RA-25-0058, Proposed Alternative for Acceptance of Through-Wall Flaw in a Reducer Snall End Tranisition Zone
| ML25080A235 | |
| Person / Time | |
|---|---|
| Site: | Brunswick  |
| Issue date: | 03/21/2025 |
| From: | Ellis K Duke Energy Progress |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| RA-25-0058 | |
| Download: ML25080A235 (1) | |
Text
Kevin M. Ellis General Manager Nuclear Regulatory Affairs, Policy &
Emergency Preparedness Duke Energy 13225 Hagers Ferry Rd., MG011E Huntersville, NC 28078 843-951-1329 Kevin.Ellis@duke-energy.com 10 CFR 50.55a Serial: RA-25-0058 March 21, 2025 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Brunswick Steam Electric Plant, Unit No. 1 Renewed Facility Operating License No. DPR-71 Docket No. 50-325
SUBJECT:
Proposed Alternative for Acceptance of Through-wall Flaw in a Reducer Small End Transition Zone Ladies and Gentlemen:
Pursuant to 10 CFR 50.55a(z)(2), Duke Energy Progress, LLC (Duke Energy) is proposing an alternative to the requirements of American Society of Mechanical Engineers (ASME) Code,Section XI for the Brunswick Steam Electric Plant (BSEP), Unit No. 1. Specifically, Duke Energy is proposing to use alternative methods to calculate the stresses that are used in evaluating a Service Water (SW) system through-wall flaw. The proposed alternative is described in Enclosure 1.
The existing SW system flaw, which is near the small end transition zone of a reducer, has been evaluated as acceptable in accordance with Code Case N-513-5, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping and Gate Valves,Section XI, Division 1. Evaluation of flaws in the small end transition zone is outside the scope of Code Case N-513-5. Therefore, if the flaw grows into the small end transition zone, this proposed alternative would be needed to prevent unit shutdown until repairs can be made during the next refueling outage, currently scheduled for March 2026. Duke Energy requests approval of this proposed alternative prior to that outage.
If you have additional questions, please contact Ryan Treadway, Director - Nuclear Fleet Licensing, at 980-373-5873.
U.S. Nuclear Regulatory Commission RA-25-0058 Page 2 Kevin M. Ellis General Manager - Nuclear Regulatory Affairs, Policy & Emergency Preparedness
Enclosures:
cc:
- 1. Proposed Alternative for Acceptance of Through-wall Flaw in a Reducer Small End Transition Zone : Digital Ultrasonic Thickness NDE Report dated December 5, 2024 : Digital Ultrasonic Thickness NDE Report dated February 25, 2025 : SIA Calculation 2551710.301, "Brunswick Unit 1 20x30-inch Reducer Wall Thinning Evaluation" M. Miller, Regional Administrator USNRC Region II (Acting)
G. Smith, NRG Senior Resident Inspector B. Purnell, NRG Project Manager, NRR
RA-25-0058 Proposed Alternative for Acceptance of Through-wall Flaw in a Reducer Small End Transition Zone 7 Pages Follow
RA-25-0058 Page 1 of 7 1.0 ASME CODE COMPONENT(S) AFFECTED:
A through-wall flaw has developed in a 20-inch x 30-inch concentric reducer in the Unit 1 Conventional Service Water Discharge Header (Line Number 1-SW-142-30-157) located downstream of Residual Heat Removal (RHR) Heat Exchange Service Water Discharge Valve 1-E11-PDV-F068A.
ASME Section XI Code Class: 3 Component
Description:
20-inch x 30-inch concentric reducer on the Unit 1 Service Water System at Weld 1-SW-911 on line 1-SW-142-30-157 Construction Code: USAS B31.1 -1967 Design Conditions:
Temperature: 33 °F to 215 °F Pressure: 150 psig (max)
Operating Conditions:
Temperature: 105 °F Pressure: 101 psig (max)
Material:
Cement lined, Carbon Steel S/A-105 or S/A-234 WPB 2.0 APPLICABLE CODE EDITION AND ADDENDA:
The current applicable Edition and Addenda of the ASME Code,Section XI is identified in Table 1.
Table 1 Plant/Unit ISI Interval ASME Section XI Code Edition/Addenda Interval Start Date Interval End Date1 Brunswick Steam Electric Plant, Unit 1 Fifth 2007 Edition, Through 2008 Addendum2 05/11/2018 05/10/2028 Note 1: Date listed is the currently planned interval end date. In accordance with IWA-2430(c)(1), this end date may be extended or shortened as necessary.
Note 2: On February 12, 2025, the NRC provided verbal approval to use Nonmandatory Appendix C of Section XI of the 2021 Edition of the ASME Code for all applicable pressure-retaining piping and components at Brunswick, Unit No. 1, for the remainder of the Fifth 10-year inservice inspection interval (Agencywide Documents Access and Management System Accession No. ML25043A229).
RA-25-0058 Page 2 of 7 3.0 APPLICABLE CODE REQUIREMENT:
In accordance with ASME Code Section XI, 2007 Edition with 2008 Addenda, subparagraph IWD-3120(b) requires that flaws in ASME Code Class components which do not meet the standards shall be subjected to supplemental examination, or to a repair/replacement activity. In regard to the flaw analysis, IWD-3500, "Acceptance Standards" for Class 3 components, states that the requirements of IWC-3500, "Acceptance Standards" for Class 2 components, may be used.
Additionally, IWA-4000 describes the repair/replacement activities to correct an unacceptable flaw. Discovery of an area below the design minimum wall thickness in the structural portion of an ASME Code Class 1, 2, or 3 component is direct evidence of a flaw in the component.
The Code does not include analytical evaluation criteria for acceptance of through-wall flaws in pressure retaining base material of ferritic pipe or fittings. Code Case N-513-5, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping Section XI, Division 1," which has been conditionally approved by the U.S.
