RC-13-0130, WCAP-17758-NP, Rev. 0, Technical Basis for Westinghouse Embedded Flaw Repair for V.C. Summer Unit 1 Reactor Vessel Head Penetration Nozzles and Attachment Welds

WCAP-17758-NP, Rev. 0, Technical Basis for Westinghouse Embedded Flaw Repair for V.C. Summer Unit 1 Reactor Vessel Head Penetration Nozzles and Attachment Welds

ML13252A242
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Site:	Summer  (NPF-012)
Issue date:	08/31/2013
From:	Glunt N Westinghouse
To:	Office of Nuclear Reactor Regulation
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RC-13-0130 WCAP-17758-NP, Rev 0
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Westinghouse Non-Proprietary Class 3 WCAP-17758-NP August 201 Revision 0 Technical Basis for Westinghouse Embedded Flaw Repair for V.C. Summer Unit I Reactor Vessel Head Penetration Nozzles and Attachment Welds

)Westinghouse 3

WESTINGHOUSE NON-PROPRIETARY CLASS 3 WCAP-17758-NP Revision 0 Technical Basis for Westinghouse Embedded Flaw Repair for V.C. Summer Unit 1 Reactor Vessel Head Penetration Nozzles and Attachment Welds N. Glunt*

Piping Analysis & Fracture Mechanics August 2013 Reviewer:

A. Udyawar*

Piping Analysis & Fracture Mechanics Approved:

S. Swamy*, Manager Piping Analysis & Fracture Mechanics

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

Westinghouse Electric Company LLC 1000 Westinghouse Drive Cranberry Township, PA 16066, USA 0 2013 Westinghouse Electric Company LLC All Rights Reserved

WESTINGHOUSE NON-PROPRIETARY CLASS 3 ii TABLE OF CONTENTS L IST O F TA B L E S.......................................................................................................................................

iii LIST OF FIGURES.....................................................................................................................................

iv I INTRODUCTION........................................................................................................................

1-1 2

TECHNICAL BASIS FOR APPLICATION OF EMBEDDED FLAW REPAIR PROCESS TO HEAD PENETRATION NOZZLES.............................................................................................

2-1 2.1 EVALUATION PROCEDURE AND ACCEPTANCE CRITERIA................................

2-1 2.1.1 Acceptance Criteria for Axial Flaws...............................................................

2-2 2.1.2 Acceptance Criteria for Circumferential Flaws...............................................

2-3 2.2 METHODOLOGY..........................................................................................................

2-3 2.2.1 Loading Conditions.........................................................................................

2-4 2.2.2 G eom etry.........................................................................................................

2-4 2.2.3 Finite Element Analysis...................................................................................

2-4 2.2.4 Crack Tip Stress Intensity Factor.....................................................................

2-5 2.2.5 Fatigue Crack Growth Analysis.......................................................................

2-6 2.3 FRACTURE MECHANICS ANALYSIS RESULTS......................................................

2-7 2.3.1 Maximum Allowable End-of-Evaluation Period Flaw Size............................ 2-7 2.3.2 Maximum Allowable Initial Flaw Size............................................................

2-7 2.4

SUMMARY

2-8 3

TECHNICAL BASIS FOR APPLICATION OF EMBEDDED FLAW REPAIR PROCESS TO PENETRATION NOZZLE ATTACHMENT WELDS.................................................................

3-1 3.1 EVALUATION PROCEDURE AND ACCEPTANCE CRITERIA................................

3-1 3.1.1 ASME Section XI Appendix K.......................................................................

3-1 3.1.2 Primary Stress Limits......................................................................................

3-2 3.2 METHODOLOGY..........................................................................................................

3-2 3.2.1 Stress Intensity Factor.....................................................................................

3-3 3.2.2 J-R Curve for Reactor Vessel Closure Head Material.....................................

3-4 3.2.3 Applied J-Integral............................................................................................

3-5 3.2.4 Fatigue Crack Growth.....................................................................................

3-6 3.3 FRACTURE MECHANICS ANALYSIS RESULTS......................................................

3-6 3.3.1 Comparison of Applied J-Integral and Material J-R Curves...........................

3-6 3.3.2 Primary Stress Limits......................................................................................

3-7 3.3.3 Fatigue Crack Growth into the Reactor Vessel Closure Head......................... 3-7 3.3.4 Fatigue Crack Growth into the Repair Weld...................................................

3-8 3.4

SUMMARY

3-8 4

SUMMARY

AND CONCLUSIONS............................................................................................

4-1 5

REFERENCES.............................................................................................................................

5-1 WCAP-17758-NP August 2013 Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 iii LIST OF TABLES Table 2-1 Maximum Allowable End-of-Evaluation Period Flaw Sizes.........................................

2-9 Table 2-2 Reactor Coolant System Transients for V. C. Summer Unit 1 [9].............................. 2-9 Table 3-1 Bounding Geometry of V.C. Summer Unit 1 Head Penetration Nozzle Attachment J-groove W elds...................................................................................................... 3-9 Table 3-2 Predicted Fatigue Crack Growth into the Repaired Weld Layer................................ 3-9 WCAP-17758-NP August 2013 Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 iv LIST OF FIGURES Figure 2-1 Schematics of the Inside Surface Flaw Repair Configuration for the Penetration Nozzle....2-10 Figure 2-2 Schematic of the Outside Surface Flaw Repair Configuration for the Penetration Nozzle... 2-11 Figure 2-3 Schematic of a Typical Closure Head Penetration Nozzle....................................................

2-12 Figure 2-4 Stress Cuts Considered in Fatigue Crack Growth Analysis..................................................

2-13 Figure 2-5 Fatigue Crack Growth Prediction for Axial Flaws in Repaired Penetration Nozzles (Uphill S id e)...............................................................................................................................

2 -14 Figure 2-6 Fatigue Crack Growth Prediction for Axial Flaws in Repaired Penetration Nozzles (Downhill S ide)...............................................................................................................................

2-15 Figure 2-7 Maximum Allowable Initial Axial Flaw Sizes for Repaired Penetration Nozzles for a 20 Year Service L ife....................................................................................................................

2-16 Figure 2-8 Fatigue Crack Growth Prediction for Circumferential Flaws in Repaired Penetration Nozzles (U phill S ide)..................................................................................................................

2-17 Figure 2-9 Fatigue Crack Growth Prediction for Circumferential Flaws in Repaired Penetration Nozzles (D ow nh ill side)..............................................................................................................

2-18 Figure 2-10 Maximum Allowable Initial Circumferential Flaw Sizes for Repaired Penetration Nozzles for a 20 Year Service Life....................................................................................................

2-19 Figure 3-1 Schematic of the Embedded Flaw Repair Configuration for the Attachment Welds............ 3-10 Figure 3-2 Finite Element Stress Cuts Along the Reactor Vessel Closure Head....................................

3-11 Figure 3-3 Sample Geometry and Terminology Used in Stress Intensity Factor Calculation................ 3-12 Figure 3-4 Applied J-integral and Material J-R Curve for Limiting Downhill Side J-Groove Weld...... 3-13 Figure 3-5 Applied J-integral and Material J-R Curve for Limiting Uphill Side J-Groove Weld........... 3-14 Figure 3-6 Fatigue Crack Growth Prediction in the Reactor Vessel Head with Maximum Postulated Flaws in the A ttachm ent W eld..................................................................................................

3-15 Figure 3-7 Definition of J-groove Weld Dimensions..............................................................................

3-16 WCAP-17758-NP August 2013 Revision 0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 1-1 1

INTRODUCTION Leakage and cracks have been reported from the reactor vessel closure head penetration nozzles in a number of plants that resulted in repairs or prompted the replacement of the reactor vessel closure head.

