ML20154A878

Rev 1 to Part 21 & Deficiency Rept 88-02 Re Improper Mounting of Armature Button on Undervoltage Device Armature. CRD Trip Breaker Removed from Svc & Placed in QC Quarantine & Maint Procedure Revised for Armature Defect

ML20154A878
Person / Time
Site:	Rancho Seco
Issue date:	05/09/1988
From:	Andognini G, Rutter S SACRAMENTO MUNICIPAL UTILITY DISTRICT
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
References
REF-PT21-88, REF-PT21-88-060-000 88-02, 88-2, GCA-88-263, PT21-88-060-000, PT21-88-60, NUDOCS 8805160219
Download: ML20154A878 (5)

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SACRAMENTO MUNICIPAL UTILITY DISTRICT C P. O. Box 1583o, Sacramento CA 95852-1830 (916) 452-3211 AN ELECTRIC SYSTEM SERVING THE HEART OF CALIFORNIA CCA 88-263 MAY 0 91988 U. S. Nuclear Regulatory Commission Attn: J. B. Martin, Regional Administrator Region V 1450 Maria Lane, Suite 210 Halnut Creek, CA 94596 Docket No. 50-312 Rancho Seco Nuclear Generating Station License No. DPR-54 10 CFR 21 REPORT 88-02, REVISION 1: MANUFACTURING DEFECT ON H0 DEL 269C282G2 GENERAL ELECTRIC UNDERVOLTAGE DEVICES

Dear Mr. Martin:

As requested by members of your staff, the Sacramento Municipal Utility District hereby submits Revision 1 to 10 CFR 21 Report 88-02.

Please contact me if you have any questions. Members of your staff with questions requiring additional information or clarifichtion may contact Mr. Steve Rutter at (916) 452-3211, extension 4674.

Sincerely, An $7 Chief Executive Officer, Nuclear Attachment PC IIYII 2 04 0 cc w/atch:

G. Kalman, NRC, Rockville (2)

A. D'Angelo, NRC, Rancho Seco J. B. Hartin (2)

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In accordance with 10 CFR 21.21(b)(2), the Sacramento Municipal Utility District hereby submits a written report concerning a manufacturing defect on undervoltage devices supplied by General Electric Company, Philadelphia Pennsylvania. The manufacturing defect is the armature "button" improperly mounted on the undervoltage device armature. This defect prevented proper operation of the Control Rod Drive (CRD) trip breakers.

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION mRovso ous o siso-oio.

EXPlaES: 8.'3i'88 F ActuTY psAASE til DOCKET NUMSE R (21 LIR NUMSER 46) PA04 m n.. " w.w.w :n Ranchn Roen Niteloar (onoratinn Rtatinn 0 l5 l0 l0 l0 lq ] 1l7 dg -

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nl3 nl7 0F gl4 l men - . w - = c % 3m w.n o, Comoanv/ Facility In accordance with 10 CFR 21.21(b)(2), the Sacramento Municipal Utility District (SHUD) hereby submits a written report to document the defective manufacture of the undervoltage device (UVD) installed on the General Electric type AK2-25 Control Rod Drive (CRD) trip breakers.

Resoonsible Officer G. Carl Andognini, Chief Executive Officer, Nuclear is the responsible officer submitting this report.

Date Resconsible Officer Received Information f The Chief Executive Officer, Nuclear received information concerning the defect on April 7, 1988. The Chief Executive Officer, Nuclear determined that this defect should be reported under the provisions of 10 CFR 21 on April 7,1988.

