NuScale Power, LLC Response to NRC Request for Additional ... · TR-0716-50439-P, Rev. 0 shows the steam plenum region. The plenum tube sheet has penetrating holes where the top end

RAIO-1017-56539

NuScale Power, LLC1100 NE Circle Blvd., Suite 200 Corvalis, Oregon 97330, Office: 541.360.0500, Fax: 541.207.3928

www.nuscalepower.com

October 10, 2017 Docket No. 52-048

U.S. Nuclear Regulatory CommissionATTN: Document Control DeskOne White Flint North11555 Rockville PikeRockville, MD 20852-2738

SUBJECT: NuScale Power, LLC Response to NRC Request for Additional Information No.162 (eRAI No. 8901) on the NuScale Design Certification Application

REFERENCE: U.S. Nuclear Regulatory Commission, "Request for Additional Information No.162 (eRAI No. 8901)," dated August 11, 2017

The purpose of this letter is to provide the NuScale Power, LLC (NuScale) response to thereferenced NRC Request for Additional Information (RAI).

The Enclosure to this letter contains NuScale's response to the following RAI Questions fromNRC eRAI No. 8901:

03.09.05-103.09.05-203.09.05-303.09.05-403.09.05-503.09.05-603.09.05-703.09.05-803.09.05-903.09.05-1003.09.05-1203.09.05-1303.09.05-1403.09.05-1503.09.05-16

The response to question 03.09.05-11 will be provided by January 26, 2018.

This letter and the enclosed response make no new regulatory commitments and no revisions toany existing regulatory commitments.

RAIO-1017-56539



If you have any questions on this response, please contact Marty Bryan at 541-452-7172 or [email protected].

Sincerely,

Zackary W. RadDirector, Regulatory AffairsNuScale Power, LLC

Distribution: Gregory Cranston, NRC, OWFN-8G9ASamuel Lee, NRC, OWFN-8G9AMarieliz Vera, NRC, OWFN-8G9A

Enclosure 1: NuScale Response to NRC Request for Additional Information eRAI No. 8901

y,

Zackary W. Rad

RAIO-1017-56539



Enclosure 1:

NuScale Response to NRC Request for Additional Information eRAI No. 8901

NuScale Nonproprietary

Response to Request for Additional InformationDocket No. 52-048

eRAI No.: 8901Date of RAI Issue: 08/11/2017

NRC Question No.: 03.09.05-1

10 CFR 50 Appendix A GDC 1 requires that structures, systems, and components important tosafety be designed, fabricated, erected, and tested to quality standards commensurate with theimportance of the safety functions to be performed.

DCD Tier 2 Section 3.9.5 states that the reactor vessel internals (RVI) is comprised of severalsub-assemblies which are located inside the reactor pressure vessel (RPV). The RVI supportand align the reactor core system, which includes the control rod assemblies (CRAs), supportand align the control rod drive rods, and include the guide tubes that support and house the in-core instrumentation (ICI).

DCD Tier 2 Section 3.9.5 states that the RVI assembly is comprised of these subassemblies:

core support assembly (CSA)1.lower riser assembly2.upper riser assembly3.flow diverter4.pressurizer (PRZ) spray nozzles5.

DCD Tier 2 Section 3.9.5 Figures 3.9-2 to 3.9-4 provide basic sketch of the upper riserassembly, lower riser assembly and the core support assembly respectively. In these figures,multiple reactor internals components are referenced. TR-0716-50439-P, Rev. 0, “NuScaleComprehensive Vibration Assessment Program Technical Report” and TR-0916-51502-P, Rev.0 “NuScale Power Module Seismic Analysis” both provide more detailed figures of the reactorinternals assemblies.

However, the applicant did not provide a list of core support structures and reactor internalscomponents. SRP Section 3.9.5 area of review specifies the physical or design arrangementsof all reactor internals structures, components, assemblies, and systems, including thepositioning and securing of such items within the RPV, the provision for axial and lateralretention and support of the internals assemblies and components, and the accommodation ofdimensional changes due to thermal and other effects. SRP Section 3.9.5 Review procedurestates that the configuration and general arrangement of all mechanical and structural internal


elements covered by the SRP section are to be reviewed and compared to those of previouslylicensed similar plants.

Since NuScale is a first of a kind reactor that has a different reactor internals design than otherPWRs, similar plant experiences cannot be drawn to compare with the NuScale design. Therefore, the applicant is requested to provide a complete list and description of all RVIcomponents identifying which are core support structures and which are reactor internals, thepositioning and securing of these components within the RPV, and the provision for axial andlateral retention and support of these components.

NuScale Response:

The lists below indicate the code classifications for the parts and assemblies within the majorsub-assemblies referred to as the NuScale reactor vessel internals (RVI). The generalarrangement of the RVI sub-assemblies is shown in FSAR Tier 2 Figure 3.9-1. The upper riseris bolted to the bottom of the pressurizer baffle plate (discussed in response to RAI 8901Question 03.09.05-3) and is horizontally restrained by the steam generator tube supports thatare located between the upper riser and the reactor vessel wall. A small leg of piping runs fromthe CVCS injection nozzle in the RPV and into the upper riser, to return CVCS flow to the RCSsystem (shown in FSAR, Tier 2 Figure 5.1-2, labeled "RCS Injection"). The lower riserassembly, which is below the upper riser, sets on top of the core support assembly and issecured by the lock plate assemblies (discussed in response to RAI 8901 Question 03.09.05-5).The upper support blocks that are welded to the core barrel retain the two assemblies in thehorizontal direction. The core support assembly mounted to the bottom head of the RPV(discussed in response to RAI 8901 Question 03.09.05-8) supplies the primary support to thereactor core.

ASME Subsection NG Code Classification for RVI Components

Miscellaneous Code ClassificationFlow Diverter Internal StructurePressurizer Spray Nozzle Internal Structure


Surveillance Capsule Assembly Code ClassificationSpecimen Enclosure Internal StructureCapsule Basket Internal StructureSupport Internal StructureProtection Guide Internal StructureScrew Locking Caps Internal StructurePlugs, Dowel Pins, Screws Internal Structure

Upper Riser Assembly Code ClassificationUpper Riser Transition Internal StructureUpper Riser Section Internal StructureRiser Backing Strips Internal StructureUpper Riser Hanger Ring and Braces Internal StructureHanger Threaded Structural Fastener Internal StructureUpper Riser Hanger Alignment Pins Internal StructureUpper Riser Hanger Washers Internal StructureCVCS injection piping and support Internal StructureUpper CRD Shaft Supports Internal StructureUpper Riser Bellows Internal StructureCVCS Injection Piping and Supports Internal StructureCVCS Injection Flexible Pipe Assembly Internal StructureIn-Core Instrumentation (ICI) Guide Tubes Internal StructureICI Centering Plate Internal Structure


Lower Riser Assembly Code ClassificationUpper Core Plate Core SupportLower Riser Section Internal StructureLower Riser Transition Internal StructureLower Riser Spacer Internal StructureLower Riser Trunnion Internal StructureICI Guide Tube Support Internal StructureICI Guide Tubes Internal StructureICI Guide Tube Bottom Flags Internal StructureCRA Guide Tube Support Plate Internal StructureCRA Guide Tube Assemblies (guide tube, cards, lower flange, CRD shaftalignment cones) Internal Structure

Fuel Pins Core SupportFuel Pin Caps Core Support

Core Support Assembly Code ClassificationCore Barrel Core SupportReflector Blocks Core SupportLower core Plate Core SupportReflector Block Alignment Pins Core SupportUpper Support Blocks Core SupportShared Fuel Pins and Nuts Core SupportLocking Plates Core SupportSpacers Internal StructureSpherical Bearing Internal StructureCheck Ball Retainer Internal StructureLocking Belleville Washers Internal StructureSet screws Internal StructureNuts, Washers, Studs Core SupportUpper and Lower Seismic Belleville Washers Core SupportSeismic Belleville Retaining Pin Core SupportSeismic Belleville Washer Retaining Nut Core Support


Impact on DCA:There are no impacts to the DCA as a result of this response.






DCD Tier 2 Section 3.9.5.1 provides a brief description of the RVI assembly. The CSA islocated near the bottom of the RPV, below the RPV flange. Above the CSA are the lower riserassembly and upper riser assembly.