Nuclear Regulatory Commission (NRC) in Regulatory Guide 1.147, "Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," Revision 21, provides analytical evaluation rules for temporary acceptance of flaws in piping. Code Case N-513-5, however, does not apply to the small end transition region of the reducer.
Relief is requested so that code repair or replacement of the non-planar flaws at the small end of the reducers transition region may be deferred until the conclusion of the BNP refueling outage B1R26 which is currently scheduled to start on March 7, 2026.
4.0 REASON FOR REQUEST:
Duke Energy Progress, LLC (Duke Energy) is requesting a proposed alternative from the requirement to perform repair/replacement activities for the degraded reducer, which has a through-wall flaw.
On December 4, 2024 a through-wall flaw was discovered in the Unit 1 Service Water (SW) system. The flaw is located on the 20-inch side of a 20-inch x 30-inch concentric reducer, located on line 1-SW-142-30-157 (Figure 1). Due to the piping configuration from the flaw to the discharge point from the unit, the piping at the flaw location is under vacuum such that there is no external leakage from the system. The flaw was initially evaluated using the methodology of ASME Code Case N-513-5 and periodic monitoring of the flaw was implemented as required by the Code Case to ensure that the flaw continues to meet the bounding requirements set forth in the Code Case evaluations.
During this periodic monitoring it was identified that the flaw growth is progressing towards the small end transition zone of the reducer. ASME Code Case N-513-5 is approved by the NRC for generic use and provides criteria to allow temporary acceptance of flaws, including through-wall flaws in moderate energy Class 2 or 3 piping without performing repair or replacement activities in accordance with ASME Code Section XI, Article IWA-4000. ASME Code Case N-513-5 includes guidance for evaluating flaws in pipe fittings including reducers. However, it does not address the evaluation that extends into the small end transition region of the reducer.
RA-25-0058 Page 3 of 7 Figure 1. Location of Reducer Flaw Characterization:
Ultrasonic thickness (UT) examinations of the reducer on December 5, 2024 (Attachment 1) identified one location associated with this component below the design minimum wall thickness, tmin of 0.120 inches. The identified flaw was 1.625 inches circumferentially and 0.75 inches axially and was located within the straight portion of the reducer. It is not possible to identify the exact cause of the through wall leak without removing the system from service and accessing the interior of the piping for examination. Corrosion that is typically experienced in cement lined carbon steel piping such as this one is localized general corrosion in areas where the cement liner has deteriorated exposing the carbon steel surface to brackish Service Water.
Code Case N-513-5 was then invoked to prove that the component is structurally stable and not subject to catastrophic failure. Per Section 5.0 Augmented Examinations of the N-513-5 Code Case and the Regulatory Guide 1.147 Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1 Conditions, five other most susceptible locations were examined, and no flaws were identified. Consistent with Code Case N-513-5 requirements, the flaw on the reducer is being monitored daily to confirm analysis conditions, while monthly re-examinations are performed to determine any flaw growth and to establish the time at which the detected flaw will reach the allowable size.
RA-25-0058 Page 4 of 7 The location of the flaw is located at the top of a vertical riser, approximately 45 feet from the bottom of the drop. From this point the piping exits into a pipe tunnel and discharges into the top of the Circulating water discharge at near atmospheric conditions. Based on the large elevation difference and the small pressure drop in the discharge piping, the pressure conditions at the flaw location are in vacuum. With a nominal flow of 7,000 gallons per minute through the piping at the flaw location, there is currently no external leakage through the flaw. Based on a review of design basis calculations, this section of piping will remain under vacuum with the design basis accident flow of 8000 gpm through the A Loop Residual Heat Removal (RHR) Heat Exchangers.
As of the most recent inspection performed on February 25, 2025 (Attachment 2), the flaw is 2.375 inches circumferentially and 1.5 inches axially, just slightly before the transition region in the small end of the reducer.
Completion of a code repair of the defect on this line will require isolation of the Conventional Service Water system discharge header. Although the time period allowed by the associated Technical Specification Required Actions for the Service Water system may provide sufficient time to complete a code repair, isolation of the affected line to perform the repair would require shutdown of the unit due to the loss of cooling water to the supported equipment. The Conventional Service Water system discharge header is the flow path for Service Water discharge from the Reactor Building Closed Cooling Water (RBCCW) system heat exchangers. The RBCCW system provides cooling for reactor building auxiliary equipment which includes Drywell Coolers, Spent Fuel Pool Cooling and Reactor Water Clean-up. Without Drywell Cooling, atmospheric temperatures in the drywell would increase and exceed Technical Specification limits.
For this reason, Code repair of the defect cannot be performed with the unit online.
Because the affected loop repair would require isolating the 1A Loop of Residual Heat Removal Service Water (RHRSW) and RBCCW Service Water, this outage would require the unit to enter Mode 5. For this shutdown, the reactor pressure vessel head would need to be removed and the reactor cavity flooded to allow placing the 1B Loop of RHR in Shutdown Cooling and Augmented Spent Fuel Pool Cooling (since RBCCW is out of service).
Plant shutdown activities result in additional dose and plant risk that would be inappropriate when a degraded condition is demonstrated to retain adequate margin to complete the component's function. The use of an acceptable alternative analysis method in lieu of immediate action for a degraded condition will allow Duke Energy time for safe and orderly long term repair actions.
