ML17059B489

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Non-proprietary Rev 0 to Gene B13-01739-22, Design Rept for Improved Shroud Repair Lower Support Latches
ML17059B489
Person / Time
Site: Nine Mile Point Constellation icon.png
Issue date: 04/30/1997
From: Deaver G, Rodabaugh J
GENERAL ELECTRIC CO.
To:
Shared Package
ML17059B487 List:
References
GENE-B13-01739, GENE-B13-01739-22, GENE-B13-1739, GENE-B13-1739-22, NUDOCS 9704100248
Download: ML17059B489 (44)


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GE Nuclear Energy GENE Bl3-07739-22 Revision 0 Class III Apm 1997 Design Report forImproved Shroud Repair Lower $upport Latches B.H. Koepke, Senior Engineer Reactor ModNcafion Services Reviewecf Oy:

6.A. cleaver, Engineering leader Reactor MocKcation Services Approved by:

.F.

odabaugh, Missi n Manager In Vessel Repairs 97oqgoo248 9704 PDR

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GENE B13-01739-22 Revision 0 April1997 REVISION STATUS SHEET Revision 0

Approval G.A. Deaver Date 4/6/97 InitialIssue Description

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GENE B53-05739-22 Revision 0 April1997 IMPORTANTNOTICE REGARDING CONTENTS OF THIS REPORT Please read carefully The only undertakings of the General Electric Company (GE) respecting information in this document are contained in the contract between Niagara Mohawk Power Corporation and GE, as identified in PO 15247, and nothing contained in this document shall be construed as changing the contract.

The use of this information by anyone other than the Niagara Mohawk Power Corporation, or for any purpose other than that for which it is intended is not authorized; and with respect to any unauthorized use, GE makes no representation or warranty, express or implied, and assumes no liability as to the completeness,

accuracy, or usefulness of the information contained in this document, or that its use may not in&inge upon privately owned rights.

GENE B13<<01739-22 Revision 0 April1997 LIST OF FIGURES Figure No.

Subject Shroud Repair Lower Support Configuration Page 13 4.1 Latch FEA Model 14 4.2 Stress Results From a 0.100" Displacement 15 4.3 Original Latch FEA Model 16 4"4 Original Latch Stress (Maximum Stress Location) 17 LIST OF TABLES Table No.

4-1 Subsection NG Stress Analysis Subject Page

'4-2 Stress Corrosion Evaluation 10

GENE B13-01739-22 Revision 0 April1997

1.0 INTRODUCTION

The purpose ofthis report is to provide the results of an evaluation performed by GE regarding the redesign ofthe spring latch which holds the lower wedge in place and is part ofthe shroud repair assembly.

The original function ofthe latch was to provide a locking feature for the lower wedge which is held onto the lower spring assembly. In the course ofinstalling the lower wedge, the latch only experiences dead weight loads.

During plant operation, the original latch was not designed to accommodate sliding ofthe lower wedge with respect to the lower spring assembly, since it was postulated that the lower wedge would slide on the vessel wall. Since slidirig will occur at the wedge to lower spring interface when the lower wedge does not slide on the vessel wall, the redesign of the latch includes a flexible member which can accommodate vertical displacements which occur during plant operation.

See Figure 4.1 for the configuration of the new latch.

2.0 SUM1VGMY This report demonstrates that the new latch design is a significant improvement over the previous

design, and that even under very conservative assumptions regarding the loading and displacement ofthe latch that no failure ofthe latch willoccur in the next operating cycle. It is fullyexpected that the new latch willlast for a significantly longer time based on a 8 to 12 factor of improvement which has been determined based on its ability to accommodate vertical movements.

For the expected sliding case where the movement is always along the lower wedge/lower spring interface, the latch willlast the remaining life ofthe plant. Therefore, based on the new latch improvements in combination with the installation change to remove looseness in the lower attachment to the shroud support, satisfactory shroud tie rod repair hardware performance is expected in the future.

