ML21200A072

ACRS July 20 - Overview of ASME Section III Division 5 and NRC Review and Potential Endorsement.Pdf

ML21200A072
Person / Time
Issue date:	07/20/2021
From:	Jeffrey Poehler NRC/RES/DE
To:
R. Roche-Rivera
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Download: ML21200A072 (52)

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Overview of Section III, Division 5 Advisory Committee for Reactor Safeguards July 20, 2021 Jeff Poehler, Sr. Materials Engineer Reactor Engineering Branch Office of Nuclear Regulatory Research 1

• ASME Section III Division 5 Scope ASME Section III, - Division 5 rules govern the construction of vessels, Rules for piping, pumps, valves, supports, core support structures and nonmetallic core components for Construction of use in high temperature reactor systems and their Nuclear Facility supporting systems Components - o Construction, as used here, is an all-inclusive Division 5, High term that includes material, design, fabrication, installation, examination, testing, overpressure Temperature protection, inspection, stamping, and Reactors certification

- High temperature reactors include

• Gas-cooled reactors (HTGR, VHTR, GFR)

• Liquid metal reactors (SFR, LFR)

• Molten salt reactors, liquid fuel (MSR) or solid fuel (FHR) 2

Examples of Different Advanced Reactor Designs Being Developed By Industry Fast Reactors Gas Reactors Molten Salt Reactors GE Hitachi TerraPower, TWR X-Energy, PRISM Xe-100 Framatome SC-HTGR Elysium, MCSFR Terrestrial Energy IMSR Advanced Reactor Concepts, ARC-100 ThorCon General Atomic EM2 Ultra Safe Nuclear MMR Flibe Energy (Gas-cooled Fast Westinghouse, LFR LFTR (thorium) TerraPower Reactor)

MCFR TerraPower & GEH Oklo, Aurora Heat Pipe Reactor Natrium Westinghouse eVinci Kairos Power KP-FHR Moltex Energy, SSR 3

Division 5 - A Component Code

• Division 5 is organized by Code Classes:

- Class A, Class B, Class SM for metallic components -

• Class A is analogous to Class 1 in Section III, Division 1

• Class B is analogous to Class 2 in Section III, Division 1

• Class SM is for metallic core supports

- Class SN for non-metallic components - e.g. graphite core supports

• Division 5 recognizes the different levels of importance associated with the function of each component as related to the safe operation of the advanced reactor plant

• The Code Classes allow a choice of rules that provide a reasonable assurance of structural integrity and quality commensurate with the relative importance assigned to the individual components of the advanced reactor plant 4

Section III, Division 5 Rules for Metallic Components do not address

• Deterioration in service due to

- Corrosion

- Mass transfer phenomena

- Radiation effects

- Other material instabilities

• Continued functional performance of deformation-sensitive structures such as valves and pumps 5

History of Construction Rules for High Temperature Reactor Components

• 159X Code Cases - complete construction rules for elevated temperature pressure boundary metallic components in early 1970s

• Regulatory Guide 1.87 (Rev 1, June 1975) endorsed 159X Code Cases with conditions

• Code Case series 1592-1596 converted to Code Case N-47, which later formed the basis for Section III, Division 1, Subsection NH

• Division 5 first published in 2011, combined NH, other high-temperature code cases, and rules for graphite core components (new).

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Section III Division 5 Organization Class Subsection Subpart Subsection ID Title Scope General Requirements Class A, B, & SM A HAA Metallic Materials Metallic HA Class SN B HAB Graphite and Composite Materials Nonmetallic Class A Metallic Pressure Boundary Components Class A A HBA Low Temperature Service Metallic HB Class A B HBB Elevated Temperature Service Metallic Class B Metallic Pressure Boundary Components Class B A HCA Low Temperature Service Metallic HC Class B B HCB Elevated Temperature Service Metallic Class A and Class B Metallic Supports Class A & B HF A HFA Low Temperature Service Metallic Class SM Metallic Core Support Structures Class SM A HGA Low Temperature Service Metallic HG Class SM B HGB Elevated Temperature Service Metallic Class SN Nonmetallic Core Components Class SN A HHA Graphite Materials Graphite HH Class SN B HHB Composite Materials Composite 7

