Enclosure 1 - Presentation Slides for Pre-Application ...

ENCLOSURE 1

M200142

Presentation Slides for Pre-Application Meeting for Planned Submittal of GE-Hitachi BWRX-300 Selected Topical Report

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Pre‐Submittal Meeting For GE Hitachi (GEH)BWRX‐300 Licensing Topical Report (LTR)

NEDC‐33914PBWRX‐300 Advanced Civil Construction and

Design Approach

October 2020

Pre‐Submittal Meeting For GE Hitachi (GEH)BWRX‐300 Licensing Topical Report (LTR)

NEDC‐33914P BWRX‐300 Advanced Civil Construction and Design Approach

Copyright 2020 GE Hitachi Nuclear Energy Americas, LLC – All Rights Reserved 3

Agenda

Description of BWRX‐300 Small Modular ReactorDescription of BWRX‐300 Advanced Construction ApproachLicensing Topical Report Purpose and ScopeRegulatory BasisInvestigations, Testing, Inspection and Monitoring ProgramsFoundation Interface AnalysisDesign AnalysesII/I Interaction Evaluations ApproachBWRX‐300 Generic Design Approach

Description of BWRX‐300 Small Modular Reactor


BWRX‐300 Nuclear Power PlantThe BWRX‐300 is an approximately 300 MWe, water‐cooled, natural circulation Small Modular Reactor (SMR) Nuclear Power Plant (NPP)

RB(SC-I)

RwB(Rw-IIa)

TB(NS)

CB(NS)

• Reactor Building (RB) hosts the BWRX‐300 Seismic Category (SC‐I) systems and components• BWRX‐300 RB foundation and structure are separated from the Control Building (CB), Radwaste Building (RwB) and Turbine Building (TB) by seismic gaps• RwB hosts tanks and equipment with high radioactivity and is seismically categorized as Rw‐IIa• CB and TB are Non‐Seismic (NS) category


BWRX‐300 Reactor BuildingThe BWRX‐300 RB structure consists of two parts:• Fuel handling equipment and pools containing water needed for the BWRX‐300 passive safety‐related cooling systems are in the above‐grade portion of the RB directly supported by the below‐grade vertical shaft• Reactor Pressure Vessel (RPV), Pressure Containment Vessel and other important safety related structures, systems and components (SSCs) located in the RB below‐grade vertical shaft to mitigate the effects of possible external events


BWRX‐300 Monitoring, Analysis and Design Process

FIA – Foundation Interface Analysis

SRA – Site Response Analysis

DRS – Design Response Spectra

ATH – Acceleration Time History

SSI – Soil‐Structure Interaction

Earth Pressure Load Validations

Probabilistic Equivalent Linear SRA

Linear Elastic 1-g SSI Analyses

Site InvestigationsField and Laboratory Tests

Excavation, Construction and In-Service Monitoring Programs

Non-Linear Soil and Rock Constitutive Model Parameters

Basecase Models of Small Strain Dynamic Soil and Rock Properties

Equivalent Linear Static Soil and Rock Properties

Non-Linear FIA

Ground Motion DRS and ATHs

Strain Compatible Soil Profiles

Linear Seismic ResponseSSI Analyses

BWRX-300 RB Design

Sensitivity Non-Linear Seismic SSI Analyses

Description of BWRX‐300 Advanced Construction Approach


Innovative Construction Methods Innovative approaches are employed for the construction of the RB below grade shaft aimed to optimize the cost of the BWRX‐300 NPP by:•Minimizing the amount of excavation;• Reducing the amounts of backfill materials; and• Reducing construction scheduleThe development and evaluation of innovative construction approaches considered a generic transition profile having soft soil strata for the upper two thirds of the profile depth followed by hard rock strata• Transition profile includes the required transition in construction techniques from soil to rock subgrade conditions

Two example methodologies are provided to illustrate the interface setting of the RB shaft after the construction and conditions relevant for its analysis, design, and inspection


Option 1: Open Caisson with Shoring Walls• A circular slurry shoring wall is installed in the softer upper soil strata and socketed into bedrock to stabilize the excavation • Excavation is continued through the rock down to the bottom of RB shaft basemat • Waterproofing is applied to the surface of the slurry wall and the rock face


Option 2: Jack Strand Open Caisson Suspension Method • A circular slurry shoring wall is installed in the softer upper soil strata and socketed into bedrock to stabilize the excavation • A circular reinforced concrete guide ring is installed around the top of the excavation supporting jack strand machines• Jack strands lower constructed sections of the RB exterior wall into the shaft while excavation is in process

Licensing Topical Report Purpose and Scope


Licensing Topical Report PurposeThis Licensing Topical Report (LTR) requests NRC review of the regulatory basis, design, monitoring and inspection requirements, criteria and guidelines specific to the innovative approaches used for the construction and design of the BWRX‐300 SMR structures: • Geotechnical site investigation and laboratory testing programs adequate to characterize the in‐situ soil and rock materials around and below the deeply embedded RB shaft • Monitoring of the effects of excavation and construction on the properties of in‐situ subgrade materials supported by the results of non‐linear Foundation Interface Analysis (FIA) • Inspection and monitoring programs of the RB structure stability during construction and power operation of the BWRX‐300 SMR supported by non‐linear FIA results• Development of equivalent linear static and dynamic properties of in‐situ soil and rock materials for use as input for the one‐step design Soil‐Structure Interaction (SSI) analyses and design • Approaches for addressing modeling uncertainties and variations of soil properties on the RB design• Approaches for demonstrating consistency between the results of deterministic SSI analyses with results from the probabilistic site response analyses (SRA)• Approach for evaluation of II/I interaction of Non‐SC‐I CB, TB and RwB with the adjacent SC‐I SSCs


Licensing Topical Report ScopeThe LTR includes: • Regulatory bases specific to the innovative approaches implemented for the analysis, design and construction of the BWRX‐300 SMR • Guidelines and requirements for characterization of the subsurface conditions including geotechnical site investigation and laboratory testing programs• Guidelines and requirements for inspection and monitoring programs performed during the excavation, construction and operation of the BWRX‐300 SMR • Design requirements and guidelines for FIA performed to ensure the stability of both structure and in‐situ soil and rock during and after construction• Design requirements, acceptance criteria and guidelines for the BWRX‐300 RB design analyses including the development of site design parameters • Approach for addressing II/I interaction between the SC‐I RB and Non‐SC‐I surrounding structures and foundations• A generic approach, seismic and geotechnical design parameters used to ensure the applicability of the RB conceptual design for a wide range of prospective candidate sites

