ML12103A277

Submittal of Analytical Evaluation in Accordance with ASME Code Section XI

ML12103A277
Person / Time
Site:	Braidwood
Issue date:	04/12/2012
From:	Enright D Exelon Generation Co, Exelon Nuclear
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
BW120036
Download: ML12103A277 (22)

Text

April 12, 2012 BW120036 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, DC 20555-0001 Braidwood Station, Unit 2 Facility Operating License No. NPF-77 NRC Docket No. STN 50-457

Subject:

Submittal of Analytical Evaluation in Accordance with ASME Code Section XI In accordance with the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, "Rules for Inservice Inspection of Nuclear Power Plant Components,"

2001 Edition through 2003 Addenda, IWC-3125, "Review by Authorities," paragraph (b), Braidwood Station is sUbmitting an analytical evaluation associated with the Unit 2 Residual Heat Removal (RHR) Mixing Tee examined during the Braidwood Unit 2 spring 2011 refueling outage (A2R15).

The mixing tee is the point where the RHR heat exchanger bypass line ties into the RHR heat exchanger discharge line. The potential for thermal fatigue exists at this location because the cooled flow from the heat exchanger mixes with the warmer flow from the bypass line.

During A2R15, Braidwood inspected the mixing tee at the discharge of the 2A RHR heat exchanger in accordance with the guidelines of Electric Power Research Institute (EPRI) Material Reliability Program (MRP)-192, "Materials Reliability Program Assessment of RHR Mixing Tee Thermal Fatigue in PWR Plants." The inspection found an indication at the toe (tee side) of weld 2RH-03-28. The size of the indication exceeds the ASME Section XI acceptance standards of IWB-3514, which was used in accordance with the provision of IWC-3514. As allowed by the ASME Section XI, a flaw evaluation in accordance with IWC-3640 was completed to determine the allowable flaw size and the time required for the flaw to grow to the maximum allowable size.

The evaluation has determined that the detected indication meets the ASME Section XI acceptance criteria. Based on the analysis of the differential temperature of interest, the time period for the flaw to grow to the maximum allowable size is more than sufficient to cover the remaining operating life of Braidwood Unit 2.

April 12, 2012 U. S. Nuclear Regulatory Commission Page 2 The nondestructive examination report concluded that no craze cracking was detected. The highly localized nature of the flaw and the absence of craze cracking are not indicative of fatigue due to thermal mixing effect. The indication can most likely be attributed to the geometrical imperfection discontinuity at the weld root that occurred during the original weld fabrication.

There are no regulatory commitments contained in this letter.

If you have any questions or require additional information, please contact Mr. Chris VanDenburgh, Regulatory Assurance Manager, at 815-417-2800.

Sincerely, Daniel J. Enrig,"'--. ...J Site Vice President Braidwood Station

Attachment:

Flaw Tolerance Evaluation of Braidwood Station Unit 2 RHR Mixing Tee Weld cc: NRC Project Manager- Braidwood Station Illinois Emergency Management Agency - Division of Nuclear Safety US NRC Regional Administrator, Region III US NRC Senior Resident Inspector (Braidwood Station)

ExelcnSM CC-AA-309-1001 Revision 6 Nuclear oeSlgn Analysis . M' ajar ReVlslon Cover Sh eet Design Analysis (Major Revision) I Last Page No.6 19 Analysis No.: 1 1100643.301 Revision: 2 0

Title:

3 Flaw Tolerance Evaluation of Braidwood Station Unit 2 RHR Mixing Tee Weld EC/ECR No.:

• 384283 Revision: 5 0 Station(s): 7 Braidwood Component(s): 14 Unit No.: 8 2 2RH03AA Discipline: 9 MEDC Descrip. Code/Keyword: 10 M04 Safety/QA Class: 11 SR System Code: 12 RH Structure: 13 N/A CONTROLLED DOCUMENT REFERENCES 15 Document No.: FromITo Document No.: FromITo Is this Design Analysis Safeguards Information? I. YesD No~ If yes, see SY-AA-101-106 Does this Design Analysis contain Unverified Assumptions? 17 YesD No~ If yes, ATI/AR#:

This Design Analysis SUPERCEDES: 18 N/A in its entirety.

