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NUREG/CR-6944, Vol. 4 ORNL/TM-2007/147, Vol. 4

Next Generation Nuclear Plant Phenomena Identification and Ranking Tables (PIRTs) Volume 4: High-Temperature Materials PIRTs

Office of Nuclear Regulatory Research

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NUREG/CR-6944, Vol. 4 ORNL/TM-2007/147, Vol. 4

Next Generation Nuclear Plant Phenomena Identification and Ranking Tables (PIRTs) Volume 4: High-Temperature Materials PIRTs Manuscript Completed: October 2007 Date Published: March 2008 Prepared by: W.R. Corwin – Panel Chair Panel Members: R. Ballinger (MIT) S. Majumdar (ANL) K.D. Weaver (INL) Oak Ridge National Laboratory P.O. Box 2008 Oak Ridge, TN 37831-6170 S. Basu, NRC Project Manager NRC Job Code N6376 Office of Nuclear Regulatory Research

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ABSTRACT

The Phenomena Identification and Ranking Table (PIRT) technique was used to identify safety-relevant/safety-significant phenomena and assess the importance and related knowledge base of high-temperature structural materials issues for the Next Generation Nuclear Plant (NGNP), a very high temperature gas-cooled reactor (VHTR). The major aspects of materials degradation phenomena that may give rise to regulatory safety concern for the NGNP were evaluated for major structural components and the materials comprising them, including metallic and nonmetallic materials for control rods, other reactor internals, and primary circuit components; metallic alloys for very high-temperature service for heat exchangers and turbomachinery, metallic alloys for high-temperature service for the reactor pressure vessel (RPV), other pressure vessels and components in the primary and secondary circuits; and metallic alloys for secondary heat transfer circuits and the balance of plant. These materials phenomena were primarily evaluated with regard to their potential for contributing to fission product release at the site boundary under a variety of event scenarios covering normal operation, anticipated transients, and accidents. Of all the high-temperature metallic components, the one most likely to be heavily challenged in the NGNP will be the intermediate heat exchanger (IHX). Its thin, internal sections must be able to withstand the stresses associated with thermal loading and pressure drops between the primary and secondary loops under the environments and temperatures of interest. Several important materials-related phenomena related to the IHX were identified, including crack initiation and propagation; the lack of experience of primary boundary design methodology limitations for new IHX structures; and manufacturing phenomena for new designs. Specific issues were also identified for RPVs that will likely be too large for shop fabrication and transportation. Validated procedures for on-site welding, postweld heat treatment (PWHT), and inspections will be required for the materials of construction. High-importance phenomena related to the RPV include crack initiation and subcritical crack growth; field fabrication process control; property control in heavy sections; and the maintenance of high emissivity of the RPV materials over their service lifetime to enable passive heat rejection from the reactor core. All identified phenomena related to the materials of construction for the IHX, RPV, and other components were evaluated and ranked for their potential impact on reactor safety.

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FOREWORD

The Energy Policy Act of 2005 (EPAct), Public Law 109-58, mandates the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Department of Energy (DOE) to develop jointly a licensing strategy for the Next Generation Nuclear plant (NGNP), a very high temperature gas-cooled reactor (VHTR) for generating electricity and co-generating hydrogen using the process heat from the reactor. The elements of the NGNP licensing strategy include a description of analytical tools that the NRC will need to develop to verify the NGNP design and its safety performance and a description of other research and development (R&D) activities that the NRC will need to conduct to review an NGNP license application.

To address the analytical tools and data that will be needed, NRC conducted a Phenomena Identification and Ranking Table (PIRT) exercise in major topical areas of NGNP. The topical areas are: (1) accident analysis and thermal-fluids including neutronics, (2) fission product transport, (3) high temperature materials, (4) graphite, and (5) process heat and hydrogen production. Five panels of national and international experts were convened, one in each of the five areas, to identify and rank safety-relevant phenomena and assess the current knowledge base. The products of the panel deliberations are Phenomena Identification and Ranking Tables (PIRTs) in each of the five areas and the associated documentation (Volumes 2 through 6 of NUREG/CR-6944). The main report (Volume 1 of NUREG/CR-6944) summarizes the important findings in each of the five areas. Previously, a separate PIRT was conducted on TRISO-coated particle fuel for VHTR and high temperature gas-cooled reactor (HTGR) technology and documented in a NUREG report (NUREG/CR-6844, Vols. 1 to 3).

The most significant phenomena (those assigned an importance rank of “high” with the corresponding knowledge level of “low” or “medium”) in the thermal-fluids area include primary system heat transport phenomena which impact fuel and component temperatures, reactor physics phenomena which impact peak fuel temperatures in many events, and postulated air ingress accidents that, however unlikely, could lead to major core and core support damage.

The most significant phenomena in the fission products transport area include source term during normal operation which provides initial and boundary conditions for accident source term calculations, transport phenomena during an unmitigated air or water ingress accident, and transport of fission products into the confinement building and the environment.

The most significant phenomena in the graphite area include irradiation effect on material properties, consistency of graphite quality and performance over the service life, and the graphite dust issue which has an impact on the source term.

The most significant phenomena in the high temperature materials area include those relating to high-temperature stability and a component’s ability to withstand service conditions, long-term thermal aging and environmental degradation, and issues associated with fabrication and heavy-section properties of the reactor pressure vessel.

The most significant phenomenon in the process heat area was identified as the external threat to the nuclear plant due to a release of ground-hugging gases from the hydrogen plant. Additional phenomena of significance are accidental hydrogen releases and impact on the primary system from a blowdown caused by heat exchanger failure.

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The PIRT process for the NGNP completes a major step toward assessing NRC’s research and development needs necessary to support its licensing activities, and the reports satisfy a major EPAct milestone. The results will be used by the agency to: (1) prioritize NRC’s confirmatory research activities to address the safety-significant NGNP issues, (2) inform decisions regarding the development of independent and confirmatory analytical tools for safety analysis, (3) assist in defining test data needs for the validation and verification of analytical tools and codes, and (4) provide insights for the review of vendors’ safety analysis and supporting data bases.

Farouk Eltawila, Director Division of Systems Analysis Office of Nuclear Regulatory Research

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CONTENTS

Page

ABSTRACT.................................................................................................................................................iii

FOREWORD ................................................................................................................................................ v

LIST OF TABLES....................................................................................................................................... ix

ACRONYMS...............................................................................................................................................xi

1. PIRT OBJECTIVES............................................................................................................................... 1

2. BRIEF INTRODUCTION TO NGNP HIGH-TEMPERATURE MATERIALS ISSUES .................... 2 2.1 Previous NRC Activities and Material ........................................................................................ 3 2.2 Major Structural Materials Phenomena Issues ............................................................................ 3

3. PIRT DESCRIPTION ............................................................................................................................ 6 3.1 Step 1—Issue............................................................................................................................... 6 3.2 Step 2—PIRT Objectives ............................................................................................................ 6 3.3 Step 3—Hardware and Scenarios ................................................................................................ 6 3.4 Step 4—Evaluation Criteria......................................................................................................... 7 3.5 Step 5—Knowledge Base............................................................................................................ 9 3.6 Step 6—Identify Phenomena....................................................................................................... 9 3.7 Step 7—Importance Ranking ...................................................................................................... 9 3.8 Step 8—Knowledge Level......................................................................................................... 10 3.9 Step 9—Document PIRT........................................................................................................... 10

REFERENCES ........................................................................................................................................... 37

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LIST OF TABLES

Table Page

1 Major classes of materials expected to be used in the NGNP............................................................... 2 2 HTGR event scenarios for materials PIRT exercise ............................................................................. 7 3 Figures of Merit and pathways to release for different reactor systems or components....................... 8 4 Phenomena importance ranking scale................................................................................................. 10 5 State of knowledge (SOK) ranking scale............................................................................................ 10 6 PIRT table for high-temperature materials ......................................................................................... 12 7 Selected PIRT phenomena from Table 6 that have particular significance due to their

high importance and low knowledge rankings ................................................................................... 30

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ACRONYMS

ANL Argonne National Laboratory ASME American Society of Mechanical Engineers ASME B&PV ASME Boiler and Pressure Vessel (Code) BOP balance of plant C–C carbon–carbon CHX compact heat exchanger DOE Department of Energy FOM figure of merit HCF high-cycle fatigue HTGR high-temperature gas-cooled reactor HX heat exchanger IHX intermediate heat exchanger INL Idaho National Laboratory KM Knowledge Management LOFC loss-of-forced circulation LWR light-water reactor MHTGR modular high-temperature gas-cooled reactor MIT Massachusetts Institute of Technology NDE nondestructive evaluation NGNP next generation nuclear plant NPP nuclear power plant NRC Nuclear Regulatory Commission PCV power conversion vessel PIRT phenomena identification and ranking table PWHT postweld-heat treatment RCCS reactor cavity cooling system RPV reactor pressure vessels SOK state of knowledge T-H thermal-hydraulic VHTR very high-temperature gas-cooled reactor

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1. PIRT OBJECTIVES

The Phenomena Identification and Ranking Table (PIRT) technique is a structured process to identify safety-relevant/safety-significant phenomena and assess the importance and knowledge base by ranking the phenomena. The Next Generation Nuclear Plant (NGNP) is anticipated to be a very high temperature gas-cooled reactor (VHTR). The NGNP high-temperature-materials PIRT identifies those phenomena important for normal operations, anticipated transients, and postulated accidents (design basis and beyond). All structural materials other than the graphite to be used in the core and core support structures were addressed in this PIRT exercise (Note: NGNP graphite issues were explicitly examined in another PIRT exercise). The results of this PIRT exercise are documented in PIRT tables and will be used as a tool for identifying and prioritizing research needs. The results and the specifics of the table are detailed below.

This NGNP is similar to other high-temperature gas-cooled reactor (HTGR) designs that the Nuclear Regulatory Commission (NRC) has come across in past years, but differs in the following ways:

1. The outlet gas and many of the primary circuit components are anticipated to operate at higher temperatures than the past.

2. A steam generator connected directly to the primary circuit is no longer anticipated to be part of the design; it has been eliminated from the design entirely by either going to a direct cycle turbine or it has been replaced by an intermediate heat exchanger (IHX) for the purposes of supplying process heat for other uses (e.g., hydrogen production) and/or downstream electric power conversion systems.

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2. BRIEF INTRODUCTION TO NGNP HIGH-TEMPERATURE MATERIALS ISSUES

The major aspects of the materials degradation phenomena for potential regulatory safety concerning the NGNP can be divided by major structural components and the materials comprising them, as follows:

$ graphite for core structures, including replaceable and permanent components, $ nonmetallic or metallic materials for control rods, $ nonmetallic materials for other reactor internals and primary circuit components, $ metallic alloys for very high temperature service for heat exchangers, $ metallic alloys for very high temperature service for turbo machinery, $ metallic alloys for high temperature service for the reactor pressure vessel, $ metallic alloys for high temperature service for other pressure vessels and components in the

primary circuit, $ metallic alloys for secondary heat transfer circuits and balance of plant (BOP), and $ materials for valves, bearings, and seals.

For each category of materials and components described above, technical data and information on material’s strength and creep, fatigue, and creep-fatigue performance for the anticipated times and temperatures of service are needed to support the design, expected performance, and the adequacy of safety margins that could potentially degrade over time. Where appropriate, it will also be necessary to understand the effects that the service environments may have on the materials baseline properties, including the effects of coolants, heat transfer media, and irradiation exposure.

For metal usage within the temperature range where time-dependent behavior occurs, it will also be necessary to ensure that a validated methodology for high-temperature design and analysis is available to predict materials performance and failure.

Several major classes of materials are considered in this PIRT exercise. They are briefly described along with component applications in Table 1.

Table 1. Major classes of materials expected to be used in the NGNP

Material type Examples of materials Potential component application Low-alloy steel SA508 steel

SA 533B steel 2-1/4 Cr–1 MoV steel 9 Cr–1MoV steel

Reactor pressure vessel and piping

Stainless steel 304 stainless steel 316 stainless steel 347 stainless steel

Core barrel Ducting Recuperators

High alloys Inconel 617 Haynes 230 Incoloy 800H Hastelloy X and XR Inconel 740

Core barrel Intermediate heat exchanger Piping Bolting Control rods Turbomachinery

Nanostructured and oxide dispersion strengthened alloys

MA 956 PM 2000

Table 1 (continued)

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Material type Examples of materials Potential component application Nonmetallic composites Carbon–carbon (C–C)

SiC-SiC Control rods Core restraints Liners for hot ducts and insulation

Nonmetallic materials (ceramics) Alumina Silica Kaowool

Insulation

Note that a companion activity will evaluate the phenomena associated with graphite, so they will

not be addressed here.

2.1 Previous NRC Activities and Material

The NRC investigation of the Modular HTGR (MHTGR) in the 1980s [1] and the supporting documentation developed by the Department of Energy (DOE) [2] provide information on extensive regulatory review of a plant similar to those currently under consideration. One major difference with respect to licensing is the former’s (MHTGR) use of a steam generator BOP approach, where the dominant risk was from water-ingress due to steam generator tube breaks. A second difference is the inclusion of process heat (hydrogen production) systems in NGNP designs. Pertinent references are currently being accumulated in the NRC Knowledge Management (KM) online database.

Additional studies [3, 4] identify most of the metallic materials degradation and performance issues associated with the codification of design of metallic materials for HTGRs. A review of American Society of Mechanical Engineers (ASME) Code issues for metals for broader high-temperature reactor usage was also performed and documented in another NRC-sponsored study [5].

