ML18101A182

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LER 94-011-00:on 940714,manual Reactor Trip Initiated Due to Loss of All Cw Pumps.Caused by Undervoltage Tripping of Cw Sys 4 Kv Switchgear Bus Infeed/Load Breakers.Time Delay Relays w/700 Millisecond installed.W/940811 Ltr
ML18101A182
Person / Time
Site: Salem PSEG icon.png
Issue date: 08/11/1994
From: Hagan J, Wiltsee F
Public Service Enterprise Group
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-94-011, LER-94-11, NUDOCS 9408180036
Download: ML18101A182 (5)
v • d • e


Text

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.. Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge,. New Jersey 08038 Salem Generating Station August 11, 1994 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 94-011-00 This Licensee Event Report is being submitted pursuant to the requirements of Code of Federal .Regulation 10CFR50.73(a) (2) (iv).

Issuance of this report is required within thirty (30) days of event discovery.

Sincerely yours, MJPJ:pc Distribution 9408180036 940811 PDR ADOCK 05000272 S PDR Ii . . l  ;

1 n_,_: po-.i,*.:r is 1n your nan.h.

95*2189 REV 7-92

NRC' FORM 366

  • NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150-0104

/5-92)- EXPIRES 5/31/95 ESTIMATED BURDEN PER RESPONSE TO COMPLY WITH THIS INFORMATION COLLECTION REQUEST: 50.0 HRS. FORWARD*

LICENSEE EVENT REPORT (LER) COMMENTS REGARDING BURDEN ESTIMATE TO THE INFORMATION AND RECORDS MANAGEMENT BRANCH (MNBB 7714), U.S. NUCLEAR REGULATO.RY .Cm-1MISSION, ,WASHINGTON, DC 20555-0001, AND TO THE PAPERWORK REDUCTION PROJECT {3150-0104), OFFICE OF (See reverse for required number of digits/characters for each block) MANAGEMENT AND,~UDGET, WASHINGTQN, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) PAGE (3)

Salem Generating Station - Unit 1 05000 272 1 OF 04 TITLE (4) Manual Reactor Trip From 100% Power Following Automatic Tripping Of All Circulating Water Pumps Due To Lightning Strike. ." ...

EVENT DATE (5) LER NUMBER (6 REPORT NUMBER (7) OTHER FACILITIES INVOLVED (8)

FACILITY NAME DOCKET NUMBER SEQUENTIAL REVISION MONTH DAY VEAR YEAR MONTH DAY. YEAR NUMBER NUMBER 05000 FACILITY NAME DOCKET NUMBER 07 14 94 94

-- Oll 00 08 ll 94 05000

'OPERATING THIS REPORT IS SUBMITIED PURSUANT TO THE REQUIREMENTS OF 10 CFR i: (Check one or more (11 MODE (9) 1 20.402(b) 20.405(c) x 50. 73{a)(2)(iv) 73.71(b)

. POWER 20.405 (a){1 )(i) 50.36(c)(1) . 50.73{a)(2)(v) 73.71(c)

LEVEL {10) 100 20.405(a){1)(ii) . 50.36(c){2) ' 50.73(a)(2)(vii) OTHER 20.405(a) (1) (iii) 50.73(a){2)(i) 50:73(a) (2) (viii)"(A) (Specify in Abstract below and in Tex!, NRC 20.405(a)(1)(iv) 50.73(a){2)(ii) *50.73(a)(2)(viii)(B) Form 366A) 20.405(a)(1)(v) 50.73(a) (2) (iii) 50. 73 (a}(2)(x)

LICENSEE CONTACT FOR THIS LEA (12)

NAME . TELEPH?NE NU!-1BER (Include Area Code)

"'.F. H. Wiltsee - LER Coordinator (609} 339-5163 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

REPORTABLE REPORTABLE CAUSE. SYSTEM COMPONENT MANUFACTURER CAUSE SYSTEM COMPONENT MANUFACTURER TO NPRDS TO NPRDS SUPPLEMENTAL REPORT EXPECTED (14)_ EXPECTED MONTH DAY YEAR I YES .

