ML18039A647

LER 98-007-00:on 981116,unplanned ESF Following Loss of 4kV Unit Board 3B Occurred.Caused by Temporary Energization of Lockout Relay on 4kV Unit Board 3B When Resistor on Relay Monitoring Lamp Circuit Shorted.Replaced Resistor

ML18039A647
Person / Time
Site:	Browns Ferry
Issue date:	12/15/1998
From:	Morrison G TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML18039A646	List: ML18039A645 ML18039A647
References
LER-98-007, LER-98-7, NUDOCS 9812230212
Download: ML18039A647 (12)

Text

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150.0104 ExPIREsoersor2oot (6-1996) Esbmated burden per response to comply with this mandatory hformstion cosection request: 50 hrs. Reported lessons learned are incorporated into the licensing process end fed back to industry. Forward comments regarding LICENSEE EVENT. REPORT (LER) burden estimate to the Records Management Branch (T< F33), V.S, Nuc(ear Regulatory Commission, Washington, DC 2055$ 0001, and to the Paperwork Reduction Project (3(500104), Office of Management and (See reverse for required number of Budget, Washington, OC 20503. If an information collection does not digits/characters for each block) display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person Is not required to respond to, the information co(lect(oIL FACIUTY NAME (I) DOCKET NUMBER (2) PAGE (3)

Browns Ferry Nuclear Plant 05000296 10f 6 TITLE (4)

Unplanned ESF Following the Loss of 4kV Unit Board 3B EVENT DATE (5) LER NUMBER (6I REPORT DATE (7) OTHER FACILITIES INVOLVED (8)

MONTH OAY YEAR YEAR SEQUENTIAL REVISION MONTH DAY FACIUTY NAME DOCKET NUMBER NUMBER NUMBER NA 05000 OOCKETNUMBER 16 1998 1998 007 000 12 15 1998 05000 OPERATING THIS REPORT IS SUBMITTED PURSUA NT To THE REQUIREMENTS OF 10 CFR rn (Check one or more) (11)

MODE (9) 20.2201(b) 20. 2203(a) (2)(v) 50.73(a)(2)(i) 50.73(a)(2) (viii)

POWER 20.2203(a)(1) 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) OTHER 20.2203(a)(2)(iii) 50.36(c)(1) 50.73(a)(2)(v) Specify in Abstract below or In NRC Form 366A 20.2203(a) (2) (iv) 50.36(c) (2) 50.73(a)(2)(vii)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (Include Ares Code)

G.M. Morrison, Senior Licensing Project Manger 256.729.7534 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE TO CAUSE SYSTEM COMPONENT MANUFACTURER REPORTABLE NPRDS TO NPROS EA IL G080

))I.: +X% M SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED 'MONTH OAY YEAR YES X NO SUBMISSION DATE (15)

(If yes, complete EXPECTED SUBMISSION DATE).

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

At 1435 CST on November 16, 1998, the supply to 4kV Unit Board 3B deenergized due to a fault protection lockout. 4kV Unit Board 3B supplies power to the Division II 4kV Shutdown Boards 3EC and 3ED. The loss of voltage caused the 3C and 3D Diesel Generators to start and tie to their respective shutdown boards. The transient loss of the shutdown boards caused Reactor. Protection System (RPS) Bus B to deenergize resulting in a half scram and Primary Containment Isolation System actuations. The Standby Gas Treatment and Control Room Emergency Ventilation systems initiated as expected due to the RPS power loss. The deenergization of 4kV Unit Board 3B resulted in the loss of its associated loads, the 3B Condensate Booster Pump, 3B Condensate Pump and the 3B Condenser Circulating Water Pump. As expected, the loss of condensate resulted in a Reactor Feed Pump Turbine 3A trip on loss of pump suction pressure. The Reactor Feed Pump Turbine 3A trip along with the resulting low water level initiated a recirculation system runback to 75% full power.

The immediate cause of this event was the temporary energization of the lockout relay on 4KV Unit Board 3B when the resistor on the relay monitoring lamp circuit shorted, allowing sufficient current to energize the lockout relay coil. The most probable root cause of this event was physical damage sustained by the relay monitoring lamp circuit voltage dropping resistor during or prior to its last replacement. Corrective actions include personnel briefings and inclusion of this event in the operations and electrical maintenance department training programs.

