BECO-91-096, Part 21 Rept Re Trip Latch Roller Interference on GE AK-50 Type Breakers Resulting in Failure of Automatic Transfer Scheme.Initially Reported on 910724.Breakers Modified to Prevent Clevis Pin Interference.Ge Notification Encl
| ML20082E404 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 07/26/1991 |
| From: | Gina Davis BOSTON EDISON CO. |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| References | |
| REF-PT21-91 BECO-91-096, BECO-91-96, NUDOCS 9108010001 | |
| Download: ML20082E404 (18) | |
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BOSTON EDISON Pilgnm Nuclear Power Station Rocky Hill Road Plymouth. Massachusetts o236o George W. Davis Sene Vee President - Nuclear BECo 91-096 July 26, 1991 Regional Administrator U.S. Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, Pennsylvania 19406 License DPR-35
! Docket 50-293 i
Report of Defect or Noncompliance as Required by 10CFR21 Concernino General Electric AK-50 Tvoe Breakers Pursuant to the requirements of 10CFR21.21(b)(2), this letter provides written l notification of a condition at Pilgrim Station that constitutes a substantial l l
safety hazard within the context of 10CFR21.3 (befinitions). '
This defect was determined to be reportable pursuant to 10CFR21 at about 1345 l on July 24, 1991. Boston Edison Executive Management was advised at about 1630 l on July 24, 1991. Initial notification wzs made to the Pilgrim Senior Resident Inspector and the Office of Huclear Reactor Regulation (Ms. Nancy Campbell) on the afternoon of July 24th. Notification was made to the NRC Region I Office l
(Mr. John Rogge) on the morning of July 25th. Corrective actions have been completed t'or affected safety-related AK-50 breakers at Pilgrim as described in Attachment 1.
Attachment 1 describes the reportable condition involving trip latch roller i
interference on General Electric AK-50 type breakers that resulted in one of four breakers in our automatic transfer scheme failing to automaticaliy close i during routine surveillance testir.g. Attachment 2 is a report of. General Electric Company's root cause investigation of the breaker failure. Attachment l 3 is a copy of GE's SAL 306.0 notifying utilities of similar failures in type l AKR and AKS (not AK-50) breakers.
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BOSTON-EDISON COMPANY-Region I Page 2 cc: Director (3 copies)
Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission
-Hashington, DC 20555-Mr. P..'Eaton, Project Manager Division of Reactor Projects - I/II
-Office of Nuclear Reactor Regulation Mail Stop: 14D1 U. S. Nuclear Regulatory Commission 1 White Flint North 11555 Rockville Pike Rockville, MD 20852 Senior NRC Resident Inspector Pilgrim Nuclear Power Station r-L I
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ATTACHMENT 1 l
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Boston Edison Company Attachment 1 Page 1 of 2 10CFR21 NOTIFICATION ON GENERAL ELECTRIC AK-50 TYPE BREAKERS I Boston Edison Company has identified a deficiency involving trip latch roller interference on General Electric (GE) AK-50 type breakers employed at Pilgrim Nuclear Power Station (PNPS). The deficiency could impair the breaker's ability to close automatically (auto-close), thereby potentially degrading safety-related equipment. The deficiency was identified during investigation of a failure of breaker B602 to automatically close during routine surveillance testing of the Bus B-6 transfer scheme.
PNPS breaker B602 is part of the automatic transfer scheme that transfers the power source for 480 volt bus B6 from bus B1 to B2. The B1/82 transfer is an essential part of the overall PNPS design for safety-related loads. We consider the loss of B6 due to the failure of breaker B602 a substantial safety hazard as defined in 10CFR21.3 because failure to transfer could result in Low Pressure Coolant Injection (LPCI) Hotor Operated Injection Valves failing to open.