TR-0716-50439-P, Rev. 0, “NuScale Comprehensive Vibration Assessment Program TechnicalReport” further provides detail of the RVI assembly and description of the steam generator andpressurizer, which are located inside and above the upper riser assembly respectively. Specifically, details are provided regarding the steam plenum and the pressurizer baffle plate,in which the pressurizer baffler plate forms plenum tube sheet which allows the steam to travelthrough on the secondary side. This report also provides detail of the steam generator tubeinlet flow restrictors and mounting plate, the helical steam generator tube bundle, and the steamgenerator support bars that provide structural integrity for the tube bundle. However, it isunclear to the staff where is the jurisdiction of boundary, or classification break for the reactorinternals relative to the steam generator, pressurizer and RPV. Therefore, the applicant isrequested to provide detailed explanation at locations in which the jurisdiction for componentsthat are categorized as reactor internals end and explain the design code/standard for thesecomponents where the transition takes place. For instance, Figure 2-5 of the reportTR-0716-50439-P, Rev. 0 shows the steam plenum region. The plenum tube sheet haspenetrating holes where the top end of the tube bundles end. The categorization (reactorinternals or pressure boundary) and design code/standard for the plenum tube sheet design isunclear to the staff.

The same conclusion can be drawn for other components inside the RPV. In a traditional PWR,all the components inside the reactor vessel are considered reactor internals (either coresupport or internal structure) with the exception of the CRDM, fuel elements, andinstrumentation. However, due to the integrating nature of the NuScale design, the staffrecognizes that this historical jurisdiction of boundary may no longer be true for the NuScale


design. Nevertheless, there are components inside the NuScale RPV that don’t seem toperform functions that would otherwise have deemed to be part of the reactor internalscomponents. For instance, the steam generator tube support bars and lower tube supportcantilevers are such components. Therefore, the applicant is requested to provide a list ofcomponents (and provide detail drawings if they are not already available to the staff in eitherthe DCD or the reports TR-0716-50439-P, Rev. 0 and TR-0916-51502-P, Rev.0) of thecomponents that are inside of the RPV but are not considered as part of the reactor internals. In addition, the applicant is requested to provide the design code/standard for thesecomponents and clearly explain where the jurisdiction is. For pressure boundary components,provide the ASME design code/standard at such locations.

NuScale Response:

The designations for the components internal to the reactor vessel (RPV) are given below.There are no separate jurisdictional boundaries for components in the pressurizer or steamgenerator (SG) region of the NuScale module. In the context of the ASME code, the steamgenerator (including tube support structures) and pressurizer are fully integral to the RPV; thesethree items are designed as a single ASME component. Other ASME components that arecontained within the volume of the RPV reactor coolant pressure boundary (RCPB) arejurisdictionally part of the Reactor Vessel Internals (RVI) component, with the exception of thecontrol rod drive (CRD) shafts which are jurisdictionally part of the control rod drive mechanism(CRDM) component. The only other items contained within the RPV volume are the fuel, controlrod assemblies (CRAs), and various instruments (e.g. In-core Instrumentation strings) which arenot addressed in this response. The code classification of “Reactor vessel internals”components (e.g. upper and lower riser, core supports, etc.) is discussed in the response to RAI8901 Question 3.09.05-1.

The integral steam plenum, including the sections that make up the SG tube sheets andpressurizer baffle plate, as shown in FSAR Tier 2, Figure 5.4-3, Figure 5.4-4 and in the NuScaleComprehensive Vibration Assessment Program (CVAP) Technical Report, TR-0716-50439,Figure 2-5, are designed in accordance with ASME BPVC, Section III, Subsection NB. Thefeedwater plenum, including the tube sheets, (FSAR Tier 2, Figures 5.4-3 and 5.4-5) aredesigned in accordance with ASME BPVC, Section III, Subsection NB. Both the integral steamplenum and the feedwater plenums form part of the RCPB. The integral steam plenum and thefeedwater plenum are best understood as being separate regions of the RPV component.

The core support blocks (NuScale CVAP Technical Report, TR-0716-50439, Figure 2-22)welded to the RPV are structural attachments to the RPV providing core support. The coresupport blocks are part of the RPV component and are designed in accordance with ASMEBPVC, Section III, Subsection NB. As "structural attachments" the core support blocks do notdirectly form part of the RCPB.


The steam generator tubes (FSAR Tier 2, Figures 5.4-1 and 5.4-2), are part of the RCPB andare designed in accordance with ASME BPVC, Section III, Subsection NB. The SG flowrestrictors and associated hardware (mounting plates, bolts, nuts, spacers, studs, etc.) asshown in the NuScale CVAP Technical Report, TR-0716-50439 Figure 2-8 and FSAR Tier 2Figure 5.4-8) are non-pressure boundary items and are not inside or integral to the RPCB andtherefore are not “reactor internals.” As discussed, the SG tubes and flow restrictors arejurisdictionally part of the RPV component.

The SG tube supports (including, upper tube support bars, and lower tube support cantilevers,and tube support bar assemblies (FSAR Tier 2, Figures 5.4-6 and 5.4-7, and NuScale CVAPTechnical Report, TR-0716-50439, Figures 2-9, 2-10, and 2-11) are a “structural attachment” tothe RPV (see NB-1132.1(b)(2)(-b) Subsection NB, ASME BPVC Section III). The SG tubesupports do not form part of the RCPB. The code classification boundary (NG to NB) betweenthe SG tube supports and the RCPB portion of the RPV is at the weld between the upper tubesupport bars and RPV shell/integral steam plenum and at the weld between the lower tubesupport cantilevers and the RPV shell. The SG tube supports are designed as internalstructures (ASME BPVC, Section III NG-1122 of Subsection NG, “Core Support Structures"). Asdiscussed the SG tube support structures are jurisdictionally part of the RPV component.

The table below summarizes the code classification and jurisdictional boundaries forcomponents inside of the RPV that are not considered part of the reactor vessel internals. Thecode classification and jurisdictional boundaries for the reactor vessel internals is discussed inthe response to RAI 8901 Question 3.09.05-1.


Part CodeClassification Figures/Drawing Notes

Integral SteamPlenum(including SG tubesheets andpressurizer baffleplate)

ASME SubsectionNB

FSAR Tier 2 Figures5.4-3 and 5.4-4,TR-0716-50439 Figure2-5

Jurisdictionally part ofRPV component. Formspart of RCPB.

Feedwaterplenum(including SGtube sheets)

ASME SubsectionNB FSAR Tier 2 Figure 5.4-5

Jurisdictionally part ofRPV component.Forms part of RCPB.

Core Support Blocks ASME SubsectionNB

TR-0716-50439 Figure2-5

Jurisdictionally part ofRPV component.

SG Tubes ASME SubsectionNB

FSAR Tier 2, Figures5.4-1 and 5.4-2

Jurisdictionally part ofRPV component.Forms part of RCPB

SG Flow restrictors N/AFSAR Tier 2 Figure 5.4-8and TR-0716-50439Figure 2-8

Non-pressure boundary,not “reactor internals”

SG Tube supportsASME SubsectionNG, internalstructure

FSAR Tier 2, Figures5.4-6 and 5.4-7,TR-0716-50439, Figures2-9, 2-10, and 2-11

Jurisdictionally part ofRPV component. Codeclassification boundaryat weld to RCPB portionof RPV component.







DCD Tier 2 Section 3.9.5.1 states that the upper riser assembly is located immediately abovethe lower riser assembly and extends upward to the pressurizer baffle plate. The upper riserchannels the reactor coolant leaving the core upward through the central riser and permits thereactor coolant to turn in the space above the top of the riser and below the pressurizer baffleplate, the reactor coolant then flows downward through the annular space outside of the riserand inside of the RPV where the steam generator helical tube bundles are located.

TR-0716-50439-P, Rev. 0, “NuScale Comprehensive Vibration Assessment Program TechnicalReport” provides more detailed explanation of the upper riser assembly. The upper riser sectionis supported by the steam generator plenums and the lower riser assembly. The upper risersection itself is an open cylinder than allows reactor coolant to flow through it. This reportfurther explains that a friction joint is located at the junction between the upper riser assemblyand the lower riser assembly. This friction joint is required to separate to allow disassemblyduring refueling. A gap exists between the friction joint and the lower riser assembly. Thisreport also explains that an upper riser hanger brace connects the upper riser section to thepressurizer baffle plate. Fasteners are used to attach the hanger ring to the baffle plate.

