ML13028A475

Response to Request for Additional Information (RAI 27) Regarding Confirmatory Action Letter

ML13028A475
Person / Time
Site:	San Onofre
Issue date:	01/25/2013
From:	St.Onge R Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME9727
Download: ML13028A475 (4)

Text

SOUTHERN CALIFORNIA Richard 1. St. Onge EDISON Director, Nuclear Regulatory Affairs and Emergency Planning An EDISON INTERN4TIONA4L& Company January 25, 2013 10 CFR 50.4 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Docket No. 50-361 Response to Request for Additional Information (RAI 27)

Regarding Confirmatory Action Letter Response (TAC No. ME 9727)

San Onofre Nuclear Generating Station, Unit 2

References:

1. Letter from Mr. Elmo E. Collins (USNRC) to Mr. Peter T. Dietrich (SCE), dated March 27, 2012, Confirmatory Action Letter 4-12-001, San Onofre Nuclear Generating Station, Units 2 and 3, Commitments to Address Steam Generator Tube Degradation

2. Letter from Mr. Peter T. Dietrich (SCE) to Mr. Elmo E. Collins (USNRC), dated October 3, 2012, Confirmatory Action Letter - Actions to Address Steam Generator Tube Degradation, San Onofre Nuclear Generating Station, Unit 2

3. Letter from Mr. James R. Hall (USNRC) to Mr. Peter T. Dietrich (SCE), dated December 26, 2012, Request for Additional Information Regarding Response to Confirmatory Action Letter, San Onofre Nuclear Generating Station, Unit 2

Dear Sir or Madam,

On March 27, 2012, the Nuclear Regulatory Commission (NRC) issued a Confirmatory Action Letter (CAL) (Reference 1) to Southern California Edison (SCE) describing actions that the NRC and SCE agreed would be completed to address issues identified in the steam generator tubes of San Onofre Nuclear Generating Station (SONGS) Units 2 and 3. In a letter to the NRC dated October 3, 2012 (Reference 2), SCE reported completion of the Unit 2 CAL actions and included a Return to Service Report (RTSR) that provided details of their completion.

By letter dated December 26, 2012 (Reference 3), the NRC issued Requests for Additional Information (RAIs) regarding the CAL response. Enclosure 1 of this letter provides the response to RAI 27.

P.O. Box 128 San Clemente, CA 92672

Document Control Desk January 25, 2013 There are no new regulatory commitments contained in this letter. If you have any questions or require additional information, please call me at (949) 368-6240.

Sincerely,

Enclosures:

1. Response to RAI 27 cc: E. E. Collins, Regional Administrator, NRC Region IV R. Hall, NRC Project Manager, SONGS Units 2 and 3 G. G. Warnick, NRC Senior Resident Inspector, SONGS Units 2 and 3 R. E. Lantz, Branch Chief, Division of Reactor Projects, NRC Region IV

ENCLOSURE 1 SOUTHERN CALIFORNIA EDISON RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING RESPONSE TO CONFIRMATORY ACTION LETTER DOCKET NO. 50-361 TAC NO. ME 9727 Response to RAI 27 Page 1 of 2

RAI 27

Reference 6, Appendix 8, "SG Tube Flowering Analysis", page 8-2 (307 of 474) - MHI concludes, in part, that the tube-to-AVB gaps in the center columns increase due to hydrodynamic pressure by [ ... ] when the manufacturing tolerance dispersion is not taken into account. MHI also concludes that the gap increase due to hydrodynamic pressure is small when the manufacturing tolerance dispersion is taken into account. Discuss whether this latter finding may simply reflect the hydrodynamic pressures acting to relieve the tube-to-AVB contact forces caused by the manufacturing tolerance dispersion, such that the gaps are relatively unchanged relative to the case where the hydrodynamic pressure is not considered.

Reference 6, Appendix 9, "Simulation of Manufacturing Dispersion for Unit-2/3," does not seem to make specific mention of whether the calculated tube-to-AVB contact forces directly considered the effect of the hydrodynamic effect on tube-to-tube contact forces, but the staff understands that they did not. If the staffs understanding is correct, explain how the resulting contact forces are conservative.

RESPONSE

Note: RAI Reference 6 is MHI Document L5-04GA564, Tube Wear of Unit-3 RSG - Technical Evaluation Report, Revision 9, October 2012, prepared by Mitsubishi Heavy Industries, LTD.

(ADAMS Accession Nos. ML12285A265, ML12285A266, and ML12285A267).

The staffs understanding is correct: the contact force analysis contained in RAI Reference 6, Appendix 9 does not consider the effect of hydrodynamic forces. Since hydrodynamic forces are very small in comparison to contact forces they were not included in the contact force analysis. To demonstrate this, a sensitivity study was performed in response to this RAI.

This study compared the probability of occurrence of in-plane fluid-elastic instability (FEI) for two cases: (1) contact force distribution including hydrodynamic forces and manufacturing dispersion and (2) contact force distribution based on manufacturing dispersion alone. For the 70% power condition, there was no statistically significant increase in the probability of in-plane FEI when hydrodynamic forces were included.

The consideration of hydrodynamic forces results in a slight reduction of average contact force at 70% power, but the tube-to-support gaps are relatively unchanged. Hydrodynamic forces are postulated to have little effect on tube-to-support gaps due to their low estimated magnitude.

The sensitivity study performed for this RAI response determined there is no statistically significant increase in the probability of in-plane FEI when the effects of hydrodynamic forces are included in the analysis.

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