5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE:
Duke Energy is requesting approval to apply ASME Section III 2007 Edition with 2008 Addenda, Design by Analysis approach in section NB-3200 to evaluate the non-uniform wall thickness and local thinning of the reducer. As a result, a detailed three-dimensional (3-D) finite element model (FEM) was utilized in the evaluation to calculate the stress field associated with the non-uniform wall thickness (SIA Calculation 2551710.301, ). In accordance with 10 CFR 50.55a(z)(2), relief is requested on the basis that compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
RA-25-0058 Page 5 of 7 Given that there is at least one reading below tmin identified, the primary stress design criteria for Service Level A (Normal) and Level B (Upset) conditions are based on the limit load design criteria of Subparagraph NB-3228.1, Limit Analysis. NB-3228.1 states:
The limits on General Membrane Stress Intensity (NB-3221.1), Local Membrane Stress Intensity (NB-3221.2), and Primary Membrane Plus Primary Bending Stress Intensity (NB-3221.3) need not be satisfied at a specific location if it can be shown by limit analysis that the specified loadings do not exceed two-thirds of the lower bound collapse load. The yield strength to be used in these calculations is 1.5Sm.
The allowable Stress, S, is used instead of the Class 1 Design Stress Intensity, Sm. As a result, the S value is substituted for the Sm, in regard to establishing the yield stress defined above. This is consistent with the design rules, as the yield stress defined here is the equivalent of the Local Primary Membrane Stress, which uses an allowable stress of 1.5Sm for Class 1 components, or 1.5S for Class 2/3 and B31.1 components.
Subparagraph NB-3213.28, Limit Analysis - Collapse Load states:
The methods of limit analysis are used to compute the maximum load that a structure assumed to be made of ideally plastic material can carry. At this load, which is termed the collapse load, the deformations of the structure increase without bound.
A total load of 1/(2/3) = 150% of the applied maximum loads on the degraded section of pipe must be sustained without any portion of the pipe plastically collapsing (i.e., the membrane stress across an entire section for a given location does not exceed the defined yield stress of 1.5S).
The primary stress design criteria Service Level D (Faulted) conditions will be based on the limit load design criteria of Appendix F, F-1200(a), and will be based on the ASME Code,Section III, Appendix F, Subparagraph F-1341.3. F-1341.3 states:
Static or equivalent static loads shall not exceed 90% of the limit analysis collapse load using a yield stress which is the lesser of 2.3Sm and 0.7Su A total load of 1/0.9 = 111.1% of the applied faulted loads on the degraded section of pipe must be sustained without any portion of the pipe plastically collapsing (i.e., the membrane stress across an entire section for a given location does not exceed the defined yield stress of 2.3S or 0.7Su).
To that end, the 3-D FEM of the degraded piping and the appropriate maximum Normal/Upset and Faulted loads (internal pressure and piping moments) was evaluated.
The total load, as a percentage of nominal load has been compared to the required 150% of the Service Level A/B (Normal/Upset) loads and 111.1% of the Service Level D (Faulted) loads as defined in the criteria identified above.
Based on the above criteria the reducer meets the limit load design criteria outlined in Subparagraph NB-3228.1, Limit Analysis with a conservatively extended hole size of 10-inch x 10-inch.
Consistent with the requirements of ASME Code Case N-513-5 Section 2, the following compensatory actions shall be performed until such time that the flaw is repaired.
RA-25-0058 Page 6 of 7 (a)
Frequent periodic examinations of no more than 30-day Intervals shall be used to determine If flaws are growing and to establish the time, at which the detected flaw will reach the allowable size.
(b)
For through-wall leaking flaws, leakage shall be monitored daily to confirm the analysis conditions used in the evaluation remain valid.
(c)
If examinations reveal flaw growth rate to be unacceptable, a repair/replacement activity shall be performed.
(d)
Repair/replacement activities shall be performed no later than when the predicted flaw size from trending periodic Inspection is expected to exceed the acceptance criteria (10-inch in either the axial or circumferential direction), or during the next scheduled refueling outage, whichever occurs first. Repair/replacement activities shall be in accordance with IWA-4000.
In conclusion, based on the above proposed alternative and the detailed evaluation in, the structural integrity and functional requirements of the pipe will be maintained. The Service Water System will continue to be capable of providing required cooling water flow to meet the required cooling loads of the Component Cooling Water and Residual Heat Removal Heat Exchangers. There will be no adverse impact on neighboring equipment due to either spray or flooding.
6.0 DURATION OF PROPOSED ALTERNATIVE:
The proposed alternative is requested to be authorized to remain in place until repairs can be made during the Spring 2026 Refueling Outage which is currently planned to begin on March 7, 2026.
7.0 PRECEDENTS
No direct precedents were identified.
8.0 REFERENCES
8.1 Duke Energy NDE Report, 94197, Digital Ultrasonic Thickness NDE Report, December 5, 2024. [Attachment 1]
8.2 Duke Energy NDE Report, 94923, Digital Ultrasonic Thickness NDE Report, February 25, 2025. [Attachment 2]
8.3 SIA Calculation 2551710.301, Brunswick Unit 1 20x30-inch Reducer Wall Thinning Evaluation, March 4, 2025. [Attachment 3]
8.4 ASME Boiler and Pressure Vessel Code, Code Case N-513-5, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping and Gate ValvesSection XI, Division 1, April 18, 2018.
8.5 ASME Boiler and Pressure Vessel Code,Section III, Rules for Construction of Nuclear Power Plant Components, 2007 Edition with 2008 Addenda
RA-25-0058 Page 7 of 7 8.6 ASME Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2007 Edition with 2008 Addenda
RA-25-0058, Attachment 1, Attachment 1 Digital Ultrasonic Thickness NDE Report dated December 5, 2024 2 Pages Follow
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DIGIT AL ULTRASONIC THICKNESS NDE REPORT
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20699327-02 Unit: 1iZ1 1 Component / Item Tested:
NDE ProcedureNOE-NE-ALL 1-SW-142-30-157 No.:
6401 Rev.: s.._
TR: N/A Component Material:
Expected 1iZ1 C/S 5A-IO(, 0 S/S N/A O Other (Specify): NIA Type Type Nominal T Range:
.100"-1. 00" Thickness Gauge:
1.10/1.20N Mfg.: Panametrics Model: 37DL+
S/N: UTG-8 Software Rev. No.:
Calibration/ Reference Std.:
O Test ltem-Mic./Caliper No.: _N_/A ____ _
[8l Step Block S/N: SW-3, 5467 liZI CIS SIS O Other (Describe Below)
Transducer:
Couplant:
Brand: UL TRAGELII Batch No.: 22D007 Primary Cal. Thickness:.100"-1.00" Cal. Check Thickness:
.100"-1. 00" Mfg.: Panametrics Model: D791-RM SIN: 503014 Diameter:,312*
Freq.:
5 MHz D Single liZI Dual Component Conditions:
Inst. Receiver Gain Setting.5_3d=B Other Test Conditions:
High Temp:
D Yes Coated I Painted: f.ZI Yes liZI No No Technique: 0 Single-Echo O Thru-Coat Ql Multiple-Echo Sketch component or item and area tested. Include thickness data.
