ML20086F952

AO 75-66:on 751020,APRM B Flow Bias Signal Failed Upscale. Caused by Internal Ground in Channel Flow Transmitter D Combined W/Installed Instrument Loop Ground,Lowering Total Loop Resistance.Defective Components Replaced

ML20086F952
Person / Time
Site:	Peach Bottom
Issue date:	10/30/1975
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Boyd R Office of Nuclear Reactor Regulation
Shared Package
ML20086F955	List: ML20086F952 ML20086F958
References
AO-75-66, NUDOCS 8401090720
Download: ML20086F952 (2)

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j v i < PHILADELPHIA ELECTRIC COMPANY 23O1 MARKET STREET PHILADELPHIA, PA.19101 (215) 841-4ooo October 30, 1974'

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Mr. Roger S. Boyd, Acting Director (

Division of Reactor Licensing

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Office of Nuclear Reactor Regulations -

i United States Nuclear Regulatory Commission ai 4 Washington, D.C. 20555 ( .'

..s G.:.u g Dear Mr. Boyd* (

Subject:

Abnormal Occurrence The following occurrence was reported to Mr. Walt Baunack, Region 1, Office of Inspection and Enforcement, United States Nuclear Regulatory Commission, on October 21, 1975. Written notification was made to Mr. James P. O'Reilly, Office of Inspection and Enforcement, Region 1, United States Nuclear Regulatory Commission on October 21, 1975. In accordance with Section 6.7.2.A of the Technical Specifications, Appendix A of DPR-44 for Unit 2 Peach Bottom Atomic Power Station, the following report is being submitted to the Directorate of Reactor Licensing as an Abnormal Occurrence.

Reference : License Number DPR-44 Technical Specification

Reference:

Tables 3.1.1-and 3.2.C Report No.: 50-277-75-66 Report Date: October 30, 1975 Occurrence Date: October 20, 1975 Facility: Peach Bottom Atomic Power Station R.D. #1, Delta, Pennsylvania 17314 Identification of Occurrence:

The "B" APRM flow bias signal failed upscale.

Conditions Prior to Occurrence: J Unit 2 at 567 power.

8401090720 751030 PDR ADOCK 05000277 PDR S

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> Mr. Roger S. Boy 50-277-75-66 .

October 30, 1975 Page 2 l

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Description of Occurrence:

The "D" channel recirculation flow loop (FT-2-110D) failed in such a manner as to drive flow indication upscale. The "D" channel is summed with the "B" flow channel to develop the "B" channel APRM flow bias signal which responded to the failure by indicating upscale.

Designation of Apparent Cause of Occurrence:

As internal ground in the "D" channel flow transmitter, combined with the installed instrument loop ground, lowered the total loop resistance. The lower resistance caused an increase in instrument loop current, hence, an increase in indicated flow.

Analysis of Occurrence:

The flow comparator circuit responded to the flow loop

" mismatch", initiated a rod block, and annunciated the condition.

For the above reason and the fact that a "B" channel manual scram was immediately inserted and maintained throughout the repair period, this occurrence has minimal safety implications.

Corrective Action:

The defe:tive components (containing the ground) in the flow transmitter were replaced. The flow transmitter was then recalibrated and returned to service.

Failure Data:

Une previous reported as 50-277-75-30 Very truly yours, M J. Cooney Superintendent Generation Div.-Nuclear cc: Mr. James P. O'Reilly, Director, Region 1 Office of Inspection and Enforcement United States Nuclear Regulatory Commission 631 Park Avenue King of Prussia, PA 19406 i

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