ML22118A090

U.S. Nuclear Regulatory Commission Technical Assessment of Cold Spray

ML22118A090
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Issue date:	05/05/2022
From:	Office of Nuclear Regulatory Research
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Bruce Lin
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U.S. Nuclear Regulatory Commission Technical Assessment of Cold Spray

1. Introduction and Purpose This document provides the U.S. Nuclear Regulatory Commissions (NRCs) technical assessment of the process considerations and knowledge gaps related to the application of the cold spray (CS) metal coating process to the nuclear power industry. This assessment is primarily based upon the technical information and gap analysis developed by Pacific Northwest National Laboratory (PNNL) in a technical letter report (TLR) entitled Assessment of Cold Spray Technology for Nuclear Power Applications, issued September 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21263A107),

hereafter referred to as the PNNL TLR. This assessment, combined with the PNNL TLR, highlights key technical information related to the application of CS in nuclear facilities and fulfills the deliverable for CS under Subtask 1A of the Action Plan for Advanced Manufacturing Technologies (AMTs), Revision 1, dated June 23, 2020 (ADAMS Accession No. ML19333B973).

2. NRC Assessment of Cold Spray Technology This section describes the CS process considerations, highlights knowledge gaps associated with using CS for nuclear applications, and assesses the properties and performance characteristics of CS for both structural and nonstructural applications. The quality of CS is influenced by many process parameters, including the selection of powders, choice of CS equipment, nozzle design, and surface preparation. Careful analysis of the application requirements and suitable process parameters and controls are necessary to achieve the desired coating performance. CS technology for corrosion and wear resistance has been successfully demonstrated in other industries (e.g., defense, aerospace). However, there are considerable knowledge gaps associated with using CS for nuclear applications due to differences in operating environments and substrate materials. The importance of these knowledge gaps depends on the specific CS application requirements. The application categories considered in the PNNL TLR include factory-applied CS coatings for chloride-induced stress corrosion cracking (SCC) mitigation, field-applied CS coatings for chloride-induced SCC mitigation and repair, light-water reactor factory-applied CS for structural fabrication, and light-water reactor field-applied CS for dimensional restoration and corrosion protection.

The results of this technical assessment are provided in two tables. Table 1 includes the CS process considerations, including equipment, process parameter control, powder quality and handling, and quality management. Table 2 includes the properties and performance characteristics for CS materials. In general, an important consideration for any nuclear application of CS is application-specific data for the proposed processing and postprocessing parameters to ensure adequate coating performance in the service environment. Such data should assess the properties required for the application (e.g., adhesion, corrosion resistance) and the effect of aging mechanisms (e.g., thermal aging, irradiation effects, and SCC) on these properties over the intended service life.

Tables 1 and 2 identify and provide technical information for the CS process and the properties and performance characteristics for CS material using the following columns:

• Topic: Key aspect of the CS process or property/performance characteristic.

• Definition: Brief description of the CS topic.

• NRC Ranking of Knowledge Gap:

Knowledge Gap: State of the knowledge gaps associated with the topic related to CS for nuclear applications:

A large gap designation indicates that few to no data currently exist.

A medium gap designation indicates that some data exist, but more are needed to confirm the acceptability of CS for nuclear applications.

A small gap designation means that the topic is relatively well understood.

Manageability: Description of how the identified gaps would be managed for nuclear applications.

• Key Technical Information: Key technical information associated with the specified topic for use in nuclear applications.

Table 2 identifies and provides technical information for the properties and performance characteristics for both structural and nonstructural applications of CS materials. Several topics in Table 2 are noted as being primarily applicable to the structural applications of CS, but they may also be applicable to nonstructural applications. The primary distinction between structural and nonstructural applications of CS is whether the CS material will be credited with bearing structural load for the component. Data and information on the structural properties and performance of CS are limited. Therefore, the information provided for the structural applications of CS is preliminary and subject to change based on new information becoming available as research progresses in this area.

In general, the structural applications of CS (1) are likely to be thicker, and (2) credit the CS material for load-bearing capacity, such that either the CS material entirely or the CS material in conjunction with the substrate and the interface meet the full structural strength requirements.

Meanwhile, the nonstructural applications of CS (1) are likely to be thinner, (2) do not credit the CS material for any load-bearing capacity, and (3) only credit the CS material for nonstructural purposes, such as corrosion mitigation or wear resistance.