HYPOTHETICAL SCENARIO A large pipe break inside Primary Containment results in a depressurized reactor with High Pressure Coolant Injection (HPCI) and Reactor Core Isolation Cooling (RCIC) isolated. Low pressure Core Standby Cooling Systems (CSCS) systems are required for coolant inventory makeup. With a loss of offsite power both diesel generators will receive start signals and supply their respective Emergeacy Buses (A5/A6). Low pressure CSCS pumps are powered from the 4160V Bus A5/A6 and each independent system is capable of meeting the core cooling requirements. Assuming that the diesel that is feeding the Bus B1 fails to start (i.e., single failure), the auto transfer scheme will attempt to shift the swing Bus (86) loads to B2. If any of the AK-50 breakers fail to close or fail to open due to trip latch roller assembly interference, then 86 will remain deenergized and as a result the LPCI motor operated injection valves for both 'A' and 'B' trains will not open. As a result only one train of core spray would be available for core cooling requirements, a
NATURE OF THE DEFECT The defect causing B602 to malfunction is a consequence of interference between the trip latch roller assembly and the clevis pin. The interference resulted from the trip latch roller assembly having slightly different dimensions than previously manufactured ones. Attachment 2 provides a detailed description of the cause of failure, nature of the defect, and corrective actions taken. The interference problem is similar to that documented in GE Service Advice Letter (SAL) 306.0 issued on May 1, 1991. The SAL (Attachment 3) addressed breaker types AKR-75/100 and AKS-50, but not AK-50 type breakers.
CORRECTIVE ACTIONS There are 12 AK-50 type breakers in service at PNPS. Six (6) are safety-re!ated. These are B101, B102, B201, B202, B601 and B602. Breaker B602 was inspected and rebuilt by GE maintenance personnel after being identified as non-functioning by a routine test of the bus B-6 transfer system.
Boston Edison Company i
I Attachment 1 Page 2 of 2 1QCFR21 MOTIFICATION ON GENERAL ELECTRIC AK-50 TYPE BREAKERS The corrective action for B602 is complete. The other five safety-related breakers (B101, B102, B201, B202 and B601) were also inspected. Although none experienced the failure to close, it was possible to manipulate the operating mechanism in two of the breakers to create the interference problem. These two breakers were repaired in accordance with the recommendations contained in SAL 306.0.
Corrective action is complete for the safety-related AK-50 type breakers.
In addition, there are six AK-50 type breakers in non-safety-related service at Pilgrim. All six were visually inspected and found to have a forged (rather than welded) latch roller assembly indicating the potential for similar failures. However, none have experienced a failure to close and five are used in an application where they are normally closed. Since the failure mechanism does not prevent opening of the breakers, we consider the five normally-closed breakers satisfactory for continued use in their present applications. The sixth is a normally opEn supply breaker to the electrically driven fire pump that is tested weekly and has never failed to close automatically. In addition, Pilgrim station has a diesel driven fire pump in the event of failure of the electric fire pump. He therefore consider this breaker satisfactory for continued use in its present application.
A ATTACHMENT 2 i
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Boston Edison Company GE Nuclear Energy Attachment 2 Page 1 of 6, 10CFR21 Notification EFS91-050 July 17, 1991- cc: S. Ciavarre
?. H: Lough' tin TO: Jchn Pawiak
SUBJECT:
Investigation into the cause of failure expertenced by the station AK Circuit Ereaker No. 8602< .
REF: GE Proposal 291-1B74J-HK1 AX 2A 50 circuit Breaker S/N 0224A1125-310 AE BEco Designation #52-8602 GENE PRC 90 16 GE EO&C Service Advice letter No. 305.0
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I su-mary on July 1,.1991 GE Nucisar Energy personnel were at Pilgrim Station to investigate the cause of the referenced circuit breaxer s failure to close. It was reported that early in the current outage the breaker failed to close and latch when it was energized during a Dus transfer.
An Investigation by GE has determined that the most probable cause of this fatlure was an interference between the trip latch roller assembly L (reset latch) and the clevis pin.
Backarcyd 7
Breaker "B602" is a GE type AK-2A-50 low voltage power circuit breaker.
