ML13317B289
| ML13317B289 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/15/1991 |
| From: | Rosenblum R SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9102200173 | |
| Download: ML13317B289 (3) | |
Text
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 February 15, 1991 TELEPHONE MANAGER OF (714) 454-4505 NUCLEAR REGULATORY AFFAIRS U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Main Feedwater Line Break Analysis/Reduced Tave Operation San Onofre Nuclear Generating Station, Unit 1 The purpose of this letter is to inform you that we are revising the acceptance criteria for the design basis accident analyses to preclude filling the pressurizer. This will ensure the pressurizer Power Operated Relief Valves (PORVs) and Safety Relief Valves (SRVs) will not discharge water during transient conditions resulting from an accident. In order for the Main Feedwater Line Break (MFLB) accident to meet this new acceptance criteria the assumption for operator action time to initiate Auxiliary Feedwater (AFW), and the initial Reactor Coolant System Average Temperature (Tave), need to be revised.
This letter is also to inform you that plant operation will be restricted to reduced Tave during Cycle 11. A proposed technical specification to address reduced Tave will be submitted 3 months after return to service.
The above items have been discussed with Mr. James E. Tatum and Mr. George Kalman of the NRC and it was agreed that this informational letter would be provided.
Background
NUREG-0737, Item II.D.1, requires pressurizer PORVs and SRVs and their associated piping to be evaluated for the worst case loads. Accidents which lead to the pressurizer being filled and water being discharged are the major concerns. In order to resolve this NUREG item we are establishing a new acceptance criteria to preclude filling the pressurizer for all design basis accidents, which will ensure the PORVs and SRVs do not discharge water.
9102?0017 -
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.Docum~nt Control Desk
-2 The second item addressed by this letter concerns operating the plant at reduced Tave. Unit 1 has operated at reduced Tave since Cycle 8 to minimize Intergranular Attack occurring in the steam generator secondary side.
From Cycle 8 through Cycle 10, the Reload Safety Evaluation has been based on both the nominal Tave and reduced Tave operating programs.
MFLB Analysis The design basis analyses of record have been reviewed and three events resulted in pressurizer fill.
These three events were previously analyzed using nominal Tave. They are the MFLB-upstream of the in-containment check valve at 100% power, and the MFLB-downstream of the in-containment check valve at both 100% power and 50% power.
These three accident cases have now been reanalyzed at reduced Tave. The results predict that the pressurizer does not fill with water assuming the reduced initial temperature condition.
In order to prevent the pressurizer from filling, for the MFLB-downstream at 100% power, we restored the previously approved 15 minute operator action time to initiate AFW flow. The 15 minute operator action time was previously approved for this MFLB case in your Amendment No. 125, dated April 25, 1989.
A more conservative operator action time of 20 minutes was used in the most recently submitted MFLB analysis (Amendment No. 138, issued November 15, 1990).
This assumption provided additional conservatism over that previously approved by the NRC and was used to increase the available time for operator action to the maximum extent without exceeding the event acceptance criteria.
However, we have now applied a more conservative acceptance criteria (no pressurizer fill) which requires that the original 15 minute operator action time be used.
Using these assumptions we meet the new acceptance criteria of no pressurizer fill for all the design basis accidents. We will update the Chapter 15 analysis to reflect these changes in the next revision of the UFSAR.
Reduced Tave Analyses For Cycle 11 we have decided to limit plant operation to reduced Tave.
Therefore, the Reload Safety Evaluation for Cycle 11 has reevaluated design basis events for reduced Tave only. Consistent with our Reload Safety Evaluation, we will restrict Tave operation to a maximum of 555.50F at 100%
power. This temperature is the actual value used in the Safety Analysis.
The instrument setting in the plant will be lower to allow for instrument error.
Docufent Control Desk
-3 The Unit 1 Technical Specifications do not have a specification for Tave operation. Since this is an important operating parameter we have decided to include this limit in the technical specifications consistent with the Westinghouse Standard Technical Specifications. We have discussed this proposed change with our current NRC Project Manager, Mr. George Kalman. We agree that a technical specification controlling Tave operation should be added to the technical specifications as an upgrade. We will submit a proposed technical specification 3 months after Cycle 11 return to service.
In the interim, we will implement administrative controls to ensure we operate within our reduced Tave limits. These administrative controls will control Tave operation until you have reviewed and approved the proposed technical specification.
If you have any questions, please contact me.
Very truly yours, cc:
George Kalman, NRC Project Manager, San Onofre Unit 1 J. B. Martin, Regional Administrator, NRC Region V C. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2, and 3 C. D. Townsend, NRC resident Inspector, San Onofre Unit 1