ML21292A188

Technical Assessment of Additive Manufacturing-Laser Directed Energy Deposition

ML21292A188
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Issue date:	11/17/2021
From:	Office of Nuclear Regulatory Research
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NRC Technical Assessment of Additive Manufacturing Laser-Directed Energy Deposition

1. Introduction and Purpose This document provides a U.S. Nuclear Regulatory Commission (NRC) technical assessment of the impact on component performance of the identified differences between additive manufacturinglaser-directed energy deposition (L-DED) and traditional manufacturing methods and the aspects of L-DED not addressed by codes and standards or regulations. This assessment is primarily based upon the technical information and gap analysis developed by Oak Ridge National Laboratory (ORNL) in a technical letter report (TLR) entitled, Review of Advanced Manufacturing Techniques and Qualification Processes for Light Water Reactors Laser-Directed Energy Deposition Additive Manufacturing (Agencywide Documents Access &

Management System (ADAMS) Accession No. ML21292A187) (hereafter referred to as the ORNL TLR). This assessment, combined with the ORNL TLR, highlights key technical information related to L-DED-fabricated components in nuclear power plants and fulfills the deliverable for L-DED under Subtask 1A of the Action Plan for Advanced Manufacturing Technologies (AMTs), Revision 1, dated June 23, 2020 (ADAMS Accession No. ML19333B973).

2. NRC Identification and Assessment of Differences This section describes the differences between an L-DED-fabricated component and a traditionally manufactured component, assesses the impact that the identified difference has on component performance, and identifies specific technical considerations related to L-DED-fabricated components. The overall impact to plant safety (e.g., safety significance) is a function of component performance and the specific component application, such as its intended safety function. This report does not include the impact on plant safety, as such an assessment would not be possible without considering a specific component application.

The staff identified the differences between L-DED fabrication and traditional manufacturing processes by reviewing the information and gap analysis rankings from the ORNL TLR and other relevant technical information (e.g., NRC regulatory and research experience, technical meetings and conferences, codes and standards activities, Electric Power Research Institute and U.S. Department of Energy products and activities). The identified differences originated either as important aspects or gaps of the L-DED process or component performance as defined here:

• important aspect: part of the AMT fabrication process or component performance that needs to be considered and carefully controlled during manufacturing (e.g., powder quality for the laser powder directed energy deposition [LP-DED] process)

• gap: part of the AMT fabrication process or component performance that is not well known or understood due to limited information and data Two tables show the results of this technical assessment. Table 1 includes the material-generic differences for the L-DED process and component performance compared to traditional manufacturing. Table 2 includes additional material-specific differences for 316L stainless steel, which is the alloy relevant to L-DED-fabricated nuclear applications with the greatest quantity of information currently available in the open literature. While Table 2 is based on the available information in the open literature for 316L stainless steel, the differences identified in Table 2

involving material-specific properties and performance would likely need to be considered for any new material to be fabricated using L-DED. In general, any nuclear L-DED-fabricated component needs to have material-specific data for the proposed processing and post-processing parameters to ensure adequate component performance in its environment, including various properties (e.g., fracture toughness, tensile strength) and aging mechanisms (e.g., thermal aging, irradiation effects, and stress-corrosion cracking (SCC)). It is important to note that the feedstock (i.e., powder vs. wire) may impact the differences listed in the tables.

Tables 1 and 2 note the impact that the feedstock has on a specific difference, as appropriate.

The following columns in Tables 1 and 2 identify and provide technical information on the L-DED process and component performance:

• Difference:

o Corresponding ORNL Gaps: Identification of corresponding gaps from Section 3.4 of the ORNL TLR.

• Definition: Brief description of the difference with the L-DED process.

• NRC Ranking:

o Importance: Impact on final component performance considering the likelihood of occurrence or magnitude of degradation in conjunction with the ease of detection or ability to mitigate.

A high ranking would signify that the difference has a significant impact on component performance.

A medium ranking would signify that the difference has a moderate impact on component performance.

A low ranking would signify that the difference has a minimal impact on component performance.

o Knowledge/Manageability: Description of how well understood and manageable the difference is.

• Key Technical Information: Technical information for the consideration of L-DED-fabricated components for use in nuclear power plants.

