United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #: 9905240114


LICENSEE EVENT REPORT (LER)
FACILITY NAME: Virgil C. Summer Nuclear Station PAGE: 1 OF 3
DOCKET NUMBER: 05000395
TITLE: Substantial Safety Hazard with GE 7.2 kV Magne-Blast Circuit Breakers
EVENT DATE: 05/02/1999 LER #: 1999-006-00 REPORT DATE: 05/17/1999
OTHER FACILITIES INVOLVED: DOCKET NO: 05000
OPERATING MODE: 6 POWER LEVEL: 0
THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR SECTION:
Other
LICENSEE CONTACT FOR THIS LER:
NAME: A. R. Rice TELEPHONE: (803) 345-4232
Manager, Nuclear Licensing and Operating Experience
COMPONENT FAILURE DESCRIPTION:
CAUSE: B SYSTEM: EB COMPONENT: 52 MANUFACTURER: G080
REPORTABLE EPIX: No
SUPPLEMENTAL REPORT EXPECTED: NO

ABSTRACT:

On April 15, 1999, V.C. Summer Nuclear Station (VCSNS) submitted a potential Substantial Safety Hazard report due to 7.2 kV Circuit Breakers which failed to close. After further investigation and testing it has been identified that a Substantial Safety Hazard could exist with this failure to close.

The identified problem deals with a cotter pin striking the latch check switch mounting bracket and bending it forward. This removes the factory set clearance between the bracket and the switch actuating paddle. This results in the paddle, which is bolted to the trip shaft, rolling the trip shaft to the trip position when the breaker attempts to close. The cotter pin problem is considered a defect in repair by the manufacturer. This condition represents a potential for a common mode failure of Safety-Related Magne-Blast circuit breakers.

These breakers are utilized at VCSNS in many applications, including the 7.2 kV Emergency Diesel Generator electrical buses.

No operability concerns currently exist as the latch check switch, latch check switch mounting bracket, and the actuating paddle have been removed from all Safety-Related circuit breakers at the station. The function of the latch check switch is to enable rapid repeated breaker closure, which is not required in the VCSNS application of these breakers.

END OF ABSTRACT


PLANT IDENTIFICATION

Westinghouse - Pressurized Water Reactor

EQUIPMENT IDENTIFICATION

All 7.2 kV circuit breakers in switchgear XSW1A, XSW1B, XSW1C, XSW1DA, XSW1DB, XSW1DX, XSW1EA, and XSW1EB.

EIIS Code - EB

IDENTIFICATION OF EVENT

Potential Substantial Safety Hazard. During testing of 7.2 kV Magne-Blast breakers, the breakers exhibit a problem in failing to close. On May 2, 1999, it was determined that the actual cause of the failure to close was movement of the latch switch mounting bracket when impacted by the cotter pin. The breakers which exhibited this problem had been recently overhauled by General Electric. Therefore, this cotter pin problem is considered a defect in repair by the original equipment manufacturer.

EVENT DATE

May 2, 1999. This is the date that it was determined that both breaker events shared a common failure mechanism, which posed a Substantial Safety Hazard.

REPORT DATE

May 17, 1999

CONDITIONS PRIOR TO EVENT

Mode 1 - Power Operations (100%) - Initial breaker
Mode 6 - Refueling Outage (0%) - Second breaker

During surveillance testing (STP0170.015) of the 7.2 kV circuit breaker in XSW1DB 14, on February 18, 1999, C Charging Pump on B-train, the breaker would attempt to close, but the mechanism would immediately collapse back to the open position. The breaker was replaced with a spare breaker and moved for further testing. This breaker was returned to General Electric (GE) for testing and determination of the root cause. On April 20, 1999, during post-overhaul testing of another 7.2 kV Magne-Blast breaker returned from the GE Atlanta refurb facility, the breaker exhibited an apparently similar problem in failing to close. V.C.Summer Nuclear Station personnel utilized high speed taping of this breaker during on-site troubleshooting. While reviewing the high speed tape, the Electrical Supervisor noticed that a cotter pin was impacting the latch check switch mounting bracket. GE was informed of this occurrence and focused the testing on the first breaker in this area. On May 2, 1999, it was determined that the actual cause of both events was movement of the latch switch mounting bracket when impacted by the cotter pin. This cotter pin problem is considered a defect in repair.

CAUSE OF EVENT

The apparent cause of this situation is the cotter pin impacting on the latch check switch mounting bracket.

ANALYSIS OF EVENT

V.C. Summer Nuclear Station personnel have, through testing and working with General Electric personnel, concluded that these breakers may not have performed their intended safety function.

CORRECTIVE ACTIONS

The latch check switch allows rapid, repeated breaker closure, which is not required in the VCSNS application of these breakers. The corrective action taken by SCE&G was to remove the latch check switch, the latch check switch mounting bracket, and the actuating paddle for this switch from each 7.2 kV Magne-Blast breaker. These action will prevent recurrence of this condition. These actions were completed on all Safety-Related breakers on May, 4, 1999.

ADDITIONAL CORRECTIVE ACTIONS

No additional corrective actions are required by V.C.Summer Nuclear Station. General Electric has initiated a potential safety concern under their 10CFR Part 21 program to provide further information on the identified problem to the industry.

PRIOR OCCURRENCES

None


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