Regulatory Basis


Regulatory Basis for BWRX‐300 SMRThis LTR describes compliance with regulatory requirements and guidance specific to the innovative approaches used for the BWRX‐300 SMR design and construction that may be referenced during future licensing activities in support of either a Design Certification Application (DCA) and Combined Operating License (COL) under 10 CFR 52, or Construction Permit (CP) and Operating License (OL) under 10 CFR 50

The innovative approaches implemented for the analysis, design, construction, and maintenance of the BWRX‐300 SMR:•Meet the intent of the current regulatory guidance for large light water reactors • Address specifics related to the seismic and structural design of deeply embedded SMRs identified in NUREG/CR‐7193


Regulatory Basis for Defining Site Subsurface ConditionsThe BWRX‐300 meets the requirements of 10 CFR 100.20(c)(1) and 10 CFR 100.23 for conducting site‐specific investigationsStatic and dynamic engineering properties and groundwater conditions are obtained from site investigations that follow the regulatory guidance of NUREG‐0800, SRP 2.5.4 • Site investigations are conducted in accordance with the regulatory guidance of RG 1.132 and NUREG/CR‐5738• Laboratory tests of subsurface materials are performed in accordance with the regulatory guidance of RG 1.138 and NUREG/CR‐5739 • Subsurface investigation spacing guidelines are provided in the LTR that are beyond those specified in Appendix D of RG 1.132 to ensure site investigations provide sufficient information to define the engineering properties of subgrade materials and their spatial distribution surrounding the BWRX‐300 RB• Innovative approach is implemented for monitoring the effects of excavation and construction on the subgrade properties that use non‐linear analysis results of subgrade response during the excavation and construction stages


Regulatory Basis for Site Design ParametersPer 10 CFR 50 Appendix A, GDC 2, requirements, the BWRX‐300 important to safety structures are designed to withstand the effects of natural phenomena such as earthquakes• The development of site‐specific safe shutdown earthquake (SSE) ground motion addresses the uncertainties in the site investigation results per the requirements of 10 CFR 100.23(d)(1)

SSE ground motion acceleration response spectra and time histories are developed following the regulatory guidance of NUREG‐0800, SRP 3.7.1 • Performance‐based approach of ASCE 43 is used to develop the SSE ground motion spectra per RG 1.208 guidance• Probabilistic SRA are performed following the Approach 3 methodology in NUREG/CR‐6372 to account for site wave propagation characteristics and to address uncertainties related to the site subgrade conditions • An approach is presented for developing strain compatible properties from the Approach 3 SRA results • Three approaches are provided for ensuring the input motion used for the deterministic SSI analyses is consistent with the probabilistic SRA results along the entire RB shaft embedment depth


Seismic Analysis RegulationsPer 10 CFR 50, Appendix S requirements, the following BWRX‐300 SSCs are designed to withstand an SSE:• SSCs that ensure the integrity of the reactor coolant pressure boundary• SSCs providing capability to shut down the reactor and maintain it in a safe‐shutdown condition• SSCs preventing or mitigating consequences of accidents that could result in potential offsite exposures comparable to the requirements of 10 CFR 50.34(a)(1) or 10 CFR 100.11

The BWRX‐300 RB seismic design basis is developed based on SSI analysis results performed following the regulatory guidance of NUREG‐0800, SRP 3.7.2• Seismic demands for RB SSCs design are obtained from analysis of the three‐dimensional (3‐D) finite element (FE) model developed following the one‐step approach requirements of ASCE/SEI 4‐16 and regulatory guidance of DC/COL ISG‐01• Effects of equipment structure interaction (ESI) and structure‐soil‐structure interaction (SSSI) are incorporated in the design of RB SSCs following the provisions of ASCE/SEI 4‐16• Soil separation, concrete cracking and soil secondary non‐linearity effects are evaluated based on responses obtained from sensitivity SSI analyses performed per requirements of ASCE 4‐16


II/I Interaction Evaluation RegulationsPer SRP 3.7.2 and SRP 3.3.2 guidance, BWRX‐300 Non‐SC‐I SSCs meet at least one of the following three II/I interaction requirements under SSE and extreme wind loading conditions:A. The collapse of the non‐SC‐I SSC does not cause the non‐SC‐I SSC to strike a SC‐I SSCB. The collapse of the non‐SC‐I SSC does not impair the integrity of SC‐I SSCs, nor result in

incapacitating injury to control room occupantsC. The non‐SC‐I structure is analyzed and designed to prevent its failureNon‐SC‐I Control, Turbine and Radwaste Buildings (CB, TB and RwB) structures are evaluated to ensure that under SSE and extreme wind loads • CB, TB and RwB structures do not collide with RB or collapse over the RB• CB structure does not collapse to result in incapacitating injury to the control room occupants• TB structure does not collapse to result in impairment of safety functions of the main steam lineII/I seismic interaction checks are performed considering limited inelastic responses in accordance to the provisions of ASCE/SEI 43‐05


Inspection and Monitoring RegulationsThe BWRX‐300 meets the maintenance requirements of 10 CFR 50.65, including monitoring of the performance or condition of structures against established goals • LTR describes techniques to quantitatively characterize the geologic and engineering rock mass properties following the guidance of RG 1.132 and NUREG/CR‐5738• Construction inspection and monitoring program are implemented during construction following the guidance of RG 1.132 and NUREG/CR‐5738, Appendix A and B• BWRX‐300 implements a structures monitoring program following the regulatory guidance of RG 1.160 and NUMARC 93‐01 • An innovative program for monitoring subsurface conditions is implemented to ensure any changes during the operational life of the BWRX‐300 NPP are bounded by the design

Investigations, Testing, Inspection and Monitoring Programs


Scope of Investigation and Monitoring ProgramsInvestigation, testing, inspection and monitoring programs ensure the safe siting of the BWRX‐300 plant throughout the following stages:• Site characterization• Excavation• Construction• Loading• Start‐up and OperationData collected from laboratory testing, field monitoring and inspection may be compared with the results of non‐linear FIA to:• Ensure the geotechnical parameters used as input to the linear elastic design SSI analysis are adequate • Assess whether the response of subsurface materials during excavation, construction and loading is within the realm of expectations• Monitor possible effects of settlements and groundwater changes on RB stability • Investigate potential seismic or flood hazards effects and subsurface deformation that originate from subgrade instabilities such as undetected subsurface conditions


