ML20210A487

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Forwards Explanation of Control Switch Circuitry in Use at Plant & Rev 0 to Emergency Procedure ES-1.1, SI Termination, Per SA Varga 870107 Request for Addl Info Re IE Bulletin 80-06
ML20210A487
Person / Time
Site: Zion  File:ZionSolutions icon.png
Issue date: 04/28/1987
From: Leblond P
COMMONWEALTH EDISON CO.
To:
NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
Shared Package
ML20210A494 List:
References
3005K, IEB-80-06, IEB-80-6, NUDOCS 8705050100
Download: ML20210A487 (7)


Text

,[ _

T Commonwealth Edison

' One First National Plaza, Chicago, Illinois l

( j" 7 Address Reply tx Post Omce Box 767 Chicago, Illinois 60690 0767 N

April 28, 1987 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555

Subject:

Zion Nuclear Power Station Units 1 and 2 Request for Additional Information -

IEB 80-06 NRC Docket Nos. 50-295 and 50-304 References (a): January 7, 1987 letter from S.A. Varga to D.L. Farrar (b): June 10, 1980 letter from D.L. Peoples to J.G. Keppler Gentlemen:

Reference (a) requested that Commonwealth Edison Company provide a discussion of the specific details of a September 4, 1986, event involving an Emergency Diesel Generator at Zion Station as they relate to IE Bulletin No. 80-06.

In addition, members of the NRC staff developed concerns after observing the resetting of a safety Injection on the Zion simulator.

Reference (a) also requested an explanation of these observed actions. to this letter contains an explanation of the control switch circuitry in use at Zion Station.

It also demonstrates that the September 4, 1986, event was caused by an unrelated problem whose correction is in progress. Thus, the information contained in reference (b) remains accurate. contains a copy of Zion Emergency procedure ES 1.1, SI Termination. While it is difficult to know precisely what was observed by the NRC staff members, it probably involved the performance of ES 1.1 or similiar guidance. Step 1.a of this procedure involves the matching of breaker targets, as discussed in Attachment 1.

This step could involve in excess of fifteen switch manipulations. However, none of these actions will affect the operating status of equipment. Thus, ES 1.1 is consistent with the information provided in reference (b).

If any further questions arise regarding this matter, please direct them to this office.

Very truly yours, q

8705050100 870428 PDR ADOCK 0500 5

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P. C. LeBlond Nuclear Licensing Administrator cc: Resident Inspector - Z J. A. Norris - NRR A. B. Davis - Reg. III Jf 3005K

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Reference (a) expressed concern about Zion Station's practice of matching targets on control switches and the trip of the 1A diesel generator during testing on 9/4/86 as related to the requirements of IE Bulletin 80-06 Engineered Safety Features (ESP) Reset Controls. Zion Station has evaluated the events involved and has determined that the 6/10/80 response to I.E.

Bulletin 80-06 is valid.

The control switches typically used to control motor driven pumps, fans and the diesel generators are three position, return to center, pistol grip style, multi contact switches. Some of the contacts in these switches are used as a mechanical memory whose position when the switch is in the center position depends on whether the last use of the switch was to close or trip the associated equipment. The position of these contacts is tracked by a two color target on the face of the switch plate. These memory contacts are used to interlock various alarm circuits and auto actuation signals based on equipment status.

When equipment is auto actuated, the practice is to match targets, i.e., place the memory contacts in the position corresponding to the equipment status. This practice enables the alarm circuits which will alert the operators should the equipment subsequently trip due to anything other than actuation of the control switch. Target matching is not required to maintain the equipment in operaticn after the ESP reset, but is done as quickly as feasible so operators will be alerted to any ESP equipment failure.

Figures A and B, attached, show a typical schematic diagram and control switch development for Zion Station. The memory contacts are shown by CS/SC on the schematic and by SC and STp on the switch development.

The 9/4/86 diesel generator trip was caused by a problem with the diesel generator control relays. Without target matching prior to ESP reset, the reset action momentarily de-energizes solenoid 20 SLO (see figure C, attached). De-energizing this relay does not normally cause a trip but does generate a voltage spike on the DC bus. This spike causes chattering j

in the 14RX and RY relays which does, in turn, cause a diesel engine trip i

thru solenoid 20s. A modification to correct this problem has been installed on diesel generators lA & IB.

Similar modifications will be done to diesel generators 0, 2A and 2B during the current Unit 2 refueling outage.

i In summary, there are no procedures which require manual actions l

prior to resetting an ESP signal in order to obtain or maintain proper system operation and the review of plant design for ESP reset control is accurate per the letter of 6/10/80 from D. L. Peoples to James G. Keppler.

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