The degradation of the reactor vessel closure head penetration nozzles increases the probability of a more significant loss of reactor coolant pressure boundary. This has led to the issuance of various regulatory requirements and guidelines in the United States imposing additional volumetric and surface examinations to supplement the existing visual inspections of the reactor vessel closure head as well as the penetration nozzles. The presence of axial cracks extending above and below the head penetration nozzle attachment J-groove welds was discovered in some of the leaking penetration nozzles. The cause of these axially oriented cracks has been determined to result from primary water stress corrosion cracking (PWSCC) that is driven by both the steady state operating stress and the residual stress resulting from the weld fabrication process. The residual stress from the weld fabrication process is due to weld shrinkage and the offset geometry of the attachment J-groove weld on the uphill and downhill sides that induces bending of the penetration nozzle.

The bending also contributes to the ovalization of the penetration nozzle over the attachment J-groove weld region.

As a part of the inspection and contingence repair efforts associated with the reactor vessel closure head inspection program at V. C. Summer Unit 1, engineering evaluations were performed to support plant specific use of the Westinghouse embedded flaw repair process in the event that repair of an unacceptable flaw is necessary. The embedded flaw repair process would involve depositing a weld material that is PWSCC resistant over a detected flaw on the inside surface of the penetration nozzle and/or right over the outside surface of the penetration nozzle of interest below the J-groove weld, as well as over the wetted surface of the J-groove weld in the event that an outside surface flaw is detected in the penetration nozzle.

As a result, the surface flaw becomes a sub-surface flaw and is no longer exposed to the primary water environment.

The methodology used is based on extensive analytical work completed by the Westinghouse Owners Group, currently the Pressurized Water Reactor Owners Group (PWROG), and a large collection of test data obtained under the sponsorship of Westinghouse, Babcock & Wilcox (B&W) and the former Combustion Engineering Owners groups (CEOG), as well as the Electric Power Research Institute (EPRI). The technical basis of the embedded flaw repair process is documented in WCAP-15987-P Revision 2-P-A [1] and has been reviewed and accepted by the Nuclear Regulatory Commission (NRC) in the United States. In the NRC Safety Evaluation Report that was incorporated in WCAP-15987-P Revision 2-P-A, the NRC staff concluded that, subject to the specified conditions and limitations, the embedded flaw repair process described in WCAP-15987-P Revision 2-P-A provides an acceptable level of quality and safety. The staff also concluded that WCAP-15987-P Revision 2-P-A is acceptable for referencing in licensing applications.

The purpose of this report is to provide plant-specific technical basis for the use of the embedded flaw repair process and to confirm that V. C. Summer Unit I meets the criteria for application of the embedded flaw repair process stated in Appendix C of WCAP-15987-P Revision 2-P-A [1]. Engineering evaluations were performed to determine the maximum flaw sizes that can be repaired using the embedded flaw repair process that would satisfy the requirements in Section XI of the ASME Code [2].

The results presented in this report support the use of the Westinghouse embedded flaw repair process as the repair option for the V. C. Summer Unit I reactor vessel head penetration nozzles and attachment J-groove welds.

Introduction August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 1-2 In this report, the technical basis and evaluation results to support the use of the embedded flaw repair process for a flawed head penetration nozzle are provided in Section 2.

The technical basis and evaluation results that support a similar application for a flawed head penetration nozzle attachment J-groove weld are provided in Section 3.

Note that there are several locations in this report where proprietary information has been identified and bracketed. For each of the bracketed locations, the reason for the proprietary classification is given, using a standardized system. The proprietary brackets are labeled with three different letters to provide this information and the explanation for each letter is given below:

a.

The information reveals the distinguishing aspects of a process or component, structure, tool, method, etc., and the prevention of its use by Westinghouse's competitors, without license from Westinghouse, gives Westinghouse a competitive economic advantage.

c.

The information, if used by a competitor, would reduce the competitor's expenditure of resources or improve the competitor's advantage in the design, manufacture, shipment, installation, assurance of quality, or licensing of a similar product.

e.

The information reveals aspects of past, present, or future Westinghouse or customer funded development plans and programs of potential commercial value to Westinghouse.

Introduction August 2013 WCAP-1 7758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-1 2

TECHNICAL BASIS FOR APPLICATION OF EMBEDDED FLAW REPAIR PROCESS TO HEAD PENETRATION NOZZLES This section provides a discussion on the technical basis for the use of embedded flaw repair process for a flawed head penetration nozzle. Such a repair would involve depositing several layers of Alloy 52/52M weld material over the flaw detected on the inside surface of the penetration nozzle or right over the outside surface of the penetration nozzle of interest below the J-groove weld, as well as over the wetted surface of the J-groove weld in the event that an outside surface flaw is detected in the penetration nozzle.

Since the Alloy 52/52M repair weld material is more PWSCC resistant than the existing Alloy 600 material, any detected surface flaws in the head penetration nozzles can then be shielded from the primary water environment and are no longer susceptible to primary water stress corrosion cracking. This is consistent with the current plant operating experiences that no primary water stress corrosion cracking initiation has been observed in Alloy 52/52M weld material so far.

For the repair of an unacceptable inside surface flaw in the head penetration nozzle, an inside surface excavation will be made. At least two layers of Alloy 52/52M weld repair material will then be deposited in the cavity. Any excess repair weld material that protrudes beyond the original inside surface of the penetration nozzle will be removed. A schematic of the repair configuration for inside surface flaws is illustrated in Figure 2-1.

For the repair of an unacceptable outside surface flaw in the head penetration nozzle, at least three layers of Alloy 52/52M material will be deposited (3600 full circumference) covering the entire wetted surface of the attachment J-groove weld. The repair weld will extend 0.5 inch past the interface between the J-groove weld buttering and stainless steel cladding as well as covering the entire outside surface of the head penetration nozzle with at least two layers of Alloy 52/52M material all the way to the bottom of the nozzle. A schematic of the repair configuration for outside surface flaws is illustrated in Figure 2-2.

Flaw evaluations were performed for various flaw sizes and shapes that are postulated to remain in the repaired head penetration nozzles. Based on the results of these evaluations, the largest acceptable flaw sizes that can be repaired using the Westinghouse embedded flaw repair process that would satisfy the requirements in ASME Section XI Code as well as Appendix C of WCAP-15987-P Revision 2-P-A can then be determined.

2.1 EVALUATION PROCEDURE AND ACCEPTANCE CRITERIA Rapid, non-ductile failure is possible for ferritic materials at low temperatures, but is not applicable to the nickel-base alloy head penetration nozzle material, Alloy 600.

Nickel-base alloy material is a high toughness material and plastic collapse would be the dominant mode of failure. Therefore, the evaluation procedures and acceptance criteria for indications in austenitic piping contained in paragraph IWB-3640 and Appendix C of the ASME Section XI Code [2] are applicable for evaluation of flaws in the head penetration nozzles and are consistent with those in Appendix C of WCAP-15987-P Revision 2-P-A.

Paragraph IWB-3660 and Appendix 0 also provide the evaluation procedures and acceptance criteria for flaws detected in the reactor vessel head penetration nozzles. However, Table IWB-3663-1 in paragraph IWB-3660 only provides acceptance criteria for a limited number of flaws in the head penetration nozzles, therefore the evaluation procedures and acceptance criteria in paragraph IWB-3640 are used in the development of plant specific technical basis for the embedded flaw repair process in order to Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-2 WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-2 supplement the acceptance criteria provided in paragraph IWB-3660. The following summarizes the acceptance criteria in Appendix C of the ASME Section XI code.

2.1.1 Acceptance Criteria for Axial Flaws For axial flaws, the allowable flaw depth for a given flaw length can be determined from the following expression in ASME Section XI Code Article C-5000 [2]:

,jaSt/

where M 1+[ 1.61 j2]/g2 M 2

[1

• .4 Rmtf1 and au + a Yf

=

u 2 Y (Average of Ultimate and Yield Strengths) 2 Cyh

=

PR,/t

-e Total Flaw Length a

Flaw Depth Rm

=

Mean Radius of Penetration Nozzle t

=

Wall Thickness of Penetration Nozzle P

Internal Pressure SFm =

Safety Factor for membrane stress:

2.7 for Level A Service Loading 2.4 for Level B Service Loading 1.8 for Level C Service Loading 1.3 for Level D Service Loading The limits of applicability of this equation are a/t < 0.75 and I < taow, where

=allow I.58(Rmt)0°5 [(Of /lh) 2

_ 1] 0.5 This limit is chosen such that surface flaws would remain below the critical size based on the plastic collapse condition if they should grow through the wall.

Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-3 2.1.2 Acceptance Criteria for Circumferential Flaws For circumferential flaws, the following relationship between the applied loads and flaw depth at incipient collapse given by equations in ASME Section XI Article C-5000 [2] is used:

b

[2 sinP tsinO1 P=-Iir - a 0-na 2

t a

-I -

where:

b

=

Bending stress at incipient plastic collapse 0

=

One-half of the final flaw angle 03

=

Angle to neutral axis of penetration nozzle a/t

=

Flaw depth to wall thickness ratio Su + Sy f

=

Flow stress =

(Average of Ultimate and Yield Strengths) 2 am

=

Applied membrane stress The allowable bending stress, S,, is as follows, which is used to calculate the maximum allowable end-of-evaluation period flaw sizes and the limit of applicability of this equation is a/t < 0.75.

SFb

[

Sm J where Sc

=

Allowable bending stress at incipient plastic collapse am

=

Applied membrane stress SFm

=

Safety factor for membrane stress

=

2.7, 2.4, 1.8 and 1.3 for Service Level A, B, C, and D respectively SFb

=

Safety factor for bending stress 2.3, 2.0, 1.6, and 1.4 for Service Level A, B, C, and D respectively 2.2 METHODOLOGY The evaluation assumed that an unacceptable flaw has been detected in a penetration nozzle and that the embedded flaw repair process is used to seal the flaw from further exposure to the primary water environment. The evaluation began with the determination of an allowable end-of-evaluation period flaw size based on the acceptance criteria described in Section 2.1 for a flaw postulated to remain in the repaired penetration nozzle. With the embedded flaw repair process, the only mechanism for sub-critical crack growth is fatigue. The maximum initial flaw size in a penetration nozzle that can be repaired using the embedded flaw repair process can then be determined by subtracting any predicted fatigue crack Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-4 growth for future plant operation from the maximum allowable end-of-evaluation period flaw size. The following provides a discussion of the loading conditions, geometry, thermal transient stress analysis and fatigue crack growth analysis used in the development of the plant specific technical basis for the embedded flaw repair process.

2.2.1 Loading Conditions The requirement for determining the maximum allowable end-of-evaluation period flaw size using the rules of ASME Section XI is that the governing loadings from the normal, upset, emergency, and faulted conditions be considered. This is necessary because, as discussed in Section 2.1, different safety margins are used for the normal, upset, emergency, and faulted conditions. Lower safety factors are used to reflect a lower probability of occurrence for the upset, emergency, and faulted conditions.

Plastic collapse is the governing mode of failure for the head penetration nozzles because the high fracture toughness of the Alloy 600 material [3] would prevent brittle fracture from occurring. Therefore, in accordance with the ASME Section XI, paragraph IWB-3640 requirement for high fracture toughness materials similar to Alloy 600 base metal, it is not necessary to consider the effects of secondary stresses resulting from thermal transient stresses and residual stresses in determining the maximum allowable end-of-evaluation period flaw size. The governing loading for determining the maximum allowable end-of-evaluation period flaw size for the head penetration nozzles is therefore those due to internal operating pressure and other applicable external mechanical loads for the normal, upset, emergency and faulted conditions.

For the fatigue crack growth prediction, the effects of secondary stresses resulting from thermal transient and residual stresses must be considered. The thermal transients that occur in the upper head region are relatively mild. The normal and upset thermal transients applicable to the head penetration nozzles are shown in Table 2-2. It should be noted that residual stress acts primarily as a mean stress and does not change the cyclic stress range, which is a key input parameter used in the fatigue crack growth calculation. However, the residual stress magnitude would have an effect on the R ratio used in the fatigue crack growth rate calculation as discussed in Section 2.2.5. For conservatism, R=I is used in the fatigue crack growth calculation to account for the effects of various types of residual stresses on the penetration nozzles.

2.2.2 Geometry There are many head penetration nozzles in the reactor vessel upper closure head. A schematic of a typical closure head penetration nozzle is shown in Figure 2-3. The dimensions of all the V. C. Summer Unit I penetration nozzles are identical, with a 4.00 inch nominal outside diameter and a nominal wall thickness of 0.625 inch [4]. The outermost penetration nozzles (46.00 intersection angle) were selected for thermal transient and residual stress analysis because the stresses in the outermost penetration nozzles are considered to be more dominating and bound all other penetration nozzles with smaller nozzle intersection angles.

2.2.3 Finite Element Analysis The distributions of residual, transient thermal, and pressure stresses in the outermost reactor vessel head penetration nozzles were obtained from detailed three-dimensional elastic-plastic ANSYS finite element Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-5 analyses [5].

Taking advantage of the symmetry through the reactor vessel closure head and penetration nozzle centerlines, only half of the outermost penetration nozzle geometry and the surrounding vessel material were modeled. In the finite element model, the lower portion of the penetration nozzle, the adjacent section of the reactor vessel closure head and the attachment J-groove weld were included.

Various materials were included in the model, namely, the reactor vessel closure head material is SA-533, Grade B, Class I low alloy steel, the penetration nozzle base metal material is nickel-chrome-iron Alloy 600, the cladding on the inside surface of the vessel closure head is stainless steel and the attachment J-groove weld is Alloy 82/182. The original penetration nozzle welding sequence was simulated using coupled thermal and structural analysis to determine the thermally induced residual stress. The thermal analysis was used to generate nodal temperature distributions at several time steps during the welding process.

The nodal temperatures were then used as loading inputs to the structural analysis, which calculated the thermally induced stresses. Both thermal and structural analyses required the use of both thermal and structural elements. In the 3-D thermal analysis, eight-node thermal solids (SOLID70) were used, while eight-node 3-D isoparametric solid elements (SOLID45) and two-node interface elements (COMBIN40) were used for the 3-D structural analysis.

Time history thermal transient analyses for the penetration nozzle were performed to determine the through-wall thermal transient stresses for those thermal transients tabulated in Table 2-2. The finite element model with the stress cuts of interest is shown in Figure 2-4. These stress cuts are located in the vicinity of the attachment J-groove weld region of the head penetration nozzle where the stresses are high.

These high stress regions are potential crack initiation locations. The through-wall stress distributions from the finite element analyses were used to determine the fatigue crack growth and the maximum allowable initial flaw sizes for flaws in the penetration nozzles of interest.

2.2.4 Crack Tip Stress Intensity Factor One of the key elements in a crack growth analysis is the crack driving force or crack tip stress intensity factor, K1.

This is based on the crack tip stress intensity factor expressions available in the public literature, such as API-579 [6]. It should be noted that the flaws in the repaired penetration nozzles are conservatively assumed to be surface flaws even though the flaws are embedded after the repair.

For a part-through wall surface flaw, the stress profile is approximated by a fourth order polynomial as follows:

a= A0 + AI(x/t) + A2(x/t)2 + A3(x/t)3 + A4(X/t)4 where:

x

=

Distance into the wall from the free surface t

=

Thickness of the penetration nozzle a

=

Stress perpendicular to the plane of the crack Ai

=

Coefficients of the 4th order polynomial fit, i = 0, 1, 2, 3, 4 For a surface flaw in the penetration nozzle, the stress intensity factor expression from API-579 [6] is used. The stress intensity factor K1(ý) can be calculated anywhere along the crack front, where ý is the elliptical angle of a point on the crack front being evaluated.

The following expression is used in calculating Kl(ý).

Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-6 KI =

-Gj (a/c,a/t,t/R, d) Aj (a/t)j Kj=0 The magnification factors Go, G1, G2, G 3 and G 4 can be found in API-579 [6]. The parameter "a" is the crack depth, "c" is the half crack length, "t" is the wall thickness, "R" is the inside radius, "f" is the parametric angle of the semi-elliptical crack, and "Q" is the shape factor.