Site Investigation and Subsurface Material Testing ProgramsSite investigations and subsurface material laboratory tests are performed to provide the necessary geotechnical input parameters for site‐specific:• Non‐linear FIA• Probabilistic SRA• Seismic and Static Analysis and DesignThe recommended extent and scope of the BWRX‐300 site investigation and laboratory test programs are beyond the guidance framework of RG 1.132 and RG 1.138 to: • Address additional requirements specific to the innovative approaches implemented for the design and construction of the BWRX‐300 RB deeply embedded in‐situ subgrade materials; • Ensure the design envelopes possible changes in the subsurface conditions during the excavation, construction and operation of the BWRX‐300 plant, and• Ensure the integrity of BWRX‐300 structures is not compromised during the constructionThis LTR recommends the number and types of field and laboratory tests necessary to meet the minimum requirements for the BWRX‐300 design and construction• Actual extent and scope of the site investigation and testing programs are dictated by site characteristics


Subsurface Investigation Program RecommendationsRG 1.132 guidance for establishing the number of borings under SC‐I foundations are applied for an area below the SC‐I RB and adjacent non‐SC‐I foundationsMaximum required boring depth is approximately 120 mBoring in rock should penetrate past weakness zones and extend at least 6 m into sound rock

Boring Depth (1)

(m)

SPT(2)/CPT(3)

Coring

VELDH(1)

VEL PS LOG(2) Well

B-01 120

B-02 120

B-03 120

B-04 60

B-05 60

B-06 60

B-07 30

B-08 60

B-09 80

B-10 80

B-11 60

B-12 60

B-13 80

B-14 80

B-15 60

B-16 80

B-17 60

B-18 80

B-19 60 (1) Subject to change based on site conditions(2) SPT: Standard Penetration Test(3) CPT: Cone Penetrometer Test(4) VEL DH: Downhole velocity (VEL) test(5) VEL PS Log: PS Suspension log velocity (VEL) test

Purpose of Recommended borings


Subsurface Material Laboratory Testing ProgramAt a minimum, the laboratory tests of soil materials include:• Index testing (classification, weight, plasticity, grain size)• Strength testing (shear tests, triaxial tests)• Deformability tests (triaxial tests, consolidation tests)• Permeability• Chemical testing (chlorides, sulfates, pH, Resistivity)• Dynamic tests (Resonant Column Torsional Shear (RCTS), cyclic triaxial)At a minimum, the rock laboratory tests include:• Uniaxial Compressive (UC) strength• Triaxial compressive strength and elastic moduli• Petrography• Dynamic tests (sonic pulse wave velocity, Free‐Free Resonant Column velocity tests)Expansion, creep, mineralogy, erodibility, durability, X‐ray diffraction tests may also be performed depending on site subsurface conditions


Characterization of Rock MassRock joints, bedding planes, discontinuity fractures and other weak zones are evaluated per RG 1.132 and NUREG/CR‐5738 guidance to determine:• Type of temporary excavation support and improvements required during construction• Required seepage control measures• Possible effects on rock pressure loads on the RB shaftDepths, orientations, aperture, and other characteristics of rock discontinuities are mapped using:• Oriented or classical rock coring methods • Optical and acoustic televiewer• Inclined borings to determine orientation of near vertical discontinuitiesGeologic and engineering parameters of rock masses are characterized using empirical rock mass classifications such as:• Rock Quality Designation (RQD) index• Rock Mass Rating (RMR) system• Geologic Strength Index (GSI)


Excavation and Foundation Construction InspectionsThe BWRX‐300 excavation and foundation inspections and testing programs satisfy the requirements of NRC Inspection Manual 88131Key Site Parameters are verified by checking if the required values for average allowable static bearing capacity and maximum allowable dynamic bearing capacity are met at the excavation depthSoundness of exposed rock is checked and confirmed during excavation and construction through visual inspection and testing of:• Rock material properties (rock type, color, particle size, hardness, and strength)• Rock mass properties (rock structure, shear strength, deformation modulus, hydraulic conductivity, and attitude)


RB Structure Construction Inspections and TestingThe BWRX‐300 RB construction inspection and testing programs are performed per:• Structural concrete activities requirements of NRC Inspection Manuals 88132 and • Structural welding inspection requirements of NRC Inspection Manual 55100 Concrete surface examinations are performed per guidance from ACI 349.3R and ASME XI, Subsections IWA and IWL• Special focus is placed on concrete surfaces exposed to soil, backfill, and/or groundwater, including determination of aggressivity of subsurface conditions and condition monitoring of installed protective barrier systems during construction

Additional inspections and testing are performed to: • Ensure an adequate installation of waterproofing and maintaining minimum coefficient of friction • Demonstrate adherence to key dimensions, e.g. shear wall thickness


In‐Service Monitoring ProgramThe scope of the BWRX‐300 Structures Monitoring and Aging Management Program (SMAMP) is:• In‐service monitoring and management of aging effects/structural degradations• Started after plant commissioning through successful plant decommissioning

The framework of the SMAMP is based on the three‐tier approach outlined in ACI 349.3RDesign details are being considered to allow monitoring of exterior wall of embedded RB shaft


Field Instrumentation PlanField instrumentation deployed to monitor:• Magnitude and distribution of pore pressure around and below the RB shaft• Rate of heave and the rate of lateral displacement of excavation walls during excavation• Total settlement and tilt of the RB shaft during construction, loading and operation• Settlements of CB, TB and RwBField instrumentation provides recordings that are benchmarked against design estimatesSensor type location is determined based on:• Subsurface conditions• Anticipated locations of maximum stress, strain, and/or pore pressure along perimeter of embedded shaft

Foundation Interface Analysis (FIA)


Purpose of Non‐Linear FIA Site‐specific non‐linear FIA are performed to:• Ensure the stability of both structure and supporting media, soil and/or rock per NUREG‐800 SRP 2.5.4 guidance• Aid in evaluating the construction plan, stability of the excavation, ground improvements and the design of excavation support systems• Provide results of ground pressure demands on the RB below‐grade exterior walls for use as input for the validation of the ground pressure design loads