It is original plant equipment, that was purchased as a connercial item. 1t's application as safety related was determined by Boston Edison,.
L The circuit breaker was maintained, by GE, in 1987 and again in. April of 1990.
Breaker "8502" is one of four AK-50 circuit breakers used in a bus transfer scheme at Pilgrim Station. Because these breakers energize safety related switchgear busses they are subject to close scrutiny and any failure is of great concern to BEco.
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. Attachment 2 Page 2 of 6, 10CFR21 Notification i k 'B50P had failed to close
-h May of 1991 GE was not fied that orea erSECo reported that the breaker faile d; ring a bus transfer. Suosequently, the breaker receivad a and latch when it was energizec.
second close signal' and functioned croperly.
On July 1, brea..er' "8502" was released to GENE personnel for evaluation I
and repair. Dur!nt the "As-Found' int.pection a numoer of ciscrepant conditions were identificc. A cc plete listing of the discrepancies and a discLssion of each is attached. The ret result of this evaluatier-was : hat the most probable cause of the creakers failure to close was an interference between the trip latch roller assembiy and '
tne clevis pin.
During the 1987 maintenance program GE replaced the original latch 1 roller assembly (#83980410Gli with an OEM supplied replaceme
(#55BB272G1). j assembly was no longer available, L
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Replacement of the latch roller assembly is a normal pr P
bu ring is difficult to lubricate.
'r The interference is documented in the ED&C switchgear operation It Service 0738-306.0. This SAL was issued 5/1/91.
. Advice Letter (SAL) addresses breaker types AKR 75/100 and AXS-50 on in service at Pilgrim. The SAL did not address the AK-50 because the Switchgear Operation did not consider the use of the "new" trip latch roller assembly in the AX-50 circuit breaker as it is no longer in production, having been replaced by the AKS-50.
l' The SAL describes the interference as a source of intennittent trip-free operations and describes how to determine if a circuitThis in breaker has the problem.
- . during the 1987 and 1990 maintenance activities, f
i p Cerrective Actions l- ihe tnspection and repair of breaker "B602" was accomplished GE under the-GENE QA Program. The applicable manual was QAN 002 Rev.1.
l procedures, approved by BECo for AK 2A-50 maintenance, were utilized L
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' Oue to outage schedule constraints it was not possible obtain The another reset-intch roller assembly as recommended in the service advice.
iatch and clevis pin were machined (at site) to establish the clearance This repair was made in accordance with l
I described in the SAL.
direction frcm the manufacture.
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- All: discrepent conditions were corrected, the breaker was operated both manually and electrically and returned to service.
The remaining five safety r. lated AK-50 breakers were also inspected.
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Although none had experienced a trip free operation (failure to close) f it was possible to manipulate the operating mechanism in two create an interference.
L these units to eliminate the condition per the SAL recommendation.
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Boston Edison Company Attachment 2 Page 3 of 6, 10CFR21 Notification Preventive Men ures SENE Field Servi:es wiii revise its maintenance crocedures to include an inspection to insure adequate cleararce exists betwesr the latch
" roller assembly and the clevis oin 9! GENE has inspected all of the station safety related AK-50 circuit creakers tc insure that they are free of the potential inter #eranca.
As the interferen:e is a random oc:urrence, it was :ecidsd not to inscoct the non-safety circuit breakers at this tima. These urfts wars insoccted and tested in 1987 and again 1990 and have not experienced trip free operations. Based on the operating history, SECo has elected to perform the inscecticn on these breakers as they receive there next scheduled maintenance.
GENE Regulatory and Analysis Servicas (RLAS) and the GE EDIC Switchgear Operation have bean advisec of the need to supplomant the information contained in the SAL. This notification will be forthcoming.