3.0 EVALUATION The following evaluations were performed using nominal conditions.

In reviewing the issues associated with the latch failure phenomena, there are numerous variables such as &iction

factors, material properties, dimensional tolerances, reactor operating conditions, hardware installation details, equipment measurement
accuracy, etc.

Therefore, the use of nominal conditions is the most realistic approach to assess the redesign ofthe lower spring latch.

GENE B13-01739-22 Revision 0 Ap)7I 1997 3.1 Plant Operating Conditions The following paragraphs identify the plant operating conditions which cause loads to occur on the latch.

The geometry of the hardware at the lower spring support of the shroud repair is shown in figure 1.1.

Relative vertical movements between the tie rod components that could affect the loading on the new latch are described in sections 3.1.1 through 3.1.5. Section 3.3 will utilize the displacements defined in sections 3.1.1 through 3.1.5 to establish the maximum latch vertical deflections for the wedge sliding scenarios defined in section 3.2.

The adequacy of the new latch to meet the required stress criteria is then demonstrated in section 4.0.

3.1.1 Hydrotest

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GENE B13-01739-22 Revision 0 Ap17I 1997 4.3 Finite Element Model A 2D plain stress finite element model was prepared for the latch and the Algor linear static analysis sofbvare (Algor Linear Stress Analysis - SSAPOH Rel. 15-FEB-95 Ver. 11.08-3H) was used to determine the latch stresses.

Figure 4-1 contains a sketch ofthe model. Figure 4-2 contains stress contour plot of the Z-direction component stress.

The plots show that at the maximum stress location, the stress is almost exclusively bending.

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GENE B13-01739-22 Revision 0 April1997 4.4 Comparison ofLatch Designs A 2D plain stress finite element analysis was also performed for the original latch.

Figure 4-3 contains a sketch ofthe model for the original latch. Figure 4-4 contains a stress contour plot of the maximum stress location for the original latch for a 0.100" applied displacement.

The calculated membrane + bending + peak stress was 772 ksi and the membrane + bending was approximately 400 ksi (using a linear elastic analysis).

The original latch was much more highly stressed (by a factor of 8 to 12 times) than the new latch.

5.0 CONCLUSION

S The new latch has been designed to accommodate larger vertical displacements while still maintaining its original function oflocking the wedge to the lower spring structure.

The stresses are within ASME code limits and the latch has been analyzed to be resistant to stress corrosion for a minimum of2 years assuming conservative worst case displacements in the latch. It is fully expected that the latch will last for a significantly longer time based on the factor of improvement which has been demonstrated

&om the original design.

For the expected sliding case where the movement is always along the lower wedge/lower spring interface, the latch will last the remaining life of the plant.

Consistent with the inspection recommendations made for the original shroud repair hardware installation, it is recommended that the latches should be visually inspected after the next operating cycle. The condition ofthe latches and the position of the lower wedge should be evaluated based on a criteria which utilizes reactor temperature and pressure information &om the operating cycle.

As discussed in this report, some amount of displacement ofthe lower wedges can be expected which would be considered normal.

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GENE B13-01739-22 Revision 0 April1997 OWER SPRING VESSEL W L

lATCH FIGURE 1.1 SHROUD REPAIR LOWER SUPPORT CONFIGURATION 13

GENE B13-01739-22 Revision 0 April1997 FIGURE 4-1 LATCHFEA MODEL 14

GENE B13-01739-22 Revision 0 April1997 FIGURE 4-2 STRESS RESULTING FROM A 0.100" DISPLACEMENT 15

GENE B13-01739-22 Revision 0 April1997 FIGURE 4-3 ORIGINALLATCHFEA MODEL 16

GENE B13-01739-22 Revision 0 Ap)7/ 1997 FIGURE 4-4 ORIGINALLATCH STRESSES (MAXIMUMSTRESS LOCATION) 17