05000395/LER-2005-001

LER-2005-001, Emergency Diesel Generator Start and Load Due To A Loss Of Vital Bus

Docket Number
Event date:	05-18-2005
Report date:	11-29-2005
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3952005001R02 - NRC Website

PLANT IDENTIFICATION

Westinghouse - Pressurized Water Reactor

EQUIPMENT IDENTIFICATION

"B" Emergency Diesel Generator (EDG) "B" Residual Heat Removal Pump (RHR)

IDENTIFICATION OF EVENT

At 0154, during relay testing, the 86T3 differential lockout was actuated. This resulted in a total isolation of XTF0031 and XTF0032 which de-energized all of the BOP power to the plant and the XSW1DB switchgear.

Plant Engineered Safeguards Features (ESF) systems responded per design as the 'B' DG started and sequenced ESF loads. There were no major problems due to the event; however, the Diesel Fire Pump did not start as expected on a loss of BOP bus 1C2.

EVENT DATE

05/18/2005

REPORT DATE

August 17, 2005, LER 2005-001-01 July 13, 2005, LER 2005-001-00 November 29, 2005, LER 2005-001-02

CONDITIONS PRIOR TO EVENT

Mode 5, Refueling

DESCRIPTION OF EVENT

VCSNS was shutdown for refueling in Mode 5. At 0154, May 18, 2005, during performance of relay testing, differential lockout 86T3 was actuated in accordance with the approved procedure, resulting in lockout of XTF0031 and XTF0032. This resulted in a loss of all balance of plant busses, an auto start of 'B' DG and the sequencing of required ESF loads.

The Control Room entered AOP-304.3, "Loss of All Balance of Plant Buses" and SOP-306, Section B.

"Operation Of Diesel Generator 'B' After An Automatic Start And Load".

Review of plant response data showed the RHR flow was in the process of coasting down and was restored to full flow within 20 seconds. The inlet temperature of the RHR Heat Exchanger increased approximately 0.3°F due to this event. There was rio change in Reactor Coolant System level. VCSNS was shutdown in Mode 5 during Refueling Outage 15.

CAUSE OF EVENT

At the time of the event, a preventive maintenance task was being performed on the 86T3 lock-out relay.

However, transformers XTF0031 and XTF0032 were not scheduled to be out of service at the same time the relay maintenance was being performed. Therefore, actuation of the relay resulted in total isolation of the transformers which de-energized all BOP power and the XSW1DB switchgear. The resulting undervoltage on the 1DB bus caused an auto start and loading of the "B" DG.

The initial investigation of the event revealed the following causes of the event: (1) the preventive maintenance task sheet was too vague, (2) the pre job brief conducted prior to the task was not thorough enough, and (3) the personnel responsible for signing for the task to start were not thorough in reviewing the consequences of tripping the lockout.

A root cause evaluation determined the following causes: (1) nothing indicated this was a new or first time performed task, (2) labeling of the lockout relay did not associate the task with the transformers, (3) the maintenance procedure did not contain precautions or information related to manual actuation of the lockout relay, (4) the task sheet did not contain any reference to the transformers, and (5) the work package review failed to identify plant effects of the relay actuation.

ANALYSIS OF EVENT

All normal offsite power sources were available at all times throughout the event. Operations personnel monitored the plant to ensure conditions were stable prior to realigning XTF0031 and XTF0032 to their normal offsite power fee'd6*:"after Which the "B" DG was subsequently secured: There-Was-no 'equipment datna.ge'and no unexpected transients occurred. The Diesel Fire Pump did not start as expected on the loss of BOP bus 1C2.

RHR flow was never completely lost and RCS temperature increase was miniscule. The RCS level did not change during the event.

CORRECTIVE ACTIONS

Condition Evaluation Report (CER) C-05-2042 was generated to document the event and lessons learned.

Immediate corrective actions taken include:

• A team of engineers, relay department personnel, and plant personnel were assembled to provide guidance for the remaining relays to be tested during the remainder of Refuel 15.

• Protection relay testing was suspended until the incident was reviewed.

• A "Protected Train" placard was placed in front of XTF0031/0032 relay panel.

• A site awareness email was distributed discussing pre-job briefs and procedure focus.

• A management review team meeting was held to review the event.

CER C-05-2033 was written to document the failure of the Diesel Fire Pump to autostart on loss of bus 1C2.

The pump circuitry was repaired and tested satisfactorily on 07/28/2005.

OTHER CORRECTIVE ACTIONS

The following corrective actions to prevent recurrence were established during the root cause evaluation performed for this event, which will be tracked under the corrective action program (CER 05-2042).

1. Change applicable planning and scheduling procedures to include guidance for determining plant effect or proper equipment associations for newly generated tasks.

2. Change the equipment labels and the computerized equipment list reference for the 86T3 lockout relay to provide proper association with XTF0031 and XTF0032.

3. Revise electrical maintenance electrical procedure EMP-405.024 to include limits and precautions which properly define plant effects.

PRIOR OCCURRENCES

There are no prior occurrences of the loss of the normal incoming ESF feed to the plant due to actuation of the 86T3 differential lockout relay while being tested.