NONE Requested by engineering to perform a UT of a through-wall leak to characterize the extent of the flaw.
UT examined 5" out from ends, top and bottom edges of the hole using a 1" X 1" grid.
Material design-.375", minimum wall-.120". The distance to the stainless reducing flange weld from the top edge of the hole was 6"; there was no weld at the transition on the reducer. A dynamic UT scan was also performed around the periphery of the CS pipe with the hole and the reducing flange below with a width of> 2" with no areas noted to be <.120" in wall thickness. See attached pages for thickness c;::,
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RA-25-0058, Attachment 2
, Attachment 2 Digital Ultrasonic Thickness NDE Report dated February 25, 2025 2 Pages Follow
RA-25-0058, Attachment 2 Page 1 of 2 QA UT-8 Rev 7
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DIGITAL ULTRASONIC THICKNESS NOE REPORT Plant: liZl BNP CR3 HNP RNP WO: 20700888-01 Unit: liZl 1 2 3 Date: 02/25/2025 Component/ Item Tested:
NOE Procedure:
NOE-NE-ALL 1-SW-142-30-157 No.:
4101 Rev.: 05 TR: NIA Component Material:
Expected liZl C/S SA-106 S/S N/A Other (Specify): N/A Type Type Nominal T Range:
0.100"- 01.50" Thickness Gauge:
Mfg.: Panametrics Model: 37DL +
SIN: UTG-8 Software Rev. No.: 1.10,uoN Calibration/ Reference Std.:
0 Test ltem-Mic./Caliper No.: _N_/A ____
~ Step Block S/N: SW-17 /SW-2 liZl CIS S/S Other (Describe Below)
Transducer:
Couplant:
Brand: ULTRAGEL Batch No.: 220007 Primary Cat Thickness: 0.100"- 01.50" Cal. Check Thickness: 0.100"-0.150" Mfg.:
PANAMETRICS Model: D791-RM SIN: 89821 Diameter:.312" Freq.: 5 MHz D Single liZl Dual Component Conditions:
Inst Receiver Gain Setting 51 dB Other Test Conditions:
High Temp:
D Yes liZl No IZl No Technique: l;z) Single-Echo Thru-Coat ALL PAINT WAS REMOVED BEFORE INSPECTION.
Coated I Painted: D Yes 0 Multiple-Echo Sketch component or item and area tested. Include thickness data.
Ut was performed on a 1"X1" grid. See page 2 for UT readings.
Min. wall -.120" Design thickness-.375" Just above transition between Line 6 and 7 readings are between.100"-.200" along the grid area.
Hole has moved down to where the transition starts to turn.
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RA-25-0058, Attachment 3
, Attachment 3 SIA Calculation 2551710.301, Brunswick Unit 1 20x30-inch Reducer Wall Thinning Evaluation 22 Pages Follow
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CALCULATION PACKAGE PROJECT NAME:
U1 BNP Finite Element Analysis and N-513 CONTRACT NO.:
03021365 00116 A001 CLIENT:
RA-25-0058, Attachment 3 File No.: 2551710.301 Page 1 of 22 Project No.: 2551710 Quality Program Type: [gl Nuclear D Commercial PLANT:
Duke Energy Brunswick Nuclear Plant, Unit 1 CALCULATION TITLE:
Brunswick Unit 1 20x30-inch Reducer Wall Thinning Evaluation Document Affected Project Manager Preparer(s) &
Revision Pages Revision Description Approval Checker(s)
Signature & Date Signatures & Date 1
1 - 20 Initial Issue A-1 -A-2
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Table of Contents RA-25-0058, Attachment 3 Page 2 of 22 1.0 OBJECTIVE.............................................................................................................. 4 2.0 METHODOLOGY...................................................................................................... 4 3.0 DESIGN INPUTS....................................................................................................... 5 3.1 Geometry and Material................................................................................... 5 3.2 Piping Loads.................................................................................................. 7 3.3 Wall Thickness Data...................................................................................... 7 4.0 ASSUMPTIONS........................................................................................................ 7 5.0 FINITE ELEMENT MODEL........................................................................................ 8 5.1 Geometry and Element Selection................................................................... 8 5.2 Boundary Conditions...................................................................................... 8 5.3 5.4 6.0 7.0 8.0 9.0 Internal Design Pressure................................................................................ 8 Piping Moment Loads.................................................................................... 8 LI MIT LOAD COLLAPSE EVALUATIONS................................................................. 9 RESULTS OF ANALYSIS.......................................................................................... 9 CONCLUSIONS........................................................................................................ 9 REFERENCES........................................................................................................ 10 APPENDIX A COMPUTER FILES..................................................................................... A-1 File No.: 2551710.301 Revision: 1 SJ I
Structural Integrity I Associates. lnc.s Page 2 of 20 F0306-01 R4 info@structint. com ~ 1-877-45!-POWER e slructint.com @)
List of Tables RA-25-0058, Attachment 3 Page 3 of 22 Table 1: Piping Loads...................................................................................................................... 7 Table 2: Final Piping Loads............................................................................................................. 9 Table 3: Results............................................................................................................................... 9 List of Figures Figure 1: Location of Flaw on Drawing [1]...................................................................................... 11 Figure 2: Through -Wall Leak Location [2]..................................................................................... 12 Figure 3: Inspection Locations....................................................................................................... 13 Figure 4: Inspection Report............................................................................................................ 14 Figure 5: Final Flaw Profile............................................................................................................ 15 Figure 6: Finite Element Model Geometry, Global View................................................................. 16 Figure 7: Mechanical Boundary Conditions.................................................................................... 17 Figure 8: Applied Pressure Loads.................................................................................................. 18 Figure 9: von Mises Stress Plot with As-Found Thinning, Service Level A/Bat 160% Load........... 19 Figure 10: von Mises Stress Plot with As-Found Thinning, Service Level D at 120% Load............ 20 File No.: 2551710.301 Revision: 1 SJ I
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1.0 OBJECTIVE RA-25-0058, Attachment 3 Page 4 of 22 A through-wall leak was discovered in the Unit 1 Service Water (SW) system at Brunswick Nuclear Plant (BNP). The leak is located on the 20-inch side of a 20 inch x 30 inch concentric reducer, located on line 1-SW-142-30-157. See Figure 1 for location of the identified leak on BNP provided drawing [1].
