ML20154P900
| ML20154P900 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/27/1988 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| 1514, NUDOCS 8806060115 | |
| Download: ML20154P900 (2) | |
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%mm EDISON A Cawu Erwgv Cervary Docket No. 50-346 DONALD C. SHELTON va w w License No. NPF-3 pm m e3oo Serial No. 1514 Itiy 27, 1988 United States Nuclear Regulatory Commission Document Control Desk Vashington, D. C.
20555
Subject:
Retention of the Auxiliary Feedvater Pump Lov Suction Pressure Interlock Gentlemen:
In Serial No. 1182, dated September 10, 1985, Toledo Edison (TED) provided its Course of Action decument in response to Mr. H. R. Denton's (Director, Office of Nuclear Reactor Regulation, NRC) letter of August 14, 1985 (Log No. 1798).
Vithin this document, in Appendix IV.C.2.1, a commitmer.c was made to remove the interlock on the steam inlet valves to the Auxiliary Feedvatcr Pump Turbines (AFPTs).
This interlock causes securing of the turbines in the event of a lov suction pressure condition to the Auxiliary Feedvater Pumps (AFPs).
Additionally, a Technical Specification change was cited as being required to be submitted to implement this change, and was committed to be submitted to support implementation of the change prior to the beginning of cycle 6 for the Davis-Besse Nuclear Power Station (DBNPS), Unit No. 1.
Further review of this itea has revealed that the deletion of the AFP lov suction pressure interlock would invalidate the acceptance provided by the NRC Staff presanted in the Safety Evaluation Report (SER) issued to address NUREG-0737, Item II.E.1.1, Auxiliary Feedvater Evaluation (Log No. 1455, dated February 21, 1984).
During 1982, based on a review of the DBNPS Auxiliary Feedvater (AFV) system design per NUREG-0737, Item II.E.1.1, the NRC issued a set of recommendations (Log No. 1052, dated August 3, 1982) to TED.
One of these recommendations, GS-4, was related to the AFP suction transfer to an alternate AFV supply in the event the primary AFV supply was not available.
This recommendation also addressed NRC's concern regarding the possibility of pump degradation during such a transfer.
In response to this NRC recommendation TED stated that the automatic transfer of AFV pump suction from the condensate storage tank to the service water system was designed to prevent any degradation of the pump performance due to loss of the primary water supply (Serial No. 857, dated September 20, 1982).
If the automatic transfer system failed to transfer to the alternate source, the transfer could 1
0 THE TOLEDO ED' SON COMPANY ED! SON PLAZA 300 MADISON AVENUE TOLEDO. OH'O 43652 8'~O6060115 880527 PDR ADOCK 05000346 l
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Dock;t No. 50-346 Lic nsa No. NPP-3 S;riol No. 1514 Page 2 be achieved manually.
If the suction pressure dropped belov 1 psig before the transfer was completed, the inlet steam to the AFPT would be isolated following a 2.5 second delay and, thereby, any pump degradation vould be prevented. The NRC addressed this interlock design in the aforementioned SER.
The SER accepted the interlock configuration in that the lov suction pressure interlock provides protection against the degradation of AFP performance in the event of an inadventent loss of AFP suction pressure.
Further review of this item has also identified that the concern associated with inadvertent securing of the AFPTs is adequately precluded in the current DBNPS design.
In the DBNPS design, steam to drive the AFPTs can be supplied from both steam generators. One steam inlet valve to each AFPT is kept open during normal operation, and, during transients that require AFV initiation, the remaining steam inlet valve receives an open signal. Therefore, in order to stop the pump it is necessary for both of the steam inlet valves to an AFPT to be closed.
There are two low-lov suction pressure switches in each AFP suction line.
When a lov-lov suction pressure (<1 psig) is detected at the AFP suction, each pressure switch provides a closure signal to the steam inlet valve corresponding to that pressure switch.
Since both steam inlet valves need to be closed to isolate steam to the AFPT and stop the AFP, a single failure (e.g. spurious actuation) of a pressure switch would not result in an inadvertent isolation of motive steam to an AFPT.
During the extended outage following the June 9, 1985 event at Davis-Besse, the time delay associated with the pressure switch trip function was evaluated and increased to 60 seconds. This des:gn modification ensures that a momentary lov suction pressure condition that may be caused by pressure oscillations during pump startun or during an automatic or manual transfer of AFP suction to an alternate supply vill not result in an unnecessary isolation of steam to an AFPT.
Iloveve r, if the lov suction pressure persists, confirming existence of an actual low suction pressure condition, the AFPT steam supply vill be isolated to effect stopping of the AFP and thereby protecting the pump from damage.
Therefore, protection against a single failure which could de;rade both AFPs is maintained.
Based on the above, Toledo Edison rescinds its commitment as stated in Appendix IV.C.2.1 of the Course of Action document related to the deletion of this interlock.
If you have any questions, please contact Mr. R. V.
Schrauder, Nuclear Licensing Manager, at (419) 249-2366.
Very truly yours,
% Mw %
RMC:t1t cc: DB-1 Resident Inspector A. B. Davis, Rek onal Administrator (2 copies) l A. V. DeAgazio, NRC/NRR Davis-Besse Project Manager