Two specific likely applications of CS that may be classified as either structural or nonstructural applications of CS are leak/flaw repair and dimensional restoration. Additional discussion follows to help determine whether such applications are structural or nonstructural.

Leak/flaw repair refers to the use of cold-sprayed material to seal a leak or cover a

surface-breaking flaw. Currently, limited data are available on this type of application, and only exploratory work has been performed. CS repair of an active leak has been demonstrated as a proof of concept. However, qualification testing is needed to demonstrate the effectiveness of CS for leak/flaw repair and that the required structural margins have been restored, if applicable. In principle, the use of CS for leak/flaw repair may not claim structural credit for the CS materials but may still require that the CS coatings exhibit greater structural performance than such coatings do for other applications, such as wear resistance or corrosion protection.

Dimensional restoration refers to the deposition of CS material to repair a damaged or corroded surface. CS for dimensional restoration has been done in many material systems in the defense, aerospace, and automotive sectors. Lessons learned from these applications can be transferred to nuclear applications. Most previous work has been performed using aluminum or nickel/chrome alloys as the CS powder materials. Like leak/flaw repair, the use of CS for dimensional restoration may not claim structural credit for the CS material; however, such applications can include requirements for material properties such as strength and wear resistance. The determination of whether a particular application is structural or nonstructural will depend largely on whether the CS material is needed to meet structural requirements.

3. Codes and Standards Currently, no codes or standards directly address CS for nuclear applications. The PNNL TLR identifies three U.S. Department of Defense (DOD) documents (MIL-STD-3021, Materials Deposition, Cold Spray, issued March 2015; MIL-DTL-32495A, Powders for Cold Spray, issued November 2018; and Uniform Industrial Process Instruction 6320-901, Processes and Quality Control of Cold Spray, issued March 2019) for the CS process, but they generally reference different powder and substrate materials than would be expected in nuclear applications. While specifically developed for DOD applications, these documents may be helpful in informing the development of standards or other guidance documents for CS in nuclear applications. In addition, several American Society for Testing and Materials (ASTM) standards pertaining to coating quality could also apply to CS coatings. Additional standards may need to be developed to support the qualification and implementation of CS for nuclear applications. Such standards should consider CS equipment, powder processing, process parameters and controls, CS test methods, and performance acceptance criteria.

It is also important to note that most current CS applications relate to nonstructural coating. Structural applications of CS will require development of standards that define how CS is to be tested and properties validated. Appendix A to MIL-STD-3021 identifies a number of tests that should be considered for structural applications. The specific test requirements should be tailored to the specific application. Whether the application is structural or nonstructural, qualification of CS for specific nuclear applications should be handled through application-specific requirements and associated test standards.

4. Summary and Conclusion The staff has identified and assessed the process considerations and knowledge gaps associated with using CS for nuclear applications, as well as the properties and performance characteristics of CS materials for both structural and nonstructural applications.

Application-specific data will also need to be generated to demonstrate adequate CS performance to meet the design requirements over the intended service life of the CS component. Because CS is a technology that has been recently developed and applied to only a limited number of applications, the staff has determined that additional codes and standards are necessary to support the use of CS in nuclear applications.

Table 1 Technical Information: CS Process Considerations Topic NRC Ranking of Knowledge Gap (Corresponding Manageability Definition Key Technical Information PNNL Report Knowledge Gap Topics)1 Factory Small: There are CS has been done

• The commonly used carrier gases are helium, nitrogen, application refers minor knowledge in many applications and air. Helium, with its low atomic weight, provides the to application of gaps in how to for the aerospace, most rapid acceleration and generally achieves the best CS in a factory execute CS on defense, and quality coatings.

setting. The materials and automotive

• High-pressure CS (HPCS) systems enable high-quality location of where substrates of industries. Nuclear CS of high-melting-point materials that are currently used CS will be applied interest in a factory applications would in the nuclear power industry, such as nickel-based alloys determines the setting. be informed by and steels.

limitations on the nonnuclear

• Low-pressure CS systems are not recommended for type of equipment experience with CS. high-quality CS of steels, Inconel, and other high-strength that can be used New and existing and high-melt-temperature materials.

Factory to implement CS. codes and

• Properties of the cold-sprayed material and process Application and standards would considerations need to be validated using equipment and Associated address nozzle types that will execute the work on mockups or Equipment application-specific witness specimens that are representative of the actual requirements. applications.

