ML18039A810

LER 99-004-00:on 990530,safety Features Sys Actuations Occurred Due to RPS Trip.Caused by Failure of MG Set AC Drive Motor Starter Contractor Coil.Licensee Placed 2B RPS Bus on Alternate Feed & Half Scram Was Reset

ML18039A810
Person / Time
Site:	Browns Ferry
Issue date:	06/28/1999
From:	Austin S TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18039A809	List: ML18039A808 ML18039A810
References
LER-99-004-01, LER-99-4-1, NUDOCS 9907070275
Download: ML18039A810 (10)

Text

NRC FORM 366 U.s. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB No. 3150-0104 EKPIREsoeisonoot (6-1996) Estimated burden'per response to comply wnh this msndatoty tnfonnetion collection request; 50 hrs. Reported lessons learned are incorporated irno the LICENSEE EVENT REPORT (LER) bcensing process end fed beck to indusuy. Fotwenf comments regarding burden esumate to the Records Management Branch IT 6 F331, u.s. Nuclear Regulatory Comnission. Washington. DC 20555 0001, end to the (See reverse for required number of Paperwork Reduction Protect (3150.0104). Offe:e of Management and Budget, Wastsngton. DC 20503. If an infonnatton cogectton does not digits/characters for each block) display a cterentty valsf OMB control number, the NRC may not conduct or sponsor, and a person is not requred to respond to. the >nfolmattcn coltectmn FACIUTY NAME (ll DOCKET NUMBER lgl PAOE ls)

Browns Ferry Nuclear Plant Unit 2 05000260 1 OF 5 TITLE l41 Reactor Protection System Trip Resulting In Safety Feature System Actuations EVENT DATE (5) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED I B)

MONTH DAY YEAR ,

YEAR SEOUENTI AL REVISION MONTH, DAY YEAR FACIUTY NAME DOCKET NVMBER NUMBER NUMBER NA 05000 FACIUTY NAME DOCKET NVMBER 05 30 99 99 004 00 06 28 99 NA 05000 OPERATING THIS REPORT IS SUBMITTED PURSUA NT TO THE REQUIREMENTS OF 10 CFR E: (Check one or more) (11)

MODE (9) 20.2201(b) 20. 2203(a) (2) (v) 50 73(a)(2)b) 50 73(a)(2)(viii)

POWER 20.2203(a)(l ) 20.2203 (a) (3) (i) 50.73(a)(2) (ii) 50.73(a) (2) (x)

LEVEL (10) 100 20. 2203(a) (2) (i) 20.2203(a)(3)(ii) 50.73(a)(2)(iii) 73.71 20.2203(a)(2)(ii) 20.2203(a)(4) 50.73(a) (2) (iv) QTHER 20.2203(a)(2)(iii) .

50.36(c)(l) 50.73(a)(2)(v) Specify in Abstract below

20. 2203(a) l2) (iv) 50.36(c)(2) 50.73(a) (2)(vii) or in NRC Form 366A LICENSEE CONTACT FOR THIS LER (12)

TELEPHONE NUMBER (Include Area Code)

Steven W Austin Site Licensing Engineer (205) 729-2070 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANVFACTURER REPORTABLE TO CAUSE SYSTEM COMPONENT MANVFACTUAEA REPOATABLE NPRDS TO NPADS JC CL GOSO SUPPLEMENTAL'EPORT EXPECTED (14) EXPECTED MONTH OAY YEAR YEs SUBMISSION (If yes, complete EXPECTED SUBMISSION DATE). DATE (15)

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

On May 22, 1999, at 0522 central daylight time CDT, Unit 2 received an unexpected channel 28 reactor protection system (RPS) actuation when power was lost to the 28 RPS.bus. The RPS actuation resulted

'in. the automatic actuation or isolation of primary containment isolation system (PCIS) groups 2, 3, 6, and 8. The loss of power also resulted in the initiation of stand by gas treatment (SGT), and control room ventilation (CREV)'. At approximately 0527 hours0.0061 days <br />0.146 hours <br />8.713624e-4 weeks <br />2.005235e-4 months <br /> CDT the 28 RPS was placed on the alternate feed and the half scram was reset and the affected PCIS groups were returned to their pre-event configuration. The SGT and CREV systems were also returned to.pre-event configuration. The cause of the event was the loss of the 28 RPS'bus when the 2B,RPS MG set shutdown. The root cause of this event was a failure of the MG set AC drive motor starter contactor coil. The failed motor starter coil on the 2B.RPS MG set AC drive motor was replaced. The plant response to this event was uncomplicated and the affected systems responded as designed during the loss of power to the.28 RPS bus. Also, there were no ongoing plant activities that could have led to the RPS actuations. The RPS is designed to fulfillthis safety function upon, loss of initiating logic power. In this event; the loss of power was to RPS

'bus 28, and because RPS bus 2A remained energized throughout the event a full,scram was not initiated. This report is submitted in accordance with 10 CFR 50.73(a)(2)(iv) as an event or condition that resulted in an automatic actuation of an engineered safety feature.

