ML17187A535
| ML17187A535 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Salem  |
| Issue date: | 07/24/1996 |
| From: | Chaffee A NRC (Affiliation Not Assigned) |
| To: | Staring K Public Service Enterprise Group |
| References | |
| NUDOCS 9607260074 | |
| Download: ML17187A535 (6) | |
Text
July 24, 1996 15'0 -.J. tf9
~o-J Mr. Ken Staring System Engineer Public Service Electric and Gas Company Salem Nuclear £enerating Station P. 0,. Box 236
- ~.'
4 Hancocks Bridge NJ 08038
SUBJECT:
REQUEST. FOR A TECHNICAL REVIEW OF JA DRAFT INFORMATION NOTICE REGARDING RECENT FA~LU~ES OF MAGNE~BLAST CIRCUIT BREAKERS Mr. Staring:'
~ -
The U.S. Nuclear.*Regul'atory Commission" (NRC) is planning to issue an information notice discussing t~e _pr9blems*with GE.Magne~Blast circuit breakers recently experienced at t~e Dresd~n ~uclear.P6wer St~tion, Unit 3 (Docket #05000249), and the Salem Nucl~ar Geheratin~*Station (Docket #05090272). We ask that you review the enclosed draff.ofttiat iiriformation notice.to e*nsure technical accuracy. Your
- co.operation in* this. matter js.appr~cfat.ed; *; Please return any comments you may have as.~con as po'ss.ible~: ' A copy of t,hfs. reque,~t. and your response wi 11 be pl aced in. the. P,uh l'i c.Document: Rooin for 'rev-i1ew 'bi' the public...Your re~ponse should be mail:ed to:
J
'i-u.*s. N'ude*~'f Re~ulato-~y C~mmjssio*~.: ""
wash i ngton' oc>-20555.:000 r '. *' /
ATTN: Vern Hqd,ge, 'NR~/PECB..... :
MAIL STOP: OllEl.
This letter follows a facsimile**'.G'Omm~nication to you on July 22, 1996.
We would appreciate your prompt rev.lewt *PJeiise address any questions you may have on this matter to Vern Hodge of my staff at (301) 415-1861. If no comments are received by close of business July 25, 1996, we will assume the technical information in the notice is correct.
DI STR I BUT ION BKGrimes AEChaffee CVHod e OFFICE PECB:NRR PECB DATE for DRPM R/F
[Original signed by R. L. fumig]
Alfred E. Chaffee, Chief Events Assessment and Generic Communications Branch Division of Reactor Project Management Office of Nuclear Reactor Regulation PDR PECB R/F
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Fri 19 Jul 96 1436 UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555-0001 July xx, 1996 NRC INFORMATION NOTICE 96-XX: FAILURES OF GENERAL ELECTRIC MAGNE-BLAST CIRCUIT BREAKERS Addressees All holders of operating licenses or construction permits for nuclear power reactors.
Purpose The U.S. Nuclear Regulatory Commission is issuing this Information Notice (IN) to alert addressees to recent failures of General Electric (GE) medium-voltage Magne-Blast circuit breakers at the Dresden Nuclear Power Station, Unit 3, because of hardened grease and at the Salem Nuclear Generating Station because of mispositioning of the prop pin. A separate information notice is being prepared to discuss failures related to refurbishment practices, including recently discovered broken lock washers from hydrogen embrittlement at Salem.
It is expected that recipients will review t~e information for applicability to their facilities and consider actions, as appropriate, to avoid similar problems.
However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is required.
Failure Due to Hardened Grease Description of Circumstances On June 11, 1996, at the Dresden Nuclear Power Station, Unit 3, a 4.16-kV GE Magne-Blast power supply breaker associated with*a low pressure coolant injection loop failed to open on demand from tbe control room following a surveillance run of the pump.
Examination of the failed breaker indicated hardened grease in the breaker.
In subsequent testing the licensee observed two indications of potential
~rease hardening on four similar breakers.
