site power source (Technical Specification 3.8.1.1 Action "a"). | |||
* LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 ANALYSIS OF OCCURRENCE: | |||
DOCKET NUMBER 5000272 (cont'd) LER NUMBER 91-024-00 Technical 3.8.1.1 Action "a" states: PAGE 6 of 8 "With either an offsite circuit or diesel generator of the above required A.C. electrical power sources inoperable, demonstrate the OPERABILITY of the remaining A.C. sources by performing Surveillance Requirements 4.8.1.1.1.a and 4.8.1.1.2.a2 within one hour and at least once per 8 hours thereafter; restore at least two offsite circuits and three diesel generators to OPERABLE status within 72 hours or be in at least HOT STANDBY within the next 6 hours and in COLD SHUTDOWN within the following 30 hours." Due to plant conditions, the Unit 1 Diesel Generators were successfully tested within one hour of Unit stabilization following the loss of the No. 2 Station Power Transformer | |||
{i.e., one of the two sources of offsite power) as per the Action Statement (on June 16, 1991 at 2154, 2155, and 2156 hours respectively). | |||
Preparations for testing the Diesel Generators was initiated approximately one hour and twenty minutes after the loss of the No. 2 Station Power Transformer. | |||
The delay in the testing of the Unit 1 diesel generators was therefore due to the time required to stabilize the Unit. However, it does constitute a noncompliance which is reportable to the Nuclear Regulatory Commission in accordance with Code of Federal Regulations lOCFR 50.73(a) (2) (i) (B). Early in the Unit 1 event, the SNSS did initiate actions to perform an operability check of the Salem Unit 2 diesel generators. | |||
This was required, per Technical Specifications (identical to the Unit 1 Action requirements), due to the loss of the offsite power source (i.e., No. 2 Station Power Transformer). | |||
The Unit 2 Diesel Generators were successfully tested within one hour. Also, following the loss of No. 2 SPT and the subsequent transfer of the No. 2B Vital Bus from the No. 22 SPT to the No. 21 SPT, a Containment Purge/Pressure Vacuum Relief {CP/P-VR) isolation signal from the 2R41C Radiation Monitoring System (RMS) {IL} Plant Vent noble gas monitor actuated. | |||
At the time of this event, the CP/P-VR valves were closed. The root cause of the CP/P-VRS actuation is attributed to equipment design. As indicated in prior LERs (e.g., 311/90-033-00), the Salem Unit 2 RMS Victoreen equipment is prone to failure on voltage transients. | |||
CP/P-VR isolation is an Engineered Safety Feature; therefore, the NRC was notified of this actuation at 2324 hours on June 16, 1991 in accordance with Code of Federal Regulations 10CFR 50. 72 (b} (2} (ii). Following the CP/P-VR isolation signal, the channel was reset and returned to service. At the time of the lightning strike, the lF Group Bus was supplying power to the Dimension Building Telephone House due to the normal UPS and generator being cleared and tagged in support of LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 ANALYSIS OF OCCURRENCE: (cont'd) | |||
LER NUMBER 91-024-00 PAGE 7 of 8 corrective maintenance. | |||
The building includes the power for transmission (i.e., microwave) for the Emergency Notification System (ENS) telephone With the loss of the Group Bus, the house power supply was lost. Subsequently, the ENS phone system was made inoperable. | |||
Emergency notifications, required by the Code of Federal Regulations lOCFR 50.72, were made over the PSE&G private CENTREX microwave system. Phone 'systems lost in addition to the ENS, due to the power loss to the Di!t)erisi:on Building Telephone House, included the "DID" system, the.Nuclear Emergency Telephone System {NETS) to all on-site Emergency Response Facilities, the NAWAS (Delaware Backup) system and the U.S. Coast Guard Repeater. | |||
As stated above, the ENS phone lines were disabled due to unavailability of the Dimension Building Telephone House power supply and the diesel generator. | |||
