ML19210A200

Abnormal Occurrence 50-289/75-23:on 750716,auxiliary Relay to Generator 1B Failed to Energize on Demand.Caused by Mfg Defect.Failed Relay Replaced & Remaining Relays Inspected

ML19210A200
Person / Time
Site:	Three Mile Island
Issue date:	07/25/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
Shared Package
ML19210A201	List: ML19210A200 ML19210A205
References
GQL-1308, NUDOCS 7910240920
Download: ML19210A200 (4)

Text

_N"".l.3TRIBUTION FOR PART 50 DC IE i MATERIAL (TEMPOR ARY FORM)

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CONTROL NO: 3056 FILE: II;0IDE?TT REPORT "IL~

F ROM:Me t . Edison Co. DATE OF DOC DATE REC'D LTR TWX RPT OTHER Reading, Pa. 19603 R.C. u nold 7-25-75 7-29-75 XX TO: ORIG CC OTHER SENT AEC POR XX NRC 1 signed SENT LOCAL PDR XX CLASS UNCLASS PROPINFO INPUT NO CYS REC'D DOCKET NO:

XXX 1 50-289 DESCRIPTION: Ler advising of Abnormal ENCLOSURES:

Occurrence A0-50-289/75-23 on 7-16-75 re failu e of an up to frequency auxiliary relay for the "B" Diesel Generator to actua te. . . . .

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METROPOLITAN EDISON COMPANY _ _ _ . POST OFFICE BOX 542 READING, PENNSYLVANIA 19603 TELEPHONE 215 - 929-3601 July 25, 1975 e ~. ' GQL a rI

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[~ ' y. - (-C' ' sj Director I ~' ~?7 ij . Division of Reactor Licensing M- r. '" [[ 'O N N, U. S. Nuclear Regulatory Commissil35 M?, hi Washington, D.C. 20555 ye; N Mbgf

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Dear Sir:

Docket No. 50-289 Operating License No. DPR-50 In accordance with the Technical Specifications of our Three Mile Island Nuclear Station Unit 1 (TMI-1) , we are reporting the following abnormal occurrence. (1) Report Number: A0 50-289/75-23 (2a) Report Date: July 25,1975 (2b) Occurrence Date: July 16, 1975 (3) Facility: Three Mile Island Nuclear Station Unit 1 (4) Identification of Occurrence:

Title:

Failure of an up to frequency auxiliary relay for the "B" Diesel Generator to actuate. Type: An abnomal occurrence as defined by the Technical Specifications, paragraph 1.8d, in that failure of the "B" Diesel auxiliary relay to actuate constituted a failure of one component of an engineered safety feature that threatened to cause the Diesel Generacor to be incapable of performing its intended function. (5) Conditions Prior to Occurrence: Power: Core: 100 *.' Elect: 833 IWe (gross) 6 RC Flow: 138 x 10 lb/hr RC Press.: 2155 psig 1476 214 pe- . v Ot

RC Temp.: 579 F PRZR Level: 240 inches PRZR Temp. : 650 F (6) Description of Occurrence: At 1315 hours on July 16, 1975, while performing the post maintenance testing for a work request , associated with the 1B Diesel Generator, it was discovered that the 81x1 auxiliary relay did not energize when required . The auxiliary relay contacts are used in a 2 out of 3 logic that permits the 13 Diesel Generator breaker G11-02 to close when the diesel generator is up to speed. The failure was discovered when the contacts for the 81-1 relay (frequency sensing relay) were manually clo s ed . Closing the 81-1 relay contacts should have energized the associated auxiliary relay (81-x1) but the 81-x1 relay f ailed to energize. The remaining two auxiliary "up to f requency" relays , 81x2 and 81x3, were verified operable for the B Diesel Generator Bkr. G11-02 closing circuit . The faulty 81x1 auxiliary relay was replaced and testing was satisfactorily completed verifying proper operation of the relay and the 2 out of 3 logic. (7) Designation of Apparent Cause of Occurrence: The apparent cause of this occurrence has been determined to be manuf actur,e. e (manuf acturing defect) , in that: The auxiliary relay is a Westinghouse MG-6,125V DC relay. After winding the coil it is sprayed with a black insulating material. The terminals of the coil are normally covered during this manufacturing process to prevent them f rom being coated by the insulating material. The coil terminals in the failed relay were not protected f rom the spray and hence became coated with the spray. In addition, the bolt holding the wire lug to the coil terminal was not tight. The resulting intermittant connection caused the relay to fail. (8) Analysis of Occurrence: It has been determined that: The f ailure of the 81x1 relay did not reprer unt a threat to the health and safety of the public in that: (1) the B Diesel Generator was operable at the time the failure was discovered in that the remaining two frequency relays were operable (the diesel had been operated on-line within the previous 6 hours) (2) the A Diesel Generator was operable and only one diesel generator is necessary to perform the safety related functions. 1476 215

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(9) Corrective Actions : In addition to the immediate actions listed above long term corrective actions are as follows: The failed relay has been replaced and the remaining auxiliary MG-6 relays used on the A and B diesel generators will be inspected for proper manufacture of the coils. The inspection will verify that the coil terminals were protected during the spray process as indicated by a bright metallic surface on the coil terminals. The manufacturer of the relays was contacted regarding the problem and asked for re-commendations on the resolution of the problem. The Plant Operations Review Committee and Station Superintendent have reviewed and approved the above corrective actions and have taken steps to ensure completion of the yet to be completed long term corrective actions. (10) Failure Data: Westinghouse MG-6 Relay S tyle No. 289B359A20 Similar Occurrences: None Sincerely, R. C. Arnold Vice President RCA:CWS:tas cc: Office of Inspection and Enforcement, Region 1 File: 20.1.1 / 7.7.3.5.1 1476 216}}