ML18095A477

LER 90-029-00:on 900817,reactor Trip from 25% Power Occurred Due to Steam Generator lo-lo Level.Caused by Equipment Failure.Circuit Breaker Encl Positive Interlock Assembly Deficiencies corrected.W/900912 Ltr

ML18095A477
Person / Time
Site:	Salem
Issue date:	09/12/1990
From:	Miller L, Pollack M Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-029-01, LER-90-29-1, NUDOCS 9009200129
Download: ML18095A477 (6)

Text

OPS~G*

Public Service Electric and Gas Company P.Q. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station September 12 *. 1990

• 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 90-029-00 This Licensee Event Report is being_submitted pursuant to the requirements of the Code of Feder~l Regulations 10CFR 50.73(a) (2) (iv). This report is required within thirty (30) days of discovery.*

Sincerely yours, L. K. Miller General Manager -

Salem Operations MJP:pc Distribution 9009200129 900912

~DR ADock 05000272 v PDC The Energy People .:r£~~

'/195-2189 (10M) 12-89

. ~* *u.a. NUCLEA"*"EGULATO"Y COMl*IOel Arl'ltOVEO OMI NO. )1I0-010i EXPl"EI: 1/31 . .

LICENSEE EVENT REPORT (LER)

DOCKIT NU119l" 121 I ca I

fACILITY NANI 111 P'AU&

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LICENSEE CONTACT FOR THll LER 1121 ll0.7S(lill211wlillll eo;1:11atl2ll*l NAME TELEPHONE NUMBER AREA CODE M. J. Pollack - LER Coordinator 61019 313 I 91-12 kl 1212 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE OEICRllED IN THll llEPORT 1111 MANUFAC. MANUFAC.

CAUSE SYSTEM COMPONENT TUR ER TURER .

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• NO I I I .

On 8/17/90, duririg power' ascension, the reactor tripped due to No. 14 Steam Generator (S/G) Lo~-Low Level. The trip occurred during*the transfer of the four Group Busses from the Station Power Transformer (SPT) to the Auxiliary Power Transformer (APT). After successfuliy transferring the lH and lE Group Busses, lG Group Bus was being transferred. The operator initiated closure of the lBGGD circuit breaker (APT side). The 12GSD breaker opened; however; the lBGGD breaker failed to close resulting in deenergization of the lG Group Bus. Consequently the No. 14 Reactor Coolant Pump (RCP) circuit breaker opened on undervoltage. The reactor subsequently tripped on No. 14 S/G Low-Low S/G Level. The root cause of this event is attributed to equipment failure. The lBGGD circuit breaker failed to 6lose during transfer due ~o its positive interlock switch not closing thereby preventing energization of the breaker close coil. The positive interlock assembly was found to be out of adjustment/worn preventing the required closing of the breaker's positive interlock switch after the .breaker was racked into its normal operating

• position. The lBGGD circuit breaker enclosure positive ~nterlock assembly deficiencies were corrected. Subsequently, the lBGGD breaker was successfully functionally checked. All 4KV and 13KV circuit

• breakers and enclosures were inspected on both Unit 1 and Unit 2. A review assessing the feasibility of adding supervisory relays across the closing contacts of critical circuit breakers will be conducted.

NRC FotRI . .19-831

/

Salem Generating Station . DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 90-029-00 2 of 5 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*2S% power, during power. ascension, due to e9uipment failure

.Ev~nt Date: 8/17/90 Report Date: 9/11/90 This report was initiated by'Incident Report No.90-595.

CONDITIONS PRIOR TO OCCURRENCE:

Mode 1 Reactor Power. 25% - Unit Load 190 MWe Power ascension in progress; Procedure IOP-3~ "Hot Standby to Minimum Load" was being used DESCRIPTION OF OCCURRENCE: I On August 17 , .. 1990 at 0612 hours0.00708 days <br />0.17 hours <br />0.00101 weeks <br />2.32866e-4 months <br />, during power ascension, the reactor tripped due to No. 14 Steam Generator (S/G) Low-Low Level.* The trip occurred during the transfer of the four G~oup Busses fro~ the Station Power Transformer (SPT) (EAi to the Auxiliary Power Transformer (APT)

{EAi. This transfer is required by Procedure IOP-3 Step 5.57. After successftilly transferring the lH and lE Group Busses, lG Group Bus was being transferred. The operator initiated closure of the lBGGD circuit breaker (APT side). The 12GSD breaker opened; *however, the lBGGD breaker failed to close resulting in deenergization of the 1G Group Bus.

The No. 14 Reactor Coolant Pump (RCP) power is supplied by the 1G Group Bus. Consequently when the Bus deenergized, the pump circuit breaker opened on undervoltage. Losing an RCP in a loop with an operating S/G results in a plant transient of rapidly decreasing S/G level in that S/G. Operators attempted to gain control of the 14 S/G level decrease by placing the feedwater control valve (14BF19) in manual; however, the reactor tripped on No. 14 S/G Low-Low S/G Level.

After the trip, the Unit was stabilized in Mo.de 3 (Hot Standby). The Nuclear Regulatory Commission was notified of the actuation of the Reactor Protection System {JCI at 0755 hours0.00874 days <br />0.21 hours <br />0.00125 weeks <br />2.872775e-4 months <br /> on August 17, 1990 in accordance with Code of Federal Regrilations 10CFR 50.72(b) (2) (ii).

