ML19210A146

Event Rept 76-11/3L:on 760221,diesel Generator Breaker 1B Failed to Close Automatically.Caused by Procedural Failure to Check Generator Frequency.Governor Setting Check Added to Quarterly Surveillance Tests as Corrective Action

ML19210A146
Person / Time
Site:	Three Mile Island
Issue date:	03/18/1976
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
ER-76-10-03L, ER-76-10-3L, NUDOCS 7910240869
Download: ML19210A146 (4)

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- n . - ass METROPOLITAN EDISON COMPANY cmr.:norcuam.mucvreuren conmricx POS T OFFICE BOX 542 READING, PENNSYLVANI A 19603 TELEPHONE 215 - 929-3601 March 18, 1976

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gegulatory Docket FIP" 33 .

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Mr. J. P. O'Reilly, Director -

Office of Inspection and Enforcenent, Regicn I -

y U. S. Nuclear Regulatory Co==ission 3 -

631 Park Avenue King of Prussia, Pennsylvania 19h06

Dear Mr. O'Reilly:

Operating License DPR-50

v. Docket 5:>. 50-289

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In accordance-vith the-Techniesl Specifications of cur,Threhbtle I'sland Iruclear Station Unit I (TMI-1), va are reporting the ode'ving reportable occurrence: ga h, (1) Report Nu=ber: ER 76-10/3L E a yAR2 3 m76> ,w, (2a) Report Date: March 18, 197o { " g ^,'j g a t 0' ww (2b) Event Date: February 21, 1976 s (3) Facility: Three Mile Island Nuclear Station Unit 1 W f:

(h) Identification of Event:

Failure of "13" Diesel Generator Breaker to close autc=atically. due te an inadequacy in procedure, which constitutes a violation of Technical Specification 6.9.2.B(3) in that the event tenporerily caused a reduction in the degree of redundancy in an engineered safet.y feature system.

(5) Conditiens prior to Event:

Power: Core: 0% ,

Elec.: 0 !Ge RC Flow: 65 x 106 lbs/hr.

RC Pressure: 21h0 psig RC Te=p: h500F PRZR Level: 150 inches PEZR Tenp.: 6350F 1490 052

r Mr. J. P. O'Reilly 2 GQ,L 0331 ER 76-10/3L (6) Description of Event:

While performing the Emergency Sequence and Power Transfer Surveillance Test, the "13" Diesel Generctor failed to close when the "1D" hic 0V Bus was deenergized. The breaker failed to close because the "B" Diesel Generatsr frequency was too lov. The lov frequency condition resulted from an incorrect diesel governor setting. When she governor setting was checked after the test, it was found that the frequency was 59.2 H:

as indicated on the control room console indication. The frequency relays for the two ott of three interlock are set at 59 H . Only one frequency relay had picked up (31-2), due to setpoint and indication tolerance. A calibration check of the relays indicated that the relays would have picked up if the diesel frequency had been closer to 60 H:.

(7) Designation of Apparent Cause of Event:

The cause of this event has been determined to be crocedurer in that they do not require periodic checks of diesel generator frequency.

(8) Analysis of Event: -

The failure of the diesel breaker to close automatically when the "lD" bus was deenergized did not represent a threat to the health and safety of the public. The engineered safeguards' loads are normally supplied from the off-site distribution system. In the event of loss of off-site power, the "lA" Diesel Generator was available for emergency power.

In addition, the "lB" Diesel Generatar could have been placed on line by increasing the diesel generator speed using the governor control switch located on the control room console.

(9) Corrective Actica:

I= ediate: The E=ergency Sequence and Pover Transfer Test was perfor=ed on the "A" Engineered Safeguards Channel, verifying that the breaker for the "1A" Diesel Generator closed properly.

The goverr.or for the "B" Diesel was adjusted and the test was successfully performed on the "B" Engineered Safeguards Channel.

Long Ters: A check of the governor setting vill be addcd to the quarterly surveillance test. The check vill ensure that the roltage and frequency interlock is satisfied as evidenced by the READY TO LOAL light The frequency meter on the control room console vill also be periodically calibrated. Further, it should be noted that drift of the control room console frequency is not thought to have contributed to this occurrence. These corrective actions, 1490 053

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'Mr. J. P. O'Reilly 3 GQL 0331 ER 76-10/3L Iong Ter=: (continued) in addition to periodic relay calibration checks, should therefore provide adequate assurance against recurrence.

(10a) Failure Dsta: Not applicable (10b) Similar Events: None Sincerely,

! Signed: R. C. ARNOLD !

R. C. Arnold Vice President RCA:JGOeg cc: Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Comission -

Washington, D. C. 20555 1490 054