ML121170488

Pump P-109A, 11-RHRSW Stuffing Box with Through-Wall Leak at Monticello Plant

ML121170488
Person / Time
Site:	Monticello
Issue date:	04/25/2012
From:	Xcel Energy, Northern States Power Co
To:	Office of Nuclear Reactor Regulation
References
Download: ML121170488 (24)

Text

ENCLOSURE2 MONTICELLO NUCLEAR GENERATING PLANT 10 CFR 50.55a REQUEST NO. 20 ALTERNATIVE TO REPAIR OF THE RESIDUAL HEAT REMOVAL SERVICE WATER PUMP NO. 11 STUFFING BOX THROUGH-WALL DEFECT STRUCTURAL INTEGRITY ASSOCIATES, INC.

FINITE ELEMENT STRESS EVALUATION OF CLASS 3 PUMP 11-RHRSW STUFFING BOX (22 Pages Follow)

V -jStructural Integrity Associates, Inc.ý File No.: 1200477.301 Project No.: 1200477 CALCULATION PACKAGE Quality Program: M Nuclear E] Commercial PROJECT NAME:

Pump P-i 09A, 11 -RHRSW Stuffing Box with Through-Wall Leak at Monticello Plant CONTRACT NO.:

00001005, Release. 00035 CLIENT: PLANT:

Xcel Energy Monticello Nuclear Generating Plant CALCULATION TITLE:

Finite Element Stress Evaluation of Class 3 Pump 11 -RHRSW Stuffing Box Document Affected Project Manager Preparer(s) &

Revision Pages Revision Description Approval Checker(s)

Signature & Date Signatures & Date 0 1-14 Initial Issue A A-8 N. G. Cofie C. J. Fourcade NGC 04/19/2012 CJF 04/19/12 F. H. Ku FHK 04/19/12 S. S. Tang SST 04/19/12 Page 1 of 14 F0306-OIR1

al bpfym ASSaCkft W Table of Contents 1.0 IN TRO D UCTION ................................................................................................... 3 2.0 M ETH OD O LO GY ................................................................................................... 3 3.0 ASSUMPTIONS / DESIGN INPUTS ...................................................................... 4 4.0 STRESS AN A LY SES ............................................................................................... 4 5.0 RESULTS OF ANALYSIS ...................................................................................... 5

6.0 CONCLUSION

S AND DISCUSSIONS ................................................................. 5 7.0 REFEREN CES ...................................................................................................... 6 APPENDIX A XCEL ENERGY DIT 1333062-01 .......................................................... A-1 List of Figures Figure 1. 11 -RHRSW Pump Stuffing Box with Leaking Hole .......................................... 7 Figure 2. General Dimensions of Leaking Hole [1] ............................................................ 8 Figure 3. General Dimensions of Stuffing Box [1] ............................................................ 9 Figure 4. Finite Element Model of the Non-Degraded Condition ...................................... 10 Figure 5. Finite Element Model of the Degraded Condition .................................................. 11 Figure 6. Applied External Pressure ................................................................................... 12 Figure 7. First Principal Stress (S1) Contour for Non-Degraded Condition ...................... 13 Figure 8. First Principal Stress (S 1) Contour for Degraded Condition .............................. 14 File No.: 1200477.301 Page 2 of 14 Revision: 0 F0306-OIRI

1.0 INTRODUCTION

During rebuild of P-109A, 11-RHRSW (residual heat removal service water) pump, a through-wall leaking hole was discovered in the stuffing box [1], as shown in Figure 1. The hole is located between the leak off line and the exterior of the stuffing box. The hole into the leak off line allows RHRSW system water to leak directly into the stuffing box within which system leakage past the stuffing box bearing and seal water is the normal source of water. Originally, there was only a very small ligament between the leak off line and the exterior of the stuffing box at the location where the hole developed. It is believed that the hole may have originated as a result of corrosion in the leak off line couple with the internal pressure. A close-up view of the hole is shown along with the dimensions in Figure 2 [1].

The objective of this evaluation is to show that the hole does not compromise the structural integrity of the component and therefore acceptable for continued operation for one cycle in the degraded condition. Two separate finite element models are created, one in the degraded condition (with the hole), and one that is intact (original as-installed condition). Stress evaluations will be performed on both, and the resulting stresses compared to show acceptability for continued operation of the ASME ISI Class 3 pump stuffing box at Monticello for one additional cycle (24 months).

