ML17252B023

Letter Reporting a 09/09/1972 Condition Relating to the Discovery of a Reactor Protection System Limit Switch on the #4 Turbine Control Valve to Be Inoperable - Dresden Unit 3

ML17252B023
Person / Time
Site:	Dresden
Issue date:	09/20/1972
From:	Worden W Commonwealth Edison Co
To:	Giambusso A US Atomic Energy Commission (AEC)
References
Download: ML17252B023 (2)

Text

Commonwealth Edison Company 50 _249 72 WEST ADAMS STREET

• CHICAGO_, ILLINOIS_

Addreu Reply to, POST OFFICE BOX 767 *CHICAGO, ILLINOIS 60690 Dresden Nuclear Power Station R. R. ill September 20, Mr. A. Giambusso Deputy Director for Reactor Projects Directorate of Licensing U. S. Atomic Energy Conunission Washington, D. C. 20545

SUBJECT:

LICENSE DPR-25, DRESDEN NUCLEAR POWER STATION, UNIT #3, SUBJECT 6.6.B.3 OF THE TECHNICAL SPECIFICATIONS.

Dear Mr. Giambusso:

This is to report a condition relating to the operation of the

. s:tation in which a reactor protection system (RPS) limit switch on the /!4

__:_;,,,,... ***~* ., ..p .. t;l.lrbine .cont;rol. V!'llv:e _wa~-* f.?un~*::*t~ _be~!t.!OJ>.era?le,. contrary to the require-

' ments of Section 3.1 of the Technical Specifications.

PROBLEM AND INVESTIGATION The reactor was in the "run" mode and operating at 560 MWe on September 9, 1972.

• At 0300, during the Turbine Weekly Checks, it was noted that the turbine generator load mfsmatch relay (590-12t:'D) scram on Channel "B" did not deenergize when the /!4 control valve was cfosed. When the

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control valve fast closure* solenoid operates, it actuates a switch which opens contacts de-energizing its RPS relay; this causes a Channel "B" trip when above 40% power. Pending correction of the problem, fuse No. 590-725H was removed to actuate a Channel "B" scram to satisfy the requirements of Section 3.1 of the Technical Specifications.

Investigation of the switch showed that the mounting bolts had worked loose allowing the switch to shift far enough so that it could not be actuated by the fast closure solenoid.

CORRECTIVE ACTION The limit switch was adjusted, tightened, and tested satisfactorily.

The limit switches on the other three control valves were similarly inspected and tightened.

Mr. A. Giambusso

• ~ September 20, 1972 A similar occurrence was experienced on July 7, 1972 as explained in the letter to Mr. Block from Mr. Worden dated July 17, 1972. The

===~c_orrective _act.ion at .. that time was to reverse *the mounting bolt. Because*

of plant condi-tions at that time only one of the limit switches had the mount reversed. During the current anomaly, the bolts were adjusted and tightened. During the next maintenance outage, the limit switch mounting bolts will be reversed and double nuts installed. This corrective action has already been completed on Unit 2.

Sincerely,

-a~J.rn~

D-A W. P. Worden

~ - Supertntendent .

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