ML13308B221

Monticello - Enclosure 5 - Structural Integrity Associates, Inc. Evaluation File No. 1300180.302 - Evaluation of the Monticello Shroud H10 Weld

ML13308B221
Person / Time
Site:	Monticello
Issue date:	04/10/2013
From:	Wong W Structural Integrity Associates
To:	Office of Nuclear Reactor Regulation
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ML13308B206	List: L-MT-13-102, Cycle 26 Inservice Inspection and In-Vessel Visual Inspection Summary Reports ML13308B217 ML13308B218 ML13308B219 ML13308B220 ML13308B221
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L-MT-13-102 1300180.302
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ENCLOSURE 5 Monticello Nuclear Generating Plant Structural Integrity Associates, Inc. Evaluation File No.: 1300180.302 Evaluation of the Monticello Shroud H10 Weld (Non-Proprietary)

(16 pages follow) 7 Strucural Integrity Associates, Inc. File No.: 1300180.302 Project No.: 1300180 CALCULATION PACKAGE Quality Program: Z Nuclear E] Commercial PROJECT NAME: Evaluation of the Monticello Shroud Support Plate Uplift Load with Indications in the H8 and H9 Welds CONTRACT NO.: 00001005 CLIENT: PLANT: XCEL Energy Monticello Nuclear Generating Plant CALCULATION TITLE: Evaluation of the Monticello Shroud H 10 Weld Document Affected Project Manager Preparer(s)

& Checker(s)

Revision Description Approval Signatures

& Date Revision Pages Signature

& Date 0 1 -9 Initial Issue Preparer: A-i -A-7 Wilson Wong 04/02/13 Computer Files Aparna Alleshwaram Checkers: 04/02/13 David Dijamco 04/02/13 Jim Wu 04/02/13 11 -9 Changed Section XI Preparer: A-i -A-7 Code Year- Wilson Wong 04/04/13 Computer Files Slight Safety Factor Aparna Alleshwaram Checker: Modification 04/04/13 David Dijamco 04/04/13 Jim Wu 04/04/13 21 -9 Revised Moment Arm Preparer: A-I -A-7 Length VJ *, -" Computer Files W s o Wilson Wong Aparna Alleshwaram 04/10/13 04/10/13 Checker: David Dijamco 04/10/13 Jim Wu 04/10/13 Page 1 of 9 F0306-OIRO Cjjs"nchwma lnlemil Associates WOc Table of Contents 1.0 O B JEC TIV E ........................................................................................................

3 2.0 D ESIG N IN PU TS .....................................................................................................

3 3.0 M ETH O D O LO G Y ...................................................................................................

4 3.1 Shroud Support Leg Safety Factor Evaluation

............................................

4 4.0 C O N C LU SIO N S ......................................................................................................

5 5.0 R EFER EN C E S .........................................................................................................

6 Appendix A ANALYSIS COMPUTER FILES ...........................................................................

A-1 List of Tables Table 1: Shroud Support Leg Geometry ..........................................................................................

7 Table 2: Shroud Weld H7 Resultant Loads and Bending Moments ...............................................

7 Table 3: Shroud Geometry and Support Leg Load Calculations at Weld H 10 ..............................

7 Table 4: Safety Factors for Monticello Shroud Support Leg Evaluation (31.2% of all leg s cracked) ..........................................................................................................................

8 List of Figures Figure 1: Schematic of CBIN/CB&I Vessel Shroud Support Structure Attachment C onfi guration .........................................................................................................................

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$ShNOWN raiI Associates, WO 1.0 OBJECTIVE The objective of this calculation is to evaluate the integrity of the Monticello reactor shroud support legs, without considering support from the shroud support plate (H8 and H9 are conservatively assumed to be fully cracked).

The weld of interest for this analysis, as designated in BWRVIP-15

[1], is the weld attaching the support leg to the shroud support cylinder (weld H 10).The shroud support plate was not considered to support any load in this analysis because indications were previously found at the shroud support plate H8 (shroud support plate-to-shroud) weld and H9 (shroud support plate-to-vessel) weld during the Spring 2011 inspections.

Also, indications had been observed in 11 of the 14 shroud support legs during the Spring 2009 inspections.

Figure 1 shows a schematic of the Monticello shroud leg configuration

[2, Figure 5-59]. The geometry of the support legs is provided in Table 1 [3].One case was evaluated where 31.2% of each leg width (in circumferential direction) was assumed to be flawed through-wall.