2.0 METHODOLOGY In performing this evaluation, the possibility of using the methodology outlined in USNRC Generic Letter 90-05 [2] and ASME Section XI Code Case N-513 [3] was explored. However, the provisions of these documents apply to pipe like components and do not apply to the condition analyzed here since the component in question is not piping. Hence an alternate approach using finite element stress analysis and comparing the resulting stresses to ASME Section III [7] allowable limits is used instead. This approach of using the acceptance criteria of the Construction Code is acceptable and consistent with that provided in NRC Inspection Manual Part 9900, C 1I and C. 12 [4].

A finite element model (FEM) which is representative of the main body of the stuffing box is developed for analysis. Two independent models are created: the original intact stuffing box (non-degraded condition);

and one with the hole that resulted in the leak (degraded condition). Since the evaluation will be for one cycle, some additional degradation of the hole due to corrosion mechanism will be considered in the degraded model.

The model is developed using the ANSYS [5] analysis software which has been routinely used for these type of analyses. Because of the configuration of the stuffing box and location of the leaking hole, a three-dimensional model will be developed for the analysis.

Stress analyses will be performed using both models discussed above. For this component, only pressure loading is applicable and other loadings such as thermal and seismic/vibration are negligible. The component is subjected to the internal operating pressure of 271 psi (RHRSW pump pressure) [1]. It is recognized that the seal water pumps are maintained below a maximum of 60 psi. However, the higher pump pressure of 271 psi is conservatively used in the evaluations performed herein. Other pressure conditions can be linearly scaled from the results of this pressure stress case considered in the evaluation.

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The results of the non-degraded model will be compared to the degraded model to show that the stresses have not changed significantly as a result of the leaking hole. Furthermore, the stress results of the degraded model will be compared to ASME Code,Section III, Class 3 allowable stresses (Table ND-3321-1) to determine acceptability.

3.0 ASSUMPTIONS / DESIGN INPUTS The design inputs for the evaluation were provided by Xcel Energy in Reference 1 and provided in Appendix A. The major dimension of the hole is 0.26" [1]. In the model, the size of the hole is approximated as an ellipse. The minor axis is taken as half of the major axis (0.13"). The evaluation has to account for future degradation of the hole during one additional cycle. This is done by linear extrapolating the hole dimensions for additional 2 years. The pump was inspected in 1998 and no degradation was identified. It took approximately 13 years for the hole to develop its present dimensions. Hence for additional two years of operation, the present dimensions have to be factored by a ratio of (15/13). This results in a hole size of 0.15" by 0.30". For conservatism, a hole size of 0.15" by 0.36" is used in the model.

The design input (dimensions, operating conditions, material spec., etc) are obtained from the OSCAR input record [1]. Design drawings of the stuffing box are not readily available at the time of performing this analysis and therefore, actual measurements were taken by plant personnel and provided to SI. The dimensions are shown in Figure 3 [1].

The material of the stuffing box is ductile cast iron [1]. However, at the time of preparing this analysis, the exact specification is not available. Hence the most conservative properties in the ASTM specifications for all ductile cast iron will be selected for the analyses. Xcel Energy reviewed applicable ASTM standards for ductile cast iron and provided the following to bound the value of the actual material [1]:

• ASTM A536, Grade 60-40-18, 60 ksi tensile, 40 ksi yield, 18% elongation.

" ASTM A439, Grade D-3, 55 ksi tensile, 30 ksi yield, 6% elongation.

" ASTM A439, Grade D-2C, 58 ksi tensile, 28 ksi yield, 20% elongation.

" ASTM A571, Class 2, 60 ksi tensile, 25 ksi yield, 25% elongation.

The lowest mechanical properties from the above list were chosen for the analyses for conservatism. This corresponds to ultimate strength (S,) of 55 ksi and yield strength (Sy) of 25 ksi at room temperature.

Using the criteria in ASME Section II Part D, Appendix 1 [6], the allowable stress is the minimum value of 2/3 Sy or Su /3.5. Hence the allowable stress value, S, is 15.71 ksi.

4.0 STRESS ANALYSES The stress analyses were performed using the ANSYS software package [5] and the dimensions shown in Figure 3. A finite element model in the non-degraded condition is shown in Figure 4; the model for the degraded condition with the hole is shown in Figure 5. Both are three-dimensional models representing one-quarter of the component, with a symmetry plane through the center of the hole location. The models File No.: 1200477.301 Page 4 of 14 Revision: 0 F0306-OIRI

1!tSfW&nI MbR* Assadatm W were developed using high order SOLID95 elements within the hole region to capture peak stresses, and low order SOLID45 elements for the rest of the model.