Description of Revision (list changed pages when all pages of original analysis were not changed): 19 Original Issue-This design analysis documents the flaw tolerance evaluation that has been performed by Structural Integrity for the RHR mixing tee weld at the discharge of the 2A RHR heat exchanger on line 2RH03AA, weld

1. 2RH-03-28.

Preparer: 20 G.A. Miessi See attached calculation Print Name Si n Name Date Method of Review: 21 Detailed Review ~ Alternate Calculations (attached) D Testing D Reviewer: 22 S. Tang/D. Harris See attached calculation Print Name Sign Name Date Review Notes: 23 Independent review'R!' Peer review D (For External Analyses Only)

External Approver: 2' G.A. Miessi See attached calculation Exelon Reviewer: 25 Print Name GIIJYl}NNJ PrintPtMII Name eI UV,VIlJ111

/

Jign la11d!£ Siqn Name Date k.-.30-Z011 Date Independent ard Party Review Reqd? 26 Yes~ NoD fZ~

Independent fQZ (;.. VI11;cr~

Reviewer Guy Deboo ne.1'm..~c.otJ 04-('3 0 t 11 Print Name

,~ Sign Name oA OA.{ ;~atI11 L-.

Exelon Approver: 27

12. .J. ~l~ '7

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Print Name Sian Name Date

Structural Integrity Associates, Inc.

L 10 P G PR Fla alu tion of raid\ ood tation nit 2 RHR ing Tee Id p

Braidw d tation, nil2 Flaw leran evaluation of the raidwood nit 2 RHR i ing T e Id Docum nt fJ td c i ion ription Re i ion Pa o t - 19 Origin II ue

~Atr-tan Tang T 04/30/11 Oa id . Ham o H 04/30/1 t Page 1 of 19 F0306-01Rl

Structural Integrity Associates, Inc.

Table of Contents

1.0 INTRODUCTION

4 2.0 METHODOLOGY 4 3.0 ASSUMPTIONS 4 4.0 DESIGN INPUTS 5 4.1 Location and Characterization of Reported Indication 5 4.2 Dimensions and Loads 5 4.3 Temperature-Time Histories 5 5.0 CALCULATIONS 10 5.1 Evaluation of Code Allowable Flaw Size 10 5.2 Crack Growth Analysis 11 5.3 Consideration of SCC for Flaws in Austenitic Welds 11 6.0 RESULTS 14 6.1 Allowable Flaw Sizes 14 6.2 Fatigue Crack Growth 14

7.0 CONCLUSION

18

8.0 REFERENCES

19 File No.: 1100643.301 Page 2 of19 Revision: 0 F0306-01Rl

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List of Tables Table 4-1: Dimensions and Operating Conditions 6 Table 4-2: Stresses from Piping Analysis 7 Table 4-3: Number of Hours Spent at L1T above 144°F 7 Table 6-1: Allowable Part Through-Wall Flaw Size 15 Table 6-2: Time for Reported Flaw to Grow to Code Allowable at a RHR HX L1Tof162°F 16 List of Figures Figure 4-1. RHR Heat Exchanger 2A Inlet-Outlet Temperature Difference (A2RI5 Coo1down) 8 Figure 4-2. RHR Heat Exchanger IB Inlet-Outlet Temperature Difference (AIRI5 Startup) 9 Figure 5-1: IGSCC Resistance in Weld Metal may be predicted by the Combined Influence of Carbon Content and Percent Ferrite 13 Figure 6-1. Crack Growth Results 17 File No.: 1100643.301 Page 3 of 19 Revision: 0 F0306-01Rl

e StflJcturallntegrify Associates, Inc.

1.0 INTRODUCTION

This calculation package is aimed at performing mixing tee thermal fatigue crack growth evaluations of the piping tee connection weld in the residual heat removal (RHR) line at the Braidwood Station, Unit 2.

The guidelines ofMRP-l92 [1] and ASME Code,Section XI [2] are used to perform a crack growth evaluation to determine the time required at the limiting frequency for a flaw to grow to the maximum allowable flaw size.

2.0 METHODOLOGY The first step in evaluating the stress intensity factor is to determine the temperature in the pipe wall for a sinusoidal temperature variation of the coolant inside the pipe. The steady state temperature solution is obtained using a plate model with convection at one surface and insulation on the opposite surface. The steady state temperature is obtained in closed-form solution and used in conjunction with the classical thermo-elastic solution for a cylinder with an axisymmetric temperature distribution through the wall.