This supply had been cleared and tagged in support of corrective maintenance. | |||
In conclusion, the Salem Unit 1 reactor trip of June 16, 1991, caused by an act of nature, resulted in limited consequence. | |||
The health and safety of the public was not Once the event occurred the plant protective design features and operator performance were adequate. | |||
However, due to the actuation of the RPS and actuation of an ESF signal (CP/P-VR isolation}, this report has been prepared in accordance with Code of Federal Regulations lOCFR 50.73(a) (2) (iv) requirements. | |||
CORRECTIVE ACTION: The damage to the Phase B GSU transformer was repaired. | |||
Subsequently, on June 24, 1991, the Unit 1 was returned to service .. A review of the lightning protection features, in use at Salem Station, was conducted by Engineering | |||
& Plant Betterment. | |||
It was found that these features are appropriate for transformer protection. | |||
An Engineering review has been initiated to assess the prevention of flashover protection actuation for a fault between the 500 KV generator breakers and the main transformer when the fault current is supplied by the generator. | |||
Design changes will be implemented as appropriate. | |||
The Procedure Upgrade Project (PUP) effort will restructure the system operating procedures for the electrical system to provide necessary guidance for energizing dead busses including all necessary relays (with reset and prerequisite condition requirements). | |||
Investigation of the inadvertent llMSlO valve opening (fulJ.), when changing its setpoint, revealed that the ''manual/auto controller" had failed. It was subsequently replaced. | |||
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 91-02_4-90 8 of 8 ijJ EM NJ 1 l Z LH"S ATTACHMENT | |||
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Revision as of 09:20, 13 December 2018
ML18096A142 | |
Person / Time | |
---|---|
Site: | Salem ![]() |
Issue date: | 07/15/1991 |
From: | POLLACK M J, VONDRA C A Public Service Enterprise Group |
To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
References | |
LER-91-024, LER-91-24, NUDOCS 9107190202 | |
Download: ML18096A142 (9) | |
Text
- ' j_ .. 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 91-024-00 July 15, 1991 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulations lOCFR 50.73(a} (2) (iv) and 50.73(a) (2) (i) (B}. This report is required to be issued within thirty (30) days of event discovery.
MJP:pc Distribution . :: -: : c* *-' . Sincerely yours, C. A Vondra General Manager -Salem Operations r / / 95* 2189 I 1 OM I 12-ec NRC F.ORM 366 -U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO. 3150-0104 (6.ari EXPIRES: 4/30/92 ESTIMATED BURDEN PEA RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD 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 (1) I DOCKET NUMBER (2) I PAGE (31 Salem Generating Station -Unit 1 015101010121 71 2 1 OF 018 TITLE (41 Reactor Trip From 100% Power Due To Lightning Strike EVENT DATE 151 LER NUMBER 161 REPORT DATE (7) OTl;tER FACILITIES INVOLVED 18) MONTH DAY YEAR YEAR SEQUENTIAL
\\ REVISION MONTH DAY YEAR FAC1 LITY NAMES DOCKET NUMBERIS)
NUMBER NUMBER Salem Unit 2 o I 5 Io Io I o I 31l11 o I 6 ii 911 -oi 21 4 -olo ol 7 ii 911 0151010101 I I 6 9 1 5 OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE RloQUl_REMENTS OF 10 CFR §:(Chock one or more of th* following}
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- -::*:-SUPPLEMENTAL REPORT EXPECTED (14) MONTH DAY YEAR EXPECTED SUBMISSION
_ n YES (If yes, comp/ere EXPECTED SUBMISSION DATE! DATE 1151 I I I NO ABSTRACT (Limit ro 1400 spaces, i.e., soproximately fifreen single-space typewritten lines) 1161 On June 16, 1991, at 1940 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.3817e-4 months <br />, during normal full power operation, Salem Unit 1 experienced a Reactor Trip/Turbine Trip. The first out overhead annunciation was "4KV Group Bus Undervoltage".
At the time of the event a severe thunderstorm was in progress.
