ML17059C550

Rev 0 to MPR-1966(NP), NMP Unit 1 Core Shroud Vertical Weld Repair Design Rept

ML17059C550
Person / Time
Site:	Nine Mile Point
Issue date:	01/31/1999
From:	Mccurdy H MPR ASSOCIATES, INC.
To:
Shared Package
ML17059C551	List: ML17059C550 ML18040A360
References
MPR-1966(NP), MPR-1966(NP)-R, MPR-1966(NP)-R00, NUDOCS 9902100204
Download: ML17059C550 (104)

Text

ENCLOSUKE3 1%1NE MHE POINT UI.'GT l (NMPl) CORE SHROUD VERTICALWELD REPAIR DESIGN REPORT NON-PROPMKTARYVERSION 9902i00204 990203'DR ADOCK 05000220 P

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raqMpR ASSOCIATES INC.

E N G I N E E R S Nine Mile Point Unit 1 Core Shroud Vertical Weld Repair Design Report MPR-1966 (NP)

Non-Proprietary Version Revision 0 January 1999 Prepared by:

H.

illiam M urdy Reviewed by:

- ai B.%wanner Approved by:

WilliamR. Schmidt Principal Contributors H. WilliamMcCurdy, MPR Associates Craig B. Swanner, MPR Associates, Benjamin R. Lane, MPR Associates QUALITYASSURANCE DOCUMENT This document has been prepared, reviewed, and approved in accordance with the Quality Assurance requirements of 10CFR50 Appendix B, as specified in the MPR Quality Assurance Manual.

320 KING STREE'T ALEXANDRIA, VA 22314-3230 703.519-0200 FAX: 703-519-0224

Table of Contents 1

Introduction and Summary

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1-1 1.1 Introduction 1.2 Summary............

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1.2.1 Repair Overview.......................................

1-1 1.2.2 Structural and Design Evaluations,.......................

1-1 1.2.3 System Evaluations..........

1.2.4 Material and Fabrication 1-2 1-2 1.2.5 Pre-Modification and Post-Modification Inspection......

2 Background

2.1 Reactor Internals Design Bases...........

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2.2 Functional Requirements 1-2 2-1 2-1 3

Description of Repair............. ~...

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~ 3-1 3.1 Design Objectives 3.2 Design Criteria....

....... 3-1 3-1 3.3 Description of Repair Components and Design Features....

4 Structural and Design Evaluation

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4.1 Design Loads and Load Combinations 4.2 Analysis Models and Methods 4.3 Repair Hardware Evaluation

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4.3.1 Repair Hardware Structural Evaluation 4.3.2 Flow Induced Vibration 4.3.3 Radiation Effects

. 3-1 4-1 4-1 4-1 4-1 4-1 4-2 4.4 Shroud Evaluation......

4-3 4.5 Impact on Tie-Rod Repair....

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4.6 Loose Parts Considerations 44 4.7 Installation Cleanliness

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Systems Evaluation.......................................

5-1 5.1 Bypass Flow for Normal Operation 5.2 Bypass Flow for Other Conditions..

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5-2 5.3 Downcomer Flow and Other Effects............

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Materials and Fabrication................................

6-1 6.1 Material Selection 6-1 6.2 Material Procurement Specifications 6.3 Material Fabrication

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6-2 7

Pre-Modification and Post-Modification inspection 7.1 Pre-Modification Inspection 7.2 Post-Modification Inspection

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~ 7 1 7.2.1 Prior to RPV Reassembly 7.2.2 During Subsequent Refueling Outages

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References..............................................

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Tables 4-1 Core Shroud Vertical Weld Repair Design Loads and Load Combinations............................................

4 6 4-2 LimitingStresses in the Repair Clamp Assembly...............

4-7 4-3 Shroud Stress Ratio Summary..............................

4-8 6-1 Repair Clamp Materials...................................

6-3 MPR-1966 (NP)

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Figures 1-1 Nine Mile Point Unit 1 Core Shroud Welds... ~...

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1-3 1-2 Nine Mile Point Unit 1 Assembly

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1-3 Nine Mile Point Unit 1 Assembly 1-4 Nine Mite Point Unit 1 Clamp Assembly 1-5 Nine Mile Point Unit 1 Assembly....

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Exploded View of V4 Vertical Weld Clamp

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Installed V4 Vertical Weld Clamp

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Exploded View of V9/V10 Vertical Weld

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Installed V9V/10 Vertical Weld Clamp

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MPR-1966 (NP)

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introduction and Summary 1.1 Introduction This report documents the design of the core shroud vertical weld repair for the Nine MilePoint Nuclear Station Unit 1 (NMP-1). The report follows the guidelines in BWRVIP-04 [1], "Guide for Format and Content of Core Shroud Repair Submittals."

Asummary of the repair design, supporting evaluations, material, fabrication and inspection requirements is provided in this report.

1.2 Summary The NMP-1 core shroud vertical weld repair addresses the cracking ofvertical welds V4, V9 and V10 (see Figure 1-1). The repair is not included under the ASME Boiler and Pressure Vessel Code Section XIdefinition for repair or replacement.

Rather, the repair is developed as an alternative repair pursuant to 10 CFR 50.55a(a)(3).

As summarized below, the repair satisfies the requirements specified in BWRVIP-02 [2],

"Core Shroud Repair Design Criteria." The repair is consistent with the current plant licensing basis and ensures that the shroud willsatisfy its operational and safety functions.

1.2.1 Repair Overview As shown in Figures 1-2 through 1-5, the repair consists of repair clamps which hold the shroud together at the failed vertical weld locations. The repair design specification is provided in Reference 3.

1.2.2 Sfrucfural and Design Evaluations As summarized below, the repair satisfies the structural requirements specified in References 2, 3 and 4.

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criteria for the repair hardware. In particular, although the repair is not considered an ASMEB&PVCode repair, the repair satisfies the Design by Analysis stress and fatigue criteria of the ASME Boiler &

MPR-1966 (NP)

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Pressure Vessel Code,Section III,Subsection NG [4]. See Section 4.3 of this report for additional information on the repair assembly structural evaluation.

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Shroud

- The stresses in the shroud resulting from the repair are within the stress allowables of Section III,Subsection NG of the ASME Boiler &Pressure Vessel Code [4]. See Section 4.4 of this report for additional information on the shroud structural evaluation.

1.2.3 System Evaiuafions The leakage through the failed vertical welds with the repair clamps installed was calculated and found to be within the acceptance criteria.

This included the leakage through the repair clamp shroud attachments.

See Section 5 of this report for additional information on these evaluations.

1.2.4 Maferiai and Fabrication The materials specified for use in the repair assemblies are resistant to stress corrosion cracking and have been used successfully in the BWR reactor coolant system environment. The repair assemblies are fabricated from solution annealed Type 304 or 316 stainless steel or solution annealed Type XM-19 stainless steel. No welding is permitted in the fabrication or installation of the repair, and special controls and process qualifications are imposed in the fabrication of the repair to assure acceptable material surface conditions after machining.

See Section 6 of this report for additional information on repair hardware materials and fabrication.

1.2.5 Pre-Modification and Post-Modification Inspections The inspections to be performed to support the repair are summarized below.

Pre-Modification Ins ection - Prior to installation of the shroud repair, visual inspections willbe performed to support the repair installation. These inspections are listed in Section 7.1.

Post Modification Ins ection - Prior to reactor pressure vessel reassembly, visual inspections willbe performed to verify the proper installation of repair. The scope of these inspections is discussed in Section 7.2.

Inspection of the shroud and the repair in future refueling outages will be based on the BWRVIP-07 [6], "Guidelines for Reinspection of Core Shrouds."