The resulting stresses are then combined with influence functions to obtain the stress intensity factors as a function of crack size.

Then, the calculated stress intensity factors are used in fatigue crack growth analyses based on the crack growth equations and material property data obtained from References 2 through 4.

3.0 ASSUMPTIONS The assumptions in this calculation package are as follows:

• The thermal problem is idealized as a slab. The thickness of the pipe is small relative to the pipe diameter (Rlt = 13.4). Thus, treating the pipe wall as a slab is reasonable for this evaluation. A comparison of figures on Pages 101 and 200 of Carslaw and Jaeger [12] shows that the temperatures near the surface at short times are very similar for a slab and solid cylinder subject to a step change at the surface. The differences between the slab and cylinder would be even smaller for a hollow cylinder.

• The stresses in a cylinder are obtained for an axisymmetric through-wall temperature distribution as obtained for a slab, using the assumptions oflinear elasticity.

• The convection heat transfer coefficient is fixed at a value determined to provide agreement on crack initiation times observed in service.

• The temperature fluctuation is assumed to occur at a certain frequency, and fracture mechanics calculations are performed to determine the size of a crack that will just grow to an ASME Code allowable crack size as a function of time for selected frequencies. The worst frequency is then identified as the one that produces the fastest average crack growth rate, da/dt, for a crack growing from the initial size to the allowable size.

File No.: 1100643.301 Page 4 of 19 Revision: 0 F0306-01RI

e Structural/nlsgr;'y Associates, Inc.

• The weld residual stresses are assumed equal to the yield stress at the ID of the pipe with a pure bending through-wall distribution per the recommendations of Reference 13.

4.0 DESIGN INPUTS 4.1 Location and Characterization of Reported Indication The indication was reported at Weld No. 2RH-03-28 on Line No. 2RH03AA-8" of the RHR "A" Train

[5]. The indication was characterized as a planar circumferential flaw with a depth of 0.14" and a length of 0.70" [5] and found unacceptable per ASME Code,Section XI, IWB -3500 acceptance criteria.

4.2 Dimensions and Loads The design input pertaining to piping section dimensions and their respective limiting loadings are obtained from Reference 5. The design inputs required in calculating the allowable flaw size and the subsequent crack growth analysis are provided in Tables 4-1 and 4-2. The stresses shown in Table 4-2 were calculated using the design equations from the original code of construction [6]; thus, the stress intensification factor and 0.75 factor included in those equation must be considered in calculating the nominal stresses. The stresses used to calculate the allowable flaw size were determined in Spreadsheet HBR WD RHR Allowable Flaw Size. xis. "

The heat transfer coefficient used in this evaluation is equal to the critical value of 6400 BtuIhr- ft2- OF obtained from Reference 7.

4.3 Temperature-Time Histories Plant monitoring data at the locations of the thermal mixing are provided in Reference 5 for the Braidwood Station, Unit 2. The temperature-time histories from Reference 5 provide the time-history of the temperature difference, ~ T, between the inlet and the outlet of the RHR heat exchanger during the Braidwood Station Unit 2 plant shutdown from the current refueling outage, as illustrated in Figure 4-1.

Similarly, the temperature difference, ~ T, between the inlet and the outlet of the RHR heat exchanger during the Braidwood Station Unit 1 plant startup is illustrated in Figure 4-2. This temperature data is assumed to be similar to the startup data for Unit 2. A summary of the data presented in Table 4-3 shows the maximum number of hours spent at ~T above 144°F, the temperature threshold established in MRP-192 [1] and the maximum ~ T that was reached during the event. This maximum ~ T is conservatively used for the entire crack growth period.

File No.: 1100643.301 Page 5 of 19 Revision: 0 F0306-01Rl

e Structural Integrity Associates, Inc.

Table 4-1: Dimensions and Operating Conditions Node 1310 Material SA-312 TP 304 Pipe OD (in) 8.625 Pipe Wall Thickness (in) 0.322 Maximum Operating Temperature (OF) 350 Maximum Operating Pressure (psi) 570 Limiting ~ T (OF) 162 File No.: 1100643.301 Page 6 of 19 Revision: 0 F0306-01Rl

Table 4-2: Stresses from Piping Analysis.