Investigation revealed that lightning had struck in the vicinity of the phase B Generator Step-Up (GSU) transformer
{EL}
- Evidence of the lightning strike included carbonization of the high voltage bushing, damage to the corona rings and lightning arrestor and eyewitness accounts.
The root cause of the reactor trip event is attributed to an act of nature; i
- e *I a lightning strike in the vicinity of the phase B GSU transformer, resulted in a 4KV Group Bus Undervoltage and subsequent reactor trip. Lightning protection was assessed by engineering and found to be appropriate.
The damage to the Phase B GSU transf orrner was repaired.
Subsequently, on June 24, 1991r the Unit 1 was returned to service. Also as a result of the lightning strike, 500 KV breaker flashover protection was initiated due to sufficient current through the transformer neutral. This resulted in the loss of the No. 2 Station Power Transformer and subsequent de-energization of the 1F and lG Group Busses. An engineering review has been initiated to prevent flashover protection actuation from a coasting generator.
Design changes will be implemented as appropriate.
NRC Form 366 (6.891
.. LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE
______________
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____ =2--'0.of 8 PLANT AND SYSTEM IDENTIFICATION:
Westinghouse
-Pressurized Water Reactor Energy Industry Identification System (EIIS) codes are identified in the text as {xxl IDENTIFICATION OF OCCURRENCE:
Reactor Trip from 100% power due to lightning strike Event Date: 6/16/91 Report Date: 7/15/91 This report was initiated by Incident Report Nos.91-441, 91-442,91-443, 91-444, and 91-479. CONDITIONS PRIOR TO OCCURRENCE:
Mode 1 Reactor Power 100% -Unit Load 1142 MWe DESCRIPTION OF OCCURRENCE:
**---
On June 16, 1991 at 1940 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.3817e-4 months <br />, during normal full power operation, Salem Unit 1 experienced a Reactor Trip/Turbine Trip. The first out overhead annunciation was "4KV G:roup Bus Undervoltage".
At the time of the event a severe thunderstorm was in progress.
Investigation revealed that lightning had struck in the vicinity of the phase B Generator Step-Up (GSU) transformer
{EL}. Evidence of the lightning strike included carbonization of the high voltage bushing, damage to the corona rings and lightning arrestor and eyewitness accounts.
The Nuclear Regulatory Commission (NRC) was notified of the actuation of the Reactor Protection System (RPS) {JC} at 2037 hours0.0236 days <br />0.566 hours <br />0.00337 weeks <br />7.750785e-4 months <br /> on June 16, 1991 in accordance with Code of Federal Regulations lOCFR 50. 72 (b) (2) (ii). APPARENT CAUSE OF OCCURRENCE:
The root cause of the Salem Unit 1 June 16, 1991 reactor trip event is attributed to an act of nature. At 1940 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.3817e-4 months <br />, a lightning strike in the vicinity of the phase B GSU transformer, resulted in a 4KV Group Bus Undervoltage and subsequent reactor trip. Lightning protection was assessed by engineering and was found to be appropriate.
Refer to the attached schematic, for additional details, when reviewing this section and the Analysis of Occurrence section.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 SEQUENCE OF EVENTS: (cont'd) Date/Time Event DOCKET NUMBER 5000272 LER NUMBER 91-024-00 PAGE 3 of 8 7-16/1940 Lightning strike in vicinity of Phase B of the Main Power Transformer (i.e., GST} Electrical fault on 500 KV Main Power Transformer Unit 1 Generator Differential Regular and Backup Trip Relays actuate 500 KV Breakers open (lOX and 12X); Generator Field Breaker opens and Turbine Trip signal initiated 4KV Group Busses transfer initiates; from the Auxiliary Power Transformer to the Nos. 11 and 12 Station Power Transformers Rx Trip Breakers open 4KV Group Bus transfer complete and Bus voltage returns to normal Flashover protection relays and alarms (Salem Units 1 and 2) actuate (to + 4 seconds) 12 and 22 Station Power Transformers trip 18 Vital Bus Transfers.to 11 SPT 2B Vital Bus Transfers to 21 SPT lF and lG Group Busses deenergize and alarm in Control Room ANALYSIS OF OCCURRENCE:
Following the GSU transformer lightning strike, the resultant phase to ground fault operated the generator differential regular and backup instantaneous trip relays on Phases B and C GSU transformers opening the lOX and 12X 500 KV breakers, opening the generator field breaker and causing a Unit 1 turbine trip (Unit Isolation Trip). The Unit Isolation Trip subsequently initiated a Group Bus transfer (i.e., fast transfer scheme) from the Auxiliary Power Transformer to the Nos. 11 and 12 Station Power Transformers, respectively.
