RA-09-011, Submittal of Analytical Evaluation in Accordance with IWB-3134(b)

Submittal of Analytical Evaluation in Accordance with IWB-3134(b)

ML090690799
Person / Time
Site:	Oyster Creek
Issue date:	03/09/2009
From:	Cowan P Exelon Generation Co, Exelon Nuclear
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RA-09-011
Download: ML090690799 (18)

Text

10 CFR 50.55a RA-09-011 March 9, 2009 U. S. Nuclear Regulatory Commission Attn: Document Control Desk 11555 Rockville Pike Rockville, MD 20852 Oyster Creek Nuclear Generating Station Facility Operating License No. DPR-16 NRC Docket No. 50-219

Subject:

Submittal of Analytical Evaluation in Accordance with IWB-3134(b)

Reference:

Letter from P. B. Cowan (Exelon Generation Company, LLC) to U. S. Nuclear Regulatory Commission, "Submittal of Analytical Evaluation in Accordance with IWB-3134(b)," dated January 21,2009 In the referenced letter, Oyster Creek Nuclear Generating Station submitted in accordance with the American Society of Mechanical Engineers (ASME) Code,Section XI, 1995 Edition through 1996 Addenda, IWB-3134(b) ("Review by Authorities"), an analytical evaluation associated with the recirculation suction (reactor pressure vessel outlet) nozzle-to-safe end weld (N1A). This analytical evaluation is not considered a proprietary report by Structural Integrity Associates, Inc.

Attached is the analytical evaluation with all references to proprietary information deleted. No other changes have been made to the evaluation. We request that the evaluation submitted with the referenced letter be replaced with the attached document.

There are no new regulatory commitments contained in this letter.

U. S. Nuclear Regulatory Commission March 9, 2009 Page 2 of 2 If you have any questions or require additional information, please contact Tom Loomis (610-765-5510).

Respectfully, Pamela B. Cowan Director - Licensing & Regulatory Affairs Exelon Generation Company, LLC cc: S. J. Collins, Administrator, USNRC, Region I M. S. Ferdas, USNRC Senior Resident Inspector, OCNGS G. E. Miller, USNRC Senior Project Manager

ATTACHMENT Oyster Creek Nuclear Generating Station Analytical Evaluation

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Associates, Inc. File No.: 0801457.301 CALCULATION PACKAGE Project No.: 0801457 Quality Program: r8J Nuclear D Commercial PROJECT NAME:

Flaw Evaluation of Oyster Creek Nl Suction (RPV Outlet) Nozzle-to-Safe End Weld CONTRACT NO.:

1002562 ReI. 44 CLIENT: PLANT:

Exelon Nuclear Oyster Creek Generating Station CALCULATION TITLE:

Flaw Evaluation of Oyster Creek Nl Suction (RPV Outlet) Nozzle-to-Safe End Weld Project Manager Preparer(s) &

Document Affected Revision Description Approval Checker(s)

