ML20012D921
| ML20012D921 | |
| Person / Time | |
|---|---|
| Issue date: | 03/21/1990 |
| From: | Berlinger C Office of Nuclear Reactor Regulation |
| To: | Strambach G GENERAL ELECTRIC CO. |
| References | |
| NUDOCS 9003290093 | |
| Download: ML20012D921 (5) | |
Text
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March 21, 1990 Mr. George Strambach General Electric Nuclear Energy Division General Electric Company 175 Curtner Avenue San Jose, California 95125
Dear Mr. Strambach:
SUBJECT:
PROPOSED NRC INFORMATION NOTICE ON THE P0TENTIAL FAILURE i
0F GENERAL ELECTRIC MAGNE-BLAST CIRCUIT. BREAKERS Enclosed for your review is a draft copy of a proposed NRC Information Notice on the Potential Failure of General Electric Magne-Blast Circuit Break-ers.
Specific comments regarding the technical accuracy of this information notice are requested from General Electric.
I would appreciate you trans-mitting.any comments developed during your review of this proposed information 4
notice concerning possible technical inaccuracies by March 30, 1990.
Sincerely, 4
Original Signed By Carl H. Berlinger Carl H. Berlinger, Chief Generic Communications Branch Division of Operational Events Assessment Office of Nuclear Reactor Regulation
Enclosure:
Draft NRC Information Notice i
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UNITED STATES NUCLEAR REGULATORY COMMISSION P4g OFFICE OF NUCLEAR REACTOR REGULATION
'g WASHINGTON, D.C. 20555-l March XX, 1990 1
NRC INFORMATION NOTICE NO. 90-XX:
POTENTIAL FAILURE OF GENERAL ELECTRIC MAGNE-BLAST CIRCUIT BREAKERS i
Addressees _:
All holders of operating licenses or construction permits for nuclear power reactors utilizing General Electric Company (GE)'4.16-350 and 4.76-250 series Magne-Blast circuit breakers used in 4.16-kV applications.
Purpose:
i This information notice alerts licensees to three safety problems involving j
possible failure of GE 4.16-350 and 4.76-250 Magne-Blast circuit breakers.
Both of these types of circuit breakers utilize ML-13 operating mechanisms to i
close or open them. GE informed the NRC-that it is aware of these problems and that GE routinely checks and corrects these specific problems if the circuit breakers are serviced at one of the four GE service centers in the United States.
The NRC is aware that some licensees have their circuit breakers repaired or serviced at places other than the four GE service centers.
It is expected that recipients will review this information for applicability and consider actions to prevent this or similar. problems at their facilities.
Suggestions contained in this' notice do not constitute NRC requirements; therefore, no specific action or written response is required.
Description of Circumstances:
i On April 7,1988, a service water pump at Peach Bottom Atomic Power Station (PBAPS)wouldnotauto-start. The pum attempt to close but would trip free. p circuit breaker (GE 4.16-kV) would The defective circuit breaker was replaced. A broken prop reset spring had prevented the defective circuit breaker from closing. The licensee for PBAPS authorized an independent analysis of the failed spring. This analysis revealed that the spring failed at a right angle bend in the wire as a result of a metal fatigue crack caused by a lap in the wire. The licensee authorized the analysis of five additional. prop reset springs. Two of the five springs tested had surface' laps similar in. depth to those of the original spring; however, no fatigue-or surface-induced cracks were found on any of the five springs. The licensee intends to replace the prop reset spring every 2000 cycles.
On August 16,'1989, a GE AMH-4.76-type circuit breaker failed to remain shut at :
FitzPatrick nuclear power plant as a result of a broken prop reset spring, i
This circuit breaker had operated for 1625 cycles. Subsequently, the licensee replaced the prop reset springs on all safety-related circuit breakers that had DRAFT 1
e IN 90-XX March XX, 1990 Page 2 of'4 operated for more than 900 cycles. On the basis of the practice recommended at PBAPS, FitzPatrick will replace the prop springs after_2000 cycles of operation.
On November 5,1988, while FitzPatrick was shut down for refueling, a 4.16-kV residualheatremoval(RHR)servicewaterpumpmotorcircuitbreakerfailedto trip on demand.
Inspection of the 4.16-kV circuit breaker revealed a bent snap ring (retaining ring) and two bent spacer washers (shims) in the bottom of the circuit breaker frame. The retaining ring and shims are part of the " prop-pin" assembly and are intended to establish the axial position of the prop pin. The' ML-13 operating mechanism opens-or closes the circuit breaker's main electrical contacts and uses a linkage that is maintained in that position by a " prop" at one point in the linkage. When the circuit breaker is tripped, the trip-latch is operated, causing the linkage to collap(makes the linkage rigid) and-se and a spring 4 open the main contacts. The prop supports the prop pin prevents the stored energy from closing the springs that in turn close the circuit breaker's main electrical contacts.
In an ecceptable prop-pin assembly, the prop pin is aligned to strike the prop and is secured in that position with shims and a retaining ring.