Pressure Moment load (ksi) (ksi)

Equation 8 3.574 0.973 Equation 9 3.574 2.2 Equation 10 0 11.471 Equation 11 3.574 12.444 Pipe Break 3.574 13.716 Faulted 3.574 3.307 Notes:

(1) The DW stress is increased by 10% and carried to the other equations per Reference 5.

(2) A stress intensification factor of 1.8 was applied to the weld location in the piping analysis (3) Given that the stresses were calculated using the equations from Reference 6, the 0.75 factor included in those equations must be considered in calculating the nominal stresses.

Table 4-3: Number of Hours Spent at AT above 144°F Maximum Inlet - Outlet Transient Date Time (hrs) Temperature Difference (OF)

A2R15 Shutdown Sprin~ 2011 0.17 162 A1R15 Startup Fall 2010 0.0 104 File No.: 1100643.301 Page 7 of 19 Revision: 0 F0306-01RI

2ARH HX~T *A2R15 Cooldown 04:00~5:00 180 - --

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File No.: 1100643.301 Page 8 of 19 Revision: 0 F0306*01RI

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5.0 CALCULATIONS The fracture mechanics analyses are performed to determine the ASME Code [2] allowable flaw sizes and evaluate the time required for a crack to grow to the maximum allowable value. Design inputs from Section 4.0 were used to perform the crack growth evaluation of the Braidwood Unit 2 RHR mixing tees and the adjacent welds. The output files associated with these evaluations have been archived as supporting files.

5.1 Evaluation of Code Allowable Flaw Size The piping section under consideration is an austenitic stainless steel (SA-312 TP 304) and hence an elastic-plastic fracture mechanics (EPFM) failure criterion is used in this evaluation. The EPFM analysis was performed to bound the mixing tee and the weld location which are conservatively assumed to be flux welds. The technical approach consists of determining the critical flaw size (circumferential extent and through wall depth) in the pipe that will cause the pipe to fracture by ductile crack extension.

The stress ratios were calculated as follows:

For combined loading, StressRatlO. =-Z O"r

( 0"m + 0"b + _e_

0" SFb J (la) and, for membrane stress, ZSF 0" Stress Ratio = m m (lb)

O"r where, Z =1.30[1 + 0.01O(NPS - 4)] for SA-312 TP-304 (conservatively assuming that the weld is SMAW or SAW flux weld) 0"m and O"b are the primary membrane and primary bending stresses, respectively.

O"e is the secondary bending stress.

0"r is the flow stress (43.3 ksi at the operating temperature of 350°F [4)).

SF;, is the safety factor for bending stress.

SFm is the safety factor for membrane stress.

The tables of ASME Code,Section XI, Appendix C [2] are used to determine the allowable flaw depth-to-thickness ratio for each service leveL Spreadsheet "B WRD RHR_Allowable Flaw Size.xls " is used for the allowable flaw size calculations.

File No.: 1100643.301 Page 10 of19 Revision: 0 F0306-01Rl

5.2 Crack Growth Analysis Fatigue crack growth relations for austenitic materials in LWR environment are obtained from Reference

3. The fatigue crack growth relation for austenitic stainless steel in PWR water is taken from Reference 3 with modifications to agree with Reference 2. As stated at the bottom of Table 2, Page 7 of Reference 3, the total fatigue crack growth rate is composed of an air and an environmental term:

dal total = dN dN dal air + dN dal env (2)

Each of the contributors is given as follows:

da I air = CairS(R)LlK3.3 dN (3) dNda Ienv

= Cenv [S/R\':1 1]0.5 T°.5 LlK1.65 R

TR is the rise time of the cycle (in seconds), which will be taken to be half the cycle period. LlK is Kma:c Kmin . The S term depends on the R-ratio, which is Kmin/Kmax.

I R~O S(R)= 1+1.8R R~0.79 (4)

{

- 43.35 + 57.97 R R > 0.79 The constants 1.8 and 0.79 in Equation 4 are in Reference 2, but the values are 1.8 and 0.8 in Reference

3. The Reference 2 values are used, because they exhibit the required behavior of a continuous S at the transition point (0.79).