(If yes, complete. EXPECTED SUBMISSION DATE) x

  • *NO SUBMISSION DATE (15)

ABSTRACT (Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)

On July 14, 1994, at 2132 hours0.0247 days <br />0.592 hours <br />0.00353 weeks <br />8.11226e-4 months <br />, during full power operation, a Unit 1 manual reactor trip was initiated due to loss of all cw pumps caused by the undervoltage (UV) tripping of the Circulating Water (CW) System 4KV bus infeed/load breakers. The UV condition resulted from a lightning-induced voltage drop of the 500KV Hope Creek - New Freedom line that transferred to Salem's switchyard via the Salem - Hope Creek tie line.

Emergency Operating Procedures were entered and at 2139 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.138895e-4 months <br /> Main steam was isolated to limit cool down of the Reactor Coolant System. The root cause of tne event is attributed to Design, Manufacturing, Con~truction/

Installation. The Unit 1 circulating water bus UV protection, installed as part of a switchyard upgrade design change in 1993, included new switchgear containing instantaneous relays. A time delay, which would have pr'ecluded UV relay actuation, was not used. Time delay relays with*

a 700 millisecond setting have now been installed. The protective relaying technical standard will be revised to provide overall guidance on the selection of UV protective relaying schemes. In addition, specific reference to the cw 4KV bus system will be provided. The*unit 2 switchyard upgrade DCP (which includes** CW bus UV protection) will be reviewed and a suitable UV time delay scheme will be incorporated.

NRC FORM 366 (5-92)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 94-011-00 2 of 4 PLANT AND SYSTEM IDENTIFICATION:

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

IDENTIFICATION OF OCCURRENCE:

Manual Reactor Trip From 100% Power Following Automatic Tripping Of All circulating Water Pumps Due To Lightning Strike Event Date: 7/14/94 Report Date: 8/11/94 This report was initiated by Incident Report No.94-195.

CONDITIONS PRIOR TO OCCURRENCE:

Mode 1 Reactor Power 100% Unit Load 1100 MWe A severe thunderstorm was in progress with frequent lightning strikes in the vicinity of Artificial Island. Due to the storm, numerous Control Room alarms on both Units were occurring and clearing shortly thereafter, including main generator voltage regulator alarms as well as carrier trouble alarms on the 500 kilovolt (KV) transmission lines.

DESCRIPTION OF OCCURRENCE:

At 2132 hours0.0247 days <br />0.592 hours <br />0.00353 weeks <br />8.11226e-4 months <br /> on July 14, 1994, a Unit 1 manual reactor trip was initiated in response to loss of all CW pumps resulting from undervoltage (UV) tripping of the Unit Circulating Water (CW) System 4KV switchgear bus infeed/load*breakers. Automatic starting of 11, 12, and 13 Auxiliary Feedwater pumps occurred due to resultant lo-lo Steam Generator (SG) levels. Emergency Operating Procedures, EOP-TRIP-1, "Reactor Trip Or Safety Injection" and EOP-TRIP-2, "Reactor Trip Response" were entered and at 2139 hours0.0248 days <br />0.594 hours <br />0.00354 weeks <br />8.138895e-4 months <br /> (same day)

Main Steam was isolated to limit cooldown of the Reactor Coolant System (RCS). The Unit was stabilized in Mode 3 and Integrated Operating Procedure IOP-8, "Maintaining Hot Standby", was entered.