Thase four breakers were formerly in service but were out of servi(e at the time of testing.
In one of the two breakers, which had a high number of cycles, hardened grease was observed on the trip lever roller bearing, making the mechanism "stiff" to operate and unreliable. In the second breaker, the latch mechanism moved freely but fibrous material from an adjacent bushing was observed in the bearing grease.
From its subsequent root cause investigation, the licensee concluded that the hardening of grease in the "trip latch roller bearing" was the most likely cause for the failure but discounted that the grease hardening was caused by the fibrous material.
The licensee identified 13 safety-related breakers on Unit 3 as susceptible to this failure mechanism because of the number of operations since the last
IN 96-XX July xx, 1996 Page 2 of 5 overhaul.
On June 20, 1996, the Dresden licensee initiated a shutdown of Unit 3 and contracted with the vendor, GE, to completely overhaul each of these 13 breakers and the similar ones on Unit 2.
Discussion In 1989, the NRC Maintenance Team Inspection at Dresden identified a lack of lubrication of these. same breakers.
At that time, the licensee instituted a preventive maintenance program as.a corrective measure.
Recent resident inspector review of that program indicates that the Dresden licensee had not fully incorporated vendor {GE) reconvnendations.
The GE vendor manuals {GEK-7320F and GEI-88771D) and GE Safety Advisory Letter
{SAL) 354.1, dated August 25, 1995, on Magne-Blast circuit breakers recominends that these circuit breakers be lubricated once every two years.
The licensee,*
however, had been using a 6-year maintenance period and had not maintained the failed breaker for 6.5 years.
The following factors may have contributed to grease aging and hardening over this protracted maintenance period:
{l) A.
degreaser was used in vendor-reconvnended maintenance in 1989; {2) Lubricating oil used contained an additive; {3} Heaters were installed within the breaker cubicles for equipment qualification purposes; and {4} Grease originally packed in the trip latch roller bearing contained lithium.
The vendor no longer recommends use of this type of grease.
Failure Due to Mispositioning of Prop Pin Description of Circumstances' On January 5, 1996, at the Salem Nuclear Generating Station, a 4.16-kV GE Magne-Blast power supply breaker associated with a service water pump failed to latch closed on demand from the control room.
On January 30 - February 1,.
1996, during the root caus~ investigation, the same breaker failed to latch closed on the seventh attempt after successfully closing six times.
On February 15, 1996, a different service water pump breaker at Salem failed to latch closed. This breaker had been returned to service after an overhaul at the ~~ Apparat**- Service Center in ?hiladelphia.
On September 27, 1993, at the Maine Yankee Atomic Power Plant, a 4.16-kV GE Magne-Blast power supply breaker associated with a component cooling water pump failed to latch closed on demand from the control room.
The licensee enabled this breaker to close reliably by replacing the installed prop spring with a heavier prop spring.
Discussion IN 96-XX July xx, 1996 Page 3 of 5 IN 94-54 alerted licensees to failures of Magne-Blast breakers to latch closed and discussed the vendor recommendation to add a second prop spring to correct the *failure.
IN 94-54 pointed out that breakers that are grossly out of adjustment or badly worn may fail to latch closed even with the addition of a second prop reset spring. This phenomenon is technically called "failure to latch closed" ~ut is often termed "trip free.
11 Through the use of high-speed digital video equipment at Salem, GE has learnec that the failure occurs when the prop pin fails to achieve the required position above the prop and causes th~ prop to hit the prop pin.
Such impact causes the prop to bounce back, allowing the prop pin to miss the prop; in this way the breaker fails to latch in the closed position.
The impact also causes the leading edges of the prop to become chipped and flattened.
In agreement with the vendor, the Salem licensee believes the prop* pin may fail to achieve the required position because of (1) the age and wear of the breaker, (2) misalignment of the prop mechanism, (3) errors that may be introduced in the alignment of the operating mechanism causing the prop and or articulated mechanism to twist, (4) misalignment of the stationary cubicle in which the breaker operates, and (5) misadjustment of the opening springs.