Revision Pages Signature & Date Signatures & Date 0 1 - 14 Initial Issue M. L. Herrera S. S. Tang A-I - A-I 11/9/08 11/9/08 M. L. Herrera 11/9/08 1 1 - 14 Incorporated Client M. L. Herrera S.S.Tang A-I - A-I Comments 11/10/08 11/10/08 M.L. Herrera 11110/08 2 1 - 14 Revised Operating Time M. L. Herrera S.S.Tang A-I - A-I to 4 years and Include 11111/08 11/11/08 Reference to TODI M.L. Herrera 11/11/08 3 1-14 Clarifications Added per M.L. Herrera S.S. Tang 11/12/08 A-I - A-I Client Comments and 11/12/08 M.L. Herrera 11/12/08 Laminar Indication Evaluation

~~~~

4 1-14 Revised Number of ~

"\.7-<=

A-I A-I Startup/Shutdown Cycles. Add SI File M.L. Herrera 12/18/08 S.S. Tang 12/18108 Numbers for References and Contract Number

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1.0 INTRODUCTION

A flaw evaluation is performed to disposition an indication associated with the Recirculation Suction (RPV Outlet) nozzle-to-safe end weld (NlA). The indication is circumferential, approximately 12.1 inches long with a through-wall depth of 0.20 inches taken from the clad base metal interface, [1]. The indication is located 0.6 inches upstream of the weld centerline (nozzle side) which would place it in the low alloy steel. The nozzle-to-safe end weld is a dissimilar metal weld joining the low alloy steel nozzle to Alloy 182 weld, Figure 1 [1]. This location was stress mitigated using Mechanical Stress Improvement (MSIP) in 1994 [1].

EPRI performed an independent evaluation of the examination results, which is documented in Reference 2. EPRI concluded that this indication was present during examinations that date back to 1991. The report also concludes that the indication is embedded at the interface between the stainless steel clad and the ferritic base metal. EPRI also states that the indication appears to be related to the fabrication process or localized repairs. Based on evidence available, EPRI states this is not a service induced flaw.

Even though the indication is considered fabrication related, this analysis conservatively assumes that the indication is an active flaw. The flaw evaluation was performed using Appendix H of Section XI of the ASME Boiler & Pressure Vessel Code (B&PV) [3].

In addition, an evaluation was performed assuming the indication to be oriented such that it would be considered and analyzed as a laminar flaw.

2.0 TECHNICAL APPROACH The evaluation consists of:

1. Allowable flaw size evaluation based on the guidelines of ASME B&PV Code,Section XI, IWB 3600 and Appendix H [3]. The allowable flaw size was determined using the tabular solutions as allowed by Article H-6300.

2. Evaluation of the stress intensity factor, stress corrosion and fatigue crack growth analyses to compare end of evaluation period flaw size to the allowable flaw size. The evaluation period is 2 operating cycles for a total of 4 years.

3. Evaluation of indication as a laminar indication.

3.0 DESIGN INPUTS The inside diameter of the recirculation suction nozzle is 24.312 inches [1]. The nominal thickness of the nozzle is 1.375 inches [1]. The clad thickness is 7/32 inches [1].

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The nozzle material is identified as SA336 Modified by Code Case 1236-1 [1]. This material is equivalent to SA 508 Class 2 in composition as discussed in Code Case 1236-1. The weld material is Alloy 182 [1].

The loading on the nozzle is shown in Table 1 [1].

The pressure and temperature conditions used in this analysis were [1]:

1. Design limiting temperature = 550°F

2. Design limiting pressure 1200 psi.

The yield and tensile strength ofSA508 Class 2 is 57.55 ksi and 80 ksi at 550 of, respectively [4]. The allowable stress intensity, Sm is 26.7 ksi at 550 of [4].

4.0 ASSUMPTIONS The following assumptions are used in the flaw evaluation:

1. The residual stress is assumed to have a through-wail cosine distribution based on the test data presented in Reference 5. It is also assumed that the through-wall residual stress distribution in the low alloy steel at the flaw location is similar in shape to that for stainless steel [5].

2. The residual stress at the inside surface is at the material yield strength of low alloy steeL

