05000296/LER-2002-002

LER-2002-002,

Event date:	03-26-2002
Report date:	05-23-2002
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation
2962002002R00 - NRC Website

TO NPRDS

SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED MONTH DAY YEAR

YES

(If yes, complete EXPECTED SUBMISSION DATE).

X NO SUBMISSION DATE (15) ABSTRACT4(Limit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16) On March 26, 2002, at 1752 hours0.0203 days <br />0.487 hours <br />0.0029 weeks <br />6.66636e-4 months <br />, while installing safety grounds to the 3B 4KV Unit Board during the Unit 3 Cycle 10 refueling outage, an electrician inadvertently caused an electric arc flashover when a safety ground connecting rod was positioned too close to an energized breaker high-side stab. The electric arc flashover resulted in de-energizing the Unit Board. Consequently, this de-energized two 4KV shutdown boards causing two emergency diesel generators to auto-start.

The root cause of the event was personnel error due to inattention to detail and failure to adequately self-check. Corrective actions include: (1) Training was given to Electrical Maintenance personnel on the proper methodology to apply safety grounds, (2) A TVA policy/ procedure will be developed for safety ground installations, (3) Training will be developed and conducted on installation of safety grounds of medium voltage compartments, and (4) As appropriate, test carts will be used to reduce the potential for inadvertent electric arc flashover.

This condition is reportable in accordance with 10 CFR 50.73 (a)(2)(iv)(A) as an event or condition that resulted in a manual or automatic actuation of a system listed in 10 CFR 50.73(a)(2)(iv)(B).

FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) Browns Ferry Nuclear Plant - Unit 3 05000296 2002 - -�� 002� ---� 000

I. PLANT CONDITION(S)

At the time of the event, Unit 3 was in Mode 4 for a planned refueling outage with moderator temperature of about 188 degrees Fahrenheit. The RHR pump 3B was in shutdown cooling with both recirculation pumps secured. Unit 2 was in Mode 1 at 100 percent reactor power, approximately 3458 megawatts thermal. Unit 1 was shutdown and defueled.

II. DESCRIPTION OF EVENT

A.� Event:

On March 26, 2002, at approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, Maintenance Electrical personnel (3 utility and 1 contractor, all non-licensed) began to install safety grounds for clearance 3-057-0001 on the Main Generator and turbine breakers to support Unit 3, Cycle 10 outage activities. This clearance involved 25 safety ground installations At 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br />, after the electricians had successfully installed safety grounds on four electric breakers and the generator potential transformers, they began the safety ground installation for the 3B Unit Board breaker (1314) [BKR]. The breaker was racked out fully and removed from the cubicle by Operations personnel (utility, non-licensed). Three separate safety grounds were clamped to a grounding strap on the floor of the breaker cubicle. The other ends of the safety grounds were attached to connecting rods and were placed on the breaker which was positioned 2 feet outside of the breaker cubicle. These connecting rods were to be attached to the three load-side stabs inside the cubicle.� Using a Detex Neon Voltage detector, one of the electricians confirmed which stabs were energized with high voltage by observing that the bulb on the detector lit when contact was made with the energized high-side stabs. Then the electrician confirmed the load-side stabs were not energized by observing that the bulb on the detector did not light when contact was made with the load-side stabs. The electrician then re-checked the energized high-side again and set the detector aside.

At 1752 hours0.0203 days <br />0.487 hours <br />0.0029 weeks <br />6.66636e-4 months <br />, the electrician lifted one of the safety grounds off the disengaged breaker, turned, and walked toward the rear of the breaker cubicle. At that time, the electrician inadvertently caused an electric arc flashover when the safety ground was positioned too close to one of the energized high-side stabs instead of a load-side stab. The flashover resulted in the de-energizing of the 3B 4 KV Unit Board due to a C phase differential current lockout. Consequently, this de-energized two 4 KV shutdown boards (3EC and 3ED) [EB] causing two (3C and 3D) emergency diesel generators (EDGs) [EK] to auto-start and their output breakers to close, re-energizing their respective shutdown boards.