(Manufacturing/

• For both factory and portable systems, coating quality is factory setting) influenced by many process parameters, including the selection of powders and their size distributions, choice of carrier gas and temperature, nozzle design, and surface preparation.

• Sections 2.1.1 and 2.4.5.2 of the PNNL TLR compare field and factory applications and associated equipment in more detail.

• Figure 2.14 of the PNNL TLR shows a framework describing process implementation, including relevant process considerations and best practices for CS applications.

Field application Medium: Portable CS has been done

• The commonly used carrier gases are helium, nitrogen, Field Application refers to HPCS equipment in many applications and air. Helium, with its low atomic weight, provides the and Associated application of CS for field application for the aerospace, most rapid acceleration and generally achieves the best Equipment in a field setting. is a newer defense, and quality coatings.

The location of technology automotive

Topic NRC Ranking of Knowledge Gap (Corresponding Manageability Definition Key Technical Information PNNL Report Knowledge Gap Topics)1 (Unconfined where CS will be compared to industries. Nuclear

• HPCS systems enable high-quality CS of space field applied stationary factory applications would high-melting-point materials that are currently used in the setting, confined determines the HPCS equipment. be informed by nuclear power industry, such as nickel-based alloys and space field limitations on the nonnuclear steels.

setting, nozzle type of equipment experience with CS.

• Low-pressure CS systems are not recommended for technology for that can be used Equipment vendors high-quality CS of steels, Inconel, and other high-strength portable CS) to implement CS. are working to and high-melt-temperature materials.

improve nozzle

• Properties of the cold-sprayed material and process designs and develop considerations need to be validated using equipment and new gas-heating nozzle types that will execute the work on mockups or strategies to witness specimens that are representative of the actual improve applications.

performance of

• For both factory and portable systems, coating quality is portable HPCS influenced by many process parameters, including the equipment. New selection of powders and their size distributions, choice of and existing codes carrier gas and temperature, nozzle design, and surface and standards preparation.

would address

• Sections 2.1.1 and 2.4.5.2 of the PNNL TLR compare application-specific field and factory applications and associated equipment in requirements. more detail.

• Field applications may be subject to additional constraints, such as access limitations and radiation exposure.

• Figure 2.14 of the PNNL TLR shows a framework describing process implementation, including relevant process considerations and best practices for CS applications.

Powder quality Small: Best Existing best

• Best practices for powder processing and handling include Powder Quality and processing practices of powder practices are likely sieving to control particle size, drying to avoid clumping, and Processing refers to powder processing and sufficient. These and storage in inert atmosphere to avoid oxidation and selection, drying, handling such as practices may need contamination. Sections 2.2.1 and 2.4.5.4 of the PNNL (Powder sieving, sieving and drying to be tailored to TLR discuss these in greater detail.

processing, contamination are well understood materials of interest

• The selection of the powder is application specific powder storage minimization, and and documented in for nuclear depending on the application requirements, such as and handling) other powder the available applications.

processing and

Topic NRC Ranking of Knowledge Gap (Corresponding Manageability Definition Key Technical Information PNNL Report Knowledge Gap Topics)1 storage and literature and corrosion resistance, wear resistance, dimensional handling standards. restoration, or a combination of these.

practices.

• Powders should be sieved to ensure that the particle average size and size distribution is within specifications.

The presence of either large or small particles reduces the velocity of particles in the stream, which in turn reduces coating properties.

Surface Small: Best Best practices for

• Poor surface preparation results in poor adhesion, or preparation refers practices for surface preparation bonding, to the substrate.

to methods used surface preparation are available that

• Failure to remove oxide layers from a substrate surface to treat the are well understood can guide selection before CS application can negatively impact coating Surface surface of the and available in the of surface performance.

Preparation substrate before literature. preparation

• Surface preparation examples include grit blasting, CS application. techniques. Existing abrasive pads, and wire brushes or wire wheels.

(Surface best practices are

• The surfaces to receive CS deposits should be cleaned to preparation) expected to be remove oil, grease, dirt, paint, oxides, and other foreign applicable to material that could affect CS adhesion.

materials and CS

• Section 2.2.4 of the PNNL TLR discuss surface applications in the preparation and postcleaning in more detail.

nuclear industry.

