Part 21 Report - 1998-107
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.
*** END OF DOCUMENT ***
Page Last Reviewed/Updated Wednesday, March 24, 2021