This report is submitted pursuant to 10 CFR 50.73(a)(2)(iv) as an event that resulted in a manual or automatic actuation of engineered safety features.

98i22302i2 98i2%5 PDR ADOCK 050002'))6 8 PDR

v NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION I6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 2of6 Browne Ferry Nuclear Fiant.- Unit 3 05000296 1996 - 007 000 TEXT (If more spece is required, use eddi rionel copies of NRC Form 366A/ {17)

I. PLANT CONDITION(S)

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

II. DESCRIPTION OF EVENT A. Event:

At 1435 CST on November'16, 1998, the supply to 4kV Unit Board 3B [EA] deenergized due to a fault protection lockout. 4kV,Unit Board 3B supplies power to the Division II 4kV Shutdown Boards 3EC and 3ED [EB]. The loss of voltage caused the 3C and 3D Diesel Generators (DG) [EK] to start and tie to their respective shutdown boards. The transient loss of the shutdown boards caused the Reactor Protection System (RPS) [JC] Division II to deenergize resulting in a half scram and Primary Containment Isolation System [JM] actuations for group 2 (primary containment water lines), group 3 (Reactor Water Cleanup), group 6 (primary containment air lines and secondary containment), and group 8 (Traversing Incore Probe). The Standby Gas Treatment (SGT) [BH] and Control Room Emergency Ventilation (CREV) [Vl]systems initiated as expected due to the RPS power loss. The DG starts caused the standby Emergency Equipment Cooling Water [BI] pumps to start.

The deenergization of 4kV Unit Board 3B resulted in the loss of its associated loads, the 3B Condensate Booster Pump [SD], 3B Condensate Pump [SD] and the 3B Condenser Circulating Water Pump [KE]. As expected, the loss of condensate resulted in a Reactor Feed Pump Turbine (RFPT) 3A [SJ] trip on loss of suction pressure.,The RFPT. 3A trip along with the resulting low water level provided a 75%

recirculation system runback initiation. Recovery from the event was completed at 1545 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.878725e-4 months <br /> CST when Unit 3 reactor power was stabilized at approximately 67% full power.

9 This report is submitted pursuant to 10 CFR 50.73(a)(2)(iv) as an event or condition that resulted in a manual or automatic actuation of any Engineered Safety Feature, including the Reactor Protection.

System.

B. Ino erable Structures Com onents orS stemsthatContributedto the Event:

None.

NRC FORM 366 I6-1998)

li" NRC FORM 366A U;S. NUCLEAR REGULATORY COMMISSION I6-1998)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISiQN NUMBER 3 of 6 Browne Ferry Nuclear Plant - Unit 3 05000296 1998 007 000 TEXT (Iimore spaceis required, use addirionai copies ofhfRC Form 366A/ I17i C. Dates and A roximate Times of Ma or Occurrences:

November 16, 1998 1435 hours0.0166 days <br />0.399 hours <br />0.00237 weeks <br />5.460175e-4 months <br /> CST Loss of Unit Board 3B received in the main control room. Diesel generators 3C and 3D receive a start signal due to loss of voltage to Shutdown Boards 3EC and 3ED.

November 16, 1998 1436 hours0.0166 days <br />0.399 hours <br />0.00237 weeks <br />5.46398e-4 months <br /> CST Recirculation system runback to 75% full power initiated.

November 16, 1998 1545 hours0.0179 days <br />0.429 hours <br />0.00255 weeks <br />5.878725e-4 months <br /> CST Recovery from the event completed. Unit 3 reactor power stabilized at -67% full power.

November 16, 1998 1706 hours0.0197 days <br />0.474 hours <br />0.00282 weeks <br />6.49133e-4 months <br /> CST A four-hour non-emergency notification is made to the NRC via the Emergency Notification System pursuant to 10 CFR 50.72(b)(2)(ii).

D. Other S stems or Seconda Functions Affected None.

E, Method of Discove The main control room operating crew received alarms associated with the deenergization of 4kV Unit Board 3B.

F. 0 erator Actions No operator actions contributed to this event. The operator actions in response to the event were proper and in accordance with plant instructions.