2.2.5 Fatigue Crack Growth Analysis The objective of calculating fatigue crack growth is to be able to determine the maximum allowable initial flaw size that can remain in a repaired head penetration nozzle after the implementation of the embedded flaw repair process. The fatigue crack growth analysis procedure involves postulating various types of flaws remaining in the repaired penetration nozzle and predicting the growth of that flaw due to an imposed series of plant operating transients. The applied loads used in the fatigue crack growth analysis include pressure, thermal transients and residual stresses. The normal and upset thermal transients as well as the associated design cycles considered in the fatigue crack growth analysis are shown in Table 2-2.

The input required for a fatigue crack growth analysis is essentially the information necessary to calculate the range of crack tip stress intensity factors, AK, which depends on the crack size and shape, geometry of the structural component where the crack is postulated, and the applied cyclic stresses. Also, the load ratio, R = Kmin/Kmax, is required for the scaling parameter in the fatigue crack growth rate equation.

Once R and AK are calculated, the crack growth due to any given stress cycle can be calculated using the applicable fatigue crack growth rate [8] for the head penetration nozzle material. This increment of crack growth is then added to the original crack size, and the analysis proceeds to the next transient. The procedure is continued in this manner until all the transients known to occur in the period of evaluation have been analyzed.

Since any flaws remaining in the repaired head penetration nozzles are no longer exposed to the primary water environment, the fatigue crack growth rate reference curve for nickel-base alloy material in air environment [8] is applicable:

da

-_=-CSRAKn dN C = 4.835x 10-14 + 1.622 x 10-16T - 1.490 x 10-" T2 + 4.355 x 10-2 1 T3 SR = [I - 0.82 R]-2 '

n=4.1 where:

T

=

Average temperature of the transient ('C)

AK

=

Stress intensity factor range (MPa Vmi)

R

=

Stress Ratio (Kmin/Km.a) da/dN =

Fatigue crack growth rate (meters / cycle)

Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-7 The crack growth rate reference curve in air for the Alloy 52/52M repair weld material is not readily available in the ASME Code. However, based on the limited test data on Alloy 52 in the Pressurized Water Reactor (PWR) water environment [8], the crack growth rates in PWR water environment for both Alloy 52 and Alloy 600 are similar. Therefore, it is reasonable to assume that the crack growth rate curves in the air environment for both Alloy 52 and Alloy 600 are also similar. Nevertheless, for the evaluations in this report, the crack growth rate for Alloy 52 in air environment is conservatively assumed to be twice that of Alloy 600 in air, which is similar to the crack growth rate of Alloy 182 in air environment.

2.3 FRACTURE MECHANICS ANALYSIS RESULTS 2.3.1 Maximum Allowable End-of-Evaluation Period Flaw Size Maximum allowable end-of-evaluation period flaw sizes for axial and circumferential flaws with various aspect ratios (flaw length/flaw depth) in the head penetration nozzles are calculated in accordance with the acceptance criteria discussed in Section 2.1. The end-of-evaluation period allowable flaw sizes are tabulated in Table 2-1 for axial and circumferential inside surface flaws. These allowable flaw sizes are applicable to both the downhill and uphill side. Some of the maximum allowable end-of-evaluation period flaw sizes are larger than 75% of the original wall thickness; however, the maximum allowable end-of-evaluation period flaw sizes are limited to only 75% of the wall thickness in accordance with the requirements of Section XI of the ASME code [2]. The maximum allowable end-of-evaluation period flaw sizes determined for the inside surface flaws in Table 2-1 can also be conservatively used for embedded flaws as well as outside surface flaws. It should be noted that these maximum allowable end-of-evaluation period flaw sizes shown in Table 2-1 must be adjusted to account for fatigue crack growth in order to determine the maximum allowable initial flaw size that can be repaired using the Westinghouse embedded flaw repair process. Since the flaw remaining in a repaired penetration nozzle is embedded and/or sealed from the primary water environment, it is no longer subjected to primary water stress corrosion cracking and therefore the only credible mechanism for sub-critical crack growth is fatigue. Adjustments to the end-of-evaluation period allowable flaw sizes are based on the fatigue crack growth results described in Section 2.3.2.

2.3.2 Maximum Allowable Initial Flaw Size A fatigue crack growth analysis was performed to determine the extent of fatigue crack growth for a given plant operation duration for postulated flaws remaining in a repaired penetration nozzle on both the downhill and uphill sides. Both axial and circumferential flaw orientations are considered in the fatigue crack growth analysis.

Figures 2-5 and 2-6 show the limiting predicted fatigue crack growth for axial flaws in the repaired head penetration nozzle for the uphill side and downhill side respectively. The postulated flaws are sealed from the primary water environment by depositing PWSCC resistant repair weld layers on the inside surface of the penetration nozzle or over the wetted surface of the attachment J-groove weld and the outside surface of the penetration nozzle below the attachment J-groove weld. The maximum allowable initial axial flaw sizes accounting for fatigue crack growth in a repaired penetration nozzle can then be determined from these figures by subtracting the fatigue crack growth increments for a given plant operation duration shown in Figures 2-5 and 2-6 from the maximum end-of-evaluation period allowable axial flaw sizes shown in Table 2-1.

Figure 2-7 shows the maximum allowable initial axial flaw sizes taking into account Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-8 of fatigue crack growth for a 20 year service life for both the downhill and uphill sides. For other plant operation durations, the maximum allowable initial axial flaw sizes can be determined directly from the fatigue crack growth results shown in Figures 2-5 and 2-6 based on the end-of-evaluation period axial flaw sizes from Table 2-1. If the initial axial flaw size detected in the penetration nozzle before the repair is below the applicable maximum allowable initial axial flaw sizes shown in Figure 2-7, the service life would be more than 20 years. It is therefore technically justified to use the embedded flaw repair process as the repair option for the reactor vessel head penetration nozzles since the criteria for application of such a process as stated in Appendix C of WCAP-15987-P Revision 2-P-A is met. If the initial axial flaw size exceeds the applicable maximum allowable initial axial flaw sizes shown in Figure 2-7, Figures 2-5 and 2-6 can be used to determine the actual service life of the penetration nozzle.

The results demonstrated in Figures 2-5 through 2-7 are applicable for axial flaws found on the inside or outside surface of the penetration nozzles which are repaired using the embedded flaw repair process.

Similarly, Figures 2-8 and 2-9 show the limiting predicted fatigue crack growth in the repaired head penetration nozzle for circumferential flaws postulated on the uphill side and downhill side, respectively.

The maximum allowable initial circumferential flaw sizes accounting for fatigue crack growth in a repaired penetration nozzle can be determined from these figures by subtracting the fatigue crack growth increments for a given plant operation duration shown in Figures 2-8 and 2-9 for the uphill and downhill side respectively from the maximum allowable end-of-evaluation period circumferential flaw sizes shown in Table 2-1.

Figure 2-10 shows the maximum allowable initial circumferential flaw sizes taking into account of fatigue crack growth for a 20 year period of service life. For other plant operation durations, the maximum allowable initial circumferential flaw sizes can be determined directly from Figures 2-8 and 2-9 based on the end-of-evaluation period circumferential flaw sizes from Table 2-1.

If the initial circumferential flaw size detected in the penetration nozzle before the repair is below the applicable maximum allowable initial circumferential flaw sizes shown in Figure 2-10, the service life would be more than 20 years. It is therefore technically justified to use the embedded flaw repair process as the repair option for the reactor vessel head penetration nozzles since the criteria for application of such a process as stated in Appendix C of WCAP-15987-P Revision 2-P-A is met. If the initial circumferential flaw size exceeds the applicable maximum allowable initial circumferential flaw sizes shown in Figure 2-10, Figures 2-8 and 2-9 can be used to determine the actual service life of the penetration nozzle. The results demonstrated in Figures 2-8 through 2-10 are applicable for circumferential flaws found on the inside or outside surface of the penetration nozzles which are repaired using the embedded flaw repair process.