MPR-1966 (NP)

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Shroud Locking Screw "t14 Vertical Weld V4 Plate Cutout ln Shroud l Wall Left Bayonet Eccentric

'8 Right Bayonet Eccentric Threaded Pln 199S NPR ASSOCIATES U.S. PATENT PENONG 5BMPR

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Figure 1-2. Nine Mile Point - Unit 1 Exploded Viewof V4 Vertical Weld Clamp Assembly

V4 Vertical Weld Loctdng Screw Shroud Right Bayonet Eccentric Left Bayonet Eccentric V4 Plate Threaded Pin ldMPR

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Figure 1-3. Nine MilePoint - Unit 1 Installed V4 Vertical Weld Clamp Assembly I998 IIPR ASSOCAIES U.S. PAIEIIT PEIIOIIIC

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V9jV10Vertical Weld Locking Screw Cutout in Shroud Wall V9/V10 Plate Left Bayonet Eccentric Threaded Pin Right Bayonet Eccentric FAHMPR

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Figure 1%. Nine MilePoint - Unit 1 Exploded ViewofV9/V10 Vertical Weld Clamp Assembly PCI99S MPR ASSOCNTES U.S. PAIENr PENQNG

V4 Vertical Weld Shroud Locking Screw Right Bayonet Eccentric Left Bayonet Eccentric V9jV10 Plate Threaded Pin QMPR t ln Ol ~ C4 IN/4I/n IAJT Figure 0-5. Nine MilePoint - Unit I Installed V9/V10 Vertical Weld Clamp Assembly PC199S IJPR ASSOCIATES IAS. PATEtIT PEIITNNO

2 Back round 2.1 Reactor internals Design Bases From the NMP-1 Final Safety Analysis Report (Updated) [5], the reactor internals are designed to:

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Provide support for the fuel, steam separators, dryers, etc., during normal operation and accident condition.

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Maintain required configurations and clearances during normal operation and accident conditions.

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Circulate reactor coolant to cool the fuel.

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Provide adequate separation of steam from water.

2.2 Functional Requirements for the Repair The functional requirements for the repair are identified in BWRVIP-02 [2]. The requirements are:

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Structurally replace the vertical welds and maintain the stresses of the affected shroud cylinder withinASME Section IIIstress allowables for all load combinations and service levels.

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Limitcoolant leakage through the cracked vertical welds to acceptable levels for normal operation and transient plant conditions. Note that the NMP-1 plant does not require a floodable volume to be maintained for accident conditions to provide fox adequate core cooling.

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Descri tionof Re air 3.1 Design Objectives The function of the repair is to structurally replace failed V4, V9 and V10 (see Figure 1-1) core shroud welds.

3.2.

Design Criteria The repair is developed as an alternative repair pursuant to 10 CFR 50.55a(a)(3).

The repair is consistent with and meets the criteria developed by the BoilingWater Reactor Vessel and Internals Project, as stated in BWRVIP-02 [2]. The design specification for the repair is provided in Reference 3.

The repair is designed to satisfy the structural requirements of Section III, Subsection NG, "Core Support Structures," of the ASME Boiler &Pressure Vessel Code [4].

3.3.

Description of Repair Components and Design Features The repair clamp is illustrated in Figures 1-2 through 1-5:

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Figures 1-2 and 1-3 show exploded and installed views of the repair clamp for vertical weld V4.

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Figures 1-4 and 1-5 show exploded and installed views of the repair clamp for vertical welds V9 and V10.

Each repair clamp consists of a clamp plate and two bayonet eccentric/threaded pin assemblies.

The clamp is installed in through-wall holes machined in the shroud by EDM processes on each side of the repaired vertical weld. The repair weld clamp transmits the shroud hoop pressure force which would normally be transmitted through the shroud vertical weld. The structural load path is from the shroud through a bayonet eccentric/threaded pin to the clamp plate and through the clamp plate and other bayonet eccentric/threaded pin assembly back to the shroud.

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The installation steps for the repair clamp are as follows:

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The repair clamp is assembled with:

The pins retracted with their flange surfaces flush with the plate inner surfaces.

The bayonet eccentrics rotated to the position where the pin axis is aligned with the center of the 1.563 inch radius portion of the shroud hole.

For the V4 clamp, the right bayonet eccentric/threaded pin assembly is inserted in the clamp plate after the clamp plate has been moved in position between the core shroud and the core spray pipe.

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The pins are threaded inward until their flanges extend beyond the shroud inside surfaces.

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The bayonet eccentrics are rotated to bring the pin shafts into the 1.265 inch radius portion of the shroud hole and into contact with the shroud hole surfaces.

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The bayonet eccentrics are fixed into position with the locking screws which extend into mating slots in the eccentrics.

The locking screws are fixed in position by crimping at two locations.

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The pins are threaded outward to bring their flange surfaces into contact with the shroud inner surface and torqued to provide a specified preload. An allowable of 50 percent for relaxation of preload due to combined thermal and irradiation effects is provided in the preload determination.

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The pins are locked in position by crimping to the eccentric at two locations.

Note that the clamp installation provides the followingfeatures:

The leakage paths through the shroud holes are effectively sealed by the extended seal ring portions of the clamp plate which are machined to a radius equal to the shroud radius and seat on the shroud surface.

The preload between the pin flanges, the clamp plate and the shroud prevents relative displacement between the repair clamp and shroud due to flowinduced vibration loading. Per Reference 10, clamp loading due to shroud vibration is negligible.

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The repair design has considered crevices and their impact on stress corrosion cracking by using materials which are highly resistant to Intergranular Stress Corrosion Cracking (IGSCC). The material's IGSCC resistance is verified by testing per requirements ofASTMA262 Practice E. See Section 6 of this design summary report for further discussion on materials and fabrication.

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Structural and Desi n Evaluation 4.1 Design Loads and Load Combinations The loads and load combinations are listed in the Design Specification for the repair [3]. These loads and load combinations are summarized in Table 4-1.

Acombination of hand calculations and finite element analyses are used to define the design loads. The core shroud pressure differentials listed in the Design Specification are used in the design of the repair.

The only design loads ofsignificance to the repair are those due to differential pressure across the shroud and those due to differential thermal expansion between the shroud and repair clamp.

4.2 Analysis Models and Methodology Analysis models and methods used to evaluate the repair hardware and existing structures are discussed below.

Acombination of hand calculations and finite element analyses were used to evaluate the repair hardware and existing structures.

Three-dimensional finite element analyses using the ANSYS code were used to determine the structural response of the shroud. Hand calculations were used in the evaluations of the repair hardware.

4.3 Repair Hardware Evaluation 4.3.7 Repair Hardware Structural Evaluation The repair hardware satisfies the structural criteria. In particular:

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The Design by Analysis stress and fatigue criteria of the ASME Boiler 8r, Pressure Vessel Code,Section III,Subsection NG are satisfied.

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The maximum fatigue usage in the repair assembly due to thermal expansion (including startup and shutdown) loads occur in the bayonet hole in the repair clamp plate. The fatigue usage at this location is less than 3%.

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The maximum fatigue usage in the shroud at the repair attachments is negligible.

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The fatigue usage from flowinduced vibration is negligible.

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There is no net section yielding for Service Levels A/8 loads.

The ratio of the calculated stress to the allowable stress for the limitingload cases is summarized in Table 4-2 for the clamp components.

4.3.2 Flow Induced Vibration The repair clamps were analyzed to ensure that reactor coolant flowwould not induce unacceptable vibration. The followingbasic approach was followed to provide resistance to flow-induced vibration loading:

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The flow-induced load per unit area of the repair clamp is conservatively calculated based on a difference in pressure equal to one-times the flowvelocity head across the clamp plate.

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The clamp is preloaded by tightening the threaded pins to a force which is greater than the sum of the flow-induced load plus the pressure lead acting to eject the clamp from the shroud. The minimum preload is increased by a factor of50% to account for relaxation due to combined thermal and irradiation effects.

