ML20100F682

Submittal of Analytical Evaluation of Recirculation Discharge Nozzle-to-Safe End Weld Indication

ML20100F682
Person / Time
Site:	Nine Mile Point
Issue date:	04/09/2020
From:	David Gudger Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML20100F682 (17)

Text

200 Exelon Way Exelon Generation © Kennett Square, PA 19348 W\VW.exeloncorp.com April 9, 2020 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washi_ngton, DC 20555-0001 Nine Mile Point Nuclear Station, Unit 2 Renewed Facility Operating License No. NPF-69 NRC Docket No. 50-410

Subject:

Submittal of Analytical Evaluation of Recirculation Discharge Nozzle-to-Safe End Weld Indication lri accordance with>the American Society of Mechanical Engineers (ASME) Code,Section XI, 2013 Edition, IWB-3134(b) ("Review by Authorities"), Nine Mile Point Nuclear Station, Unit 2 is submitting an analytical evaluation associated with the recirculation discharge (reactor pressure vessel inlet) nozzle-to-safe end weld (N2J).

As discussed in the attached report, an analytical evaluation of an indication was performed to disposition an indication associated with one of the recirculation discharge (reactor pressure vessel inlet) nozzle-to-safe end weld (N2J). The indication is circumferentially oriented, measured by ultrasonic testing to be approximately 6.1 inches long, 0.3 inches through wall, and a surface separation distance of 0.5 inches from the outside surface. The indication is located at the weld centerline (nozzle side), which would place it in the weld material. This is an embedded flaw and does not contain any characteristics of an IGSCC flaw. Instead, this is likely a construction flaw that is now visible due to the change in ultrasonic examination technology. The nozzle-to-safe end weld is a dissimilar metal weld joining the low alloy steel nozzle to the stainless steel safe end with an lnconel 82 weld.

As concluded in this evaluation, the required safety factors will be maintained during operation with this indication over the next five operating cycles, by which time the weld/indication will be examined in accordance with BWRVIP-75A requirements.

There are no regulatory commitments in this letter.

If you have any questions concerning this letter, please contact Tom Loomis at (610) 765-5510.

Respectfully, jptLV,c) f.

David T. Gudger Senior Manager - Licensing Exelon Generation Company, LLC

Submittal of Analytical Evaluation April 9, 2020 Page 2

Attachment:

Recirculation Inlet Nozzle DMW No. 2RPV-KB11 (N2J) Flaw Evaluation cc: Regional Administrator, Region I, USNRC USNRC Senior Resident Inspector, NMP Project Manager USNRC, NMP A. L. Peterson, NYSERDA

Attachment Recirculation Inlet Nozzle DMW No. 2RPV-KB11 (N2J) Flaw Evaluation

File No.: 2000401.301 Project No.: 2000401 Quality Program Type: Nuclear Commercial CALCULATION PACKAGE PROJECT NAME:

NMP2 N2J Nozzle Flaw Evaluation CONTRACT NO.:

00609093, Release 120 CLIENT: PLANT:

Exelon Generation Nine Mile Point Nuclear Station, Unit 2 CALCULATION TITLE:

Recirculation Inlet Nozzle DMW No. 2RPV-KB11 (N2J) Flaw Evaluation Project Manager Preparer(s) &

Document Affected Revision Description Approval Checker(s)

Revision Pages Signature & Date Signatures & Date 0 1 - 12 Initial Issue A A-2 Computer Files Charles Fourcade Richard Mattson 3/25/20 03/25/20 Stan Tang 03/25/20 Do Jo Shim 03/25/20

Table of Contents

1.0 INTRODUCTION

....................................................................................................... 3 2.0 OBJECTIVE .............................................................................................................. 3 3.0 METHODOLOGY ...................................................................................................... 3 4.0 ASSUMPTIONS ........................................................................................................ 4 5.0 INPUTS ..................................................................................................................... 4 6.0 CALCULATIONS ....................................................................................................... 6 6.1 Crack Growth ................................................................................................. 6 6.2 Allowable Flaw Size ....................................................................................... 7 7.0 RESULTS OF ANALYSIS .......................................................................................... 8

8.0 CONCLUSION

S ........................................................................................................ 8

9.0 REFERENCES

.......................................................................................................... 9 LIST OF SOFTWARE FILES....................................................................... A-1 List of Tables Table 1. Allowable Flaw Size.............................................................................................. 10 List of Figures Figure 1. Measured Flaw Dimensions from UT Data [1] ..................................................... 11 Figure 2. Fracture Mechanics Flaw Model .......................................................................... 12 File No.: 2000401.301 Page 2 of 12 Revision: 0 F0306-01R4