Figure 2 provides an image of the leak location and reducer configuration [2]. The 20-inch x 30-inch reducer is carbon steel, S/A-105, with a cement lining, and is safety-related Class 3 piping [1 and 2].
Structural Integrity Associates, Inc. (SI) has been contracted to perform a detailed finite element analysis incorporating non-uniform wall thinning determined from the UT thickness data to justify continued operation utilizing ASME Code, Section Ill design by analysis criteria. The objective of this calculation is to develop the finite element model, define the loads, and to perform limit analysis -
collapse load evaluations utilizing the ASME Code, Section Ill design by analysis rules [3].
The final of this calculation is to provide BNP with an allowable hole size based on ASME Code structural stability acceptance limits.
2.0 METHODOLOGY The original Code of Construction is B31.1, 1967 Edition with load combinations/allowable stresses from USAS B31.1.0-1967 [4] or ANSI B31.1-1973 [16]. The B31.1 Design by Rule approach does not provide specific criteria for the evaluation of non-uniform wall thickness or local thinning. However, B31.1 was written to provide flexibility in analysis as shown below [4, p. xi]:
"The specific design requirements of the Code usually revolve around a simplified engineering approach to a subject. It is intended that a designer capable of applying more complete and rigorous analysis to special or unusual problems shall have latitude in the development of such designs and the evaluation of complex or combined stresses. In such cases the designer is responsible for demonstrating the validity of his approach."
To evaluate non-uniform wall thickness/local thinning, or "complex or combined stresses," detailed design qualification rules are taken from the ASME Code Design by Analysis approach (Section Ill, NB-3200 [3]). As a result, a detailed three-dimensional (3-D) finite element model (FEM) will be utilized in subsequent evaluations to calculate the stress field associated with localized thinning, which is a more rigorous methodology than the Design by Rule approach in B31.1 and is consistent with the Design by Analysis approach of NB-3200.
Given that there is at least one reading below tmin identified, the primary stress design criteria for Service Level A (Normal) and Level B (Upset) conditions are based on the limit load design criteria of Subparagraph NB-3228.1, Limit Analysis [3]. NB-3228.1 states:
"The limits on General Membrane Stress Intensity (NB-3221. 1 ), Local Membrane Stress Intensity (NB-3221.2), and Primary Membrane Plus Primary Bending Stress Intensity (NB-3221.3) need not be satisfied at a specific location if it can be shown by limit analysis that the specified loadings do not exceed two-thirds of the lower bound collapse load. The yield strength to be used in these calculations is 1.5Sm."
The allowable Stress, S, is used instead of the Class 1 Design Stress Intensity, Sm. As a result, the S value is substituted for the Sm, in regard to establishing the yield stress defined above. This is consistent with the design rules, as the yield stress defined here is the equivalent of the Local Primary Membrane Stress, which uses an allowable stress of 1.5Sm for Class 1 components, or 1.5S for Class 2/3 and B31.1 components.
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Subparagraph NB-3213.28, Limit Analysis Collapse Load [3] states:
RA-25-0058, Attachment 3 Page 5 of 22 "The methods of limit analysis are used to compute the maximum load that a structure assumed to be made of ideally plastic material can carry. At this load, which is termed the collapse load, the deformations of the structure increase without bound. "
Thus, a total load of 1/(2/3) = 150% of the applied maximum loads on the degraded section of pipe must be sustained without any portion of the pipe plastically collapsing (i.e., the membrane stress across an entire section for a given location does not exceed the defined yield stress of 1.5S).
The primary stress design criteria Service Level D (Faulted) conditions will be based on the limit load design criteria of Appendix F, F-1200(a), and will be based on the ASME Code, Section Ill, Appendix F, Subparagraph F-1341.3 [3]. F-1341.3 states:
"Static or equivalent static loads shall not exceed 90% of the limit analysis collapse load using a yield stress which is the lesser of 2. 3Sm and 0. 7Su... "
Thus, a total load of 1/0.9 = 111.1 % of the applied faulted loads on the degraded section of pipe must be sustained without any portion of the pipe plastically collapsing (i.e., the membrane stress across an entire section for a given location does not exceed the defined yield stress of 2.3S or 0.7Su).
To that end, the 3-D FEM of the degraded piping and the appropriate maximum Normal/Upset and Faulted loads (internal pressure and piping moments) will be evaluated. Additional uniform wall thinning will be applied until the structure meets the limit load criteria, or plastically collapses (in terms of FEM this will be at the point of numerical instability). The total load, as a percentage of nominal load will be compared to the required 150% of the Service Level A/B (Normal/Upset) loads and 111.1 % of the Service Level D (Faulted) loads as defined in the criteria identified above.