In order for the staff to make a safety finding, the following information is requested from theapplicant:

Provide detailed design description, including drawing, of the upper riser hanger brace and1.explain how the hanger brace is connected to the upper riser assembly and the pressurizerbaffle plate, its classification, and its design code/standard. Provide detailed designdescription of the fasteners used.Provide detailed design description, including drawing, of the slip joint and explain how the2.slip joint is connected to the upper riser assembly, its classification, and its designcode/standard.


Provide detailed design description, including drawing, of the upper riser supports that are3.used to support the in-core instrument guide tubes and control rod drive shafts, itsclassification, design/standard and means in which these supports are attached to theupper riser.

DCD Tier 2 Section 3.9.5.1 states that the upper riser assembly hangs from the pressurizerbaffle plate. It also states that the upper riser assembly is supported from the RPV integralsteam plenum (e.g. below the bottom of the pressurizer). The applicant is requested to providedetailed description, including the point of attachment, of how the upper riser hangs from thepressurizer baffle plate as stated in DCD Tier 2 Section 3.9.5.1.

NuScale Response:

Addressing the individual information requests:

1. The general arrangement of the upper riser hanger assembly is shown in FSAR Tier 2Figure 3.9-2. A detailed depiction of the upper riser hanger assembly is shown inNuScale Comprehensive Vibration Assessment Program (CVAP) Technical ReportTR-0716-50439, Figure 2-15. This assembly includes a "hanger ring" with welded bracesconnecting it to the upper riser section. The braces are welded to the upper riser section.The attachment of the hanger ring to the bottom of the pressurizer baffle plate is bythreaded fasteners as shown in NuScale Power Module (NPM) Seismic AnalysisTechnical Report TR-0916-51502, Figure C-15. The upper riser hanger threadedfasteners are 304 SS as shown in FSAR, Tier 2 Table 4.5-2. The fasteners are shown inTR-0916-51502 Figure C-15, and are the same configuration as standard socket headcap screws. The components in the upper riser assembly are classified as ASMESubsection NG internal structures and are designed using NG-3000 as a guide.

2. The slip joint is the connection (interface) between the upper and lower riserassemblies. This joint is shown in NuScale CVAP Technical Report TR-0716-50439,Figure 2-13 and the NPM Seismic Analysis Technical Report TR-0916-51502, FigureC-18. This conical shaped interface is maintained closed by force exerted by a bellowsassembly in the upper riser (discussed in response to RAI 8901 Question 03.09.05-4).The upper riser and the lower riser transition that form this interface are both classifiedas ASME Subsection NG internal structures and are designed using NG-3000 as aguide.

3. A general depiction of the ICI guide tube and CRD shaft supports that are internal tothe upper riser is shown in FSAR Tier 2 Figure 3.9-2. There are a total of five supports(common to both CRD shafts and ICI guide tubes) that are welded to the inside of theupper riser shell. More detail of the support design is shown in NuScale NPM SeismicAnalysis Technical Report TR-0916-51502, Figure 4-7 and Figure C-20. The five


supports are generically referred to as control rod drive shaft supports, however each ofthe supports also includes holes to support the in-core instrument guide tube. Thesupports are part of the upper riser assembly and are classified as ASME subsection NGinternal structures and are being designed using NG-3000 as a guide.

The attachment of the upper riser (via upper riser hanger assembly) to the pressurizer baffleplate is discussed in the response to item 1 above.







DCD Tier 2 Section 3.9.5.1 states that there is a bellows assembly in the lower portion of theupper riser to provide added flexibility in the vertical direction to accommodate circumstancesthat involve sufficient thermal growth to close the vertical gap between the upper and lower riserassemblies.

The applicant is requested to provide detailed design description, including drawing, of thisbellows assembly in the lower portion of the upper riser and explain how it is connected to theupper riser assembly, its classification, and its design code/standard.

The applicant is also requested to describe the vertical gap that exists between the upper riserassembly and the lower riser assembly and how this vertical gap is affected under normaloperating conditions and Level D condition such as a SSE.

Furthermore, if the upper riser assembly is not physically attached to the lower riser assembly, itwould mean that the upper riser assembly is only attached to the pressurizer baffle plate at thetop of the upper riser, and thus, the upper riser assembly essentially behaves like a verticalcantilever attached at the top. The applicant is requested to provide more detailed explanationabout this design, and what is the mechanism to prevent the upper riser assembly fromswinging laterally during all service level conditions and how this affects the structural integrityof the in-core instrumentation guide tubes and the control rod drive shafts.

NuScale Response:

The bellows is part of the upper riser assembly as shown in FSAR Tier 2 Figure 3.9-2. Thebasic configuration of the bellows is also shown in NPM Seismic Analysis Technical Report


TR-0916-51502, Figure C-19. The approximate location is a few inches above the conestructure at the base of the upper riser. This location can be seen in NuScale ComprehensiveVibration Assessment Program (CVAP) Technical Report TR-0716-50439, Figure 2-14. Theupper riser assembly, including the bellows, is classified as an "internal structure" and isdesigned using Subsection NG as a guide. In the cold condition, the bellows appliesapproximately 500 lbs. to the lower riser interface. Final design of the bellows is not yetcomplete. Consequently, the bellows figures are illustrations. The reference in the FSAR to agap was for an earlier design configuration before the leakage flow was evaluated and found notto be acceptable. The referenced gap no longer exists. FSAR Tier 2 Section 3.9.5.1 has beenupdated with the current configuration.

The cone shaped interface between the upper and lower risers is described in NuScale CVAPTechnical Report TR-0716-50439, Paragraph 2.3.3.2, and shown in TR-0716-50439 Figure2-13. An additional detail is shown in NPM Seismic Analysis Technical Report TR-0916-51502,Figure C-18. Under normal conditions the lower riser provides vertical and lateral support for theupper riser at this interface.

The annulus between the upper riser and the vessel wall contains the steam generator tubesand the tube supports. An overview of this area is shown in FSAR Tier 2 Figure 5.4-2 and NPMSeismic Analysis Technical Report TR-0916-51502, Figure C-1. Additional details are shown inFigures C-11, C-12 and C-13 of the TR-0916-51502. The upper riser is supported radially by thesteam generator tube supports. The tube supports are stacked to provide radial support to theupper riser. At the base of the steam generator, there are eight SG lower tube support cantileverbeams that are part of the steam generator tube support structure, shown in NPM SeismicAnalysis Technical Report TR-0916-51502, Figure C-11 and FSAR Figure 5.4-6. Thesecantilever supports limit extreme motion of the upper riser.

A control rod drive shaft alignment drop test (discussed in FSAR Tier 2 Section 1.5.1.12) is tobe conducted to determine the displacement limits for the control rod drive shaft supports. Forclarification, the support for the in-core instrumentation (ICI) guide tubes and the control roddrive shafts are the same structure.

Impact on DCA:Tier 2 FSAR Section 3.9.5.1 has been revised as described in the response above and as shown in the markup provided with the response to question 03.09.05-12.






DCD Tier 2 Section 3.9.5.1 states that the lower riser assembly includes the lower riser, uppercore plate, CRA guide tubes, CRA guide tube support plate and ICI guide tube supportstructure. The lower riser assembly is located immediately above the CSA and is aligned withand supported on the CSA by four upper support blocks.

TR-0716-50439-P, Rev. 0, “NuScale Comprehensive Vibration Assessment Program TechnicalReport” provides a more detailed explanation of the lower riser assembly and provides a moredetailed figure of the lower riser assembly.


Provide detailed design description, including drawing, of the CRA guide tube support1.plate, its classification, design code/standard, and the means in which it is attached to thelower riser.Provide detailed design description, including drawing, of the CRDS support structure, its2.classification, design code/standard, and the means in which it is attached to the lowerriser and CRA guide tube support plate.Provide detailed design description, including drawing, of the ICI guide tube support3.structure, its classification, design code/standard, and the means in which it is attached tothe lower riser.Provide detailed design description, including drawing, of the upper core plate and fuel4.pins, its classification, design code/standard.DCD Tier 2 Section 3.9.5.1 briefly states that the upper core plate is attached to the bottom5.of the lower riser by lock plate assemblies. Provide detailed design description, includingdrawing and its design code/standard, of this lock plate assembly.Provide detailed explanation of the load transfer as briefly described in the report6.


TR-0716-50439-P.

NuScale Response:

Detailed design information for the NuScale Reactor Vessel Internals - Lower Riser and ReactorVessel Internals - Core Support was made available for NRC audit.