Metal Maximum Use Temperature Temperature Creep Affects Cyclic Life Negligible Creep (Creep-fatigue Interaction)

Division 5 Temperature Temperature Creep Does Not Affect Cyclic Life Boundaries (Negligible Creep Regime)

Code Temperature for Class A Division 1 No Creep Effects Boundary (700F ferritic; 800F Components austenitic)

Design Lifetime 8

HBB Materials and Design Data

• Limited set of materials:

Minimum carbon content of 0.04

- Type 304 Stainless Steel*

weight % required for better high

- Type 316 Stainless Steel* temperature properties - Type 304H

- Alloy 800H and Type 316H - this designation is not used in Section III-5.

- 2.25Cr-1Mo

- 9Cr-1Mo-V (Grade 91)

- Alloy 617 (Code Cases N-872 and N-898)

• Design parameters are mostly self contained in Division 5, except the following contained in Section II:

- Elastic constants

- Thermal properties

- Part of yield strength ( ) table

- Part of ultimate tensile strength ( ) table 9

Failure Modes Addressed by Section III-5 Failure Mode Type Prevented By Location Analysis Method(s)

Plastic collapse Load controlled Primary load design HBB-3000 Elastic Creep-rupture Load controlled Primary load design HBB-3000 Elastic Creep-fatigue Deformation controlled Creep-fatigue rules HBB-T Elastic, Inelastic, EPP Gross distortion due to Deformation controlled Strain limits HBB-T Elastic, Inelastic, EPP incremental collapse and ratcheting Buckling due to short- Load controlled or strain Buckling limits (time- HBB-T Elastic, Inelastic term loadings controlled, or both independent)

Creep buckling due to Load controlled or strain Buckling limits (time- HBB-T Elastic, Inelastic long term loadings controlled, or both dependent) 10

HBB Primary Load Design

• Based on elastic analysis.

Design Load

• Load-controlled

• Uses stress classification and Single temperature, Time-history of loading pressure, and set of linearization. forces Time-dependent Uses the allowable

• Design and service level load Time-independent stress Uses allowable stress checks.

Unique to Division 5

• Accounts for thermal aging Service Load Very similar to Section I and VIII effects with factors on yield and ultimate strength

• Welds: Strength reduction factor applied 11

HBB - Allowable Stresses

• Both time-dependent and time-independent allowable stresses included.

• S0 - Allowable stress for design loadings

• Service Level Loading Allowable stresses

- Sm - Time independent

- St - Time dependent

- Smt - Allowable limit for general primary membrane stress for Service Level A and B

- Sr - Expected minimum stress-to-rupture. Used for Level D limits and in deformation-controlled analyses (HBB-T) 12

HBB - Basis for Allowable Stresses

• S0 - Equal to the higher of S values from Section II-D, Subpart 1, Table 1A, or 300,000 hour0 days <br />0 hours <br />0 weeks <br />0 months <br /> Smt

• Sm - From Section II-D, Table 2A, Sm values at lower temperatures, extended to higher temperatures using same criteria

• Smt is the lower of Sm (time-independent) and St (time-dependent) 13

• The lowest of:

(a) 100% of the average stress required to obtain a total (elastic, plastic, primary, and secondary creep) strain of 1%;

HBB - Basis (b) 80% of the minimum stress to cause for St (HBB- initiation of tertiary creep; and 3221) (c) 67% of the minimum stress to cause rupture (Sr).

• Determination of St is inherently conservative because of the 80% and 67%

factors applied to tertiary creep initiation and stress-to-rupture.

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• Sy - yield stress as function of temperature

• Su - ultimate strength Other

• R - Weld strength reduction factors Stresses/Material

• Tensile and yield strength reduction Properties factors for longtime services (Table HBB-3225-2)

• Isochronous stress-strain curves (ISSCs) 15

Deformation Controlled Quantities (HBB-T)

Characteristics Evaluation Methods

• A subset of the design limits: Elastic

• All Class A materials

• Rules found in Nonmandatory Appendix

- Strain accumulation analysis HBB-T

• Bounding analysis

- 1% average strain

- 2% linearized bending

- 5% maximum strain Inelastic

• All Class A materials

• Rules found in NMA HBB-T

- Creep-fatigue analysis

• But no material models in Code (currently)