The full range of K is considered (i.e. the negative stress intensity factor is included.) The constants Cair and Cenv for austenitic stainless steel are given in Reference 3 for crack growth rates in meters/cycle and stress intensity factors in MPa-m 1l2

• The maximum operating temperature of 350°F [5] is used in the evaluation. Also, it should be noted that the frequency effect on the crack growth per cycle (rise time, TR ) appears in Equation 3.

5.3 Consideration of SCC for Flaws in Austenitic Welds Sensitization is a term that describes the precipitation of chromium carbides at the grain boundaries of austenitic stainless steel and nickel-base alloys and the subsequent susceptibility of these alloys to intergranular corrosion in aqueous media following certain heat treatments such as welding or furnace File No.: 1100643.301 Page 11 of 19 Revision: 0 F0306-01Rl

post weld heat treatments (PWHTs). The precipitation of chromium-rich carbides (e.g., Cr23C6 in austenitic stainless steel and Cr7C3 in Alloy 600) along grain boundaries depletes the region adjacent to the boundaries of chromium and induces susceptibility to intergranular corrosion due to the creation of a small anodic area surrounded by a much larger cathodic area. The most common example of sensitization is the intergranular corrosion (lOA) or intergranular stress corrosion cracking (IOSCC) susceptibility of the HAZ near the weld.

The superior resistance of duplex stainless steels to sensitization and the high resistance of the weld material to lOA and IOSCC have been known for over 70 years [8]. Many studies have demonstrated that the resistance of two-phase, austenitic-ferritic stainless steel weld metal and castings is a strong function of microstructure. Specifically, in work performed on wrought duplex stainless steels, the resistance to sensitization was shown to be a function of chemistry (e.g., carbon and chromium), as well as the amount and distribution of ferrite [8, 9].

Figure 5-1 presents material failure / non-failure data on a graph of carbon versus ferrite for various types of specimens (e.g., full size pipes, constant extension rate, variable-load and constant load) exposed an environment of high purity water <<1 IlS/cm) with 6 +/- 2 ppm dissolved oxygen at a temperature 550°F (288°C) [9]. This plot represents the traditional approach of evaluating various casting heats. The results of this extensive test program revealed that for welded applications, a control on ferrite of 5% is recommended, and in furnace-sensitized applications, 12% ferrite will assure resistance to IOSCC.

These measurements should be made after the mill solution heat treatment.

The U. S. Nuclear Regulatory Commission (NRC) considers weld metal and castings to be resistant to IOSCC: "Low carbon weld metal, including types 308L, 316L, 309L and similar grades, with a maximum carbon content of 0.035% and a minimum of7.5% ferrite (or 7.5 FN) as deposited" are considered resistant to IOSCC [10, 11]. The NRC further states that "welds joining resistant material that meet the ASME Boiler and Pressure Vessel Code requirement of 5% ferrite (or 5 FN), but are below 7.5% ferrite (or 7.5 FN) may be sufficiently resistant, depending on carbon content and other factors.

These will be evaluated on an individual case basis." Since these data represent IOSCC at 550°F (288°C), results at lower temperatures demonstrate even better resistance to stress corrosion cracking in these aggressive oxygenated environments.

Thus, since the Braidwood Station, Unit 2 RHR mixing tee flaw is located in the weld, SCC crack propagation is not anticipated due to the high SCC resistance of the duplex microstructure of the weld metal.

File No.: 1100643.301 Page 12 of 19 Revision: 0 F0306-01Rl

0.10,...--------------------------------------..

CLOSED SYMBOL - IGSCC 0.0& UHl:S Rl:'RESENT LOWER BOUNDARY Of' STRESS CORROSION FAILURES OPEN SYMBOL - NO IGSCC HAI.F-FII.I.ED SYMIlOI. IGSCC - AT LEAST OftE SAMPlE CROSS-HATCHED SYMBOL - MINOR ENVIROftMENTAl INFLUENCE 0.08

<> 6:n"c 11150"Fln4h t> 10ll0"F/.