It is not uncommon, when you have single phase to ground faults, for only two (2) of the three (3) phases to pick-up the instantaneous relays initiating the Unit Isolation Trip (i.e., Phase A instantaneous relays did not pick-up) . At the time of the Phase B phase to ground fault, voltages on the LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 ANALYSIS OF OCCURRENCE:
DOCKET NUMBER 5000272 (cont'd) LER NUMBER 91-024-00 PAGE 4 of 8 electric distribution system for the four (4) 4KV Group Busses and the three (3) 4KV Vital Busses decayed. All 4KV Vital Bus voltages recovered within 4 cycles while the Group Bus voltages recovered after completion of the fast transfer (in approximately 12 cycles). This degraded Group Bus voltage (below 70% rated voltage) lasted sufficiently long to initiate a Reactor Trip signal via the Group Bus undervoltage relays. Also as a result of the lightning strike, 500 KV breaker (lOX and 12X) flashover protection initiated due to sufficient current through the transformer neu"tral.
The flashover protection occurred four (4) seconds following the fault, on the phase B GSU transformer, causing: 1) all adjacent 500 KV breakers to open; 2) loss of half of the 13 KV ring bus (13 KV 4-5 and 3-4 breakers opened); 3) lockout of the Unit 3 (Gas Turbine) 13 KV breaker; 4) the New Freedom Line was remote tripped to the New Freedom Substation; and 5) of the Salem New Freedom Line from Section 2 (of the 500 KV Switchyard) . Flashover protection actuation should have occurred approximately 13 cycles after fault occurrence.
It could not be determined why flashover protection was delayed; however, the delay did not have an impact on this event. Testing was performed but the circuits timed correctly and the event could not be duplicated.
The loss of 500 KV power to Section 1' (of the 500 KV Switchyard) resulted in the loss of the No. 2 Station Power Transformer
{SPT). With the loss of the No. 2 SPT, 13 KV power to the Nos. 12 and 22 SPTs was lost. After the loss of the No: 12 SPT, the lF and lG Group Busses de-energized (i.e., the Auxiliary Power Transformer was already de-energized due to the Unit Isolation signal) and the lB Vital Bus transferred from the No. 12 SPT to the No. 11 SPT. Due to the loss of the No. 22 SPT, the 2B Vital Bus successfully transferred from No. 22 SPT to the No. 21 SPT. An extensive analysis provided by oscillograph, digital fault recordeJ*
and sequence of events recorder records indicated that the relay operations were correct for the conditions.
Although the breaker flashover scheme is designed to protect against the flashover of either 500 KV generator breaker, it also operates for a fault between the 500 KV generator breakers and the main transformer when the fault current is supplied by the generator.
There was no evidence, either oscillographic or physical, of the flashover of either 500 KV generator breaker. Therefore it is concluded that the flashover relay scheme was operated by the current contributed by the coasting generator.
An Engineering review, along with appropriate modifications, has been initiated.
After the loss of the "lF" and "lG" Group Busses, the following
--LICENSEE EVENT REPORT {LER) TEXT CONTINUATION Salem Generating Station Unit 1 ANALYSIS OF OCCURRENCE:
DOCKET NUMBER 5000272 (cont'd) significant equipment was LER NUMBER 91-024-00 PAGE 5 of 8 1. Nos. 13 and 14 Reactor Coolant Pumps {RCPs); The loss of No. 13 RCP resulted in limited pressurizer spray capability; however, the No. 11 RCP was available for pressurizer spray and was successfully used. 2. Control Pressurizer Heaters and pne set of Backup Pressurizer Heaters 3. Plant Vent composite sample pump; this pump is required to remain operable as per Technical Specification 3.3.3.9 Table 3.3-13. Chemistry was notified and alternate sampling was initiated.