APPARENT CAUSE OF OCCURRENCE:

The root cause of this event is attributed to equipment failure. The

• 'it I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit.1 5000272. 90-029-00 3 of 5 lBGGD circuit breaker failed to close during the transfer from the* SPT to_ the APT because its positive interlock switch, which is in the breaker close circuit, was not closed thereby preventing energization of the breaker close coil. The positive interlock assembly, located in the b+eaker cubicle, was found to be out of adjustment/worn preventing the required closing of the breaker's.positive interloc~

switch after the breaker was racked into its normai operating position.

The positive interlock assembly prevents the circuit breaker from.

closing if the breaker is not fully racked into its operational position. -This is accomplished by an electrical contact closure in serie.s with the circuit breaker closing coil when the circuit breaker is fully racked into position. Excessive play in the mechanical -

portion of the interlock assembly allowed the electrical interlock switch to change position.

As stat_ed above, the breaker cubicle positive interlock assembly was found to be out of adjustment (i.e., worn). This allowed the breaker's positive interlock rolfer to be moved causing the opening of-the positive interlock switch. The roller could be moved by closing the enclosure door, by tapping on the. enclosure, and by moving the assembly handle. *The three (3) other.APT infeed breaker.enclosure assemblies were checked and found to operate correctly with no movement of the interlock. switch.

The closing circuit was verified to be ready for closure prior to the event; however, an electrical check following the event indicated that the interlock switch opened after th~ initial-check as *tated above.

It was also noted that a relay installed on the lBGGD enclosure door impacteQ. the racking motor when closing the door. Interference -

between the relay and the racking motor may have* contributed to the.

failure by causing additional* jarring of the breaker cubicle* .positive interlock assembly during door closure.

ANALYSIS OF OCCURRENCE:

Loss of an RCP will result in significant shrink phenomenon in the associated S/G, as occurred in this event. This shrink is sufficient to drive S/G level to the Low-Low S/G Level trip setpoint. The Low-Low S/G Level reactor trip prevents operation with the steam generator water level below the minimum volume required for adequate heat removal*.. The trip is actuated on two out of three low-low level signals in any S/G. The setpoint ensures adequate S/G inventory, at the time of a reactor trip, to allow for possible starting delays of the Auxiliary Feedwater Pumps {BAI; thus preventing S/G dryout and Reactor Coolant System f ABJ thermal and hydraulic transients associated with a loss of the heat sink.

The RPS functioned as designed and the heat sink was maintained during this event. Since the RPS is designed to withstand.the thermal and hydraulic effects of four-hundred (400) reactor trips from full power and this was the 167th trip, this event involved no undue risk to the health or safety of the public. However, ~ue to the actuation of

. , I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE unit 1 5000272 90-029-00 4 of 5 ANALYSIS OF OCCURRENCE: (cont'd) the RPS, this event is reportable in accordance with *code of Federal Regulations 10CFR 50.73(a} (2) (iv)~.

CORRECTIVE ACTION:

The. identified lBGGD circuit breaker enclosure positive interlock.

assembly deficiencies have been corrected. Also, verification of the gap settings of the interlock switch, removal and relocation of the racking motor, and testing of the breaker to verify correct operation was completed.

• The lBGGD breaker was successfully functionally checked in the test position to demonstrate proper control circuit and breaker operation.

All switch contacts on the lBGGD circuit breaker were checked and found to be satisfactory.

All 4KV and 13KV circuit breakers and enclosures were inspected on both Unit 1 and Unit 2 for similar positive interlock concerns as exhibited by the lBGGD circuit breaker . . All were found to be satisfactory except:

1. 1H3D - Unit 1 Lighting Transformer (non-vital); The positive interlock assembly requires adjustment. *A work order has been initiated to cor~ect this concern~

2. 22BSD - Unit 2 No. 22 SPT B Bus In-Feed (vital); The positive interlock assembly required adjustment (work completed)*~

3. 2G2D - Unit 2 No. 23 Heater Drain Pump (non-vital); The racking mechanism handle was found bent and was**

subsequently straightened.

3. 2H3D - Unit 2 Lighting Transformer (non-vital); The positive interlock assembly requires adjustment. A work order has been initiated to correct this concern.

4. 2E4D - Unit 2 No. 22 RCP motor (non-vital); A defective interlock switch was repaired.

An operating experience search was conducted. *salem and industry (i.e., NPRDS) identified several failures associated with breakers and breaker enclosures. However, the failures appear to be random as was the failure which caused this event.

A review assessing the feasibility of adding supervisory relays across the closing contacts of critical circuit breakers, to ensure closing circuit continuity, will be conducted.

A review of this event did identify that a "Recurring Task" (RT) for preventive maintenance of Magne-Blast circuit breaker switchgear

. .,_ .* I '

LICENSEE> EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station DOCKET NUMBER LER NUMBER PAGE Unit 1 5000272 90-029-00 5 of 5 CORRECTIVE ACTION: (cont'd) enclosures exists. This maintenance is performed to procedure M3H, "ACB Enclosure Test". The RT was created circa 1988/89. The first Unit. 1 performance of tne RT is scheduled for.the upcoming refueling outage~

FAILURE DATA:

lBGGD Circuit Breaker Manufacturer: General Electric Model: Magne~Blast Type: AM-4.16-350-2H General Manager -

Salem Operations MJP:pc SORC Mtg.90-128