• Exact analysis

- Buckling

• Typically are driven by secondary (self limiting) stresses Elastic

• Subset of materials (304 and 316 SS, A617, perfectly- soon to be Grade 91) plastic

• Rules in N-861 and N-862

• Bounding analysis analysis (EPP) 16

Creep-fatigue (HBB-T-1411)

• Basically:

1. Compute creep damage based on life fraction:

2. Compute fatigue damage based on a cyclic life fraction:

Creep damage

3. Consult interaction diagram for pass/fail

• Welds: same interaction diagram, factors on damage Fatigue damage 17

Creep Damage (HBB-T-1433)

Stress relaxation profile stress

• Construct a stress relaxation curve for each hold in each cycle type time

• Determine creep damage with a time fraction rule for each time interval Minimum stress-to-rupture for Alloy 617

=1

• Sum creep damage for all time intervals needed to represent the specified elevated temperature service life = =1(/

)

• Database: creep rupture tests

• Welds: use stress rupture factor to reduce the creep rupture strength of the base metal 18

Buckling and Instability (HBB-T-1500)

• Limits for both time-independent (creep not significant) and time-dependent (creep-significant) buckling are provided.

• Load factors for both load-controlled and strain-controlled bucking provided.

• Figures provide temperature/time combinations below which the time-independent buckling limits may be used.

• For conditions where stain-controlled and load-controlled buckling may interact, or significant elastic follow-up may occur, the load factors for load-controlled buckling are also to be used for strain-controlled bucking.

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Elastic, Perfectly Plastic (EPP) Analysis

• Use different allowable stresses as pseudo yield stress in EPP finite element analysis to determine different bounding characteristics for different failure modes

• Intended as simplified screening tools in place of elastic analysis methods

• No stress classification

• Any geometry or loading

• Accounts for redundant load paths

• Simpler to implement

- Based on finite element results at integration points, no linearization

• Current status EPP Design Check EPP Code Case Materials Currently Covered Grade 91, Alloy Primary Load Under development All Class A materials 617 covered by Strain Limits N-861 304H, 316H, Grade 91, Alloy 617 revision of code cases. Not reviewed by NRC Creep-fatigue N-862 304H, 316H, Grade 91, Alloy 617 20

Inelastic Analysis Methods Currently the Code does not Historical experience on the provide reference inelastic Clinch River Breeder Reactor Current status models for any of the Class A Project shows that inelastic materials analysis is:

• Specification of the

• The least over-conservative

• Unified viscoplastic material model left to of the Division 5 options constitutive models for owners Design

• Necessary in critical 316H stainless steel and Specification or designers locations where design by Grade 91 steel have been

• Limits application of the elastic analysis is too developed inelastic rules conservative to produce a

• Action to add Grade 91 reasonable design model just balloted.

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Class B Rules HCA - Class B Low Temperature

• Essentially reference III-1, Class 2 rules HCB - Class B High Temperature

• Allows more materials than HBB

• Mandatory Appendix HCB-II contains allowable stress values

• Different allowable stresses for:

• Negligible creep

• Non-negligible creep

• Mandatory Appendix HCB-III defines times and temperatures where creep effects can be neglected.

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Class B Rules Extend rules of Division 1, Class 2 (Subsection NC) to elevated temperature service.

Based on a design-by-rule approach. Design Lifetime concept is not used.

Allowable stresses based on extrapolated 100,000 hour0 days <br />0 hours <br />0 weeks <br />0 months <br /> creep-rupture properties.

Fatigue damage from cyclic service is addressed only for piping with creep effects (HCB-3634).

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Core Supports HGA- Low Temperature

• mainly references Section III-1 rules.

HGB - Similar to HBB rules.

• Same materials and allowable stresses.

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Construction Rules For

• Section III Division 5 is the only Nonmetallic design code that provides construction rules for graphite.

Components (Class SN)

• Graphite materials are used in thermal spectrum advanced reactors because of their excellent neutron moderation properties 25

• There is no single nuclear grade of graphite -

therefore, cant design around a specific nuclear Graphite grade as metals can (i.e., 316H)

• Graphite is heterogeneous by nature, and contains significant pores and cracks.