Because GENE RLAS has previously notified both the BWR utilities (May, 1991) and the NRC (May 24,1991) about this interference condition, a follow up communication will be provided upon conclusion of the GENo ED&C Switchgear Operation evaluation of the need for a SAL supplement.
further GENE RLAS evaluatien as to 10CFR Part 21 safety significance will be undertaken because GENE does not have the application information necessary to conduct sucn an evaluation. The information contaned in this reoort, the reference GENE PRC 90 16 coecunication to BEco, and the Pilgrim breaker application information should allow BECo to complete such a 10CFR Part 21 evaluation.
Should you require additional information on this matter please do not hesitate to contact me.
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._ .i L 0H-Boston Edisor. Company Attachment 2 Page 4 of 6, 10CFR21 Notification ATTACHWERT A EFS-31 0050 i
Boston Edison Pilgrim Statten '
Type A<-2A-50 Circuit Breaker Station Designation; 52-B602 S/N 22A1126-310 AE The following ciscrepancies were identified during an Inspectten of the referenced circuit breaker tenducted at Pilgrim Station on 7/1 and 7/2/5).
The reason for performing the inspection was to determine the cause of the failure to close (trip free operation) experienced by the breaker in May of '91.
- This breaker was converted to Micro Versa Trip in 1987.
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- 1. The trip latch buffer stop was found to be out of position. As a result the positive intericck pin to trip paddle clearance and the flux shifter to trip paddle gap were out of specification.
Loose mounting hardware was found on the trip latch buffer stop.
The service was performed This breaker on site under the was maintained BECo by GE in 1990.One of the primary reasons for this QA Program.
service was to confirm that all of the fasteners in the breaker were in pl ace. A review of the 1990 document package indicates that the breaker was complete and properly adjusted.
The loss of clearance could cause a trip free operation. However, since it is not an intermitter.t condition it is probably not the cause of the failure under investigation.
- 2. The prop to link roller and trip latch to roller clearances were out of specification.
Both clearances should have been from .015 .030 inches. Exact as found data was not taken, it was only noted that both adjustments wers out of specification.
However In combination these could result in a trip free operation.
Civen the extensive testing of the breaker by GE and BECo in 1990 this does not appear to be true in this instaace. This condition has probably existed since the 1990 services.
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Attachment:
-2 Page 5 of 6. 10CFR21-Notification t
- 3. One of;two snap rings which hold the clevis sin in place was nissing and the pin snowed s15ns of "namering". A check of the mechanism revealed an interfererce could exist tetween tha clevis pin and the
-iatch roller assemoly depending on the ald gnment of the various
,echanism parts.
As was noted previously documented from the--1990 service confirmed that
. the snap r4ng was in place a, t.at tirre.
The interference was found to exist when the reset latch and clovis.pir, were trayed to worst case -alignment. This would explain the intermittent nature of 1.he failure.
Tne reset latch probably hit the clevis pin durirg the first closing operation, knocking tne snap ring off, and driving the pin out of its path. This interference would definitely cause 2 trip-free operation.
With the alignment changed the breaker successfully closed on its next operation.
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' This condition is described in sal. 306.0 and is probably the cause of the failure.
The latch roller assembly and clevis pin were machined to provide -l adequate clearance.
'4 The cross-arts buffer to buffer stop clearance was not the same on both
' sides of the cross arm. The right sido had slightly more clearance.
If excessive, the unavon gaps.could (over time) cause excessive In wear any in l the breaker, However, in this instance it was not excessive. d l
'. event it would not cause the breaker to "go trip free .
- 5. Tho breaker interlock asseenbly was bent.
4 This was probably do'ne when the breaker was being racked in or out of
.the cubicle. : 0.ce the breaker was properly racked in -and operated it would not have been a problert it.could indicate missadjustment of the cubidle. '
,The cubicle was serviced this cutage. A check prior to installing the 7 breaker did not reveal a problev. .
S. The flux shifter is mounted to the breaker frafre with m1 chine screws and nuts with nylon locking insurts. These fasteners turned, however the assembly did not move.
