ML20246C433

Discusses Steam & Feedwater Rupture Control Sys Mods. Pneumatic Relays in Control Circuit of MSIV to Be Deleted

ML20246C433
Person / Time
Site:	Davis Besse
Issue date:	04/24/1989
From:	Shelton D TOLEDO EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
1644, NUDOCS 8905090363
Download: ML20246C433 (2)

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%ss EDISON A Centenor Energy Company DONALD C. SHELTON Docket Number 50-346 Va Preent-N@ar (410] P49 2300 License Number NPF-3 Serial Number 1644 April 24, 1989 United States Nuclear Regulatory Commission Document Control Desk Vashington, D. C. 20555 Subj ect: Steam and Feedvater Rupture Control System Modifications Gentlemen:

Toledo Edison's Course of Actic.n (COA), Appendix IV.C.2.2, dated September 5, 1985, (Serial Number 1182) detailed actions related to the Steam and Feedvater Rupture Control System (SFRCS). Those actions.resulted from the Decay Heat Removal Task Force review to improve the overall system reliability. One of the recommended actions was to delete the pneumatic relays in the control circuit of the Main Steam Isolation Valves (MSIV).

Toledo Edison's letter dated June 9, 1988 (Serial Number 1468) provided additional information concerning this action and committed to completing evaluations to determine the necessary actions and advise you of our plan and schedule.

Toledo Edison's review of this concern has concluded the following:

The root cause of the June 9, 1985 SFRCS actuation was determined to be Steam Generator (SG) level oscillations caused by Turbine Stop Valve closure. This problem has been corrected by damping all eight SG 1evel transmitter outputs.

Additionally, in the new SFRCS system (modified during the fifth refueling outage) the inputs to the SFRCS logic from the SFRCS bistables are paired such that both trip inputs from the same parameter must be present to actuate a logic channel. Both logic channel trips in a single actuation channel must now be present for an SFRCS actuation. This pairing of inputs ensures that spurious trips from different inputs will not cause an actuation of the SFRCS.

The above described SFRCS design modification ensures that spurious closure of the MSIVs vill not occur following momentary, short-lived SFRCS actuation signals similar to the one experienced during the June 9, 1985 event at Davis-Besse.

8905090363 890424 goof PDR ADOCK0500gg6 1 P i t THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO, OHIO 43652

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, 3 pocket Number 50-346 License Number NPF-3 Serial-Number 1644 i Page 2 Since the SFRCS is an automatic reset system, seal-in features are provided for SFRCS actuated equipment to ensure full actuation and to satisfy IEEE-279.

Additionally, after the SFRCS trip input signal is received, there is a two second seal-in in the logic to ensure the SFRCS actuated equipment seal-in features discussed above are satisfied.

Furthermore, a review of previous operatirg history, conducted during the System Review and Test Program (SRTP), indicated that pneumatic relay failures have not caused spurious MSIV closures. Additionally, a single failure of one of the pneumatic relays by itself vill neither result in a spurious closure of the MSIV nor culminate in a failure of the MSIV to close in response to an SFRCS signal. This is due to component redundancy in the valve control circuitry. These relays are currently actuated during SFRCS testing on a 30 day frequency and actuation verified on an eighteen month frequency during SFRCS initiated MSIV testing.

Based on the above considerations, the current SFRCS design has been '

significantly enhanced as compared to the system design present on June 9, 1985. Therefore, Toledo Edison believes the original intent of C0A Appendix  !

IV.C.2.2, to improve the adequacy of the design and operation of the SFRCS  !

is complete and no further modifications are considered necessary.

If you have any questions concerning this matter, please contact Mr. R. V.

Schrauder, Nuclear Licensing Manager, at (419) 249-2366. l Very trul. yours, s

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JCS/dlm cc: P. M. Byron, DB-1 NRC Resident Inspector {

A. B. Davis, Regional Administrator, NRC Region III 1 T. V. Vambach, DB-1 NRC Senior Project Manager l