2.2 Major Structural Materials Phenomena Issues

High-Temperature Metals—It is necessary to develop data and models needed by ASME Boiler & Pressure Vessel (B&PV) Code subcommittees to formulate time-dependent failure criteria that will assure adequate life and safety for metallic materials in the NGNP. Specifically, experimentally based constitutive models that are the foundation of the inelastic design analyses specifically required by ASME B&PV Sect. III Division I Subsect. NH must be developed for the construction materials safety assessments, dependent on time-dependent flaw growth and the resulting leak rates from postulated pressure-boundary breaks, will require a flaw assessment procedure capable of reliably predicting crack-induced failures as well as the size and growth of the resulting opening in the pressure boundary. Additionally, materials data and extrapolation procedures must be developed and guidance provided to ensure that allowable operation period and range of stress and temperature for materials of construction are extended to meet the proposed operating temperatures and lifetimes. Creep-fatigue rules are an area of particular concern for the materials and temperatures of interest and must be updated and validated.

Of all the high-temperature metallic components, the one most likely to be heavily challenged in the NGNP that includes the use of secondary loops for power generation or process heat applications will be the IHX. Its thin, internal sections must be able to withstand the stresses associated with thermal loading and pressure drops between the primary and secondary loops, which may be quite substantial. Additionally, since these sections must operate at the full exit temperature of the reactor, metallurgical stability and environmental resistance of the materials comprising them in anticipated impure helium coolant environments must be adequate for the lifetimes anticipated. Several materials-related

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phenomena related to the IHX were identified as having a high importance for potentially contributing to fission product release at the site boundary and a low level of knowledge with which to assess their contribution to such a release. These included crack initiation and propagation (due to creep crack growth, creep, creep-fatigue, and aging); the lack of experience of primary boundary design methodology limitations for new IHX structures; manufacturing phenomena for new designs (including joining issues); and the ability to inspect and test new IHX designs. These are called out in Table 6 as phenomena 35, 36, 37, and 38, respectively.

An alternative to a very high-temperature metallic heat exchanger being considered is one made of ceramics or ceramic composites. This would dramatically reduce concerns about high-temperature operation, because such materials have much higher temperature capabilities, but would introduce major concerns about design and fabrication methods as well as use of brittle materials in a nuclear pressure boundary.

Specific issues must be addressed for reactor pressure vessels (RPVs) that are too large for shop fabrication and transportation. Validated procedures for on-site welding, postweld heat treatment (PWHT), and inspections will be required for the materials of construction. For vessels using materials other than those typical of light-water reactor (LWR) construction to enable operation at higher temperatures, confirmation of their fabricability (especially, effects of forging size and weldability) and data on their irradiation resistance will be needed. Three materials-related phenomena related to the RPV fabrication and operation were identified as having a high importance for potentially contributing to fission product release at the site boundary and a low level of knowledge with which to assess their contribution to such a release, particularly for 9 Cr–1 MoV steels capable of higher temperature operation than LWR vessel steels. These included crack initiation and subcritical crack growth, field fabrication process control, and property control in heavy sections. These are called out in Table 6 as phenomena 5, 16, and 17, respectively.

Small amounts of impurities that will contaminate the reactor coolant can degrade the materials both by corrosion processes and by effects on mechanical properties. Carburization, decarburization, and internal oxidation are issues of particular concern in high-temperature metals. The effects of corrosion of the impure helium environment on metals and nonmetals must be evaluated. Moreover, since the actual levels of impurities within the coolant of the NGNP will be controlled largely by the presence of large quantities of hot graphite, in conjunction with all sources of contamination, the ability to accurately simulate this environment for meaningful laboratory evaluations is critical. The overall stability of the proposed helium environment that will be representative of the NGNP must be evaluated in order to ensure any testing is performed in environments that have chemical potentials consistent with that encountered in the reactor. General corrosion evaluations of the candidate materials to establish their overall compatibility with that environment must also be performed for all temperatures of interest. This will include determining the effects that the helium environment has on long-term mechanical properties, such as creep, or creep-fatigue, as well as the impact on microstructural stability of aging in the environments of interest.

Environmental effects of other heat transfer media outside the primary circuit on the corrosion behavior and the mechanical properties of the structural materials must also be evaluated. Of particular concern are gas mixtures that may be used in Brayton-cycle power conversion cycles (e.g., 80% N–20% He) and heat transfer fluids associated with process heat applications (e.g., molten salt).

Because the ability to passively reject heat adequately during certain transients in the NGNP is dependent upon transmitting decay heat from the core and radiating it from the exterior of the RPV, it is critical that emissivity of the various potential candidate materials for the RPV and core barrel remains sufficiently high over their lifetimes. Depending on the emissivity of the selected materials, it may be necessary to qualify and incorporate high-emissivity, durable coatings on the surfaces of these

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components. Two materials-related phenomena related to the RPV and core barrel emissivity were identified as having a high importance for potentially contributing to fission product release at the site boundary and a low level of knowledge with which to assess their contribution to such a release. This is the potential loss of passive heat rejection ability due to compromise of emissivity caused by loss of desired surface layer properties (phenomena 11and 46 in Table 6).

High-level issues for high-temperature metallic components that will require evaluation include the following:

$ inelastic materials behavior for materials, times, and temperatures for very high temperature structures (e.g., creep, fatigue, creep-fatigue, etc.);

$ adequacy and applicability of current ASME Code allowables with respect to service times and temperatures for operational stresses;

$ adequacy and applicability of current state of high-temperature design methodology (e.g., constitutive models, complex loading, failure criteria, flaw assessment methods, etc.);

$ effects of product form and section thickness; $ joining methods including welding, diffusion bonding, and issues associated with dissimilar

materials in structural components; $ effects of irradiation on materials strength, ductility, and toughness; $ degradation mechanisms and inspectibility; $ oxidation, carburization, decarburization, and nitriding of metallic components in impure

helium and helium-nitrogen; $ microstructural stability during long-term aging in helium environment; $ effects of short- and long-term exposure on mechanical properties (e.g., tensile, fatigue, creep,

creep-fatigue, ductility, toughness, etc.); $ high-velocity erosion/corrosion; $ rapid oxidation of graphite and C–C composites during air-ingress accidents; $ compatibility with heat-transfer media and reactants for hydrogen generation; and $ development and stability of surface layers on RPV and core barrel affecting emmissivity.

Control Rods—Considering that the control rods (and possibly some other internals) in the NGNP may see temperatures in excess of those that can be safely handled by commercial high-temperature alloys, it may be necessary to use structural composites such as carbon–carbon or SiC–SiC. If these materials are used, it will be essential that their design and fabrication methods be evaluated to ensure their structural integrity. Additionally, testing methods must be developed (and standardized, if possible) to reliably characterize their mechanical properties in the nonirradiated and irradiated conditions

If metallic materials are used for control rods, their satisfactory performance under all anticipated temperatures and irradiation doses must be demonstrated.

High-level issues that will need to be evaluated related to the use of structural composites as described above include the following:

$ effects of composite component selection and infiltration method; $ effects of architecture and weave; $ material properties up to and including very high temperatures (e.g., strength, fracture, creep,

corrosion, thermal shock resistance, etc.); $ effects of and relationship between specimen and component geometries; $ effects of irradiation on materials strength and dimensional stability; $ fabrication scaling processes; $ adequacy and validation of design methods; and $ degradation mechanisms and inspectibility.

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3. PIRT DESCRIPTION

There are nine steps in conducting the PIRT exercise. Each step is enumerated and described here:

3.1 Step 1—Issue

The issues driving this PIRT exercise may be summarized as follows:

1. NGNP is a major design change from the current LWR design. Materials, coolant, moderators, and potential applications are different.

2. Both the industry and NRC experience base is very limited with respect to the NGNP. While a few HTGRs have been constructed, the operational history has been mixed, and the current plans are a radical extrapolation of the past technology. In particular, with regard to past HTGRs we are interested in the higher temperature effects of the NGNP on materials of construction. Additionally, the adequacy of design methodology for use of materials in the high-temperature regime, where time-dependent behavior must be considered, is also of significant concern.

3. The database for these new designs is not nearly as well developed as the LWR database, or for that matter, other past or existing HTGRs. The materials database to support the NGNP is incomplete, and the current high-temperature design methodology is inadequate.

3.2 Step 2—PIRT Objectives

The major objectives of the NGNP high-temperature materials PIRT exercise are to (1) identify and rank potential degradation mechanisms for structural materials under normal operating, transient, and accident conditions, (2) identify important parameters and dependencies that affect the degradation processes, (3) assess material performance requirements to assure safety, including needs for additional codes and standards, and (4) assess material properties data bases and identify new data needs, where appropriate. Because the NGNP exists as only a rough concept, it was not possible to perform this exercise for a specific plant design; however, it was surmised that the NGNP would share much in common with past HTGR designs. Moreover, several new preconceptual designs are being actively developed. These were cumulatively used as a reference. Phenomena and knowledge base were evaluated with respect to normal operations, anticipated transients, and postulated accidents (design basis and beyond).

3.3 Step 3—Hardware and Scenarios

NGNP systems and/or components (e.g., reactor vessel, core, internals, IHX, etc.) were identified with regard different scenarios that could challenge them. This was done with the current, but incomplete, knowledge of component hierarchy and their safety significance, consistent with the overall PIRT exercise scope and objectives.

Possible accidents were presented at the February 2007 PIRT meeting, which outlined the expected behavior of the NGNP. The three areas discussed by the panel follow.

Normal operation, which for the purposes of the high temperature materials PIRT provided the long-term, baseline loading conditions for the components and materials of construction.

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Anticipated transients that can cause changes in temperature, pressure, flow, and mechanical vibrations or shocks and can increase the potential for developing failures, leaks, or ruptures in components that would provide a pathway for the release of fission products.

Postulated accidents drew the majority of the panel’s time because they had the greatest likelihood for producing challenges to materials that increase the potential for developing failures, leaks, or ruptures in components that would provide a pathway for the release of fission products.

The NGNP event scenarios, contained below in Table 2, identify the conditions to which plant and components are exposed and provide a key to the situations for which the phenomena in Table 6 were evaluated.

Table 2. HTGR event scenarios for materials PIRT exercise

Normal operations 1. Startup 2. Shutdown 3. Steady state 4. Helium inventory control

Transients 5. Anticipated transient without scram (ATWS) 6. Turbine trip 7. Loss of load

Postulated accidents 8. Pressurized loss of forced circulation 9. Depressurized loss of forced circulation

10. Rupture with air ingress 11. Rupture with water ingress 12. Reactivity events

3.4 Step 4—Evaluation Criteria

Step 4 of the process involved the selection of a figure of merit (FOM) related to each system or component. These were the criteria against which importance of phenomena is judged. While these are often derived from regulations (e.g., dose limit, siting criteria) at top levels and related to the issue being addressed, and scenario and component selected at subsidiary levels, in all cases the FOMs provided guidance with regard to the likelihood of radiation release at the site boundary.

The process by which the panel developed the FOMs is described, because it is important to understand the relationship between the reactor system or component being considered, the FOM itself, and the potential development of a pathway for the release of fission products at the site boundary. The first step that the panel took was to identify the major reactor system or structural components that were felt to have the potential to contribute to fission product release, such as the RPV, the piping, etc. Criteria were then established by which the significance of individual phenomena could be evaluated with regard to their contribution to release at the site boundary, for example, maintaining the integrity of the pressure boundary in the RPV or piping, limiting the peak temperature of the fuel, maintaining the geometry of core support structures and their related nuclear characteristics, etc. These criteria were the FOMs. The

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component-specific phenomena were then evaluated against each FOM for their contribution to fission product release via a specific pathway, for example, breach of piping or pressure vessels, excessive deformation of core supports, and coolant flow blockage from debris or component passage collapse.

Hence, it is important to understand that each phenomenon identified is ranked for its importance and knowledge base with respect to a particular component, FOM, and pathway to release. Table 3 contains the FOMs and pathways to release used to rank the phenomena identified for each component.

Table 3. Figures of Merit and pathways to release for different reactor systems or components

FOM (evaluation criteria) Pathways to release Reactor pressure vessel (RPV)

RPV integrity Breach, excess deformation FOM1: RPV integrity; FOM2: peak fuel temperature Inadequate heat transfer

Power conversion vessels (PCVs) and turbomachinery FOM1: primary system pressure boundary integrity, FOM2: integrity of rotating equipment

Breach of vessel, turbine failure

Circulators FOM1: primary system pressure boundary integrity, FOM2: integrity of rotating equipment

Oil bearing failure, impeller failure

Piping Primary system pressure boundary integrity Breach, failure to insulate Peak fuel temperature Insulation debris generation

Intermediate heat exchanger (IHX) vessel FOM1: integrity of IHX; FOM2: integrity of vessel Breach to ambient

Intermediate heat exchanger (IHX) FOM1: integrity of IHX; FOM2: secondary loop failure/breach

Breach to secondary system

FOM1: integrity of IHX; FOM2: integrity of hot duct (and other systems)

Breach from secondary to primary

Integrity of IHX Catastrophic loss of function Control rods (nonmetallic)

Maintain insertion ability Failure to insert Control rods (metallic)

Maintain insertion ability Failure to insert RPV internals (metallic)

Maintain heat transfer capability Inadequate heat transfer Maintain structure geometry; Excess deformation and fracture/failure FOM1: core barrel integrity; FOM2: RPV integrity Failure

Table 3 (continued)

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FOM (evaluation criteria) Pathways to release RPV internals (nonmetallic)

FOM1: maintain structure geometry; FOM2: maintain insulation capability

Core restraint and support failure

Maintain structure geometry Core restraint failure Maintain insulation capability Fibrous insulation degradation

Reactor cavity cooling system (RCCS) Emergency heat removal capability Inadequate heat removal

Auxiliary shutdown system Primary system pressure boundary integrity Water contamination of primary coolant

Valves Primary system pressure boundary integrity Malfunction, failure to operate and breach

3.5 Step 5—Knowledge Base

To establish the state of the knowledge base, it is necessary to compile and review background information that captures relevant knowledge for the materials of interest for the conditions they are expected to experience during operating, upset, and accident conditions. Because the NGNP does not have a firm design at this time, it was necessary to envelop the range of materials and their operating conditions currently under discussion for the various systems and components. A comparison of this envelop of candidate materials and their operating conditions with the overall knowledge base for such materials was used to rank the specific knowledge base available to assess the phenomena identified.