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Boston Edison Company Attachment 2 Page 6 of 6. 10CFR21 Notification
- 7. The flux shifter tric rea has a double lock not configuratto.n used to maintain its adjustment. The lock nut was found to be ionse. The adjustmen- was acceptab'e. Tnis aisc wou'.d not have caused the trip free operation.
- 3. The trip shaft return spring was defctmed. A couple of the turns on the sprir.g were elongatec. Had the elongation teen sufficient to affect the breskers cperatico the malfunctio.1 would not have been intermitten;. This also can be aliminated as tne cause of *.ne failure.
The spring was replacec.
- 9. The shur.1 trip armature was not centered on the trip paddle. Inis would not haYe caused 5 problem.
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a2_ -- nr ,_-, iL L 4 A' A e . he,AL*,-- no 4 rL- 9 4 k 4 4.As 4 J,ai@4-wA-6M*1.A-e ou-*4a1di.-L.- a6-- nAnuA-sa.- 4M-%,ou m wsas&rAirAA4s J u m. .M -- + 4+-s ATTACHMENT 3 9
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10CFR21 Notificttion i
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, . , - s May 17, 1991 cc: E.S. Kraft W.S. Clancy F.N. Famulari H.V. 0heim Mr. R. V. Fairbank M.E. Shepherd, GE Nuclear Engineering Manager Boston Edison Company 25 Braintree Hill Office Park Braintree, MA 02184 REC'D M AY 21 1991
Subject:
GE PRC 9')-16, GE AKS/AKR DC Circuit Breake"W. S. CLANCY
Dear Mr. Fairbank:
The following information is supplied as part of the GE Program for evaluation of Potentially Reportable Conditions in satisfaction of the U.S. 2 ode of Federal Regulations 10 CFR Port 21. GE has concluded that this information is Germane to Safety and that a Reportable Condition does not exist within the scope of technical information available to GE.
Boston Edison should evaluate this information as it relates to existing or future plant equipment, conditions, procedures or plans.
GE is notifying all BWR owners of the attached information. GE is not aware that this information affects Pilgrim Station, however, it is being supplied as a contingency. This information will be made available to the NRC on or about May 24, 1991.
Sincerely, i
k A. David Himler Nuclear Services Manager Attachment Notice This 10 CFR Part 21 information pertains only to GE BWRs. GE Nuclear Energy (GE-NE) has not considered or evaluated the applicability, if any, of this information to any plant or facility other than GE BWRs. The evaluation was for the GE-NE designed applications and did not include any application in plants other than those for which the equipment was purchased from GE-NE. Determination of applicability of this information to a specific GE BWR and implementation of recommended action are the responsibilities of the Owner of that BWR.
I Boston Edison Company ATTACHMENT Attachment 3 Page 2 of 5, 10CFR21 Notification i
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Background
During receipt inspection of two GE Model AKS-50 circuit breakers at a BWR/3 plant, it was discovered that the clevis pin in both breakers showed evidence of contacting the reset latch on the closure stroke. If this
+ occurs during operation, the clevis pin could displace the reset latch and
. cause the breaker to fail to close. Depending on the plant specific safety application (e.g., an ECCS application), this postulated condition
- could have safety significance. ,
l In 1989, a similar clevis pin condition was discovered at a BWR/2 plant. l GE-NE performed a 10 CFR Part 21 evaluation and concluded that this was the only plant, to GE's knowledge, that had experienced this particular breaker problem. Therefore, this condition represented a random failure and was not a precursor of a generic deficiency in the circuit breakers.
The condition was not communicated to other utilities, Additionally, in 1988, GE Electrical Distribution and Control (ED&C), the breaker product department, had implemented an unrelated product imprpvement on the circuit breaker design. ED&C concluded that this improvement would most likely eliminate any future clevis pin _ interference problems in breakers manufactured after 1988. However, the recent
- condition found at the BWR/3 plant indicates that the product improvement did not eliminate the problem and that the condition may be a generic deficiency. ED&C also concluded that this condition could occur on AXS-50, AKR-75 and AKR-100 circuit breakers shipped prior to July 1990.