9907070275 990628 PDR ADQCK 05000260 S PDR

Ik )l I

I'

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION I6-19981 LICENSEE EVENT REPORT (LER),

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER I6 PAGE 3 YEAR SEOUENTIAL REVISION NUMBER 2OF 5 Browns.Ferry Nuclear Plant Unit 2 05000260 1999 004 - 00 TEXT (If more spece is required. use edditionel copies of NRC Form 366AI l17)

PLANT CONDITION(S)

At the time the event occurred, Units 2 and 3 were in Mode 1, 100 percent reactor power, at 3458 megawatts thermal. Unit 1 was shutdown and defueled.

II. DESCRIPTION OF EVENT A. Event:

On May 22, 1999, at 0522 hours0.00604 days <br />0.145 hours <br />8.630952e-4 weeks <br />1.98621e-4 months <br /> central daylight time CDT, Unit 2 received an unexpected channel 2B reactor protection system (RPS) [JC] actuation when power was lost to the 2B RPS bus.

The loss of power to the 2B RPS bus resulted in the automatic actuation or isolation of the following primary containment isolation system (PCIS) [JE] systems and components:

~ PCIS group 2, shutdown cooling mode of Residual Heat Removal (RHR) [BO] system; drywell floor drain isolation valves; drywell equipment drain isolation valves [WP].

~ PCIS group 3, Reactor Water Cleanup (RWCU) system [CE].

~ PCIS group 6, primary containment purge and ventilation [JM], Unit 2'reactor zone ventilation [VB]; refuel zone ventilation [VA]; Standby Gas Treatment (SGT) [BH],system; Control Room Emergency Ventilation (CREV) [Vl] system.

~ PCIS group 8, Traversing Incore Probe (TIP) [IG].

At approximateiy 0527 hours0.0061 days <br />0.146 hours <br />8.713624e-4 weeks <br />2.005235e-4 months <br /> CDT, the 2B RPS was placed on the alternate feed, PCIS isolations and actuations were reset. The SGT and CREV systems were subsequently returned to pre-event configuration.

At, approximately 0633 hours0.00733 days <br />0.176 hours <br />0.00105 weeks <br />2.408565e-4 months <br /> CDT, a Unit Supervisor dispatched to the MG set determined that the 2B RPS MG set [JC] control power fuse had cleared. Following initial trouble shooting, a maintenance work order was then generated to troubleshoot and determine the cause of 2B RPS MG set trip.

This event is reportable in accordance with 10 CFR 50.73 (a)(2)(iv), as an event that resulted in an automatic actuation of an engineered safety feature, including the reactor protection system.

B. Ino erable Structures, Com onents, or S stems that Contributed to the Event:

None.

NRC FORM 366 {6-1996)

gl l

FORM 366A U.S. NUCLEAR REGULATORY COMMISSION

] NRC1998) 16 UCENSEE EVENT REPORT ILER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE (3 YEAR SEQUENTIAL REVISION NUMBER 3OF5 Browns Ferry Nuclear Plant Unit 2 05000260 1999 - 004 - 00 TEXT flfmore space is required, use additional copies of NRC Form 866A) I17I C. Dates and A roximate Times of Ma'or Occurrences:

May 30, 1999 at 0522 hours0.00604 days <br />0.145 hours <br />8.630952e-4 weeks <br />1.98621e-4 months <br /> CDT Unit 2 received trip of the 2B RPS MG set.

Expected isolations and'initiations occurred.

May 30, 1999 at 0527 hours0.0061 days <br />0.146 hours <br />8.713624e-4 weeks <br />2.005235e-4 months <br /> CDT Operations reset the PCIS isolations and actuations. The CREV and SGT systems were returned to pre-event status.

May 30, 1999 at 0700 hours0.0081 days <br />0.194 hours <br />0.00116 weeks <br />2.6635e-4 months <br /> CDT A four-hour non-emergency report is made to NRC in pursuant to 10 CFR 50.72 (b)'(2)

(ii) as an event that resulted in a manual or automatic actuation of an Engineered Safety Feature.

D. Other S stems or Seconda Functions Affected None.

E. Method of Discove This condition was discovered when the Unit 2 control room operators received the RPS actuation.

No operator actions contributed to the event.

G. Safe S stem Res onses The safety systems operated as expected in response to this event.

III. CAUSE OF THE EVENT A. Immediate Cause The immediate cause of the event was the loss of the 2B RPS bus that occurred when the 2B RPS MG set shutdown. This was caused by a failure of the motor starter contactor coil (CL) for the 2B RPS MG set AC drive motor.