At 2250 hours0.026 days <br />0.625 hours <br />0.00372 weeks <br />8.56125e-4 months <br /> (same day) the Nuclear Regulatory Commission (NRC) was notified of this event, in accordance with 10CFR50.72(b) (2) (ii).-

ANALYSIS OF OCCURRENCE:

The electrical bus powering the Units' six CW pumps consists of two bus sections (13 and 14) with three pumps per section. Each section

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 94-011-00 3 of 4 ANALYSIS OF OCCURRENCE: (cont'd) is fed by a separate string of transformers: 500/13KV and 13/4KV and is separated from the other section by a normally open tie breaker.

System design provides for automatic opening of the feeder breaker to a bus section and automatic closure of the tie breaker upon receipt of any of a number of actuation signals, signifying a faulted condition of the respective infeed. The Unit 1 cw bus UV protection, installed as part of a Unit 1 switchyard upgrade (design change) in 1993, included new switchgear containJng new instantaneous relays, General Electric (GE) type NGV.

A manual reactor trip was initiated in response to simultaneous loss (tripping) of all CW pumps due to UV on both cw 4KV buses and line sections (13 and 14). The UV condition existed for approximately 42 milliseconds and resulted from a lightning-induced voltage drop of the 500KV Hope Creek - New Freedom line that transferred to Salem's switchyard via the Salem - Hope Creek tie line. The 500KV grid voltage decreased to 379KV and the CW system 4KV bus voltage decreased to 2.9KV, 69% of bus voltage. No other undervoltage actuations occurred on the other 4KV buses, 4KV vitals use GE type IAV time delay style UV relays which have an inherent time delay built in. The Unit 2 group buses that feed CW did not trip because they use GE type IAV time delay style UV relays. In addition, the group buses are powered from the Auxiliary Power Transformer the output of which remained stable by the on line Main Generator.

The plant response to cooldown was improved over that of prior events; however, closure of the MS167s (Main Steam Isolation Valves) was required to limit cooldown.

APPARENT CAUSE OF OCCURRENCE:

This event is attributed to "Design, Manufacturing, construction/

Installation" as classified in Appendix B of NUREG-1022.

The switchyard upgrade design specification did not adequately address the importance of power systems UV protective relaying requirements for individual subparts of the overall design. During development of the switchyard upgrade design change package (DCP),

emphasis was focused on providing the ability of the electrical buses to successfully transfer motor loads without immediate or long-term degradation. Consequently, a time delay which would have precluded UV relay actuation was not used.

PREVIOUS OCCURRENCES:

A similar event involving a lightning strike and resultant reactor trip was reported in LER 272/91-024-00 due to a strike in the

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 94-011-00 4 of 4 PREVIOUS OCCURRENCES: (cont'd) vicinity of the Phase B Generator Step-up Transformer. Lightni~g protection was assessed by Engineering and found to be appro~riate.

SAFETY SIGNIFICANCE:

This event is reportable pursuant to the requirements of 10CFR50.73(a) (2).(iv) and did not affect the :health and safety of the public. The Reactor Protection System (RPS) {JC} functioned as designed and.the heat sink was maintained. The event, i.e. the manual reactor trip, was an anticipatory action to a low vacuum condition resulting from the loss of CW pumps.

CORRECTIVE ACTION:

Time delay relays with a 700 millisecond setting have been installed in.the Unit 1 CW btis UV protection scheme to provide the capability of the infeed breaker UV trip logic to withstand short duration

Engin-eering will revise the protective relaying technical standard to provide overall guidance on the selection of undervoltage protective relaying schemes. In addition, specific reference to. the CW 4KV bus system will be provided.

Engineering will review the Unit 2 switchyard upgrade DCP (which includes CW bus UV protection) and incorporate a suitable UV time delay scheme prior to implementation.

Design changes have been implemented to minimize post-trip RCS excessive cooldowns and EOP-TRIP-1 has been revised to provide direction on throttling auxiliary f eedwater flow to minimize cooldowns resulting from excessive feedwater flow. Engineering is continuing to assess additional corrective actions to minimize cooldowns following reactor trips.

MJPJ:pc SORC Mtg.94-063

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