Process Medium: Process This issue is

• One governing process parameter is the critical velocity parameters and control can be manageable with (Vcr), defined as the velocity above which the particles are controls refers to implemented to appropriate quality sufficiently plastically deformed upon impact and adhere key aspects of CS monitor relevant assurance to the substrate, or previous coating layers, as Process operation that process requirements and appropriate.

Parameters and impact CS quality parameters. The the use of in situ

• Nozzle clogging is one of the most common problems Controls and performance range of allowable monitoring and with the CS process and requires continuous monitoring.

and thus should qualified process environmental Nozzle clogging reduces particle velocity, resulting in (In-process: be monitored and parameters is sensor data to reduced mechanical properties and increased porosity.

statistics process controlled, such expected to monitor essential

• Algorithms to flag operators at the onset of preclogging control) as temperature, depend on the parameters. conditions and record clogging conditions in data logs can pressure, and flow application and Allowable ranges for be developed as an automated quality tool.

rates (in part for materials. parameters for

• The primary defects in CS are caused by variations in nozzle clogging specific nuclear process parameters, such as gas temperature, substrate detection). applications should temperature, powder size, powder oxidation or

Topic NRC Ranking of Knowledge Gap (Corresponding Manageability Definition Key Technical Information PNNL Report Knowledge Gap Topics)1 be determined and contamination, nozzle-to-surface distance, nozzle validated. clogging, and powder impact angle.

• Process parameters such as those identified in Table 2.2 of PNNL TLR should be implemented.

Postprocessing SmallGrinding Surface and thermal

• For all postprocessing approaches, application-specific includes methods and Machining: postprocessing demonstration is important to identify adequate heat used after the There are minor should be treatment to achieve the desired improvements in initial deposition of knowledge gaps demonstrated and properties.

CS material, such related to the range of

• Heat-treating CS coatings is uncommon because the as surface postprocessing postprocessing as-deposited coating typically has the required grinding, grinding and parameters mechanical properties for coating and dimensional machining, or heat machining. Best established through restoration applications that dominate CS applications.

treatments. practice should be testing, Heat treatment is also typically impractical for field followed to nondestructive mitigation and repair applications, which also represent a Postprocessing minimize residual examination (NDE), sizeable percentage of CS applications.

stress effects. and measurements

• Thermal postprocessing may also be complicated by (Postprocessing to ensure application-specific considerations of distortion between for mechanical MediumHeat conformance with the CS coating and the substrate, as well as impacts of properties, Treatment: application heat treatment on the substrate materials properties.

as-deposited Postprocessing requirements.

• Postprocess grinding or machining may be needed for surface heat treatment for final dimensional control and blending contours.

roughness) conventional materials is fairly well understood and reported in the literature, but there is limited experience for CS materials for nuclear applications.

Witness Medium: Witness Witness specimens

• Table 2.3 of the PNNL TLR indicates CS property specimens are specimens are may be subjected to variables that may be important to evaluate to ensure Witness test specimens commonly used for postprocess good CS performance.

Specimens that are placed demonstrating and destructive and

• Destructive coupon tests can include appropriate adjacent to the actually applying nondestructive specimens to assess surface profiles, porosity, tensile

Topic NRC Ranking of Knowledge Gap (Corresponding Manageability Definition Key Technical Information PNNL Report Knowledge Gap Topics)1 part being CS to provide examinations to bond/yield strength, hardness, and corrosion sprayed and used empirical evidence demonstrate the susceptibility. Some relevant standards for testing to provide of acceptable CS process parameters properties of CS coatings include the following:

confirmation of CS properties such as that produce an - ASTM E8/E8M for tensile testing quality and spray thickness, acceptable CS - ASTM E92 for hardness testing performance. porosity, and coating. The - ASTM D4541 for bond strength using adhesive pull adhesion strength. specific coating testing The representative- properties of interest - ASTM E2109 for porosity measurement ness of the witness can vary depending specimens to the on application.

actual application should be demonstrated.

The geometry of Medium: CS has Local geometry

• Local geometry can impact CS process parameters such the component to been done in many impacts are highly as nozzle-to-surface distance and powder impact angle, be sprayed can applications for the dependent on the which can affect the local microstructure and properties.

affect CS material aerospace, CS equipment and

• Geometric features such as obstructions and internal properties and defense, and geometry of the corners may be challenging to obtain necessary coverage performance. automotive component. They and result in significant variation in coating depth.