This is a very conservative assumption given that the observed indications only appear to be limited to a fillet weld applied to the full penetration weld to reduce the stress concentration between the H 10 weld and the bottom of the shroud support cylinder.Because no credit is taken for either the H8 or H9 welds, the observed indications at these locations do not impact these results. Taking no credit for these welds is essentially equal to assuming through-wall flaws in the H8 and H9 welds.2.0 DESIGN INPUTS Since this evaluation does not consider the shroud support plate, the design input is focused on the shroud support legs only. The shroud support design implemented at Monticello is the Chicago Bridge & Iron Nuclear (CBIN) flat plate design with support legs that connect to the reactor pressure vessel (RPV) bottom head. A stub is welded to an attachment pad on the inside of the RPV lower head, and then the leg is welded to the top of the stub and the bottom face of the shroud support cylinder (refer to Figure 2.9.2.4 of Reference 1). There are fourteen support legs, each with a thickness of 1.75 inches [3], located 200 or 30' apart (see Table 1). The legs are fabricated from Alloy 600 material (Sin = 23.3 ksi) with multiple Alloy 182 welds joining the various leg sections to each other, to the low alloy steel RPV, and to the Alloy 600 shroud support cylinder.All of the relevant load [4] and shroud geometry data [3] for the Monticello support legs are summarized in Table 2 for upset and faulted conditions.

The resultant shear and moment loads on weld H7 come from the SRSS of SSE and AC loads. Per Reference 10, the AC loads must be doubled. This modification is reflected in the loads shown in Table 2. Primary stresses calculated for use in the structural evaluation of the support legs are included in Table 3. The methodology used to compute these stresses is described in detail below.File No.: 1300180.302 Page 3 of 9 Revision:

2 F0306-OIRO jstc&NaI Ing" AssocIat , lIc 3.0 METHODOLOGY 3.1 Shroud Support Leg Safety Factor Evaluation Access to the shroud support legs is severely limited because of their location in the RPV bottom head region beneath the shroud support structure.

Xcel Energy has performed a visual inspection of the legs via access through the jet pump assemblies.

Provision for inspecting the support legs in lieu of a detailed inspection of welds H8 and H9 was also addressed in BWRVIP-38

[5]. Flaw tolerance evaluations are provided in Section A.2.7 of BWRVIP-38 that can be used to structurally evaluate the support legs. The methodology conservatively assumes that all of the applied loading is structurally taken by the legs. Therefore, welds H8 and H9 are not structurally required, other than to maintain the support structure configuration (i.e., jet pump support, shroud repair, etc.). As a result, analyses similar to those shown in Section A.2.7 of BWRVIP-38 were performed for Monticello to confirm the structural adequacy of the support legs, for upset and faulted conditions, conservatively including assumptions regarding the support leg flaws. As per the recommended approach documented in Section A.2.7 of BWRVIP-38

[5], structural acceptability was demonstrated by maintaining minimum ASME Code,Section XI safety factors [7].The shroud support legs are located sufficiently below the core such that they do not receive significant amounts of radiation.

Therefore, linear elastic fracture mechanics (LEFM)techniques are not necessary, and limit load techniques are valid due to material ductility.

Since the shroud support legs are essentially "a cylindrical shell with holes," a limit load solution applicable to cylinders may be used. Therefore, the ANSC computer program [6] was selected for use. The ANSC program was used because of its ability to analyze cracks in cylindrical structures without taking benefit of the cracks taking compression.

This was important for this evaluation since the spaces between legs, which are effectively treated as flaws in this analysis, have no capability to take compression.

Consistent with limit load techniques, two stresses were computed for use in the analysis:

(1)the primary membrane stress, Pmo, and (2) the primary bending stress, Pb. Consistent with BWRVIP-38 methodology, calculation of these stresses was based on the stresses for the shroud H7 weld, as provided in Reference

4. The determination of each of these stresses is detailed below: Pro: Pm-legs = Pm-shroud (t/tlegs)where: Pm-legs = primary membrane stress in the legs (psi).Pno-shroud

= primary membrane stress in the shroud at weld H7 (psi), 4Fa/n(Do-Di) 2 Fa is the axial resultant force.t = shroud thickness at weld H7 (inches).tiegs -support legs minimum thickness (inches).Pb: Pb-legs = (Pb-shroud

+ Ms/Z) (t/tlegs)where: Pbiegs = primary bending stress in the legs (psi).Pb-shroud

= primary bending stress in the shroud at weld H7 (psi) M/Z where File No.: 1300180.302 Page 4 of 9 Revision:

2 F0306-01 RO VjjsiniiuAi bWegil Associates, lnc M is the bending moment in (in-kips).

NI= additional moment for legs due to the shear load applied at weld H7 (inch-lbs).