2.4

SUMMARY

Unacceptable axial and circumferential flaws detected on the inside surface or outside surface of a head penetration nozzle can be repaired using the embedded flaw repair process by shielding them from the primary water environment. The maximum allowable initial axial and circumferential flaw sizes that can be repaired using the Westinghouse embedded flaw repair process are shown in Figures 2-7 and 2-10 respectively for a plant service life of 20 years.

For other plant operation durations, the maximum initial allowable flaw sizes that can be repaired using the Westinghouse embedded flaw repair process can be determined directly from Figures 2-5, 2-6, 2-8 and 2-9 based on the maximum allowable end-of-evaluation period flaw sizes for the applicable flaw orientation shown in Table 2-1. If the initial flaw size exceeds the applicable maximum allowable initial flaw sizes shown in Figures 2-7 and 2-10, Figures 2-5, 2-6, 2-8 and 2-9 can be used to determine the actual service life of the penetration nozzle. If the initial flaw size detected in the penetration nozzle before the repair is below the applicable maximum allowable Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-9 initial flaw sizes shown in Figures 2-7 and 2-10 for axial and circumferential flaws respectively, the service life would be more than 20 years.

It is therefore technically justified to use the embedded flaw repair process as the repair option for the reactor vessel head penetration nozzles since the criteria for application of such a process as stated in Appendix C of WCAP-15987-P Revision 2-P-A is met.

Table 2-1 Maximum Allowable End-of-Evaluation Period Flaw Sizes (Percentage of Nominal Wall Thickness)

Aspect Ratio Circumferential Flaw Axial Flaw (Depth/Length) 0.100 0.41 0.75 0.167 0.52 0.75 0.333 0.73 0.75 0.500 0.75 0.75 Table 2-2 Reactor Coolant System Transients for V. C. Summer Unit 1191 Design Transients Design Cycles Normal Conditions Heatup/Cooldown 200 Plant Loading/Unloading 18300 Step Load Increase/Decrease 2000 Large Step Load Decrease with Steam Dump 200 Turbine Roll Test 80 Feedwater Heaters Out of Service 40 Steady State Fluctuation (Initial) 150000 Steady State Fluctuation (Random) 3000000 Upset Conditions Loss of Load 200 Loss of Flow 80 Loss of Power 40 Reactor Trip From Full Power 400 Inadvertent Auxiliary Spray 10 Excessive Feedwater Flow 30 Operating Basis Earthquake 400 Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-10 Nozzle As-Found NOzl Repaired

,Y i

i airi Figure 2-1 Schematics of the Inside Surface Flaw Repair Configuration for the Penetration Nozzle Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-11 WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-Il Nozzle I

Alloy Figure 2ORepair Weld Figure 2-2 Schematic of the Outside Surface Flaw Repair Configuration for the Penetration Nozzle Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-12 WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-12 5::ýDownhill Cadn Side 1

J Weld Head Penetration Nozzle Figure 2-3 Schematic of a Typical Closure Head Penetration Nozzle Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-13 Cut 6 Cut 5 Cut 4 Cut 3 Cut 2 Cut 1 Figure 2-4 Stress Cuts Considered in Fatigue Crack Growth Analysis Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-14 WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-14 0.8 0.7 0.6 0.5 0.4 0

0.3 01 0.2 LL 0.1 0.0 5

10 15 20 25 30 35 lime (Years) 40 Figure 2-5 Fatigue Crack Growth Prediction for Axial Flaws in Repaired Penetration Nozzles (Uphill Side)

Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-15 WESTNGHOSE ON-POPRITAR CLAS 32-15

'U

E 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0

5 10 15 20 25 30 35 40 Time (Years)

Figure 2-6 Fatigue Crack Growth Prediction for Axial Flaws in Repaired Penetration Nozzles (Downhill Side)

Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-1 7758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-16 0.8 0.7 0.

DownhillSide 0.6 4 0 0.3

.0 0.2.__:.

1U--

-- --i--

0.

=

=.....

I

..1.

> - J

. - * =

.2 0.2 0.1 00

'0' 0.1 0.15 0.2 0.25 03 0.35 0.4 0.45 0.5 Flaw Depth to Flaw Length Ratio (a/l)

Figure 2-7 Maximum Allowable Initial Axial Flaw Sizes for Repaired Penetration Nozzles for a 20 Year Service Life Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-17 WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-17 0.8 0.7 0.6 2

oU 0.

4.s i

0.4 CL A

0.4 0.1 0

0 5

10 15 20 25 30 35 40 Time (Years)

Figure 2-8 Fatigue Crack Growth Prediction for Circumferential Flaws in Repaired Penetration Nozzles (Uphill Side)

Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-18 0.8 0.7 4*

0.6 tU 0

4-u 0.4 S0.3

@3 CL U.

0.4 0

0.1 0.0

-- " I 7

i* !!.-Aspect Ratiol(AR)=Flaw Length/Flaw Depth

_12

• .*i.L 2i2222 0

5 10 15 20 25 30 35 40 Time (Years)

Figure 2-9 Fatigue Crack Growth Prediction for Circumferential Flaws in Repaired Penetration Nozzles (Downhill side)

Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 2-19 40 0

VC 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Flaw Depth to Flaw Length Ratio (a/t)

Figure 2-10 Maximum Allowable Initial Circumferential Flaw Sizes for Repaired Penetration Nozzles for a 20 Year Service Life Technical Basis for Application of Embedded Flaw Repair Process to Head Penetration Nozzles August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-1 3

TECHNICAL BASIS FOR APPLICATION OF EMBEDDED FLAW REPAIR PROCESS TO PENETRATION NOZZLE ATTACHMENT WELDS This section provides a discussion on the technical basis for the use of embedded flaw repair process for a flawed head penetration attachment J-groove weld. Such a repair process would involve depositing Alloy 52/52M repair weld material over the wetted surface of the attachment J-groove weld and on the outer diameter of the penetration nozzle below the attachment J-groove weld in order to seal the crack from the primary water environment. At least three weld layers of Alloy 52/52M repair weld material will be deposited (3600 full circumference) covering the wetted surface of the penetration nozzle J-groove weld including at least 0.5 inch past the J-groove weld buttering and stainless steel cladding interface.

In addition, at least two weld layers will be deposited covering the outside diameter of the head penetration nozzle all the way to the bottom of the nozzle. A schematic of the repair configuration for a flawed head penetration attachment J-groove weld is illustrated in Figure 3-1. Since the current available technology cannot characterize the depth of a flaw in the attachment weld, it is therefore conservatively assumed that the flaw extends radially over the entire attachment J-groove weld cross-section. A flaw evaluation was performed by postulating a flaw of that size and shape in the reactor vessel head in developing the technical basis for the embedded flaw repair process.

3.1 EVALUATION PROCEDURE AND ACCEPTANCE CRITERIA 3.1.1 ASME Section XI Appendix K The evaluation procedure and acceptance criteria used to demonstrate structural integrity of the reactor vessel closure head is contained in Appendix K of ASME Section XI Code [2] as well as Regulatory Guide 1.161 [10]. Although the original purpose of Appendix K was to evaluate reactor vessels with low upper shelf fracture toughness, the general approach in paragraph K-4220 is equally applicable to any region of the reactor vessel where the fracture toughness can be described with elastic plastic parameters.

The closure head region of the V. C. Summer Unit 1 reactor vessel has an operating temperature of approximately 557'F. This would result in ductile behavior and therefore the use of elastic-plastic fracture mechanics method is appropriate.

The approach to evaluating the integrity of a reactor vessel has been developed over a ten-year period, and has been illustrated with a number of example problems [11 ] to demonstrate its use. The extension of this methodology to issues other than the low shelf fracture toughness issue is appropriate when service conditions (temperature) promote ductile behavior.

The extension of the Elastic Plastic Fracture Mechanics (EPFM) method to the reactor vessel head is appropriate, as discussed above.

The acceptance criteria are to be satisfied for each category of transients, namely, Service Load Level A (normal), Level B (upset), Level C (emergency) and Level D (faulted) conditions and two criteria must be satisfied.