The pump was returned to service when lF Group Bus was restored {at 0041 hours4.74537e-4 days <br />0.0114 hours <br />6.779101e-5 weeks <br />1.56005e-5 months <br /> on June 17, 1991) An excessive cooldown occurred following the reactor trip. This was due to Auxiliary Feedwater making up for Steam Generator shrink from the trip and loss of Nos. 13 and 14 Reactor Coolant Pumps. In accordance with the guidance provided by the EOPs, closure of the main steam isolation valves was successfully performed.
Excessive cooldown is a concern identified from prior plant trips. Engineering has assessed this phenomenon and concluded that it does not pose a safety concern; however, corrective actions are being pursued (reference LER 311/91-029-00).
The 11MS10 atmospheric relief valve (SB} changed operational modes from automatic to manual and then went full open while reducing its setpoint (to 1005 psig) to control Stearn Generator pressure.
A work order was initiated to investigate and correct this concern. Operator actions following the automatic actuation of the reactor trip began with the NCO initiating a manual trip. Procedure EOP-TRIP-1 was then entered followed by entry into EOP-TRIP-2.
Actions required by these procedures were complied with including closure of the main steam isolation valves due to Tavg excessive cooldown.
Operators compensated for the inadvertent full opening of the 11MS10 valve (following its setpoint adjustment}, and subsequent lower level in No. 11 Steam Generator, by adjusting the Auxiliary Feedwater flow to the No. 11 Steam Generator.
With the loss of the 1F and 1G Group Busses, the Control Pressurizer Heaters and one set of Backup Pressurizer Heaters were unavailable.
Also, as stated above, the No. 13 RCP became unavailable.
Using the available Backup Pressurizer Heaters and the No. 11 RCP Pressurizer spray capability Operators were abJ.e to to maintain RCS pressure control. After completing the actions required by EOP-TRIP-1 and EOP-TRIP-2, IOP-8 was entered. Using this procedure, the plant was stabilized (in Mode 3) with the twc (2) operating Reactor Coolant Pumps (i.e., Nos. 13 and 14 RCPs were not operating due to the loss of the 1F and 1G Group Busses). After stabilization of the plant, Technical Specifications were reviewed and required actions performed due to the loss of an off-site power source (Technical Specification 3.8.1.1 Action "a").
- LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 ANALYSIS OF OCCURRENCE:
DOCKET NUMBER 5000272 (cont'd) LER NUMBER 91-024-00 Technical 3.8.1.1 Action "a" states: PAGE 6 of 8 "With either an offsite circuit or diesel generator of the above required A.C. electrical power sources inoperable, demonstrate the OPERABILITY of the remaining A.C. sources by performing Surveillance Requirements 4.8.1.1.1.a and 4.8.1.1.2.a2 within one hour and at least once per 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> thereafter; restore at least two offsite circuits and three diesel generators to OPERABLE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />." Due to plant conditions, the Unit 1 Diesel Generators were successfully tested within one hour of Unit stabilization following the loss of the No. 2 Station Power Transformer
{i.e., one of the two sources of offsite power) as per the Action Statement (on June 16, 1991 at 2154, 2155, and 2156 hours0.025 days <br />0.599 hours <br />0.00356 weeks <br />8.20358e-4 months <br /> respectively).
Preparations for testing the Diesel Generators was initiated approximately one hour and twenty minutes after the loss of the No. 2 Station Power Transformer.
The delay in the testing of the Unit 1 diesel generators was therefore due to the time required to stabilize the Unit. However, it does constitute a noncompliance which is reportable to the Nuclear Regulatory Commission in accordance with Code of Federal Regulations lOCFR 50.73(a) (2) (i) (B). Early in the Unit 1 event, the SNSS did initiate actions to perform an operability check of the Salem Unit 2 diesel generators.