3. Codes and Standards Section 3.5 of the ORNL TLR provides a comprehensive overview of the existing standards relevant to L-DED as well as a detailed analysis of standards identified as highly relevant to nuclear applications. Significantly fewer standards are available for L-DED than for laser powder bed fusion (LPBF). One standard, American Welding Society (AWS) D20.1M, Specification for Fabrication of Metal Components using Additive Manufacturing, is generic to both LPBF and L-DED and may serve as a reasonable starting point for the consideration and development of codes and standards for L-DED for nuclear applications.

In addition, Table 15 from the ORNL TLR identifies several LPBF-specific standards that have no L-DED equivalents to date. These LPBF standards cover a range of important topics that should also be addressed for L-DED, including the following:

• design (LPBF specific: International Standards Organization (ISO)/American Society for Testing and Materials (ASTM) 52911-1:2019, Additive manufacturingDesignPart 1:

Laser-based powder bed fusion of metals)

• 316L stainless steel composition and tensile specifications (LPBF specific:

ASTM F3184-16, Standard Specification for Additive Manufacturing Stainless Steel Allow (UNS S31603) with Powder Bed Fusion)

• process control (LPBF specific: MSFC-SPEC-3717, Specification for Control and Qualification of Laser Powder Bed Fusion Metallurgical Processes; ASTM/ISO 52904:2019, Additive manufacturingProcess characteristics and performancePractice for metal powder bed fusion process to meet critical applications)

• material property evaluation specifications (LPBF specific: MSFC-STD-3716, Standard for Additively Manufactured Spaceflight Hardware by Laser Powder Bed Fusion in Metals)

• thermal post-processing (LPBF specific: ASTM F3301-18a, Standard for Additive ManufacturingPost Processing MethodsStandard Specification for Thermal Post-Processing Metal Parts Made Via Powder Bed Fusion)

In general, the ORNL TLR recommendations emphasize that properties and microstructure cannot be extricated from the geometry and scan strategy. Therefore, the codes and standards approach for L-DED should focus on establishing a consistent process for component qualification that recognizes that geometry affects material properties and performance and allows the process to vary the geometry while still maintaining qualification. The use of in-process data combined with destructive sampling and modeling and simulation tools may be one approach that could enable the qualification process to be robust and aligned with the unique aspects of L-DED and other AM technologies.

4. Summary and Conclusion In Tables 1 and 2 of this report, the staff has identified and assessed the material-generic differences for the L-DED process and component performance as well as the material-specific differences for 316L stainless steel compared to conventional manufacturing. The staff also discussed gaps in existing codes and standards that should be addressed to support L-DED use in nuclear applications.

Table 1 Technical InformationL-DED Generic Difference NRC Ranking (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability Machine process Medium Machine Machine process

• Control of L-DED files is needed to ensure process control includes the process control control is very control. Improper file control can significantly impact software controlling could impact final manageable with QA final component properties and performance and affect L-DED Machine the scan strategy of component including appropriate fabrication replication. Cybersecurity, database Process Control the L-DED machine performance, but calibration. traceability, management of software updates, and and the machine it is expected to similar items are highly important to ensuring end-use (Software and File calibration to be managed component quality.

Control, L-DED reliably fabricate through

• Machine calibration is vital for fabrication replication, Machine components. appropriate quality particularly ensuring correct feedstock deposition Calibration) assurance parameters, laser power, laser spot size, travel speed, (QA)provisions. and atmospheric quality control in addition to geometric tolerances. For LP-DED, this includes contamination minimization if recycling powder.

Powder quality High Powder Powder quality can

• Detailed powder characterization and control, covers the quality can have a be challenging to preventing powder contamination, and maintenance of important significant impact manage, and the an inert gas environment are important factors in characteristics of on the final effects on final ensuring powder quality and reducing powder variability.

the powder, such component component

• Powder contamination is a critical issue that may as composition and performance and performance are adversely affect material properties and process by size distribution, knowledge/ material specific. introducing oxides and changing chemical composition.

Powder and how it is manageability Powder quality is an

• Thorough cleanliness activities, dedication of LP-DED Feedstock Quality managed in the challenges. area of active machines to specific alloys, and periodic replacement of production process research to feedstock conveying tubes and components can (Contamination before the build understand the address powder contamination.

Management for process critical powder

• LP-DED can achieve high powder utilization exceeding LP-DED, (e.g., sieving, characteristics for a 90 percent in some cases, which makes powder reuse Feedstock reuse, storage, given alloy and their less essential than in LPBF.