This approach provides assurance that no clamp displacements and no alternating stress willresult from the flow-induced vibration loading. Note that per Table B.6.1 of Reference 10, the shroud vibration amplitude is only one mil and therefore has a negligible effect on the repair clamp vibration.

4.3.3 Radiation Effects The effects of radiation were considered in the selection of the repair materials and fabrication processes.

Relaxation due to thermal and irradiations effects was considered in the determination of threaded pin preload. As discussed in Section 6, all materials used in the repair have been used successfully for years in the BWR environment.

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4.4 Shroud Evaluation The stresses 1n the core shroud were evaluated to the stress criteria of the ASME B&PVCode,Section III,Subsection NG [4]. The ratio of calculated shroud stresses to the allowable stress for the limitingload cases is summarized in Table 4-3. As shown in the table, the shroud can carry the applied loads within the code stress allowables for all defined loadings.

4.5 Impact on Tie-Rod Repair The safety, stress and seismic analyses for the core shroud tie-rod repair (References 7, 8 and 9) were reviewed and evaluated to determine ifthere is any impact from the vertical weld repair. Results of the review/evaluation are:

No specific discussion of requirements for the shroud vertical welds was found in References 7, 8 and 9. However, it is clear that the design and the analyses of the tie-rod repair are based on the shroud retaining a cylindrical configuration in the event of cracking in the vertical welds. Accordingly, the vertical weld repair is required to preserve the cylindrical shroud configuration for all applied loads and load combinations.

As identified in Section 2.2 above, this is one of the functional requirements for the vertical weld repair.

No allowance for coolant leakage through cracked vertical welds is considered in the safety analysis for the tie-rod repair (Reference 7).

Therefore, the vertical weld repair is required to limitvertical weld leakage, in combination with other leakage sources, to within acceptable levels for all plant conditions.

This is a functional requirement for the vertical weld repair as stated in Section 2.2 above.

Per Reference 9, the seismic fuel loads are transmitted directly through the top guide or core support plate rings to the tie-rod radial restraints.

Therefore, it is the stiffness ofthese rings and not the stiffness of the shroud cylinders that affects the fuel seismic response.

For a shroud cylinder with fullycracked vertical welds and end conditions that provide no lateral shear restraint, the lateral stiffness would be reduced.

Since shroud stiffness is a parameter in the shroud seismic model, this reduction could impact the seismic analysis results.

However, this potential impact is not significant since for all of the seismic cases considered in Section 5 of Reference 9, the H1-H2 and H4-H5 shroud cylinders have hinged connections to the adjacent cylinders. This hinged connection MPR-1966 (NP)

Revision 0 4-3

provides shear transfer between the shroud cylinders and permits the shroud cylinders to retain their uncracked moment of inertia and rotational stiffness.

For the tie-rod design basis configuration with a clearance of 0.75 inch between the shroud and the mid-supports, Reference 9 determines that there are no lateral seismic loads applied to the shroud during a seismic event. However, with the as-installed clearance of 0.375 inch between the shroud and the mid-supports, there are several Level D load combinations where the relative seismic displacement at the mid-support exceeds the 0.375 inch clearance.

The resulting mid-support load was evaluated as a primary load, and the loads reacted by the vertical weld repair were determined to be acceptable.

Based on the above, the vertical weld repair has no impact on the tie-rod repair and the supporting safety, stress and seismic analyses.

4.6.

Loose Parts Consideration The various pieces that make up the repair assemblies are captured and restrained by appropriate locking devices such as locking cups and crimping. These locking device designs have been used successfully for many years in reactor internals.

Loose pieces cannot occur without failure of the locking devices or repair assembly components.

Such locking devices and the stresses in the pieces which make up the repair clamps are well within allowable limits for normal plant operation.

4.7.

Installation Cleanliness Alltooling used for installation willbe inventoried and subjected to foreign material exclusion procedures when in the reactor vessel area. Tooling willbe checked for loose parts prior to installation into the canal. Furthermore, the tooling willbe extensively field hardened prior to site deployment to reduce the possibility of tool failures and/or breaks which could potentially result in loose parts remaining in the vessel. Iffailures occur, the parts willbe retrieved from the reactor vessel or cavity.

For each repair clamp, through-thickness holes are machined in the shroud support using the EDM process. This process results in a very fine debris (swarf'eing generated.

This debris is primarily comprised of carbon, nickel, iron, chromium, etc., which are the primary elements contained in the shroud and EDM electrode material. This swarf is flushed and vacuumed from the cut during the machining operation, then filtered prior to discharge back into the cavity. The EDM electrode is designed to only generate swarf. Aslug is not generated as the electrode breaks through the inside surface of the shroud.

Also, a debris collection system is MPR-1966 (NP)

Revision 0 44

positioned on the shroud inside surface to collect the EDM swarf generated when the EDM electrode breaks through the inside surface of the shroud.

The EDM debris system has a 10 micron and a 2 micron filterin series.

Each filter has 200 sq. ft. of effective surface area. The 10 micron filteris rated at 99% efficient for 10 microns and 80% efficient forjust below 2.5 microns. The 2 micron filteris 99% efficient for 2 microns and 90 to 93% efficient for 1 micron. As these filters are loaded, their efficiency willgreatly increase.

The total amount of swarf collected by this EDM debris collection system has been qualified. The debris system collected over 95% of the debris that was generated.

This qualification was performed withoutaninternaldebriscup.

Therefore, thetestwasconservative.

Thesmall amount of swarf not collected by the EDM debris system is not detrimental to the BWR system.

'I Subsequent to completion of the repair hardware installation activities, a final video inspection in the reactor vessel and cavity willbe performed to verify no foreign object entry during the repair.

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Table 4-1 Core Shroud Vertical Weld Repair Design Loads and Load Combinations No.

Event Normal Operation Upset No. 1 Upset No. 2 Emergency No. 1 Emergency No. 2 Emergency No. 3 Faulted No. 1 Faulted No. 2 Faulted No. 3 Load Combination<'1't'1'<'1 Normal Pressure + DW + Steady State Thermal Upset Pressure + DW + Upset Thermal Upset Pressure + DW +OBE + Steady State Thermal"'ormal Pressure + DW +DBE Steam Line LOCA+ DW Recirculation Outlet Line LOCA + DW Steam Line LOCA + DW + DBE Recirculation Inlet Line LOCA + DW + DBE Recirculation Outlet Line LOCA + DW + DBE Notes:

(1)

Load combinations as specified in Table 2-2 of GENE-B13-01739-04 [8].

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DW = Deadweight, LOCA = Loss of Coolant Accident, DBE = Design Basis Earthquake, OBE = Operating Basis Earthquake.

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Allevents include flowloads.

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OBE loads are equivalent to DBE loads.

(5)

The only design loads for the repair clamp are expected to be those due to differential pressure across the shroud and those due to differential thermal expansion between the shroud and repair clamp. Other loads shall be evaluated to confirm that they need not be considered as design-basis loads.