3.6 Step 6—Identify Phenomena

All plausible materials-related phenomena that could contribute to the overall concern of radiation release at the site boundary were identified by system or component. In this case, the term “phenomenon” is broadly defined to include not only “physical phenomenon” but also a process or a property.

3.7 Step 7—Importance Ranking

In this step, the panel developed importance ranking and rationale for the phenomena identified in Step 6. The phenomenological hierarchy starts at the system level and proceeds through component and subcomponent level. Also, the lowest level of hierarchical decomposition should be consistent with the data and modeling needs from a regulatory perspective.

The importance rankings process consisted of the generation of individual and independent ranking by panel members, discussion and documentation of the rationale for such rankings (including references to published information on the subject), and finally the development of a collective panel ranking based on the discussion. Note that the collective ranking assigned by the panel was not an average ranking but rather was reached as a consensus among the panel members following individual rankings and discussion of the phenomenon. Importance was ranked relative to the evaluation criteria adopted in Step 4. A qualitative ranking, that is, High (H), Medium (M), Low (L), and Unknown (UNK) was adopted.

10

Table 4 defines the scale used to provide guidance in ranking the importance of the individual phenomena.

Table 4. Phenomena importance ranking scale

Rank Definition Application outcomes

High (H) Phenomenon has a controlling impact on the FOM

Experimental simulation and analytical modeling with a high degree of accuracy is critical

Medium (M) Phenomenon has a moderate impact on the FOM

Experimental simulation and/or analytical modeling with a moderate degree of accuracy

Low (L) Phenomenon has a minimal impact on the FOM

Modeling must be present to preserve functional dependencies

3.8 Step 8—Knowledge Level

In this step, the panel assessed the level of knowledge regarding each phenomenon identified in Step 6, and for which an importance ranking is assigned in Step 7. The process consisted of the generation of individual and independent ranking by panel members, discussion and documentation of the rationale for such rankings (including references to published information on the subject, for example, experimental data base, analytical tools, etc.), and finally the development of a collective panel ranking based on the discussion. Note that the collective ranking assigned by the panel was not an average ranking but rather was reached as a consensus among the panel members following individual rankings and discussion of the knowledge level. A qualitative ranking, that is, High (H), Medium (M), Low (L), and Unknown (UNK) was used. Table 5 defines the scale used to provide guidance in ranking the knowledge base of the individual phenomena.

Table 5. State of knowledge (SOK) ranking scale

Rank Definition

High (H) Experimental simulation and analytical modeling with a high degree of accuracy is currently possible

Medium (M) Experimental simulation and/or analytical modeling with a moderate degree of accuracy is currently possible

Low (L) Experimental simulation and/or analytical modeling is currently marginal or not available

3.9 Step 9—Document PIRT

The objective of this step was to provide sufficient coverage and depth in the documentation so that a knowledgeable reader could understand what was done to develop and substantiate the outcome of the NGNP high-temperature materials PIRT exercise. This includes a listing of background materials, PIRT

11

objectives, tables of identified phenomena, their importance and knowledge level ranking, and associated text describing the process of phenomena identification and rationale of the ranking process. This document fulfills this step.

The overall summary containing the phenomena identified, their rankings of importance and knowledge base, and related rationale for all systems and their respective FOMs is provided in Table 6. Note that the collective rankings assigned by the panel for both importance and knowledge level were developed as a panel consensus, though individual rankings were retained and reported to show where an individual panel member ranked an item with respect to the panel consensus.

Table 7 contains the group of selected phenomena that the panel considered to be of particular significance due to their combination of a high ranking of importance and a low or moderate ranking of low knowledge. The reader should be cautioned that merely selecting phenomena based on high importance and low knowledge may not capture the true uncertainty of the situation.

12

Tab

le 6

. PI

RT

tabl

e fo

r hi

gh-t

empe

ratu

re m

ater

ials

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

Rea

ctor

pre

ssur

e ve

ssel

1

RPV

inte

grity

B

reac

h/1–

4 Th

erm

al a

ging

(lon

g te

rm)

H

Unc

erta

inty

in p

rope

rties

of

9 C

r–1

Mo

stee

l (gr

ade

91),

espe

cial

ly d

egra

datio

n an

d ag

ing

of b

ase

met

als a

nd w

elds

fo

r a c

ritic

al c

ompo

nent

like

the

RPV

, mus

t be

addr

esse

d fo

r 60-

year

life

times

. A

lthou

gh it

was

no

t dis

cuss

ed in

our

mee

ting,

Ty

pe IV

cra

ckin

g ha

s bee

n ob

serv

ed in

ope

ratin

g fo

ssil

plan

ts a

t 545°C

afte

r 20,

000

h.

Alth

ough

unl

ikel

y, is

Typ

e IV

cr

acki

ng a

t NG

NP

oper

atin

g te

mpe

ratu

res p

ossi

ble

for v

ery

long

tim

e (6

0 ye

ars)

exp

osur

e?

M

It is

ass

umed

that

Gra

de

91 is

the

prim

e ca

ndid

ate

for N

GN

P, a

nd n

o ba

ck

up m

ater

ial i

s con

side

red

in th

is re

port

for d

esig

ns

with

out a

ctiv

e co

olin

g.

This

is b

eyon

d ex

perie

nce

base

for

cond

ition

s of i

nter

est,

exte

nsiv

e fo

ssil

ener

gy

expe

rienc

e an

d co

de

usag

e, th

ough

sign

ifica

nt

agin

g da

ta e

xist

at h

igh

tem

pera

ture

s (>5

00°C

).

Nee

d is

for l

ong-

term

ag

ing

data

at N

GN

P re

leva

nt te

mpe

ratu

res.

[10,

15–

17]

2 R

PV in

tegr

ity

Bre

ach/

1–4

Ther

mal

agi

ng (l

ong

term

) L

LWR

stee

ls w

ithin

exi

stin

g ex

perie

nce.

H

Ex

tens

ive

data

base

for

LWR

app

licat

ions

3

RPV

inte

grity

B

reac

h/8,

9 Th

erm

al a

ging

(s

hort

term

, hig

h te

mpe

ratu

re)

M

Gra

de 9

1 ag

ing

durin

g hi

gh-

tem

pera

ture

, sho

rt-te

rm

excu

rsio

ns o

f ~10

0 h,

eco

nom

ic

impa

ct o

n co

ntin

ued

plan

t op

erat

ion,

pot

entia

l for

m

icro

stru

ctur

al c

hang

es a

nd

impa

ct o

n pr

oper

ties.

M

Gra

de 9

1, e

xten

sive

da

taba

se fo

r fos

sil

ener

gy a

pplic

atio

ns.

Som

e da

ta e

xist

for P

91

at N

GN

P-re

leva

nt

tem

pera

ture

s. [1

0, 1

5–17

] 4

RPV

inte

grity

B

reac

h/8,

9 Th

erm

al a

ging

(s

hort-

term

, hig

h te

mpe

ratu

re)

L LW

R st

eels

with

in e

xist

ing

expe

rienc

e.

H

Mor

e kn

own

on 5

08,

(mor

e in

form

atio

n ne

eded

on

exte

nded

tim

es, t

empe

ratu

res f

or

Cod

e C

ase

499)

T

able

6 (c

ontin

ued)

13

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

5 R

PV in

tegr

ity

Bre

ach/

1–7

Cra

ck in

itiat

ion

and

subc

ritic

al c

rack

gr

owth

H

9 C

r–1

Mo

stee

l (gr

ade

91)

mus

t be

asse

ssed

for

phen

omen

a du

e to

tran

sien

ts

and

oper

atio

nally

indu

ced—

ther

mal

load

ing,

pre

ssur

e lo

adin

g, re

sidu

al st

ress

, ex

istin

g fla

ws (

degr

adat

ion

of

wel

ds, c

yclic

load

ing,

low

cy

cle

fatig

ue).

L Th

ere

is a

lim

ited

data

base

from

foss

il en

ergy

app

licat

ions

at

thes

e te

mpe

ratu

res.

Low

cy

cle

fatig

ue d

ata

in a

ir,

vacu

um a

nd so

dium

(A

NL

unpu

blis

hed

data

) at

>48

2°C

show

life

is

long

est i

n so

dium

, fo

llow

ed b

y va

cuum

and

ai

r. A

ging

in h

eliu

m

(dep

endi

ng o

n im

purit

ies)

will

mos

t lik

ely

be g

reat

er th

an in

ai

r. A

ging

in im

pure

he

lium

may

per

haps

de

pend

on

impu

rity

type

an

d co

nten

t [10

, 15–

17]

6 R

PV in

tegr

ity

Bre

ach/

1–7

Cra

ck in

itiat

ion

and

subc

ritic

al c

rack

gr

owth

H

LWR

stee

ls w

ithin

exi

stin

g ex

perie

nce.

Diff

erin

g op

inio

ns;

ques

tion

rais

ed a

bout

whe

ther

im

porta

nt fo

r HTG

R

appl

icat

ion.

The

rmal

gra

dien

ts

not e

xpec

ted

to b

e as

seve

re a

s fo

r LW

Rs.

H

Exte

nsiv

e da

taba

se fo

r LW

R a

pplic

atio

ns

7 R

PV in

tegr

ity

Bre

ach/

1–7

Hig

h cy

cle

fatig

ue

(HC

F)

L G

rade

91

HC

F lo

adin

g ex

pect

ed to

be

min

imal

in

vess

el.

M

Exte

nsiv

e da

taba

se fo

r fo

ssil

ener

gy

appl

icat

ions

. HC

F lif

e be

ing

spen

t mos

tly o

n in

itiat

ion,

is l

ikel

y to

be

a fu

nctio

n of

the

envi

ronm

ent [

10, 1

5–17

]

T

able

6 (c

ontin

ued)

14

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

8 R

PV in

tegr

ity

Bre

ach/

1–7

Hig

h cy

cle

fatig

ue

L LW

R st

eels

HC

F lo

adin

g ex

pect

ed to

be

min

imal

in

vess

el.

H

Exte

nsiv

e da

taba

se fo

r LW

R a

pplic

atio

ns.

Des

ign

curv

e in

ASM

E co

de (N

H) f

or 1

000E

F [1

5–17

] 9

RPV

inte

grity

B

reac

h/3

Rad

iatio

n de

grad

atio

n M

G

rade

91

for f

luen

ces,

tem

pera

ture

s, an

d flu

xes o

f in

tere

st—

need

to d

emon

stra

te

lack

of r

adia

tion

degr

adat

ion

over

60

year

.

L M

oder

ate

data

bas

e at

hi

gh fl

ux a

vaila

ble

from

fu

sion

pow

er p

rogr

am

reso

urce

s [10

, 15–

17]

10

RPV

inte

grity

B

reac

h/3

Rad

iatio

n de

grad

atio

n L

LWR

stee

ls—

som

e qu

estio

n ab

out s

ofte

r spe

ctru

m e

ffec

ts,

but n

ot e

xpec

ted

to c

ontro

l m

ater

ial r

espo

nse.

H

Exte

nsiv

e da

taba

se fr

om

LWR

app

licat

ions

[10,

15

–17]

11

FOM

1: R

PV

inte

grity

; FO

M2:

pe

ak fu

el

tem

pera

ture

Inad

equa

te h

eat

trans

fer/1

–3

Com

prom

ise

of

emis

sivi

ty d

ue to

lo

ss o

f des

ired

surf

ace

laye

r pr

oper

ties

H

To e

nsur

e pa

ssiv

e sa

fety

, hig

h em

issi

vity

of t

he R

PV is

re

quire

d to

lim

it co

re

tem

pera

ture

s—m

ust m

aint

ain

high

em

issi

vitie

s on

both

insi

de

and

outs

ide

surf

aces

. For

mat

ion

and

cont

rol o

f sur

face

laye

rs

mus

t be

cons

ider

ed u

nder

bot

h he

lium

and

air

envi

ronm

ents

.

L Th

ere

are

limite

d st

udie

s on

SS

and

on 5

08 th

at

show

pot

entia

l for

m

aint

aini

ng h

igh

emis

sivi

ty.

(4/1

6/07

no

te fo

llow

ing

mee

ting

with

T/F

PIR

T pa

nel,

ther

e ar

e so

me

stud

ies

curr

ently

bei

ng

cond

ucte

d by

UIU

C, U

. M

ich.

on

emis

sivi

ty b

ut

NO

T on

mat

eria

ls o

f co

ncer

n).