With the loss of the 3C 4KV shutdown board, the RPS Bus B [JC] was de-energized. This caused a half scram and the expected automatic full or partial actuations or isolations of the following PCIS [JM] systems occurred:

FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) Browns Ferry Nuclear Plant - Unit 3 05000296 2002 - - 002 --- 000

• PCIS group 1, Main Steam Isolation Valves (MSIV)[SB].

• PCIS group 2, Shutdown Cooling mode of the Loop II Residual Heat Removal (RHR) pump 3B [BO]; drywell floor drain isolation valves; drywell equipment drain isolation valves [WP].

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

• PCIS group 6, primary containment purge and ventilation [JM], Unit 3 reactor zone ventilation [VB]; Units 1, 2, and 3 refuel zone ventilation [VA]; Standby Gas Treatment system [BH]; Control Room Emergency Ventilation system [VI].

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

The 3B Unit Board was secured for investigation. At 1802 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.85661e-4 months <br />, Operations personnel returned 3B RPS to service and reset PCIS. At 1807 hours0.0209 days <br />0.502 hours <br />0.00299 weeks <br />6.875635e-4 months <br />, 3D RHR pump was placed into service for shutdown cooling. At 1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br />, A, B, and C SGT trains were secured. At 2320 hours0.0269 days <br />0.644 hours <br />0.00384 weeks <br />8.8276e-4 months <br />, the 3B Unit Board was tagged out to permit disassembly and inspection for extent of damage.

On March 27, 2002, at 1622 hours0.0188 days <br />0.451 hours <br />0.00268 weeks <br />6.17171e-4 months <br />, the 3B 4KV Unit Board was energized through its alternate feeder breaker. At 1749 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.654945e-4 months <br />, the 3C EDG was returned to standby. At 1831 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.966955e-4 months <br />, the 3D EDG was returned to standby.

This condition is reportable in accordance with 10 CFR 50.73 (a)(2)(iv)(A) as an event or condition that resulted in a manual or automatic actuation of a system listed in 10 CFR 50.73(a)(2)(iv)(B).

B. Inoperable Structures, Components, or Systems that Contributed to the Event:

None.

C. Dates and Approximate Times of Major Occurrences:

March 26, 2002, at 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, CST Electricians began to install 25 safety grounds.

March 26, 2002, at 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br />, CST Electricians began to install safety grounds in the 3B Unit Board breaker (1314).

March 26, 2002, at 1752 hours0.0203 days <br />0.487 hours <br />0.0029 weeks <br />6.66636e-4 months <br />, CST Electrician inadvertently caused an electric arc flashover which de-energized the 3B 4KV Unit Board. Consequently, two EDGs auto-started.

March 26, 2002, at 1802 hours0.0209 days <br />0.501 hours <br />0.00298 weeks <br />6.85661e-4 months <br />, CST Operations personnel began to return affected equipment back to service.

FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) Browns Ferry Nuclear Plant - Unit 3 05000296 2002 - -�� 002� ---� 000 March 27, 2002, at 1622 hours0.0188 days <br />0.451 hours <br />0.00268 weeks <br />6.17171e-4 months <br />, CST� The 3B Unit Board was energized by its alternate feeder breaker.

March 27, 2002, at 1749 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.654945e-4 months <br />, CST� The 3C EDG was returned to standby.

March 27, 2002, at 1831 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.966955e-4 months <br />, CST� The 3D EDG was returned to standby.

D. Other Systems or Secondary Functions Affected

Unit 3 shutdown cooling isolated as expected and was promptly returned to service by Operators.

E. Method of Discovery

This condition was discovered when the Unit Operator (utility, licensed) in the control room received indications and alarms [ALM] associated with the loss of the 3B 4KV Unit Board.

F. Operator Actions

Operator actions taken during this event were appropriate.

G. Safety System Responses

All safety systems responded as designed.

HI.� CAUSE OF THE EVENT

A. Immediate Cause

A de-energized condition on the 3EC and 3ED shutdown boards due to the de-energized 3B Unit Board resulted in the EDGs to auto-start.