The first criterion is that the crack driving force must be shown to be less than the material toughness as follows:

Japplied < J0.I Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-2 where Japplied is the J-integral value calculated for the postulated flaw under the applicable Service Level condition and J0.1 is the J-integral characteristic of the material resistance to ductile tearing at a crack extension of 0.1 inch.

The second criterion is that the flaw must also be stable under ductile crack growth as follows:

ai applied dJ material aa da at Japplied = Jmaterial

where, Jmaterial

=

J-integral resistance to ductile tearing for the material aJapplied

=

Partial derivative of the applied J-integral with respect to flaw depth, a aa dJmaterW =

Slope of the J-R curve da 3.1.2 Primary Stress Limits In addition to satisfying the above acceptance criteria, the primary stress limits of paragraph NB-3000 in Section III of the ASME Code must be satisfied. The effects of a local area reduction of the pressure retaining membrane that is equivalent to the area of the postulated flaw in the reactor vessel head attachment J-groove weld must be considered to reflect the reduced cross section.

3.2 METHODOLOGY The evaluation assumed that a flaw has been detected in a penetration nozzle attachment J-groove weld and that the embedded flaw repair process is used to seal the flaw from further exposure to the primary water environment. The evaluation was performed to demonstrate the stability of a postulated flaw that encompasses the entire attachment J-groove weld region in the reactor vessel head near the penetration nozzle. The postulated flaw is stable under ductile crack growth if the acceptance criteria in Section 3.1 are met. With the embedded flaw repair process, the only mechanism for sub-critical crack growth is fatigue. Therefore, fatigue crack growth evaluations for the postulated flaw in the reactor vessel head were also performed to demonstrate structural integrity. The requirement for evaluating flaw stability in the reactor vessel upper closure head in accordance with the evaluation procedures and acceptance criteria in ASME Section XI code is that the governing transient resulting from the normal/upset conditions as well as the emergency/faulted conditions be considered.

There are many head penetrations in the reactor vessel upper closure head, and the outermost head penetration nozzles (46.00 intersection angle) were chosen for thermal transient and residual stress analysis because the stresses at the outermost head penetration nozzle are, in general, more dominating Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle August 2013 Attachment Welds WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-3 and bound all other penetration nozzles with smaller nozzle intersection angles.

The diametric dimensions of all the V. C. Summer Unit 1 Control Rod Drive Mechanism head penetration nozzles are identical, with a 4.00 inch nominal outside diameter and a nominal wall thickness of 0.625 inch [4]. The distribution of residual, transient thermal, and pressure stresses in the closure head region were obtained from detailed three-dimensional elastic-plastic finite element analyses [5] of the head penetration nozzle region as discussed in Section 2.2.3.

The through-wall stress distributions from the finite element analyses were used to determine the acceptability of the postulated flaw in the attachment J-groove weld as well as the associated fatigue crack growth. The stress cuts on the reactor vessel closure head selected for the analysis are shown in Figure 3-2. The through-wall stress distribution from these stress cuts is used in the flaw stability evaluation as well as the fatigue crack growth analysis.

3.2.1 Stress Intensity Factor One of the key elements in the fracture mechanics evaluation is the determination of the crack driving force or stress intensity factor (K1). The stress intensity factor expression for two comer flaws emanating from the edge of a hole in a plate [6] was used in determining the stress intensity factor for the postulated flaw in the attachment J-groove weld as shown in Figure 3-3. The stress intensity factor can be expressed in terms of the membrane and bending stress components as follows:

Ki = (Mm.Ym + Mbyb) (7ta/Q)1/2

where, K,

=

Crack Tip Stress Intensity Factor a,

Remote Membrane Stress Component Gb

=

Remote Bending Stress Component Mm

=

Membrane Boundary Correction Factor Mb

=

Bending Boundary Correction Factor Q

=

Shape Factor a

=

Depth of the Comer Flaw (See Figure 3-3)

Use of this method requires that the stresses remote from the hole be resolved into membrane and bending stress components. The attachment J-groove weld shapes were based on the J-groove geometry shown in the head penetration nozzle drawing [4] for the V. C. Summer Unit 1 head penetration nozzles.

The stress intensity factor expression shown above is applicable for a range of flaw shapes, with the depth of the flaw defined as "a", and the width of the flaw defined as "c", as shown in Figure 3-3. This flexibility is necessary because this expression can be applied to different attachment J-groove weld shapes in V. C. Summer Unit I as shown in Table 3-1. The attachment J-groove weld shapes in V. C.

Summer Unit I were based on the J-groove geometry shown in the head penetration nozzle drawings [4].

The expressions for boundary correction factors Mm and Mb can be found in API-579 [6] and are calculated based on the outside radius of the penetration nozzle, the wall thickness of the reactor vessel head and the J-groove sizes.

Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-4 3.2.2 J-R Curve for Reactor Vessel Closure Head Material One of the most important pieces of information on the toughness of pressure vessel and piping materials is the J-R curve of the material, where J-R stands for material resistance to crack extension, as represented by the measured J-integral value versus crack extension. Simply put, the J-R curve to cracking resistance is as significant as the stress-strain curve to load-carrying capacity and ductility of a material. Both the J-R curve and the stress-strain curve are properties of a material.

Directly measured J-R curves are not generally available for a specific material of interest. The J-integral fracture resistance of the material is determined using the methodology in Regulatory Guide 1.161 [10]

and NUREG/CR-5729 [12] based on available data such as material chemistry, radiation exposure, temperature and Charpy V-notch energy. NUREG/CR-5729 [12] summarizes a large collection of public test data, which were fitted into a multivariable model based on advanced pattern recognition technology.

Separate analysis models and databases were developed in NUREG/CR-5729 [12] for different material groups, including reactor pressure vessel (RPV) welds, RPV base metals, piping welds, piping base metals and a combined materials group.

The material resistance, Jmat, are fitted into the following equation [10, 12]:

Jmat = (MF)C1 (Aa)c 2 exp [C3(Aa)C4]

where C 1, C2, C3, and C4 are fitting constants, and Aa is crack extension MF is the Margin Factor from Regulatory Guide 1.161 [10]:

= 0.749 for Service Levels A, B and C

= 1.0 for Service Level D For the RPV base metal model, the constants Cl, C2, C3, and C4 are obtained from Table 11 of NUREG/CR-5729 [12], and shown below:

lnC=a 1

+a 2 In CVN+ a 3 T+a 4 In B.

C2=dI +d 2 1nCl+d 3 InB, C3=d 4 +d 5 lnCl+d 6 lnB.

C4 = d7 where T

=

Temperature ('F)

Bn

=

Section thickness (inches)

CVN Charpy impact energy (ft-lbs) a, and di are constants given in Table 11 of NUREG/CR-5729 [12] are shown as follows:

a, = -2.44 a2 = 1.13 Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-5 a3 = -0.00277 a4 = 0.0801 d, = 0.0770 d2 = 0.116 d3 = -0.0412 d4 = -0.0812 d5 = -0.00920 d6 = -0.0295 d 7 = -0.409 Neutron irradiation has been shown to produce embrittlement that reduces the toughness properties of the reactor vessel ferritic steel material. The irradiation levels are very low in the reactor vessel closure head region and therefore the fracture toughness will not be measurably affected. Based on a review of the certified material test reports [13] pertaining to the Charpy Impact Test on the reactor vessel closure head material, an upper shelf Charpy impact energy of [

]".e is used in the development of the J-R curve for the V. C. Summer Unit I reactor vessel closure head material.

3.2.3 Applied J-Integral For small scale yielding, the applied J-integral, Japplied, of a crack can be calculated using the Linear Elastic Fracture Mechanics (LEFM) method based on the crack tip stress intensity factor, KI, calculated as discussed in Section 3.2.1. However, a plastic zone correction must be considered to account for plastic deformation at the crack tip similar to the approach in Regulatory Guide 1.161 [10].

The plastic deformation ahead of the crack front is regarded as a failed zone and the crack size is, in effect, increased.