T

able

6 (c

ontin

ued)

15

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

12

RPV

inte

grity

Ex

cess

de

form

atio

n/8,

9 C

reep

(tra

nsie

nt)

M

Gra

de 9

1, c

reep

dur

ing

high

-te

mpe

ratu

re, s

hort-

term

ex

curs

ions

of ~

100

h, e

cono

mic

im

pact

on

cont

inue

d pl

ant

oper

atio

n, p

oten

tial f

or

exce

ssiv

e ve

ssel

def

orm

atio

n co

uld

pote

ntia

lly a

ffec

t cor

e ge

omet

ry.

M

Mod

erat

ely

exte

nsiv

e fo

ssil

ener

gy d

atab

ase.

M

ost o

f the

labo

rato

ry

cree

p da

ta a

re a

t >5

50°C

. Lo

wer

te

mpe

ratu

re d

ata

are

need

ed, s

peci

ally

for

thic

k se

ctio

n sp

ecim

ens

[10,

15–

17]

13

RPV

inte

grity

Ex

cess

de

form

atio

n/ 8

,9

Cre

ep (t

rans

ient

) M

LW

R m

ater

ials

, cre

ep d

urin

g hi

gh-te

mpe

ratu

re, s

hort-

term

ex

curs

ions

of ~

100

h ea

ch,

econ

omic

impa

ct o

n co

ntin

ued

plan

t ope

ratio

n, p

oten

tial f

or

exce

ssiv

e ve

ssel

def

orm

atio

n co

uld

pote

ntia

lly a

ffec

t cor

e ge

omet

ry.

M

Exis

ting

code

cov

erag

e,

but n

eces

sary

to a

sses

s tim

e an

d te

mpe

ratu

re

[15–

17]

14

RPV

inte

grity

Ex

cess

de

form

atio

n/

1–7

Cre

ep (n

orm

al

oper

atio

ns)

M

Gra

de 9

1, d

iffer

ing

defin

ition

s of

wha

t is d

efin

ed a

s neg

ligib

le

cree

p un

der d

iffer

ent c

odes

,*

ensu

re n

eglig

ible

cre

ep d

urin

g no

rmal

ope

ratio

ns.

L In

adeq

uate

dat

a at

tim

e an

d te

mpe

ratu

res o

f in

tere

st [1

0, 1

5–17

]

15

RPV

inte

grity

Ex

cess

de

form

atio

n/

1–7

Cre

ep (n

orm

al

oper

atio

ns)

L LW

R m

ater

ials

—en

sure

ne

glig

ible

cre

ep d

urin

g no

rmal

op

erat

ions

. Pr

oble

m n

ot

antic

ipat

ed fo

r LW

R m

ater

ials

; de

sign

will

lim

it te

mpe

ratu

res

of o

pera

tion

to re

gim

es w

here

th

is is

not

an

issu

e.

M

Tem

pera

ture

of u

se fo

r LW

R m

ater

ial i

s bel

ow

defin

ed in

sign

ifica

nt

cree

p ra

nge,

ASM

E co

de

cove

rage

[10,

15–

17]

T

able

6 (c

ontin

ued)

16

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

16

RPV

inte

grity

B

reac

h, e

xces

s de

form

atio

n/

1–9

Fiel

d fa

bric

atio

n pr

oces

s con

trol

H

Bec

ause

of v

esse

l siz

e, m

ust

addr

ess f

ield

fabr

icat

ion

[incl

udin

g w

eldi

ng, p

ostw

eld

heat

trea

tmen

t, se

ctio

n th

ickn

ess (

espe

cial

ly w

ith 9

C

r–1

Mo

stee

l)] a

nd p

rese

rvic

e in

spec

tion.

L Fo

ssil

ener

gy e

xper

ienc

e in

dica

tes t

hat c

autio

n ne

eds t

o be

take

n. O

n-si

te n

ucle

ar v

esse

l fa

bric

atio

n is

un

prec

eden

ted.

[1

0, 1

5–17

] 17

R

PV in

tegr

ity

Bre

ach,

exc

ess

defo

rmat

ion/

1–

9

Prop

erty

con

trol i

n he

avy

sect

ions

H

H

eavy

-sec

tion

prop

ertie

s are

di

ffic

ult t

o ob

tain

bec

ause

of

hard

enab

ility

issu

es.

Ade

quat

e la

rge

ingo

t met

allu

rgy

tech

nolo

gy d

oes n

ot e

xist

for

9 C

r–1

Mo

stee

l. M

aint

aini

ng

frac

ture

toug

hnes

s, m

icro

stru

ctur

al c

ontro

l, an

d m

echa

nica

l pro

perti

es in

th

roug

h-th

ickn

ess o

f hea

vy

sect

ions

, 9 C

r mat

eria

ls m

ust b

e m

aint

aine

d. (U

tiliti

es c

onsi

der

heat

trea

tmen

t of P

91, >

3-in

. di

amet

er p

ipin

g ch

alle

nge)

.

L V

ery

limite

d da

ta, n

ot

muc

h ov

er 3

to 4

in.

thic

knes

s. Fe

w d

ata

avai

labl

e fo

r spe

cim

ens

from

300

-mm

-thic

k fo

rgin

gs sh

ow th

ick

sect

ion

prop

ertie

s low

er

than

thin

sect

ion.

[10,

15

–17]

Pow

er c

onve

rsio

n ve

ssel

s (PC

Vs)

and

turb

omac

hine

ry

18

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Bre

ach

of

vess

el/1

–7

Ther

mal

agi

ng

L O

pera

tion

expe

cted

with

in

exis

ting

LWR

exp

erie

nce

data

base

rang

e.

H

Exte

nsiv

e LW

R

data

base

[15–

17]

T

able

6 (c

ontin

ued)

17

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

19

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Bre

ach

of

vess

el/1

–7

Cra

ck in

itiat

ion

and

subc

ritic

al c

rack

gr

owth

in p

ower

co

nver

sion

ves

sel

(PC

V).

L O

pera

tion

expe

cted

with

in

exis

ting

LWR

exp

erie

nce

data

base

rang

e.

H

Exte

nsiv

e LW

R

data

base

[15–

17]

20

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Bre

ach

of

vess

el/3

,4

Hig

h cy

cle

fatig

ue

in P

CV

M

Lo

adin

g de

rivin

g fr

om

rota

tiona

l and

ther

mal

-hy

drau

lic (T

-H) f

eedb

ack.

Se

verit

y m

ust b

e as

sess

ed.

H

Exte

nsiv

e LW

R

data

base

[15–

17]

21

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Bre

ach

of

vess

el/1

–7

Mis

sile

(dis

c fa

ilure

) M

Tu

rbom

achi

nery

failu

re c

ould

be

cau

sed

durin

g no

rmal

op

erat

ions

—an

alog

with

jet

engi

nes (

cree

p, c

reep

cra

ck

grow

th, t

herm

al lo

adin

g,

rota

tiona

l stre

sses

, fat

igue

, cr

eep-

fatig

ue o

f tur

bine

dis

k).

M

Jet e

ngin

e an

d ga

s tu

rbin

e ex

perie

nce

[15–

17]

22

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Turb

ine

failu

re/1

–7

Cre

ep, c

reep

cra

ck

grow

th, t

herm

al

load

ing,

rota

tiona

l st

ress

, fat

igue

, cre

ep

fatig

ue

M

Con

cern

abo

ut d

ebris

plu

ggin

g co

re c

oolin

g ch

anne

ls, c

ausi

ng

dam

age.

M

Jet e

ngin

e an

d ga

s tu

rbin

e ex

perie

nce

[5, 1

6–24

]

T

able

6 (c

ontin

ued)

18

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

23

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Oil

bear

ing

failu

re/1

–7

Prim

ary

cool

ant

cont

amin

atio

n (c

arbu

rizat

ion?

)

M

Coo

lant

che

mis

try c

an b

e af

fect

ed b

y oi

l con

tam

inat

ion

and

exac

erba

tes i

ssue

s with

he

at e

xcha

nger

.

M

Expe

rienc

e w

ith c

oola

nt

chem

istry

con

trol i

n ea

rlier

HTG

R sy

stem

s.

Cir

cula

tors

24

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Oil

bear

ing

failu

re/1

–7

Prim

ary

cool

ant

cont

amin

atio

n (c

arbu

rizat

ion?

)

M

Coo

lant

che

mis

try c

an b

e af

fect

ed b

y oi

l con

tam

inat

ion

and

exac

erba

tes i

ssue

s with

he

at e

xcha

nger

.

M

Expe

rienc

e w

ith c

oola

nt

chem

istry

con

trol i

n ea

rlier

HTG

R sy

stem

s.

25

FOM

1: p

rimar

y sy

stem

pre

ssur

e bo

unda

ry

inte

grity

, FO

M2:

in

tegr

ity o

f ro

tatin

g eq

uipm

ent

Impe

ller f

ailu

re/

1–7

Cre

ep, c

reep

cra

ck

grow

th, t

herm

al

load

ing,

rota

tiona

l st

ress

, fat

igue

, cre

ep

fatig

ue

M

Con

cern

abo

ut d

ebris

plu

ggin

g co

re c

oolin

g ch

anne

ls, c

ausi

ng

dam

age.

M

Jet e

ngin

e an

d ga

s tu

rbin

e ex

perie

nce.

Pipi

ng

26

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Bre

ach/

1–7,

9

Ther

mal

agi

ng

L Th

erm

al a

ging

due

to lo

ng-te

rm

cond

ition

s and

shor

t-ter

m h

igh

tem

pera

ture

; ass

umin

g al

l fe

rriti

c pi

ping

ope

rate

d be

low

th

e cr

eep

rang

e.

M

Exte

nsiv

e in

dust

rial u

se.

27

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Bre

ach

Cra

ck in

itiat

ion

and

subc

ritic

al c

rack

gr

owth

M

Ope

ratio

n ex

pect

ed w

ithin

ex

istin

g LW

R e

xper

ienc

e da

taba

se ra

nge.

M

Exte

nsiv

e LW

R

data

base

.

T

able

6 (c

ontin

ued)

19

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

28

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Bre

ach/

1–7

Hig

h cy

cle

fatig

ue

M

HC

F fr

om T

-H lo

adin

g; fr

om

reso

nanc

e—de

sign

still

not

w

ell e

noug

h kn

own

to d

ism

iss

HC

F; h

owev

er, o

pera

tion

expe

cted

with

in e

xist

ing

LWR

ex

perie

nce

data

base

rang

e.

M

Exte

nsiv

e LW

R

data

base

.

29

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Bre

ach/

1–7

Eros

ion

M

The

pote

ntia

l exi

sts f

or p

artic

le

eros

ion

in th

e pi

ping

syst

em,

parti

cula

rly a

t elb

ows,

due

to

entra

inm

ent o

f gra

phite

dus

t in

high

-vel

ocity

hel

ium

.

M

Ther

e is

a re

lativ

ely

exte

nsiv

e op

erat

ing

hist

ory

of h

eliu

m-c

oole

d gr

aphi

te-m

oder

ated

re

acto

rs th

at c

an b

e ev

alua

ted

to p

rovi

de

syst

em e

xper

ienc

e w

ith

resp

ect t

o th

is

phen

omen

on

30

Peak

fuel

te

mpe

ratu

re

Insu

latio

n de

bris

ge

nera

tion/

1–7

Agi

ng fa

tigue

, en

viro

nmen

tal

degr

adat

ion

of

insu

latio

n

H

Con

cern

is a

bout

insu

latio

n de

bris

plu

ggin

g co

re c

oolin

g ch

anne

ls, c

ausi

ng d

amag

e du

e to

chu

nks o

f int

erna

l ins

ulat

ion

falli

ng o

ff (c

eram

ic sl

eeve

s or

carb

on–c

arbo

n co

mpo

site

s w

ould

be

mos

t lik

ely

sour

ce o

f pr

oble

ms)

.

L Li

ttle

syst

em-r

elev

ant

info

rmat

ion

abou

t in

sula

tion

failu

re

mec

hani

sm is

ava

ilabl

e.

31

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Failu

re to

in

sula

te/1

–7

Agi

ng fa

tigue

, en

viro

nmen

tal

degr

adat

ion

of

insu

latio

n

M

Faile

d in

sula

tion

lead

s to

hot

spot

s or c

oolin

g sy

stem

leak

(in

PBM

R)—

focu

s is o

n fa

ilure

to

insu

late

and

eff

ect o

n pi

ping

du

e to

tran

sien

ts o

pera

tiona

lly

indu

ced—

ther

mal

load

ing,

pr

essu

re lo

adin

g, re

sidu

al

stre

ss, e

xist

ing

flaw

s.

L Li

ttle

syst

em-r

elev

ant

info

rmat

ion

abou

t in

sula

tion

failu

re

mec

hani

sm is

ava

ilabl

e.

T

able

6 (c

ontin

ued)

20

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

Inte

rmed

iate

hea

t exc

hang

er (I

HX

) ves

sel

32

FOM

1: in

tegr

ity

of IH

X; F

OM

2:

inte

grity

of

vess

el

Bre

ach

to

ambi

ent/1

–9

Ther

mal

agi

ng

L O

pera

tion

expe

cted

with

in

exis

ting

LWR

exp

erie

nce

data

base

rang

e bu

t sho

rter

serv

ice

life

due

to re

plac

emen

t.

H

Exte

nsiv

e LW

R

data

base

.

33

FOM

1: in

tegr

ity

of IH

X;

FOM

2: in

tegr

ity

of v

esse

l

Bre

ach

to

ambi

ent/1

–9

Cra

ck in

itiat

ion

and

subc

ritic

al c

rack

gr

owth

M

Ope

ratio

n ex

pect

ed w

ithin

ex

istin

g LW

R e

xper

ienc

e da

taba

se ra

nge

but s

horte

r se

rvic

e lif

e du

e to

repl

acem

ent.