Characterization, contamination). impacts on

• Powder reuse can provide substantial cost benefits but Powder Reuse component can introduce significant variability in powder Management) performance. Powder composition. Powder characterization and the also has more establishment of associated acceptance criteria may be variables to control, warranted to reuse powder, especially for and industry has less safety-significant components.

experience with it as compared to wire feedstock.

Difference NRC Ranking (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability Wire quality covers Medium Wire The ability to ensure

• Laser wire directed energy deposition (LW-DED) the important quality can have a the conformance of applications almost always use welding wire feedstock characteristics, significant impact welding consumables certified by the manufacturer to conform to AWS or ISO such as wire on the to applicable standards for the specific alloy and wire product in Wire Feedstock composition and performance of standards is well question.

Quality diameter and how it the final established for

• There is a long-established history of ensuring welding is managed in the component, but industrial welding consumables conform to applicable standards for (Feedstock production process wire generally applications, with a industrial welding applications.

Characterization) before the build involves fewer lengthy history of

• Wire chemistry and processing path must be tightly process variables and established quality controlled.

(e.g., storage). uncertainties than control.

• Contamination concerns are well understood and are powder. less of a concern than for powder feedstock.

Build process Medium Build This issue is

• Build interruptions (planned and unplanned) can have a management and interruptions and manageable with QA very significant impact on component quality and L-DED Build control includes loss of process and the use of in situ should be avoided.

Process monitoring control can monitoring and

• In situ monitoring without feedback control can be used Management and parameters during adversely impact environmental sensor to identify issues in the build process in real time and Control fabrication using component data. may be used in conjunction with other approaches to environmental performance by demonstrate process control.

(L-DED sensors, in situ creating defects, Knowledge is

• In situ monitoring with feedback control is still a Environmental monitoring, and altering local relatively limited and developing area of research and should be carefully Sensor Data, In evaluating the material still maturing on the managed and its effectiveness definitively Situ Monitoring effects of build microstructure use of in situ demonstrated if proposed for use during production.

and Feedback, interruptions. and properties, monitoring with

• Management, storage, retrieval, and analysis of the Planned and and creating feedback control data generated during the L-DED process are critical Unplanned Build warping and designed to correct for accelerating process optimization, although Interruptions, Data distortion due to defects automatically guidance for the proper identification, handling, and Management) changing the during the build evaluation of this information is still under development.

thermal process.

distribution by cooling.

Witness specimens Medium Witness Witness specimens

• The most highly representative test specimens are Witness or witness coupons specimens offer may be useful for obtained from end-use component geometries.

Specimens are test specimens one approach to identifying build o Geometry impacts, particularly thickness, on witness that are fabricated demonstrating issues such as specimen microstructure and properties should be concurrently with e process control by delamination or other considered and addressed.

Difference NRC Ranking (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability nd-use measuring events that may

• Optimal witness specimen parameters (geometry, size, components and properties from result in component location, spatial orientation, and frequency) depend used to confirm parts built rejection. However, highly on the end-use component geometry and the build quality and coincidentally with the use of witness goal of the witness testing approach (e.g., monitoring component the service specimens for build issues as part of process control or generating performance. component. optimizing and representative material properties data as part of generating process qualification).

quantitative data for

• When sectioning end-use geometries is not feasible, qualification is less functional evaluations of the relationship between the well established and acceptability of the end-use geometries (e.g., burst could involve tests, inspections) and the use of simplified witness demonstration that specimen geometries would need to be demonstrated.

the specimen is representative of the final component.

Thermal post- High Thermal Post-processing heat

• Post-processing heat treatments without HIP generally processing post-processing treatments are are designed to provide two benefits, stress relief or includes methods should make commonly done for annealing (or both), but they likely have little impact on used after the initial material L-DED and porosity or flaws.

component build properties and conventional o Stress-relief heat treatments will primarily reduce that involve performance more materials and are residual stresses from the as-built part without elevated homogeneous fairly well otherwise affecting the microstructure or properties.

temperatures, such and similar to understood. HIP is o Annealing heat treatments should greatly reduce or as hot isostatic those of also a eliminate residual stress as well as coarsen the pressing (HIP) and conventional well-established microstructure (to improve toughness) and reduce Thermal Post- heat treatments, to forged materials method, but it is less heterogeneity in microstructure and properties.

processing improve material and may commonly used for

• HIP may be beneficial for reducing residual stress, properties and significantly conventional porosity, heterogeneity, and internal cracks, while also performance by impact materials where coarsening the microstructure (to improve toughness).

increasing density considerations porosity is not a

• For all thermal post-processing approaches, and reducing related to the significant issue. material-specific demonstration is important to identify porosity. other L-DED- adequate heat treatment or HIP parameters to achieve specific topics desired improvements in microstructure, properties, identified in lower heterogeneity, porosity, and fabrication flaws.

rows. Conversely,

• Thermal post-processing may significantly impact component considerations related to the other L-DED-specific performance may

Difference NRC Ranking (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability be degraded if topics identified in lower rows (e.g., porosity, residual thermal post- stress, initial fracture toughness).

processing is not used.