1. The control rod assembly (CRA) guide tube support plate is a grid structure with circularopenings for the CRA guide tubes. Four equally spaced lugs extend to the ring at the top of thelower riser and are welded at these locations. The CRA guide tube support plate is classified asan internal structure but is designed using Subsection NG as a guide. An isometric view of theCRA guide tube support plate can be seen as part of Figure 2-16 in NuScale ComprehensiveVibration Assessment Program (CVAP) Technical Report TR-0716-50439.

2. & 3. The control rod drive shaft (CRDS) support structure is a grid structure as shown inNuScale CVAP Technical Report TR-0716-50439, Figure 2-16. This structure is also called thein-core instrumentation (ICI) guide tube support; see FSAR Tier 2 Figure 3.9-3. Both functionsare performed by the same structure. The CRDS support structure is welded in eight locationsto the lower riser transition (conical shape), located at the top of the lower riser assembly. TheCRDS support structure is classified as an internal structure and similar to the CRA guide tubesupport plate is being designed to Subsection NG as a guide. The use of the acronym CRDShas been corrected to CRD shaft since CRDS is used in other locations as the control rod drivesystem. This edit has been implemented consistently throughout the FSAR. See the NuScaleresponse to NRC Request for Additional Information No. 58 (eRAI No. 8835).

4. The upper core plate is the base of the lower riser and has square openings that contain thefuel pins. This is shown in the NuScale NPM Seismic Analysis Technical ReportTR-0916-51502, Figure 2-6. The fuel pin is inserted from the bottom with a special nutconfiguration, which fits in a counter bore, on the top of the upper core plate. This special nut isan internally threaded cylinder with wrench flats and a rounded top, and is called the fuel pincap. It functions as the alignment pin for the lower flange on the CRA guide tube. The uppercore plate and fuel pins are classified as core support structures and are designed perSubsection NG.

5. The lock plate assemblies fit through the slots in the tab on the upper core plate. The slotsare shown in FSAR Tier 2 Figure 3.9-3, and the lock plate assemblies in NuScale NPM SesimicAnalysis Technical Report TR-0916-51502, Figure 2-6 and CVAP Techncial ReportTR-0716-50439, Figure 2-18. When rotated, the lock plate assemblies are held in position byball detents. The load-carrying parts of the assembly are classified as core support structuresand the ball detent components are internal structures.

6. Detail load path information is shown in NuScale NPM Seismic Analysis Technical Report


TR-0916-51502, Figure 2-7.







DCD Tier 2 Section 3.9.5.1 states that there are 16 CRA guide tubes that are attached to theupper core plate and extend upward to the CRA guide tube support plate. These guide tubeshouse the portion of the CRAs that extend above the top of the reactor core.

TR-0716-50439-P, Rev. 0, “NuScale Comprehensive Vibration Assessment Program TechnicalReport” provides a more detailed explanation of the CRA guide tubes. Specifically, each CRAguide tube consists of 4 CRA cards, a CRA lower flange and an alignment cone. All of thesecomponents are welded to the CRA guide tubes.

The applicant is requested to provide the detailed design, including drawing, of the CRA guidetubes including the guide tube’s internal mechanism such as guide cards and continuoussection, if applicable, its classification and the design code/standard. Provide the means whichthe guide tubes are attached to the CRA guide tube support plate and the upper core plate. Iffasteners or split pins are used, the applicant is requested to provide detailed designdescription, including drawing, of these components, their classification and designcode/standard.

The applicant is also requested to provide information on the relative location of a control rodrelative to a guide tube when the control rod is at its fully inserted and fully withdrawn positions.

NuScale Response:

Detailed design information for the NuScale Reactor Vessel Internals - Lower Riser Assemblywas made available for NRC audit. This information provided the details and assembly of theguide tubes and how they are configured in the lower riser assembly.


The control rod assembly (CRA) guide tube, as shown in the NuScale Comprehensive VibrationAssessment Program Technical Report TR-0716-50439, Figure 2-17, consists of a hollowcylinder with slots for the CRA cards that are welded to the cylinder. A CRA alignment cone,with an internal taper, is welded at the top of the cylinder. A CRA lower flange, containing tabswith alignment holes, is welded to the bottom of the cylinder. The holes in the lower flange fitover the fuel pin caps (nut for fuel pins), and the flange sets on the upper core plate. The top ofthe CRA guide tube assembly fits into a counter bore, with a slip fit, in the lower side of the CRAguide tube support plate. The CRA guide tube is classified as an internal structure but is beingdesigned per Subsection NG as a guide. The following figure shows the CRA in the fullywithdrawn and fully inserted position.







DCD Tier 2 Section 3.9.5.1 states that an ICI guide tube support structure is located inside thelower riser to support and align ICI guide tubes with their respective fuel assemblies. Figure3.9-3 shows a typical ICI guide tube.

The applicant is requested to provide detailed description, including drawing, of the ICI guidetubes, its classification and design code/standard. In addition, the applicant is requested todescribe the means at which the ICI guide tubes are attached to the ICI guide tube supportplate, the CRA guide tube support plate and the upper core plate.

NuScale Response:

The NuScale reactor design includes twelve incore instrument (ICI) guide tubes that have a 1.00inch OD tube with a 0.188 inch wall. The ICI guide tubes in the RPV are divided into fourseparate segments to facilitate assembly/dis-assembly of the NPM. There is a segment from theinstrument seal assemblies on the RPV head, through the pressurizer region, to the baffle plateat the base of the pressurizer, terminating in a slip fit. The next segment is connected to theunderside of the hanger plate (the top of the upper riser) with a socket weld. This segmentextends through the length of the upper riser. Within the upper riser, each ICI guide tube issupported by the five control rod drive shaft supports (labeled "CRA drive shaft support" inFSAR Figure 3.9-2). Note that the ICI guide tube support shares a common grid supportstructure with the control rod drive shaft support. The interface between the ICI guide tube andthe CRD shaft support grid structure is a clearance/slip fit; there is no welding or expansion ofthe guide tubes at this interface.

The third segment of each ICI guide tube spans the height of the lower riser as shown in FSAR


Figure 3.9-3. The top end of this segment fits in the socket (counter bore) in the lower side ofthe ICI guide tube support (shown in FSAR Figure 3.9-3), at the top of the lower riser assembly.The tube is a slip/clearance fit in the ICI guide tube support at this location to allow for thermalexpansion. Note that the ICI guide tube support and control rod drive shaft support are the samegrid structure at this location. An isometric view of this assembly is shown in NuScaleComprehensive Vibration Assessment Program Technical Report TR-0716-50439, Figure 2-16.The ICI guide tubes do not make contact with the control rod assembly (CRA) guide tubesupport plate shown in the TR Figure 2-16. The bottom end of these guide tube segments arewelded to a short cruciform shape at the bottom (below upper core plate) for centering in thesquare openings in the upper core plate (bottom of the assembly). The cruciform shape at thebottom of the tube is then welded to the square opening in the upper core plate (the base of thelower riser assembly). The cruciform shapes are for alignment with the fourth segment of theguide tubes.

The upper three ICI guide tube segments are classified as "internal structures" in accordancewith NG-11222(c) and are being designed using Subsection NG as a guide.

The fourth segment of each ICI guide tube, the instrument tube, is part of the fuel assemblies.See FSAR Section 4.2 for information/discussion about the instrument tube.







DCD Tier 2 Section 3.9.5.1 states that the core support assembly includes the core barrel,upper support blocks, lower core plate, lower fuel pins and nuts, reflector blocks, lock plateassembly, lower core support lock inserts, and the RPV surveillance specimen capsule holderand capsules. The core barrel is a continuous ring with no welds. The upper support blocks,which are welded to the core barrel, serve to center the core barrel in the lower RPV. One ofthe upper support blocks engages a core barrel guide feature on the lower RPV to providecircumferential positioning of the core barrel as it is lowered into the lower RPV. The lower coreplate, which is welded to the bottom of the core barrel, serves to support and align the bottomend of the fuel assemblies. Locking devices align and secure the lower core plate to the coresupport blocks located on the RPV bottom head. TR-0716-50439-P, Rev. 0, “NuScaleComprehensive Vibration Assessment Program Technical Report” provides a brief descriptionof each of the major components for the CSA.


