ML023330416
| ML023330416 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/26/2002 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| GL-96-006, TAC M96862, TAC M96863 | |
| Download: ML023330416 (4) | |
Text
I*
SOUTHIHN CLIFORNIA EDISON An EDISOrT' 1
10\\ Al, (',M ainy A. Edward Schcrer Manager of Nuclear Regulatory Affairs November 26, 2002 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C., 20555-0001
Subject:
Docket Nos. 50-361 and 50-362 Supplemental Response to Generic Letter 96-06 "Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions,"
San Onofre Nuclear Generating Station, Units 2 and 3 (TAC Nos. M96862 and M96863)
References:
See Enclosure
Dear Sir or Madam:
This letter is to revise the Southern California Edison (SCE) response to Generic Letter (GL) 96-06 "Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions."
By letters dated February 3, 1997, July 10, 1998, October 30, 1998, July 2, 1999, and April 19, 2000, (References 1 through 5) SCE provided responses to GL 96-06 for San Onofre Nuclear Generating Station (SONGS) Units 2 and 3. Based on the information provided in these letters, the NRC closed Technical Assignment Control numbers M96862 and M96863 by a letter dated May 1, 2000 (Reference 6).
SCE indicated in a letter dated July 30, 2002 (Reference 7), that SCE was re-evaluating the analytical tools used by SCE in the analysis described in Reference 1 and the potential impact on the containment boundary. SCE completed the re-evaluation in October 2002.
The original GL 96-06 analysis for the San Onofre Nuclear Generating Station (SONGS)
Units 2 and 3 containment emergency cooling units (ECU) was performed in 1997 using the American Air Filter (AAF) "COOLNUC" computer Code. AAF verified this program against test data, which resulted in a good correlation at normal flow rates. In the original analysis, the "COOLNUC" program was used with an assumed cooling water flow rate of 100 gpm. The resulting forced convection heat transfer coefficient was P.O. Box 128 San Cleimcntc, CA 92674-0128 949-368-7501 Fax 949-368-7575 (V
V "1K)
November 26, 2002 Document Control Desk assumed to adequately represent stagnant conditions in the ECU. The resulting heat transfer rate calculated by the "COOLNUC" program was then applied to determine the heatup rate of the ECU tubes and stagnant water in the tubes. The original analysis concluded that boiling in the ECU's would not take place during the transient described in GL 96-06.
Based on information acquired since 1997, SCE questioned the adequacy of the "COOLNUC" program for analyzing the GL96-06 scenario. As a result, additional analyses using different analytical tools were performed. Based on these analyses, the original results were found to be potentially non-conservative for two reasons:
- 1.
The "COOLNUC" program does not allow for switching the heat transfer coefficient between the tube wall and water inside the tube from convective to boiling when the wall temperature is sufficiently high to result in local sub-cooled boiling of the water inside the tubes. The magnitude of boiling heat transfer coefficients is higher than the convective heat transfer coefficients. As a result, the heat transfer rate was originally underestimated during the latter portion of the heat up scenario when the tube wall temperature increased to the point where it exceeded the saturation temperature of the water.
- 2.
The "COOLNUC" program performs steady state heat balance analysis for the entire ECU, which consists of ten coils stacked on top of each other. Within each coil, there are 4 rows of tubes. The original analysis was based on the heat removal rate calculated by the "COOLNUC" program for the entire ECU, and did not consider the variation of coil performance row by row through each coil.
Considering the heat up rate in the worst-case row results in a shorter predicted time until boiling could occur.
Based on the above, additional heat transfer calculations were performed. The most conservative of these calculations indicated that boiling and formation of steam bubbles could occur as soon as 11.8 seconds following onset of the postulated limiting accident.
When these bubbles collapse following pump restart, the resultant water hammer would generate loads that could potentially exceed the loads for which the ECU's and the associated piping were analyzed.
Preliminary analysis of a representative portion of the Component Cooling Water (CCW) system, including the ECU's, was performed in support of the operability assessment for this issue. The analysis indicated that the ECU's and associated piping could withstand the loads generated by the postulated waterhammer. SCE plans to finalize all necessary calculations and complete a summary report by the end of the second quarter of 2003. SCE intends to submit this summary report and provide a status of the GL 96-06 issue by August 1, 2003.
Should any corrective actions be required following completion of the analysis, SCE will plan to complete these corrective actions by the end of the Unit 3 Cycle 13 refueling outage, currently scheduled for the end of 2004.
We will keep the staff informed, but should you have any questions or would like additional information, please feel free to contact Mr. Jack Rainsberry at (949)368-7420.
Sincerely, Enclosure cc:
E. W. Merschoff, Regional Administrator, NRC Region IV B. M. Pham, NRC Project Manager, San Onofre Units 2, and 3 C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 & 3 November 26, 2002 Document Control Desk
REFERENCES:
- 1)
Letter from J. L. Rainsberry (SCE) to the Document Control Desk (NRC), dated February 3, 1997;
Subject:
120 Day Response to Generic Letter 96-06:
"Assurance of Equipment Operability and Containment Integrity During Design Basis Accident Conditions," San Onofre Nuclear Generating Station Units 2 and 3
- 2)
Letter from J. L. Rainsberry (SCE) to Document Control Desk (NRC) dated July 10, 1998;
Subject:
Generic Letter 96-06: "Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions,"
Additional Information, San Onofre Nuclear Generating, Station Units 2 and 3
- 3)
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC), dated October 30, 1998;
Subject:
Generic Letter 96-06: "Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions,"
Additional Information, San Onofre Nuclear Generating Station, Units 2 and 3
- 4)
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC), dated July 2, 1999;
Subject:
Additional Information Regarding Generic Letter 96-06:
"Assurance of Equipment Operability and Containment Integrity During Design Basis Accident Conditions," San Onofre Nuclear Generating Station, Units 2 and 3
- 5)
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC), dated April 19, 2000;
Subject:
Completion of Commitments for Generic Letter 96-06:
"Assurance of Equipment Operability and Containment Integrity During Design Basis Accident Conditions," San Onofre Nuclear Generating Station, Units 2 and 3
- 6)
Letter from L. Raghavan (NRC) to H. B. Ray (SCE) dated May 1, 2000;
Subject:
San Onofre Nuclear Generating Station, Units 2 and 3 - Evaluation of Responses to Generic Letter 96-06:"Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions," (TAC Nos. M96862 and M96863)
- 7)
Letter from A. E. Scherer (SCE) to the Document Control Desk (NRC) dated July 30, 2002;
Subject:
Docket Nos. 50-361 and 50-362, SCE Actions Required by Electric Power Research Institute (EPRI) Report TR-1 13594, "Resolution of Generic Letter 96-06 Waterhammer Issues," Volumes 1 and 2, (TAC NOS.
M96862 and 96863), San Onofre Nuclear Generating Station, Units 2 and 3