ML20084S913

Ro:Four Permissive Relays (R/Rs 1-4)in Shutdown Rod Permissive Circuit Would Not Actuate After 21 Regulating Rod Limit Switches (LS-3) Closed Shut & Some Control Rod Driving Mechanisms Were Not Operating within Desired Accuracy

ML20084S913
Person / Time
Site:	Palisades
Issue date:	03/15/1971
From:	Youngdahl R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Morris P US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8306200075
Download: ML20084S913 (2)

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R. C. You ngd ahl JJ 4 h Senior Mce Prevdent x / h ~ - ? ,\

General Offices: 212 50/estiMlIhgan Avenue, Jackson, Michigan 49201. Area Code 517 788-0500 i

March 15, 1971 i Docket No. 50-255 1

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Dr. Peter A. Morris, Director Division of Reactor Licensing U.S. Atomic Energy Commission Washington, D.C. 20545

Dear Dr. Morris:

.During preoperational checkout of the Palisades control rod drive mcchanisms (CRIM), minor difficulties were encountered which

. required modifications to improve the operating performance. The Divi-sion of Compliance has requested that we provide a summary description Gg of two of these problems and their correction for your information.

Shutdown Rod Permissive Interlock ,

In the shutdown rod permissive circuit it was found that the four permissive relays (R/RS 1-4) would not actuate after the 21 regu-lating rod limit switches (LS-3) c1csed shut. Thus, the interlock logic was not followed in that after all 21 regulating rods were inserted, the shutdown rods were not permitted to be driven in. The trip function was /,// Jt /

unaffected by this problem, however. The problem was determined to have been caused by the high resistance of the series cable % between eaciNw dd CRIN and the control rod panel (C-15). This resulted in an insufficient current to actuate the four permissive relays.-

The modification to resolve this problem was to replace the four parallel' wired permissive relays in the circuit with an auxiliary - CM ii relay,with low current requirements and to install the permissive relays /JMIj l4 in'a separate circuit. Actuation of the auxiliary relay after all regu- ,/b6ectI lating rods are inserted will now result in actuation of a contact in the circuit of the permissive relays, energizing them and permitting shutdown rod insertion. All operational considerations of this circuit remain the same.

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Dr. Patsr A. Mo uis 2 Docket No. 50-255 March 15, 1971 Control Rod Drive Mechanism Limit Switches It was noted during exercising of the CRIMs that some CRD4 limit switches were not operating within the accuracy desired even though they were within the operational range.

• Investigation revealed that the set screws and grooved pins installed in the primary position indication camshaft drive gear could allow a small relative motion between the gear and shaft. To increase the limit switch and primary position accuracy, the grooved pins were removed and replaced with spring roll pins to elimi-nate all motion between the shaft and gear. The balance of the gear train was also inspected to verify that it was properly pinned and secured.

These modifications have been completed and the control rod drive mechanisms will again be completely rechecked prior to initial criticality.

Yours very truly, YIN RCY/lb E

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