ML17238A744

Section 6.6.B.2 of the Technical Specifications - Wiring Error Found in the Logic Circuitry During Monthly Surveillance Testing of the Low Pressure Coolant Injection System

ML17238A744
Person / Time
Site:	Dresden
Issue date:	03/17/1972
From:	Worden W Commonwealth Edison Co
To:	Morris P US Atomic Energy Commission (AEC)
References
Download: ML17238A744 (3)

Text

Commonwealth Edison Company ONE FIRST NATIONAL PLAZA

• CHICAGO, ILLINOIS Addrou Reply to, POST OFFICE BOX 767 *CHICAGO, ILLINOIS 60690 Dr~ Peter A. Morris Division* of Reactor Licensing U. S. *Atomic Energy Commission Washington, D. C.

205~5 Dresden Nuclear Power Station R. R. #1 Morris, Illinois 604'50

• March 17, 1972

'&O.... 2 4 9

SUBJECT:

LICENSE DPR-25; DRESDEN NUCLEAR POWER STATION UNIT #3, SECTION 6.6.B... 2 OF THE TECHNICAL SPECIFICATIONS 1

Dear Dr. Morris:

• This is to report** a condition relating to the operation of the station when, during monthly surveillance testing of the Low Pressure Coolant Injection System (LPCI), a wiring error was found iri the logic circuitry which provides a permissive to utilize containment sprays under accident conditions, provided reactor water level is greater than 2/3 core height.

PROBLEM AND INVESTIGATION

• 0n March 7, 1972, at 1500 hours0.0174 days <br />0.417 hours <br />0.00248 weeks <br />5.7075e-4 months <br />, while conducting monthly surveillance tests on the"Low Pressure Coolant Injection System (LPCI), a containment spray interlock relay (1530-1.IOAW) would not** energize. This relay proVides permissive to.utilize containmerit spray if reactor water level is greater than 2/3 core height. Investigation revealed that one side of* the relay was wired such that the 11LPCI System low flow" switch, (3-1501-58B) was included in the relay circuit, contrary to the wiring

\\:iiagram.

.(Refer to attached schema.tic. )

. The n1PCI System low flow11 switch contact is ~orma.lly closed when. the -surveillance test is conducted.

During this particular surveillance testing, however, the 11low flow" switch calibration had drifted and the contact on this switch.was open.

This resulted in the de-energization of relay 1530-llOAW.

The drift.in the calibration of the 11low flow 11 switch was* thus responsible for the events which led to the discovery of the wiring error and this also explains the. fact that this wiring error was not detected during previous surveillance testing.

~

Dr.* Peter March 17, 1972 A review of the construction and preoperational tests indicated that the relay was tested, *but not with the LPCI pumps:running and hence with the LPCI System low flow switch open.

These facts explain why the wiring error was not detected during the construction and preoperational test phases.

It should be noted that the LPCI.Subsystem was always operable during the period when the wiring error existed. The effect of this wiring error was only to prohibit a permissive signal to spray the contain-ment when the reactor water level was higher than the two-thirds core height position during an accident condition. This operation, in spite of the wiring error, could have been performed by means* of a bypass switch which is part of this subsystem. In addition, it was determined that there was no safety significance related to the calibration drift of the low flow switch.

(These switches are calibrated routinely.)

The circuits on similar relays on the corresponding subsystems on Dresden Units 2 and J were checked and found to be wired properly.

CORRECTIVE ACTION.

The wiring circuit for relayl5JO-llOAW was changed to correspond with that on the wiri.rig diagram* and the 11LPCI System low nowr1 switch was recalibrated. The required surveillance test was repeated satisfactorily following the wiring change.

WPW:ls Enc.

Sincerely,

w. P. Worden

• Superintendent

F-1 FF-81 EE-2 TB 5-18 t-- --'-.,

I I

1 I Yarway 1..

1 263-73A I

I I_ __ J_L TB 5..;17 EE-1 13 1530-ll.O AW 14

~

~_J_~~~~~~~-

F -2 Correct Wiring as.shown on print 12E3437

~~-~~~~~~~~--.--f~F-F:S-...-1~~-

F-l 1501-5SB LPCI Min.

Flow Sw&

r---~--~ FF-80

. W' EE-2 TB5-1B.

i----~

1 1Yarway I

1263-73A I

I I

7 I

I _____ 1 TB5-17 EE-1 13 13 1530-11 1530-220BA AW 14

. 14 F-2 Wiring as found.*** Wire from EE-2

• to FF-80 sho:uld be from EE-2 to FF-81