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Table 4-2 LimitingStresses in the Repair Clamp Assembly Repair Location LimitingStress Location Service Level:

Service Condition Stress type Stress Limit Stress Ratio V9 or V10 Bayonet Connection Bayonet Connection Bayonet Connection A: Normal Operation B: Upset Pressure B: Lossof Feedwater Thermal Transient Bearing Bearing Bearing 1.0 Sy 0.400 1.0 Sy 0.604 1.0 Sy 0.636 Bayonet Connection C: Steam Line Break Bearing 1.5 Sy 0.994 Plate at Bayonet Hole A: Normal Operation Membrane Plus Bending 1.5 Sm 0.367 Plate at Bayonet Hole B: Upset Pressure Membrane Plus Bending 1.5 Sm 0.555 V4 Bayonet Connection B: Lossof Feedwater Thermal Transient Bearing 1.0 Sy 0.479 Plate at Bayonet Hole C: Steam Line Break Membrane Plus Bending 2.25 Sm 0.915 MPR-1966 (NP)

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Table 4-3 Shroud Stress Ratio Summary Repair Location V9 or V10 V4 Service Level:

Service Condition A: Normal Operation B: Upset Pressure B: Loss of Feedwater Transient C: Main Steam Line Break A: Normal Operation B: Upset Pressure B: Loss ofFeedwater Transient Stress Type Primary Membrane Primary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Primary Membrane Primary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Primary Plus Secondary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Primary Membrane Primary Membrane Plus Bending Primary Membrane Primary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Primary Membrane Primary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Primary Plus Secondary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Stress Limit Sm 1.5 Sm 3Sm Sm 1.5 Sm 3Sm 3Sm 3Sm 1.5 Sm 2.K Sm Sm 1.5 Sm 3Sm Sm 1.5 Sm 3Sm 3Sm 3Sm Stress Ratio 0.20 0.19 0.41 0.30 0.29 0.54 0.66 0.55 O.e7 0.46 0.07 0.08 0.31 0.11 0.11 0.41 0.57 0.49 C: Main Steam Line Break Primary Membrane Primary Membrane Plus Bending 1.5 Sm 2.25 Sm 0.17 0.18 MPR-1966 (NP)

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5.2 Bypass Flow for Other Conditions As discussed in Part B. 3 of Reference 7, there are no detrimental effects of shroud bypass floweither on plant anticipated abnormal transients or on emergency core cooling system performance.

5.3 Downcomer Flow and Other Effects The'effects of the repair clamp assembly on the flowin the reactor vessel downcomer region are:

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The V4 repair clamp reduces the flow area in the downcomer at the top of the core shroud by approximately 2.5 percent. The V9/VO clamps would reduce the flow area by a lesser amount because they are positioned at a lower elevation where the downcomer flow area is greater.

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The pressure drop associated with the V4 clamp is approximately 0.006 psid for normal operation and 0.044 psid for the recirculation line break condition. For the V9/V10 clamps, the pressure drop is less than for the V4 clamp.

For the V4, V9 and V10 clamps, the total weight is less than 1000 lbs which is negligible compared to the total shroud weight. The displaced reactor water inventory is less than two cubic feet ofwater, which is also negligible.

MPR-1966 (NP)

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Materials and Fabrication 6.1 Material Selection The materials specified for use in the repair clamps are resistant to stress corrosion cracking and have been used successfully in the BWR reactor coolant system environment. As shown in Table 6-1, the repair clamps are fabricated from solution annealed Type 304 or 316 or Type XM-19 stainless steel. XM-19material is used for all parts except the locking screw where Type 304/316 or Type XM-19 stainless steel is used.

As required by the Design Specification, all materials specified for use in the shroud repair are in accordance with ASME or ASTM approved specifications. All materials have been previously used in the BWR environment similar to that experienced by the repair clamps. The materials are not susceptible to general corrosion and are resistant to Intergranular Stress Corrosion Cracking (IGSCC) in a BWR environment.

Additional information on material specification, procurement and fabrication requirements implemented to ensure that the repair hardware is highly resistant to IGSCC is provided in Sections 6.2 and 6.3.

Material properties and allowable stresses for repair components are as specified in the ASME B&PVCode, Sections IIand III,1989 Edition for Class 1 components.

6.2 Material Procurement Specifications Allhardware is constructed from austenitic stainless steel material. Welding on these materials is prohibited by the procurement requirements.

These materials as procured, are highly resistant to IGSCC. NDE of material used for load-bearing members is performed in accordance with ASME Code Section III,Subsection NG-2000. Specific material requirements are summarized below for the material used in the repair.

Allstainless steel material is procured in accordance with the applicable ASME or ASTM standards supplemented by the following:

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Type 304/316 alloys have 0.03% maximum carbon. Type XM-19 alloy has 0.04% maximum carbon. Allstainless steel materials are fullcarbide solution annealed and either water or forced air quenched from the solution annealing MPR-1966 (NP)

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temperature sufficient to suppress chromium carbide precipitation to the grain boundaries in the center of the material cross section.

Solution annealing of the material is the final process step in material manufacture.

ASTMA262 Practice E tests are performed on each heat/lot of stainless steel material to verify resistance to intergranular attack and that a non-sensitized microstructure exists (no grain boundary carbide decoration).

Pickling, passivation or acid cleaning of load bearing members is prohibited after solution annealing unless an additional 0.010 inches material thickness is removed by mechanical methods.

For other non-load bearing items, metallography at 500X is performed on materials from each heat, similarly processed, to verify excessive intergranular attack has not occurred.

Controls are also specified in the procurement documents to preclude material contamination during material processing and handling from low melting point metals, their alloys and compounds, as well as sulfur and halogens.

6.3 Material Fabrication No welding or thermal cutting is used in the fabrication and assembly of the items.

Cutting fluids and lubricants are approved prior to use. Controls are also specified to preclude material contamination during processing and handling from low melting point metals, their alloys and compounds, as well as sulfur and halogens.

Passivation, pickling or acid cleaning of the items is prohibited. Liquid penetrant testing after final machining or grinding on critical surfaces is performed.

Abusive machining and grinding practices are avoided. Machining and grinding process parameters and operations are controlled. Additionally, machining process parameters in critical load bearing threaded areas are controlled, based on qualification samples, which have been subjected to macroscopic and metallographic examinations and microhardness testing. Evaluations include hardness magnitudes and depths, depth of severe metal distortion, depth ofvisible evidence of slip planes and depth of cold work.

MPR-1966 (NP)

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t

Table 6-1 Repair Clamp Materials Parti' Plate Ba onet Eccentric Threaded Pin V4 Clam XM-19 XM-19 XM-19 Material'"

V9/V10 Clam XM-19 XM-19 XM-19 Locking Screw Type 304/316 or XM-19@

Type 304/316 or XM-1 9"'otes:

(1)

See Figures 1-2 and 1A for identification of parts.

(2)

Allmaterial is solution annealed.

(3)

XM-19 material is used for the locking screws for the NMP-1 repair clamps.

MPR-1966 (NP)

Revision 0 6-3

Pre-Modification and Post-Modification Ins ection 7.1 Pre-Modification Inspection The followingvisual inspections willbe performed to support the repair installation:

The azimuthal locations of the V4, V9 and V10 vertical welds willbe identified using visual, ultrasonic or eddy current methods. Ifwelds cannot be identified visually, a method for visually identifying the weld locations willbe developed which involves marking the shroud or indexing to the weld from other internals.

Following identification of the V4 weld, measurements willbe made to verify that adequate clearance exists between the vertical weld and the core spray vertical piping to allow installation of the repair clamp.

TVvisual inspection willbe performed at the V4, V9 and/or V10 vertical welds where the vertical repair clamps willbe installed to assure that there are no interferences or additional cracking. An engineering evaluation willbe performed to address any interferences or additional cracking identified.

7.2 Post-Modification Inspection 7.2.1 Prior to RPV Reassembly Proper installation of each vertical weld repair clamp assembly willbe confirmed and recorded by TVvisual inspection from both the inside and outside of the shroud. The inspection willverif'y that all parts are installed as required and no foreign objects remain. As a minimum, the following areas willbe inspected:

The top and bottom of the repair clamp to verify that the clearance between the plate and the shroud surface is consistent with the design clearance.

The slots in the plate and the eccentrics to verif'y that the eccentrics are properly aligned with the plate.

The top of the locking screw to verify that the locking screw is fully engaged with the eccentric.

MPR-1966 (NP)

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The pin lip to verify that the pin lip area overlapping the shroud inside surface is consistent with the design configuration.

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The axial location of the threaded pin relative to the eccentric to qualitatively verify that the threaded pin is engaged with the shroud inner diameter.

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The locking screws and threaded pins to confirm crimping.