H

Exte

nsiv

e LW

R

data

base

.

34

FOM

1: in

tegr

ity

of IH

X;

FOM

2: in

tegr

ity

of v

esse

l

Bre

ach

to

ambi

ent/1

–9

Hig

h cy

cle

fatig

ue

L H

CF

from

T-H

load

ing;

from

re

sona

nce—

desi

gn st

ill n

ot

wel

l eno

ugh

know

n to

dis

mis

s H

CF;

how

ever

, ope

ratio

n ex

pect

ed w

ithin

exi

stin

g LW

R

expe

rienc

e da

taba

se ra

nge

but

shor

ter s

ervi

ce li

fe d

ue to

re

plac

emen

t.

H

Exte

nsiv

e LW

R

data

base

.

Inte

rmed

iate

hea

t exc

hang

er (I

HX

)

35

FOM

1: in

tegr

ity

of IH

X;

FOM

2:

seco

ndar

y lo

op

failu

re/b

reac

h

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Cra

ck in

itiat

ion

and

prop

agat

ion

(due

to

cree

p cr

ack

grow

th,

cree

p, c

reep

-fat

igue

, ag

ing

(with

or

with

out l

oad)

, su

bcrit

ical

cra

ck

grow

th)

H

Envi

ronm

enta

l eff

ects

on

subc

ritic

al c

rack

gro

wth

—su

bjec

t to

impa

cts o

f des

ign

issu

es, p

artic

ular

ly fo

r thi

n-se

ctio

n m

ust b

e ad

dres

sed.

St

ress

es o

n IH

X (b

oth

thin

and

th

ick

sect

ions

) can

lead

to th

ese

failu

re p

heno

men

a; th

erm

al

trans

ient

s can

cau

se to

ughn

ess

conc

erns

and

car

bide

re

dist

ribut

ion

as a

func

tion

of

ther

mal

stre

ss c

an c

hang

e th

roug

h-th

ickn

ess p

rope

rties

.

L M

ore

is k

now

n ab

out

617

from

HTG

R a

nd

indu

stry

usa

ge th

an fo

r 23

0. B

oth

envi

ronm

ent

and

cree

p pl

ay

sign

ifica

nt ro

les i

n in

itiat

ion

and

cycl

ic

crac

k gr

owth

rate

of 6

17

and

230.

Mec

hani

stic

m

odel

s for

pre

dict

ing

dam

age

deve

lopm

ent

and

failu

re c

riter

ia fo

r tim

e-de

pend

ent

phen

omen

a ha

ve to

be

deve

lope

d to

ena

ble

T

able

6 (c

ontin

ued)

21

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

cons

erva

tive

extra

pola

tion

from

shor

t te

rm la

bora

tory

test

dat

a to

long

term

des

ign

life.

36

FO

M1:

inte

grity

of

IHX

; FO

M2:

se

cond

ary

loop

fa

ilure

/bre

ach

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Prim

ary

boun

dary

de

sign

met

hodo

logy

lim

itatio

ns fo

r new

st

ruct

ures

(lac

k of

ex

perie

nce)

H

Tim

e-de

pend

ent d

esig

n cr

iteria

fo

r com

plex

stru

ctur

es n

eed

to

be d

evel

oped

and

ver

ified

by

stru

ctur

al te

stin

g. A

SME

Cod

e ap

prov

ed si

mpl

ified

met

hods

ha

ve n

ot b

een

prov

en a

nd a

re

not p

erm

itted

for c

ompa

ct IH

X

com

pone

nts.

L N

o ex

perie

nce

for t

he

com

plex

shap

e IH

X. N

o ex

perie

nce

for d

esig

ning

an

d op

erat

ing

high

te

mpe

ratu

re c

ompo

nent

s in

the

clas

s 1

envi

ronm

ent.

Diff

icul

ties

of d

esig

n an

d an

alys

es

of c

ompa

ct IH

X a

re

disc

usse

d in

the

refe

renc

es.

37

FOM

1: in

tegr

ity

of IH

X;

FOM

2:

seco

ndar

y lo

op

failu

re/b

reac

h

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Man

ufac

turin

g ph

enom

ena

(suc

h as

jo

inin

g)

H

Com

pact

hea

t exc

hang

er

(CH

X) c

ores

(if u

sed)

will

re

quire

adv

ance

d m

achi

ning

, fo

rmin

g, a

nd jo

inin

g (e

.g.,

diff

usio

n bo

ndin

g, b

razi

ng,

etc.

) met

hods

that

may

impa

ct

com

pone

nt in

tegr

ity.

Mus

t as

sess

CH

X v

s tra

ditio

nal t

ube

and

shel

l con

cept

s. H

owev

er,

thes

e ph

enom

ena

are

gene

ric

and

exte

nd b

eyon

d th

e C

HX

s to

all

the

very

hig

h-te

mpe

ratu

re

heat

exc

hang

ers (

HX

s).

L H

Xs h

ave

not b

een

used

in

nuc

lear

app

licat

ions

; th

e ca

ndid

ate

allo

ys a

nd

thei

r joi

ning

pro

cess

es

not a

dequ

atel

y es

tabl

ishe

d in

no

nnuc

lear

app

licat

ions

.

38

FOM

1: in

tegr

ity

of IH

X;

FOM

2:

seco

ndar

y lo

op

failu

re/b

reac

h

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Insp

ectio

n/te

stin

g ph

enom

ena

H

Trad

ition

al n

onde

stru

ctiv

e ev

alua

tion

(ND

E) m

etho

ds w

ill

not w

ork

for C

HX

s bec

ause

of

geom

etric

al c

onst

rain

ts.

Proo

f-te

stin

g of

som

e ki

nd w

ill b

e re

quire

d (m

aybe

leak

test

ing

with

trac

er).

Pres

ervi

ce te

stin

g

L Pr

eope

ratio

nal t

estin

g,

pres

ervi

ce in

spec

tion,

fit

ness

for s

ervi

ce, i

ssue

w

ith le

ak te

sts,

have

ve

ry li

ttle

know

ledg

e he

re. W

hat i

s the

m

argi

n?

T

able

6 (c

ontin

ued)

22

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

will

be

diff

icul

t, an

d in

-ser

vice

te

stin

g w

ill b

e ev

en h

arde

r.

Con

ditio

n m

onito

ring

may

be

usef

ul.

39

FOM

1: in

tegr

ity

of IH

X;

FOM

2: in

tegr

ity

of h

ot d

uct (

and

othe

r sys

tem

s)

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Wat

er o

r che

mic

al

ingr

ess/

atta

ck

M

Con

side

ring

that

all

curr

ent

prop

osed

syst

ems f

or th

e N

GN

P w

ill u

tiliz

e he

lium

or

heliu

m n

itrog

en o

n th

e se

cond

ary

side

of t

he IH

X, t

he

norm

al o

pera

ting

envi

ronm

ent

will

be

mod

erat

ely

beni

gn.

The

pote

ntia

l exi

sts f

or

cont

amin

atio

n of

the

seco

ndar

y ci

rcui

t with

wat

er o

r pro

cess

ch

emic

als f

rom

the

hydr

ogen

pr

oduc

tion

plan

t. In

the

shor

t te

rm, e

ven

for s

igni

fican

t in

trusi

on, s

uch

cont

amin

atio

n is

no

t exp

ecte

d to

cha

lleng

e th

e IH

X.

Long

-term

mild

co

ntam

inat

ion

is a

gre

ater

co

ncer

n, b

ut sh

ould

be

able

to

be a

void

ed b

y pr

oces

s con

trol.

M

Ther

e is

a fa

irly

exte

nsiv

e bo

dy o

f dat

a re

gard

ing

the

effe

ct th

at

wat

er o

r lik

ely

proc

ess

chem

ical

s cou

ld h

ave

on

the

IHX

mem

bran

e m

ater

ials

, but

littl

e op

erat

ing

or sy

stem

ex

perie

nce

to sh

ed li

ght

on th

e pr

obab

ility

of

such

an

occu

rren

ce

40

Inte

grity

of I

HX

C

atas

troph

ic lo

ss

of fu

nctio

n/9

Plas

tic in

stab

ility

M

D

egra

datio

n du

e to

bra

zing

, di

ffus

ion-

bond

ing,

nex

t ge

nera

tion

join

ing

tech

niqu

es

can

resu

lt in

stru

ctur

al

inst

abili

ty a

nd p

last

ic c

olla

pse

(buc

klin

g pr

oble

m).

May

be

ultim

atel

y sa

fety

issu

e be

caus

e of

cor

e ov

erhe

atin

g, a

nalo

gous

in

som

e re

spec

ts to

tube

pl

uggi

ng a

nd le

akag

e ab

ove

thre

shol

d. E

xace

rbat

ed b

y ex

trem

e hi

gh se

rvic

e

L Ex

pert

opin

ion

[12–

17]

T

able

6 (c

ontin

ued)

23

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

tem

pera

ture

s with

rega

rd to

av

aila

ble

mat

eria

l cap

abili

ties

(e.g

., lo

w m

argi

n).

Con

trol

rods

(non

met

allic

)

41

Mai

ntai

n in

serti

on a

bilit

y Fa

ilure

to in

sert/

1–

12

Rad

iatio

n-in

duce

d de

grad

atio

n M

Li

mits

on

stre

ngth

and

di

men

sion

al st

abili

ty d

urin

g irr

adia

tion;

ass

umpt

ion

that

di

men

sion

al st

abili

ty a

lso

incl

udes

ani

sotro

py.

L Li

mite

d da

ta fr

om fu

sion

po

wer

pro

gram

, but

ap

plic

abili

ty n

eeds

to b

e as

sess

ed.

42

Mai

ntai

n in

serti

on a

bilit

y Fa

ilure

to in

sert/

1–

12

Oxi

datio

n M

Lo

ng-te

rm e

xpos

ure

to lo

w

parti

al p

ress

ure

of o

xyge

n an

d m

ore

rapi

d ox

idat

ion

durin

g ai

r in

gres

s.

M

Lim

ited

data

from

fusi

on

pow

er p

rogr

am, b

ut

appl

icab

ility

nee

ds to

be

asse

ssed

. 43

M

aint

ain

inse

rtion

abi

lity

Failu

re to

inse

rt/

1–12

C

ompo

site

s st

ruct

ural

des

ign

met

hodo

logy

lim

itatio

ns fo

r new

st

ruct

ures

(lac

k of

ex

perie

nce)

H

Car

bon–

carb

on c

ompo

site

s are

pr

ime

cand

idat

es, b

ut n

eed

appr

oved

met

hod

of d

esig

ning

, pr

oof t

estin

g, m

odel

test

ing,

te

stin

g st

anda

rds,

and

valid

atio

n te

sts.

L So

me

code

wor

k is

be

ing

deve

lope

d by

A

SME,

AST

M, a

nd

inte

rnat

iona

l par

tner

s.

Exte

nsiv

e ae

rosp

ace

indu

stry

des

ign

and

usag

e ca

n be

ass

esse

d fo

r app

licab

ility

.

Con

trol

rods

(met

allic

)

44

Mai

ntai

n in

serti

on a

bilit

y Fa

ilure

to in

sert/

1–

12

Rad

iatio

n de

grad

atio

n (e

mbr

ittle

men

t/ sw

ellin

g/ ra

diat

ion

cree

p)

M

Inse

rtion

issu

e pa

rticu

larly

for

allo

y 80

0H re

low

-dos

e du

ctili

ty re

duct

ion,

and

di

men

sion

al c

hang

es a

ssoc

iate

d w

ith N

i-allo

y ba

sed

swel

ling

and

radi

atio

n-in

duce

d cr

eep

at

mod

erat

ely

low

dos

es.

M

Lim

ited

info

rmat

ion

avai

labl

e on

swel

ling

and

duct

ility

redu

ctio

n at

m

oder

ate

dose

s, no

in

form

atio

n on

irr

adia

tion

cree

p [1

2–17

]

T

able

6 (c

ontin

ued)

24

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

45

Mai

ntai

n in

serti

on a

bilit

y Fa

ilure

to in

sert/

8,

9, 1

2 Lo

ss o

f stre

ngth

at

high

tem

pera

ture

s (tr

ansi

ent)

M

Pote

ntia

l for

tem

pera

ture

to

exce

ed sh

ort-t

erm

stre

ngth

of

met

allic

mat

eria

ls. P

anel

stat

es

that

for i

nser

tion

it is

an

H, b

ut

for s

afet

y, a

n M

.

M

Shor

t-ter

m m

echa

nica

l pr

oper

ty d

ata

are

avai

labl

e fr

om p

revi

ous

nucl

ear a

pplic

atio

ns (s

ee

ASM

E da

taba

se b

eing

as

sess

ed u

nder

DO

E-A

SME

cont

ract

) [12

–17]

RPV

inte

rnal

s (m

etal

lic)

46

Mai

ntai

n he

at

trans

fer

capa

bilit

y

Inad

equa

te h

eat

trans

fer/8

,9

Cha

nge

in

emis

sivi

ty

H

To e

nsur

e pa

ssiv

e sa

fety

, hig

h em

issi

vity

is re

quire

d to

lim

it co

re te

mpe

ratu

res (

affe

ct

cool

ant p

athw

ay)—

need

for

high

em

issi

vitie

s on

both

su

rfac

es o

f the

cor

e ba

rrel

, and

fo

rmat

ion

and

cont

rol o

f su

rfac

e la

yers

in h

eliu

m

envi

ronm

ents

).

