ML19263C911
| ML19263C911 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/26/1979 |
| From: | Domeck C TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML19263C907 | List: |
| References | |
| TASK-TF, TASK-TMR TAC-11050, NUDOCS 7903120331 | |
| Download: ML19263C911 (3) | |
Text
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Docket No. 50-346 License No. hTF-3 Serial No. 485 g,
February 26, 1979 SAFETY EVALUATION STEAM GENERATOR DUAL LEVEL SETPOINT FOR AUXILIARY FEEDWATER CONTROL DAVIS-BESSE NUCLEAR POWER STATION UNIT 1 FEBRUARY, 1979 790312033l<
SAFETY EVALUATION FCR 78-485 The " auto-essential", SG level control has been modified to include a dual set-point. Following automatic actuation c# auxiliary feedwater by the Steam and Feedwater Rupture Control System (SFRCS), SG IcVel will be controlled to 35 inches on the startup range indicators if no SFAS actuation (low RCS pressure or high CV pressure) of the High Pressure Injection (HPI) System occurs. For accident conditions where both auxiliary feedwater and HPI are automatically actuated (indicative of loss of coolant accident conditions), the auto-essential level control will regulate water addition to the SG's to achieve and maintain a 120" level (96" indicated) on the startup range instrumentation. The use of a dual setpoint is a change to SG level controls as described in the Davis-Besse, Unit 1 FSAR; and the safety evaluation provided belca is the 10CFR50.59 review of this change. The information provided, herein, is an extension of documentation supplied by letters 1,2 in December of 1978. These previous submittals were in support of interim measures, utilizing operator action, to control SG levels.
Incorporation of the dual setpoints into the " auto-essential" level control on the SG's automate the operator actions which have been used in the interim pending completion of permanent design changes.
Design changes to provide the dual level setpoint control, in lieu of a single setpoint when auxiliary feedwater is required, have been made to maintain adequate 3
decay heat removal and indicated pressurizer level during anticipated events and to maintain consistency with the small break LOCA analysis (BAW-10075A), which is applicable for SG 1evels as low as 120 inches.
Test data and supplemental B&W analysis provided the design basis for the 35 inch (indicated) level which will be utilized for all anticipated events requiring auxiliary feedwater at the Davis-Besse Power Station Unit 1.
The natural circulation test (TP 800.04) demonstrated that the 35 inch (indicated) SG level will provide adequate loop circulation for decay heat removal (see Note 1 for additional infor-mation).
B&W analyses further show that pressurizer level is maintained on scale for reactor trips due to or followed by a loss of main feedwater or a loss of off-site power.
The high, SG level setpoint (96 inches indicated) anticipated usage is during design basis events only where both auxiliary feedwater and HPI are required. The accident analysis presented in the Davis-Besse Unit 1 FSAR for these events (LOCA's, Steam Line Break, etc.) remain valid with no decrease in margin relative to established acceptance criteria.
In summary, the incorporation of the dual level setpoint control for the steam generators is a desirable design change which will lead to improved plant perfor-This design change does not involve an unreviewed safety question and will mance.
not require a license amendment because:
1.
The probability of occurrence or the consequence of an accident or malfunction of equipment important to safety previously evaluated in the FSAR has not been increased.
SAFETY EVALUATION FCR 78-485 (cont'd) 2.
The possibility of an accident or malfunction of a different type that is not bounded by a previous analysis in the FSAR has not been created.
3.
The margin of safety as defined in the basis for any Technical Specification has not been decreased.
4.
No changes to the facility Technical Specifications are required.
NOTES:
1.
TECo letter to R. W. Reid, Chief Operating, Reactor Branch No. 4, Division of Operating Reactors, Serial No. 471, dated December 11, 1978.
2.
TECo letter to R. W. Reid, Chief Operating Reactor Branch No. 4, Division of Operating Reactors, Serial No. 475, dated December 22, 1978.
3.
SG level is but one factor that contributes to maintaining pressurizer level on scale during anticipated events. Auxiliary feedwater addition rates and secondary steam pressure control are also important.
The dual level setpoint control provides an integrated system to coordinate steam generator level and auxiliary feedwater addition rates. Measures to provide proper equipment operation which affect secondary pressure have been taken. However, equipment malfunctions cannot be prevented with absolute certainty.
If pressure level indication is lost (for any reason) during anticipated events, this occurrence is considered an operational inconvenience and not a safety problem.
The operator can rely on RC system pressure to assure that a level of water in the pressurizer is maintained.
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C. R. Domeck