3.0 DESIGN INPUTS 3.1 Geometry and Material The following inputs for the section of 20-inch x 30-inch reducer are used in this analysis:
Code of Construction: B31.1 1967 Edition [2]
Reducer small end outside diameter= 20.0 inches [1, 5]
Reducer large end outside diameter= 30.0 inches [1, 5]
Length of reducer= 24 inches [5]
Length of reducer transition= 9 inches [14]
Nominal wall thickness of reducer = 0.375-inch [2]
Reducer material: Carbon Steel S/A-105 or S/A-234 WPB [1]
Straight pipe connecting to reducer outside diameter= 30.0 inches [1]
Nominal wall thickness of straight pipe connected to the reducer= 0.375 inches [1]
Straight pipe material: S/A-155 GR. KC70, Class 1 [1]
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20" Flange material: S/A-182 F316L 150# [1, 6]
Maximum operating temperature = 105°F [2]
Design Pressure = 150 psig [1]
Youngs Modulus at design temperature, 105°F:
o S/A-234 WPB: 27.8x106 psi [4]
o S/A-105 GR 11: 27.8x106 psi [4 and 17]
o S/A-155 GR. KC70, Class 1: 27.8x106 psi [4]
o S/A-182 F316L: 27.3x106 psi [4]
Allowable stress at design temperature, 105°F:
RA-25-0058, Attachment 3 Page 6 of 22 o
S/A-234 WPB: 15.0x103 psi [16], taken from a later code year, since A-234 is not in the 1967 edition.
o S/A-105 GR 11: 17.5x103 psi [4 and 17]
o S/A-155 GR. KC70, Class 1: 17.5x103 psi [4]
o S/A-182 F316L: 15.48x103 psi [7]
Ultimate tensile strength, Su:
o S/A-234 WPB: 60.0x103 psi [16], taken from a later code year, since A-234 is not in the 1967 edition.
o S/A-105 GR 11: 70.0x103 psi [4]
o S/A-155 GR. KC70, Class 1: 70.0x103 psi [4]
o S/A-182 F316L: 65.0x103 psi [7]
Dimensions for the flange are based on Reference [8]
The reducer includes a transition and a straight pipe at each end of the transition. Both of the straight pipe portions in the reducer (red elements in Figure 6) are modeled as 7.5". The total reducer length is 24" and the transition length is 9" [14].
Since allowable stress and ultimate stress of S/ A-234 WPB bound that for SI A-105 GR II, the S/A-234 WPB is used for this analysis.
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3.2 Piping Loads RA-25-0058, Attachment 3 Page 7 of 22 Piping moments are provided from Reference [9 and 17], and are in Table 1:
Table 1: Piping Loads Loads Mx (ft-lb)
My (ft-lb)
Mz (ft-lb) ow
-4128 1212
-7234 T1 4257
-2517 7376 T2
-11585 6917
-24862 T3
-9403 5649
-22959 T4
-2190 1267
-1915 T5
-5282 1911
-7428 T6
-11590 6908
-25367 T7
-11235 6707
-24926 TB
-10456 6293
-23501 T9 5576
-1888 7910 T10 4267
-2513 7810 T11 3977
-2349 7445 T12 3313
-1997 6240 OBE 9948 6284 7293 DBE 15114 8988 10927 TR 1074 307 5888 T max range 17166 9434 33277 (OBE2+ TR2).5 10006 6291 9373 (DBE2+ TR2).5 15152 8993.24 12412.4 Per stress report [1 0] and stress analysis isometric drawing [11 ], Y direction in Table 1 is axial direction.
3.3 Wall Thickness Data The wall thickness used for this evaluation was taken from the examination report [12, 15] and shown in Figure 3 and Figure 4.
The final thinning map in Figure 5 is based on examination report Figure 4 with treating the thickness greater than 0.375" as 0.375" and adding the mark up data to show 1 "x1" grid since part of examination report [15] shows 3"x3" grid. In the final thinning map, the hole is conservatively extended to 10"x10" to reach the maximum allowable size (see Figure 5 and Figure 6).
4.0 ASSUMPTIONS The following assumptions are used in this evaluation:
SA-105 and SA-155 Poisson's ratio and density are assumed to be 0.30 and 0.283 lb/in3, respectively, for carbon steel. SA-182 F316L Poisson's ratio and density are assumed to be 0.31 and 0.29 lb/in3, respectively, for stainless steel. These are typical values for carbon steel and stainless steel and do not affect the results of the evaluation.
As the specific directionality of the piping moment is not known, the moment is conservatively applied in the worst orientation.
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RA-25-0058, Attachment 3 Page 8 of 22 The connection of two flanges is modeled with a bonded surface between the contact areas instead of bolt connection. This does not affect the results since this surface boundary is far away from the area of interest.
5.0 FINITE ELEMENT MODEL A three dimensional (3-D) finite element model (FEM) of the thinned location is developed with the ANSYS finite element analysis software [13]. A FEM is developed to incorporate each of the grid locations as described in Figure 5.
5.1 Geometry and Element Selection The FEM is constructed using ANSYS 8-node SOLID185 structural solid elements. Figure 6 shows a global view of the geometry used to develop the FEM. Note that an additional length of pipe is modeled on the end of the 30" pipe and an additional two flange connection on the end of 20" pipe to remove local effects of boundary conditions and applied load.
5.2 Boundary Conditions The free end of the modeled 30" pipe is fixed in the axial and circumferential directions. The radial direction is left unconstrained to allow for expansion due to internal pressure. The free end of the flange is left free in order to apply the bending moment and torque loads. The applied boundary conditions are shown in Figure 7.
5.3 Internal Design Pressure The Design Pressure, P, is 150 psig [9] and is applied to the interior surfaces of the model. In order to properly model the longitudinal stresses caused by pressure on the interior surface of the piping, and induced end-cap load is applied to the unconstrainted free end of the flange, calculated as follows:
- where, n:. rnz Pend-cap = P * -
4 Pend-cap= End cap force on free end of flange (lb)
P
= Internal pressure (psi)
ID
= Inside diameter of the flange (in)
The end-cap force is applied to the pilot node on free end surface of the flange. The pilot node is described in Section 5.4. The internal pressure and end-cap pressures are shown in Figure 8.
5.4 Piping Moment Loads The piping loads are applied by making use of a pilot node to transfer the loading. The TARGE170 target element type from the ANSYS element library is used to create the pilot node. The CONT A 175 contact element is used to create the contact surfaces that are aligned with the pilot node. The pilot node and surfaces are bonded together such that the loads applied to the pilot node are transferred to the respective surfaces on the flange.
The load combination for Service Level NB is DW+(OBE2+ TR2}°*5+ Thermal, and for Service Level D is DW+(DBE2+ TR2) 0*5+ Thermal. The maximum thermal range load in Table 1 is applied. The following piping loads in Table 2 are applied to the model.
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Table 2: Final Piping Loads Bending Moment (Mx2+Mz2) 0*5 (in-lb)
Service Level A/B 706688 DW+(OBE2+ TR2}°*5+ T max ranqe Service Level D 771107 DW+(DBE2+ TR2) 0*5+ T max ranqe RA-25-0058, Attachment 3 Page 9 of 22 Torsional (My) (in-lb) 203250 235671 Since the moment loads evaluated do not include specific directionality, the two worst directions are applied to the model as following:
The moment is perpendicular to the axial center line of the hole.
The moment is parallel to the axial center line of the hole.
6.0 LIMIT LOAD COLLAPSE EVALUATIONS Per Section 2.0, the static or equivalent static loads shall not exceed 2/3 (for Normal/Upset) or 90% (for Faulted) of the limit analysis collapse load. Thus, a total load of 1/(2/3) = 150% (Normal/Upset) or 1/0.9
= 111.1 % (Faulted) of the applied load must be sustained without plastic collapse. All loads (piping loads, end-cap pressure, and internal pressure) are applied simultaneously for the evaluation and a load factor of 1.6 (Normal/Upset) or 1.2 (Faulted) is applied for margin. The piping moment is conservatively applied in the worst direction, as determined in Section 5.4.
7.0 RESULTS OF ANALYSIS The model with as-found thinning successfully meets the criteria specified in Section 2.0 for both Normal/Upset and Faulted conditions. Table 3 tabulates the results for the evaluations).
Table 3: Results Percentage of Service Level A/B Load Percentage of Service Level D Applied <1>
Load Applied (2) 151.7%
120%
Notes:
- 1.
Using Service Level A/B loads, a passing score of greater than 150% is needed. The 160% applied load is arbitrary and is only intended to show margin.
- 2.
Using Service Level D loads, a passing score of greater than 111 % is needed. The 120% applied load is arbitrary and is only intended to show margin.
Von Mises stress plots are shown for the flaw profile based on Figure 5 in Figure 9 and Figure 10.
8.0 CONCLUSION
S Based on the application of wall thinning data provided to SI [12] for the reducer, the components meet the limit load design criteria outlined in Subparagraph NB-3228.1, Limit Analysis [1] with a conservatively extended hole size of 10"x 10".
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9.0
- 1.
- 2.
- 3.
- 4.
- 5.
- 6.
- 7.
- 8.
- 9.
REFERENCES RA-25-0058, Attachment 3 Page 10 of 22 BNP Drawing FSP-26094 Sheet 42, Rev 5, "Reactor Building Service Water System EL. 20' - O" Piping Line Isometric", SI File 2451427.205.
Email Chain from William Keith (BNP), John Goelz (BPN),
SUBJECT:
"N-513 Evaluation for BNP Reducer", Dated 12/6/2024, SI File 2451427.208.
ASME Boiler and Pressure Vessel Code, Section Ill, Rules for Construction of Nuclear Facility Components, 2007 Edition with Addenda through 2008.
USAS B31.1.0, "Power Piping," 1967 Edition.
ASME B16.9-1993, "Factory-Made Wrought Steel Buttwelding Fittings," 1993 Edition.
BNP Drawing FSP-26095 Sheet 102, Rev 3, "Reactor Building Service Water Discharge from RHR Heat Exchange "1A" Elevation 50'-0" Piping Isometric", SI File 2551710.205.
ANSI B31.1, "Power Piping," 1973 Edition.
USAS B16.5 - 1968, "Steel Pipe Flanges and Flanged Fittings," 1968 Edition.
Email from K. William Howe (Duke) to Y. Patten (SI), "RE: [EXTERNAL] Re: N-513 Evaluation for BNP Reducer," Dec. 07, 2024, 04:26 PM, SI File No. 2551710.208.
- 10. Nuclear Generation Group Calculation No. SA-SW-761/762/763, Revision 3, "Stress Analysis CALC. F/ISOS. 761, 762, 763 (Long-Term)," SI File No. 2551710.201.
- 11. Carolina Power & Light Company Drawing No. D-28046, Sheet 763, Revision 1, January 1998, "Stress Analysis Isometric, Closed Colling Water Heat Exchangers Outlet Line," SI File No.
2551710.205.
- 12. Progress Energy NOE Report No. 94490, 1/28/2025, "Digital Ultrasonic Thickness NOE Report, Component 1-SW-142-30-157, SI File No. 2551710.203.
- 13. ANSYS Mechanical APDL (UP20170403), Release 18.1, SAS IP, Inc.
- 14. E-mail from J. Goelz (BNP) to Y. Patten (SI) 2/19/2025, 12:34PM, RE: [EXTERNAL] Re: N-513 Evaluation for BNP Reducer,
Attachment:
Reducer As-Built Data.pdf, SI File No. 2551710.103.