• Graphite is not ductile - Brittle or quasi-brittle fracture behavior Irradiation significantly alters the graphite behavior - Behavior is completely different before and after turnaround dose is achieved.

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ASME Code Considerations 50X

• Because all graphite is brittle and contains preexisting flaws, 100X

• Core components need to be designed to accept 200X some amount of cracking.

500X

• Probabilistic versus deterministic design approach

• Deterministic is generally too limiting for a brittle material

• A distribution of possible strengths in a material is needed for quasibrittle materials (i.e., flaw size for graphite).

• Probability of failure in component based upon inherent strength of graphite grade and applied stresses during operation.

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Structural Integrity Assessment Methods

• Simplified Assessment (HHA-3220)

1. Simplified Analysis Method

- Simplified conservative method based on ultimate strength derived from Weibull statistics.

• Full Assessment (HHA-3230)

- Weibull statistics for failure probability

- Maximum allowable probability of failure defined for three Structural Reliability Classes (SRCs).

Structural Reliability Class Maxi. Prob. of Failure SRC-1 1.00E-04 SRC-2 1.00E-02 SRC-3 1.00E-01

• Design by Test (HHA-3240)

- Full-scale testing to demonstrate that failure probabilities meet criteria of full analysis. Graphite code is a process.

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Special How toConsiderations apply degradation to POF in Design of Graphite Core Components

• Oxidation (HHA-3141)

- Loss of strength and geometry changes to be considered

• Irradiation (HHA-3142)

- Property changes to be Irradiation Degradation addressed

• Abrasion and Erosion (HHA-3143)

- To be considered when there is relative motion or high gas flow rate in gas-cooled designs From Dr. Mark Mitchell - PBMR Inc.

Designer should determine the specific changes for their selected graphite grade

Graphite Degradation (Form MDS-1 Material Data Sheet)

ASME BPVC Data sheets capture:

• Material properties

- Strength

- Elastic modulus

- CTE

- Conductivity

- Thermal conductivity (Diffusivity)

• Irradiation effects

• Temperature dependence

- Temperature affects everything

• Oxidation effects

Summary Division 5 covers the rules Division 5 was issued as Though the design rules for the design, fabrication, part of the 2011 Addenda development for metallic inspection and testing of to the 2010 Edition of the components traced all the components for high BPV Code way to the 1960s temperature nuclear reactors ASME Code committees are The rules for nonmetallic actively pursuing code rules Construction rules for both components are unique improvement and metallic and nonmetallic among all design codes developing new components are provided world-wide technologies to support Advanced Nuclear 31

NRC Review and Potential Endorsement of ASME BPVC,Section III, Division 5 Advisory Committee for Reactor Safeguards July 20, 2021 Jordan Hoellman, Jeff Poehler, Project Manager Sr. Materials Engineer Advanced Reactor Policy Branch Reactor Engineering Branch Office of Nuclear Reactor Regulation Office of Nuclear Regulatory Research

Purpose Provide an overview of the process for NRCs review and Discuss likely exceptions and potential endorsement of limitations to NRCs 2017 ASME BPVC Section III, endorsement.

Division 5, High Temperature Materials (Section III-5) 33

NRC Guidance Documents for Section III-5 Endorsement NUREG-2245 Technical Review of the 2017 Edition Regulatory Guide (RG) - Acceptability of ASME of ASME Section III, Division 5, Section III, Division 5, High Temperature Reactors High Temperature Reactors (DG-1380)

• Document the staffs technical evaluation of the

• Describes an approach that is acceptable to the 2017 Edition of Section III, Division 5 and Code NRC staff to assure the mechanical/structural Cases N-861 and N-862 for acceptability integrity of components for use in in elevated and endorsement. Provide technical basis for DG- temperature environments, which are subject to 1380. time-dependent material properties and failure modes.

• Contains exceptions and limitations to the staffs endorsement.

• The regulatory guide will update the guidance of RG 1.87.

• Appendix A of DG-1380 contains staff guidance on quality group classification for high-temperature reactors.

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Scope of Staff Review 1 2 3 Section III-5, 2017 Code Cases N-861 Alloy 617 Code Cases Edition and N-862

• Separate technical basis

• Did not review document being Nonmandatory Appendix developed HBB-Y, so not endorsing.

