ML13080A406

Response to Request for Additional Information (RAIs 39, 43, 44, 58 and 61) Regarding Confirmatory Action Letter, (TAC Me 9727)

ML13080A406
Person / Time
Site:	San Onofre
Issue date:	03/20/2013
From:	St.Onge R Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC ME9727
Download: ML13080A406 (11)

Text

SOUTHERN CALIFORNIA Richard I. St. Onge EDISON Director, Nuclear Regulatory Affairs and Emergency Planning An EDISON INTERNATIONAL Company March 20, 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 (RAIs 39, 43, 44, 58 and 61)

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. Email from Mr. James R. Hall (USNRC) to Mr. Ryan Treadway (SCE), dated February 20, 2013, Request for Additional Information (RAIs 38-52) Regarding Response to Confirmatory Action Letter, San Onofre Nuclear Generating Station, Unit 2

4. Email from Mr. James R. Hall (USNRC) to Mr. Ryan Treadway (SCE), dated February 21, 2013, Request for Additional Information (RAIs 53-67) 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 emails dated February 20, 2013 (Reference 3) and February 21, 2013 (Reference 4), the NRC issued Requests for Additional Information (RAIs) regarding the CAL response.

Enclosure 1 of this letter provides the response to RAIs 39, 43, 44, 58 and 61.

P.O. Box 128 San Clemente, CA 92672

Document Control Desk March 20, 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,

Enclosure:

1. Response to RAIs 39, 43, 44, 58 and 61 cc: E. E. Collins, Regional Administrator, NRC Region IV J. 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 RAIs 39, 43, 44, 58 and 61

RAI 39

In Reference 2, p. 36, Bottom of page, the term P is not defined. Please define the parameter, and explain (1) how it is formulated, and (2) how it is related to the ATHOS computed nodal void fraction.

RESPONSE

Note: RAI Reference 2 is "Evaluation of Stability Ratio for Return to Service," prepared by MHI, Document No. L5-04GA567, Revision 6.

Define the parameter 13 As used in RAI Reference 2, P is the homogeneous void fraction defined by the volumetric flow rates of the gas and liquid phases:

V9 + V The correlations used in the stability ratio evaluation depend, in part, on the homogeneous void fraction. Experiments control void fraction by varying the volumetric flow rate of the two phases, so experimental data are correlated to homogeneous void fraction. Homogeneous void fraction distribution along the tube length is not an ATHOS output. The homogeneous void fraction is calculated by using the Smith correlation and nodal void fraction obtained from ATHOS output as outlined below.

1) Explain how 13 is formulated The homogeneous void fraction, P, is formulated in terms of quality (x, vapor mass flow fraction). The definition for quality is:

Mrg + 1711 The mass flow rate of each phase is defined as;

=h pg - V1 Substitute the definition for each mass phase into the expression for quality:

X=-

Th liui + Pvf V1 The liquid volume flow fraction (11- p)is derived from the homogeneous void fraction:

1g 1ý +3V, Page 2 of 9

Substitute in the quality expression:

PgPg*+_

gg + fl, 3 +PI-(1/l)

Pgg+i~ 1I4 V, Pgfl Vg + i;' P~g V~+V9 I "Vg+ V, Solve for P3as a function of quality, x:

P 9f =pPg f X + Pp X - P 'fl X P, "" X + Pg " - P9 " l " X = P" X PI .x P 'x + Pg (- x)

2) Explain how P3is related to the ATHOS computed nodal void fraction a Homogenous void fraction (P) is obtained from local void fraction (a) through the use of the Smith correlation and saturated density for liquid and vapor.

" ATHOS provides nodal void fraction (a) as a function of position along the tube.

• Nodal void fraction (a) is converted to quality (x) by using the Smith correlation:

Pa p 1 x ) 1 p- )P

• Quality is used to calculate homogeneous void fraction (p3):

Pi.x P 'X + Pg (1- x)

Terminology a: Nodal Void Fraction p9: Vapor Density fl: Homogeneous Void Fraction (vapor volume fraction)

PI: Liquid Density mg: Vapor Mass mi: Liquid Mass Vg: Vapor Volume V1 : Liquid Volume x : Mixture Quality (vapor mass fraction) e: Entrainment Coefficient (ratio of the mass of liquid flowing in the homogeneous mixture to the total mass of water flowing)

Page 3 of 9

RAI 43

In Reference 4, p. 15, Section 6.3, "Assumption," Item (1) "Fluid force," please explain the basis for the statement, "The turbulent excitation force is evaluated and fluid force caused by FEI is not taken into account..." It is not clear how the turbulent excitation force is used to determine when the friction force is adequate to assume that there is no in-plane motion at the subject AVB intersection. Please clarify the statement, "When the friction force due to contact force is smaller than the turbulent excitation force at an AVB support point, a tube can slide in the in-plane direction."