0.04 d AS*WE I.DEO. AW + L1'$. AW + SHT V STULITE HAROSVRFACED 0.03 t>

o 0 00 l> o

°0~--~-~--~-~ -~-~~-~--~-~:--~-~~-~--~-~~-~30 FERRITt -I Figure 5-1: IGSCC Resistance in Weld Metal may be predicted by the Combined Influence of Carbon Content and Percent Ferrite [9]

File No.: 1100643.301 Page 13 of 19 Revision: 0 F0306-01Rl

6.0 RESULTS 6.1 Allowable Flaw Sizes ASME Code allowable flaw sizes have been evaluated for semi-elliptical flaws with an aspect ratio al2e, of 0.2, where a is the crack depth and e is the half crack length. The results of the allowable flaw size calculations are presented in Table 6-1. The table presents the calculated allowable semi-elliptical flaw depth for various flaw lengths for the different service levels. It can be seen that the most limiting service level is Service Level D with the pipe break load. The corresponding allowable flaw size is 75%

of the wall thickness, i.e., 0.242 inches, for a flaw length up to 20% of the pipe circumference, i.e., 5.4 inches.

Also, the total piping stress to be used as the mean stress in the fatigue crack growth evaluation, in addition to the room temperature yield stress of 30 ksi, is shown in Table 6-1.

6.2 Fatigue Crack Growth The crack growth analysis is performed for a range of cyclic temperature frequencies and results are reported herein for the frequency that results in the minimum computed time to grow from the initial flaw size to the maximum allowable flaw depth. Calculations are performed with a fixed crack aspect ratio of 0.2. The results of the fatigue crack growth evaluations for the RHR mixing tees and adjacent welds are presented in Figure 6-1 and summarized in Table 6-2.

Figures 6-1 shows the predicted time for a semi-elliptical crack to grow to the calculated ASME Code allowable crack depth for all service levels. It can be observed from the output and Figure 6-1 that at a

~T = 162°F, it would take approximately 3692 hours0.0427 days <br />1.026 hours <br />0.0061 weeks <br />0.0014 months <br /> for the flaw to reach the Code allowable depth of 0.242 inch for the bounding thermal cycling frequency of 0.135 Hz.

File No.: 1100643.301 Page 14 of19 Revision: 0 F0306-01RI

Table 6-1: Allowable Part Through-Wall Flaw Size Allowable Flaw Size Calculation Circumferential Flaw Dimensjons

= Ro (in) 4.31 Ri (in) 3.99 tnom (in) 0.32 (in Z

3

)

16.8 NPS 8

Zfactor 1.352 p MX MY MZ cr Load (psi) (in-Ib) (in-Ib) (in-Ib) (ksi)

Pressure --- --- --- --- 3.574 OW --- --- --- --- 0.793 Thermal --- --- --- --- 6.373 Occasional --- --- --- --- 1.829 Pipe Break --- --- --- --- 10.160 Faulted --- --- --- --- 2.695 Total 11.776

• Stress RaYos 0

Type 304 SS @ 350 F Service cr m crb cr. SFm SF b S. Su crf Stress Ratio Applicability Level (ksi) (ksil (ksi) Iksil (ksi) (ksi) Comb Memb Check A 3.574 1.829 6.373 2.7 2.3 21.55 65.1 43.3 .30 YES B 3.574 1.829 6.373 2.4 2.0 21.55 65.1 43.3 0.268 0.27 YES 0 3.574 10.160 6.373 1.3 1.4 21.55 65.1 43.3 0.571 0.14 YES 0 3.574 2.695 6.373 1.3 1.4 21.55 65.1 43.3 0.338 0.14 YES 11.776

~ Allowable Flaw Depth-to-Thickness Ratio Ratio of Flaw Length to Pipe Circumference, l(nD 0 I 0.1 0.2 0.3 0.4 I 0.5 0.6 0.75 Service Flaw Length, 11 (degree)

Level 0 36 72 108 144 180 216 270 A 0.75 0.75 0.75 0.75 0.74 0.672 0.62 0.58 B 0.75 0.75 0.75 0.75 0.75 0.70 0.65 0.61 0 0.75 0.75 0.75 0.69 0.56 0.49 0.44 0.41 0 0.75 0.75 0.75 0.75 0.75 0.71 0.66 0.61

• Total Piping Stress (Pressure Stress + DW + Thermal + Seismic)