The operating pressure of 271 psi given in the source document [1 ] is applied to the external surfaces of both models, which becomes an internal pressure inside the leak off line. Two separate cases were evaluated for the non-degraded and degraded conditions. Since either side of the casing may be subjected to either the pump pressure (271 psi) or the seal pressure (60 psi). For conservatism, the 271 psi pressure is applied to the leak off line. The pressure application is shown in Figure 6.

Symmetry boundary conditions are applied at the planes of symmetry, at the 0- and 90-degree planes. The bottom surface of the flange is fixed in the vertical direction. The ANSYS input files for the analyses are NOHOLE.INP and WITHHOLE.1NP for the non-degraded and degraded conditions, respectively.

5.0 RESULTS OF ANALYSIS The first principal stress (S 1) contour plots are shown in Figures 7 and 8 for the non-degraded and degraded conditions, respectively.

As can be found by comparing Figures 7 and 8, there is no appreciable difference in the stresses between the non-degraded and the degraded conditions from the applied pressure loading. Furthermore the stresses are relatively small. The maximum S I is found at the surface of leak off line hole. The maximum stress associated with the pressure loading is 1.412 ksi and 1.416 ksi for the non-degraded and degraded conditions, respectively. From Table ND-3321-2 of ASME Section III, Class 3 allowable stress for general primary membrane is S and for local primary membrane plus bending is 1.5S [7]. The calculated maximum nodal stresses at the hole are well below the general membrane stress of 15.71 ksi, even though it can be considered a local membrane stress in which case the allowable value is 23.57 ksi. The internal pressure can be an order of magnitude higher and the resulting stresses will still be below the allowable limits.

6.0 CONCLUSION

S AND DISCUSSIONS The analyses have demonstrated that the stresses resulting from the leaking hole in the stuffing box at Monticello does not compromise the structural integrity of the component. The maximum calculated principal stress of 1.416 ksi is below the conservatively determined allowable value of 15.71 ksi.

Furthermore, there is no appreciable difference in the stress distributions between the degraded and non-degraded conditions. The stuffing box at Monticello is therefore acceptable for continued operation for one cycle.

The analyses presented herein have only looked at the structural integrity of the component.

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7.0 REFERENCES

1. Xcel Energy Design Information Transmittal Tracking Number 133062, "11 RHRSW Pump Stuffing Box Leakage," MNGP Unit 1, From M. Marashi (Xcel Energy) to N. Cofie (SI) dated 04/18/2012, SI File No. 1200477.206.

2. NRC Generic Letter 90-05, "Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1, 2, and 3 Piping," June 1990.

3. ASME Section XI Code Case N-513-3, "Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping," Approved January 26, 2009.

4. NRC Inspection Manual Part 9900: Technical Guidance, "Operability Determinations & Functionality Assessments for Resolution of Degraded or Non-Conforming Conditions Adverse to Quality or Safety," Issue date 04/16/08.

5. ANSYS Mechanical APDL and PrepPost, Release 12.1 x64, ANSYS, Inc., November 2009.

6. ASME Boiler and Pressure Vessel Code,Section II, Part D, Material Properties, 2004 Edition.

7. ASME Boiler and Pressure Vessel Code,Section III, 2004 Edition.

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Figure 1. 11-RHRSW Pump Stuffing Box with Leaking Hole File No.: 1200477.301 Page 7 of 14 Revision: 0 F0306-O1RI

VSuuwINWONMEN Awsd~n WO Figure 2. General Dimensions of Leaking Hole I1l File No.: 1200477.301 Page 8 of 14 Revision: 0 F0306-O1RI

9 Atff 1 af Awaaftkia a= 3.30" b= 0.60" c= 0.72" d : 0.88" e 1.0" f : 4.5" g : 1.572" h = 3.25" 1= 0.41" J = 4.237" k = 0.539" L = 0.50" m = 0.75" n = 0.25" o = 0.983" p = 0.25" x 0.125" approx.

Thk.-' Q 9116" Figure 3. General Dimensions of Stuffing Box [1]

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HAT 1 Figure 4. Finite Element Model of the Non-Degraded Condition File No.: 1200477.301 Page 10 of 14 Revision: 0 F0306-O1RI

M4T NMh Figure 5. Finite Element Model of the Degraded Condition File No.: 1200477.301 Page 11 of 14 Revision: 0 F0306-OIRI

~jSV WbihfpEf ASsdaftw kn 271 Figure 6. Applied External Pressure Note: Degraded model shown File No.: 1200477.301 Page 12 of 14 Revision: 0 F0306-O1R1

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-258.871

-20.189 218.493 457.176 695. 858 934.54 1173 1412 Figure 7. First Principal Stress (S1) Contour for Non-Degraded Condition Note: Units shown in psi File No.: 1200477.301 Page 13 of 14 Revision: 0 F0306-OIRI I