~

Afinal video inspection in the reactor vessel and cavity willbe performed to verify no foreign object entry during the repair.

7.2.2 During Subsequent Refueling Outages Inspection of the repair clamps in future refueling outages willbe based on the requirements in Section 4.2 ofBWRVIP-07 [6], "Guidelines for Reinspection of Core Shrouds." The inspection willinvolve the visual inspection of the overall clamp and the threaded pin-to-eccentric and locking screw-to-eccentric crimp areas to confirm no change from their condition during the post-installation inspection. Inspection frequency will be in accordance with BWRVIP-07 requirements.

MPR-1966 (NP)

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References 1.

EPRI Report TR-105692, "BWRVIPVessel and Internals Project, Guide for Format and Content of Core Shroud Repair Design Submittals (BWRVIP-04)," October 1995.

2.

EPRI Report, "BWRVIPVessel and Internals Project, Core Shroud Repair Design Criteria (BWRVIP-02)," Revision 2, Fifth Draft Report, April1988.

3.

MPR Specification No. 249014-001, "Design Specification for Nine Mile Point Nuclear Station Unit 1 (NMP1) Core Shroud Vertical Weld Repair,"

Revision 1, October 12, 1998.

4.

ASME Boiler and Pressure Vessel Code,Section III,Division 1-Subsection NG, "Core Support Structures," 1989 Edition.

5.

Nine MilePoint Nuclear Station Unit 1 Final Safety Analysis Report (Updated), Revision 15, November 1997.

6.

EPRI Report TR-105747, "BWRVessel and Internals Project, Guidelines for Reinspection ofBWR Core Shrouds (BWRVIP-07)," February 1996.

7.

Nine MilePoint Unit 1 Safety Evaluation Number 94-080, Rev. 1 for Modification N1-94-003, Reactor Core Shroud Repair.

8.

GENE-B13-01739-04, "Nine MilePoint Unit 1 Shroud Repair Hardware Stress Analysis (NMPC Calculation No. SO-Vessel-M028)," Revision 0.

9.

GENE-B13-01739-03, "Nine MilePoint Unit 1 Nuclear Power Station, Seismic Analysis, Core Shroud Repair Modification (NMPC Calculation No. SO-Vessel-M027)," Revision 0.

10. NEDE-13109, "Oyster Creek Startup Test Results," July 1970.

MPR-1966 (NP)

Revision 0 8-1

ENCLOSURE4 Y OF NIAGARAMOHAWK10CFR50.59 SAFETY EVALUTION

CORE SHROUD VERTICALWELDREPAIR CLAMPS SAFETY EVALUATION

SUMMARY

DI<'.SCRIPTION t

The NMP-1 core shroud vertical weld repair addresses the cracking of vertical welds V4, V9 and V10 (see Figure 1-1). The repair basically consists of a clamp with a plate with attached pins which are inserted into holes which are machined by the Electric Discharge Machining (EDM) process on either side of the flawed vertical weld. The clamps bridge across the flawed vertical weld and transmit the pressure load normally transmitted through the vertical weld. Two clamps are used for the V9 weld, two clamps for the V10 w'eld and one clamp is used for the shorter V4 weld. The repair clamps can be installed on each weld independently, that is any one, two or three welds can be repaired with these repair clamps. Prior to this repair being utilized as a structural replacement for the welds, an NRC approval willbe required.

As summarized below, the repair satisfies the requirements specified in BWRVIP-02 [1], "Core Shroud Repair Design Criteria." The repair is consistent with the current plant licensing basis and ensures that the shroud willsatisfy its operational and safety functions. For details of the repair clamp evaluations, which are summarized below, see the design report for the repair, reference 9.

PART A.1-GE<NERAL The repair clamp design is illustrated iri Figures 1-2 through 1-5:

~

Figures 1-2 and 1-3 show exploded and installed views of the repair clamp for vertical weld V4.

~

Figures 1-4 and 1-,5 show exploded and installed views of the repair clamps for vertical welds V9 and V10.

Each repair clamp consists of a clamp plate and two bayonet eccentric/threaded pin assemblies.

The clamps are installed in through-wall holes machined in the shroud by EDM processes on each side of the repaired vertical weld. The repair weld clamps transmit the shroud hoop pressure force which would normally be transmitted through the shroud vertical weld. The structural load path is from the shroud through a bayonet eccentric/threaded pin to the clamp plate and through the clamp plate and other bayonet eccentric/threaded pin assembly back to the shroud.

The installation steps for the repair clamps are as follows:

~

The repair clamps are assembled with:

The pins retracted with their flange surfaces flush with the plate inner surfaces The bayonet eccentrics rotated to the position where the pin axis is aligned with the center of the larger portion of the shroud hole.

For the V4 clamp, the right bayonet eccentric/threaded pin assembly is inserted in the clamp plate after the clamp plate has been moved in position.

~

The pins are threaded inward until their flanges extend beyond the shroud inside surfaces.

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The bayonet eccentrics are rotated to bring the pin shafts into the smaller radius portion of the shroud hole and into contact with the shroud hole surfaces.

I

~

The bayonet eccentrics are fixed into position with the locking screws which extend into mating slots in the eccentrics.

The locking screws are fixed in position by crimping at two locations.

~

The pins are threaded outward to bring their flange surfaces into contact with the shroud inner surface and torqued to provide a specified preload.

~

The pins are locked in position by crimping to the eccentric at two locations.

Note that the clamp installation provides the followingfeatures:

~

The leakage paths through the shroud holes are effectively sealed by the extended seal ring portions of the clamp plate, which are machined to a radius equal to the shroud radius and seat on the shroud surface.

~

The preload between the pin flanges, the clamp plate and the shroud prevents relative displacement between the repair clamp and shroud due to flow induced vibration loading.

PART A.2 - MATERIALS PART A. 2. 1 - MATERIALSELECTION The materials specified for use in the repair clamps are resistant to stress corrosion cracking and have been used successfully in the BWR reactor coolant system environment.

The repair clamps are fabricated from solution annealed Type XM-19 stainless steel

~

As required by the Design Specification [2], all materials specified for use in the shroud repair are in accordance with ASME or ASTM approved specifications. Allmaterials have been previously used in the BWR environment similar to that experienced by the repair clamps. The materials are not susceptible to general corrosion and are resistant to Intergranular Stress Corrosion'Cracking (IGSCC) in a BWR environment.

Additional information on material specification, procurement and fabrication requirements implemented to ensure that the repair hardware is highly resistant to IGSCC is provided in A.2.2 and A.2.3 below.

Material properties and allowable stresses for repair components are as specified in the ASME B&PVCode, Sections IIand III, 1989 Edition for Class 1 components, MPR-1966 [9].

PART A.2.2 - MATERIALPROCUREMENT SPECII'ICATIONS Allhardware is constructed from austenitic stainless steel material. Welding on these materials is prohibited by the procurement requirements.

These materials as procured, are highly resistant to IGSCC. NDE of material used for load-bearing members is performed in accordance with ASME Code Section III,Subsection NG-2000. Specific material requirements are summarized below for the material used in the repair.

Allstainless steel material is procured in accordance with the applicable ASME or ASTM standards supplemented by the following:

~

Type 304/316 alloys have 0.03% maximum carbon. Type XM-19 alloy has 0.04% maximum carbon. Allstainless steel materials are fullcarbide solution annealed and either water or forced air quenched from the solution annealing temperature sufficient to suppress chromium carbide precipitation to the grain boundaries in the center of the material cross section.

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~

Solution annealing of the material is the final process step in material manufacture.

ASTM A262 Practice E tests are performed on each heat/lot of stainless steel material to verify resistance to intergranular attack and that a non-sensitized microstructure exists (no grain boundary carbide decoration).

~

Pickling, passivation or acid cleaning of load-bearing members is prohibited after solution annealing unless an additional 0.010 inches material thickness is removed by mechanical methods.