1.0 INTRODUCTION

Exelon Generation (Exelon) performed inspections of various dissimilar metal welds (DMWs) during the Spring 2020 refueling outage at the Nine Mile Point Nuclear Station, Unit 2 (NMP-2). A rejectable subsurface (embedded) non-service induced indication, which was seen in previous examinations, was reported during the inspection of the recirculation inlet nozzle DMW No. 2RPV-KB11 (N2J) in the recirculation system [1]. The flaw sizing reported during the Spring 2020 inspection was not acceptable in accordance with the acceptance standards of the ASME Code,Section XI, Subparagraph IWB-3514.4 [2]. Therefore, Exelon contracted Structural Integrity Associates, Inc. (SI) to perform an analytical flaw evaluation in accordance with the ASME Code,Section XI, Paragraph IWB-3640 [2].

2.0 OBJECTIVE This calculation package documents the ASME Code,Section XI, Paragraph IWB-3640 [2] flaw evaluation of the indication reported in Weld No. 2RPV-KB11 (N2J) [1].

3.0 METHODOLOGY The methods used for the flaw evaluation documented in this calculation package are described in ASME Code, Section XI:

• Paragraph IWB-3640,

• Nonmandatory Appendix A

• Nonmandatory Appendix C Paragraph IWB-3640 [2] provides methods for analytical acceptance of flaws that are not acceptable in accordance with the acceptance standards of Paragraph IWB-3514 [2]. These methods are accepted by the U.S. Nuclear Regulatory Commission (NRC) in 10 CFR 50.55a [3].

Fatigue crack growth and allowable flaw size determination are performed using the methods of Nonmandatory Appendix C. The subsurface flaw linear elastic fracture mechanics model given in Nonmandatory Appendix A, Paragraph A-3300 [2] is used to calculate a range of stress intensity factor, KI, to be used with the fatigue crack growth (FCG) equation given in Nonmandatory Appendix C, Subsubarticle C-3210 and Subarticle C-8400 [2]. The fracture mechanics flaw evaluation is performed using the SI pc-CRACK software [4].

The following notes apply to the methods used for this calculation:

1. For the allowable flaw sizing, the primary membrane and bending piping stresses reported for the nozzle-to-safe end location (at nozzle N2J) [5, Table 3] are combined with the secondary stresses for each service level.

2. The yield and ultimate tensile strength material properties for the TP316L stainless steel replacement safe end [6, Page 8] are bounding (lower than the Alloy 82/182 DMW properties),

and are therefore used for the allowable flaw size evaluation. The material properties are obtained from the 2013 Edition of the ASME Code,Section II, Part D [7].

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3. The number of anticipated fatigue cycles applicable for the crack growth evaluation interval are obtained from Reference [8, Table 33], where 470 design cycles (12 cycles per year) will be used herein:

4. The crack growth evaluation is performed using a bounding stress value (using the bounding stress intensity value, SINT, from the Stress Report [6]), and conservatively applied to all operating cycles shown above. Therefore, the bounding SINT is assumed to cycle 470 times over the original 40-year design life, equal to 118 cycles (rounded up to 120) per a 10-year operating interval.

4.0 ASSUMPTIONS The following assumptions are used for the flaw evaluation documented in this calculation package:

1. To account for potential uncertainty in the UT measurement data, a value of 0.125 inch is added to the measured flaw depth, 2a (0.0625 inch added to each side of the flaw), and 0.75 inch is added to the measured flaw length (l).

2. The fracture mechanics model for a subsurface flaw in a plate is used for the fatigue crack growth evaluation. The model is consistent with ASME Code,Section XI, Appendix A methodology [4], and is therefore considered adequate to represent the subsurface flaw in a cylinder.

5.0 INPUTS The following design inputs are used for this evaluation:

1. Initial Flaw Size: 2ao = 0.276 in. [1] + 0.125 in. (assumed uncertainty) 2ao = 0.401 in.

lo = 6.14 in. [1] + 0.75 in. (assumed uncertainty) lo = 6.89 in.