1. Provide detailed design description, including drawing, of the core barrel, its classificationand design code/standard. Both DCD Tier 2 Figure 3.9-4 and report TR-0716-50439-PFigure 2-18 show the top of the core barrel to have the shape of a castle nut, but it is unclearto the staff how the top of the core barrel is fitted with the bottom of the lower riser assembly. The applicant is requested to describe how the lower riser assembly fits onto the core barrel,and what mechanism is there to align these two components.


2. Provide detailed design description, including drawing, of the upper support blocks, itsclassification, design code/standard and the number of upper support blocks that are weldedon the core barrel. DCD Tier 2 Section 3.9.5.1 states that one of the upper support blocksengages a core barrel guide feature on the lower RPV to provide circumferential positioningof the core barrel as it is lowered into the lower RPV. It is unclear to the staff why only oneupper support block is engaged. In addition, the applicant is requested to provide detaileddesign description, including drawing, of the core barrel guide feature on the lower RPV thata upper support block is engaged to when the core barrel is at its normal operation position,its classification and design code/standard.

3. Provide detailed design description, including drawing, of the lower core plate, itsclassification and design code/standard. The applicant is also requested to describe whatkind of locking devices are used to align and secure the lower core plate to the core supportblocks. DCD Tier 2 Figure 3.9-4 shows two inverted pins at the bottom of the lower coreplate, while report TR-0716-50439-P Figure 2-22 shows two pins that are located at the topof the core support block. Figure 2-18 also shows a lower core support lock insert and lockplate assembly. The applicant is requested to provide detailed design description, includingdrawing, of this lock plate assembly and the corresponding lock inserts/pins, how theyfunction, their classification and design code/standard.

4. Provide detailed design description, including drawing, of the core support blocks, itsclassification and design code/standard. Specify the number of core support blocks and themechanism at which they are attached to the RPV bottom head. Specify under whichconditions, if not all conditions, at which the core support blocks directly support the core. Insome large light water PWRs, a spring like structure is built in at the bottom of the reactorvessel to absorb the impact load from a beyond design basis core drop event so the bottomof the reactor vessel would not be damaged, provide detail description that in such event,how the core support blocks would prevent the CSA assembly from dropping to the bottom ofthe RPV bottom head.

5. Provide detailed design description, including drawing, of the reflector blocks, itsclassification and design code/standard. DCD Tier 2 Figure 3.9-4 and reportTR-0716-50439-P Figure 2-18 both show that there are 6 levels of reflector blocks attachedto each other with alignment pins. Provide detailed design description, including drawing,of these reflector block alignment pins, how they function, their classification and designcode/standard. In addition, provide detailed description on how the reflector blocks areattached and secured to the core barrel.

6. Provide detailed design description, including drawing, of the fuel pins and nuts at the lowercore plate, its classification and design code/standard.

7. Provide detailed design description, including drawing, of the surveillance capsule holdersand capsules, their classification and design code/standard. The applicant is also requestedto specify the number of surveillance capsule holders and the mechanism at which they areattached to the core barrel. If fasteners and dowel pins are used, provide detailed designdescription of such, their classification and design code/standard.


NuScale Response:

The NuScale reactor design includes a core support assembly (CSA). Details of thecomponents that comprise the CSA are as follows:

1. The core barrel is a cylindrical shell, with eight cutouts at the top which facilitate alignmentand coupling with the lower riser assembly. Eight tabs extend radially from the perimeter of theupper core plate (bottom of lower riser assembly) and fit into cutouts at the top of the corebarrel; the tabs can be seen in FSAR Tier 2 Figure 3.9-3, which shows an overhead (plan) viewof the lower riser assembly. The outer diameter of the upper core plate fits inside the corebarrel. Four of the eight tabs are used only for circumferential alignment, while four of the tabsprovide alignment, but also include a cutout to mechanically couple the lower riser to the corebarrel via the locking mechanism that is part of the upper support blocks (discussed below). SeeNuScale Power Module (NPM) Seismic Analysis technical report TR-0916-51502, Figure C-17for this configuration. The core barrel is classified as an ASME Subsection NG core supportstructure.

2. There are four upper support blocks welded to the core barrel, spaced at 90 degree intervals.The upper support blocks configuration can be seen in NuScale TR-0916-51502, Figures 2-6,C-10 and C-17. The blocks are classified as core support structures because they transferhorizontal loads to the pressure vessel wall (shown in TR-0916-51502, Figure C-10). One of thefour upper support blocks functions to circumferentially align the core barrel during assembly(via a guide feature discussed below). The blocks are approximately 2 feet tall and 10 incheswide and fill the space between the core barrel and the reactor pressure vessel. The 10 inchwidth tapers down to a large radius at the bottom. This taper interfaces with NPM liftingequipment used during module assembly and dis-assembly. The top of each block includes alocking mechanism to couple the core support assembly to the lower riser. The upper supportblocks are classified as ASME Subsection NG core support structures.

The purpose of the guide feature on the reactor pressure vessel wall is to assure that the coresupport assembly is properly oriented within the reactor pressure vessel. There is a single guidefeature, therefore only one upper support block performs this orientation function; one of thefour upper support blocks has notches on the upper portion of the taper so that it can slide intothe alignment feature. The four lugs on the lower core plate (shown in FSAR Tier 2 Figure 3.9-4)perform the circumferential alignment and support function for the core support assembly basedon its interface with the core support blocks (shown in Technical Report TR-0916-51502, FigureC-9). The guide feature on the reactor pressure vessel wall consists of two rectangular bars,1.25 x 1.75 x 40 inches, placed approximately 8 inches apart and bent at the top to generate alead-in. There are notches in the outer corners of the upper support block for clearance.Because there is a possibility that the support block may apply a load during a seismic event,the guide feature hardware is classified as an ASME Subsection NG core support structure and


the weld to the vessel wall is part of the vessel. The figure below indicates the approximateposition of the upper support block during normal operation.

3. The lower core plate is a circular plate with a grid of square cutouts located at the base of thecore support assembly. A plan view of the grid cutout section of the lower core plate is shown inFSAR Tier 2 Figure 3.9-4 and additional views of the lower core plate are provided in NuScalePower Module (NPM) Seismic Analysis Technical Report TR-0916-51502, Figure 2-6 andNuScale Comprehensive Vibration Assessment (CVAP) Program technical reportTR-0716-50439, Figure 2-18.

FSAR Tier 2, Figure 3.9-4 has recently been updated (see NuScale Power, LLC Submittal ofChanges to Final Safety Analysis Report, Sections 3.9, Mechanical Systems and Components,4.5, Reactor Materials, and 5.2, Integrity of Reactor Coolant Boundary, dated July 20, 2017); theinverted pins identified in this RAI 8901 question have subsequently been removed from theNuScale design. Likewise, the NuScale CVAP technical report TR-0716-50439 Figure 2-22 hasbeen updated to reflect the current lower core plate design. The updated CVAP TR-0716-50439Figure 2-22 markup will be provided with the response to RAI 8884.

An extension from each of the core support blocks locate and secure the lower core plate usingthe Belleville retainer nut as shown in the Seismic Analysis TR-0916-51502, Figure C-9.TR-0916-51502 Figure C-9 has been revised to show this mounting configuration (see theresponse to RAI 8911 for the markups associated with this Figure C-9 revision. The lower coreplate is classified as an ASME subsection NG core support structure.

4. There are four core support blocks welded to the bottom head of the reactor pressure vessel.Each core support block houses a stack of Belleville washers that support the core supportassembly. Although the core support blocks perform a core support function, they arejurisdictionally part of the reactor pressure vessel and are designed and fabricated inaccordance with ASME Subsection NB. This mounting configuration is shown in NPM Seismic


Analysis Technical Report TR-0916-51502, Figure C-9. The core support blocks directly supportthe core under all service level conditions. The core support assembly is secured to the coresupport blocks at all times, and therefore, the core barrel is not suspended from the RPV headflange.

5. The heavy reflector is composed of a stack of blocks as shown in FSAR Tier 2 Figure 3.9-4.Each block is a circular plate with a stepped cutout that matches the perimeter of the fuel. Thestack of reflector blocks are not fastened or physically connected to the core barrel. Each blockcontains cooling channels; the cooling channels are labeled as "flow holes" in FSAR Figure3.9-4. The blocks are located with respect to each other by alignment pins; pins are also shownin Figure 3.9-4. Likewise, the bottom reflector block is aligned with the lower core plate byalignment pins. These pins only perform an alignment function but may be loaded during aseismic event. Therefore, the pins are classified as ASME Subsection NG core supportstructures. The reflector blocks themselves are also classified as ASME Subsection NG coresupports structures.

6. The 52 fuel pins in the lower core plate include a shaft with threads at the end for a nut on thelower side of the lower core plate. The nut is mounted in a counter bore and has a cup on theperimeter for locking. A cross section of the fuel pin can be seen in the NPM Seismic AnalysisTechnical Report TR-0916-51502, Figure 2-6. The fuel pins, including nuts, are classified asASME Subsection NG core support structures.

7. There are four surveillance specimen capsule holders and the support (base of eachsurveillance specimen capsule holder) is welded to the core barrel. The welds are part of thecore barrel and therefore are classified as ASME Subsection NG core supports. Thesurveillance capsule holders are shown in FSAR Tier 2 Figure 5.3-2. FSAR Tier 2 Section5.3.1.6 contains additional description of the specimen holders. The surveillance specimencapsule holders are classified ASME subsection NG "internal structures" and are designedusing NG-3000 as a guide.







10 CFR 50 Appendix A GDC 2 requires that structures, systems and components important tosafety are designed to withstand the effects of natural phenomena, such as earthquakes,without loss of capability to perform their safety-related functions.

DCD Tier 2 Section 3.9.5.1 states that a flow diverter is attached to the RPV bottom head underthe CSA. This flow diverter smooths the turning of the reactor coolant flow from the downwardflow outside the core barrel to upward the flow through the fuel assemblies. The flow diverterreduces flow turbulence and recirculation and minimizes flow related pressure loss.

The applicant is requested to provide detailed design description, including drawing, of the flowdiverter, its classification and design code/standard. In addition, the applicant is requested toprovide the method at which the flow diverter is attached to the RPV bottom head and how itinterfaces with the core support blocks and clarify if the flow diverter supports any load from theCSA during all service level conditions.

NuScale Response:

Detailed design information for the Flow Diverter and Reactor Vessel Internals was provided forNRC audit.

The flow diverter is a thin disc with a raised bubble shape in its center as shown in FSAR Figure3.9-1. It is welded to the interior center of the bottom head of the reactor pressure vessel (RPV).The weld is part of the RPV and the flow diverter is classified as an ASME Subsection NG"internal structure." The outer perimeter of the flow diverter does not reach the core supportblocks. The top is below the lower core plate. Therefore, the flow diverter does not interface with


the core support blocks and does not carry loads from the core support assembly.

Additional depictions of the flow diverter are provided in NuScale Comprehensive VibrationAssessment Program Technical Report TR-0716-50439, Figure 2-22, and in NuScale PowerModule Seismic Analysis Technical Report TR-0916-51502, Figure 2-6. The two "dots" (shown90 degrees apart) in TR-0916-51502 Figure 2-6 are not fasteners, they are two of five smallholes in the flow diverter that prevent development of a differential pressure across the plate.







DCD Tier 2 Section 3.9.5 provides no information about core bypass flow. The applicant isrequested to provide detailed design description about core bypass flow, the locations at whichcore bypass flow are expected to occur, and the percentage of core bypass flow to full flow atthese locations. A figure similar to Figure 2-3 in report TR-0716-50439-P, Rev. 0 showing corebypass flow is needed for the staff to understand where core bypass flow is expected to occur.

NuScale Response:

NuScale core bypass flow is through two paths, the cooling channels (holes) in the reflectorblocks, and the fuel assembly guide tubes and instrument tubes as discussed in FSAR Tier 2,Section 4.4.3.1.1. The reflector blocks and cooling channels (labeled as "flow holes") are shownin FSAR, Tier 2 Figure 3.9-4.

The best estimate bypass flow through the reflector cooling channels is 4%, and through thefuel assembly guide and instrument tubes is 3.3%, of total flow. The total best estimate bypassflow is shown in FSAR, Tier 2 Table 4.1-1.







10 CFR 50 Appendix A GDC 2 requires that structures, systems and components important tosafety are designed to withstand the effects of natural phenomena, such as earthquakes,without loss of capability to perform their safety-related functions.

DCD Tier 2 Section 3.9.5.1 states that under normal operation, the reactor core is supported bythe core support structures of the CSA that surround the fuel assemblies. The deadweight andother mechanical and hydraulic loads from the fuel are transferred to the upper and lower coresupport plates. The motion of the upper and lower core support plates is coupled through thecore barrel. Under seismic and accident conditions, the core barrel transfers lateral loads to theRPV shell through core support blocks at the bottom of the RPV and the upper support blocksthat are attached to the upper portion of the core barrel. The vertical loads are transferred fromthe core barrel to the RPV head through the core support blocks.

It is unclear to the staff that in this particular paragraph in DCD Tier 2 Section 3.9.5.1, which arethe upper and lower core support plates the applicant refers to. The applicant is requested toclarify, in the next revision of the DCD, the nomenclature used for upper core plate versus uppercore support plate, as well as for lower core plate versus lower core support plate.

In addition, it is unclear to the staff that during seismic and accident conditions, how the lateralload is transferred from the core barrel to the RPV shell through the core support blocks, whichare located at the bottom of the RPV, and through the upper support blocks, which are locatedat the upper portion of the core barrel. The applicant is requested to provide a simple figure ofthe load transfer from component to component during both normal and accident conditions,and to provide more detailed description of the load path during accident condition.


NuScale Response:

The upper core plate in FSAR Section 3.9.5.1 is shown in FSAR Figure 3.9-3. The upper coreplate is located at the bottom of the lower riser assembly. The lower core plate in FSAR Section3.9.5.1 is shown in FSAR Figure 3.9-4. The lower core plate is located directly below the corebarrel and reflector blocks and directly above the lower seismic Belleville washer stacks.NuScale Power Module (NPM) Seismic Analysis Technical Report TR-0916-51502, Figure 2-6provides a depiction of both the upper and lower core plates in a figure which providesclarification of the position of these plates in relation to each other. The reference to upper andlower core support plates in FSAR Section 3.9.5.1 should not include “support.” These parts arenamed "upper core plate" and "lower core plate," respectively. The text in FSAR Section 3.9.5.1has been corrected.

The FSAR text and figures (Figure 3.9-4) have been updated to include views and discussion ofthe upper and lower seismic Belleville washer stacks (see NuScale Power, LLC Submittal ofChanges to Final Safety Analysis Report, Sections 3.9, Mechanical Systems and Components,4.5, Reactor Materials, and 5.2, Integrity of Reactor Coolant Boundary, dated July 20, 2017).

The NPM Seismic Analysis Technical Report TR-0916-51502 also has been revised to includeupdates to the figures (as identified below) that are pertinent to this RAI response (the TRmarkups associated with this RAI 8901 Question 03.09.05-12 response will be included with theNuScale response to RAI 8911).

The lateral load paths from the core barrel to the RPV are shown in NPM Seismic AnalysisTechnical Report TR-0916-51502, Figures 2-6 and 2-7 with details of the hardware shown in theNPM Seismic Analysis TR Figures C-9 and C-10. During normal operating conditions (i.e.Service Level A) there are no lateral loads transmitted between the core barrel and the RPV.During some Service Level, B, C or D conditions (e.g., seismic or blowdown events) lateralloads are transmitted through either/both the upper support blocks (FSAR Figure 3.9-4 andTR-0916-51502, Figure C-10) and the core support blocks (located at the bottom of the RPV,TR-0916-51502, Figure C-9) to the RPV. The core support blocks are integral to the RPV.

The load path from the core barrel through the upper support blocks is a direct radial path asshown in TR-0916-51502, Figure C-10. The load path from the core barrel to the core supportblocks is as follows. The core barrel is welded to the lower core plate. The Belleville washerinterface at the core support block is described in FSAR Tier 2 Section 3.9.5.1. The Bellevillewasher interface at the core support blocks is also shown in the NPM Seismic AnalysisTechnical Report TR-0916-51502, Figure 2-6 and C-9. The Belleville retainer nut verticallysecures the lower core plate to the core support block. Lateral loads between the lower coreplate and the core support blocks are transmitted in the circumferential direction though the studthat is integral with each core support block, which extends through the slotted holes in thelower core plate.


Impact on DCA:FSAR Tier 2 Section 3.9.5.1 has been revised as described in the response above and as shown in the markup provided in this response.

NuScale Final Safety Analysis Report Mechanical Systems and Components

Tier 2 3.9-48 Draft Revision 1

Surveillance specimen capsule holders are welded to the outer surface of the core barrel at about the mid height of the CSA.

A flow diverter is attached to the RPV bottom head, under the CSA, as shown in Figure 3.9-1. This flow diverter smoothes the turning of the reactor coolant flow from the downward flow outside the core barrel to upward flow through the fuel assemblies. The flow diverter reduces flow turbulence and recirculation and minimizes flow related pressure loss in this region.

The lower riser assembly includes the lower riser, the upper core plate, CRA guide tubes, CRA guide tube support plate, and ICI guide tube support structure (see Figure 3.9-3). The lower riser assembly is located immediately above the CSA and is aligned with and supported on the CSA by the four upper support blocks.

The lower riser channels the reactor coolant flow leaving the reactor core upward toward the central upper riser, and separates this flow from the flow outside the lower riser which is returning from the SGs.

The upper core plate which is attached to the bottom of the lower riser by lock plate assemblies, serves to support and align the top end of the fuel assemblies. Sixteen CRA guide tubes are attached to the upper core plate and extend upward to the CRA guide tube support plate. These guide tubes house the portion of the CRAs that extend above the top of the reactor core.

An ICI guide tube support structure is located inside the lower riser to support and align ICI guide tubes with their respective fuel assemblies.

The upper riser assembly is located immediately above the lower riser assembly and extends upward to the PZR baffle plate. It channels the reactor coolant leaving the core upward through the central riser and permits the reactor coolant to turn in the space above the top of the riser and below the PZR baffle plate, and then flow downward through the annular space outside of the riser and inside of the RPV where the SG helical tube bundles are located.

RAI 03.09.05-4, RAI 03.09.05-12

The upper riser assembly includes the upper riser, a series of CRA shaft and ICI guide tube supports referred to as upper CRDS supports, and the upper riser hanger assembly. The upper riser assembly also accepts and positions the RCS injection piping. The ICI guide tubes, which are supported by the upper riser assembly, extend from their respective penetrations in the RPV top head downward through the PZR space, the upper riser, and the lower riser to their respective fuel assemblies. The portion of the ICI guide tubes extending from the RPV upper head penetrations to the bottom of the upper riser assembly is depicted in Figure 3.9-2. The upper riser assembly hangs from the pressurizer baffle plate. A small vertical clearance is provided between the upper riser and the lower riser to accommodate thermal growth in the vertical direction. In addition, there is a bellows assembly in the lower portion of the upper riser (see Figure 3.9-2) to provide added flexibility in the vertical direction to accommodate circumstances that involve sufficient thermal growth to close the vertical gap between the upper and lower riser assemblies.There is a bellows assembly in the lower portion



of the upper riser (see Figure 3.9-2). This bellows assembly exerts an initial contact load, in the cold condition, on the lower riser interface, and then allows for the vertical thermal expansion. The RVI materials including base materials and weld filler materials are discussed in Section 4.5.2 and are designed to minimize the number of welds and bolted interfaces within the high neutron flux regions.

During refueling and maintenance outages the upper riser assembly stays attached to the upper section of the NPM (upper CNV, upper RPV and SG) while providing physical access for potential inspection of the feedwater plenums, SG, RPV and control rod drive shaft supports. The lower riser assembly and CSA remain with the lower NPM (lower CNV, lower RPV, core barrel, and core plates) when the module is parted for refueling and maintenance.

The RVI upper riser assembly is supported from the RPV integral steam plenum (e.g., below the bottom of the PZR).

RAI 03.09.05-4, RAI 03.09.05-12

Under normal operation, the reactor core is supported by the core support structures of the CSA (seismic Belleville washers, core support blocks, core barrel, lower core plate and upper core plate) that surround the fuel assemblies. The deadweight and other mechanical and hydraulic loads from the fuel are transferred to the upper and lower core support plates. The motion of the upper and lower core support plates is coupled through the core barrel. Under seismic and other accident conditions, the core barrel transfers lateral loads to the RPV shell through the core support blocks at the bottom of the RPV and the upper support blocks that are attached to the upper portion of the core barrel. The vertical loads are transferred from the core barrel to the RPV head through the seismic Belleville washers and core support blocks.

The fuel is surrounded by a heavy neutron reflector made of reflector blocks stacked on top of each other. The heavy reflector reflects neutrons back into the core to improve fuel performance. The heavy reflector provides the core envelope and directs the flow through the core. Under normal operation the heavy reflector does not provide support to the core and performs as an internal structure. During seismic and other accident events the heavy reflector limits the lateral movement of the fuel assemblies and transfers those loads to the core barrel.

A set of upper CRDM supports in the upper riser assembly, in conjunction with the CRA guide tube support plate, CRA guide tubes, and upper core plate in the lower riser assembly properly align and provide lateral support for the CRAs. The clearances provided at all these supporting members are intended to ensure adequate alignment of the CRDS with the fuel assemblies and permit full insertion of control rods under all design basis events (DBEs).

3.9.5.2 Loading Conditions

Design, construction, and testing of the RVI core support structures and internal structures are in accordance with ASME BPVC Section III, Division 1, Subsection NG.






DCD Tier 2 Section 3.9.5.1 states that during refueling and maintenance outages, the upperriser assembly stays attached to the upper section of the NuScale Power Module (NPM) (uppercontainment vessel (CNV), upper RPV and SG) while providing physical access for potentialinspection of the feedwater plenums, SG, RPV and control rod drive shaft supports. The lowerriser assembly and CSA remain with the lower NPM lower CNV, lower RPV, core barrel andcore plates) when the module is parted for refueling and maintenance.


1. Provide detailed design description, including drawing, of the location and stand at whichthe upper section NPM is located in the refueling pool during refueling. Describe thelocation(s) on the upper section NPM (whether it’s the CNV, RPV or upper riser assembly)at which the upper NPM will rest on the stand and describe the impact of the deadweightload on the upper riser assembly.

2. Provide detailed design description, including drawing, of the location and stand at whichthe lower riser assembly is located in the refueling pool during refueling. Describe the pointof rigging attachment of the lower riser assembly. Describe the location(s) on the lowerriser assembly at which the lower riser assembly will rest on the stand; depending on thislocation on lower riser assembly, describe if any of the fuel pins located below the uppercore plate will be adversely affected due to the weight of the lower riser assembly.

NuScale Response:

During refueling, the lower containment vessel (CNV) section (shown in FSAR Tier 2 Figure6.2-2b), the lower reactor pressure vessel (RPV) section (shown in FSAR Tier 2 Figure 5.3-1)


including the fuel, the core support structure (shown in FSAR Tier 2 Figures 3.9-1 and 3.9-4),and the lower riser assembly (shown in FSAR Tier 2 Figures 3.9-1 and 3.9-3) are separatedfrom the rest of the NuScale Power Module (NPM). The portion of the NPM (with the lower RPVand CNV sections removed) is referred to as the "upper NPM."

The upper NPM is stored in the Module Inspection Rack (MIR). The MIR is located in thereactor building pool, within a "drydock" area which may be maintained partially or fully floodedas needed to support specific inspection and maintenance activities. While in the MIR, the upperNPM is laterally and vertically supported by the three seismic support lugs (spaced 90 degreesapart) on the upper CNV that are normally used to laterally support the NPM in the operatingbay. The upper support lugs are shown in FSAR Tier 2 Figure 6.2-2a (labeled as "support"). TheUpper Riser is supported in its normal configuration suspended from the RPV integral steamplenum.

During refueling the lower riser assembly (LRA) is located in one of two configurations. The LRAmay be located on top of the core support assembly (in the same configuration and with thesame support as when the NPM is fully assembled), with the core support assembly placed inthe lower RPV section. In this configuration the lower RPV/fuel/LRA assembly is located in thereactor flange tool (RFT). To gain access to the fuel, the LRA may be detached from the CoreSupport Assembly (CSA) and lifted using the lower riser assembly lifting lugs and stored in adesignated stand in the refueling pool.

While the LRA is in the stand it is supported by load bearing features that prevent the loading ofthe fuel pins or in-core instrumentation (ICI) guide tubes that protrude below the upper coreplate of the LRA. The LRA stand is not a safety-related component; its detailed design has notyet been completed at this time.

Detailed design information (drawings) for the Lower Riser Assembly and equipment placementwithin the Reactor Building (RXB) were provided for NRC audit.