The geometry of High Local Local geometry

• The role of geometry on local microstructure and the component and geometry impacts impacts are highly properties is one of the key differences between the heat transfer can have a dependent on the L-DED-produced components and conventionally characteristics from significant impact material and produced ones.

the component on component geometry of the final

• Local geometry significantly impacts thermal profiles build directly affect performance if not component. They can during fabrication, which affects the local microstructure Local Geometry local microstructure managed or be managed through and properties.

Impacts on (e.g., grain size addressed. post-processing and o For example, a thin section with relatively rapid Component and orientation), sampling/witness cooling rates will likely have a much finer Properties and which can affect specimens to microstructure than a thicker section with a slower Performance material properties measure the impacts. cooling rate because more surrounding material is and performance, melted.

(L-DED Design including SCC o As a result, the variation in microstructure as a Considerations, susceptibility. function of geometry will affect local material Geometry-Scan properties such as strength, ductility, and toughness.

Strategy

• Post-processing and scan strategy refinement have the Interactions, potential to minimize the local geometry impacts; Inspection of however, the effects on properties and performance can Fabricated vary significantly based on the geometry and materials Components) used.

• If used, witness specimens representing the thinnest section are needed to bound the material properties of the component.

• The advantages of L-DED to fabricate components with as-built internal features can make the inspection of the component features more difficult.

Heterogeneity and Heterogeneity and High This effect is

• Heterogeneity generally manifests with different Anisotropy in anisotropy Heterogeneity and generally well properties in the build direction relative to the other two Properties generally manifest anisotropy in L- understood but directions due to the nature of the layer-by-layer build as different DED-fabricated requires specific process. This impacts the microstructure and fabrication (Material Property properties in the components differ measures to defect structure and generally creates poorer properties Sampling build direction significantly from manage, whether between build layers.

Difference NRC Ranking (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability Methodology, relative to the other those in through an

• Thermal post-processing with appropriate parameters Heterogeneity) two directions due conventional appropriate sampling would be expected to make material properties and to the nature of the materials, which methodology performance more homogeneous and similar to those of layer-by-layer build are largely (e.g., witness conventionally forged materials.

process. This isotropic, and can specimens) or

• For example, in as-fabricated and stress-relieved 316L impacts the have a significant thermal post- stainless steel, the variation in microstructure due to microstructure and impact on processing, to help geometry causes preferential crack growth directions for fabrication defect component minimize this effect. fatigue cracks.

structure and performance if not generally creates addressed in the poorer properties design, between build fabrication, or layers. post-fabrication process.

Residual stresses Medium Residual There is significant

• L-DED components typically experience significant as-form during the stress and knowledge related to fabricated residual stress.

Residual Stress L-DED build associated managing the

• High residual stress may result in warping, cracking, and process and can defects can potential negative delamination; however, these events typically can be (Residual Stress lead to warping, negatively impact impacts of residual detected visually.

Warping, cracking, and component stress, including

• In addition, residual stress can make the component Cracking, and delamination if not performance. through optimizing susceptible to future degradation such as SCC or fatigue Delamination) properly managed. the build process, from the presence of high tensile residual stress on the post-processing, or surface.

inspection.

• Thermal post-processing with appropriate parameters would be expected to relieve residual stress.

Porosity includes High Techniques to

• Porosity is known to adversely affect fatigue life, SCC, the size, Unacceptable manage porosity in and irradiation-assisted stress-corrosion cracking distribution, and levels of porosity the build process are (IASCC), though the precise quantitative impact total volume of can have a known, but porosity depends on the material and porosity characteristics Porosity voids and pores in significant impact can be challenging to (pore frequency, pore size, pore morphology, and total the L-DED on component mitigate through void fraction).