It is believed that the pro prop in the failed circuit breaker were not aligned properly,p pin and the and the misalign-ment permitted the prop to strike the retaining-ring and the shims instead of the prop pin, causing the retaining ring and the shims to bend and eventually to fail. With the loss of the retaining ring and the shims from the prop-pin assembly, the prop pin was free to drift far enough to hang up in the frame and eventually to prevent the circuit breaker from tripping.
FitzPatrick reported (Licensee Event Report 88-014-01).thatthis'andother circuit breakers had been refurbished during 1986 and 1987 at the GE service center located in King of Prussia, Pennsylvania. -During the refurbishing-process, GE technicians apparently did not specifically verify ~the alignment of the prop pin.
If the prop pin is not properly aligned and secured in the correct position with a retaining ring and spacer washers, then the prop pin will be free to drift far enough to hang up and ultimately )revent the circuit breaker from tripping. The licensee corrected the problem >y properly-aligning the prop pin with spacers and securing it in that position with a snap ring.
As a result of this problem, GE has imposed'an additional inspection step to check the alignment after reassembling the circuit' breaker. GE informed the-NRC that the other three GE service centers have'been alerted to this problem and that corrective action has been taken to preclude recurrence of this problem.
On December 2,1989, a GE AM-4.16-350-1H-type circuit breaker being used to operate a safety injection pump motor failed to remain closed at the Turkey Point nuclear power plant Unit 4 (Turkey Point) as a result of a broken prop reset spring. The circuit breaker had operated for approximately 1400 cycles before the failure. The broken prop reset spring was replaced and the circuit breaker was returned to service on December 3, 1989. Florida Power and Light Company (FPL), the licensee for Turkey Point,- examined the failed spring-metallurgically and determined that the fatigue fracture occurred at'the end of the coil where the wire was bent 90 degrees to form the hook.
Examination of the surface revealed a number of small extrusion marks which ran longitudinal i
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IN 90-XX o
March XX, 1990 Gage 3 of 4
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to the wire axis along the entire length of the s> ring.- FPL has established a schedule to replace the existing springs on all tie remaining circuit breakers with a new style spring supplied by GE. The new GE springs are reported to I
have a slight taper on the spring barrel before the hook is formed.
In a letter dated November 18, 1988, the licensee for the Wolf Creek nuclear power plant notified the NRC that welds attaching the latch roller link striker plate to the operating mechanism frame were observed to be broken on 12 of 16 GE AM-4.16-350-2H Magne-Blast circuit breakers. The licensee determined that the welds were not strong enough to resist impact loads generated during circuit _
breaker operation and subsequently had to be repaired. Broken welds on striker plates were previously identified in the mid-1970s and were the subject of GE Service Advisory Letter (SAL) No. 325.1, dated March 3,1978. SAL No. 325.1 identified this problem and recommended that the striker plate be rewelded to the frame. The SAL stated that this AM-4.76-250-1 and 4.16-250-6 (H or C) problem should be checked only in
-type circuit breakers and several other 5, 7, and 13-kV circuit breakers shipped between 1964 and 1973. As the Wolf Creek-type circuit breakers are not listed in SAL No. 325.1, it is possible that similar broken welds can exist in other types of circuit breakers outside
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the scope of the SAL.
During an NRC inspection in January 1990 at the GE service center in Philadelphia, Pennsylvania,)the inspectors determined that the D50H15-and D50H47-type grease-(blackgrease in the stationary cubicles of the switchgear ma completely removed before the D50HD38-type grease (red grease)y not have been was applied.
GEServiceInformationLetter(SIL)No.448,datedDecember 23, 1986, expressly requires that the black grease be removed completely before applying the red grease.
It is possible for licensees or their service agents to overlook removing the existing black grease in the stationary cubicles. The black grease in the-stationary cubicles is not compatible with the red grease in the overhauled draw-out circuit breakers. When GE overhauls the draw-out circuit breakers, GE reminds the licensee to remove the black grease from the stationary cubicles.
Licensees wno overhaul their draw-out switchgear at locations other than GE service centers, should consider measures to ensure that both the stationary cubicles and draw-out circuit breakers are properly lubricated with red grease supplied by GE.
Discussion:
Licensees may want to review this information to determine the applicability -
of the failure mechanisms to circuit breakers at their plants and to ascertain if their circuit breakers are susceptible to this possible failure.
Those addressees that are utilizing service facilities other than GE facilities are reminded that the circuit breakers that failed were outside the population previously identified by GE and that the correct grease should be used in both stationary cubicles and draw-out circuit breakers in the switchgear.
Licensees and construction permit holders may wish to review the performance of their circuit breakers in light of this information.
-IN 90-XX March XX, 1990' Page 4 of 4
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No specific action or response is required by this information notice. -If you have any questions regarding this notice, please contact the Regional Administrator of the appropriate NRC office or the technical contact listed below.
i Charles E. Rossi, Director.
4 Division of Operational Events Assessment Office of Nuclear Reactor Regulation 1
Technical Lentact:
K. Naidu, NRR (301)492-0980 lL
Attachment:
List of.Recently Issued NRC Information Notices i
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