B. Root Cause The root cause of this event was a failure of the MG set AC drive motor starter contactor

.coil. The motor starter contactor coil for the RPS MG set was found to have extremely low re'sistance, approximately 0.003 ohms. As such, this is considered a short'circuit and would result in the clearin .of the u stream control ower fuse and the subsequent loss of ower NRC FORM 366 I6-1998I

41 NRC FORM 366A U.s. NUCLEAR REGULATORY COMMISSION (6.1998)

LICENSEE EVENT REPORT.ILER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL. REVISION NUMBER 4OF5 Browns Ferry Nuclear Plant Unit 2 05000260 1999 - 004 00 TEXT (If more space is required, use addi donal copies of hlRC Form 366A/ I17) to the 2B RPS bus.

Visual. inspection indicated no physical damage to the epoxy encapsulated coil. There is no periodic testing that is performed that could damage or degrade the coil insulation nor predict its failure. Also, there is no suggested preventative maintenance activity or replacement frequency required by the vendor. A review of the plant maintenance history has indicated that this is the first failure of an RPS MG set AC drive. motor starter contactor coil at BFN.

Additionally, BFN has six RPS MG sets, two for each of the three units. A review of the operating history of these MG sets has indicated there is no difference in the manner in which the MG sets are operated which could, have led to a failure. Moreover, there were no plant no plant evolutions or operations associated with the loss of the 2B RPS MG set.

Therefore, the most probable cause of the contactor coil failure is a random failure.

C. Contributin Factors None.

IV. ANALYSIS OF THE EVENT The RPS actuations that occurred on Unit 2 resulted from a loss of the Unit 2 RPS bus B. The normal power to RPS bus B is supplied'by a MG set. The MG set flywheel maintains voltage to the bus within 5 percent of rated for at least one second following a total loss of power to the MG set AC drive motor. On Unit 2, the alternate power is supplied through a transformer shared'ith the unit preferred system, from 480 reactor motor operated valve board 2B [EC]. Following the trip of the 2B motor-generator set, Unit 2 RPS bus 8 was manually transferred to the alternate power supply and the PCIS isolations and actuations were manually reset in accordance with plant procedures.

The effects on Units 1 and 3 were limited to the start of SGT, CREV initiation and the isolation of. the respective unit's Refuel Zone Ventilation.

V. ASSESSMENT OF SAFETY CONSEQUENCES The plant response to this event was uncomplicated and the affected systems responded as designed during the loss of power to the 2B RPS bus. Also, there were no ongoing plant activities that could have led to the RPS,actuations. The systems affected during the event are designed to shutdown the reactor, contain and process and radioactive releases. The RPS is designed to fulfillthis safety function upon loss of initiating logic power. In this event, the loss

of power was-to RPS bus 2B, and because RPS bus 2A remained energized throughout the event a full scram was not initiated. The effected systems were returned to the pre-event status on the assigned alternate power supply in approximately five minutes. If a design basis event had occurred during the five minutes that the 2B RPS bus was tripped, the 2A RPS system would have tripped as designed initiating a full scram. If a design basis accident had occurred while the 2B RPS bus was powered from its'lternate power supply, both the 2A and,2B RPS systems would have tripped as designed. Therefore, the event did not affect the safety of the plant personnel or the public.

NRC FOAM,366 {6-1998I

0 0 NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION IS )998)

LICENSEE EVENT REPORT ILER)

TEXT CONTINUATION FACILITY NAME 1 ,DOCKET ER NUMBER 6) PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 5OF 5 Browns Ferry Nuclear Plant Unit 2 05000260 1999 - 004 00 TEXT flfmore spece is required, use eddidonel copies of AIRC Form 388AI I17)

VI. CORRECTIVE ACTIONS A. Immediate Corrective Actions The 2B RPS bus was placed on the alternate feed, the half scram was reset and affected systems were returned to the pre-event configuration.

B. Corrective Actions to Prevent Recurrence The failed motor starter coil on the 2B RPS MG set-AC drive motor was replaced. The 2B RPS bus was transferred from the alternate feed back to the MG set. Because the failure of the MG set starter coil is.,considered a random failure, there are no further corrective actions required.

Vl. ADDITIONALINFORIVIATION A. Failed Com onents:

The starter contactor coil for the AC drive motor, a 115 VAC 60 HZ General Electric model 55-501336G2 coil failed.

B. Previous I.ERS on Similar Events:

None.

C. Additional Information:

None.

D. Safe S stem Functional Failure:

Although the RPS was involved, there was no failure of a reactor scram function during the event. Therefore, the event.did not result. in a safety system functional failure in, accordance with NEI 99-02.

Vll. COMMITIVIENTS None.

Energy Industry Identification System (EIIS) system and component codes are identified in the text with brackets.

NRC FORM 366 )6-1998)

J.