For other non-load bearing items, metallography at 500X is performed on materials from each heat, similarly processed, to verify excessive intergranular attack has not occurred.

~

Controls are also specified in the procurement documents to preclude material contamination during material processing and handling from low melting point metals, their alloys and compounds, as well as sulfur and halogens.

PART A.2.3 - MATERIALFABRICATION No welding or thermal cutting is used in the fabrication and assembly of the items. Cutting fluids and lubricants are approved prior to use. Controls are also specified to preclude material contamination during processing and handling from low melting point metals, their alloys and compounds, as well as sulfur and halogens. Passivation, pickling or acid cleaning of the items is prohibited. Liquid penetrant testing after final machining or grinding on critical surfaces is performed.

Abusive machining and grinding practices are avoided. Machining and grinding process parameters and operations are controlled. Additionally, machining process parameters in critical load bearing threaded areas are controlled, based on qualification samples, which have been subjected to macroscopic and metallographic examinations and microhardness testing.

Evaluations include hardness magnitudes and depths, depth of severe metal distortion, depth of visible evidence of slip planes and depth of cold work. The machining practices used in the fabrication process for the clamps willbe qualified to ensure the cold work layer at the surface has been maintained to reduce the potential for IGSCC initiation sites.

PART 8 - ANALYSIS PART 8.1 - REPAIR DESIGN LIFE CRITERIA The design lifeof the repair shall be for 25 calendar years (remaining lifeof the plant including life extension) to include 20 effective fullpower years.

PART 8.1.1 - REPAIR DESIGN LIFE CONFORMANCE Allrepair hardware has been designed for 25 calendar years to include 20 effective fullpower years. This includes:

~

Selection of.stainless steel repair materials which have been successfully used in a boiling, water reactor environment and which are resistant to IGSCC.

~

Consideration ofplant transients representative of 20 effective fullpower years of operation (i.e.,120 thermal transients from startups and shutdowns and 30 scrams with loss of feedwater pumps.)

~

Consideration of radiation fluence induced relaxation of repair hardware preload.

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PART 8.2 - FUNCTIONALRE UIREMENTS CRITERIA The functional requirements for the repair are identified in BWRVIP-02 [1]. The requirements are:

1.

Structurally replace the vertical welds and maintain the stresses of the affected shroud cylinders within ASME Section IIIstress allowables for all load combinations and service levels.

2. Limitcoolant leakage through the cracked vertical welds to acceptable levels for normal operation and transient plant conditions. Note that the NMP-1 plant does not require a floodable volume to be maintained for accident conditions to provide for adequate core cooling.

PART 8.2.1 - FUNCTIONALRE UIREMENTS CONFORMANCE The repair hardware satisfies the structural criteria for the repair hardware.

In particular:

~

The Design by Analysis stress and fatigue criteria of the ASME Boiler 8r, Pressure Vessel Code,Section III,Subsection NG are satisfied for the shroud and for the repair clamps. A comparison of the calculated and allowable stress intensities for the repair clamps is shown in the followingtable:

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LimitingStresses in the Repair Clamp Assembly Repair Location LimitingStress Location Bayonet Connection Bayonet Connection Service Level:

Service Condition A: Normal Operation B: Upset Pressure Stress type Bearing Bearing Stress Limit 1.0 Sy 1.0 Sy Stress Ratio 0.400 0.604 Bayonet Connection B: Lossof Feed water Thermal Transient Bearing 1.0 Sy 0.636 V9 or V10 Bayonet Connection C: Steam Line Break Bearing 1.5 Sy 0.994 Plate at Bayonet Hole Plate at Bayonet Hole Bayonet Connection A: Normal Operation B: Upset Pressure B: Lossof Feedwater Thermal Transient Membrane Plus Bending Membrane Plus Bending Bearing 1.5 Sm 1.5 Sm 1.0 Sy 0.367 0.555 0.479 V4 Plate at Bayonet Hole C: Steam Line Break Membrane Plus Bending 2.25 Sm 0.915

~

The maximum fatigue usage in the repair assembly due to thermal expansion (including startup and shutdown) loads occur in the threaded pins. The fatigue usage at this location is less than 3%.

~

The maximum fatigue usage in the shroud at the repair attachments is negligible.

~

The fatigue usage from flow induced vibration is negligible.

Coolant leakage criteria and conformance are discussed in Parts B.3, B.3.1, B.3.1.1 and B.3.1.2 below.

PART B.3 - FLOW PARTITION CRITERIA Sof14

The repairs shall consider leakage through the repaired vertical welds V4, V9 and V10 as well as through the attachment holes in the core shroud.

The leakage shall be less than allowables which are determined based on consideration of leakage from other sources (cracked horizontal welds, tie-rod lower connection, etc.).

PART 8.3.1 - FLOW PARTITION CONI'ORMANCE The repair design limits shroud leakage to the allowables defined in Reference 2 for all plant operating conditions. Specifically, the leakage is within limits established for core bypass leakage and steam carry-under as discussed in Part B.3.1.1 below. As discussed in Part B.3.1.2, the effects of leakage on core monitoring, anticipated abnormal transients, emergency core coolant and fuel cycle length are negligible.

PART 8.3.1.1 - LEAKAGEFLOW EVALUATION As stated in Part B.2 (Functional Requirements (Criteria)) of this report, the repair is required to limitleakage of reactor coolant through the repaired vertical welds during normal plant operation. This includes the leakage through the vertical welds and the leakage through the holes machined through the shroud wall for the repair clamp installation.

Considering leakage from all other sources, allowable leakage rates were established for the vertical'weld repair as described in Section 6.2 of the Design Specification [2]. These limits are:

~

The combined leakage rate through welds V9 and V10 and their repair clamps shall be less than 0.25% of the total core flow (2% of the core bypass flow) for normal differential pressure.

~

The combined leakage rate of steam through weld V4 and its repair clamp shall be less than 0.08% of the recirculation (core minus steam) flow for normal differential pressure.

The calculated leakage flow rates through repaired vertical welds V4, V9 and V10 are summarized as follows:

Repaired Vertical Weld Leakage Leakage Flow Rate (gpm)

Repaired Welds Calculated Allowable V4 1.63 96 V9 and V10 247 337 PART 8.3.1.2 - CORE MONITORING ANTICIPATEDABNORMALTRANSIENTS EMERGENCY CORE COOLING SYSTEM ANDFUEL CYCLE LENGTH As discussed in Parts B.3.1.3 through B.3.1.6 of Reference 6, the effect of shroud leakage on core monitoring, anticipated abnormal transients, emergency core cooling and fuel cycle length are considered to not be significant.

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PART 8.3.1.3 - CONCLUSION The impact of the leakage through the repaired shroud vertical welds on plant operation has been evaluated as discussed above and found to be acceptable.,

PART 8.4 - FLOW-INDUCEDVIBRATION CRITERIA Evaluations shall be performed of repair clamp vibration and wear for flow-induced vibration.

The alternating stress from the repair clamp vibration shall be limited to the material endurance stress or the ASME Code allowable stress for the number of vibration cycles.

PART 8.4.1 - FLOW-INDUCEDVIBRATION CONFORMANCE The repair clamps were analyzed to ensure that reactor coolant flow would not induce unacceptable vibration. The following basic approach was'followed to provide resistance to flow-induced vibration loading:

~

The flow-induced load per unit area of the repair clamp is conservatively calculated based on a difference in pressure equal to one-times the flow velocity head across the clamp plate.

~

The clamp is preloaded by tightening the threaded pins to a force which is greater than the sum of the flow-induced load plus the pressure load acting to eject the clamp from the shroud.

This approach provides assurance that no clamp displacements and no alternating stress willresult from the flow-induced vibration loading for normal plant conditions.

