05000282/LER-2006-001

LER-2006-001,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation 10 CFR 50.73(a)(2)(v), Loss of Safety Function
2822006001R01 - NRC Website

FACILITY NAME (1)� DOCKET NUMBER (2) LER NUMBER (6)� PAGE (3) 06�01�1

EVENT DESCRIPTION

On April 14, 2006, Prairie Island Nuclear Generating Plant (PINGP) Unit 1 was operating at 100% power. At approximately 1425 CDT, an 11 FEEDWATER1 PUMP2 LOCKED OUT annunciator was received in the control room. Unit 1 operators responded per the alarm response procedure and manually tripped the reactor. The auxiliary feedwater3 pumps started automatically in response to the low narrow range steam generator level, which was caused by shrink resulting from the reactor trip.

The trip was uncomplicated and all systems operated as expected and operator response and recovery actions were as expected.

EVENT ANALYSIS

The trip of the Unit 1 reactor and the actuation of the auxiliary feedwater system are required to be reported per 10 CFR 50.73(a)(2)(iv)(A).

Impact on Safety System Functional Failure Performance Indicator The affected condensate and feedwater pumps have no active safety function. All other systems performed as expected during the event. Therefore, this event does not represent a loss of safety function. Consequently, this event is not reportable per 10CFR 50.73(a)(2)(v).

SAFETY SIGNIFICANCE

The plant was stabilized in Mode 3 after the trip with all systems performing as expected in response to the reactor trip. Therefore, this event did not affect the health and safety of the public.

CAUSE

Initial investigation of the cause of the 11 Feedwater Pump trip determined the feedwater pump tripped because the 11 Condensate Pump had tripped. Troubleshooting identified the cause of the condensate pump trip to be a ground between the 11 Condensate4 Pump and Bus 13. The condensate pump motor was determinated and a zero ohm ground was measured on the motor. The motor was shipped off site for repairs and the stator windings were found to have grounded.

1 EIIS System Code: SJ 2 EUS Component Identifier: P 3 EIIS System Code: BA 4 EIIS System Code: SD FACILITY NAME (1) �DOCKET NUMBER�(2) LER NUMBER (6) �PAGE (3) 06 -- 01 -- 1 NMC conducted a root cause evaluation (RCE) and determined that the equipment cause of the condensate pump motor trip was degraded motor insulation due to aging and environmental conditions. The RCE further determined that the organizational root cause of the condensate pump motor trip was a lack of an adequate long range planning and budgeting process to prioritize and budget large motor maintenance.

CORRECTIVE ACTION

Interim Actions:

1. NMC performed a baseline off-line monitoring for Unit 1 large balance of plant motors in the May 2006 (1R24) refueling outage. All data was in acceptable ranges.

Planned Actions:

2. Rewind all Unit 1 and Unit 2 condensate pump motors with Class F insulation.

3. Develop a Large Motor Plan for Prairie Island that includes frequency and scope of testing, preventative maintenance and frequency of major maintenance activities.

4. Revise long range plan and budgets to include major maintenance activities.

5. Investigate trip logic for the condensate pumps to determine the feasibility of modifying the logic to prevent a unit trip following a condensate pump trip.

PREVIOUS SIMILAR EVENTS

Both Unit 1 and Unit 2 have experienced unplanned reactor trips in the past, however, the most recent unplanned reactor trip of either unit occurred in 2002.