L Li

mite

d st

udie

s on

SS

and

on 5

08 sh

ow

pote

ntia

l for

mai

ntai

ning

hi

gh e

mis

sivi

ty [1

2–17

]

47

Mai

ntai

n st

ruct

ure

geom

etry

Exce

ss

defo

rmat

ion/

1–9

Rad

iatio

n-cr

eep

H

Irra

diat

ion

cree

p an

d di

men

sion

al c

hang

es

parti

cula

rly fo

r allo

y 80

0H a

t m

oder

atel

y lo

w-d

ose

shou

ld b

e as

sess

ed.

L Li

ttle

info

rmat

ion

on

irrad

iatio

n cr

eep

is

avai

labl

e fo

r Allo

y 80

0H

[12–

17]

48

Mai

ntai

n st

ruct

ure

geom

etry

Frac

ture

/failu

re/

1–9

Rad

iatio

n-in

duce

d em

britt

lem

ent

M

Parti

cula

r iss

ue fo

r allo

y 80

0H

rega

rdin

g m

oder

ate

low

-dos

e du

ctili

ty re

duct

ion.

M

Lim

ited

info

rmat

ion

avai

labl

e on

duc

tility

re

duct

ion

at m

oder

ate

dose

s [12

–17]

49

FO

M1:

cor

e ba

rrel

inte

grity

; FO

M2:

RPV

in

tegr

ity

Failu

re/1

–9

Cre

ep, c

reep

cra

ck

grow

th, t

herm

al

load

ing

L C

rack

ing

or fa

ilure

of g

raph

ite

can

caus

e a

hot p

lum

e/st

ream

to

impi

nge

on th

e co

re b

arre

l and

ca

use

a lo

cal h

ot sp

ot, b

ut m

ay

be d

iffic

ult d

ue to

low

(to

zero

) pr

essu

re d

iffer

entia

l and

hig

h pa

thw

ay re

sist

ance

. H

owev

er,

the

cons

eque

nce

of th

is

M

Ther

e is

a re

lativ

ely

exte

nsiv

e op

erat

ing

hist

ory

of h

eliu

m-c

oole

d gr

aphi

te-m

oder

ated

re

acto

rs th

at c

an b

e ev

alua

ted

to p

rovi

de

syst

em e

xper

ienc

e w

ith

resp

ect t

o th

is

T

able

6 (c

ontin

ued)

25

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

affe

ctin

g th

e co

re g

eom

etry

or

prov

idin

g a

path

way

for

exte

rnal

leak

age

is h

ighl

y un

likel

y.

phen

omen

on

RPV

inte

rnal

s (no

nmet

allic

)

50

FOM

1: m

aint

ain

stru

ctur

e ge

omet

ry;

FOM

2: m

aint

ain

insu

latio

n ca

pabi

lity

Cor

e re

stra

int a

nd

supp

ort f

ailu

re/

1–12

Rad

iatio

n-in

duce

d de

grad

atio

n M

R

PV in

tern

als (

nonm

etal

lic)

incl

ude

(1) i

nsul

atio

n, su

ch a

s un

der c

ore,

am

orph

ous c

arbo

n un

derla

id b

y al

umin

a pr

ovid

ing

com

pres

sive

non

met

allic

m

ater

ial,

(2) n

onm

etal

lic

stru

ctur

al m

ater

ials

(e.g

., ca

rbon

–car

bon

com

posi

tes)

. N

eed

to a

sses

s eff

ects

on

stre

ngth

, fra

ctur

e, d

imen

sion

al

stab

ility

, and

ther

mop

hysi

cal

prop

ertie

s dur

ing

irrad

iatio

n.

L Li

mite

d da

ta fr

om fu

sion

po

wer

pro

gram

, but

ap

plic

abili

ty n

eeds

to b

e as

sess

ed.

51

FOM

1: m

aint

ain

stru

ctur

e ge

omet

ry;

FOM

2: m

aint

ain

insu

latio

n ca

pabi

lity

Cor

e re

stra

int a

nd

supp

ort f

ailu

re/

1–12

Oxi

datio

n M

R

PV in

tern

als (

nonm

etal

lic)

incl

ude

(1) i

nsul

atio

n, su

ch a

s un

der c

ore,

am

orph

ous c

arbo

n un

derla

id b

y al

umin

a pr

ovid

ing

com

pres

sive

non

met

allic

m

ater

ial,

(2) n

onm

etal

lic

stru

ctur

al m

ater

ials

(e.g

., ca

rbon

–car

bon

com

posi

tes)

. Ef

fect

s of l

ong-

term

exp

osur

e to

low

par

tial p

ress

ure

of

oxyg

en a

nd m

ore

rapi

d ox

idat

ion

durin

g ai

r ing

ress

m

ust b

e as

sess

ed.

Oxi

datio

n ef

fect

s for

irra

diat

ed

com

posi

tes a

nd c

arbo

n in

sula

tion

are

unkn

own.

M

Dat

a fr

om fu

sion

pow

er

prog

ram

and

com

mer

cial

ap

plic

atio

ns, b

ut

appl

icab

ility

nee

ds to

be

asse

ssed

.

T

able

6 (c

ontin

ued)

26

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

52

Mai

ntai

n st

ruct

ure

geom

etry

Cor

e re

stra

int

failu

re/1

–12

Com

posi

tes

stru

ctur

al d

esig

n an

d fa

bric

atio

n m

etho

dolo

gy

limita

tions

for n

ew

stru

ctur

es (l

ack

of

expe

rienc

e)

H

Car

bon–

carb

on c

ompo

site

s are

pr

ime

cand

idat

es, b

ut n

eed

appr

oved

met

hods

for

desi

gnin

g, p

roof

test

ing,

mod

el

stan

dard

test

ing,

val

idat

ion

test

s, an

d pr

obab

ilist

ic m

etho

ds

of d

esig

n. S

cala

bilit

y an

d fa

bric

atio

n is

sues

mus

t be

addr

esse

d. L

arge

-sca

le (m

eter

s in

dia

met

er) s

truct

ures

as w

ell

as sm

alle

r one

s mus

t be

cove

red.

L Ex

tens

ive

expe

rienc

e w

ithin

the

aero

spac

e in

dust

ry; a

pplic

abili

ty

mus

t be

asse

ssed

.

53

Mai

ntai

n in

sula

tion

capa

bilit

y

Fibr

ous i

nsul

atio

n de

grad

atio

n/1–

12

Envi

ronm

enta

l and

ra

diat

ion

degr

adat

ion

and

ther

mal

stab

ility

at

tem

pera

ture

H

Rel

ativ

ely

low

dos

e an

d ex

posu

re is

exp

ecte

d, b

ut lo

ss-

of-f

orce

d ci

rcul

atio

n (L

OFC

) ca

n re

sult

in te

mpe

ratu

res h

igh

enou

gh to

cha

lleng

e st

abili

ty o

f fib

rous

insu

latio

n su

ch a

s K

aow

ool.

Nee

d to

ass

ess

effe

cts o

n m

icro

stru

ctur

al

stab

ility

and

ther

mop

hysi

cal

prop

ertie

s dur

ing

irrad

iatio

n an

d hi

gh te

mpe

ratu

re e

xpos

ure

in im

pure

hel

ium

.

L Li

mite

d co

mm

erci

al

info

rmat

ion

avai

labl

e fo

r co

nditi

ons o

f int

eres

t.

Rea

ctor

Cav

ity C

oolin

g Sy

stem

(RC

CS)

54

Emer

genc

y he

at

rem

oval

ca

pabi

lity

Inad

equa

te h

eat

rem

oval

/8,9

A

queo

us c

orro

sion

an

d fo

ulin

g L

Pote

ntia

l con

cern

of w

ater

in

gres

s int

o R

PV a

nd fa

ilure

of

RC

CS

due

to a

queo

us

corr

osio

n.

H

Exte

nsiv

e co

mm

erci

al

and

LWR

exp

erie

nce

in

aque

ous c

orro

sion

co

ntro

l

T

able

6 (c

ontin

ued)

27

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

Aux

iliar

y sh

utdo

wn

syst

em

55

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Wat

er

cont

amin

atio

n of

pr

imar

y co

olan

t/2

Fatig

ue, c

orro

sion

-fa

tigue

, stre

ss

corr

osio

n cr

acki

ng,

crac

k in

itiat

ion

and

subc

ritic

al c

rack

gr

owth

, hig

h cy

cle

fatig

ue.

L Po

tent

ial c

once

rn o

f wat

er

ingr

ess i

nto

RPV

and

failu

re o

f R

CC

S du

e to

aqu

eous

co

rros

ion.

H

Exte

nsiv

e co

mm

erci

al

and

LWR

exp

erie

nce

in

aque

ous c

orro

sion

co

ntro

l.

Val

ves

56

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Mal

func

tion,

fa

ilure

to o

pera

te

and

brea

ch/1

,2,5

,9

Isol

atio

n va

lve

failu

re

H

Isol

atio

n va

lve

failu

re (i

nclu

des

cate

gorie

s suc

h as

self-

wel

ding

, ga

lling

, sei

zing

) is p

ossi

ble.

C

once

rns a

bout

isol

atio

n va

lves

ar

e si

mila

r to

‘bre

ach

to

seco

ndar

y’ is

sues

on

IHX

sinc

e th

ey w

ould

pro

vide

bar

riers

to

seco

ndar

y he

at tr

ansp

ort

syst

em.

L In

form

atio

n po

ssib

ly

avai

labl

e fr

om

prev

ious

ly c

onst

ruct

ed

HTG

Rs b

ut re

leva

nce

need

s to

be a

sses

sed.

St

ate

of k

now

ledg

e ab

out h

eliu

m-le

ak-

tight

ness

in la

rge

valv

es

is u

nkno

wn

[15–

17]

57

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Failu

re to

ope

rate

, br

each

/1–1

2 V

alve

failu

re

H

Con

cern

s abo

ut a

var

iety

of

valv

e fa

ilure

mec

hani

sms t

hat

will

be

desi

gn-d

epen

dent

(in

clud

es c

ateg

orie

s suc

h as

se

lf-w

eldi

ng, g

allin

g, se

izin

g)

will

nee

d to

be

asse

ssed

onc

e de

sign

-spe

cific

det

ails

are

av

aila

ble.

Hel

ium

-trib

olog

y is

sues

mus

t be

cons

ider

ed.

Allo

wab

le id

entif

ied

and

unid

entif

ied

cool

ant l

eaka

ge

mus

t be

esta

blis

hed.

L In

form

atio

n av

aila

ble

from

pre

viou

sly

cons

truct

ed H

TGR

s but

re

leva

nce

need

s to

be

asse

ssed

[15–

17]

T

able

6 (c

ontin

ued)

28

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

Rea

ctor

Cav

ity C

oolin

g Sy

stem

(RC

CS)

58

Emer

genc

y he

at

rem

oval

ca

pabi

lity

Inad

equa

te h

eat

rem

oval

/8,9

C

hang

e in

RC

CS

pane

l em

issi

vity

M

Th

is w

as th

e on

ly p

heno

men

on

for w

hich

the

pane

l was

una

ble

to re

ach

cons

ensu

s with

rega

rd

to it

s im

porta

nce.

Thi

s was

due

to

a d

iffer

ence

of o

pini

on a

s to

whe

ther

or n

ot th

is w

as a

safe

ty

or a

n ec

onom

ic is

sue.

Pan

el

mem

bers

who

felt

it w

as a

sa

fety

issu

e ra

nked

it h

igh.

Pa

nel m

embe

rs w

ho fe

lt it

was

a

sim

ply

an e

cono

mic

pr

otec

tion

issu

e ra

nked

it lo

w.

The

rank

ing

prov

ided

for t

his

phen

omen

on o

nly

is a

n av

erag

e, n

ot a

con

sens

us.

Pane

l mem

ber c

omm

ents

fo

llow

. M

ajum

dar:

to e

nsur

e pa

ssiv

e sa

fety

, hig

h em

issi

vity

is

requ

ired

to li

mit

core

te

mpe

ratu

res (

affe

ct c

oola

nt

path

way

)—ne

ed fo

r hig

h em

issi

vitie

s on

both

surf

aces

of

the

core

bar

rel,

and

form

atio

n an

d co

ntro

l of s

urfa

ce la

yers

un

der h

eliu

m e

nviro

nmen

ts.

Cor

win

dis

agre

es w

ith th

e af

oreg

oing

ratio

nale

bec

ause

th

e fa

ilure

in th

e R

CC

S pa

nel

mer

ely

resu

lts in

deg

rada

tion

of

the

conc

rete

surr

ound

ing

the

RPV

, not

a si

gnifi

cant

re

duct

ion

in h

eat r

emov

al fr

om

it. T

his i

s an

econ

omic

issu

e,

H

Ther

e ar

e a

wid

e ra

nge

of d

ata

for c

orro

sion

of

stee

l in

low

tem

pera

ture

en

viro

nmen

ts (e

.g.,

<60°

C) f

or lo

ng

expo

sure

s, bu

t les

s in

form

atio

n on

the

effe

cts t

his c

orro

sion

has

on

em

issi

vity

T

able

6 (c

ontin

ued)

29

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

scen

ario

s*

Phen

omen

a Ph

enom

ena

impo

rtan

ce

Rat

iona

le fo

r ra

nkin

gs o

f ph

enom

enon

impo

rtan

ce

Kno

wle

dge

leve

l R

atio

nale

for

rank

ings

of

kno

wle

dge

not a

safe

ty o

ne. W

eave

r co

mm

ent:

In re

cent

co

nver

satio

ns w

ith th

e ve

ndor

s, th

ey h

ave

stat

ed th

at th

e R

CC

S is

con

side

red

a sa

fety

syst

em.