2. Distance to Free Surface (Figure 1): S = 0.4485 in. (0.511 [1] - 0.125/2)

3. Flaw Orientation: Circumferential [1]

4. Flaw Location: In Alloy 82 weld material (not in fusion line)

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5. Pipe Dimensions [5,9]: OD = 14.25 in.

ID = 11.51 in. (using 1.37 in. [1] measured thickness) t = 1.37 in. (measured thickness [1])

6. TP316L Material Properties: Yield Strength: 16.0 ksi at 550°F [7]

Ultimate Tensile Strength: 61.75 ksi at 550°F [7]

Flow Strength: 38.88 ksi at 550°F

7. Evaluation Interval: 10 years [assumed]

8. Fatigue Cycles in Evaluation Interval: 120 cycles [8] Rounded 470/4 design cycles/10 years

9. Piping Loads: Obtained from [5, Table 3], as shown below.

Bounding values for Service Levels A, B, C, and D The following primary-plus-secondary piping loads are used in the allowable flaw size evaluation, along with the appropriate safety factors, for each Service Level [5, Table 3]:

Secondary Primary Primary Se(1)

Service (ksi)

Case m b SFm(2) SFb(2)

Level (ksi) (ksi) m b TE-1 Total (ksi) (ksi) (ksi) (ksi)

A Prim2+Sec2 2.672 4.891 2.683 6.704 1.064 10.451 2.7 2.3 B Prim2+Sec2 2.672 4.891 2.683 6.704 1.064 10.451 2.4 2.0 11.69 C Prim10/12+Sec5 2.797 9.315 2.801 1.064 15.560 1.8 1.6 5

11.69 D Prim10/12+Sec5 2.797 9.315 2.801 1.064 15.560 1.3 1.4 5

Notes: 1. Se includes the addition of thermal expansion case TE-1 = 1.064 ksi. All stress values are increased by a factor of 1.4/1.37 since the stress results in Reference

[5, Table 3] were determined for a thickness of 1.4 inches; whereas, this evaluation conservatively uses the 1.37 inch measured value [1].

2. From Section XI of the ASME Code, Paragraph C-2621 [2].

Per Reference [10, Section 4.1], the original design basis normal and upset temperatures and pressures are not exceeded under EPU operating conditions, and therefore, the original loads given above remain bounding. Per Reference [12, Page 3], the comparison ratio, New/Old, for all the Service Level C/D piping stresses and the snubber loads are less than 1.0. Therefore, the original stresses remain bounding for analysis.

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10. The bounding normal/upset alternating SINT stress range of 38.1 ksi [6, Page 6] is used for the crack growth calculation, based on the updated stress analysis report [6]. The bounding Sn value (SINT = 38.1/2 = 19.1 ksi) is conservatively used to bound the needed axial stresses (due to thermal transient events) acting on the circumferential crack.

6.0 CALCULATIONS Fatigue crack growth is performed to determine the flaw size at the end of the 10-year evaluation interval. The final flaw size is then compared to the allowable flaw size to determine acceptability.

6.1 Crack Growth The fatigue crack growth analysis is performed to determine the final crack size for a 10-year evaluation period. The crack growth evaluation is performed using the SI pc-CRACK [4] fracture mechanics software. The bounding normal/upset SINT alternating stress range (38.1 ksi [6, page 6]) is conservatively used to calculate stress intensity factors, using the subsurface flaw model shown in Figure 2 (pc-CRACK Model 208). As shown in Figure 2, the K values are calculated at both Point 1 and Point 2 of the subsurface flaw. The higher K value from Point 1 and Point 2 is used for the crack growth calculation in the thickness direction. The crack growth in the length direction is assumed to be equal to the growth in the depth direction.

The normal/upset (Service Level A/B) stress used for the maximum stress state is, therefore, assumed to be +/-(19.1 ksi). The minimum stress state (to define the crack growth K range) is represented by the negative value (-19.1 ksi) in order to maximize the stress range and K.

The flaw model requires the following parameters:

• Initial half flaw depth, ao = 0.201 in.

• Initial flaw length, lo = 6.89 in.

• Wall thickness, t = 1.37 in.

• Eccentricity Ratio, 2e/t = 0.0526 (where e = 1.37/2 - {(0.8495+0.4485)/2} = 0.036), refer to Figure 1 and Figure 2. Note: UT flaw depths given at 0.511 and 0.787 [1] are modified to 0.4485 and 0.8495 (accounting for 0.125 assumed uncertainty on flaw size).

