05000348/LER-2002-001

LER-2002-001,

Docket Number
Event date:	0-3-2002
Report date:	06-20-2002
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
3482002001R00 - NRC Website

Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]

Description of Event

On May 3, 2002, surveillance testing on the "A" Reactor Coolant Pump (RCP) bus undervoltage relays had placed a relay in the trip condition. Additionally, the main control board neutron flux recorder was being reinstalled following repair. The power supply for both the Reactor Protection System [JC] field input relays for the "B" RCP bus undervoltage signal and the "B" RCP breaker open signal, as well as the main control board neutron flux recorder, is the "B" 120 VAC vital instrument bus [EF]. The "B" vital bus is powered by the "B" inverter.

Following maintenance on the neutron flux recorder, the recorder power leads, energized and taped with a single layer of tape over each lead, were to be reterminated. The power leads (3) were to be routed through a condulet type sleeve to the back of the recorder. While routing the second lead through the condulet, the electrical tape was breached and an arc occurred creating a short to ground on the "B" vital instrument bus. Based on engineering evaluation, the arc resulted in sufficient short term current in excess of the "B" inverter rating to cause the inverter [EF] to shift to the bypass source. In addition, the ground current resulted in a voltage drop on the associated distribution panel to an estimated 30 — 60 volts. This drop in voltage caused solid state protection system input relays, "B" undervoltage and "B" RCP breaker position, to deenergize sending trip signals into the Reactor Protection System "B" channel.

On May 3, 2002 at 1321, with the Unit 1 reactor at 100% power, the dropout of the "B" undervoltage relay made up the 2 out of 3 coincidence requirement for RCP bus undervoltage causing an automatic reactor trip. A second trip signal was generated 2 milliseconds later due to a 1 out of 3 RCP breaker open signal resulting from the "B" vital instrument bus undervoltage condition alone.

The RCP busses and pumps continued to operate normally throughout the event and all safeguards equipment functioned as designed. The bypass source and distribution panel current ratings were not exceeded and these components remained energized. Other equipment supplied by the "B" 120VAC vital bus continued to operate.

Following investigation, the surveillance test procedure was performed satisfactorily on the "B" inverter. The inverter was then returned to its normal alignment on the evening of May 3, 2002. The main control board neutron flux recorder was also returned to service.

Cause of Event

The cause of the event was that planning and scheduling of work activities, which involve energized conductors, requires unique actions and precautions. However, no procedural guidance prompted additional considerations for this type work function.

A second cause was inadequate management expectations with respect to taping of electrical leads.

Electrical and I&C procedures identified the need to tape energized leads with approved electrical tape. The individual involved taped the electrical lead consistent with the management expectations at the time, however, that taping proved to be inadequate.

Safety Assessment All safety systems functioned as designed following the trip. The "B" inverter shifted to bypass per design and the associated loads remained energized on the alternate source. The other three vital instrument inverters and their loads were unaffected by this event. The actual RCP bus voltage and breaker conditions were unaffected by this event. Therefore, all RCPs continued to function normally and forced reactor coolant flow was maintained. There was no abnormal release of radioactive material during this event; therefore, the health and safety of the public were unaffected by this event.

This event does not represent a Safety System Functional Failure.

Corrective Action Procedural guidance has been developed to require work planning, specifically, to identify work activities associated with energized conductors and the affected power source.

Procedural guidance has been developed to evaluate work activities involving energized conductors during work scheduling.

Procedural guidance has been developed and personnel working on energized conductors have been trained on enhanced taping/insulating techniques for energized leads.

Additional Information

The following LERs have been submitted in the past 2 years on reactor trips: