ML19204A358

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WCAP-18258-NP, Revision 1, Flaw Tolerance Evaluation for Susceptible Reactor Coolant Loop Cast Austenitic Stainless Steel Elbow Components for Surry Units 1 and 2.
ML19204A358
Person / Time
Site: Surry  Dominion icon.png
Issue date: 06/30/2019
From: Song X, Udyawar A
Westinghouse
To:
Office of Nuclear Reactor Regulation, Virginia Electric & Power Co (VEPCO)
References
19-260 WCAP-18258-NP, Rev 1
Download: ML19204A358 (35)
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Text

Serial No.19-260 Docket Nos. 50-280/281 Enclosure 8 WCAP-18258-NP, "FLAW TOLERANCE EVALUATION FOR SUSCEPTIBLE REACTOR COOLANT LOOP CAST AUSTENITIC STAINLESS STEEL ELBOW COMPONENTS FOR SURRY UNITS 1 AND 2" Virginia Electric and Power Company (Dominion Energy Virginia or Dominion)

Surry Power Station Units 1 and 2

Westinghouse Non-Proprietary Class 3 WCAP-18258-NP June 2019 Revision 1 Flaw Tolerance Evaluation for Susceptible Reactor Coolant Loop Cast Austenitic Stainless Steel Elbow Components for Surry Units 1 and 2

Westinghouse Non-Proprietaiy Class 3 WCAP-18258-NP Revision 1 Flaw Tolerance Evaluation for Susceptible Reactor Coolant Loop Cast Austenitic Stainless Steel Elbow Components for Surry Units 1 and 2 Xiaolan Song*

Reactor Internals Design and Analysis II Anees Udyawar*

Structural Design and Analysis III June2019 Reviewer: Alexandria M. Carolan*

Structural Design and Analysis III Manager: Lynn A. Patterson*

Structural Design and Analysis III

  • Electronically approved records are authenticated in the electronic document management system.

Westinghouse Electric Company LLC 1000 Westinghouse Drive Cranberry Township, PA 16066, USA

© 2019 Westinghouse Electric Company LLC All Rights Reserved

iii RECORD OF REVISIONS Rev Date Revision Description The proprietary information in the brackets has been deleted in this report.

This information is to be withheld from public disclosure in accordance with the Rules of Practice 10CFR2.390 and the information presented herein is to be safeguarded in accordance with 10CFR2.390. The deleted information is provided in the proprietary version of this report (WCAP-18258-P, Revision 1). Note that the non-proprietary report herein starts with Revision 1 in order to match WCAP-18258-P, Revision 1; thus, there is no WCAP-18258-NP, Revision O.

To be consistent with WCAP-18258-P, Revision 1 this report addresses two discrepancies in the certified material test report (CMTR) data in Tables 3-1 and 3-2:

1. In Table 3-1 for Surry Unit 1, the chemical composition for heat number 10243-2 was mistyped. In Table 3-2 for Surry Unit 2, the chemical composition for heat number 15769-1 and 12087-3 was mistyped. The corrections of CMTR discrepancies for these three heat numbers are shown in bold font in Tables 3-1 and 3-2.

June I It is determined that the correction of the chemical content 2019 discrepancies for these three heat numbers does not affect the thermal aging susceptibility screening results.

2. During the replacement steam generator program, nine elbows were replaced in Surry Unit 1, as shown in Table 3-1 with grey-shaded color. Based on the new CMTR properties from the Unit 1 replacement elbows, the maximum allowable end of evaluation flaw size for crossover leg is affected by a slight amount. Figures 6-3 and 6-4, and Table 6-1 are updated for the revised crossover leg results. The hot and cold leg calculations are not affected.

Note that References 5 and 7 are updated to the latest revision. The updates to these two references do not have any impact on the conclusions of this report.

Changes in the text of this report are shown with revision bars in the left margin.

WCAP-18258-NP June 2019 Revision 1

iv TABLE OF CONTENTS LIST OF TABLES ......................................................................................................................................... V LIST OF FIGlJRES ..................................................................................................................................... vi EXECUTIVE SUMMA.RY......................................................................................................................... vii 1 INTRODUCTION ........................................................................................................................ 1-l 2 LOADINGS, STRESSES AND GEOMETRY ............................................................................. 2-1 3 MATERIAL PROPERTIES .......................................................................................................... 3-l 4 ACCEPTANCE CRITERIA ......................................................................................................... 4-1 5 FATIGUE CRACK GROWTH ..................................................................................................... 5-J 6 FLAW TOLERANCE EVALUATION ......................................................................................... 6-1 7 SUMMA.RY AND DISCUSSION ................................................................................................ 7-1 8 REFERENCBS ............................................................................................................................. 8-1 WCAP-18258-NP June2019 Revision 1

V LIST OF TABLES Table 2-1: Dimensions, Operating Temperatures and Pressure of RCL CASS Components .................... 2-2 Table 2-2: Bounding Suny Units I and 2 Piping Loads for Susceptible Piping Components in Each Leg of the RCL ....................................................................................................................... 2-3 Table 2-3: Surry Units 1 and 2 80-Year Design and Projected Transients ................................................. 2-4 Table 3-1: Surry Unit 1 Primary Loop Piping Cast Elbow (A351-CF8M) CMTR Chemistry, Delta Ferrite, and Thermal Aging Susceptibility Screening................................................................... 3-3 Table 3-2: Suny Unit 2 Primary Loop Piping Cast Elbow (A351-CF8M) CMTR Chemistry, Delta Ferrite, and Thermal Aging Susceptibility Screening................................................................... 3-5 Table 6-1: Acceptable Initial Flaw Sizes (% Through-wall Thickness) for Susceptible CASS Elbow Components ..................................................................................................................... 6-2 WCAP-18258-NP June 2019 Revision 1

vi LIST OF FIGURES Figure 2-1 Axial and Circumferential Residual Stress Distributions for Austenitic Stainless Steel Pipe Welds (Reference 8) ......... ................................................................................................ 2-5 Figure 6-1 Axial Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Hot Leg ......... 6-3 Figure 6-2 Circumferential Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Hot Leg ................................................................................................................................... 6-4 Figure 6-3 Axial Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Crossover Leg ................................................................................................................................... 6-5 Figure 6-4 Circumferential Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Crossover Leg .................................................................................................................. 6-6 Figure 6-5 Axial Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Cold Leg ....... 6-7 Figure 6-6 Circumferential Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Cold Leg ................................................................................................................................... 6-8 WCAP-18258-NP June2019 Revision 1

vii EXECUTIVE

SUMMARY

The primary reactor coolant loop (RCL) elbow components in Surry Units 1 and 2 are constructed from cast austenitic stainless steel (CASS) A351 CF8M material. The CASS material may be suscepti'ble to thermal aging at the reactor operating temperature. Thermal aging of CASS material results in embrittlement, that is, a decrease in the ductility, impact strength, and :fracture toughness and an increase in hardness and tensile strength of the material. As stated in the Orimes's Letter (Reference 1) and incorporated in NUREG-2191 (Reference 2), since the base metal of reactor coolant loop piping does not receive periodic inspection in accordance with Section XI of the ASME Code (Reference 3), the susceptibility of piping components constructed from CASS material should be assessed for each heat of material. Susceptibility of RCL CASS piping components in Surry Units 1 and 2 can be determined using the screening criteria given in NUREG-2191 based on the molybdenum content, casting method, and ferrite content If a particular heat is found to be "not susceptible," no additional inspections or evaluations are required to demonstrate that the material has adequate toughness. Otherwise; aging management can be accomplished through volumetric examination or plant specific flaw* tolerance evaluations using plant specific geometry and stress information.

In determining susceptibility of the CASS piping components to thermal aging, the delta ferrite content for Surry Units 1 and 2 is estimated using Hull's Equivalent Factor from NUREG/CR-4513 (Reference 4) according to the Grimes's Letter and NUREG-2191.

Flaw tolerance evaluation of the susceptible CASS elbow components in Surry Units 1 and 2 are performed in accordance to Appendix C of ASME Section XI based on guidelines from Grimes's Letter (Reference I). Based on the flaw tolerance analysis results of the susceptible CASS elbow components in Surry Units 1 and 2, it is concluded that even with thermal aging, the susceptible CASS elbow components are flaw tolerant for 80 years of service.

WCAP-18258-NP June2019 Revision 1

1-1 1 INTRODUCTION The primary reactor coolant loop (RCL) elbow components in Surry Units 1 and 2 are constructed from cast austenitic stainless steel (CASS) A351 CF8M material. The CASS material may be susceptible to thermal aging at the reactor operating temperature. Thermal aging of CASS material results in embrittlement, that is, a decrease in the ductility, impact strength, and fracture toughness and an increase in hardness and tensile strength of the material. Depending on the material composition, the Charpy impact energy of a component made of CASS material could decrease to a small fraction of its original value after prolonged exposure to reactor coolant temperatures during service.

As stated in the Grirnes's Letter (Reference 1) and in NUREG~219I (Reference 2), since the base metal of the reactor coolant loop piping does not receive periodic inspection in accordance with Section XI of the ASME Code (Reference 3), the susceptibility of piping constructed from CASS material should be assessed for each heat of material. Susceptibility of RCL CASS piping components in Surry Units 1 and 2 can be determined using the screening criteria given in the Grimes's Letter and NUREG-2191 based on the molybdenum content, casting method, and ferrite content If a particular heat is found to be "not susceptible," no additional inspections or evaluations are required to demonstrate that the material has adequate toughness. Otherwise, aging management can be accomplished through volumetric examination or plant specific flaw tolerance evaluations using plant specific geometry and stress infonnation. This report will provide a plant specific flaw tolerance evaluation to demonstrate that the elbow components have adequate fracture toughness and are flaw tolerant for 80 years of service life.

According to NUREG-2191, material heats with high Molybdenum content (2-3% weight) for statically cast elbow components which have delta ferrite content greater than 14% are potentially susceptible to thermal aging. For low Molybdenum content (0.5% weight max), statically cast elbow components which have delta ferrite content greater than 20% are also potentially susceptible to thermal aging.

In detennining susceptibility of the CASS piping components to thermal aging, the delta ferrite content for Surry Units 1 and 2 is estimated using Hu!Ps Equivalent Factor in NUREG/CR-4513 (Reference 4) according to the Grimes's Letter and NUREG-2191. Based on NUREG/CR-4513, Revision 2, the delta ferrite correlations used for the full aged condition is applicable for plants operating at and beyond 15 EFPY (Effective Full Power Years) for the CF8M materials. As of January 2017, Surry Units 1 and 2 are operating at 33.78 and 33.69 EPFY, respectively.

Therefore, the RCL CASS CFSM materials at Surry Units 1 and 2 are currently in the fully aged condition.

Flaw tolerance evaluation of the susceptible CASS elbow components in Surry Units 1 and 2 can be performed in accordance to Appendix C of ASME Section XI based on recommendations from the Grimes's Letter. The objective of the flaw tolerance evaluation is to demonstrate that even with thermal aging, the susceptible CASS components are flaw tolerant for 80 years of service.

WCAP-18258-NP June2019 Revision 1

1-2 The Westinghouse Electric Company LLC proprietary information and data which is identified by brackets in this document has been deleted. The deleted information is provided in the proprietary version of this report (WCAP-18258-P, Revision 1). Coding (a,c,e) associated with the brackets sets forth the basis on which the information is considered proprietary. These code letters are listed with their meanings in BMS-LGL-84 (Reference 12).

WCAP-18258-NP June2019 Revision 1

2-1 2 LOADINGS, STRESSES AND GEOMETRY In order to perform the flaw tolerance evaluation for Surry Units I and 2 RCL CASS piping components, the first step is the determination of the maximum allowable end-of-evaluation period flaw sizes. The maximum allowable end-of-evaluation period flaw size is the size to which an indication is allowed to grow to until the next inspection or evaluation period. This particular flaw size is determined based on the piping loads, geometry and the material properties of the component. The evaluation guidelines and procedures for calculating the maximum allowable end-of-evaluation period flaw sizes are described in paragraph IWB-3640 and Appendix C of the ASME Section XI Code (Reference 3). The maximum allowable end-of-evaluation period flaw sizes are established based on the limiting loadings for the components of interest from the nonnal, upset, test, emergency, and faulted conditions.

The geometry along with the normal operating temperature and pressure for the elbow components for Surry Units 1 and 2 are given in Table 2-1. The loadings considered in this analysis were based on the Leak-Before-Break evaluation and loss of coolant accident (LOCA) loadings on the reactor coolant loop based on Reference 5 and Reference 6, respectively. The piping loads considered in the flaw tolerance evaluation consist of loads due to pressure, deadweight, thennal expansion, seismic (operational basis earthquake and safe shutdown earthquake), and pipe break loads from surge line, residual beat removal, and accumulator line breaks. The bounding piping loads for each leg are shown in Table 2-2.

Design pressure and thermal transients are used in the fatigue crack growth (FCG) analysis for the susceptible locations in the hot leg, crossover leg, and cold leg of the reactor coolant loop.

The design transient definitions and cycles used in the fatigue crack growth analyses were taken from CN-PAFM-16-55 (Reference 7) based on a design life of 80 years. The bounding design transients and the number of occurrences for 80 years are shown in Table 2-3. Based on the past plant operation history, Table 2-3 also provides projected cycles for 80 years of service. The FCG evaluation in this report is based on the design cycles from Table 2-3, which is conservative for the flaw tolerant analysis.

Residual stresses due to the weld fabrication process are also considered in the fatigue crack growth analysis. The residual stress values were obtained from the technical basis document for austenitic steel piping flaw evaluation (Reference 8) and used in the evaluation of the heat affected zones of the susceptible CASS piping components. The through-wall axial and circumferential residual stress profiles used in the fatigue crack growth analysis are shown in Figure 2-1.

WCAP-18258-NP June2019 Revision 1

2-2 Table 2-1: Dimensions, Operating Temperatures and Pressure of RCL CASS Components WCAP-18258-NP June2019 Revision I

2-3 Table 2-2: Bounding Surry Units 1 and 2 Piping Loads for Susceptible Piping Components in Each Leg of the RCL a,c,e WCAP-18258-NP June2019 Revision 1

2-4 Table 2-3: Surry Units 1and280-Year Design and Projected Transients a,c,e WCAP-18258-NP June2019 Revision I

2-5 Through-Wall Residual Stress1 Wall Thickness~--------------~

Axial Circumferential 2 s s

< 1 inch I

ID OD ID OD 2:: 1 inch See Note 3 Note I: S == 30 ksi Note 2: Considerable variation with weld heat input Note 3: O":::: Oi [1.0 - 6.9l(a/t) + 8.69(a/t)2- 0.48(a/t)3 - 2.03(aJt)4]

cri = stress at inner surface (a== 0) a = distance through pipe weld thickness t = pipe weld thickness Figure 2-1 Axial and Circumferential Residual Stress Distributions for Austenitic Stainless Steel Pipe Welds (Reference 8)

WCAP-18258-NP June2019 Revision I

3-1 3 MATERIAL PROPERTIES The pre-service fracture toughness of cast stainless steel has been found to be very high at operating temperatures. However, cast stainless steel is susceptible to thermal aging after prolonged exposure to the reactor coolant operating temperature. Thermal aging of CASS material results in embrittlement, that is, a decrease in the ductility, impact strength, and fracture toughness and an increase in hardness and tensile strength of the material. Depending on the material composition, the Charpy impact energy of a cast stainless steel component could decrease to a small fraction of its original value after prolonged exposure to the reactor coolant operating temperatures during service.

Susceptibility ofRCL CASS piping components in Surry Units 1 and 2 can be determined using the screening criteria given in the Grimes's Letter (Reference 1) and NUREG-2191 (Reference 2) based on the molybdenum content, casting method, and ferrite content. According to NUREG-2191, material heats with high molybdenum content (2-3% weight) for statically cast piping components (e.g., elbows) which have delta ferrite content greater than 14% are potentially susceptible to thermal aging. For low molybdenum content (0.5% weight max), statically cast piping components which have delta ferrite content greater than 20% are potentially susceptible to thermal aging.

Based on the guidance in the Grimes's Letter and NUREG-2191, the delta ferrite contents are calculated using the Hull's Equivalent Factor Method from NUREG/CR-4513 (Reference 4) for the Surry Units 1 and 2 elbow components (A351 CF8M). Tables 3-1 and 3-2 provide the delta ferrite calculation per NUREG/CR-4513, based on Surry specific Certified Material Test Reports (CMTR) chemistry values for all the elbow heats ([13] and [14]). As indicated in the record of revisions table, this report is revised to address CMTR discrepancies in Tables 3-1 and 3-2 for Surry Units I and 2, and to address updated CMTRs from the replacement steam generator (RSG) replacement elbows in Surry Unit 1 RCL. As shown in the revised Tables 3-1 and 3-2, the corrections of CMTR discrepancies (shown in bold font) and updates due to additional CMTRs (marked by grey-shaded color) have been included in this report.

Based on the screening criteria given in the Grimes's Letter and NUREG-2191 along with the data in Tables 3-1 and 3-2, at least one elbow component that is potentially susceptible to thermal aging is present in each hot leg, crossover leg and cold leg in Surry Units 1 and 2. According to Grimes's Letter (Reference 1), the results from the Argonne National Laboratory Research Program indicate that the lower-bound fracture toughness of thermally aged cast stainless steel (CF8M) with 15 to 25% ferrite content is similar to that of submerged arc welds. Therefore the effects of unstable ductile tearing due to the reduced toughness of thermally aged cast stainless steel can be addressed in a flaw tolerance evaluation in accordance with the evaluation procedures in Appendix C of ASME Section XI for submerged arc welds.

The calculation of maximum allowable end-of-evaluation period flaw sizes from paragraph IWB-3 640 in ASME Section XI for the high toughness materials were determined based on the assumption that plastic collapse would be achieved and would be the dominant mode of failure.

However, based on Grimes's Letter (Reference 1) and the technical basis for the Grimes's Letter, EPRI TR-106092 (Reference 11), the reduction in fracture toughness for the aged CF8M is WCAP-18258-NP June2019 Revision 1

3-2 comparable to lower bound fracture toughness for Type 316 SAW welds. Therefore, the successful comparison of fracture toughness data for SAW welds with the CASS materials based on Reference 11 provides justification for applying the evaluation procedures contained in ASME Section IWB-3640 and Appendix C. Due to the reduced toughness of the susceptible material, it is possible that crack extension and unstable ductile tearing could occur and be the dominant mode of failure. This reduction in fracture toughness is accounted for in the evaluation by including the Z-factors for SAW welds from Appendix C of the ASME Code to the maximum allowable end-of-evaluation period flaw size calculations. This consideration, in effect, reduces the maximum end-of-evaluation period allowable flaw sizes for the susceptible heats and has been incorporated directly into the evaluation.

In contrast to the decrease in fracture toughness and ductility caused by the embrittlement of thermally aged stainless steel components, the tensile properties, such as the flow stress, increase for the fully aged saturation condition of the A351 CF8M castings. The age hardening parameters can be determined based on methodology contained in NRC approved NUREG/CR-4513 (Reference 4) using the chemical and material properties of the aged component, aging temperature, and aging time. Therefore, the determination of the maximum allowable end-of-evaluation period flaw sizes for the most limiting of the susceptible CASS CF8M material heats take into account the increase in tensile properties (age hardening effect). Consideration of the increased tensile properties of the susceptible CASS CF8M material is appropriate since the application of the SAW weld Z-factors already represent the fully aged reduced fracture toughness condition. The embrittlement effects of thermal aging on both the fracture toughness and tensile properties for the CASS material represent the appropriate fully aged saturated condition of the CASS material.

The aged hardened material properties are used in the determination of the maximum allowable end-of-evaluation period circumferential flaw sizes for the susceptible heats on the cold leg where the high pipe break loads would limit the allowable flaw sizes otherwise. For the calculation of aged flow stress in the Surry Units 1 and 2 susceptible cold leg components, the aged hardened material properties are determined at 33.78 and 33.69 EFPY (effective full power years),

respectively, which currently represent the operating lives for both units as of January 2017. The aged flow stress at the design life of 80 years is conservatively bounded by the use of the aged flow stress values at 33. 78 and 33.69 EPFY for Surry Units 1 and 2, respectively.

WCAP-18258-NP June 2019 Revision 1

Table 3-1: Surry Unit 1 Primary Loop Piping Cast Elbow (A351-CF8M) CMTR Chemistry, Delta Ferrite, and Thermal Aging Susceptibility Screening a,c,e WCAP-18258-NP June2019 Revision 1

3-4 Table 3-1: Surry Unit 1 Primary Loop Piping Cast Elbow (A351-CF8M) CMTR Chemistry, Delta Ferrite, and Thermal Aging Susceptibility Screening (Continued) a,c,e WCAP-18258-NP June2019 Revision 1

3-5 Table 3-2: Surry Unit 2 Primary Loop Piping Cast Elbow (A351HCF8M) CMTR Chemistry, Delta Ferrite, and Thermal Aging Susceptibility Screening a,c,e WCAP-18258-NP June 2019 Revision l

4-1 4 ACCEPTANCE CRITERIA The acceptance criteria for the determination of allowable flaw sizes in high toughness base materials are contained in paragraph IWB-3640 in the ASJ\.1E Section XI Code. Although rapid, nonductile failure is possible for ferritic material at low temperatures, it is not applicable to high toughness material such as austenitic stainless steel. In high toughness materiai the higher ductility leads to two possible modes of failure: plastic collapse or unstable ductile tearing. The second mechanism can occur when the applied J integral exceeds the J1c fracture toughness, and some stable tearing occurs prior to failure. If this mode of failure is dominant, the load carrying capacity is less than that predicted by the plastic collapse mechanism. The allowable flaw sizes of paragraph IWB-3640 in the ASME Section XI Code for the high toughness base materials were determined based on the assumption that plastic collapse would be achieved and would be the dominant mode of failure. However, due to the reduced toughness of the submerged arc and shielded metal arc welds, it is possible that crack extension and unstable ductile tearing could occur and be the dominant mode of failure. To account for this effect, penalty factors called "Z factors" were developed in ASME Section XI Code, which are to be multiplied by the loadings at these welds.

According to the Grimes's Letter (Reference 1), the results from the Argonne National Laboratory Research Program indicate that the lower bound :fracture toughness of thermally aged cast stainless steel is similar to that of submerged arc welds. In accordance with the flaw evaluation guidelines in Grimes's Letter (Reference 2) if the delta ferrite content for the cast stainless steel does not exceed 25%, the flaw evaluation can be performed in accordance with the evaluation procedures in paragraph IWB-3640 for submerged arc welds. This is an acceptable approach as stated in the Grimes's Letter due to the similarity between the lower bound :fracture toughness data for CF8M steels with 15 to 25% ferrite and the IWB-3640 submerged arc weld data. Since the delta ferrite contents for the susceptible RCL CASS piping components for Surry Units l and 2 was shown to be less than 25% per Tables 3-1 and 3-2, a flaw tolerance evaluation can therefore be performed using the evaluation procedures and acceptance criteria for indications in submerged arc welds contained in paragraph IWB-3640 of ASME Section XI. The effects of unstable ductile tearing due to reduced toughness of thermally aged cast stainless steel can therefore be addressed through the use of"Z" factors for submerged arc welds in accordance with the IWB-3640 flaw evaluation procedure and acceptance criteria.

WCAP-18258-NP June 2019 Revision 1

5-1 5 FATIGUE CRACK GROWTH In applying the ASME Section XI (Reference 3) acceptance criteria, the final flaw size (af) used is defined as the flaw size to which the detected or postulated flaw is calculated to grow to until the next inspection period. For the RCL CASS piping components in pressurized water reactors, only fatigue crack growth needs to be considered because three conditions must exist simultaneously for stress corrosion cracking to occur in stainless steel piping components: high tensile stresses, susceptible material, and an environment that is conducive to stress corrosion cracks. Although some residual stress and some degree of material susceptibility exist in any stainless steel piping component, the reactor coolant water chemistry is monitored and maintained within very specific limits. Contaminant concentrations are kept below the thresholds known to be conducive to stress corrosion cracking with the major water chemistry control standards being included in the plant operating procedures as a condition for plant operation. The RCL CASS piping component material in pressurized water reactors is therefore unlikely to be susceptible to stress corrosion cracking and therefore only fatigue crack growth needs to be considered.

To determine fatigue crack growth for the susceptible CASS piping components, the loadings used consist of loads due to thermal expansion, deadweight, pressure, residual stresses and thermal transient loads. The design transients shown in Table 2-3 are used in the fatigue crack growth analysis. The analysis procedure involves postulating an initial flaw at the susceptible piping components and predicting the flaw growth due to an imposed series of loading transients.

The input required for a fatigue crack growth analysis is basically the information necessary to calculate the crack tip stress intensity factor range (LiK1), which depends on the geometry of the crack, its surrounding structure, and the range of applied stresses in the crack area.

The stress intensity factor calculations were performed for semi-elliptical inside surface axial and circumferential flaws using the stress intensity factor expressions from References 9 and I 0, respectively. The fatigue crack growth rate for embedded and outside surface flaws in an air environment is lower than that for inside surface flaws exposed to the Pressurized Water Reactor (PWR) water environment. Therefore, embedded flaw and outside surface flaw evaluations are conservatively bounded by the inside surface flaw tolerance analysis in this report.

Once .6.Kr is calculated, the growth for inside surface flaws due to a particular stress cycle can be calculated using the applicable fatigue crack growth reference curves for stainless steel in PWR water environments. To represent the PWR water environment for stainless steel, an environment factor of2 for PWR environment (Reference 8) was applied to the reference fatigue crack growth curve for austenitic stainless steel in an air environment, as provided in Appendix C of ASME Section XI. The incremental growth from fatigue crack growth is then added to the original crack size, and the analysis proceeds to the next cycle or transient. The procedure is continued in this manner until all of the analytical transients known to occur in the 80 years of operation have been analyzed.

WCAP-18258-NP June2019 Revision 1

6-1 6 FLAW TOLERANCE EVALUATION Axial and circumferential surface flaws are defined respectively as flaws oriented along and perpendicular to the centerline axis of the piping components of interest. Two basic dimensionless parameters, flaw shape parameter ( all) and flaw depth parameter (alt) can fully address the characteristics of a surface flaw, where:

t = wall thickness a = flaw depth I= flaw length Based on the screening criteria in the Grimes's Letter (Reference 1) and in NUREG-2191 (Reference 2), at least one elbow component in each hot leg, crossover leg and cold leg in Surry Units 1 and 2 is potentially susceptible to thermal aging. As a result, flaw tolerance evaluations were performed based on the bounding material properties, geometry, and stresses of all the susceptible piping components in each leg of the reactor coolant loop. The flaw tolerance charts for the susceptible piping components in the hot leg, crossover leg, and cold leg are shown in Figures 6-1 through 6-6 for both axial and circumferential flaws. The purpose of these flaw tolerance charts is to identify the maximum acceptable initial flaw size for a given plant operation duration.

The results presented in Figures 6-1 through 6-6 represent the limiting results for inside surface, outside surface and embedded flaws which are characterized in accordance with IWA-3300 of the AS:ME Section XI Code. For a typical flaw tolerance chart, the flaw shape parameter (all) is plotted as the abscissa from 0.1 to 0.5 and the flaw depth parameter (alt) expressed as a ratio of the through-wall thickness is plotted as the ordinate from 0.0 to 0.8. Therefore, the flaw tolerance charts in Figures 6-1 to 6-6 encompass various postulated flaw cases based on different aspect ratios (ranging in I/a from 2 to 10). The allowable flaw size curves show the maximum acceptable initial flaw depth beyond which repair is required for continued service. The curves in Figures 6-1 through 6-6 are for a service life of 80 years from the time that a flaw is discovered, based on fatigue crack growth calculations. Any flaw which falls below the allowable flaw size curve is acceptable in accordance with the IWB-3640 acceptance criteria for 80 years.

As an illustration, using the curves shown in Figures 6-1 through 6-6, the maximum acceptable initial flaw depths for the susceptible RCL CASS piping components in the hot leg, crossover leg and cold leg for a service life of 80 years are summarized in Table 6-1 as a percentage of the through-wall thickness for a hypothetical flaw with an aspect ratio (!/a) of 6 (or a/lof0.167). The maximum acceptable initial flaw sizes for all other analyzed aspect ratios can be obtained directly from Figures 6-1 through 6-6 for the susceptible CASS piping components in the hot leg, crossover leg and cold leg. The allowable end-of-evaluation period flaw sizes shown in Table 6-1 (for the example aspect ratio I/a of 6) were determined in accordance with the flaw evaluation guidelines and acceptance criteria contained in IWB-3640 using the piping loads from Table 2-2.

The acceptable initial flaw sizes shown in Table 6-1 were obtained by subtracting the fatigue crack growth for 80 years of service life from the maximum allowable end-of-evaluation period flaw sizes. In Table 6-1, the difference between the acceptable initial flaw sizes and the maximum allowable end~of..evaluation period flaw sizes is the amount of fatigue crack growth WCAP-18258-NP June 2019 Revision I

6-2 over 80 years of plant life. The magnitude of FCG is dependent on the geometry, temperature, severity of the design transients, and the range of stress intensity factor at the location of interest.

In Revision 1 of this report, it is determined that the maximum acceptable initial flaw size for crossover leg is affected by the additional CMTR data for RSG replacement elbows in Surry Unit 1 RCL; therefore, Figures 6-3 and 6-4, along with the crossover leg results in Table 6-1 for axial flaw are updated. The flaw tolerance results for hot leg and cold leg are not affected.

Table 6-1: Acceptable Initial Flaw Sizes(% Through-wall Thickness) for Susceptible CASS Elbow Components (Aspect Ratio= 6, For a Service Life of 80 years)

Axial Flaw Circumferential Flaw Maximum Maximum Location Acceptable Initial Allowable End-of- Acceptable Initial Allowable End-of-Flaw Size Evaluation Period Flaw Size Evaluation Period Flaw Size Flaw Size Hot Leg 46% 60% 59% 71%

Crossover Leg 51% 57% 68% 75%

Cold Leg 54% 60% 49% 50%

Based on the results tabulated in Table 6-1 for a hypothetical postulated flaw with an aspect ratio of 6, the most limiting maximum acceptable initial flaw depth is for an axial flaw in the susceptible CASS piping components of the hot leg, which is 46% of the wall thickness.

[

WCAP-18258-NP June 2019 Revision 1

6-3 0.7 0.6 0.2 -t Wall Thicl<Jw,s.,--

(t) 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Flaw Shape - a//

Figure 6-l Axial Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Hot Leg WCAP-18258-NP June 2019 Revision 1

6-4 0.8.

0.7 0.6 0.2 0.1 0

0.1 0.15 9.2 0.25 0.3 0.35 0.4 0.45 0.5 Flaw Shape ** a//

Figure 6-2 Circumferential.Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Hot Leg WCAP-18258-NP June2019 Revision l

6-5 0.8 0.6

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~

I 0.5 Q,

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a E,-1 0.4

~

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~

~

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FltttD<plh (a) 0.1 0

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Flaw Shape - a//

Figure 6-3 Axial Flaw Toleranee Chart for Susceptible CASS Elbow Components in the Crossover Leg WCAP-18258-NP June2019 Revision 1

0.7 0.6

~

  • 0.5

~

~

a E-< 0.4 0.2 0.1 0 ...-............_........_.._-J.---'----'--

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Flaw Shape - al/

Figure 6-4 Circumferential Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Crossover Leg WCAP-18258-NP June2019 Revision l

6-7 0.8 0.7 0.6 0.2 i

0.1 I-Fl7,~-I t 1

..,---~,_,--,-*-r-<<<<<<*,

0 .j....._.__,___,__,__ _,___,___,_.......c 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Flaw Shape - a//

Figure 6-5 Axial Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Cold Leg WCAP- I 8258-NP June20l9 Revision l

6-8 0.8 0.6

~

= 0.5 I

ell

~

]

.....ccJ E-<

'i 0.4

~

Q i:i.

~

0.3 r;

c::

~

0.2 0.1.

0 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Flaw Shape - a//

Figure 6-6 Circumferential Flaw Tolerance Chart for Susceptible CASS Elbow Components in the Cold Leg WCAP-18258-NP June 2019 Revision 1

7-1 7

SUMMARY

AND DISCUSSION Based on the flaw tolerance analysis results of the susceptible CASS elbow components in Suny Units 1 and 2, it is concluded that even with thermal aging, the susceptible CASS elbow components are flaw tolerant for 80 years of service.

The primary reactor coolant loop elbow components in Surry Units 1 and 2 are constructed from cast austenitic stainless steel A351 CF8M material. The pre-service fracture toughness of cast stainless steel has been found to be very high at operating temperatures. However, cast stainless steel may be susceptible to thermal aging after prolonged exposure to the reactor coolant temperature. Thermal aging of cast stainless steel results in embrittlement, that is, a decrease in the ductility, impact strength and fracture toughness, and an increase in hardness and tensile strength of the material. Depending on the material composition, the Charpy impact energy of a cast stainless steel component could decrease to a small fraction of its original value after prolonged exposure to the reactor coolant temperature during service.

Susceptibility of RCL CASS elbow components in Surry Units I and 2 was determined using the screening criteria given in the Grimes's Letter (Reference 1) and NUREG-2191 (Reference 2) based on the molybdenum content, casting method, and ferrite content. In determining susceptibility of the CASS elbow components to thermal aging, the delta ferrite content is estimated using Hull's Equivalent Factor in NUREG/CR-4513 (Reference 4).

Based on the screening criteria for thermal aging susceptibility, at least one elbow component is potentially susceptible in each hot leg, crossover leg, and cold leg of Suny Units 1 and 2 as shown in Tables 3-1 and 3-2. However, none of the delta ferrite contents estimated for the CASS elbow components exceeded *2s%. According to the Grimes's Letter (Reference 1), the results from the Argonne National Laboratory Research Program indicate that the lower-bound fracture toughness of thermally aged cast austenitic stainless steel (CF8M) with 15 to 25% ferrite is similar to that of submerged arc welds. Therefore in accordance with the guidelines given in the Grimes's Letter (Reference 1), the Suny Units 1 and 2 susceptible CASS elbow components can be evaluated using the evaluation procedures and acceptance criteria in paragraph IWB-3640 of the ASME Section XI Code for submerged arc welds.

Flaw tolerance charts were generated for the susceptible CASS elbow components in the hot leg, crossover leg and cold leg as shown in Figures 6-1 through 6-6 for both axial and circumferential flaws. The results presented in Figures 6-1 through 6-6 represent the limiting results for inside surface, outside surface and embedded flaws. The purpose of these flaw tolerance charts is to identify the maximum acceptable initial flaw size for a service life of 80 years. Any flaw which falls below the allowable flaw size curve is acceptable in accordance with the IWB-3640 acceptance criteria for 80 years.

Based on the results tabulated in Table 6-1, for an aspect ratio of 6 the maximum acceptable initial flaw depth is for an axial flaw in the susceptible CASS piping components of the hot leg, which is 46% of the wall thickness. [

]a,c,e For all other flaw WCAP-18258-NP June2019 Revision 1

7-2 configurations and susceptible CASS elbow component locations tabulated in Table 6-1 for the Surry Units 1 and 2 reactor coolant loops, the maximum acceptable initial flaw depths are even larger. Therefore, the graphical results per Figures 6-1 through 6-6 demonstrate that the RCL components are highly flaw tolerant, since a significantly large flaw size is necessary to cause structural integrity concern for the CASS components. These large flaw sizes would have been originally detected during fabrication of the components and subsequently repaired. Furthermore, operational experience has demonstrated that these types of large flaw sizes are not present in the CASS components for PWRs. In conclusion, this report presents a plant specific flaw tolerance evaluation which demonstrates that the RCL elbow components at Surry Units 1 and 2 have adequate fracture toughness and are flaw tolerant for 80 years of service life.

WCAP-18258-NP June 2019 Revision 1

8-1 8 REFERENCES

1. Letter from Christopher I. Grimes, U.S. Nuclear Regulatory Commission, License Renewal and Standardization Branch, to Douglas J. Walters, Nuclear Energy Institute, License Renewal Issue No. 98-0030, "Thermal Aging Embrittlement of Cast Stainless Steel Components," ML003717179, May 19, 2000.
2. U.S. Nuclear Regulatory Commission, NUREG-2191, "Generic Aging Lessons Learned for Subsequent License Renewal (GALL-SLR) Report-Draft Report for Comment," December 2015.
3. ASME Code Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components," 2004 Edition.
4. 0. K. Chopra, "Estimation of Fracture Toughness of Cast Stainless Steels During Thermal Aging in LWR Systems," NUREG/CR-4513, Revision 2, U. S. Nuclear Regulatory Commission, Washington DC, May 2016.
5. Westinghouse Report No. WCAP-15550-P., Rev. 2, "Technical Justification for Eliminating Large Primary Loop Pipe Rupture as the Structural Design Basis for Surry Units 1 and 2 Nuclear Power Plants for Subsequent License Renewal Program (80 Years) Leak-Before-Break Evaluation," March 2019.
6. Westinghouse Report No. WCAP-17361-P, Rev. 1, "Reload Transition Safety Report Surry Units 1 and 2 15x15 Fuel Upgrade," February 2011.
7. Westinghouse Calculation CN-PAFM-16-55, Rev. 1, "Transient Basis for Surry Units 1 and 2 80-year License Renewal Evaluations," September 2018.
8. "Evaluation of Flaws in Austenitic Steel Piping," Trans ASME, Journal of Pressure Vessel Technology, Vol. 108, Aug. 1986, pp. 352-366.
9. S. R. Mettu, I. S. Raju, "Stress Intensity Factors for Part-through Surface Cracks in Hollow Cylinders," Jointly developed under Grants NASA-JSC 25685 and Lockheed ESC 30124, Job Order number 85-130, Call number 96N72214 (NASA-TM-111707), July 1992.

I 0. S. Chapuliot, M. H. Lacire, and P. Le Delliou, "Stress Intensity Factors for Internal Circumferential Cracks in Tubes Over a Wide Range of Radius Over Thickness Ratios,"

ASME PVP Vol. 365, 1998.

11. Electric Power Research Institute Technical Report TR-I 06092, W02643-33, "Evaluation of Thermal Aging Embrittlement for Cast Austenitic Stainless Steel components in LWR Reactor Coolant Systems," September 1997.

WCAP-18258-NP June2019 Revision 1

8-2

12. BMS-LGL-84, Revision 0.00, "Protection of Proprietary Infonnation Regarding Submittals to the USNRC including Safety Analysis Reports for Commercial Nuclear Power Plants,"

Effective Date: April 15, 2017.

13. Westinghouse Letter VRA-19-17, Rev. 1, "Dominion Energy Surry Power Station Units 1

& 2 Design Information Request- Surry 80 Year License Renewal Evaluations," March 10, 2019.

14. Westinghouse Letter LTR-SDA-II-18-77, Rev. 1, "Surry Unit 1 and 2 Certified Material Test Reports for the Reactor Coolant Loop Cast Austenitic Stainless Steel Elbow Components," January 8, 2019 ..

WCAP-18258-NP June 2019 Revision 1

WCAP-18258-NP Revision 1 Proprietaiy Class 3

"*This page was added to the quality record by the PRIME system upon its validation and shall not be considered in the page numbering of this document.**

Author Approval Song Xiaolan Jun-12-2019 10:24:18 Author Approval Udyawar Anees Jun-12-201910:55:55 Reviewer Approval Carolan Alexandria M Jun-12-2019 12:35:50 Manager Approval Patterson Lynn Jun-13-2019 08:17:09 Fifes approved on Jun-13-2019

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