The predicted foundation interface behavior is compared against physical observations from the field excavation plan and the excavation, construction and in‐service monitoring programs to:• Allow for confirmation of the analyzed stability conditions• Assess the effects of excavation and construction on the properties of in‐situ subgrade materials • Evaluate the effects of new loads or changes in the site conditions that may occur during the operational life of the BWRX‐300 plant • Evaluate potential subsurface deformations that may originate from subsurface instabilities


FIA ModelsFIA is performed on three‐dimensional (3‐D) models representing the site conditions during different stages, starting with possible ground improvements before the excavation through the start‐up and operation of the BWRX‐300 plant• Non‐linear constitutive models are used representing the behavior of subgrade materials at low and high strains and even cases where physical instabilities may be present • Non‐linear interface modes define the behavior at the SSI interfaces and account for the construction method and finishing configurations at the interfaces between the subgrade materials and the structure• Non‐linear interface models define the behavior and failure criteria between geometric zones used to analyze faults, rock slip surfaces, or other discontinuities around the structure• Linear elastic model is used to represent the stiffness of the RB structure that is limited to the main RB structural components• Elements are introduced in the model to simulate soil/rock anchors and geogrids used for stabilization of the excavation and any associated potential failure surfaces


Soil Non‐Linear Constitutive ModelsMohr‐Coulomb constitutive model is used to define the response of soil materials as purely linear elastic until plastic failure is reached, after which the response is purely plastic • Linear elastic behavior is defined by soil Young’s modulus and Poisson’s ratio • Plastic failure is defined by dilation angle, friction angle and cohesion interceptMore advanced soil constitutive models may be used:• Strain‐hardening/softening (HS) model used for soils whose behavior cannot be adequately represented by a linear elastic behavior and the use of a single elastic modulus•Modified Cam‐clay (MCC) model used for soft clayey soils that undergo time‐dependent volumetric changes that impacts the strength• HS and MCC models require additional stress dependent input parameters to be defined based on results of field and laboratory tests and thus may offer little to no advantage from the Mohr‐Coulomb approach if the confidence in the input data is not adequate


Rock Non‐Linear Constitutive ModelsNon‐linear FIA consider the rock mass as a discontinuous or continuous material depending on the size, density and configuration of the rock discontinuities and weak zones that control the strength and stability of the rock massGeneralized Hoek‐Brown (GHB) model is used to represent the behavior of continuous isotropic rock mass where the rock stiffness is nearly constant over a range of stresses, but the shear strength is variable due to the presence of discontinuities and weak zones• GHB model is adequate for representing responses of rock masses with confining stresses below the transition to ductile failure which is anticipated for most BWRX‐300 deployment sites• GHB criterion strength and deformation parameters are developed from measurements of intact rock unconfined strength and the GSI geomechancial rock mass classification

Mohr‐Coulomb failure criterion may be used in conjunction with the ubiquitous‐joint model to include weak planes with specific orientationsNon‐linear interface models are used to represent the behavior at rock discontinuities and weak zones when the rock mass is modeled as a discontinuous material


Non‐Linear Interface ModelingNon‐linear interface models are used in the FIA to represent the friction resistance, deformations and gap displacements at:• Interfaces between the subgrade and structures or foundations• Faults or joint planes or interfaces between bedding units in a geologic formation

Rheological models are used to define the elastoplastic response at the interfaces between the stress and relative displacements based on an elastic deformation modulus and shear resistance


FIA Staged Approach A staged approach is implemented for the non‐linear FIA to:• Capture the non‐linear behavior of the site subgrade material under different loading conditions • Establish initial conditions for the non‐linear analysis of subsequent stages The FIA are performed for the following five BWRX‐300 plant life stages:a. Site characterization – representing the initial native subgrade conditions at the site prior to any

excavation or construction activitiesb. Excavation – representing the excavation simulation, including possible ground improvements and

excavation support system installations made before and during the excavationc. Construction ‐ representing the different site loading conditions for different construction stages d. Loading – representing the placement of water in the pools, fuel, cranes and other permanent loads

after the completion of the construction of civil structures and foundations and the placement of heavy equipment, such as the reactor vessel

e. Start‐up and Operation – representing the conditions during the start‐up and operation of the plant, which are subject to change due to ground motions, floods and potential subsurface deformations that originate from subgrade instabilities


Excavation Stage FIA FIA excavation simulation resembles the planned construction scheme by staging the installation of excavation supports and removal of soil layers as excavation progresses

• Stability of the excavation during the different excavation sequences is verified by the results of FIA and later is compared with the field monitoring data to ensure safe excavation• Changes in the behavior of in‐situ subgrade materials are also monitored and later compared with the field monitoring data to ensure there are no significant changes in subgrade materials properties as result of the excavation that can affect the design• The calculated site response at the end of the excavations serves as initial condition for the next construction stage


Construction Stage FIA FIA construction simulation continues to represent the planned construction scheme by staging the reloading of the subgrade as the construction progresses• Contraction stage FIA uses input subgrade parameters that are different from those used for the excavation stage FIA to adequately capture the reloading behavior of the soil and rock materials


Operation Stage FIA Operation stage FIA provide results for sensitivity studies of potential subsurface instabilities during BWRX‐300 plant operation that may be a result of site condition changes• Results of operation stage FIA may be compared with the data collected from the field and in‐service monitoring programs to ensure continuous safe operation of the plant • Elements modeling the site improvements, such as consolidation grouting, rock reinforcement and soil support made during the excavation, are kept in the FIA model to account for their effects when monitoring subgrade conditions during start‐up and operation • The improvement elements are removed for purposes of earth pressure load validations

Design Analyses


One‐Step Design ApproachThe one‐step approach is implemented for the design of the deeply embedded RB structure where static earth gravity (1‐g) and seismic SSI analyses of combined models, including FE representations of the RB structure and the surrounding soil provide stress demands from:• Self‐inertia loads, including loads from equipment and pool water;• Mass and impedance of the surrounding in‐situ subgrade materials; • Groundwater hydrostatic pressure; and • Overburden loads and interaction with the surrounding RwB, CB and TB foundationsSeparate FE analyses provide the structural demands due to normal operating and accidental pressure and thermal loadsStructural model includes FE representations of all load carrying RB structural members and their eccentricities• Springs connecting the RB structural and subgrade FE models provide contact stresses at SSI interfaces • Refined FE mesh is used to adequately capture stress distributions in the structural members • FE mesh of subgrade is refined to enable transmitting seismic waves for the entire frequency range of interest for the seismic design of RB SSCs