• Will merge results into final DG-1380 35

Contractor Expert Recommendations

• To ensure an independent review of the technical adequacy of Section III, Division 5, NRC used contractors not directly involved with Division 5 code development

• NRC also used contractors more involved with code development on a limited basis to provide historical perspective on Division 5.

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Relied on previous reviews when possible.

- Code Cases 1592-1596.

- Section III, Division 1.

The NRC staffs review was augmented by Review input from several national laboratories Process - and commercial contractors.

General See NRCs Advanced Reactor Public Website:

https://www.nrc.gov/reactors/new-reactors/advanced.html#endorev 37

Contractor Reports Contractor Topics ML #

PNNL Design, Fabrication, Examination, Testing (HBB/HCB/HGB-3000, 4000, ML20269A145 5000, 6000)

Mechanical design appendixes for metallic core supports (HGB-I, HGB-II, HGB-III, HGB-IV)

ORNL Materials (HBB/HCB/HGB-2000) ML20269A125 Tables and Figures (Mandatory Appendix HBB-I-14)

Guidelines for Restricted Material Specifications (Non-Mandatory Appendix HBB-U)

NUMARK Mechanical Design Appendixes for Class A and Class B components ML20349A003

/EMC2 (HBB-II, HBB-T, HCB-I, HCB-II, HCB-III)

Technical Requirements - Graphite Materials and Design ML20358A145 Code Cases N-861 and N-862 (all aspects) ML20349A002 ANL Historical Context and Perspective on Materials Properties ML21090A033 38

Review Process - General Requirements Staff compared the 2017 Edition of ASME Code III-5-HAA and -HAB to the 2017 Edition of ASME Code III-NCA to ensure consistency with what the NRC has endorsed in 10 CFR 50.55a.

Similarly, the staff compared the 2017 Edition of ASME Code III-5-HAA and -HAB to the 2019 Edition of ASME Code III-5-HAA and -HAB to ensure consistency with those items that were corrected in the 2019 Edition.

Exceptions or limitations proposed where there are differences.

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Limitation: Staff does not endorse use of a Certifying Engineer who is not also a Registered Professional Engineer.

Basis: Consistency with a similar condition in 10 CFR 50.55a on 2017 Edition of Section III-NCA.

General Requirements Limitation: When using HAB-3126(b), HAB-3127(b),

- Examples of and HAB-3855.3(c)(2) and (d)(2): The procurement Exceptions/Limitations documents should specify that the service will be provided in accordance with the accredited ISO/IEC 17025 program and scope of accreditation.

Basis: This is one of several limitations included for consistency with the updated ILAC accreditation process that is called out in NCA-3126 and also in the 2019 edition of Section III-5.

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Mechanical Design - Exceptions and Limitations

• The staff identified exceptions and limitations related to mechanical design (HBB-3000, HBB-T) for several reasons:

- Consistency with Section III-1 conditions in 10 CFR 50.55a

• Socket weld design condition.

- Consistency with RG 1.87 conditions on Code Case 1592 -

• Use of strain-controlled buckling factors.

- Lack of guidance in Section III-5

• Inelastic analysis for meeting HBB-T deformation limits .

• Stress relaxation cracking.

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Limitation:

When using HBB-T-1710 applicants and Mechanical licensees should develop their own plans to Design - address the potential for stress-relaxation Exceptions and cracking in their designs.

Limitations -

Stress Relaxation Basis:

Cracking Stress relaxation cracking is a mechanism causing enhanced creep crack growth in certain materials caused by relaxation of weld residual stresses in components in high-temperature service. Section III-5 does not contain any provisions addressing stress-relaxation cracking.

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Review Process - Class A Metallic materials (HBB-I-14)

Metallic and

• Did not primarily rely on previous reviews.

• Independent analysis of materials properties and allowable stresses by NRC contractor.

Graphitic Materials

• Additional input by subject matter experts familiar with the development of Section III-5.

Graphite (HHA)

• Did not rely on previous reviews.

• Graphite provisions were not in 159X Code Cases - New to Section III-5.

• Technical review of Section III-5 by subject matter experts.

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Metallic Materials In some cases, contractor independent analysis determined properties and allowable stresses with lower values than the code, suggesting code values are nonconservative.

Lower values were typically only at higher temperatures and longer times for time-dependent properties.