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761.319

-519.34

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-35.382 206.597 448.577 690.556 932.535 1175 1416 Figure 8. First Principal Stress (S1) Contour for Degraded Condition Note: Units shown in psi File No.: 1200477.301 Page 14 of 14 Revision: 0 F0306-OIRI

APPENDIX A XCEL ENERGY DIT 1333062-01 File No.: 1200477.301 Page A-I of A-8 Revision: 0 F0306-O1RI

ISVAuulh ryWAsmft& W QF-0545 (FP-E-MOD-1 1) Rev. 3 Page I of 2 4-f_ Xlr-cj ' Design Information Transmittal (DIT)

From: Mo Marashi To: Nat Cofle (Structural Integrity Associates)

Mod or Tracking Number: 13302 Date: 4/18/2012 DIT No: 1333062-1333062 _01 Mod

Title:

11 RHRSW Pump Stuffing Box Leakage Plant MNGP Unit 1 I] Unit 2 0 Quality Safety Related Common 0 Classification:

SUBJECT:

Check If applicable:

O This DIT confirms Information previously transmitted orally on by

[1 This Information Is preiminary. See explanation below.

SOURCE OF INFORMATION (Source documents should be uniquely identified)

Drawing ND-57664-2, Line Designation Table RHR & Emergency Service Water, Rev. 76. (Line SW9-12"-GF)

OWI-02.03 (OPERATOR ROUNDS) for the Turbine Building West.

Operations Manual B.08.03-02 Rev. 2 Pump Technical Manual NX-8936-32.

Field measurements Photos DESCRIPTION OF INFORMATION (Write the information being transmitted or list each document being transmitted)

Stuffing box measurements (see attachment 1)

Hole dimensions (see photos attachment 2)

RHRSW pump operating pressure = 271 psig RHRSW pump discharge design pressure = 450 psig Maximum Seal Water pumps discharge pressure = 60 psi.

Stuffing box material: ductile iron Applicable ASTM standards for ductile cast iron and the lowest values for several properties as follows:

ASTM A536, Grade 60-40-18, 60 ksi tensile, 40 ksl yield, 18% elongation.

ASTM A439, Grade D-3, 55 ksi tensile, 30 ksi yield, 6% elongation.

ASTM A439, Grade D-2C, 58 ksi tensile, 28 ksi yield. 20% elongation.

ASTM A571, Class 2, 60 ksi tensile, 25 ksi yield, 25% elongation.

Use the lowest tensile (55 ksi), lowest yield (25 ksi) and Ifelongation is required, lowest elongation (6%) from the applicable ASTM standards.

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1CSMWkui MbP fy AssOdte kne DISTRIBUTION (Recipients should receive all attachments unless otherwise indicated. All attachments are uncontrolled unless otherwise indicated)

PREPARED BY (The Preparer and Approver may be the same person if the person has completed the FL-ESP-GEN-OIOM, *Engineering Change Preparation and Revlew" qualification.)

Mo Marashi Senior Engineer -

______________ Plant Engineering Preparer Name Position Signature Date APPROVED BY (Approval of this form requires completion of FL-ESP-GEN-010M qualification per procedure FP-E-MOD-1 1, *Control of Design Interfaces".)

Mo Marashi Senior Engineer -

_____________ Plant Engineering Approver Name Position Signature Date A copy of the DIT (along with any attachments not on file) should be sent to the modification file.

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QF-0212, Revision 4 (FP-SC-RSI-04) Page 1 of 1 j9XcelEnergys SHIPPING DOCUMENT NORTHERN STATES POWER -MN Xcel Energy 2807 County Rd 75 Monticello MN 55362 Shipping Document Date: April 25, 2012 Tracking Number: 5-q / r2--620e Ship To:

USNRC 11555 Rockville Pike Rockville, MD 20852-2738 Attention Of: Document Control Desk SHIPMENT SHIPMENT PO NUMBER: RMA NO.:

PACKAGING SHIPPING BY Pallet, Box, Etc.

Fed Ex ORIGINAL PO NUMBER: BUYER:

Town Run Motor Freight FREIGHT TRACKING NO. JDE NUMBER:

Vendor UPS Reason for shipment: Overnight Shipment to USNRC Other Item No. Qty Unit Description Catalog ID I Q 1 Letter Monticello 10 CFR 50.55a Request #20 for RHR SW Pump #11 Shipment Requester SWIP Making Shipment 1A DeNae Sievers - Please ensure that a tracking number is communicated to me.

Use of this form as a procedural aid does not require retention as a quality record.