SSI Modeling AssumptionsLinear elastic constitutive models are used for the subgrade materials• Equivalent linear subgrade materials properties used for the 1‐g SSI analysis provide upper bound (UB) earth pressure demands on RB below‐grade shaft• Seismic demands are obtained as envelope of results of SSI analyses of subgrade profiles with best estimate (BE), lower bound (LB) and UB dynamic properties that account for the variability and uncertainties in the subgrade material properties • Dynamic soil properties compatible to the free‐field strains generated by a typical SSE level earthquake are used to address the effects of primary soil non‐linearity

Non‐linearities at soil‐structure interfaces are neglected • Contact springs in the direction normal to the RB exterior walls are assigned properties representing UB stiffness conditions at the SSI interfaces• Friction at the RB exterior walls is neglected by assigning very low stiffness properties to the contact springs in vertical and tangential direction


SSI Modeling AssumptionsRock strata in the SSI models are modeled based on continuum mechanics principles using isotropic linear elastic properties• Rock masses are assumed continuous and possible rock cavities, fracture zones, joints, bedding planes, discontinuities and other weak zones are not explicitly included in the design SSI models• Rock isotropic properties are developed using empirical engineering and geomechancial rock mass classifications that assume closely‐spaced rock discontinuities with similar characteristics

The rock layers in the 1‐g SSI analysis models are assigned zero‐unit weight by assuming the rock is self‐supporting• Rock reinforcement provided during excavation is considered only as initial ground support• Rock loads, remaining after the initial ground support degrades, are addressed by including the potential rock weight of the solid rock in the design 1‐g SSI analysis based on the results of non‐linear FEA


Design Earth Pressure ValidationEarth pressure results of linear‐elastic 1‐g SSI analysis are compared to the results of non‐linear FIA that provide best estimates of soil and rock pressures on the RB below‐grade shaft to:• Assess the effect of the non‐linear and anisotropic response of subgrade materials on the soil and rock pressure demands• Demonstrate that the SSI assumptions used for the linear SSI analyses yield a conservative design of RB structure • Assess the conservativism of the soil and rock pressure demands used for the RB structural designEnvelope of FIA results of all analyzed post‐construction stages and scenarios are used for the comparisons that may not consider the subgrade improvements made during the construction• Improvements, like consolidation grouting, rock reinforcement, and soil support, are only considered initially because their effectiveness may deteriorate during the operational life of the BWRX‐300 plant

If the magnitude of earth pressure loads used for the design are deemed inadequate to address the uncertainties and variations of subgrade properties, the rock weight or the equivalent linear soil and rock stiffness properties used for the 1‐g design SSI analysis are adjusted


Probabalisitic Earth Pressure AnalysisAdequacy of design margin in the soil and rock pressure loads to address the uncertainties and variations of subgrade properties is judged based on:• Variability of soil and rock properties used as input for the non‐linear FEA • Significance of non‐linear and anisotropic subgrade response on the soil and rock pressure demandsProbabilistic analyses may be performed to demonstrate that the magnitude of earth pressures used for the design are adequate to address:• Parameter uncertainties related to natural randomness and uncertainties in measurements• Model uncertainties related to the models used for earth pressure calculationsProbability distributions of soil and rock pressures are calculated using:• First Order Second Moment (FOSM) method and/or Monte Carlo Method• Results of statistical analysis of geotechnical site investigations and laboratory tests data• Belief probabilities based on engineering judgment • Simple mathematical models relating the subgrade parameters to the earth pressures Model uncertainties are addressed by considering different models utilizing fewer input parameters


Equivalent Linear Subgrade Static Properties To calculate UB earth pressure demands for the design of RB structure, profiles of the following equivalent linear properties of subgrade materials are developed for use as input for the 1‐g SSI analysis based on the site investigation and laboratory testing program results:• UB values for effective unit weights of soil materials calculated as mean plus one standard deviation of the measured data• LB values for soil Young’s moduli calculated as weighted log mean plus one log standard deviation of the data obtained from field and triaxial laboratory tests • Poisson’s ratio (𝜈 ) of soil representative of at‐rest lateral pressure conditions calculated as

𝜐 using UB values for at‐rest coefficient (𝐾

• LB values for rock Young’s moduli (𝐸 ) calculated based on data obtained from field and triaxial laboratory tests and using empirical correlations and Geotechnical Strength Index or Rock Mass Rating (RMR) qualifications of rock mass properties


Site‐Specific Design Ground Motion5% damped broad frequency band spectra define the amplitude and frequency content of design ground motion for site‐specific SSI analysis of the deeply embedded RB structure:• Foundation Input Response Spectra (FIRS) at bottom of RB foundation• Performance Based Surface Response Spectra (PBSRS) at ground surface• Performance Based Intermediate Response Spectra (PBIRS) at intermediate embedment depth elevationsPBIRS are developed for one or more elevations between the PBSRS and FIRS elevations:• Corresponding to significant shear wave velocity (VS ) contrasts in the basecase subgrade profiles• Central elevation may be used for basecase profiles with a relatively uniform VS variation with depth FIRS, PBSRS and PBIRS are developed following the ASCE 43‐05 performance‐based approach• One‐dimensional (1‐D) Approach 3 probabilistic Site Response Analyses (SRA) are performed to account for the local site wave propagation characteristics• Different Vertical/Horizontal (V/H) ratios may be used to define the vertical FIRS, PBSRS, and PBIRS for sites characterized by variations in subgrade conditions with depth per EPRI Report 3002011804 guidance

5 sets of acceleration time histories (ATHs) are developed for the SSI analyses per requirements of ASCE 43‐05, Chapter 2 by fitting 5 sets of ground motion seed records to the target spectra


Strain Compatible Subgrade Dynamic Properties SSI analysis of deeply embedded RB structure use:• BE, LB and UB subgrade profiles to account for the uncertainties and variations of the dynamic properties of subgrade materials• Dynamic stiffness and damping properties compatible to the free‐field strains induced by an SSE level seismic event to account for primary non‐linearity of subgrade materials • Strain‐compatible stiffness and damping properties consistent with the site‐specific probabilistic hazard parameters considered for development of FIRS, PBSRS and PBIRS