How

ever

, it i

s not

cle

ar

whe

ther

the

RC

CS

is n

eces

sary

to

mai

ntai

n fu

el te

mpe

ratu

res

belo

w th

e lim

it du

ring

an

acci

dent

.

*Sce

nari

o nu

mbe

r ref

ers t

o Ta

ble

2.

30

Tab

le 7

. Se

lect

ed P

IRT

phe

nom

ena

from

Tab

le 6

that

hav

e pa

rtic

ular

sign

ifica

nce

due

to th

eir

high

impo

rtan

ce a

nd lo

w k

now

ledg

e ra

nkin

gs

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

sc

enar

ios*

Ph

enom

ena

Phen

omen

a im

port

ance

R

atio

nale

for

rank

ings

of

phen

omen

on im

port

ance

K

now

ledg

e le

vel

Rat

iona

le fo

r ra

nkin

gs

of k

now

ledg

e

Rea

ctor

pre

ssur

e ve

ssel

(RPV

) 1

RPV

inte

grity

B

reac

h/1–

4 Th

erm

al a

ging

(lo

ng te

rm)

H

Unc

erta

inty

in p

rope

rties

of 9

C

r–1

Mo

stee

l (gr

ade

91),

espe

cial

ly d

egra

datio

n an

d ag

ing

of b

ase

met

als a

nd

wel

ds fo

r a c

ritic

al

com

pone

nt li

ke th

e R

PV,

mus

t be

addr

esse

d fo

r 60-

year

life

times

M

It is

ass

umed

that

Gra

de 9

1 is

th

e pr

ime

cand

idat

e fo

r NG

NP

and

no b

ack

up m

ater

ial i

s co

nsid

ered

in th

is re

port

for

desi

gns w

ithou

t act

ive

cool

ing.

Thi

s is b

eyon

d ex

perie

nce

base

for c

ondi

tions

of

inte

rest

, ext

ensi

ve fo

ssil

ener

gy e

xper

ienc

e an

d co

de

usag

e; th

ough

sign

ifica

nt

agin

g da

ta e

xist

at h

igh

tem

pera

ture

s (>5

00°C

). N

eed

is fo

r lon

g-te

rm a

ging

dat

a at

N

GN

P-re

leva

nt te

mpe

ratu

res

[10,

15–

17].

5 R

PV in

tegr

ity

Bre

ach/

1–7

Cra

ck in

itiat

ion

and

subc

ritic

al

crac

k gr

owth

H

9 C

r–1

Mo

stee

l (gr

ade

91)

mus

t be

asse

ssed

for

phen

omen

a du

e to

tran

sien

ts

and

oper

atio

nally

indu

ced–

ther

mal

load

ing,

pre

ssur

e lo

adin

g, re

sidu

al st

ress

, ex

istin

g fla

ws (

degr

adat

ion

of w

elds

, cyc

lic lo

adin

g, lo

w

cycl

e fa

tigue

)

L Th

ere

is a

lim

ited

data

base

fr

om fo

ssil

ener

gy

appl

icat

ions

at t

hese

te

mpe

ratu

res.

Low

cyc

le

fatig

ue d

ata

in a

ir, v

acuu

m,

and

sodi

um (A

NL

unpu

blis

hed

data

) at >

482°

C

show

life

is lo

nges

t in

sodi

um,

follo

wed

by

vacu

um a

nd a

ir.

Agi

ng in

hel

ium

(dep

endi

ng

on im

purit

ies)

will

mos

t lik

ely

be g

reat

er th

an in

air.

Agi

ng in

im

pure

hel

ium

may

per

haps

de

pend

on

impu

rity

type

and

co

nten

t [10

, 15–

17]

T

able

7 (c

ontin

ued)

31

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

sc

enar

ios*

Ph

enom

ena

Phen

omen

a im

port

ance

R

atio

nale

for

rank

ings

of

phen

omen

on im

port

ance

K

now

ledg

e le

vel

Rat

iona

le fo

r ra

nkin

gs

of k

now

ledg

e

11

FOM

1: R

PV

inte

grity

; FO

M2:

pea

k fu

el

tem

pera

ture

Inad

equa

te

heat

tran

sfer

/ 1–

3

Com

prom

ise

of

emis

sivi

ty d

ue to

lo

ss o

f des

ired

surf

ace

laye

r pr

oper

ties

H

To e

nsur

e pa

ssiv

e sa

fety

, hi

gh e

mis

sivi

ty o

f the

RPV

is

requ

ired

to li

mit

core

te

mpe

ratu

res—

mus

t mai

ntai

n hi

gh e

mis

sivi

ties o

n bo

th

insi

de a

nd o

utsi

de su

rfac

es.

Form

atio

n an

d co

ntro

l of s

ur-

face

laye

rs m

ust b

e co

n-si

dere

d un

der b

oth

heliu

m

and

air e

nviro

nmen

ts

L Th

ere

are

limite

d st

udie

s on

SS a

nd o

n 50

8 th

at sh

ow

pote

ntia

l for

mai

ntai

ning

hig

h em

issi

vity

16

RPV

inte

grity

B

reac

h,

exce

ss

defo

rmat

ion/

1–9

Fiel

d fa

bric

atio

n pr

oces

s con

trol

H

Fabr

icat

ion

issu

es m

ust

addr

ess f

ield

fabr

icat

ion

beca

use

of v

esse

l siz

e

[incl

udin

g w

eldi

ng, p

ost-

wel

d he

at tr

eatm

ent,

sect

ion

thic

knes

s (es

peci

ally

with

9

Cr–

1 M

o st

eel)

and

pres

ervi

ce in

spec

tion]

L Fo

ssil

ener

gy e

xper

ienc

e in

dica

tes t

hat c

autio

n ne

eds t

o be

take

n. O

n-si

te n

ucle

ar

vess

el fa

bric

atio

n is

un

prec

eden

ted

[10,

15–

17]

17

RPV

inte

grity

B

reac

h,

exce

ss

defo

rmat

ion/

1–9

Prop

erty

con

trol i

n he

avy

sect

ions

H

H

eavy

-sec

tion

prop

ertie

s are

di

ffic

ult t

o ob

tain

bec

ause

of

hard

enab

ility

issu

es.

Ade

quat

e la

rge

ingo

t m

etal

lurg

y te

chno

logy

doe

s no

t exi

st fo

r 9 C

r–1

Mo

stee

l. M

aint

aini

ng fr

actu

re to

ugh-

ness

, mic

rost

ruct

ural

con

trol,

and

mec

hani

cal p

rope

rties

in

thro

ugh-

thic

knes

s of h

eavy

se

ctio

ns, 9

Cr m

ater

ials

mus

t be

mai

ntai

ned

L V

ery

limite

d da

ta, n

ot m

uch

over

3 to

4 in

. thi

ckne

ss. F

ew

data

ava

ilabl

e fo

r spe

cim

ens

from

300

-mm

-thic

k fo

rgin

gs

show

thic

k se

ctio

n pr

oper

ties

low

er th

an th

in se

ctio

n [1

0,

15–1

7]

T

able

7 (c

ontin

ued)

32

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

sc

enar

ios*

Ph

enom

ena

Phen

omen

a im

port

ance

R

atio

nale

for

rank

ings

of

phen

omen

on im

port

ance

K

now

ledg

e le

vel

Rat

iona

le fo

r ra

nkin

gs

of k

now

ledg

e

Pipi

ng

30

Peak

fuel

te

mpe

ratu

re

Insu

latio

n de

bris

ge

nera

tion/

1–

7

Agi

ng, f

atig

ue, a

nd

envi

ronm

enta

l de

grad

atio

n of

in

sula

tion.

H

Con

cern

is a

bout

insu

latio

n de

bris

plu

ggin

g co

re c

oolin

g ch

anne

ls, c

ausi

ng d

amag

e du

e to

chu

nks o

f int

erna

l in

sula

tion

falli

ng o

ff

(cer

amic

slee

ves o

r car

bon–

carb

on c

ompo

site

s wou

ld b

e m

ost l

ikel

y so

urce

of

prob

lem

s)

L Li

ttle

syst

em-r

elev

ant

info

rmat

ion

abou

t ins

ulat

ion

failu

re m

echa

nism

is a

vaila

ble

[16–

25]

Inte

rmed

iate

hea

t exc

hang

er (I

HX

) 35

FO

M1:

in

tegr

ity o

f IH

X;

FOM

2:

seco

ndar

y lo

op fa

ilure

/ br

each

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Cra

ck in

itiat

ion

and

prop

agat

ion

(due

to c

reep

cra

ck

grow

th, c

reep

, cr

eep-

fatig

ue,

agin

g (w

ith o

r w

ithou

t loa

d),

subc

ritic

al c

rack

gr

owth

)

H

Envi

ronm

enta

l eff

ects

on

subc

ritic

al c

rack

gro

wth

—im

pact

s of d

esig

n is

sues

, pa

rticu

larly

for t

hin-

sect

ion

mus

t be

addr

esse

d. S

tress

es

on IH

X (b

oth

thin

and

thic

k se

ctio

ns) c

an le

ad to

thes

e fa

ilure

phe

nom

ena;

ther

mal

tra

nsie

nts c

an c

ause

to

ughn

ess c

once

rns a

nd

carb

ide

redi

strib

utio

n as

a

func

tion

of th

erm

al st

ress

can

ch

ange

thro

ugh-

thic

knes

s pr

oper

ties.

L M

ore

is k

now

n ab

out 6

17

from

HTG

R a

nd in

dust

ry

usag

e th

an fo

r 230

. Bot

h en

viro

nmen

t and

cre

ep p

lay

sign

ifica

nt ro

les i

n in

itiat

ion

and

cycl

ic c

rack

gro

wth

rate

of

617

and

230

. M

echa

nist

ic

mod

els f

or p

redi

ctin

g da

mag

e de

velo

pmen

t and

failu

re

crite

ria fo

r tim

e-de

pend

ent

phen

omen

a ha

ve to

be

deve

lope

d to

ena

ble

cons

erva

tive

extra

pola

tion

from

shor

t-ter

m la

bora

tory

test

da

ta to

long

-term

des

ign

life

[16–

25]

T

able

7 (c

ontin

ued)

33

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

sc

enar

ios*

Ph

enom

ena

Phen

omen

a im

port

ance

R

atio

nale

for

rank

ings

of

phen

omen

on im

port

ance

K

now

ledg

e le

vel

Rat

iona

le fo

r ra

nkin

gs

of k

now

ledg

e

36

FOM

1:

inte

grity

of

IHX

; FO

M2:

se

cond

ary

loop

failu

re/

brea

ch

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Prim

ary

boun

dary

de

sign

m

etho

dolo

gy

limita

tions

for n

ew

stru

ctur

es (l

ack

of

expe

rienc

e)

H

Tim

e-de

pend

ent d

esig

n cr

iteria

for c

ompl

ex

stru

ctur

es n

eed

to b

e de

velo

ped

and

verif

ied

by

stru

ctur

al te

stin

g. A

SME

Cod

e ap

prov

ed si

mpl

ified

m

etho

ds h

ave

not b

een

prov

en a

nd a

re n

ot p

erm

itted

fo

r com

pact

IHX

com

pone

nts

L N

o ex

perie

nce

for t

he

com

plex

shap

e IH

X. N

o ex

perie

nce

for d

esig

ning

and

op

erat

ing

high

-tem

pera

ture

co

mpo

nent

s in

the

clas

s 1

envi

ronm

ent.

Diff

icul

ties o

f de

sign

and

ana

lyse

s of

com

pact

IHX

are

dis

cuss

ed in

th

e re

fere

nces

[16–

25].

37

FOM

1:

inte

grity

of

IHX

; FO

M2:

se

cond

ary

loop

failu

re/

brea

ch

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Man

ufac

turin

g ph

enom

ena

(suc

h as

join

ing)

H

CH

X c

ores

(if u

sed)

will

re

quire

adv

ance

d m

achi

ning

, fo

rmin

g, a

nd jo

inin

g (e

.g.,

diff

usio

n bo

ndin

g, b

razi

ng,

etc.

) met

hods

that

may

im

pact

com

pone

nt in

tegr

ity.

Mus

t ass

ess C

HX

s vs

tradi

tiona

l tub

e an

d sh

ell

conc

epts

. H

owev

er, t

hese

ph

enom

ena

are

gene

ric a

nd

exte

nd b

eyon

d th

e C

HX

s to

all t

he v

ery

high

-tem

pera

ture

H

Xs.

L C

HX

s hav

e no

t bee

n us

ed in

nu

clea

r app

licat

ions

; the

ca

ndid

ate

allo

ys a

nd th

eir

join

ing

proc

esse

s are

not

ad

equa

tely

est

ablis

hed

in

nonn

ucle

ar a

pplic

atio

ns

[16–

25]

38

FOM

1:

inte

grity

of

IHX

; FO

M2:

se

cond

ary

loop

failu

re/

brea

ch

Bre

ach

to

seco

ndar

y sy

stem

/1–9

Insp

ectio

n/te

stin

g ph

enom

ena

H

Trad

ition

al N

DE

met

hods

w

ill n

ot w

ork

for C

HX

s be

caus

e of

geo

met

rical

co

nstra

ints

. Pr

oof-

test

ing

of

som

e ki

nd w

ill b

e re

quire

d (m

aybe

leak

test

ing

with

tra

cer)

. Pre

serv

ice

test

ing

will

be

diff

icul

t, an

d in

-se

rvic

e te

stin

g w

ill b

e ev

en

hard

er.