3. Alloy 182 is assumed to have the same material properties as Alloy 600. Alloy 182 is the corresponding SMAW wire for Alloy 600 and the composition elosely matches. Use of Alloy 600 properties for the Alloy 182 material is consistent with general industry practice.

4. The load from OBE is 0.8 times the load from SSE.

5. The indication is in the low alloy materiaL

6. The flaw is an active stress corrosion flaw.

7. No credit is taken for the MSIP treatment.

Note that since the weld has been treated with MSIP, using a residual stress for the as-welded condition with a maximum stress equivalent to the low alloy steel yield strength is conservative. It is likely that the MSIP process significantly improved the residual stress with regards to intergranular stress corrosion cracking. Using the cosine shape for the residual stress in the low alloy steel does not significantly impact the results since the driving force for crack extension is the stress distribution from the inside surface to the crack tip. The distribution shape between the crack tip and the outer surface does not impact the results. Even if a linear (bending) distribution was assumed for the residual stress distribution, the stress between the inside surface and crack tip does not differ enough to have a significant impact on the results. Again note that the maximum stress is being assumed to be the yield strength of the low alloy steel even though the weld was subjected to MSIP.

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5.0 CALCULATIONS 5.1 Allowable Flaw Size The resulting forces and moments due to Dead Weight (DW), SSE and thermal are obtained from Reference 1 and shown in Table 2. The resultant forces and moments due to OBE are calculated assuming the OBE loads are 80% of the SSE loads.

The nozzle area and moment of inertia is calculated as:

A ~ trR' = 3.1416' ( (24.312 + 2 '1.~75)' - 24.312') llO.96in' (I)

S=~(d4-d4)= Jr ((24.312+2*1.375)4 -24.312 4 )= 678.29in 4 (2) 32d I 32*(24.312+2*1.375)

The primary stresses for normal operating conditions are:

<J m= PR/(2t)+F/A 1200*13.53/(2*1.375)+(2860+7115)1110.96 = 5904+90 =5994 psi (3)

<Jb = M/S (25217+49678)*12/678.29 1323 psi (4)

<Je F/A+M/S=25089I1l0.96+138777*12/678.29 226+2455=2681 psi (5)

For faulted conditions, <Jm 6.01ksi, <Jb = 1.55 ksi and <Je = 2.68 ksi.

For screening criteria as stated in H-4221.1 [3], SC is calculated using the following equations:

sc= K~ (6)

S; K; =(IO~OKi )0,5 (7)

E J/ c S; = ~J + Pc for (<Jb+<Je)::::<Jm (8)

(Jb Kl=Klm+Klb (9)

K 1m = <J m-V(na)F m (10)

K1b ==<Jb -V(na)Fb (11)

B1 0.855 ( B))

[ (

F m= 1.1 + x 0.15241 + 16.772 .: ) -14.944 .: (12)

F b=1.1+x -0.09967+5.0057( xJrB)' 0.565 -2.8329 ( .: B)J (13)

[

x aft (14)

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a = crack depth (15) t wall thickness (16) 91n ratio of crack length to pipe inner circumference (17)

()h 2()y ['"'

LSIn a. LlJ fJ -[SInU for (9+f3):'Sn (18) fJ=~[1C-aB-1C. Pm ] (19) 2 t 2.4Sm

()h 2()" [(.2 aJ

[sinfJ ] for (9+f3>>n (20) t 2.4S m fJ = 1C -'------'-- (21) 2- a t

Using a lIe of 350 in-lb/in2 for ferritic steel base metal (Table H-4211.1 from [3]), Young's Modulus 25.45x10 6 psi, crack size a 0.2", and 1 = 12.1", and the above equations, SC is calculated to be 1.55.

As shown in Figure H-4220-l, for 0.2:'SSC:'S1.8, the failure mode is EPFM.

For the EPFM failure mode, the stress ratio is calculated as for test, normal and upset conditions (22) for emergency and faulted (23)

For conservatism, Z is calculated as material category 2 from Table H-6310-1 [3]. The stress ratio for normal operating conditions is:

SR = 1.82(5.994 ksi +1.323 ksi+2.681 ksi/2.77)/26.7 = 0.56 For II(nD) 12.1I(n*24.3l2) 0.1584, the allowable flaw size for normal operating conditions, Table H-5310-1 is 75% of the wall thickness (I flaw length = 12.1 in).

For faulted conditions, SFb is taken as 1.39, the stress ratio is SR = 1.82(6.01 ksi+ 1.55 ksi+ 2.68 ksi/1.39)/26.7 0.65 For lie nD) 12.1/(n*24.312) = 0.1584, the allowable size for faulted conditions from Table H-531 0-2 is 75% of the wall thickness.

Based on these the allowable flaw size is 75% of the wall thickness for all cases.