PART 8.5 - LOADINGON EXISTINGINTE<RNALCOMPONENTS CRITERIA The loading and resulting stresses for the shroud shall be evaluated and shown to be within allowables, as specified in References 1, 2 and 3.

PART 8.5.1 - LOADINGON E<XISTINGINTE<RNALCOMPONENTS

~CONFORM*NCR The stresses in the core shroud were evaluated to the stress criteria of the ASME BEcPV Code,Section III,Subsection NG [3]. The shroud can carry the applied loads within the code stress allowables for all load cases as shown in the followingtable.

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Shroud Stress Ratio Summary Repair Location Service Level:

Service Condition Stress Type Stress Limit Stress Ratio A: Normal Operation Primary Membrane Primary Membrane Plus Bending Sm 0.20 1.5 Sm 0.19 I

Primary Plus Secondary Membrane at Hole 3Sm 0.41 B: Upset Pressure Primary Membrane Primary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Sm 0.30 3 Sm 0.54 1.5 Sm 0.29 V9 or V10 B: Loss ofFeedwater Transient C: Main Steam Line Break Primary Plus Secondary Membrane Plus Bending Primary Plus Secondary Membrane at Hole Primary Membrane Primary Membrane Plus Bending 3 Sm 066 3 Sm 0.55 1.5 Sm 0.47 2.25 Sm 0.46 A: Normal Operation Primary Membrane Sm 0.07 Primary Membrane Plus Bending 1.5 Sm 0.08 Primary Plus Secondary Membrane at Hole 3Sm 0.31 B: Upset Pressure Primary Membrane Sm 0.11 Primary Membrane Plus Bending Primary Plus Secondary Membrane at Hole 1.5 Sm 0.11 3 Sm 0.41 B: Loss ofFeedwater Transient Primary Plus Secondary Membrane Plus Bending Primary Plus Secondary Membrane at Hole 3Sm 3Sm 0.57 0.49 V4 C: Main Steam Line Break I

Primary Membrane Primary Membrane Plus Bending 1.5 Sm 0.17 2.25 Sm 0.18 8of14

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PART 8.6 - SEISMIC ANALYSIS CRITE<RIA The existing seismic evaluations of the core shroud and horizontal weld repair hardware shall be reviewed to determine ifthe vertical weld repair hardware needs to address any seismic loads or displacements.

Stresses for any vertical weld repair seismic loading shall be calculated and compared with allowables as specified in References 1, 2 and 3.

PART 8.6.1 - SEISMIC ANALYSIS CONFORMANCE Existing seismic evaluations were reviewed and several loading cases identified where a seismic load was applied to the H4-H5 shroud cylinder by the mid-support of the core shroud repair. The resulting loads and stresses on the vertical weld repair clamps were evaluated and found to be acceptable.

PART 8.7 - ANNULUSFLOW DISTRIBUTION CRITERIA Analyses shall be performed to show that the repair design does not adversely affect the in-vessel flow characteristics in the downcomer annulus region.

PART 8.7.1 - ANNULUSFLOW DISTRIBUTION CONFORMANCE The evaluation of the effects of the repair clamp assembly on the flow in the reactor vessel downcomer region determined that:

~

The V4 repair clamp reduces the flow area in the downcomer at the top of the core shroud by approximately 2.5 percent.

The V9/V10 clamps would reduce the flow area by a lesser amount because they are positioned at a lower elevation where the downcomer flow area is greater.

~

The pressure drop associated with the V4 clamp is approximately 0.006 psid for normal operation and 0.044 psid for the recirculation line break condition. For the V9/V10 clamps, the pressure drop is less than for the V4 clamp.

The flow area restriction and pressure drop increase are concluded to have a negligible effect on the annulus flow distribution.

PART 8.8 - E<ME<RGE<NCY OPE<RATING PROCEDURE<S'<OPs'ALCULATIONS CRITERIA Inputs to the EOP calculations such as bulk steel residual heat capacity and reduction of reactor water inventory shall be addressed based on repair hardware mass and water displacement.

PART 8.8.1 - EME<RGENCY OPERATING PROCE<DURES' OPs'ALCULATIONS CONFORMANCE The weight for each repair clamp was determined.

For the V4, V9 and V10 clamps, the total weight is less than 1000 Ibs which is negligible compared to the total shroud weight.

The displaced reactor water inventory is less than two cubic feet which is also negligible.

These are negligible effects on the EOP calculations.

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PART 8.9 - RADIATIONE<F<FE<CTS ON REPAIR DESIGN CRITE<RIA The repair design shall consider the effects of radiation on materials and on radiation fluence induced relaxation of preloads.

PART 8.9.1 - RADIATIONEFFECTS ON REPAIR DESIGN CONFORMANCE The effects of radiation were considered in the selection of the repair materials and

'abrication processes.

As discussed in Part A.2.1, all materials used in the repair have been used successfully for years in the BWR environment.

Also, the effect of relaxation of the pin preload due to radiation fluence was considered in the preload selection.

PART 8.10 - THERMALCYCLES CRITERIA The repair analyses shall consider the plant thermal cycles over the remaining life as specified in Appendix A of Reference 2.

PART 8.10.1 - THE<RMALCYCLE<S CONFORMANCE The repair analyses show that the fatigue usages in the shroud and repair hardware are acceptable for the specified plant thermal cycles.

PART 8.11 - CHE<MISTRY/FLUX CRITERIA The repair design shall use materials which are suitable for use with the existing and anticipated reactor water chemistry control measures.

Any effects of neutron flux on materials used in the repair shall be considered.

PART 8.11.1-CHE<MISTRY/FLUX CONFORMANCE The 300 series and XM-19 materials selected for the repair are suitable for use with the existing and anticipated reactor water chemistry control measures.

The materials are not susceptible to general corrosion and are resistant to Intergranular Stress Corrosion Cracking (IGSCC) in a BWR environment. Also, the maximum radiation fluences will have no effect on repair material properties.

PART 8.12 - LOOSE PARTS CONSIDE<RATION DURING OPERATION CRITERIA The designed repair shall have features which ensure all parts are secured so as to prevent parts from becoming loose and entering the core or being carried into downstream systems.

PART 8.12.1 - LOOSE PARTS CONSIDERATION DURING OPE<RATION

~CC

'C MANC

'he various parts that make up the repair clamp assemblies are secured and restrained by appropriate locking devices such as locking cups and crimping. These locking device designs have been used successfully for many years in reactor internals.

Loose pieces cannot occur without failure of the locking devices or repair assembly components.

Such locking devices and the stresses in the parts which make up the repair clamps are well within allowable limits for all plant operating conditions. Ifany of the locking cup parts I

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were to fail, any of the parts which were subsequently released would have to pass through the recirculation pumps and lower reactor internals to reach the core. Large parts would not be able to pass through the recirculation pumps. Although not specifically analyzed, the consequences of the smaller parts would be consistent with the consequences of other postulated loose pieces.

PART 8.13 - INSPECTION ACCE<SS CRITERIA The design shall consider the followinginspection access requirements:

~

The repair hardware shall not adversely impact the access to other reactor internals, reactor vessel or ECCS components.

~

The repair hardware shall not interfere with refueling operations or other in-vessel activities.

~

The repair shall be removable as frequently as each outage without permanent damage to the repair components and/or existing internals.

~

Allrepair parts shall be readily removable and replaceable.

~

The repair design shall permit future inspection of the repair hardware per the requirements of Reference 5.

PART 8.13.1 - INSPECTION ACCESS CONFORMANCE The design of the repair is in conformance with all criteria listed in Part B.13 above based on the following:

~

The repair clamps have a low profile and fitsnugly against the cor'e shroud.

~

The repair clamps can be removed in a straightforward manner by reversing the installation steps discussed in Part A.1 above.