The cause of any particular failure to latch may have to be determined on an individual basis.
The following vertical lift circuit breakers with ML-13 mechanism which have close and latch ratings of 77 kA or above may fail to latch closed under certain conditions:
4.16 KV-250MVA-8~ -9HB 7.2 KV-500MVA-6HB 13.8 KV-750MVA-5, -6HB 4.16 KV-350MVA-2H 13.8 KV-lOOOMVA-3, -4H The Salem licensee concluded the following conditions indicate that a breaker is likely to fail to latch closed:
The prop stop pin is not in the fully forward position in the inspection winiow when the breaker is closEd.
The leading edges of the prop are chipped or have a flattened tip.
(The prop tips may be viewed through both inspection holes.)
- The. breaker has a previous history of intermittently failing to latch closed.
If the arcing contacts have overstroked, the tips of the arcing contacts will probably be damaged by their impact on the dividers in the stationary arcing contacts, and the buffer blocks may be cracked.
There is unequal prop wipe, ind:cating prop twist.
IN 96-XX July XX, 1996 Page 4 of 5.
In agreement with the vendor, the corrective action taken at Salem was to raise the preload on the opening spring to slow down the closing action, thus allowing more time for the prop to get in~o position.
However, this approach is limited by the minimum speed that must be achieved by the moving contacts in order to maintain the 78-kA (high momentary) close-latch rating.
The GE Specialty Breaker Plant (SBP), where the circuit breakers were originally manufactured, is pursuing an alternative solution: (1) replacing the second prop spring with a heavier one, (2) installing a second prop stop to restrict the prop movement on the left hand side, and (3) adjusting the wipe on the main contacts.
GE SBP informed the NRC that it has not completed testing ~his remedy, needs some time to manufacture the required parts, and will issue a SAL on this subject.
Related Generic Communications
- 1.
Information Notice 95-22, "Hardened or Contaminated Lubricants Cause Metal-Clad Circuit Breaker Failure," April 21, 1995
- 2.
Information Notice 94-54, "Failures of General Electrii Magne-Blast Circuit Breakers to Latch Closed," August l, 1994
- 3.
Information Notice 94-02, "lnoperability of General Electric Magne-Blast Bre.aker Because of Mi sa 1 ignment of Close-Latch Spring," January 7, 1994
- 4.
Information Notice 93-91, "Misadjustment Between General Electric 4.16-KV Circuit Breakers and Their Associated Cubicles," December 3, 1993
- 5.
Inform~tion Notice 93-26, "Greaie Solidification Causes Molded.Case Circuit Breaker Failure to Close," April 7, 1993
- 6.
Information Notice 90-41, "Potential Fail~re of General Electric Magne-Blast Circuit Breakers and AK Circuit Breakers," June 12,* 1990
- 7.
Information Notice 84-29, "General
~lectric Magne-Blast Circuit Breaker Problems," April 11, 1984
- 8.
Bulletin 74-09, "Deficiency in General Electric Model 4KV Magne-Blast Breakers," August 6, 1974
IN 96-XX July xx, 1996 Page 5 of 5 This information notice requires no specific action or written response. If you have any questions *about the information herein, please contact on~ of the technical contacts listed below or the appropriate NRR project manager.
Brian Grimes, Director Division of Reactor Program Management Office of Nuclear Reactor Regulation Technical Contacts:
D. Skeen, NRR (301). 415-1174 E-mail: dls@nrc.gov
- S. Mitra, NRR
... (301) 415-2783 E-mail: skml@nrc.gov K. Naidu, NRR (301) 415-2980 E-mail: krn@nrc.gov J. Shannon, Region I (610) 337-5132.
E-mail: jmsl@nrc.gov
Attachment:
List of Recently Issued NRC Information Notices