05000282/LER-2007-001

LER-2007-001,

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function
2822007001R01 - NRC Website

EVENT DESCRIPTION

On April 3, 2007, Prairie Island Nuclear Generating Plant (PINGP) operators discovered the closing springs on the breaker' for the 12 safety injection (SI) pump2 were discharged with the breaker open.

NMC believes the charging motor3 failed the last time the breaker was closed to run the pump, which was March 15, 2007. The breaker was replaced with a spare and on April 4, 2007, the 12 SI pump was declared operable after successful testing of the breaker.

EVENT ANALYSIS

The breaker for the 12 SI pump was discovered to be inoperable on April 3, 2007. Indications are that the breaker had been inoperable since the last time the pump was run on March 15, 2007.

Technical Specification (TS) 3.5.2, Condition A, allows 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to restore operability of an inoperable emergency core cooling system4 (ECCS) train. If the Required Action and Completion Time of TS 3.5.2, Condition A, is not met, Condition B requires the affected unit be in Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 4 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. In this case one train of ECCS (12 SI pump) was inoperable for longer than allowed by TS 3.5.2, Condition A, without taking Unit 1 to Mode 3 in 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or Mode 4 in 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

Thus, this event is being reported in accordance with 10 CFR 50.73.(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

Impact on Safety System Functional Failure Performance Indicator The redundant 11 SI pump was operable during the time the 12 SI pump was inoperable. 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

This event did not result in a loss of the emergency core cooling system function, since the 11 SI pump remained operable. Thus, this event did not affect the health and safety of the public and the safety significance of this event is considered minimal.

1 EIIS Component Code: BKR 2 EIIS Component Code: P 3 EIIS Component Code: MO 4 EIIS System Code: BQ FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) 07 -- 01 -- 1

CAUSE

Failure of 12 Safety Injection Pump closing spring motor brushes was due to exceeding the end of the useful life for the brushes. The closing spring charging motor brushes were wore down (past its useful length), resulting in arcing across the gap between the brush and commutator. This would have resulted in inconsistent operation of the closing spring charging motor and the brush wear and charring observed.

CORRECTIVE ACTION

1. The 12 SI pump was restored to operability by replacing the breaker.

2. As an interim measure, operators have been performing additional inspections on 4kV safeguards breakers to verify the closing springs are charged.

3. Establish the appropriate maintenance procedures for switchgear closing spring charging motor inspection and replacement.

4. Inspect and replace (as necessary) all Safeguards Switchgear breaker closing spring charging motors.

PREVIOUS SIMILAR EVENTS

Review of Licensee Event Reports for Unit 1 and Unit 2 since 2004 found no previous similar events.