File No.: 1100643.301 Page 15 of 19 Revision: 0 F0306-01Rl

Table 6-2: Time for Reported Flaw to Grow to Code Allowable at a RHR HX AT of 162°F Crack Aspect Ratio (a/I) = 0.2, Limiting Frequency = 0.15 Hz Temp Time Amp a c da/dN (Hours) (OF) (in) (in) (in/cycle) 19 81 0.143 0.3576 3.21E-07 57 81 0.1487 0.3717 2.90E-07 95 81 0.1538 0.3845 2.63E-07 133 81 0.1584 0.396 2.38E-07 171 81 0.1626 0.4065 2.17E-07 209 81 0.1664 0.4161 1.98E-07 247 81 0.1699 0.4249 1.82E-07 285 81 0.1732 0.4329 1.67E-07 323 81 0.1761 0.4403 1.54E-07 361 81 0.1789 0.4472 1.43E-07 399 81 0.1814 0.4535 1.32E-07 437 81 0.1838 0.4594 1.23E-07 475 81 0.186 0.4649 1.15E-07 513 81 0.188 0.47 1.08E-07 551 81 0.1899 0.4748 1.01E-07 589 81 0.1917 0.4794 9.50E-08 3420 81 0.2409 0.6024 8.57E-09 3439 81 0.241 0.6026 8.48E-09 3458 81 0.2411 0.6028 8.39E-09 3477 81 0.2412 0.6029 8.30E-09 3496 81 0.2413 0.6031 8.21E-09 3572 81 0.2416 0.6039 7.88E-09 3591 81 0.2416 0.6041 7.80E-09 3610 81 0.2417 0.6042 7.72E-09 3667 81 0.2419 0.6048 7.50E-09 3686 81 0.242 0.6049 7.42E-09 3692 81 0.242 0.605 7.40E-09 File No.: 1100643.301 Page 16 of19 Revision: 0 F0306-01Rl

RHR Mixing Tee Crack Growth 0.3 0.25 0.2 g

...c-

.r:.

(lJ 0.15 Q

~

U u

III 0.1 0.05 0

0 500 1000 1500 2000 2500 3000 3500 4000 Time (Hours)

Figure 6-1. Crack Growth Results File No.: 1100643.301 Page 17 of 19 Revision: 0 F0306*01Rl

7.0 CONCLUSION

A thermal fatigue crack growth evaluation has been performed for the RHR mixing tee at the Braidwood Station Unit 2. The calculated time it would take for the semi-elliptical, 43% wall thickness (0.14 inch) deep flaw to grow to the ASME Code allowable flaw depth, at the maximum ilT of 162°F, has been determined to be at least 3692 hours0.0427 days <br />1.026 hours <br />0.0061 weeks <br />0.0014 months <br />. This allowable fatigue crack growth time far exceeds the number of hours the thermal mixing locations would be at ilT above 144°F in multiple cycles of operation.

The evaluation documented herein includes many conservative assumptions including the use of the maximum ilT of 162°F for the entire fatigue crack growth period which reduces the time it takes a postulated flaw to reach the ASME Code allowable size.

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8.0 REFERENCES

1. Materials Reliability Program: Assessment ofRHR Mixing Tee Thermal Fatigue in PWR Plants (MRP-192), EPRI, Palo Alto, CA: 2006. 1013305.

2. ASME Boiler and Pressure Vessel Code,Section XI, 2001 Edition with Addenda through 2003.

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4. ASME Boiler and Pressure Vessel Code,Section II, Part D, 2001 Edition with Addenda through 2003.

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8. H. Menendez, J. S. Chen and T. M. Devine, "The Influence of Microstructure on the Sensitization Behavior of Duplex Stainless Steel Welds," paper 562 presented at Corrosion 89, NACE, New Orleans, Louisiana, April 17-21, 1989.

9. N. R. Hughes, W. L. Clarke and D. E. Delwiche, "Intergranular Stress Corrosion Cracking Resistance of Austenitic Stainless Steel Castings," Stainless Steel Castings. ASTM STP 756, V. G.

Behal and A. S. Melilli, Eds. American Society for Testing and Materials, 1982, p. 26.

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January 25, 1988.

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Westinghouse and CE Plant Designs," EPRI, Palo Alto, CA, TP-I00l491.

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