= S, (27tRt) H Ss= shear stress at weld H7 (psi)H = "lever arm" between shroud weld H7 and H10 (inches).Z = section modulus for unflawed shroud cross section (inches 3).= c 2t= 7tR~t R = shroud mean radius (inches).t = shroud thickness at weld H7 (inches).tlegs support legs minimum thickness (inches).After the simplifications, Pb: Pb-legs = (Pb-shroud

+ 2S, H / R) (t/tlegs)The calculated values for each of the above stresses are included in Table 3.Table I summarized the computed azimuths for each support leg. This information, combined with the appropriate stress information in Table 2, was input to ANSC to determine whether the assumed leg configuration maintains minimum required ASME Code,Section XI safety factors[7] (2.4 for upset conditions, 1.4 for faulted conditions).

Evaluations were performed for both the upset and faulted conditions, and the resulting ANSC output is included in Appendix A. It is noted from the output that through-wall flaws were placed in the spaces between the legs to represent both the assumed through wall flaws (31.2% of each leg width) and the fact that there is actually no material present in between legs.From the ANSC results, the safety factor was calculated using the following relationship:

Safety Factor, SF -Pb + Pm Pb +P, where: Pb' = minimum failure bending stress from ANSC output (ksi).The resulting safety factors are shown in Table 4.

4.0 CONCLUSION

S Up to 31.2% of each support leg H 10 weld may be flawed through-wall and still meet the required safety factors of BWRVIP-38.

The resulting safety factors are compared to the required safety factors in Table 4. These results are considered to be extremely conservative because no structural support from welds H8 and H9 was considered.

Therefore, if some structural support from welds H8 and H9 is considered, it is expected that significantly larger margins would be obtained.File No.: 1300180.302 Page 5 of 9 Revision:

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5.0 REFERENCES

1. EPRI Report No. TR-106368, BWR Vessel and Internals Project, "Configurations of Safety-Related BWR Reactor Internals (BWRVIP-15)," EPRI PROPRIETARY, March 1996, SI File No. BWRVIP-01-215P.

2. EPRI Report No. NP-7139-D, "Reactor Pressure Vessel Attachment Welds: Degradation Assessment," May 1991.3. Structural Integrity Associates Calculation No. EPRI-98Q-314, Revision 1, "Shroud Support Legs Structural Evaluation," 6/16/97.4. Design Information Transmittal (DIT), DIT 13638-05, EC 13638, Extended Power Uprate (EPU), GE Hitachi Report No. 0000-0122-2954, RI, Structural Integrity Associates, SI File No. 1001207.201.

5. EPRI Report No. TR-108823, BWR Vessel and Internals Project, "BWR Shroud Support Inspection and Flaw Evaluation Guidelines (BWRVIP-38)," EPRI PROPRIETARY, SI File No. BWRVIP-01-238P.

6. ANSC, "Arbitrary Net Section Collapse for Thin Cylinder," Version 2.0, Structural Integrity Associates, SI File No. QA-1900.7. ASME Boiler and Pressure Vessel Code,Section XI, Rules for Inservice Inspection of Nuclear Power Plant Components, 2007 Edition with Addenda through 2008.8. Email from Verne Thompson (XCEL Energy) to Jim Wu (SI), "RIPD Load verification," 11/22/2010, SI File No. 1001207.202.

9. General Electric Drawing, "Shroud Support for 17'2" ID x 63'2" INS Heads," No.NX8290-971, SI File 1300180.205.

10. Xcel Energy Design Information Transmittal (DIT), "2013 Shroud Support Plate Uplift Analysis," EC 21839, Date 3-29-2013, DIT No. 21839-1, SI File 1300180.208.

11. Email from Wynter S. McGruder (XCEL Energy) to Jim Wu (SI), "Minor change for H8-H9 Eval and big change for the H10 eval," 04/10/13, SI File No. 1300180.210.