BE, LB and UB profiles are developed for the SSI analysis based on weighted median (𝜇 ) and log‐normal variances (Var ) of results of probabalisitic equivalent‐linear SRA

• 𝜇 rock and soil mass density properties are assigned to the BE, LB and UB profiles• 𝜇 strian‐compatible VS and damping are assigned to the BE profile• 𝜇 Var strian‐compatible VS and 𝜇 Var damping are assigned to the LB profile• 𝜇 Var strian‐compatible VS and 𝜇 Var damping are assigned to the UB profile

• UB VS are adjusted to ensure are at least 1.5 times larger than the BE Vs, and UB VS are at least 2 3⁄times smaller than the BE VS per recommendations of ASCE 4‐16


Seismic SSI Analysis Methodology Seismic demands for the design of RB SSCs are developed from results of site‐specific SSI analyses of deeply embedded RB structure that are performed using:• The SASSI (a system for analyses of soil‐structure interaction) sub‐structuring frequency domain method• A set of frequencies of analysis that ensure accurate SSI analysis results for the whole range of frequencies of interest

SASSI extended subtraction method (ESM) simplification may be used for calculations of the SSI system impedance matrix with interaction nodes established at: • Interfaces between the excavated volume and structural models• Horizontal planes at PBSRS and PBIRS elevations The accuracy of the ESM solution is demonstrated based on the guidelines provided in SRP 3.7.2 or by comparing results of two analyses of RB quarter model using the SASSI ESM and direct method, where all nodes of the excavated volume are specified as interaction nodes


Seismic SSI Analysis Methodology SASSI analyses use models that include linear elastic representations of:• The RB structure and surrounding foundations and structures• Surrounding subgrade layered continuum• The excavated volume of subgrade materials replaced by the embedded part of the structural model

outer wall

inner shaft

basematfloors

shear walls

Below-grade RB shaft FE Model Excavated Volume FE Model


Seismic SSI Analysis Methodology SASSI extended subtraction method (ESM) simplification may be used for calculations of the SSI system impedance matrix with interaction nodes established at: • Interfaces between the excavated volume and structural models• Horizontal planes at PBSRS and PBIRS elevations The accuracy of the ESM solution is demonstrated based on the guidelines provided in SRP 3.7.2 and through comparison of results of two analyses of RB quarter model using • The SASSI ESM simplification, where a selected number of the excavated volume nodes are specified as interaction nodes, and • The SASSI direct method (DM), where all nodes of the excavated volume are specified as interaction nodes

SSI analyses of deeply embedded RB capture effects of SSSI by using simple models:• Representing BE dynamic properties of surrounding RwB, CB and TB structures and foundations • Capable of capturing all global modes of vibration of RwB, CB and TB structures with significant (> 20%) modal mass participations in the three orthogonal directions


Modeling of Equipment Structure Interaction (ESI)Dynamic properties of subsystems, components, and equipment are included in the SSI analysis model based on the decoupling criteria of SRP 3.7.2.3.B• Dynamic properties of the Reactor Pressure Vessel (RPV) and its components are represented by a lumped mass stick model capable of capturing all significant modes of RPV seismic response

ESI may be considered for the development of ISRS for equipment qualification by using: • Direct method, which consists of explicit modeling of the equipment mass, stiffness, and damping characteristics as one or more additional degrees of freedom in the primary model•Mass‐impedance ESI method, in which the equipment mass and dynamic stiffness impedance are used to calculate ESI‐modified ISRS at the secondary system support location• Generalized ESI method in 2017 EPRI Report 3002010666: “Coupled Analysis of Primary‐Secondary System to Generate Floor Response Spectra, Quantifying Reduction Factors for Coupled In‐Structure Response Spectra Amplitudes”, which allows for considering multiple degrees‐of‐freedom for secondary systems attached to the primary structure at multiple node locations


Approaches for Meeting ISG‐017 Requirement Either one of the following three approaches may be used to meet the intent of DC/COL ISG‐017 to ensure the deterministic SSI analysis of embedded RB structure use ground motion inputs that are hazard consistent with the results of probabilistic SRA:1. Performing NEI checks described in Section 3.2.3 of 2009 NEI white paper: “Consistent Site‐

Response/Soil‐Structure Interaction Analysis and Evaluation” to ensure the horizontal and vertical ground input to the SSI analysis BE, LB and UB profiles at FIRS elevation envelopes the free field design motion at the PBSRS and PBISRS elevations

2. Enveloping the results of three or more sets of SSI analysis of BE, LB and UB profiles with FIRS, PBSRS and PBIRS compatible input motions applied at the corresponding FIRS, PBSRS and PBIRS elevations

3. Performing approach 1 NEI checks only for the horizontal direction and using vertical free‐field input motion for the SSI analysis of BE, LB and UB profiles that are constrained along the embedment depth of the SSI profiles based on the same V/H ratios used for the probabilistic SRA as described in EPRI report 3002011804: “Modeling Vertical Free‐Field Motion for Soil‐Structure Interaction of Embedded Structures”

Alternatively, a probabilistic SSI analysis may be performed following the requirements of ASCE 4‐16, Section 5.5 that by definition satisfies the DC/COL ISG‐017 requirement


SSI Effects Sensitivity Evaluations Demands from seismic design of RB SSCs are developed using an envelope of results from design basis SSI analyses performed:• BE, LB and UB profiles of subgrade dynamic properties compatible to the strains generated by free field motion and representative of fully saturated soil conditions below nominal groundwater level• Vertically propagating shear (SV) wave and compression (P) wave ground motion inputs in the horizontal and vertical direction, respectively• FE model representing BE structural stiffness and damping properties• Fully bonded conditions at SSI interfaces that neglects the resistance and stiffness of excavation supports or lean concrete used to fill the gaps between the RB exterior walls and the excavated subgrade

Sensitivity SASSI analyses are performed to address SSI uncertainties related to:• Effects of non‐vertically propagating seismic waves• Effects of structural properties variations• Excavation support and fill concrete effects• Soil separation effects• Groundwater level variation effects


SSI Effects Sensitivity Evaluations In general, the effects of SSI parameter variations on the RB seismic response are evaluated:• Using results of SSI analyses of models with BE subgrade properties representing bounding conditions of the SSI parameter being evaluated that use broad frequency band input ground motion• Comparing in‐structure responses at selected key nodal locations and main stress demand components calculated for selected cross sections in the main RB below‐grade seismic load resisting members