G. Safet S stem Res onses All safety systems responded as expected.

NRC FORM 366 I6-199BI

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6- I 998)

LlCENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME' DQGKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISiON NUMBER 4of6 Browne Ferry Nuclear Plant - Unit 3 05000296 1998 - 007 - 000 TEXT flfmore spece is required, use eddi rionel copies of fVRC Form 366AJ I 17)

III. CAUSE OF THE EVENT A. Immediate Cause The immediate cause of this event was the temporary energization of the lockout relay on 4KV Unit Board 3B when the resistor in the relay monitoring lamp circuit shorted, allowing sufficient current flow to energize the lockout relay coil.

B. Root Cause The most probable root cause of this event was physical damage sustained by the relay monitoring lamp circuit voltage dropping resistor during or prior to its last replacement. (Infrequent resistor failures necessitate replacement.) The insulating material between the resistor anode and cathode is a glass composite. The resistor is installed in the lamp circuit via a push/twist receptacle. It was concluded that the most likely scenario is that the glass insulation was damaged from a pre-installation impact and continued to degrade from panel vibration and holder spring tension until the short occurred. The failed resistor is shown on Figure 1.

C. Contributin Factors None.

IV. ANALYSIS OF THE EVENT The event was uncomplicated operationally. The half-scram occurred due to the loss of power to RPS Bus 3B. A full-scram was not initiated because RPS Bus 3A remained energized throughout the event. The only impact of this event on Units 1 and 2 were Refuel Zone isolations and the autostart of the SGT and CREV systems which are expected responses to the loss of RPS Bus 3B. Operations personnel immediately recognized the cause of the ESF actuation and took appropriate actions in accordance with plant procedures.

Proper communications and coordination took place between the Operations personnel in the Units 1, 2, and 3 control rooms. The initiations and actuations/isolations were consistent with the loss of RPS Bus 3B.

V. ASSESSMENT OF THE SAFETY CONSEQUENCES There were no actual or potential safety consequences as a result of this event. The failed lamp circuit voltage dropping resistor which initiated this event does not perform a safety function. Plant safety systems performed as designed, operator actions were in accordance with plant procedures, and no other potential problems were created by this event. Therefore, this event did not adversely affect the safety of plant personnel or the public.

NRC FORM 366 {6-1998)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMiSSiON IS-1998I LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1 DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 5 or 6 Browne Ferry Nuclear Plant - Unit 3 05000296 1 998 007 000 TEXT llfmore space is required, use,addirional copies of ftfRC Form 366Al i17)

VI. CORRECTIVE ACTIONS A. Immediate Corrective Actions Electrical troubleshooting was performed which identified the damaged resistor in the in the 4kV Unit Board 3B lockout relay monitoring lamp circuit: After replacement of the resistor and testing of the relay, 4kV Unit Board 3B was reenergized.

B. Corrective Actions to Prevent Recurrence Engineering, Operations, and Maintenance personnel will be briefed on this event'.

This event will be added to the lesson plans for Operations Department electrical training'.

This event will be added to the lesson plans for Electrical Maintenance continuing training'.

Vi). ADDITIONALINFORMATION A. Failed Com onents Troubleshooting into the cause of this event revealed a shorted 5100 ohm dropping resistor, General Electric part number 0165A7844P004, in the 4kV Unit Board 3B lockout relay monitoring lamp circuit.

The dropping resistor had apparently sustained impact damage during or prior to its last replacement.

B. Previous LERs on Similar Events No previous LERs have resulted from relay monitoring lamp circuit voltage dropping resistor failures at Browns Ferry..

Vill. COMMITMENTS None.

'VAdoes not consider these corrective actions regulatory commitments. The, completion of these items will be tracked in TVA's Corrective Action Pro ram.

NRc FQRM 366 l6-1998)

C~

L

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION (6-1998I LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME 1I DOCKET LER NUMBER 6 PAGE 3 YEAR SEQUENTIAL REVISION NUMBER 6 of 6 Browne Ferry NUclear Plant - Unit 3 05000296 1998 007 000 TEXT (If more space'is required, use additional copies of lVRC Form 366A/ (17I Figure 1 Photograph of Failed Relay Monitoring Lamp Circuit Resistor Multiple Indentations On The Anode, Caused From The Varying Angles Of Impact From The Holder Socket Glass Insulation:: .::s Anod Damage To The Cathode Cath Ode Glass i nsulatio n is damaged and some is rnlsslrl g. This resulted in .,'P.':.,'".!!:.:.":.p':".,'ng the ano de short to the .'. igQg~r,Ar~

cathode NRC FORM 366 I6-1999)

0 0 I I