NRC staff considered these findings in a holistic manner, including how these properties are used, inherent conservatism of the Division 5 design rules, and historical context.

Input from ANL provided historical context and perspective on materials properties.

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Metallic Materials - Exceptions and Limitations

• For time-dependent allowable stresses, staff placed limitations on endorsement for several materials.

• Limitations in form of maximum temperature limit for several materials.

Material Properties Temperature Limit Type 304 Smt , St , Sr 1300 °F, 700 °C Type 316 Sr 1300 °F, 700 °C 2-1/4 Cr-1 Mo Smt , St , Sr 950 °F, 510 °C

• For 9Cr-1Mo-V, 2019 Section III-5 properties are endorsed in lieu of 2017 Section III-5 properties.

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Example of Basis for Conditions on Allowable Stresses For Type 304, ORNL independent analysis suggested significant non-conservatism of Section III-5 St values for most times and temperatures. At 300,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />, non-conservatism was suggested at temperatures 850 °F or 450 °C. This is based on independent analysis values more than 10% lower than Section III-5 values.

Most of the apparent non-conservatism driven by the tertiary creep criterion for St .

Tertiary creep criterion for St is a known issue in the Code. It was not intended that this criterion should control most time-dependent allowable stresses.

ANL performed an alternate analysis using a different approach for tertiary creep data. This analysis showed significant non-conservatism only at temperatures 1300 °F or 700 °C.

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• Numark Associates Inc. provided a technical assessment of Subsection HH, Class A Nonmetallic Core Support Structures, Subpart A, Graphite Materials.

Graphite

• Staff has completed the review of the above Materials and report and all applicable sections of ASME Section III, Division 5 and obtained clarifications Design and feedback from NRC contractors (NUMARK and INL) in order to come up with the conclusions identified in the NUREG.

• The staff's independent review of the code requirements considered the holistic design of graphite core support structures.

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Graphite Materials and Design -

Exceptions and Limitations Limitations identified by staff where Division 5 has a numerical parameter limit, but staff not convinced the limit is generically applicable to all designs. Design-specific justification is requested for the parameter value in these case:

Paragraph Parameter Limit in Section III-5 HHA-3141, Oxidation Weight Loss Limit 30%

HHA-3142.4, Graphite Cohesive Life Limit +10%

Cohesive Life Limit HHA-3143, Abrasion and Gas Flow Velocity 100 m/s (mean)

Erosion HHA-4233.5, Repair of Allowed repair depth 2 mm (0.079 inch)

Defects and Flaws 48

Graphite Materials and Design - Other Exceptions and Limitations Limitation: The NRC Basis: HHA-3330 (g) Staff is not endorsing The provision related staff is not endorsing allow for access to this provision to operational the provisions of performing inservice because monitoring is the one HHA-3330(g). inspection. If requirements for that the staff finds necessary, inservice inservice inspection out of scope.

inspection may be are outside of the replaced by scope of Section III-5, operational HHA.

monitoring 49

Four Quality Groups and associated standards (from DG-1380, Appendix A)

Quality Group A Quality Group B Quality Group C Quality Group D

• Safety-related

• Safety-related

• Non-safety-

• Non-safety-SSCs SSCs related SSCs with related SSCs with

• Use ASME

• Use ASME safety no special Section III, Section III, significance treatment Division 5 Class Division 5 Class

• Use ASME

• Owner to A for safety B for safety Section VIII, establish related SSCs related SSCs Division 1 or 2 standards for that have with low safety use safety significance significance

Summary The NRC staff has completed its initial review of Section III-5 for potential endorsement.

DG-1380 contains the staffs regulatory position on The NRCs review is documented in NUREG-2245.

Section III-5, including some exceptions and limitations.

Exceptions and limitations were generally identified when the staff found that additional guidance was needed to augment the provisions of Section III-5, or where material properties and allowable stresses are potentially nonconservative.

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Next Steps The NUREG and DG will be issued for public comment.

Alloy 617 Code Cases technical review (in progress).

Make changes as necessary to NUREG and DG to address public comments.

Reissue DG for a second public comment period incorporating Alloy 617 results and resolution of public comments.

Issue draft Alloy 617 technical basis document concurrently with DG.

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