Complex industries. Nuclear can be managed

• Properties of the cold-sprayed material and process Local Geometry geometries or applications would through process considerations need to be validated, most likely through Impacts on areas that are be informed by qualification and qualification on representative mockups, using the Properties and difficult to spray nonnuclear witness specimens planned equipment and process parameters that will be Performance (e.g., internal experience with to measure the used in the actual application.

corners or areas CS. impacts.

• Witness specimens developed under conditions with obstructions) representative of the areas of concern within complex are the biggest geometries could be used to assess the impacts on challenges. material properties and performance due to geometries or areas that are difficult to spray.

NDE refers to Large: Limited Further studies of

• Visual testing can be used to examine the CS surface for NDE methods used to information is NDE methods to imperfections such as chipping, cracking, and flaking.

assess the quality available on the assess CS quality Penetrant testing can also be used, but surface (NDE and of CS coatings, applicability and are needed to roughness or porosities may obscure cracks or other statistical including demonstration of establish a technical imperfections.

process control) detection of NDE methods for foundation and best

Topic NRC Ranking of Knowledge Gap (Corresponding Manageability Definition Key Technical Information PNNL Report Knowledge Gap Topics)1 defects, CS applications, practices for

• It is expected that both ultrasonic testing (UT) and verification of including NDE inspection of CS. eddy-current testing (ET) can be used to examine the coating properties methods to detect quality of CS coatings. Surface roughness may affect the such as porosity, coating properties ability to inspect CS depositions. The effectiveness of bond quality, and such as porosity these methods requires further investigation.

inspection of and adhesion

• UT and ET can penetrate CS coatings and be used to substrate quality. inspect the underlying material. Thick coatings may materials through Accessibility and present problems for inspection, particularly if they the CS coating. harsh contain porosity.

environments such

• It is anticipated that ET is appropriate for thin coatings as high radiation (i.e., several millimeters); however, additional work should present additional be done to verify the effective thickness limits.

NDE challenges.

• Cracks and lack of adhesion can be measured using established UT methods. Understanding the limitations caused by coating porosity and thickness requires further investigation.

• Section 2.4.3.2 of the PNNL TLR discusses CS coating quality verification with NDE.

1 Section 4.1 of the PNNL TLR discusses the corresponding PNNL gaps.

Table 2 Technical Information: CS Properties and Performance Characteristics for Structural and Nonstructural Applications NRC Ranking of Knowledge Gap Topic Definition Key Technical Information Knowledge Gap Manageability Adhesion strength SmallFactory Established test

• Adhesion strength of 10-20 kilopounds per refers to the Applications: For methods are generally square inch (ksi) is common on a properly minimum force stationary factory sufficient to ensure prepared surface, and adhesion strengths greater needed to separate equipment, adhesion adequate adhesion than 30 ksi are not uncommon for CS adhesion a coating from the values are known for strength is strength of higher strength alloys.

substrate. many powder-substrate demonstrated for new

• Thick oxides and surface contamination can Adhesion combinations. powder-substrate significantly reduce the adhesion strength of the Strength combinations and CS coating.

MediumField applications.

• Adhesion strength may be limited by the bond (Adhesion Applications: Portable strength of the epoxy when epoxy-based strength)

HPCS of adhesion tests (ASTM-C633, ASTM-D4541) are high-melt-temperature used. The triple-lug shear testing described in materials will require MIL-J-24445A can be used to reach adhesion further investigation. values not limited to epoxy strength.

Porosity includes SmallFactory Appropriate use of

• Porosity is known to adversely affect fatigue life, the size, distribution, Applications: For destructive testing and SCC, and irradiation-assisted SCC, though the and total volume of stationary factory witness specimens for precise quantitative impact depends on the voids. Porosity can equipment, expected process qualification, material and porosity characteristics (e.g., pore have a significant porosity is understood control and verification frequency, pore size, pore morphology, total void impact on coating and can be negligible for should be adequate to fraction).

Porosity performance. most material systems manage porosity.

• Porosity within a qualified process is usually when done correctly. caused by nozzle clogging. Process control to (Porosity) monitor relevant parameters such as gas MediumField pressure and flow rate should be implemented to Applications: Portable detect nozzle clogging. Automated nozzle HPCS of clogging detection could be integrated in CS high-melt-temperature equipment to ensure clogging does not happen in materials will require the field.

further investigation.