RESPONSE

Note: RAI Reference 4 is "Analytical Evaluations for Operational Assessment," prepared by MHI, Document No. L5-04GA585, Revision 2.

It is important to note that the analysis in RAI Reference 4, Section 6, was ultimately not used in the Operational Assessment (OA) contained in Return to Service Report Attachment 6, Appendix B. As explained in the response to RAI 35, an alternate analysis was developed and validated based on the observed performance of Unit 3 and Unit 2.

Explain the basis for the statement "The turbulent excitation force is evaluated and fluid force caused by FEI is not taken into account ... "

The condition being evaluated is the design condition with no relative motion between the tube and the AVB. In the design condition FEI is not occurring so the only driving force is from turbulence.

Please clarify the statement, "When the friction force due to contact force is smaller than the turbulent excitation force at an AVB support point, a tube can slide in the in-plane direction."

The support effectiveness criterion developed in RAI Reference 4, Section 6, assumed only one AVB support resists all the flow force along the U-bend tube. As long as the static resisting friction force at an AVB intersection is greater than the driving force due to flow, the tube will not move in the in-plane direction at the AVB intersection. For this support effectiveness criterion, the AVB intersection was considered to be an active support. As indicated above and as discussed in the response to RAI 35, this support effectiveness criterion was not used for the OA contained in Return to Service Report Attachment 6, Appendix B.

Page 4 of 9

RAI 44

In Reference 4, p. 15, Section 6.3, "Assumption," Item (1) "Fluid force," it is assumed there is no in-plane motion if the stability ratio (SR) is less than 1.0. How has MHI accounted for the potential that in-plane tube motion may occur at a SR less than 1.0 and how is the analysis result affected if a smaller value is used for this threshold?

RESPONSE

Note: RAI Reference 4 is "Analytical Evaluations for Operational Assessment," prepared by MHI, Document No. L5-04GA585, Revision 2.

RAI Reference 2 is "Evaluation of Stability Ratio for Return to Service," prepared by MHI, Document No. L5-04GA567, Revision 6.

RAI Reference 4, p. 15, Section 6.3, "Assumption," Item (1) "Fluid force," does not assume there is no in-plane tube motion when the SR is less than 1.0. The assumption is that no in-plane FEI occurs when the SR is less than 1.0. This is consistent with the definition of FEI.

How has MHI accounted for the potential that in-plane tube motion may occur at a SR less than 1.0?

RAI Reference 4 does not address the potential that in-plane tube motion may occur at a SR less than 1.0. The in-plane motion that occurs at SR less than 1.0 is accounted for in RAI Reference 2. The dynamic analysis model described in RAI Reference 2 allows for in-plane motion.

How is the analysis result affected if a smaller value is used for this threshold?

Stability analysis is performed subsequent to the calculation of required contact force. The stability ratio threshold has no effect on the contact force analysis result. In the response to RAI 35, we have explained that this derivation of contact force was not used in the Operational Assessment (OA) contained in Return to Service Report Attachment 6, Appendix B.

Page 5 of 9

RAI 58

In Reference 3, Appendix 9, Table 6.2-1, which parameters are sampled randomly at each tube/AVB intersection? Why is this appropriate in lieu of assuming a functional relationship for each given parameter from tube to tube in a given column of tubes? For parameters (e.g., AVB twist) assumed to follow a functional relationship from tube to tube in the same column, provide the basis for the assumed relationship. For AVB twist, how does the assumed relationship relate to Figure 6.2-2?

RESPONSE

Note: RAI Reference 3 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report." prepared by MHI, Document No. L5-04GA564, Revision 9.

Six parameters representing manufacturing variations were considered for the contact force analysis: tube ovality (G value), tube pitch, tube flatness, AVB thickness, AVB twist, and AVB flatness.

