ML20151W824
| ML20151W824 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 04/28/1988 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 1498, NUDOCS 8805030508 | |
| Download: ML20151W824 (2) | |
Text
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TOLEDO
% EDISON A Ccwxr Energy Cmyw3 DONALo C. SHELTON
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Docket No. 50-346 License No. NPF-3 Serial No. 1498 April 28, 1988 United States Nuclear Regulatory Commission Document Control Desk Vashington, D. C.
20555 Subj ec t:
Davis-Besse Course of Action Commitment to Provide Turbine Gland Seal and Air Steam Ejector Motive Steam from Both Hain Steam Headers Gentlemen:
Toledo Edison completed a Task Force reviev of the design of systems utilized for decay heat removal at the Davis-Besse Nuclear Power Station and documented the results in a final report dated October 15, 1985 (Serial No. 1182). This reviev resulted in short and long-term recommendatiorie intended to improve the overall reliability of the various systems utilized to remove decay heat by:
Simplifying emergency initiation logics, Reducing unnecessary system challenges, Reducing the potential for common mode ft.ilures, and/or Implementing redundancy, where necessary.
As e result of one of the long-term recommendations, Toledo Edison committed (in the Davis-Besse Course of Action (C0A) plan) to modify the Main Steam System such that Turbine Gland Seal and Air Ejector motive steam would be available from more than one source.
In the current configuration, Auxiliary Steam is only available from Main Steam Header No. 1.
By installing new piping and valves between Main Steam Header No. 2 and the Auxiliary Steam line from Main Steam Header No. 1, a redundant source of Auxiliary Steam would be available, thus reducing the likelihood of a loss of both main feedvater pumps. The benefits of this modification could only be realized however, by implementing a change to the Steam and Feedvater Rupture Control System (SFRCS) logic such that, in the event of a lov main steam pressure, only the affected steam generator vould be isolated (i.e., only the Main Steam Isolation Valve (HSIV) in the loop experiencing a failure / break would receive an isolation signal). At present, the SFRCS provides an isolation signal to both MSIVs as a result of lov main steam pressure.
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l Dockot No. 50-346 License No. NPP-3 Serial No. 1498 Page 2 A detailed engineering review of the proposed SFRCS logic change determined that this change should not be implemented since, if the turbine stop valves fall to close during a main steam line break accident (MSLB) inside the Davis-Besse cor.tainment, the resultant steam blevdown and containment heat load could exceed that previously analyzed. This increased blovdown vould occur in the event of a MSLB and the assumed single failure of the logic controlling the turbine stop valves (which vould result in cross-connecting the Main Steam Loops), due to the fact that the MSIVs are not designed to prevent back flov.
For example, if Main Steam Header No. I were to break inside containment, the proposed SFRCS logic change vould result in a signal to close MSIV No. 1, which should limit the blovdovn to the contents of Steam Cenerator No. 1.
However, given the failure of the turbine stop valves to close, Steam Generator No. 2 could also blovdown.
The flow path for this blovdown vould be through the unisolated MSIV No. 2, the open turbine stop valves, backwards through the isolated MSIV No. 1, and into the containment via the break.
Based on the above determination and the fact that the additional containment heat load is not bounded by the current analysis, the SFRCS logic change vill not be implemented. Thus, implementing the subject auxiliary steam modification, which would have orly been of benefit upon completion of the SFRCS logic change, is no longer practical.
Toledo Edison has therefore canceled plans to provide turbine gland seal and air ejector motive steam from both Main Steam headers.
I Verytruy9ours,
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CFMitit l
cc A. B. Davis, Regional Administrator 1
DS-1 NRC Resident Inspector A. V. DeAgazio, NRC/NRR, DB-1 Project Manager 4
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