Edge effects refer to Large: Very limited Edge effects at the

• Data in representative environments are Edge Effects the impacts, such as data are available on interface between the important to demonstrate that coating edge stress concentration edge effects at the CS material and the effects will not lead to unacceptable increases in (Edge effects) or corrosion interface between the substrate would need corrosion susceptibility near the edge of the CS initiation, at the coating and substrate. to be evaluated coating.

NRC Ranking of Knowledge Gap Topic Definition Key Technical Information Knowledge Gap Manageability interface between The relevant considering the

• Edge effects due to stress concentration such as the CS material and phenomena and their specific nuclear effects on fatigue susceptibility (including thermal the substrate that is impact depend on the material combinations fatigue) and residual stress should be adequately exposed to the material combinations and environmental investigated to ensure sufficient performance in environment. and environmental conditions in the service.

conditions. intended application.

• Galvanic potentials can exist at component edges and crevices can exist if the edge is not properly blended.

Corrosion/ Corrosion/erosion Medium: While data Exploratory work has

• For corrosion resistance, the most used coatings Erosion resistance refers to exist that show excellent shown CS may have are forms of nickel, copper, aluminum, or Resistance the materials ability erosion/corrosion the ability to improve titanium.

to resist the loss of resistance using CS, erosion/corrosion

• Short-term testing using ASTM standards may be (Erosion/ material due to nuclear resistance for a few used to screen corrosion and erosion resistance corrosion corrosion/ application-specific specific nuclear of material combinations in representative resistance, flow-assisted material combinations applications. environments.

effects of surface corrosion or and environments have Nuclear-specific

• Corrosion testing using representative test finish on cavitation erosion yet to be evaluated. material combinations conditions may be necessary to demonstrate the corrosion processes. and environments long-term behavior of CS protective coatings.

resistance) need to be tested.

Wear resistance Medium: Data exist Mechanical wear

• CS can produce hard surfaces with excellent refers to the ability that show excellent wear resistance of CS is wear resistance, especially when blended to avoid the removal resistance using CS in well understood and powders with hard particles are used.

and deformation of nonnuclear applications. documented in the

• CS materials generally exhibit higher hardness material from the Nuclear literature. than those of the corresponding powders and Wear Resistance surface when in application-specific Nuclear-specific CS bulk alloys due to the plastic deformation induced contact with another material combinations materials and during deposition. The CS process parameters (Mechanical component. and environments have environments need to can be adjusted to achieve a range of surface wear resistance) yet to be tested. be tested. hardness and ductility properties.

• Additional data on wear behavior may be needed if new CS powders or environments with high-wear stressors will be present.

SCC Resistance SCC resistance Large: Very limited Significant work is

• Data in representative environments is important refers to the ability data are available on the needed to quantify to demonstrate that resistance to SCC will be (SCC to resist stress use of CS for mitigation SCC performance, adequate to meet component design performance) corrosion crack and prevention of SCC. including SCC requirements and confirm the appropriateness of initiation and growth initiation and arresting aging management approaches.

NRC Ranking of Knowledge Gap Topic Definition Key Technical Information Knowledge Gap Manageability in susceptible preexisting SCC flaws,

• Limited testing of CS commercially pure nickel materials under for any SCC mitigation appears to show substantial resistance to primary operating conditions or repair applications. water SCC, as discussed in Section 2.3.8 of the of roughly constant PNNL TLR.

stress due to the

• Some qualification testing has been performed corrosive using either commercially pure nickel or environment. titanium/titanium carbide to demonstrate SCC protection with various Inconel and SS substrates.

• SCC initiation prevention is likely more important in nonstructural applications due to the smaller thickness of the coatings.

• For structural applications of CS, SCC growth properties of the CS material are likely to be more important than for nonstructural applications.

Fatigue resistance Large: Fatigue data for Understanding fatigue

• CS is expected to improve the mechanical fatigue refers to the ability the range of material performance requires life of performance because CS can induce to resist initiation combinations likely for analysis and testing of compressive residual stresses in the coating and and propagation of CS of nuclear the component with in the base metal directly beneath the coating, cracks due to cyclic applications do not exist. CS material. Testing like shot peening.

loading with or needs to be

• The potential for thermal fatigue due to different without representative of the coefficients of thermal expansion for the coating Fatigue environmental conditions that the and substrate should be considered.