File No.: 1300180.302 Page 6 of 9 Revision:

2 F0306-OIRO TableW : rdSptly AssociateG, ft?Table 1: Shroud Support Leg Geometry Leg Leg Leg Min. Leg Starting Ending Center Leg Thickness.

Azimuth Azimuth Leg Azimuth Width. W lit (degrees) (degrees)No. (degrees)

Onehes) inche [see Notel Isee Natoe 1 10 7.0 1.75 7.52 12.48 2 30 7.0 1.75 27,52 32.48 3 60 7.0 1.75 57.52 62.48 4 90 7.0 1.75 87.52 92.48 5 120 7.0 1.75 117.52 122.48 6 151 7.0 1-75 147.52 152.48 7 170 7.0 1.75 167.52 172.48 8 190 7.0 1.75 187.52 192.48 9 210 7.0 1.75 2D7.52 212.48 10 240 7.0 1.75 237.52 242.48 11 270 7.0 1.75 267.52 272.48 12 300 7.0 1.76 297.52 302.48 13 330 7.0 1,75 327.52 332,48 14 350 7.0 1.75 347.52 352.48 Note: The leg azimuths are estimated as + tan-'[(W/(2R)I from the leg centerline Table 2: Shroud Weld H7 Resultant Loads and Bending Moments Weld Resultant Axial Force (Fa) Resultant Bending Moment (M) Resultant Shear Force (F)(kip) (kip-in) (kip)H7 Upset 463.33 41733.89 258.63 H7 Faulted 977.80 216130.5 2171.76 Note: RIPD Loads in Reference 4 is included in the above resultant forces and moment per Reference 8 Table 3: Shroud Geometry and Support Leg Load Calculations at Weld H10 Condition Shroud Shroud Leg Leg Loads and Stresses OD Thickness, (=Shroud)

Height, Pm at P., for Shear Pb at Pb Due Total Pb (inches) t (inches) Mean Weld Weld Legs (psi) Force Fs Weld to (psi)Radius, R HIO -H7, H7 (psi) [See Note at Weld H7 Shear [See Note 3](inches) H(inches)

[See 1] H7, (psi) (psi)[=(OD-t)/2]

[See Note Note 41 (kips) [See [See 6] Note 5] Note 2]Upset 163.5 1.75 80.9 18.0 521 521 258.63 1173 129.4 1302.4 Faulted 163.5 1.75 80.9 18.0 1100 1100 2171.76 6073 1086.4 7159.4 Notes: 1. The Pm for the legs is the Pm at weld H7 scaled by t/tiegs.2. The moment due to the shear is conservatively calculated as FH. Thus, the Pb due to shear is FsH/(iR 2 t).3. The Total Pb is the sum of the Pb due to shear and the Pb at weld H7, scaled by t/tlegs 4. Pm=4Fan(Do-Di) 2 5. Pb=MDo/21 6. Leg Height H (moment arm) is obtained from Reference

[9] and [ 1].File No.: 1300180.302 Revision:

2 Page 7 of 9 F0306-01R0 a b lC Ie R 4 : S a f t y A W scito s Wtic Table 4: Safety Factors for Monticello Shroud Support Leg Evaluation (31.2% of all legs cracked)Pb' (1) Computed Allowable Condition (ksi) Safety Factor, SF Safety Factor Upset 10.661 6.13 2.40 Faulted 10.473 1.40 1.40* /t % ,1 f' , , * * ---]" I INote: (I)Keter to the AN SU output containea in Appendix A.File No.: 1300180.302 Revision:

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" l M l Msoat f, WIe"qE Ii8 .3/16" SHROUD BAFFLE PLATE TIE-IN OVERLAY ER 308L OR ER 309L 114" ENiCrFe-3 (182) OR ERNICr-3 (82)ENiCrFe-3 (162) OR ERNiCr-3 (82)SHROUD LEDGE SB-I 68 SHROUD SUPPORT STUBS (1,4 TOTAL)S-i-168 ENiCrFe-3 OR} BUILD-UP ERNiCc3 j LD ER 308L OR ERI 309L WER HEAO GM ENT-533 GR B ENiCrFe-3 OVERLAY Figure 1: Schematic of CBIN/CB&I Vessel Shroud Support Structure Attachment Configuration Dnc a nf 0 File No.: 1300180.302 Revision:

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