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5.2 Stress Intensity Factor A linear elastic fracture mechanics analysis is performed for the observed indication to obtain the crack growth due to stress corrosion crack growth and fatigue crack growth.

The fracture mechanics model is a full 360° circumferential crack in a cylinder.

In additional to the applied stresses calculated in Section 5.1, the stress intensity factor due to residual stress is also obtained. The residual stress is a cosine through-wall distribution with the residual stress at the inside surface equal to the yield strength of the low alloy steel (57.55 ksi). The residual stress is curve-fit to a 3rd order polynomial for the stress intensity factor calculation, Figure 2.

Also, the ()b and ()e are combined and treated as a bending load case since the axial stress in ()e is very small.

The stress intensity factor is calculated using pc-CRACK [6].

The stress intensity factors for membrane ()m, bending and residual stress are shown in Figure 3.

5.3 Stress Corrosion Crack Growth Analysis A stress corrosion crack growth (SCCG) analysis is performed to determine the crack growth for 2 operating cycles (4 years).

Since the indication is 0.6 inches from the weld center line, it is assumed that the indication is in the low alloy base metal. Therefore, BWRVIP-60A [7] provides the stress corrosion crack growth in low alloy steel in the BWR environment. The stress corrosion crack growth law is da/dr 6.82xlO- I2 K 4 (in/hr) for K > 50 ksiv'in (24) da/dr 2.83xl0-6 in/hr for K::: 50 ksiv'in (25)

From Figure 3, for an initial crack size of 0.2 inch, the total K is less than 50 ksiv'in. Recall that the residual stress being used is considered very conservative since this location has been treated with MSIP.

Therefore, Equation (25) can be used for SCCG. the total SCCG for 4 years is da 2.83x 10-6 in/hr *4

• 365*24 0.0992 in.

The final flaw size is 0.2" + 0.0992" 0.2992", corresponding to alt = 0.2992/1.375 0.2176, less than the allowable flaw size.

Since the crack is in the vicinity of the Alloy 182 weld metal, the potential for growth into the Alloy 182 cannot be ruled out and therefore the stress corrosion crack growth rate in the Inconel 182 is also evaluated. BWRVIP-59 [8] provides stress corrosion crack growth for high nickel bases austenitic File No.: 0801457.301 Page 6 of 14 Revision: 4 F0306-01

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alloys for different reactor pressure vessel water chemistry conditions. The see growth law for normal water chemistry is:

da/dT 1.6xlO-8K 2.s (in/hr) for K:::: 25 ksi-Vin (26) da/dT =5.0xI0-S in/hr for K > 25 ksi-Vin (27)

From Figure 3, it is shown that when the crack size is larger than 0.6 inches and in the Alloy 182, the total K is less than 25 ksi-Vin. Therefore, for conservatism, the initial crack size is assumed to be 0.6 inch and in the Alloy 182 weld metal allowing the use of Equation (4). The crack depth after 4 years of operation is 0.736 inches for this conservatively assumed initial flaw. The resulting aft 0.54 which is less than the allowable of75%.

5.4 Fatigue Crack Growth Fatigue crack growth for 2 operating cycles is not significant due to a limited number of cycles that result in significant stress. For the purpose ofthis evaluation, 5 startup/shutdown cycles per year will be assumed (20 cycles total over 4 years) which conservatively bounds actual plant experience. Even with a L1K of 50 ksi-Vin, the total fatigue crack growth in the low alloy steel exposed to the water environment is estimated to be 4.15xlO-3 inches using Figure A~4300-2 of Reference 3 and an R ratio:::; 0.25. This is conservative since no credit is taken for the beneficial compressive residual stress caused by MSIP.

Thus, fatigue crack growth, even with the conservative assumption on the number of significant cycles, is small.

5.5 Laminar Flaw Evaluation In Reference 2, it was mentioned that there is a presence of a laminar indication that directly correlates with the planar indication. No other detailed information was provided regarding this potential laminar indication.

Per IWA-3360 of Reference 3, planar indications oriented within 10 degrees of a plane parallel to the surface of the component shall be considered laminar flaw. For the purpose of this calculation, the entire planar flaw will be assumed as laminar.