Resistance effects playing a component will see in

• Data in representative environments are significant role in the operation. important to demonstrate that fatigue resistance (Fatigue process. will be adequate to meet component design performance) requirements and confirm the appropriateness of aging management approaches.

• Fatigue initiation prevention is likely more important in nonstructural applications due to the small thickness of the coatings.

• For structural applications of CS, fatigue crack growth properties of the CS material are likely to be more important than for nonstructural applications.

NRC Ranking of Knowledge Gap Topic Definition Key Technical Information Knowledge Gap Manageability Irradiation effects Large: No experimental Irradiation effects are

• Data in representative environments are refer to the impact of work has been known for substrate important to demonstrate that irradiation effects neutron irradiation completed to evaluate materials in nuclear will not be significantly greater in CS materials Irradiation Effects on various aspects the irradiation applications. than substrate materials and that CS materials on Properties of material performance of CS Evaluation of CS will be adequate to meet component design and Performance properties and coating. materials may be requirements and to confirm the appropriateness performance, required where data of aging management approaches.

(Irradiation including (but not are insufficient.

• For structural applications of CS, irradiation performance) limited to) loss of effects on bulk mechanical properties fracture toughness, (e.g., tensile, toughness) of the CS material are irradiation-assisted likely to be more important than for nonstructural SCC, and void applications.

swelling.

Tensile properties Large: Very limited Tensile property

• Data in representative environments are refer to the ultimate data are available on requirements may be important to demonstrate that tensile properties tensile and yield bulk CS material tensile application specific. will be adequate to meet component design strength of the properties. Applications of requirements and confirm the appropriateness of material. existing standard aging management approaches.

Tensile testing methods to

• Tensile properties are primarily applicable to Properties CS materials need to structural applications of CS.

be validated.

(Tensile Application-specific strength) testing should also consider anisotropic and inhomogeneous properties of CS materials, especially in areas more difficult to spray.

Initial fracture Large: Very limited Evaluation of CS

• Data in representative environments are toughness refers to data are available on materials fracture important to demonstrate that fracture the materials fracture toughness for toughness may be toughness will be adequate to meet component Initial Fracture starting fracture CS materials. required for some design requirements and confirm the Toughness toughness upon applications. appropriateness of aging management entering service Postprocessing may approaches.

after fabrication. improve fracture

• For factory applications of CS on new toughness. components, thermal postprocessing may be

NRC Ranking of Knowledge Gap Topic Definition Key Technical Information Knowledge Gap Manageability feasible and, with appropriate parameters, would be expected to improve fracture toughness.

• Initial fracture toughness is primarily applicable to structural applications of CS.

Thermal aging Large: Very limited Data in

• Data in representative environments are refers to changes in data are available on representative important to demonstrate that fracture microstructures thermal aging effects environments will be toughness and mechanical properties do not after a significant for CS materials, but needed to assess the unacceptably degrade due to thermal aging and time at elevated the initial fracture potential for thermal will be adequate to meet component design temperature, which toughness is expected aging effects in a requirements and confirm the appropriateness of can alter to be lower than that of given application. aging management approaches.

mechanical conventionally

• For factory applications of CS on new Thermal Aging properties, processed materials. components, thermal postprocessing may be including reducing Thermal aging impacts feasible, and with appropriate parameters would fracture toughness will depend primarily on be expected to make material properties and and ductility and the operating performance more similar to conventional increasing temperature and time processed materials.

hardness and for the component in

• Thermal aging is primarily applicable to strength. service. structural applications of CS.

High-temperature, Large: Significant data in

• Data in representative environments are time-dependent High-temperature, representative important to demonstrate that high-temperature aging effects refers time-dependent aging environments will be performance will be adequate to meet to mechanisms effects are of high needed to assess the component design requirements and confirm the High-relevant to elevated importance to suitability of CS appropriateness of aging management Temperature, temperatures (as component integrity for materials for these approaches.

Time- Depende discussed in ASME the elevated operating applications.

• High-temperature, time-dependent aging effects nt Aging Effects Boiler and Pressure temperatures expected are primarily applicable to structural applications (e.g., creep and Vessel Code, for many advanced of CS.

creep-fatigue)

Section III, Division reactor designs, and 5), including creep, there are no known creep-fracture, and data for CS materials in creep-fatigue. these environments.

1 Section 4.1 of the PNNL TLR discusses the corresponding PNNL gaps.