This was required, per Technical Specifications (identical to the Unit 1 Action requirements), due to the loss of the offsite power source (i.e., No. 2 Station Power Transformer).
The Unit 2 Diesel Generators were successfully tested within one hour. Also, following the loss of No. 2 SPT and the subsequent transfer of the No. 2B Vital Bus from the No. 22 SPT to the No. 21 SPT, a Containment Purge/Pressure Vacuum Relief {CP/P-VR) isolation signal from the 2R41C Radiation Monitoring System (RMS) {IL} Plant Vent noble gas monitor actuated.
At the time of this event, the CP/P-VR valves were closed. The root cause of the CP/P-VRS actuation is attributed to equipment design. As indicated in prior LERs (e.g., 311/90-033-00), the Salem Unit 2 RMS Victoreen equipment is prone to failure on voltage transients.
CP/P-VR isolation is an Engineered Safety Feature; therefore, the NRC was notified of this actuation at 2324 hours0.0269 days <br />0.646 hours <br />0.00384 weeks <br />8.84282e-4 months <br /> on June 16, 1991 in accordance with Code of Federal Regulations 10CFR 50. 72 (b} (2} (ii). Following the CP/P-VR isolation signal, the channel was reset and returned to service. At the time of the lightning strike, the lF Group Bus was supplying power to the Dimension Building Telephone House due to the normal UPS and generator being cleared and tagged in support of LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 1 DOCKET NUMBER 5000272 ANALYSIS OF OCCURRENCE: (cont'd)
LER NUMBER 91-024-00 PAGE 7 of 8 corrective maintenance.
The building includes the power for transmission (i.e., microwave) for the Emergency Notification System (ENS) telephone With the loss of the Group Bus, the house power supply was lost. Subsequently, the ENS phone system was made inoperable.
Emergency notifications, required by the Code of Federal Regulations lOCFR 50.72, were made over the PSE&G private CENTREX microwave system. Phone 'systems lost in addition to the ENS, due to the power loss to the Di!t)erisi:on Building Telephone House, included the "DID" system, the.Nuclear Emergency Telephone System {NETS) to all on-site Emergency Response Facilities, the NAWAS (Delaware Backup) system and the U.S. Coast Guard Repeater.
As stated above, the ENS phone lines were disabled due to unavailability of the Dimension Building Telephone House power supply and the diesel generator.
This supply had been cleared and tagged in support of corrective maintenance.
In conclusion, the Salem Unit 1 reactor trip of June 16, 1991, caused by an act of nature, resulted in limited consequence.
The health and safety of the public was not Once the event occurred the plant protective design features and operator performance were adequate.
However, due to the actuation of the RPS and actuation of an ESF signal (CP/P-VR isolation}, this report has been prepared in accordance with Code of Federal Regulations lOCFR 50.73(a) (2) (iv) requirements.
CORRECTIVE ACTION: The damage to the Phase B GSU transformer was repaired.
Subsequently, on June 24, 1991, the Unit 1 was returned to service .. A review of the lightning protection features, in use at Salem Station, was conducted by Engineering
& Plant Betterment.
It was found that these features are appropriate for transformer protection.
An Engineering review has been initiated to assess the prevention of flashover protection actuation for a fault between the 500 KV generator breakers and the main transformer when the fault current is supplied by the generator.
Design changes will be implemented as appropriate.
The Procedure Upgrade Project (PUP) effort will restructure the system operating procedures for the electrical system to provide necessary guidance for energizing dead busses including all necessary relays (with reset and prerequisite condition requirements).
Investigation of the inadvertent llMSlO valve opening (fulJ.), when changing its setpoint, revealed that the manual/auto controller" had failed. It was subsequently replaced.
LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 91-02_4-90 8 of 8 ijJ EM NJ 1 l Z LH"S ATTACHMENT
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