The KI-values based on the plastic zone adjusted crack depth can then be converted to Japplied by the following equation:

Japplied

where, Kep is the elastically calculated KI-value based on the plastic zone adjusted crack depth E' = E/(1-v 2) for plane strain, E is the Young's Modulus and v, the Poisson's Ratio.

The plastic zone correction, rp, can be calculated as follows:

rp = 61t ýT.

Sy) where Sy is the yield strength of the material and K1 is the stress intensity factor calculated in accordance with Section 3.2.1.

Assuming that the original crack depth under consideration is a,, Kep can now be calculated based on the plastic zone adjusted crack depth, ak + rp.

Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle August 2013 Attachment Welds WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-6 Once the applied J-integral is calculated, flaw stability for the postulated flaw in the attachment J-groove weld can be determined using the J-R curve developed in Section 3.2.2 for the V. C. Summer Unit 1 reactor vessel closure head material.

3.2.4 Fatigue Crack Growth The fatigue crack growth analysis involves postulating planar flaws that extend radially over the entire attachment J-groove weld cross-section in the reactor vessel closure head and calculating the crack growth resulting from the postulated cracks being subjected to a series of operating transient loadings.

The loadings included pressure, thermal transients, and residual stresses. The design thermal transients as well as the associated design cycles are listed in Table 2-2.

The design transient cycles are distributed evenly over the plant design life. The stress intensity factor range, AKI, which controls the fatigue crack growth, depends on the geometry of the crack, its surrounding structure and the range of applied stresses in the region of the postulated crack. The methodology used in determining the stress intensity factor, K1, is discussed in Section 3.2.1. Once AK1 is calculated, the fatigue crack growth due to a particular stress cycle can be determined using a crack growth rate reference curve applicable to the material where the crack is postulated.

The crack growth rate curves used in the analyses for the postulated flaws in the reactor vessel closure head are taken directly from Appendix A in the ASME Section XI code [2] for ferritic steel material.

Since any flaws in the attachment J-groove weld will be sealed from the primary water environment, the crack growth rate reference curve for the air environment can be used. This curve is a function of the applied stress intensity factor range (AK1) and the R ratio, which is the ratio of the minimum to maximum stress intensity factor during a thermal transient.

Once the incremental crack growth corresponding to a specific transient for a small time period is calculated, it is added to the original crack size and the analysis continues to the next time period and/or thermal transient. The procedure is repeated in this manner until all the significant analytical thermal transients and cycles known to occur in a given period of operation have been analyzed.

3.3 FRACTURE MECHANICS ANALYSIS RESULTS 3.3.1 Comparison of Applied J-Integral and Material J-R Curves The geometry or weld shape for the V. C. Summer Unit 1 head penetration attachment J-groove welds [4]

are shown in Table 3-1, which forms the basis for the geometry of the postulated flaws in the attachment J-groove weld region.

The applied J-integral values were then calculated based on the elastically calculated K1 adjusted for the plastic zone correction as discussed in Section 3.2.3. The material J-R curve was obtained as discussed in Section 3.2.2 and the applied J-integral values and the material J-R curves for the limiting penetration nozzles on the downhill and uphill sides were plotted in Figures 3-4 and 3-5 respectively. Using the acceptance criteria discussed in Section 3.1, the structural integrity of the reactor vessel closure head with the postulated flaw that is assumed to encompass the entire attachment J-groove region can then be determined.

The key aspects of the structural integrity evaluation are the values of the Japplied versus Jmaterial for the reactor vessel closure head material and the slope of the Japplied curve versus the slope of the material J-R curve as discussed in Section 3.1.1. Figures 3-4 and 3-5 show the Japplied versus Jmaterial curves for the Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-7 limiting downhill and uphill side flaw shapes without the weld fillet for all the head penetration nozzles in the closure head. For the downhill side of all penetration nozzles, the limiting flaw shape is that of the 46.0* degree nozzles and for the uphill side of all penetration nozzles, the limiting flaw shape is that of the 0.00 degree nozzle. In Figures 3-4 and 3-5, it can be seen that for a crack extension of 0.1 inch, the applied J-integral value is below that of the material J-R curve. In addition, the slope of the material J-R curve exceeds that of the J-applied curve at the equilibrium point where Japplied curve intersects the Jmaterial curve. Since the acceptance criteria in Section 3.1 is met for the limiting J-groove shapes in the reactor vessel head, it can be concluded that structural stability can be demonstrated for any planar flaws detected in the attachment J-groove welds, regardless of size.

3.3.2 Primary Stress Limits In addition to satisfying the above acceptance criteria, the primary stress limits of paragraph NB-3000 in Section III of the ASME Code must be satisfied. The effects of a local area reduction of the pressure retaining membrane that is equivalent to the area of the postulated flaw in the vessel head must be considered to reflect the reduced cross section. The allowable local area reduction was determined by evaluating the primary membrane stress of a spherical head with reduced wall thickness and based on a conservative maximum operating pressure under various service conditions of [

Ia"c'e. The result shows that the allowable flaw depth is 1.718 inches which is deeper than the maximum J-groove depth of 1.62 inches for the V. C. Summer Unit I head penetration nozzles shown in Table 3-1. For a more realistic maximum operating pressure of [

]ace under various service conditions for V.C. Summer Unit 1, the allowable flaw depth can be increased to 1.933 inches.

3.3.3 Fatigue Crack Growth into the Reactor Vessel Closure Head Fatigue crack growth into the reactor vessel closure head was determined for postulated flaws with the limiting J-groove weld shapes shown in Table 3-1 on the uphill and downhill sides of the outermost penetration nozzles.

The flaw is conservatively assumed to be a surface flaw even though it is a subsurface flaw after the repair. The crack growth rate curves used in the fatigue crack growth analysis are taken directly from Appendix A in the ASME Section XI code [2] for ferritic steel material. Since any potential flaws in the attachment J-groove weld are sealed from the primary water environment after the repair, the crack growth rate reference curve for the air environment can be used, however, the limiting crack growth rate curve for air and water environments is conservatively used. This curve is a function of the applied stress intensity factor range (AKI) and the R ratio, which is the ratio of the minimum to maximum stress intensity factor during a thermal transient.

As shown in Figure 3-6, the predicted crack growth for the bounding J-groove weld shape on the downhill and uphill side of all head penetration nozzles is below the allowable primary stress limit flaw depth of 1.933 inches even after 20 years. Based on the fatigue crack growth results, any planar flaws which encompass the entire attachment J-groove shape for the V.C. Summer Unit 1 head penetration nozzles can be shown to be acceptable for at least 20 years of service life based on the design thermal transients and cycles tabulated in Table 2-2.

Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-8 3.3.4 Fatigue Crack Growth into the Repair Weld The attachment J-groove weld repair is performed by depositing a minimum of three layers (-3/16 inch) of Alloy 52/52M repair weld material onto the wetted surface of the flawed attachment J-groove weld.

The flaw is thus sealed from the primary water environment, and the thickness of the reactor vessel head is conservatively assumed to be locally increased by approximately 3/16 inch. In the fatigue crack growth analysis, an embedded flaw is assumed, which starts conservatively from 5/32 inch above the free surface on the inside surface of the reactor vessel head. The depth of the embedded flaw is conservatively assumed to be 3.08 inches and 3.28 inches representing the limiting flaw depth for the downhill and uphill sides, respectively, as shown in Table 3-1.

The assumed limiting flaw depths consist of the entire attachment J-groove as well as the weld fillet shown in Figure 3-7 and the maximum J-groove weld depth from UT data for each penetration row is tabulated in Table 3-1. The embedded flaw depths used in the fatigue crack growth analysis would envelop all the head penetration nozzles on the corresponding downhill and uphill side in V. C. Summer Unit 1. In other words, the postulated initial embedded flaw has a total crack depth of 3.08 inches on the downhill side and 3.28 inches on the uphill side with a crack front that is located at 5/32 inch above the free surface. The fatigue crack growth law used for the repair layer (Alloy 52/52M) is based on the crack growth rate for nickel-base alloy material (Alloy 600) in air environment [8] with a factor of 2 as discussed in Section 2.2.5 and assumed to be the same as those for Alloy 182 weld material in air environment. The fatigue crack growth results are shown in Table 3-2 and the resulting fatigue crack growth for 20 years is insignificant. Therefore the structural integrity of the repaired weld layer is expected to be maintained for at least 20 years of service life.