If comparisons show significant exceedances (> 10%) in the RB response due to effects of evaluated SSI parameter, the results of the sensitivity analysis are included in the RB seismic design basisSensitivity non‐linear seismic SSI analyses may be performed for sites characterized by a high seismicity and a highly non‐linear subgrade materials to assess• Secondary non‐linearity of subgrade materials, including non‐linearities at rock discontinuities• Non‐linearity at soil‐structure interfaces, such as separation and sliding A set of control motions and subgrade material constitutive models are used for non‐linear SSI analyses that are consistent with:• Design earthquake ground motion levels considered for development of strain‐compatible properties • Soil and rock constitutive models and BE basecase models used for 1‐g non‐linear FIA and probabilistic SRA


Effects of Non‐Vertically Propagating Seismic WavesSite‐specific sensitivity evaluations are performed on the potential effects of non‐vertically propagating seismic waves resulting from:• Multidimensional, two‐ or three‐dimensional (2‐D or 3‐D), wave propagation site significantly different from horizontally infinite horizontal layers assumed by the 1‐D probabilistic SRA and deterministic SSI analyses • Local seismic sources generating inclined waves, located at distances no more than 15 km from the plant Deterministic wave propagation analyses may be performed on 2‐D or 3‐D site models to study potential generation of inclined seismic waves and their effect on the free‐field ground motion For sites with dipping bedrock surfaces of more than 30 degrees and dipping soil layers of more than 20 degrees (NUREG/CR‐0693)Deterministic analyses may be performed on free‐field and RB SSI models to study potential effects of inclined vertical waves on the free‐field ground motion and RB seismic designSensitivity evaluation performed for sites with relatively uniform subgrade conditions with depth (for non‐uniform sites the effects of inclined waves are reduced due to Snell’s law, NUREG/CR‐6728 ) Sensitivity analyses are performed on models representing BE material properties


Effects of Structural Properties VariationsBE effective stiffness properties are assigned to RB concrete made structural members depending on the level of stress they experience under the most critical seismic load combination• SSI analysis is performed for the BE profile using RB model with full (uncracked concrete) stiffness properties and lower OBE damping to calculate seismic stresses in reinforced concrete (RC) and/or steel‐concrete (SC) composite members • Stiffness properties are assigned to RC members per ACI‐349 standard and reduced as specified in ASCE 43‐05 to account for concrete cracking if the stress levels exceed specified cracking stress limits• Stiffness properties are assigned to SC members per AISC N690 standard depending on the stress levels in reference to concrete cracking threshold limits• Higher SSE damping is assigned to cracked RC and SC members to account for a higher energy dissipation• Another SSI analysis is performed for the BE profile on the structural model with the modified effective stiffness properties to ensure no additional cracking will occur due to stress redistribution

Alternatively, design basis SSI analyses may use structural stiffness properties that yield conservative design demands for the site‐specific conditions• Conservative seismic design demands for hard‐rock‐high‐frequency sites may be developed from structural models with UB stiffness properties


SSI Interface Modeling EffectsSensitivity seismic SSI analysis may be performed for BE subgrade profile on an RB structural model with BE properties that includes the excavation support structure and the fill concrete• Shell and beam elements represent the BE dynamic properties of the excavation support structure and Solid elements represent the dynamic properties of concrete fill• In‐structure responses at key locations are compared with results from the design basis SSI analyses model that excludes the excavation support and concrete fill to evaluate their effects on RB seismic response and design

Sensitivity evaluations are performed to evaluate effects of separation at soil‐structure interfaces• Contact spring results of seismic and 1‐g SSI analyses are compared to assess the extent of possible soil separation at SSI interfaces• Significance of soil separation on RB seismic design is conservatively evaluated based on results of sensitivity SSI analysis performed on a model in which SSI interfaces that may experience soil separation are assumed to remain unbonded for the total duration of the earthquake• Non‐linear SSI analyses may be performed using non‐linear contact elements at SSI interfaces and a set of narrow frequency band motions representative of SSE level earthquake events to obtain less conservative estimates of the significance of soil separation on the RB design at high seismicity sites


Groundwater Variation Seismic SSI EffectsPotential effects of groundwater variability on RB seismic response and design are assessed by comparing the seismic responses obtained from two sensitivity RB SSI analyses for:• Fully saturated soil profile with BE soil dynamic properties representative of accidental flood groundwater level; and • Dry soil profile with BE soil dynamic properties representative of the extreme conditions when the groundwater is located below the RB foundation bottom elevation

The results of sensitivity analyses are also compared with enveloping results of design basis SSI analyses of BE, LB and UB profiles representative of fully saturated soil below the nominal groundwater elevation• The results of the two sensitivity analyses are included in the RB seismic design basis if their results significantly exceed (>10%) the design basis demands

II/I Interaction Evaluations Approach


CB, TB and RwB Structural Design Bases CB, TB and RwB structures are in close proximity to the Seismic Category I (SC‐I) RB and are designed in accordance with their seismic classification• CB and TB are classified and designed per IBC and ASCE‐7 as Risk Category IV (TB and CB are part of emergency backup power‐generating station and the CB control room serves as emergency shelter) • RwB is classified and designed as RW‐IIa per regulatory guidance of RG 1.143 (RwB contains radioactive materials with high release consequences)

Building Class.Design Loads Structural Design Codes

Basis Seismic Extreme Wind Flood RC members

Steel members

SC Members

CBNon-SC I IBC ASCE 7 Risk

Category IVRisk Category IV;ICC 500 (Storm Shelter) ASCE-7 ACI-318 AISC 360 N/A

TB

RwB RW-IIa RG 1.143 ½(SSE)

Tornado: 3/5 x (RG 1.76, Table 1)Tornado Missiles: Sch. 40 pipe and automobile per SRP 3.5.1.4

½ x (RG 1.59 Probable Maximum Flood)