Con

ditio

n m

onito

ring

may

be

usef

ul

L Pr

eope

ratio

nal t

estin

g,

pres

ervi

ce in

spec

tion,

fitn

ess

for s

ervi

ce, i

ssue

with

leak

te

sts,

have

ver

y lit

tle

know

ledg

e he

re. W

hat i

s the

m

argi

n? [1

6–25

]

T

able

7 (c

ontin

ued)

34

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

sc

enar

ios*

Ph

enom

ena

Phen

omen

a im

port

ance

R

atio

nale

for

rank

ings

of

phen

omen

on im

port

ance

K

now

ledg

e le

vel

Rat

iona

le fo

r ra

nkin

gs

of k

now

ledg

e

Con

trol

rods

(non

met

allic

) 43

M

aint

ain

inse

rtion

ab

ility

Failu

re to

in

sert/

1–12

C

ompo

site

s st

ruct

ural

des

ign

met

hodo

logy

lim

itatio

ns fo

r new

st

ruct

ures

(lac

k of

ex

perie

nce)

H

Car

bon–

carb

on c

ompo

site

s ar

e pr

ime

cand

idat

es, b

ut

need

app

rove

d m

etho

d of

de

sign

ing,

pro

of te

stin

g,

mod

el te

stin

g, te

stin

g st

anda

rds,

and

valid

atio

n te

sts

L So

me

code

wor

k is

bei

ng

deve

lope

d by

ASM

E, A

STM

an

d in

tern

atio

nal p

artn

ers.

Ex

tens

ive

aero

spac

e in

dust

ry

desi

gn a

nd u

sage

can

be

asse

ssed

for a

pplic

abili

ty.

[19–

25]

RPV

inte

rnal

s (m

etal

lic)

46

Mai

ntai

n he

at

trans

fer

capa

bilit

y

Inad

equa

te

heat

tran

sfer

/ 8,

9

Cha

nge

in

emis

sivi

ty

H

To e

nsur

e pa

ssiv

e sa

fety

, hi

gh e

mis

sivi

ty o

f the

cor

e ba

rrel

is re

quire

d to

lim

it co

re te

mpe

ratu

res—

need

hi

gh e

mis

sivi

ties o

n bo

th

insi

de a

nd o

utsi

de su

rfac

es,

and

form

atio

n an

d co

ntro

l of

surf

ace

laye

rs in

hel

ium

en

viro

nmen

ts.

L Li

mite

d st

udie

s on

SS a

nd o

n 50

8 sh

ow p

oten

tial f

or

mai

ntai

ning

hig

h em

issi

vity

[1

2–17

]

47

Mai

ntai

n st

ruct

ure

geom

etry

Exce

ss

defo

rmat

ion/

1–9

Rad

iatio

n-cr

eep

H

Irra

diat

ion

cree

p an

d di

men

sion

al c

hang

es

parti

cula

rly fo

r allo

y 80

0H a

t m

oder

atel

y lo

w-d

ose

shou

ld

be a

sses

sed

L Li

ttle

info

rmat

ion

on

irrad

iatio

n cr

eep

is a

vaila

ble

for A

lloy

800H

[12–

17]

T

able

7 (c

ontin

ued)

35

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

sc

enar

ios*

Ph

enom

ena

Phen

omen

a im

port

ance

R

atio

nale

for

rank

ings

of

phen

omen

on im

port

ance

K

now

ledg

e le

vel

Rat

iona

le fo

r ra

nkin

gs

of k

now

ledg

e

RPV

inte

rnal

s (no

nmet

allic

) 52

M

aint

ain

stru

ctur

e ge

omet

ry

Cor

e re

stra

int

failu

re/1

–12

Com

posi

tes

stru

ctur

al d

esig

n an

d fa

bric

atio

n m

etho

dolo

gy

limita

tions

for n

ew

stru

ctur

es (l

ack

of

expe

rienc

e)

H

Car

bon–

carb

on c

ompo

site

s ar

e pr

ime

cand

idat

es, b

ut

need

app

rove

d m

etho

ds o

f de

sign

ing,

pro

of te

stin

g,

mod

el st

anda

rd te

stin

g, a

nd

valid

atio

n te

sts.

Sca

labi

lity

prob

abili

stic

met

hods

of

desi

gn a

nd fa

bric

atio

n is

sues

m

ust b

e ad

dres

sed.

Lar

ge-

scal

e (m

eter

s in

diam

eter

) st

ruct

ures

, as w

ell a

s sm

alle

r on

es, m

ust b

e co

vere

d.

L Ex

tens

ive

expe

rienc

e w

ithin

th

e ae

rosp

ace

indu

stry

; ap

plic

abili

ty m

ust b

e as

sess

ed

[19–

25]

53

Mai

ntai

n in

sula

tion

capa

bilit

y

Fibr

ous

insu

latio

n de

grad

atio

n/

1–12

Envi

ronm

enta

l and

ra

diat

ion

degr

adat

ion

and

ther

mal

stab

ility

at

tem

pera

ture

H

Rel

ativ

ely

low

dos

e an

d ex

posu

re is

exp

ecte

d, b

ut

LOFC

can

resu

lt in

te

mpe

ratu

res h

igh

enou

gh to

ch

alle

nge

stab

ility

of f

ibro

us

insu

latio

n su

ch a

s Kao

woo

l.

Nee

d to

ass

ess e

ffec

ts o

n m

icro

stru

ctur

al st

abili

ty a

nd

ther

mop

hysi

cal p

rope

rties

du

ring

irrad

iatio

n an

d hi

gh

tem

pera

ture

exp

osur

e in

im

pure

hel

ium

L Li

mite

d co

mm

erci

al

info

rmat

ion

avai

labl

e fo

r co

nditi

ons o

f int

eres

t [19

–25]

T

able

7 (c

ontin

ued)

36

ID

No.

FOM

(e

valu

atio

n cr

iteri

a)

Path

way

s to

rele

ase/

sc

enar

ios*

Ph

enom

ena

Phen

omen

a im

port

ance

R

atio

nale

for

rank

ings

of

phen

omen

on im

port

ance

K

now

ledg

e le

vel

Rat

iona

le fo

r ra

nkin

gs

of k

now

ledg

e

Val

ves

56

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Mal

func

tion,

fa

ilure

to

oper

ate

and

brea

ch/1

,2,5

,9

Isol

atio

n va

lve

failu

re

H

Isol

atio

n va

lve

failu

re

(incl

udes

cat

egor

ies s

uch

as

self-

wel

ding

, gal

ling,

se

izin

g) is

pos

sibl

e.

Con

cern

s abo

ut is

olat

ion

valv

es a

re si

mila

r to

‘bre

ach

to se

cond

ary’

issu

es o

n IH

X

beca

use

they

wou

ld p

rovi

de

barr

iers

to se

cond

ary

heat

tra

nspo

rt sy

stem

L In

form

atio

n po

ssib

ly a

vaila

ble

from

pre

viou

sly

cons

truct

ed

HTG

Rs,

but r

elev

ance

nee

ds

to b

e as

sess

ed.

Stat

e of

kn

owle

dge

abou

t hel

ium

-leak

-tig

htne

ss in

larg

e va

lves

is

unkn

own

[15–

17]

57

Prim

ary

syst

em

pres

sure

bo

unda

ry

inte

grity

Failu

re to

op

erat

e,

brea

ch/1

–12

Val

ve fa

ilure

H

C

once

rns a

bout

a v

arie

ty o

f va

lve

failu

re m

echa

nism

s th

at w

ill b

e de

sign

-dep

ende

nt

(incl

udes

cat

egor

ies s

uch

as

self-

wel

ding

, gal

ling,

se

izin

g) w

ill n

eed

to b

e as

sess

ed o

nce

desi

gn-s

peci

fic

deta

ils a

re a

vaila

ble.

H

eliu

m-tr

ibol

ogy

issu

es m

ust

be c

onsi

dere

d. A

llow

able

id

entif

ied

and

unid

entif

ied

cool

ant l

eaka

ge m

ust b

e es

tabl

ishe

d

L In

form

atio

n av

aila

ble

from

pr

evio

usly

con

stru

cted

H

TGR

s but

rele

vanc

e ne

eds t

o be

ass

esse

d [1

5–17

]

*S

cena

rio

num

ber r

efer

s to

Tabl

e 2.

37

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HTGR Components, NUREG/CR-6816, June 2003. 4. K. Natesan, A. Purohit, and S. W. Tam, Materials Behavior in HTGR Environments,

NUREG/CR-6824, July 2003. 5. R. L. Huddleston and R. W. Swindeman, Materials and Design Bases Issues in ASME Code Case

N-47, NUREG/CR-5955, April 1993. 6. K. Natesan, S. Majumdar, P. S. Shankar, and V. N. Shah, Preliminary Materials Selection Issues for

the Next Generation Nuclear Plant Reactor Pressure Vessel, ANL/EXT-06/45, 2006. 7. K. Natesan, A. Moisseytsev, S. Majumdar, and P. S. Shankar, Preliminary Issues Associated with

the Next Generation Nuclear Plant Intermediate Heat Exchanger, ANL/EXT-06/46, 2006. 8. W. R. Corwin, T. D. Burchell, W. G. Halsey, G. O. Hayner, Y. Katoh, J. W. Klett, T. E. McGreevy,

R. K. Nanstad, W. Ren, L. L. Snead, R. E. Stoller, and D. F. Wilson, Updated Generation IV Reactors Integrated Materials Technology Program Plan, ORNL/TM-2003/244/R2 and ORNL/TM-2005/556 (Revision 2), December 2005.

9. W. R. Corwin, “U.S. Generation IV Reactor Integrated Materials Technology Program,” Nucl. Eng. Tech. 38(7) (October 2006).

10. G. O. Hayner, R. L. Bratton, R. N. Wright, W. E. Windes, T. C. Totemeier, K. A. Moore, W. R. Corwin. T. D. Burchell, J. W. Klett, R. K. Nanstad L. L. Snead, Y. Katoh, P. L. Rittenhouse, R. W. Swindeman, D. F. Wilson, T. E. McGreevy, and W. Ren, Next Generation Nuclear Plant Materials Research and Development Program Plan, U.S. Department of Energy Generation IV Nuclear Reactor Program, Office of Nuclear Energy Science and Technology, U.S. Department of Energy, INL/EXT-05-00758 (Revision 2), September 2005.

11. G. O. Hayner, R. L. Bratton, R. E. Mizia, W. E. Windes, W. R. Corwin (Director), T. D. Burchell, C. E. Duty, Y. Katoh, J. W. Klett, T. E. McGreevy, R. K. Nanstad, W. Ren, P. L. Rittenhouse, L. L. Snead, R. W. Swindeman, and D. F. Wilson, Next Generation Nuclear Plant Materials Research and Development Program Plan, INL/EXT-06-11701 (Revision 3), August 2006.

12. R. L. Klueh, Elevated-Temperature Ferritic and Martensitic Steels and Their Application to Future Nuclear Reactors, ORNL/TM-2004/176, Oak Ridge National Laboratory, November 2004.

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14. K. Natesan et al., Materials Behavior in HTGR Environments, NUREG/CR-6824 (ANL-02/37), July 2003.

15. Preliminary Safety Evaluation Report (PSER) for the PRISM LMR, NUREG-1368. 16. C. R. Brinkman et al., Development of Stress-Rupture Reduction Factors for Weldments, and the

Influence of Pretest Thermal Aging to 50,000 h on Stress-Rupture and Microstructural Properties of Modified 9Cr-1Mo Steel, ORNL/9Cr/90-1, February 1990.

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38

20. ASME Boiler and Pressure Vessel Code, Code Case N-201. 21. R. I. Jetter, “Subsection NH-Class 1 Components in Elevated Temperature Service,” in Companion

Guide to the ASME Boiler and Pressure Vessel Code, 2002. 22. R5, Assessment Procedure for the High Temperature Response of Structures (1999). 23. R. A. Ainsworth, “R5 Procedures for Assessing Structural Integrity of Components Under Creep and

Creep-Fatigue Conditions,” Int. Mater. Rev., 51(2), 107 (2006). 24. D. S. Griffin, “Elevated-Temperature Structural Design Evaluation Issues in LMFBR Licensing,”

Nucl. Eng. Des., 90, 299–306 (1985). 25. M. J. Cohn et al., “Fabrication, Construction, and Operation Problems for Grade 91 Fossil Power

Components,” J. Press. Vessel Tech., 127(2), 197–203 (May 2007). 26. R. W. Swindeman, et al., “Issues in Replacing Cr-Mo Steels and Stainless Steels with 9 Cr–1 Mo–V

Steel,” Int. J. Press. Vessels Pip., 81(6), 507–512 (June 2004). 27. P. E. MacDonald, J. W. Sterbentz, R. L. Sant, P. D. Bayless, R. R. Schultz, H. D. Gougar, R. L.

Moore, A. M. Ouqouag, and W. K. Terry, NGNP Point Design Results of the Initial Neutronics and Thermal-Hydraulic Assessments During FY-03, INEEL/EXT-03-00870 (Revision 1), September 2003.

28. P. Hildebrandt et al., Design Features and Technology Uncertainties for the Next Generation Nuclear Plant, INEEL/EXT-04-01816.

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