Basic Comoonent Descriotion Specifications of the CRD trip breaker with the UVD are:

Type: AK2-25-2 Model: None Voltage: 125V DC l Serial No.: 224A3515-506CG-2 Specifications of the UVD with the defect are:

Type: Undervoltage Device Model: 269C282G2 Rating: 115V 60 Hz Firm Sucolvina Basic Comoonent The firm that supplied the CRD trip breaker was:

General Electric Company Philadelphia, Pennsylvania j g ro. = .uscci...on sa.u J

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ERPtRES 8/31/8B F ACILIT y asAug (11 DocatT8evuSER821 PAGE131 LE R NUM88 A tel 9== I" tll;".*'  ;'##:

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0I1 0l3 F 0h l rarsu - e w . , ~ ucr.,,, w anin Descriotion of the Defect and Substantial Safety Hazard That Could Have Been Caused On March 23, 1988, during the surveillance test of the CRD trip breakers, the

1. 3 DC CRD trip breaker failed to open when Reactor Protection System (RPS) channel D was tripped. The reactor was in hot shutdown and subcritical at the time of the event. A subsequent investigation on Harch 27, 1988, by SMUD technicians and vendor representatives disclosed that the armature "button" on the UVD was mounted much lower (not centered vertically) on the armature during the manufacture of the UVD (see drauirig). This changed the armature's relationship to the trip paddle causing point-to-point contact instead of the required surface-to-surface contact. The clearance between the trip paddle and the button also appeared much closer than normal, which allowed the UVD armature and the trip paddle to repeatedly contact each other due to normal vibration. Due to the repeated contact and small contact surface, excessive wear occurred on both parts, eventually allowing the possibility of the trip paddle becoming wedged against the UVD armature, which would prevent a UVD trip of the CR0 trip breaker. When the UVD armature and trip paddle arm were removed and inspected, pronounced wear damage was apparent.

UNDERVoLTAGE TRIP PADDLE UNDERVOLTAGE TRIP PADDLE ARMATURE ARMATURE

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ARMATURE BUTTON ARMATURE BUTTON UNACCEPTABLE ACCEPTABLE Each group of safety control rods is held in the fully withdrawn position during reactor operation. When 120V AC from RPS is removed from the breaker controls, the UVDs open the CRD trip breakers causing loss of power to the CR0 mechanisms. This action releases the control rods which drop into the reactor core by gravity. In addition to the UVDs, each CR0 trip breaker has a shunt trip device which provides a redundant means to open the CRD trip breakers.

The shunt trip device could trip the CR0 trip breaker if the UVO failed to operate properly.

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The CRD trip breakers were supplied during initial plant construction. These CRD trip breakers were refurbished by Babcock and Hilcox in 1985. Markings on the UVD indicate that the UVD in question was installed on the breaker when it was first manufactured by General Electric in 1973.

Number and Locattion of Such Comoonents at Rancho Seco Rancho Seco has six AK2-25 CRD trip breakers. These CRD trip breakers supply power to the safety group CRDs.

Corrective Action On March 23, 1988, the #3 CRD trip breaker was removed from service and placed in QC quarantine. General Electric and Babcock & Hilcox were contacted and requested to send representatives to Rancho Seco to assist in performing an indepth investigation of the breaker failure. After an initial meeting to describe the failure circumstances, the vendor representatives assisted in the formation of a work plan and, in conjunction with Rancho Seco personnel, performed an investigation of the breaker failure mode. The vendor representatives concluded that the root cause of the failure of the CRD trip breaker to trip was the improper positioning of the armature button on the armature during the manufacture of the UVD. Once the cause of the problem was determined, each CRD trip breaker was removed from service and inspected for a similar defect. No defects were found. The CR0 trip breakers were then successfully surveillance tested and returned to service.

In parallel with the investigation of the breaker, an indepth review of the maintenance history of the Rancho Seco CRD trip breakers was performed.

Additionally, the Babcock & Hilcox Owners Group breaker experience summary reports for 1985 and 1986 were researched for similar events. None were found.

The maintenance procedure for the CR0 trip breakers was evaluated based on the events described in the breaker summary reports. One possible weak area was identified. The maintenance procedure was then revised to include checks for the UVD armature defect. The revised maintenance procedure was reviewed by the vendor representatives for weaknesses and errors. None were found.

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