ML19261F249

Environ Rept 76-29/3L:on 760830,power Range Instrument Channels Temporarily in one-of-two Trip Logic Configuration, Causing Operation in Degraded Mode.Caused by Loose Mounting Nut for Cable Connector Due to Repeated Maint Work

ML19261F249
Person / Time
Site:	Three Mile Island
Issue date:	09/29/1976
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-1357, NUDOCS 7910250677
Download: ML19261F249 (4)

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ENCLOSURE L b neh LTR FURNISHING REPORTAH2 OCCURPSTCS: ER 76-29/3L ON 8-30-76 REF POWER PANGE INSTRUMENT CHANNELS IN A ONE-OUT-OF-TWO TRIP "*e:

IOGIC CONFIGUPATION. . . . . . -' /.

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Dear Sir:

4 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 reportable occurrence:

1. Report Nu=ber: ER 76-29/3L s yi 0 F' C)

2. a. Required Report Date: September 29, 1976 '

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b. Date of Occurrence: August 30, 197o- S- e,p 6k -

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3. Facility: Three Mile Island Nuclear Station - Unit 1

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h. Identification of Occurrence:

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Title:

Power Range Instrument Channels in a One-Out-of-Wo Trip A' ' l ' ' ' '

Logic Configuration Type : A reportable occurrence as defined by Technical Specificaticn 6.9.2.3.(2) in that the unit's power range instrument channels were temporarily in a en - -cut-of-two trip logic configuration, thus leading to operation in a degraded =cde permitted by a limiting conditicn for operaticn as defined by Technical Specifications Table 3.5-1, Item 2.

5 Cend.itions Prior to Occurrence:

Pcver: Core: 925 Elec.. 768 ige (Grcss)

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Mr. J. P. O'Reilly, Directcr Septe=ber 25/, 1976 GQL 1357 BC Flcv: lho x 10 lbs./hr.

FC Pressure: 2155 psig RC Temperature: 579 F PR"R Level: 2h0 inches PR"R Te e - 655 F

6. Description of Occurrence:

On September 30, 1976, the Reactor Protection System (RPS) "D" channel tripped on a flux / imbalance / flow signal. Because the counting nut for the cabla connector of nuclear Instrumentation detector NI-8 lover chamber was loose at the connector junction box in RPS "D" cabinet, the connector rotated and shorted the inner shield against a screw in the junction box. The short caused the channel to trip as stated above. At that time, the RPS "C" channel was in manual bypass for heat balance adjustment. This constituted operation in a degraded mode since the unit's power range instrument channels were temporarily in a one-out-of-two trip logic configuration.

I==ediately, the loose connector was repositioned and the nut tightened to eliminate further shorting. RPS "C" channel was then taken out of

=anual bypass to return to the required three operable channels.

7 Designation of Apparent Cause of Occurrence:

The mounting nut for the cable connector of NI-8 apparently became loose due to repeated disconnections and reconnections of the cable to allow for maintenance an't core physics testing.

S. Analysis of Occurrence:

It has been determined that this occurrence did not constitute a threat to the health and safety of the public in that:

a. The subject degraded mode operation is per=itted by the Technical Specifications for a maximum of four hcurs; and

b. The number of operable channels was returned to the required three channels within four hours when RPS "C" channel was taken cut of

=anual bypass.

9 Corrective Action:

In addition to the in=ediate corrective action described above, the counting nuts for all remaining HI detectors vill be examined and 1481 246

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Mr. J. F. 'O'Reilly, Director September 29, 1976 GQL 1357 tightened if necessary. Further, a thin red aligreent mark will be painted en the ecnnector and junction bcx. The scnthly surveillance procedure 1303-h.1 (Feactor Protection Syste= Surveillance) vill be revised to include a connector alignment check.

The Plant Operations Review Committee and Station Superintendent have reviewed and approved the above corrective action and have taken steps to assure its completion.

10. Failure Data: N/A Similar Events: None Sincerely, J

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R. C. Arnold Vice President RCA:JMC:sft

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