PART 8.14 - CREVICE< SCRITE<RIA The repair design shall be reviewed for crevices between repair components and between repair components and original structures to assure that criteria for crevices immune to stress corrosion cracking acceleration are satisfied.

PART 8.14.1 - CREVICES CONI ORMANCE The repair design has considered crevices and their impact on stress corrosion cracking by using materials which are highly resistant to Intergranular Stress Corrosion Cracking (IGSCC). The material's IGSCC resistance is verified by testing per requirements of ASTM A262 Practice E.

PART 8.15 - MATERIALS CRITE<RIA Allmaterials shall be in conformance with BWRVIP-02 (Reference

1) requirements.

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PART 8.15.1 - MATERIALS CONFORMANCE Allmaterials are used in conformance with BWRVIP-02 (Reference

1) requirements.

Specifically, all requirements for stainless steel materials as specified in BWRVIP-02 are met for the repair materials as discussed in Part A.2 above.

PART 8.16 - MAINTE<NANCE/INSPECTIONOF REPAIR HARDWARE

~CRITRRIA The designed repair shall minimize future inspections and maintenance of repair components and permit future inspection of the repair hardware.

PART 8.16.1 MAINTENANCE/INSPECTIONOF REPAIR HARDWARE CONFORMANCE Inspection of the repair clamps in future refueling outages willbe based on the requirements in Section 4.2 of BWRVIP-07 [5], "BWR Vessel Internals Project, Guidelines for Reinspection of Core Shrouds." The inspection willinvolve the visual inspection of the overall clamps and the threaded pin-to-eccentric and locking screw-to-eccentric crimp areas to confirm no change from their condition during the post-installation inspection PART 8.17 - IMPACTON TIE-ROD HORIZONTALWELD RE<PAIR

~CRITRRI The vertical weld repair shall not impact the core shroud tie-rod repair and the supporting safety, stress and seismic analyses (References 6, 7 and 8).

PART 8.17.1 - IMPACTON TIE-ROD HORIZONTALWE<LD RE<PAIR

~CONRORMANCR The safety, stress and seismic analyses for the core shroud tie-rod repair (References 6, 7 and 8) were reviewed and evaluated to determine ifthere is any impact from the vertical weld repair. Results of the review/evaluation are:

~

No specific discussion of requirements for the shroud vertical welds was found in References 6, 7 and 8. However, it is clear that the design and the analyses of the tie-rod repair are based on the shroud retaining a cylindrical configuration in the event of cracking in the vertical welds. Accordingly, the vertical weld repair is required to preserve the cylindrical shroud configuration for all applied loads and load combinations.

As identified in Part B.2 above, this is one of the functional requirements for the vertical weld repair.

~

No allowance for coolant leakage through cracked vertical welds is considered in the safety analysis for the tie-rod repair (Reference 6). Therefore, the vertical weld repair is required to limitvertical weld leakage, in combination with other leakage sources, to within acceptable levels for all plant conditions. This is a functional requirement for the vertical weld repair as stated in Part B.2 above.

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Per Reference 8, the seismic fuel loads are transmitted directly through the top guide or core support plate rings to the tie-rod radial restraints.

Therefore, it is the stiffness of these rings and not the stiffness of the shroud cylinders that affects the fuel seismic response.

~

For a shroud cylinder with fullycracked vertical welds and end conditions that provide no lateral shear restraint, the lateral stiffness would be reduced.

Since shroud stiffness is a parameter in the shroud seismic model, this reduction could impact the seismic analysis results.

However, this potential impact is not significant since for all of the seismic cases considered in Section 5 of Reference 8, the Hl-H2 and H4-H5 shroud cylinders have hinged connections to the adjacent cylinders. This hinged connection provides shear transfer between the shroud cylinders and permits the shroud cylinders to retain their uncracked moment of inertia and rotational stiffness.

Based on the above, the vertical weld repair has no impact on the tie-rod repair and the supporting safety, stress and seismic analyses.

PART C - CONCLUSIONS This safety evaluation has determined that the addition of vertical weld repair to the NMP-1 core shroud does not increase the probability of occurrence or consequences of an accident previously evaluated in the NMP-1 Updated Final Safety Analysis Report (UFSAR)(Ref. 4), does not increase the probability of occurrence or consequences of a malfunction of equipment important to safety evaluated previously in the UFSAR, does not create the possibility of an accident or malfunction of equipment important to safety of a different type evaluated previously in the UFSAR or reduce the margin of safety as defined in the basis for any technical specification. Therefore, it is concluded that the addition of a vertical weld repair does not constitute an unreviewed safety question.

PART D - REFERENCES

l. EPRI Report, "BWRVIPVessel and Internals Project, Core Shroud Repair Design Criteria (BWRVIP-02),"Revision 2, Fifth Draft Report, April 1988.

2. MPR Specification No. 249014-001, "Design Specification for Nine MilePoint Nuclear Station Unit 1 (NMP1) Core Shroud Vertical Weld Repair," Revision 2, December 28,1998.

1

3. ASME Boiler and Pressure Vessel Code,Section III,Division 1 - Subsection NG, "Core Support Structures,"

1989 Edition.

4. Nine MilePoint Nuclear Station Unit 1 Updated Final Safety Analysis Report, Revision 15, November 1997.

5. EPRI Report TR-105747, "BWR Vessel and Internals Project, Guidelines for Reinspection ofBWR Core Shrouds (BWRVIP-07)," February 1996.

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6. Nine MilePoint Unit 1 Safety Evaluation Number 94-080, Rev.

1 for Modification N1-94-003, Reactor Core Shroud Repair.

7. GENE-B13-01739-04, "Nine MilePoint Unit 1 Shroud Repair Hardware Stress Analysis (NMPC Calculation No. SO-,Vessel-M028),"

Revision 0.

8. GENE-B13-01739-03, "Nine MilePoint Unit 1 Nuclear Power Station, Seismic Analysis, Core Shroud Repair Modification (NMPC Calculation No. SO-Vessel-M027)," Revision 0.

9. MPR-1966, "Nine MilePoint Unit 1 Core Shroud Vertical Weld Repair Design Report," December 1998, Revision 1.

PART E< ATTACHME<NTS 1.

Figures 1-1 through 1-5.

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0

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Figure M NMP-1 Core Shroud%'clds

Shroud Locidng Screw "V4 Vertical Weld V4 Plate Cutout ln Shroud i Wall Left Bayonet Eccentric I

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Right Bayonet Eccentric Threaded Pin l99S NPR ASSOCIATES U.S. PATENT PENO9IC MMPR

/ Nl Oll 0$ IXI l0/N/N IMI Figure 1-2. Nine Mile Point - Unit 1 Exploded View of V4 Vertical Weld Clamp Assembly

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V4 Vertical Weld Locking Screw Shroud Right Bayonet Eccentric Left Bayonet Eccentric Threaded Pin lalMPR I ln only Ol/1$/l4 1ALI)

Figure 0-3. Nine MilePoint - Unit i Installed V4 Vertical Weld Clamp Assembly 1998 LIPR ASSOOAIES U.S. PA1ENr PEtlDNG

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Shroud V9/V10 'I/eNcal Weld I

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'all V9/V10 Plate Left Bayonet Eccentric Threaded Pin Aight Bayonet Eccentric LLMPR

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Figure 1R. Nine Mile Point - Unit 1 Exploded ViewofV9/V10 Vertical Weld Clamp Assembly l

998 IIPR ASSOCIATES U,S. PAIENr PENOINC

V4 Vertical Weld Shroud Locking Screw Right Bayonet Eccentric Left Bayonet Eccentric V9/Vt0 Plate Threaded Pin QMPR t I<0 Oll OI ot/ol/04 IMt Figure 1-5. Nine Mile Point - Unit 1 Installed V9/V10 Vertical Weld Clamp Assembly PC199S llPR ASSOCIAIES U.S. PATOll PEIIDIIIG

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