- 15. E-mail from J. Goelz (BNP) to Y. Patten (SI) 2/19/2025, 1 :06PM, RE: [EXTERNAL] Re: N-513 Evaluation for BNP Reducer,
Attachment:
Reducer Picture.png, SI File No. 2551710.103.
16.ANSI B31.1.0 Power Piping Code, 1973 Edition.
- 17. Owner's Acceptance Review, "SI File 2551710.301 ", March 1, 2025, SI File. No.
25517010.210.
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COMT. ON
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1-SW-2815 File No.: 2551710.301 Revision: 1 SJ I
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Structural Integrity I Associates. lnc.s Figure 2: Through - Wall Leak Location [2]
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Figure 3: Inspection Locations RA-25-0058, Attachment 3 Page 13 of 22 Note: Per note in Reference [12], the 01/28/25 inspection with the centerline of the hole moved from G6/F6 to G7/F7.
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Note: In this table the grid is 1" in both axial and circumferential direction. The hole is extended to 10"X10".
File No.: 2551710.301 Revision: 1
~
Structural Integrity Associates, Inc."'
Figure 5: Final Flaw Profile i nfo@structint.com 1-877-451-POWER e Page 15 of 20 F0306-01 R4 structinl.com @
1 ELEMENTS lvJAT NUM RA-25-0058, Attachment 3 Page 16 of 22 20X30 Thinne:l Re:lucer File No.: 2551710.301 Revision: 1 SJ I
Structural Integrity I Associates. lnc.s Figure 6: Finite Element Model Geometry, Global View Page 16 of 20 F0306-01 R4 info@structint. com ~ 1-877-45!-POWER e slructint.com @)
1 EI..EMENTS lvJAT NUM u
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Pilot Node for Applying Piping Loads 20X30 Thi nne::::l Re::::lucer File No.: 2551710.301 Revision: 1 SJ I
Structural Integrity I Associates. lnc.s Figure 7: Mechanical Boundary Conditions RA-25-0058, Attachment 3 Page 17 of 22 Circumferential Displacement Constraints (Cyan)
Page 17 of 20 F0306-01 R4 info@structint. com ~ 1-877-45!-POWER e slructint.com @)
1 EI..EMENTS lvJAT NUM PRES-NORM 240 20X30 Thi nne::::l Re::::lucer RA-25-0058, Attachment 3 Page 18 of 22 ANSYS R18.l Plill NO.
1 Applied Internal Pressure (Red)
Figure 8: Applied Pressure Loads (Units are in terms of psi. For this example, the pressures shown are increased by 160% for Service Level AIB (Normal/Upset) Case.)
File No.: 2551710.301 Revision: 1 SJ I
Structural Integrity I Associates. lnc.s Page 18 of 20 F0306-01 R4 info@structint. com ~ 1-877-45!-POWER e slructint.com @)
1 NCDAL SOLUTICN STEP=l SUB =22 TIME=l51.685 SEQV (AVG)
RSYS=0 OMX =2.31327.
SfvN =82.27 SMX =2986 RA-25-0058, Attachment 3 Page 19 of 22 ANSYS R18.l Plill NO.
1 82.2758 6700.44 13318.6 19936.8 26554.9 3391.36 10009.5 16627.7 23245.9 29864 20X30 Thinne::::l Re::::lucer Figure 9: von Mises Stress Plot with As-Found Thinning, Service Level A/B at 160% Load File No.: 2551710.301 Revision: 1 SJ I
Structural Integrity I Associates. lnc.s (Units are in terms of psi.)
Page 19 of 20 F0306-01 R4 info@structint. com ~ 1-877-45!-POWER e slructint.com @)
1 NCDAL SOLUTICN STEP=l SUB =6 TIME=l20 SEQV (AVG)
RSYS=0 OMX =.190069 SfvN =56. 0397 SMX =39151. 9 RA-25-0058, Attachment 3 Page 20 of 22 ANSYS R18.l Plill NO.
1 56.0397 8744 17432 26119. 9 34807.9 4400.02 13088 21776 30463.9 39151. 9 20X30 Thinne::::l Re::::lucer Figure 10: von Mises Stress Plot with As-Found Thinning, Service Level D at 120% Load File No.: 2551710.301 Revision: 1 SJ I
Structural Integrity I Associates. lnc.s (Units are in terms of psi.)
Page 20 of 20 F0306-01 R4 info@structint. com ~ 1-877-45!-POWER e slructint.com @)
File No.: 2551710.301 Revision: 1 ~-1 Structural Integrity I Associates, /nc.s APPENDIX A COMPUTER FILES RA-25-0058, Attachment 3 Page 21 of 22 Page A-1 of A-2 F0306-01 R4 info@structint.com m 1-877-4SI-POWER e structint.com ~
I File Name Reducer.I NP Reducer-LIMIT-LOAD-AB.I NP Reducer-LIMIT-LOAD-AB-90.INP Reducer-LIMIT-LOAD-CD.I NP Reducer-LIMIT-LOAD-CD-90.INP UT-Data.pm File No.: 2551710.301 Revision: 1 ~-1 Structural Integrity I Associates, /nc.s II RA-25-0058, Attachment 3 Page 22 of 22 Description ANSYS input file to generate the finite element model.
ANSYS input file which applies Service Level NB loads with moment perpendicular to the hole centerline for as found model.
ANSYS input file which applies Service Level NB loads with moment parallel to the hole centerline for as found model.
ANSYS input file which applies Service Level D loads with moment perpendicular to the hole centerline for as found model.
ANSYS input file which applies Service Level D loads with moment parallel to the hole centerline for as found model.
Thinning map data I
Page A-2 of A-2 F0306-01 R4 info@structint.com m 1-877-4SI-POWER e structint.com ~