Per IWB-351 0.2 of Reference 3, the allowable laminar flaw shall not exceed the limits specified in Table IWB-35 10-2. For component with a thickness ofless than 2 inches, the allowable area is 7.5 inches.

The area of the postulated laminar indication is 0.2 x 12.1 = 2.42 in 2. Even with the conservative assumption that the indication is oriented purely as a laminar indication the area of the indication is well below the limit specified in Table IWB-35 10-2.

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6.0 CONCLUSION

S A flaw evaluation has been performed conservatively assuming that the fabrication related flaw at nozzle NIA is an active stress corrosion flaw for an operating period of 4 years. Fatigue crack growth was also evaluated and was determined to be smalL Results of this evaluation demonstrate that growth of the observed flaw, whether assumed in the nozzle or Alloy 182, will remain less than the allowable flaw size of75% of the pipe wall. Therefore, the required safety factors will be maintained during operation with this flaw over the next 2 operating cycles.

In addition, the flaw was assumed to be oriented such that it would be considered and analyzed as a laminar flaw. Results of this evaluation showed that even with the conservative assumption that the indication is oriented purely as a laminar indication, the area of the indication is well below the limit specified in Table IWB-351O-2 and therefore acceptable.

7.0 REFERENCES

1. Exelon TODI 00842492-02, November 10,2008, SI File 0801457.210.

2. EPRI Report IR-2008-340, "Evaluation of Dissimilar Metal Weld Examinations Performed at Oyster Creek during Refueling Outage 22 (R22) November 2008.

3. ASME, Boiler and Pressure Vessel Code,Section XI, 1995 Edition with 1996 Addenda.

4. ASME, Boiler and Pressure Vessel Code,Section II, Part D, 1995 Edition with 1996 Addenda.

5. NUREG-0313, Rev. 2, 'Technical Report on Material Selection and Processing Guidelines for BWR Coolant Pressure Boundary Piping.'

6. pc-CRACK, Version 3.1-98348, December 1998.

7. BWRVIP-60A: BWR Vessel and Internals Project Evaluation of Stress Corrosion Crack Growth in Low Alloy Steel Vessel Materials in the BWR Environment.

8. BWRVIP-59A, BWR Vessel and Internals Project, Evaluation of Crack Growth in BWR Nickel Base Austenitic Alloy in RPV Internals,' EPRI Report TR-108710, Palo Alto, CA 1998.

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Table 1: Recirculation Suction Nozzle Load

~u NUCLEAR CAl.CUl.ATION SHEET iRef. Ep*0061 Calculation No.

A c~ I:102*2.23*E540-0J4 Calculated nozzle [oreM and moments are listed In Table C*S Absen! loads and IOIlO comblnatiuns, such as OBE D+/-SSE, are not limiting. 'TIle maximum resultants In Table COS life used In the Nozzle Evaluation in Seetion C*7 4A~

Tuble (;*8 Forces lll1d Moments on the Nozzles Mz 1l.eSllltlillt (ft-lll) (fNb)

Nates:

I. in the Au!oPIPEmodel the positive X direction north, the positive Y direction is vertical, and the posi!!ve Z direction eas!

2. Maximum vailles are hold~

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Table 2: Loads due to Thermal and SSE Resultant Foree (lb) Resultant Moment (ft-Ib)

DW 2860 25217 SSE 8894 62098 Thermal 25089 138777 aBE 7115 49678 Note: Thermal loads were ealculated usmg the dIfference between the load case D and load case D+T3 resultants.

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OYSTER CREEK REACTOR vessel REciRCUlAT10N SYSTEM SAFE END DETAILS FIGURE 1 Figure 1. Oyster Creek Reactor Vessel Recirculation System Safe End Details File No.: 0801457.301 Page 11 of 14 Revision: 4 F0306*01

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100 80 60 40

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40

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-60 o 0.2 0.4 0.8 1.2 Figure 3: Stress Intensity Factor File No.: 0801457.301 Page 13 of 14 Revision: 4 F0306-01

StrJiJctttrallnlf1.0rllV Associates, Inc.

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Figure 4 Crack Growth Assuming in Inconel File No.: 0801457.301 Page 140f14 Revision: 4 170306-01

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APPENDIX A COMPUTER FILES File No.: 0801457.301 Page A-I of A- I Revision: 4 F0306*0JRO