ACI 349AISC

N-690AISC

N-690


II/I Seismic Interaction EvaluationsPer Criterion C of SRP 3.7.2, seismic II/I interaction evaluations are performed to ensure: • CB, TB and RwB structures do not collapse or collide with the RB to impair RB structural integrity or the safety functions of RB SC‐I SSCs; • CB structure does not collapse and result in incapacitating injury to the control room occupants; and • TB structure does not collapse and result in impairment of main steam line safety functionsBased on results of seismic analyses of CB, TB and RwB, II/I seismic evaluations demonstrate that:• Integrity of CB, TB and RwB lateral load resisting system under SSE loading is not compromised, • Stability of CB, TB and RwB foundations under SSE loading is not compromised• Gap distances with the RB are sufficient to prevent physical interactionsSeismic II/I interaction evaluations consider limited inelastic responses:• Limit State C (LS‐C) inelastic energy absorption factors in ASCE 43‐05, Table 5‐1 are used to calculate seismic demands for II/I interaction evaluations of CB, TB and RwB structural members• Seismic displacements calculated from seismic analysis of linear elastic structural models are increased to account for inelastic deformations (1.8 times increase may be conservatively applied in accordance with ASCE 41‐17, Table 7‐3)


II/I Extreme Wind Loads Interaction EvaluationsII/I interaction evaluations are performed per SRP 3.3.2.III.8 guidance to demonstrate the ability of CB, TB and RwB structures to prevent adverse interactions with CSC‐I SSCs under:• Tornado wind loadings specified by RG 1.76 • Hurricane wind loadings specified by RG 1.221 II/I evaluations are performed on primary members of wind force resisting systems of CB, TB and RwB structures ensure adequate global response• Secondary members (e.g. components and cladding) not evaluated for II/I Interaction• Inelastic response of the CB and TB steel braced frames may be considered in accordance with the provisions of AISC 360, Appendix 1.3

Extreme wind missiles not considered for the CB, TB and RwB II/I interaction evaluations because:• Effects of missile loads are localized and do not affect the global stability of CB, TB and RwB structures• RB design basis missile loads envelope effects of localized failure of CB and TB components/cladding• RwB is designed for design basis tornado‐generated missiles• Safety‐related SSCs housed in non‐SC I structures have adequately designed missile barriers

BWRX‐300 Generic Design Approach


BWRX‐300 Generic Design ApproachUtilizing an innovative approach focused on cost, the BWRX‐300 RB structure is conceptually designed to meet an economically viable cost target by reducing the required material quantities • Sizes of structural members are limited based on a cost target required for an economically viable BWRX‐300 SMR• Generic evaluations are being performed using a set of generic site input parameters to evaluate the applicability of the innovative design‐to‐cost solution for a wide range of seismological and geotechnical site conditions

Generic SSI analyses are performed on FE model of deeply embedded BWRX‐300 RB structure representative of the design‐to cost solution:• Static demands on key structural members due to self‐weight, equipment, live, hydrostatic pressure and soil pressure loads• SSE seismic demands on key structural members and SSE in‐structure responses for evaluation of key equipment and systems• Calculated demands are used to check the applicability of the BWRX‐300 RB design for different types of generic site conditions defined by the site location, seismicity and geology to ensures the design is economically viable for the majority of candidate sites across North America


Generic Site ParametersGeneric evaluations of the BWRX‐300 RB use generic site input parameters representative of a wide range of seismological and geotechnical conditions for candidate sites that are: • Developed from an extensive database of information collected from North American candidate sites following the approach described in SMiRT‐22 Division VI paper: “Generic Input for Standard Seismic Design of Nuclear Power Plants” • Representative of realistic subgrade property variations with depth at typical candidate sites• Compatible to the strain levels generated by applied loading• Developed to provide UB static earth pressure demands for site‐specific conditions• Representative of saturated soil conditions with groundwater table at plant grade elevation• Representative of upper bound estimate of seismic hazard at Central and Eastern US (CEUS) candidate sites• Representative of median estimate of seismic hazard at Western US (WUS) candidate sites


Generic Design Response SpectraThree sets of horizontal and vertical Generic Design Response Spectra (GDRS) define the design ground motion at plant grade elevation for firm, median and hard CEUS and WUS sites• 5% damped GDRS are anchored at Peak Ground Acceleration (PGA) of 0.3 g


Generic Subgrade ProfilesEight generic layered subgrade profiles representative of as‐built subgrade geotechnical conditions across the North American continent are used for the generic evaluationsThe generic profiles are categorized in terms of average measured shear‐wave velocity of top 30 m of soil (𝑉𝑠 ) and the depth of base rock: • 𝑉𝑠 = 180 m/sec profiles are representative of medium stiff soil sites, • 𝑉𝑠 = 270 m/sec profiles are representative of firm soil sites;• 𝑉𝑠 = 400 m/sec profiles are representative of stiff soil sites;• 𝑉𝑠 = 500 m/sec and 760 m/sec profiles are representative of soft rock sites;• 𝑉𝑠 = 900 m/sec representative of firm rock sites; and • 𝑉𝑠 = 2032 m/sec representative of hard rock sites


Generic Subgrade ProfilesGeneric seismic SSI analyses are performed for eight generic profiles of dynamic subgrade properties representative of wide range of geotechnical site conditions

Stiffness and damping dynamic properties are compatible to strains generated by a design level earthquake


Generic Subgrade ProfilesEight generic subgrade profiles for static FE analyses

Self supporting rock (𝑉 1000 𝑚/sec) is modeled weightless


Generic Analysis CasesSelf‐weight, slab load and soil pressure load demands for the generic evaluations are obtained from analyses of the seven generic subgrade profiles

Static Analysis

Case

Static Subgrade Properties Profile

NameNominal 𝐕𝐬𝟑𝟎

(m/sec)Bedrock

Depth (m)1 180-600 180 6102 270-60 270 61.03 400-300 400 3054 500-21 500 21.35 760-15 760 15.26 760-60 760 60.67 900-8 900 7.68 2032-30 2032 30.5


Generic Analysis CasesSeismic demands for generic evaluations are obtained from asset of eleven SSI analyses representing different geomechancial and seismological site conditions

SSI Analysis Case

Subgrade ProfileSeismic Region

GDRSName

Nominal 𝐕𝐬𝟑𝟎(m/sec)

Bedrock Depth (m)

1 180-600 180 610 WUSFirm2 270-60 270 61.0 WUS

3 760-15 760 15.2 WUS4 400-300 400 305 CEUS

Median5 500-21 500 21.3 WUS6 760-15 760 15.2 WUS7 900-8 900 7.6 WUS8 500-21 500 21.3 CEUS

Hard9 760-60 760 60.6 CEUS

10 900-8 900 7.6 WUS11 2032-30 2032 30.5 CEUS

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