DCD Tier 2 Table 3.9-5 provides a list of load combinations under all four service levelconditions. Under plant event rod ejection accident, the service level is categorized as servicelevel D, however, the allowable limit is categorized as level C.

Acceptance criterion 2 under SRP Section 15.4.8 requires that the postulated reactivity accidentwould result in neither damage to the reactor coolant pressure boundary greater than limitedlocal yielding nor sufficient damage to impair significantly core cooling capacity. The applicantis requested to explain the rational of using level C allowable limit for a service level D condition.

NuScale Response:

The rod ejection accident is classified as a Level D event because of the low number ofanticipated occurrences and consequence of the event over the 60 year design life.Classification of the rod ejection accident as a Level D event is consistent with the classificationused in other recent design control documents (e.g., AP1000, US-APWR, and US-EPR). Thestress limits are set to Level C limits per the guidance provided in RG 1.77 C.2, which states:"Maximum reactor pressure during any portion of the transient will be less than the value thatwill cause stresses to exceed the Emergency (Level C) Condition stress limit as defined inSection III of the ASME Boiler and Pressure Vessel Code." The ASME BPVC permits a morerestrictive stress limit be specified than the service limit the event is classified. The morerestrictive service limit reduces or eliminates potential damage that may occur using the higherservice limit.







DCD Tier 2 Section 3.9.5 provides no information regarding deformation limits, such as anacceptable deformation limits for reactor internals at which safety function can still bemaintained, and the justification of which. Therefore, the applicant is requested to provideinformation regarding deformation limits for reactor internals components under all service levelconditions.

NuScale Response:

The internal components of the NPM that require deflection limits are the upper riser (includingcontrol rod drive (CRD) shaft supports), and the lower riser (including, control rod assembly(CRA) guide tubes and upper core plate). Deflection limits are imposed on these components toassure the CRD shaft is sufficiently aligned so that the capability to insert the CRAs is notcompromised. CRA drop and CRD shaft alignment testing, as discussed in FSAR Tier 2 Section1.5.1.12, will provide data to support determination of specific values for the maximumdeflections that allow CRA insertion requirements to be met. The deflection limits includeconsiderations for both fabrication tolerances and static, thermal, and dynamic motion fromapplicable service loads. The testing includes imposed deflections along the length of the CRDshaft at each of the support locations in the upper riser. Deflections (offsets) in the lower riser,which contains the CRA guide tubes, are also part of the testing.







DCD Tier 2 Section 3.9.3.1.2, “Load Combinations and Stress Limits” Subsection “Core SupportStructures” states that the steam generator tube supports are internal supports and aredesigned to the same criteria as the core support structure. It is unclear to the staff the meaningof this statement. Specifically, it is unclear to the staff whether the steam generator tubesupports are classified as core support structure and are thus designed to ASME SubsectionNG, or if they are classified as internal structures and are designed to ASME Subsection NG asa guide. Therefore, the applicant is requested to clarify the classification of the steam generatortube supports, including its seismic classification.

NuScale Response:

The NuScale Steam Generator (SG) tube supports are classified as “Internal Structures” andare constructed in accordance with ASME BPVC, Section III, Subsection NG as a guide. TheSeismic Category of the SG tube supports is Seismic Category I.

FSAR Tier 2 Section 3.9.3.1.2 has been revised to clarify the SG tube support classification.This is consistent with FSAR Tier 2 Sections 5.4.1.2 and 5.4.1.5 and FSAR Tier 2 Table 3.2-1,as revised in the response to RAI 8948 Question 03.02.02-3.

Impact on DCA:

FSAR Tier 2 Section 3.9.3.1 has been revised as described in the response above and asshown in the markup provided in this response.



3.9.3.1.2 Load Combinations and Stress Limits

The RPV is a Seismic Category 1, ASME Section III, Class 1 component. The load combinations and stress limits for the RPV and its supports are presented in Table 3.9-3.

The CNV is a Seismic Category 1 component. The ASME classification of the CNV and its supports is described in Section 3.8.2.2. The load combinations and stress limit for CNV and its supports are presented in Table 3.9-43.8.2-2.

The RVI are Seismic Category 1 components. Portions of the RVI, which perform a core support function, are classified as Class CS components in accordance with ASME Section III, Subsection NG. The remaining portions of the RVI are designated as internal structures; however, they are designed using NG-3000 as a guide and constructed to ASME Subsection NG. The load combinations and stress limit are presented in Table 3.9-5.

RAI 03.09.05-16

The SG tube supports are Seismic Category 1 components. The SG tube supports are designated as internal structures and are designed using ASME Section III, Subsection NG as a guide. The load combinations and stress limit are consistent with those presented in Table 3.9-5.

The portions of the CRDM providing a RCPB function are ASME Code Class 1, Seismic Category I components. The CRDM coil heat exchangers, tubes, and connections, which provide cooling water and are external to the RCPB, are ASME Code Class 2, Seismic Category III components. The CRDM pressure housing is a Class 1 appurtenance per ASME BPVC, Section III, NCA-1271. The load combinations and stress limit are presented in Table 3.9-6. The CRDM seismic supports located on both the RPV and CNV head are ASME Code Class 1, Seismic Category I component supports.

The DHRS condensers are Seismic Category I components and are classified as ASME Section III, Class 2 components. The condenser supports are classified as ASME Section III, Subsection NF, Class 2 supports. The load combinations and stress limit are presented in Table 3.9-7.

Load combinations for the ECCS valves, containment isolation valves, RSVs, thermal relief valves and the DHRS actuation valves are presented in Table 3.9-9 through Table 3.9-14.

ASME Class 1 Piping

The loading combinations and corresponding stress design criteria per ASME service level for ASME Class 1 piping are presented in Table 3.12-1 in Section 3.12.

ASME Class 2 and 3 Piping



The loading combinations and corresponding stress design criteria per ASME service level for ASME Class 2 and Class 3 piping are presented in Table 3.12-2 of Section 3.12.

RAI 03.09.05-16

Core Support Structures

The core support structures are designed to ASME BPVC Section III Subsection NG. The SG tube supports are internal supports and, therefore, are designed to the same criteria as the core support structure. The loading combinations and corresponding stress design criteria per ASME service level for ASME core support structures are consistent with the RVI load combinations and acceptance criteria (see Table 3.9-5).

ASME Class 1, 2, and 3 Component Supports

The ASME Class 1, Class 2, and Class 3 components and piping supports are designed in accordance with ASME BPVC Section III, Subsection NF. These supports include the CNV support skirt, the CNV lugs, the top support structure mounting assemblies, the RPV support plate/gusset, the DHRS condenser supports, the top support structure, and the CRDM seismic support structure. The load combinations are included in Table 3.9-3, Table 3.9-43.8.2-2, Table 3.9-7 and Table 3.9-8. The allowable stress criteria are supplemented by RGs 1.124 and 1.130 for Class 1 linear-type and plate-and-shell-type support structures.

The top support structure is mounted to the CNV top head, and it provides support for piping systems and valves attached to penetrations in the CNV top head and for electrical cables and conduit for various equipment in the NPM. It is a Seismic Category 1 component and classified as an ASME III, Subsection NF Class 2 support. The ASME BPVC Code analysis is in accordance with NF-3350 and it is designed to withstand the service loads and loading combinations specified in Table 3.9-8.

ASME Class 1, 2, and 3 Pipe Supports

The loading combinations and corresponding stress design criteria per ASME service level for ASME Class 1, Class 2, and Class 3 pipe supports is provided in Table 3.12-3 in Section 3.12.

3.9.3.2 Design and Installation of Pressure Relief Devices

ASME Class 1 Pressure Relief Valves

The RCS reactor safety valves (RSV) are designed as ASME BPVC Code, Section III, Class 1 pressure-relief, pilot-operated devices. They are part of the RCPB and are located on the RPV head. There are two RSVs, which are not connected to any piping on their discharge sides and vent directly into the CNV. The RSV function is to prevent RCS pressure from exceeding 110 percent of design pressure under normal and abnormal conditions and to prevent exceeding service limits. The two valves, each with sufficient capacity to limit overpressurization of the RPV, are normally closed, low leakage, and

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NuScale Power, LLC Response to NRC Request for Additional ... · TR-0716-50439-P, Rev. 0 shows the steam plenum region. The plenum tube sheet has penetrating holes where the top end