Tube G value Tube pitch Tube Flatness (True position of land)

I I:*1H AVB thickness AVB twist AVB Flatness The input values were randomly sampled at each tube/AVB intersection for the first four parameters. AVB twist was randomly sampled at each AVB and then varied at each tube intersection along the AVB following a functional relationship. AVB flatness was not used in contact force analysis. The basis for using either random sampling or a functional relationship for each parameter follows:

Page 6 of 9

Tube Ovality (G value):

Tube ovality was randomly sampled at each tube/AVB intersection. The random distribution of tube ovality from tube-to-tube was based on actual tube manufacturing data which provide more accurate results than assuming a functional relationship.

Tube Pitch (TSP hole variation from true position):

The contact force model included the effect of tube pitch by using gap elements at TSP holes.

The gap size was randomly sampled at each tube-to-TSP intersection at the top TSP from a distribution based on the fabrication tolerance for TSP hole pitch. Therefore, random sampling is more appropriate than assuming a functional relationship.

Tube Flatness:

Tube flatness was randomly sampled at each tube/AVB intersection from a distribution based on the fabrication tolerance. Random sampling for this parameter is appropriate because actual flatness varies randomly both from tube-to-tube and along the tube length.

AVB Thickness:

AVB thickness was randomly sampled at each tube/AVB intersection. As Table 6.2-1 shows, separate AVB thickness distributions were sampled for Unit 2 and Unit 3 based on measurement results. Therefore, random sampling is appropriate.

AVB Flatness:

AVB flatness was not used in the contact force analysis. AVB flatness variations have a negligible effect on contact forces.

Page 7 of 9

AVB Twist:

AVB twist was randomly sampled as a property of each AVB, then varied systematically along the length of the AVB using a functional relationship. AVB twist is generated by bending a straight AVB bar during AVB manufacturing, as shown in the following figure. As a result of this process, an unloaded AVB (i.e., before insertion in the tube bundle) has a uniform twist along each straight leg.

• b bending Twisted Twisted Figure 6.2-2 shows the functional form of the AVB twist factor that represents the variation of torsional stiffness along the length of an AVB in the contact force model. Since the AVB has uniform cross section, its torsional stiffness at each tube/AVB intersection along its length is inversely proportional to the distance of the intersection from the nose and retaining bar endpoints of the AVB. This is the reason for the characteristic "bathtub" shape of the AVB twist factor depicted in Figure 6.2-2. For more details regarding the basis for the AVB twist factor, please see the response to RAIs 64 through 66.

Page 8 of 9

RAI 61

Reference 3, Appendix 9, Attachment 9-3, Figure 4.1.2-3. Discuss the pedigree of the data in this figure and how it differs from Reference 2, Figure 6-19 and 6-20. Please explain the differences between the Reference 3 versus the Reference 2 figures for dings exceeding 0.5 volts?

RESPONSE

Note: RAI Reference 3 is "Tube Wear of Unit-3 RSG - Technical Evaluation Report." prepared by MHI, Document No. L5-04GA564, Revision 9.

RAI Reference 2 is "SONGS U2C1 7 Steam Generator Operational Assessment for Tube-to-Tube Wear," prepared by Areva NP Inc. Document No. 51-9187230-000, Revision 0.

The data plotted in Figure 4.1.2-3 of Appendix 9, Attachment 9-3 in RAI Reference 3 and those in Figures 6-19 and 6-20 in RAI Reference 2 use the same Pre-Service Inspection Eddy Current Testing (ECT) data. The ECT data were obtained under AREVA's 10 CFR 50 Appendix B program for the Pre-Service Inspection and are retained under SONGS Steam Generator Program.

The differences between the figures in RAI References 2 and 3 are:

" The figures in RAI Reference 2 cover the signals on the U-bend region, which include the signals on freespan area and those at U-bend AVB locations but do not include the signals at TSP locations. The plotted data cover the voltage range from 0.5 to 1.5 Volts.

" The figures in RAI Reference 3 cover the signals on the locations of structures, which include the signals at U-bend AVB locations and those at TSP locations but do not include the signals on freespan area. The plotted data cover the full voltage range of the reported ding indications.

RAI Reference 2 RAI Reference 3 Figures 6-19 Figure 4.1.2-3 and 6-20 Pre-service ECT Inspection Data Yes Yes U-bend Freespan Dings Yes No TSP Dings No Yes AVB Dings < 0.5 Volts No Yes AVB Dings 0.5-1.5 Volts Yes Yes AVB Dings > 1.5 Volts No Yes Despite these differences, the figures support the comparison of the relative numbers of contact signals in the upper bundle for Units 2 and 3 and demonstrate that contact forces are more significant in Unit 2 than in Unit 3.

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