3.4

SUMMARY

The results of the evaluation have demonstrated that the embedded flaw repair process is a viable method for repairing any potential flaws found in the attachment J-groove welds of the head penetration nozzles at V. C. Summer Unit 1. The fracture mechanics evaluation demonstrated that the flaws in the penetration nozzle J-groove weld that are assumed to encompass the entire attachment J-groove weld shape is stable even when the fatigue crack growth of at least 20 years was taken into consideration.

Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle August 2013 Attachment Welds WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-9 a,c,e Table 3-1 V.C. Summer Unit I Head Penetration Nozzle Attachment J-groove Weld Geometry (All dimensions in inches)

Table 3-2 Predicted Fatigue Crack Growth into the Repaired Weld Layer Distance of the Crack Front from the Nearest Free Surface (inch) 0 0.156 Downhill 20 0.116 0

0.156 Uphill 20 0.114 Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-10 WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-10 NozzleI Alloy 52152M Repair Weldj Figure 3-1 Schematic of the Embedded Flaw Repair Configuration for the Attachment Welds Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-11 WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-11 Uphill Cut 1 Uphill Cut 2 Downhill Cut 2 Figure 3-2 Finite Element Stress Cuts Along the Reactor Vessel Closure Head Downhill Cut 1 Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-12 WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-12 Figure 3-3 Sample Geometry and Terminology Used in Stress Intensity Factor Calculation Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-13 WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-13 1.60 1.40 1.20 Material JR R" 1.00 a

7 0.60 Applied J 0.40 0.20 0.00 1.6 1.65 1.7 1.75 1.8 1.85 Crack Depth (inch) 1.9 Figure 3-4 Applied J-integral and Material J-R Curve for Limiting Downhill Side J-Groove Weld Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-14 1.60 1.40 1.20 Material JR a" 1.00 0.80 0 0.60 Applied J 0.40 0.20 0.00 1.1 1.15 1.2 1.25 1.3 1.35 Crack Depth (inch) 1.4 Figure 3-5 Applied J-integral and Material J-R Curve for Limiting Uphill Side J-Groove Weld Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-15 WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-15

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Figure 3-6 Fatigue Crack Growth Prediction in the Reactor Vessel Head with Maximum Postulated Flaws in the Attachment Weld Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-16 WESTINGHOUSE NON-PROPRIETARY CLASS 3 3-16 a (without weld fillet) a (with weld fillet)

Figure 3-7 Definition of J-groove Weld Dimensions Technical Basis for Application of Embedded Flaw Repair Process to Penetration Nozzle Attachment Welds August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 4-1 4

SUMMARY

AND CONCLUSIONS Engineering evaluations were performed to provide plant specific technical basis for the use of the Westinghouse embedded flaw repair process that is associated with the reactor vessel head penetration nozzle inspection and contingence repair program in V. C. Summer Unit 1.

The technical basis for the use of the embedded flaw repair process if unacceptable flaws are detected in the head penetration nozzle is provided in Section 2. Axial and circumferential flaws found on the inside surface or outside surface of a head penetration nozzle can be repaired using the embedded flaw repair process to seal them from the primary water environment so that they are no longer subjected to primary water stress corrosion cracking. The maximum allowable initial axial and circumferential flaw sizes that can be repaired using the Westinghouse embedded flaw repair method are shown in Figures 2-7 and 2-10 respectively for a plant service life of 20 years. If the initial flaw size exceeds the applicable maximum allowable initial flaw sizes shown in Figures 2-7 and 2-10, Figures 2-5, 2-6, 2-8 and 2-9 can be used to determine the actual service life of the penetration nozzle. If the initial flaw size detected is below the applicable maximum allowable initial flaw sizes shown in Figure 2-7 for axial flaws and Figure 2-10 for circumferential flaws, the service life would be more than 20 years. It is therefore technically justified to use the embedded flaw repair process as the repair option for the reactor vessel head penetration nozzles since the criteria for application of such a process as stated in Appendix C of WCAP-15987-P Revision 2-P-A is met.

The technical basis for the use of the embedded flaw repair process if indications or flaws are found in the head penetration attachment J-groove welds is provided in Section 3. The results of the evaluation have demonstrated that the embedded flaw repair process is a viable method for repairing any flaws detected in the attachment J-groove weld. Structural stability has been demonstrated for a plant service life of at least 20 years regardless of the size of the flaw found in the penetration nozzle attachment J-groove weld.

Therefore, it is technically justified to use the embedded flaw repair process as the repair option for the reactor vessel head penetration nozzle attachment J-groove welds since the criteria for application of such a process as stated in Appendix C of WCAP-15987-P Revision 2-P-A is met.

Summary and Conclusions August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 5-1 5

REFERENCES

1.

Westinghouse WCAP-15987-P, Revision 2-P-A, "Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations," December 2003.

2.

ASME Section XI Code:

a. ASME Boiler & Pressure Vessel Code, 1998 Edition through 2000 Addenda,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components.

b. ASME Boiler & Pressure Vessel Code, 2007 Edition with 2008 Addenda,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components.

3.

Brown, C. M., and Mills, W. J., "Fracture Toughness, Tensile and Stress Corrosion Cracking Properties of Alloy 600, Alloy 690, and Their Welds in Water," in Proceedings of Corrosion 96, Paper 90.

4.

V. C. Summer Unit I Reactor Head Penetration Nozzle Drawings:

a. Chicago Bridge & Iron Company Drawing No. 71-2631-40, Rev. 5, "157" PWR Control Rod Drive Mechanism Housings Detail."

b.

Chicago Bridge & Iron Company Drawing No. 71-2631-42, Rev. 6, "157" PWR CRDM Housing Installation."

c.

Chicago Bridge & Iron Company Drawing No. 71-2631-43, Rev. 3, "157" PWR CRDM Housing Locations Outside View."

5.

Dominion Engineering, Inc. Report C-8849-00-01 Rev. 0, "V.C. Summer RPV Head CRDM Nozzle Welding Residual Stress plus Transient Analysis". (Dominion Engineering Inc.

Proprietary Document)

6.

American Petroleum Institute, API 579-1/ASME FFS-1 (API 579 Second Edition), "Fitness-For-Service," June 2007.

7.

Marston, T. U. et al., "Flaw Evaluation Procedures: ASME Section XI," Electric Power Research Institute Report EPRI-NP-719-SR, August 1978.

8.

NUREG/CR-6721, ANL-01/07, "Effects of Alloy Chemistry, Cold Work, and Water Chemistry on Corrosion Fatigue and Stress Corrosion Cracking of Nickel Alloys and Welds," April 2001.

9.

Design Specification DS-MRCDA-09-10, Rev. 0, "Reactor Vessel - Virgil C. Summer Nuclear Station Addendum to Equipment Specification 679105 Rev. 2."

10.

Regulatory Guide 1.161, "Evaluation of Reactor Pressure Vessel with Charpy Upper-Shelf Energy Less Than 50 ft-lb."

References August 2013 WCAP-17758-NP Rev.0

WESTINGHOUSE NON-PROPRIETARY CLASS 3 5-2

11.

"Development of Criteria for Assessment of Reactor Vessels with Low Upper Shelf Fracture Toughness," Welding Research Council Bulletin 413, July 1996.

12.

E. D. Eason, J. E. Wright, E. E. Nelson, "Multivariable Modeling of Pressure Vessel and Piping J-R Data," NUREG/CR-5729, MCS 910401, RF, R5, May 1991.

13.

Westinghouse Document CMTR-RV-CGE, "CGE Reactor Vessel Certified Material Test Reports."

References August 2013 WCAP-17758-NP Rev.0