• Yield strength of Alloy 82/182 weld metal1 = 30.1 ksi [7]

• Aspect ratio, ao/lo = 0.201/6.89 = 0.0291 The fatigue crack growth rate for Alloy 82/182 in air is based on NUREG/CR-6907 [11], which applied a factor of 2 on Alloy 600 fatigue crack growth in air. The crack growth is calculated using a Paris law for Alloy 600 in air (subsurface flaws) per ASME Code,Section XI, Paragraph C-8411 [2]:

da/dn = Co(K)n 1 Yield strength of Alloy 82/182 is only used in calculating the plastic zone correction factor to calculate the stress intensity factor of a subsurface crack in the Alloy 82/182 material.

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where, n = 4.1 [2, C-8411(b)]

Co = CTSRSENV CT = 2.606x10-12 + 7.06x10-15x(T) - 3.080x10-17x(T)2 + 4.327x10-20x(T)3 SR = (1 - 0.82R)-2.2 SENV = 1 [2, C-8411(b)]

An R-ratio of 0.9 (which conservatively assumes the upper bound value given in [2, Figure C-8410-1]) is assumed for calculation of SR. Normal operating temperature of T = 550°F is used to calculate CT. An additional factor of 2 is applied to the crack growth Co term of the Alloy 600 growth rate, per NUREG/CR-6907 [11, Section 5.1], to account for the Alloy 82/182 weld metal.

Therefore, Co = 2 x 8.32382x10-11 = 1.66476x10-10 da/dn = 1.66476x10-10(K)4.1 The crack growth is performed using the defined number of cycles in Section 5.0 (120 cycles per 10 years, equivalent to 12 cycles per year), and the flaw model shown in Figure 2. At the end of the 10-year evaluation period, the crack growth results in a final crack depth of af = 0.246 in. (2af = 0.492 in.), and final crack length of lf = 6.981 in. (6.89 + 0.091), assuming that the same amount of crack growth occurs in the length direction as in the depth direction.

6.2 Allowable Flaw Size Calculations for the allowable flaw size are performed in Excel spreadsheet Nine_Mile_Recirc_N2J.xls.

The appropriate membrane, bending, and secondary stresses are used to evaluate the flaw acceptability. Per ASME Code,Section XI, Paragraph C-4210 and Figure C-4210-1 [2], Article C-6000 methodology is applied, since Alloy 82/182 welds are assumed flux welds. Tables C-5310-1 through C-5310-5 are used along with a Z-factor load multiplier from Subsubarticle C-6330:

For Alloy 82/182 weld metal:

Z = 2.2 x10-6(D)3 - 2.0 x10-4(D)2 + 0.0064*(D) + 1.1355 (for 8 in. < D 40 in. )

Hence, for an outside pipe diameter (D) of 14.25 in., Z = 1.192.

The allowable flaw size is tabulated in Table 1, for a range of flaw depths and lengths for each Service Level. Note that the flow stress of TP316L stainless steel (38.88 ksi) was used in calculating the allowable flaw size per Subparagraph C-6330(c).

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7.0 RESULTS OF ANALYSIS The calculations contained herein use conservative methods in which the bounding stresses for Service Levels A, B, C, and D are used with the most limiting flaw acceptance tables of ASME Code,Section XI, Nonmandatory Appendix C, Table C-5310-1 [2]. A conservative approach is used in which the bounding stress (SINT stress from the stress and fatigue analysis) is treated as pure membrane stress and assumed to apply for all fatigue cycles for calculation of fatigue crack growth. Further, the design number of fatigue cycles is conservatively used, rather than actual projected cycles. The results documented in this calculation package are considered to be a bounding treatment for all applicable service levels.

The crack growth was performed for a 10-year interval. The initial flaw size (2ao= 0.401, lo = 6.89) grows to 2af = 0.492 in. and lf = 6.981 in. The flaw remains subsurface, since S > 0.4a per Reference

[2, Figure IWB-3610-1], as follows:

S = 0.4485 - (0.492 - 0.401)/2 = 0.403 (nearest flaw edge to OD surface; refer to Figure 1) 0.4af = 0.098.

Hence, S > 0.4af The results show that the allowable flaw depth to thickness ratio, 2a/t, for an end-of-interval (EOI) flaw of length to pipe circumference ratio, lf/(D) = 0.156, is 0.622, corresponding to 2aallowable = 0.851 in.

