ML19319B856

Deficiency Rept Re Safety Features Actuation Sys Analog Amplifier & Bistable Grounding.Vendor Will Modify Drawings Showing Separation Between Ground & Common Connections

ML19319B856
Person / Time
Site:	Davis Besse
Issue date:	04/19/1976
From:	Roe L TOLEDO EDISON CO.
To:
Shared Package
ML19319B847	List: ML19319B853 ML19319B856
References
NUDOCS 8001280681
Download: ML19319B856 (2)

Text

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%= iifDiSO?d i LOWELL E. ROE e Vice President Facd. tees Deve'coment Docket No. 50-346 m eiass-5242 April 19, 1976 Dr. Ernst Volgenau, Director Office'of Inspection and Enforcement U. S.UNuclear Regulatory Commission

• Washington, D. C. 20555

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Dear Dr. Volgenau:

This letter is submitted in~accordance with 10 CFR Part 50.55 regarding the apparent deficiency of the Safety Features Actuation System (SEAS) as previously discussed with Mr. C. C. Williams on March 19, 1976 and Mr. R. S. Martin, on April 13, 1976, both of Region III.

Report on SFAS Analog Amplifier and Bistable Grounding Deficiency

) This report is being made pursuant to 10 CFR Part 50.55(e) on Significant Deficiencies, V and documents the evaluation of the possible significant deficiency in the method of grounding the Analog Amplifiers and Bistables in the SFAS.

Identification of Problem a

The Davis-Besse Nuclear Power Station Unit 1 SFAS was purchased from the Consolidated Controls Corporation (CCC). This system has.16 Analog Amplifiers that are used to condition the input signals for use with the trip bistables installed in the system.

Each of these Analog Amplifers supply a low voltage signal (approximately 0.25 to 7.25 volt s) to six trip bistables. The CCC drawings showing the connections from the Analog Amplifier output to the input of the trip bistables did not show in de-tail the method that CCC was using for the grounding and ground connections for this portion of their system.

l Analysis The trip bistables for this system were bench tested and calibrated on site using the detailed instructions in the CCC Instruction Manual. After the modules were inserted into the SFAS cabinetry, it was detected during system check out that the trip poiats did not correspond with their original settings.

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1 TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISDN AVENUE TOLEDO. CHIO 43652

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\j Page Two April 19, 1976 Upon investigation it was determined that there was a voltage difference between the common point on the analog output of the Analog Amplifier and the common point on the anal"3 input to the trip bistable. This voltage difference was caused by ,

an external current flowing in the co==cn leads in the common-to-ground connection of the circuitry between the trip bistables and the Analog Amplifiers due to the

" chaining" of the grounds between modules.

This problem is considered to be a significant deficiency as defined by 10 CFR Part 50.55(e), because (1) there was a significant deficiency in the design details in that specific grounding requirements were not adequately identified, and (2) it cannot be shown that the bistables would have tripped within the tolerances allowed in the FSAR.

• Corrective Action -

CCC will modify their drawings to show a separate connection between ground and the output-of the analog module and a separate ground connection from the common terminal to ground for the input to the trip bis. table. No other currents will be allowed to flow in these ground connections. In addition, the CCC drawings will be madified to show the details for all ground and common connections in their cabinetry. Appropriate grounding changes will be made, and system checkout and

(S cesting performed to assure trip bistable actuation in accordance with FSAR

\,v) comnitments. .

Safety Implications Based on the above, we conclude that the grounding sys em used by CCC was inadequately -

identified on their design drawings. While the trip points would not have been exactly as desired, this condition was determined during the thorough and stringent testing and checkout by the Applicant on site prior to the time the equipment was turned over for operation. Thus, the safety of the station and the public were not jeopardized.

Yours very truly, LER: cts b .

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