United States Nuclear Regulatory Commission - Protecting People and the Environment


ACCESSION #: 9809030209


10CFR Part 21 Report - Westinghouse DB50 Circuit Breakers

After completion of surveillance test PMT-170 Auxiliary Feed Water Pump

(AFWP) actuation functional test, Operations made an attempt to start 21

AFWP from CCR control switch. The breaker did not close.



During step by step investigation and inspection, it was determined that:

(1) The inertia latch failed to reset in its normal position to enable the

operating mechanism closing the breaker. (The visual inspection found

the inertia latch to be in a position to preclude the operating

mechanism from closing the breaker)

(2) The inertia latch initially was binding severely. After manipulation

of the latch the friction decreased to a point where the movement was

normal. When the latch was moved axially toward the snap ring it

would bind at that point.

(3) The cause of failure was due to spalling or breaking-away of surface

coating on the pivot pin and possibly the bushing (pivot pin hole) of

the inertia latch. The fragments of the coating accumulated on the

surfaces of the pin and the bushing in discreet locations, reduced the

clearance between the pivot pin and the bushing. The reduction in

clearance resulted in binding of the inertia latch. This inertia

latch binding prevented the latch to reset in its normal position and

prevented the breaker from closing. (The dimensions of the 21

Auxiliary feed Pump breaker inertia latch pivot pin and pivot pin hole

(bushing) were found to be nominal 0.375" and 0.376" respectively.



The immediate corrective action that was taken, was to inspect all DB-50

breakers having new inertia latches. All the DB-50 breakers having new

inertia latches with gold color plating were cleaned, adjusted and tested

for proper clearance (between pivot pin hole and pivot pin) and proper

operation as required by the design.



Altran Corporation was requested to determine the cause failure of an

inertial latch from a DB-50 circuit breaker mechanism. During testing of

the operation during the week of August 9 the latch was observed to bind in

the closed position. This latch is an inertial latch and is designed to

revert to the position after activation. Failure to fall to the open

position results in an inoperable circuit breaker. The cause of failure

was due to spalling or breaking-away of the surface coating on the shaft

pin and possibly the bushing of the latch. The surface coating was made

using a zinc material via a process involving a dip in gold dichromate

solution followed by a plating process. The fragments of the coating

accumulated on the surfaces of the pin and the bushing in discreet

locations and reduced the clearance between the shaft and the bushing. The

reduction in clearance resulted in binding of the latch during operation.

Residue of lubricant (molybdenum disulfide) was observed on the surfaces of

the shaft pin and the inside diameter of the bushing. However, the

lubricant was insufficient to prevent failure of the coating. The

examination of the coating on the shaft pin clearly showed that the coating

was breaking away from a surface. The damage may have been initiated

during treatment with the emery cloth as part of the custom fitting

process. However, it appears that during service material was dislodged

from the surfaces. The visual examination indicates that the quality of

bonding of the coating on the shaft was inadequate.



The results obtained to date indicate that the coating on the inside

diameter of the bushing and on the outside diameter of the shaft pin is

spalling from the surface and causing improper operation of the inertial

latch. Therefore, it is recommended that the coating be removed from the

inside diameter surfaces of the bushing and on the outside surface of the

shaft pin.



POWER REACTOR EVENT NUMBER: 34713



FACILITY: INDIAN POINT REGION: 1 NOTIFICATION DATE: 08/29/98

UNIT: [21 [ I [ ] STATE: NY NOTIFICATION TIME: 17:12 [ET]

RX TYPE: [2] W-4-LP, [3] W-4-LP EVENT DATE: 08/29/98

EVENT TIME: 00:00 (EDT]

NRC NOTIFIED BY: JOHN BALLETTA LAST UPDATE DATE: 08/29/98

HQ OPS OFFICER: BOB STRANSKY



NOTIFICATIONS



EMERGENCY CLASS: NOT APPLICABLE

10 CPR SECTION: WILLIAM COOK RDO

CCCC 21.21 UNSPECIFIED PARAGRAPH

V. HODGE (via fax) NRR



UNIT SCRAM CODE RX CRIT INIT PWR INIT RX MODE CURR PWR

2 N N 0 HOT SHUTDOWN 0



CURR RX MODE

HOT SHUTDOWN



EVENT TEXT



10 CFR PART 21 REPORT REGARDING BINDING OF WESTINGHOUSE DB-50 CIRCUIT

BREAKERS



"AFTER COMPLETION OF SURVEILLANCE TEST PMT-170 AUXILIARY FEEDWATER PUMP

(AFWP) ACTUATION FUNCTIONAL TEST, OPERATIONS MADE AN ATTEMPT TO START 21

AFWP FROM CCR CONTROL SWITCH. THE BREAKER DID NOT CLOSE.



"DURING STEP BY STEP INVESTIGATION AND INSPECTION, IT WAS DETERMINED THAT:



(1) THE INERTIA LATCH FAILED TO RESET TO ITS NORMAL POSITION TO

ENABLE THE OPERATING MECHANISM CLOSING THE BREAKER. (THE VISUAL

INSPECTION FOUND THE INERTIA LATCH TO BE IN A POSITION TO

PRECLUDE THE OPERATING MECHANISM FROM CLOSING THE BREAKER.)



(2) THE INERTIA LATCH INITIALLY WAS BINDING SEVERELY. AFTER

MANIPULATION OF THE LATCH THE FRICTION DECREASED TO A POINT WHERE

THE MOVEMENT WAS NORMAL. WHEN THE LATCH WAS MOVED AXIALLY TOWARD

THE SNAP RING IT WOULD BIND AT THAT POINT.



(3) THE CAUSE OF THE FAILURE WAS SPALLING OR BREAKING-AWAY OF SURFACE

COATING ON THE PIVOT PIN AND POSSIBLY THE BUSHING (PIVOT PIN

HOLE) OF THE INERTIA LATCH. THE FRAGMENTS OF THE COATING

ACCUMULATED ON THE SURFACES OF THE PIN AND THE BUSHING IN

DISCREET LOCATIONS, REDUCED THE CLEARANCE BETWEEN THE PIVOT PIN

AND THE BUSHING. THE REDUCTION IN CLEARANCE RESULTED IN BINDING

OF THE INERTIA LATCH. THE INERTIA LATCH BINDING PREVENTED THE

LATCH TO RESET IN ITS NORMAL POSITION AND PREVENTED THE BREAKER

FROM CLOSING. THE DIMENSIONS OF THE 21 AUXILIARY FEED PUMP

BREAKER INERTIA LATCH PIN AND PIVOT PIN HOLE (BUSHING] WERE FOUND

TO BE NOMINAL 0.375" AND 0.376" RESPECTIVELY.)



(Continued on next page)



FACILITY: INDIAN POINT PAGE # 2 OF EVENT NUMBER: 34713



"THE EXAMINATION OF THE COATING ON THE SHAFT PIN CLEARLY SHOWED THAT THE

COATING WAS BREAKING AWAY FROM THE SURFACE. THE DAMAGE MAY HAVE BEEN

INITIATED DURING TREATMENT WITH THE EMERY CLOTH AS PART OF THE CUSTOM

FITTING PROCESS. HOWEVER, IT APPEARS THAT DURING SERVICE MATERIAL WAS

DISLODGED FROM THE SURFACES. THE VISUAL EXAMINATION INDICATES THAT THE

QUALITY OF BONDING OF THE COATING ON THE SHAFT WAS INADEQUATE."



THE NRC RESIDENT INSPECTOR WILL BE INFORMED BY THE LICENSEE.



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Page Last Reviewed/Updated Thursday, March 29, 2012