B. Root Cause

The root cause of this event was a result of personnel error in that there was inattention to detail and failure to adequately self-check. Even though successfully completing safety ground installations (12) on four other similar breakers, the electrician did not maintain adequate distance from energized equipment when applying grounds causing the electric arc flashover.

C. Contributing Factors

None.

IV.� ANALYSIS OF THE EVENT On March 26, 2002, safety grounds were scheduled to be attached to several load-side stabs to support a clearance process for outage activities. Operations was responsible for disengaging the breaker from its cubicle. The electricians were responsible for installing the safety grounds on the load-side stabs.

FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE 13) Browns Ferry Nuclear Plant - Unit 3 05000296 2002 - -�� 002� ---� 000 At 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br />, after Operations had removed the 3B Unit Board breaker from its cubicle.

The electricians began the installation of a safety ground when an electric arc flashover occurred.

The flashover was the result of positioning a safety ground too close to the energized high-side stabs.

The flashover caused the Unit Board to de-energize resulting in a de-energizing two 4 KV shutdown boards.

Consequently, the associated EDGs auto-started. The cause of the event was personnel error, namely, inattention to detail and failure to adequately self-check when a safety ground was positioned too close to the energized high-side stabs.

Power to the shutdown boards is normally supplied from the appropriate 4KV Unit Boards. If necessary, power to the shutdown boards is supplied from the EDGs. In this event, it was necessary to supply the shutdown board's power from the EDGs. The EDGs functioned as designed. Operator actions were in accordance with plant procedures. All expected isolations and actuations occurred as designed.

V. Assessment of Safety Consequences

The response of the plant to the loss of 3B 4KV Unit board was as expected and designed. Loop 2 of RHR was in shutdown cooling at the time of the event. Shutdown cooling isolated as expected in response to loss of power to RPS Bus B.

The purpose of Shutdown Cooling is to remove decay heat necessary to achieve and maintain the reactor in COLD condition. In this event, the plant was in a COLD SHUTDOWN condition, the containment was open and the primary system was still intact. Shutdown cooling tripped and isolated as designed on loss of power and was promptly placed back in service manually as designed. Although decay heat removal was temporarily interrupted, the function was available throughout the event using onsite power sources.

Had onsite power (EDGs 3C and 3D) failed, the RPV would have pressurized and excess energy would have been retained in the primary system until another loop of RHR shutdown cooling could be established. The Torus and Safety Relief Valves were also available to establish a decay heat removal path using suppression pool cooling had the vessel pressurized.

Primary containment was not established at the time of the event nor was it required by Technical Specifications at any time during the event. Based on the fact that all systems operated as designed, there was no loss of safety function, and all technical specification requirements were met, this event did not adversely affect the health and safety of the public.

VI. CORRECTIVE ACTIONS

A.� Immediate Corrective Actions Operations acknowledged associated alarms and reset RPS and PCIS. Appropriate AOls were entered. The affected equipment was returned to service/standby.

-_ ..

FACILITY NAME (1) DOCKET LER NUMBER (6) PAGE (3) Browns Ferry Nuclear Plant - Unit 3 05000396 2002 ---22 0022 ---2 000 B. Corrective Actions to Prevent Recurrence 1 Corrective actions to preclude recurrence include: (1) Training was given to Electrical Maintenance personnel on the proper methodology to apply safety grounds, (2) A TVA policy/procedure will be developed for safety ground installations, (3) Training will be developed and conducted on installation of safety grounds of medium voltage compartments, and (4) As appropriate, test carts will be used to reduce inadvertent electric arc flashover.

VII.2 ADDITIONAL INFORMATION

A. Failed Components

None.

B. Previous LERs on Similar Events There have been several LERs due to personnel error in which one or more EDGs were inadvertently started. However, no previous events were identified that were caused by improper installation of grounds. Therefore, no previous LER corrective actions would have precluded this event.

C. Additional Information

None.

D. Safety System Functional Failure Consideration:

This event is not considered a safety system functional failure in accordance with NEI 99-02 in that it did not prevent the fulfillment of safety functions of structures or safety systems that were needed.

VIII. COMMITMENTS

None.

TVA does not consider these corrective actions as regulatory commitments. The completion of these items will be tracked in TVA's Corrective Action Program.