(bounding Service Level C; see Table 1). The EOI flaw depth to thickness ratio is 2af/t = 0.492/1.37 =

0.359, which is less than the allowable ratio of 0.622; therefore, the flaw reported in NMP-2 Weld No.

2RPV-KB11 (N2J) is acceptable for the desired evaluation interval of 10 years.

8.0 CONCLUSION

S The flaw reported in the Nine Mile Point recirculation inlet DMW No. 2RPV-KB11 (N2J) is acceptable for an evaluation interval of at least 10 years. This flaw should be re-inspected at the end of the evaluation interval.

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9.0 REFERENCES

1. General Electric Hitachi, UT Examination Summary Sheet, Report No. N2R17-APR-06, SI File No.

2000401.201.

2. American Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2013 Edition.

3. 10 CFR 50.55a, Codes and Standards, December 02, 2015.

4. pc-CRACK 4.3, Version Control No. 4.3.0.0, Structural Integrity Associates, November 2019.

5. SI Calculation NMPC-17Q-301, Rev. 1, Weld Overlay Design and Allowable Flaw Size Calculation for Recirculation Inlet Nozzles.

6. General Electric Stress Report 22A6593, Rev. 0, Reactor VesselRecirculation Inlet Nozzle, SI File No. NMPC-17Q-201.

7. American Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section II, Part D, Materials, Properties (Customary), 2013 Edition.

8. SI Calculation 1500838.301, Rev. 0, Environmentally Assisted Fatigue for NUREG/CR-6260 Locations.

9. Nozzle drawings, SI File No. 2000401.201.

10. General Electric Hitachi Design Specification 26A7561, Rev. 2, Reactor VesselExtended Power Uprate, SI File No. 2000401.201.

11. NUREG/CR-6907 (ANL-04/3), Crack Growth Rates of Nickel Alloy Welds in a PWR Environment, May 2006.

12. General Electric Hitachi, Report 0000-0098-7386-R0, Assessment of the Effects of EPU Annulus Pressurization (AP) Amplified Response Spectra on the Recirculation Piping Systems, Revision 3, SI File No. 2000401.201.

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Table 1. Allowable Flaw Size Ratio of Flaw Length to Pipe Circumference, lf /Do 0 0.1 0.2 0.3 0.4 0.5 0.6 0.75 Service Flaw Length, lf (degrees)

Level 0 36 72 108 144 180 216 270 Allowable Flaw Depth, 2a/t A 0.75 0.75 0.75 0.65 0.52 0.46 0.42 0.41 B 0.75 0.75 0.75 0.73 0.59 0.51 0.48 0.46 C 0.75 0.75 0.52 0.37 0.29 0.26 0.24 0.24 D 0.75 0.75 0.69 0.48 0.39 0.33 0.30 0.29 Ratio of Flaw Length to Pipe Circumference, lf /Do 0 0.1 0.2 0.3 0.4 0.5 0.6 0.75 Service Flaw Length, lf (inches)

Level 0.0 4.5 9.0 13.4 17.9 22.4 26.9 33.6 Allowable Flaw Depth, 2a (inch)

A 1.03 1.03 1.03 0.89 0.71 0.63 0.58 0.57 B 1.03 1.03 1.03 1.00 0.81 0.70 0.66 0.63 C 1.03 1.03 0.71 0.50 0.40 0.35 0.33 0.32 D 1.03 1.03 0.95 0.66 0.53 0.45 0.42 0.39 File No.: 2000401.301 Page 10 of 12 Revision: 0 F0306-01R4

Note: To account for uncertainty, 0.75 inch is added to the flaw length (l), and 0.125 inch is added to the flaw depth (2a). Hence, the initial flaw size used in the present calculation is lo = 6.89 inch and 2ao = 0.401 inch, which gives S = 0.4485 inch Figure 1. Measured Flaw Dimensions from UT Data [1]

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Figure 2. Fracture Mechanics Flaw Model File No.: 2000401.301 Page 12 of 12 Revision: 0 F0306-01R4

LIST OF SOFTWARE FILES File No.: 2000401.301 Page A-1 of A-2 Revision: 0 F0306-01R4

Filename Description Nine_Mile_Recirc_N2J.xls Excel spreadsheet containing allowable flaw size calculation Sn_range.pcf pc-CRACK database file Sn_range.rpt pc-CRACK result file File No.: 2000401.301 Page A-2 of A-2 Revision: 0 F0306-01R4