No date codes have been established.
Safety Basis GE-NE's evaluation of the circuit breaker deviation found at the BWR/3 concluded that this condition is not reportable for this plant because the deviation was found upon the utility's receipt inspection and the breakers 1 were not accepted into their stock.
For other'potentially affected BWR utilities, GE-NE is unaware of the utilities' specific applications and, therefore, cannot determine the safety impact'of a deficient circuit breaker. GE will inform all BWR utilities of the potential for this condition so that the utilities can evaluate their installed equipment and application.
Corrective Actions and Preventive Measures GE ED&C has modified the AKS-50, AKR-75 and the AKR-100 circuit breaker designs so that any breakers supplied after June 1990 will not have the clevis pin interference problem.
GE ED&C issued the attached Service Advice Letter (SAL), which advises utilities to inspect all suspect breakers at the next planned maintenance unless a trip-free malfunction has occurred. In this case, the inspection should be made immediately. The attached SAL 306.0 also instructs users
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. Boston Edison Company Attachment 3 Page 3 of 5, 10CFR21 Notification
'of AKS-50 (replacement for AK 50), AKR-75 and AKR-100 circuit breakers to use the SAL inspection procedures to determine the adequacy of the clearance between the reset latch and clevis pin.
For non-safety related replacement parts, utilities should contact their-Customer Service Representative at GE ED&C Switch Gear Operation Product
! Service Department in Burlington, Iowa. For safety related replacement I parts, utilities should contact their Customer Service Representative at GE Nuclear Energy in San Jose, California, j i
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- 50scon Edison Company S UBJICI: INTERMITTENT TRIP-FREE 3REAXER Attachment 3 Page 4 of 5, CAUSED DY INADEQUATE CLEARANCE 10CFR21 Notification BETWEEN RESIT LATCH.AND cLgvIs BW ITCIGBAR PIN OPERATION ___
F* 073B SA No.
SERVICE ADVICE 8WGR OPER 3c6.0 Sub4act Product All AKR-75/100 and AXS-50 breakers shipped prior to July j 1990.
I Problem There have been instances reported of inadegaate clearance between the resat latch # 56BB270P1 and clevis pin 4 3 9 A7573p229 in such avant lateral =cvement =ay cause these parts to centact each other during a clesing eparation possibly pushing the reset relaer out of align = ant and preventing the trip latch fren l res'atting . A trip free operation =ay result.
If attempted operations continue, the prop latch bracket t
pessibly could knock the retaining ring off the clavis pin when they contact. We have had ene report of this occurring in the field.
l Continued operations could result in a =ajor breaker failure.
l Recommended Actie 1
1 Inspection shculd be mada at the next planned maintenance unless a trip-free =alfuncticn has occurred, and in such a case, inspection should be ade i= sdiately.
E' corrective Action i
1 ihe breaker must be cpan with all power re:cvad and close springs di;scharged then rancved fre cubical, The best view can be obtained by turning the breaker over carefully on it's primary stabs te view the =echanism frem the bottem.
i See Maintenanca Manual #GIK-64460, page 26, 27 Figure 22A, B, I c, D. The breaker should be in the resa pcsiticn as shown in flyure 223. Inspect for the relativa pccitien of rasat latch (part l 14) and clavis pin (part 12), with parts pushed to shev vorst case for interfarance. Clavis pin shculd be pushed to the right and raset latch pushed to the left. Fiald units will be acceptable if there is clearance of at least 0.00S inches. See attached sheet for better clarification.
In the event that clearance is inadequate, a replacanent part 5683272G1 should be installad, which GE will provide at ne ecst te tha user, although the field installation is the responsibility of the user.
PREPARED BY ISSUID BY DATE SUPERSEDES PAGE 1 IS8CE DATED er 2 COEN JAEGER DON LIsnt? 5-1-4i ( N E',M '
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