(Porosity component. performance. By thermal post-

• Machine parameters and scan strategy refinement have Measurement) the nature of processing. the potential to address porosity concerns; however, L-DED, the they may vary significantly based on the geometry and porosity may have materials used.

smaller size and higher density

Difference NRC Ranking (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability than in forged

• Porosity is more prevalent in LP-DED than LW-DED due materials. to the internal porosity and trapped gas in powder feedstock that does not exist in wire feedstock.

• For post-processing, HIP with appropriate parameters has been demonstrated to reduce porosity and produce properties more similar to those of conventionally forged materials.

Surface finish (or High Surface L-DED components

• Surface roughness is generally greater in as-built L-DED surface roughness) finish can have a can be finished using parts than in similar forged materials.

refers to the significant impact traditional post- o The layer-by-layer nature of LP-DED, combined with measure of the on component processing the tendency to weld unmelted powder particles to the texture of the part performance, techniques. component surfaces, produces a rough outer surface surface. particularly in LP-DED.

Processing through increased o LW-DED typically results in a bead-like surface due to Surface Finish techniques that are susceptibility to the layer-by-layer deposition but does not give the conducted to fatigue and SCC added roughness of attached particles.

(Surface improve surface initiation.

• Higher surface roughness can lead to reduced fatigue Roughness) finish include life and lower SCC and corrosion resistance.

machining, shot

• Surface finish can be improved by post-processing such peening, and as subtractive machining or other surface treatments.

chemical treatment.

• For components with complicated geometries, hybrid manufacturing approaches (iterating between additive and subtractive steps) may be necessary to reach all surfaces for post-processing.

Note 1: Section 3.4 of the ORNL TLR discusses the corresponding ORNL gaps.

Table 2 Technical Information316L L-DED Stainless Steel Material Specific Difference NRC Ranking of Significance (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability Tensile properties. Low Failure due to 316L L-DED stainless

• High porosity would likely degrade tensile tensile overload is not a steel materials have performance but would have a greater impact common failure mode generally sufficient data on other material properties.

Tensile Properties in nuclear components, showing similar or and it is no more likely superior tensile (Tensile in L-DED materials due properties compared to Properties) to their similar or those of similar forged superior tensile materials.

properties.

Initial fracture High Low initial Limited data are

• Limited data on 316L L-DED stainless steel toughness refers to fracture toughness can available on fracture materials have shown significantly lower initial the materials lead to brittle toughness for 316L L- fracture toughness, depending on post-starting fracture component failure if not DED stainless steel processing, than for similar forged materials.

toughness upon adequately managed. materials. Post- This may be due to porosity or other defects that entering service processing should may be reduced with optimized processing Initial Fracture after fabrication. improve fracture parameters and thermal post-processing.

Toughness toughness and minimize o However, 316L L-DED stainless steel is still any difference. expected to have adequate initial toughness.

(Fracture

• Data in representative environments are Toughness) important to demonstrate that fracture toughness will be adequate to meet component design assumptions.

• Thermal post-processing with appropriate parameters would be expected to improve fracture toughness.

Thermal aging High Thermal aging The NRC is not aware of

• Data in representative environments are refers to the can lead to brittle any significant data on important to demonstrate that fracture reduction in component failure if not thermal aging behavior toughness does not degrade excessively due to fracture toughness adequately managed. of 316L L-DED stainless thermal aging and will be adequate to meet Thermal Aging after significant steel materials. component design assumptions.

time at elevated

• Thermal post-processing with appropriate temperature, which parameters would be expected to make material is a known aging properties and performance more similar to mechanism for those of conventional forged materials.

stainless steels containing

Difference NRC Ranking of Significance (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability significant levels of ferrite.

SCC refers to High SCC can lead to Very limited data exist

• Data in representative environments are stress-corrosion component failure if not on SCC behavior of important to demonstrate that material crack initiation and adequately managed. 316L L-DED stainless performance due to SCC will not be degraded to growth of Local material steel materials, although a greater degree in L-DED materials than in susceptible characteristics SCC is a known forged materials.

SCC and materials under (i.e., grain boundary degradation mode in

• Post-processing with appropriate parameters Corrosion roughly constant chemistry and light-water reactors. would be expected to make material properties Resistance stress operating microstructure) may and performance more similar to those of conditions due to amplify differences with conventional forged materials.

(SCC and IASCC, the corrosive conventional materials

• In 316L stainless steel, the silicon content in the Corrosion environment. not apparent in other powder can create oxides that have adverse Resistance)

Corrosion refers to tests (e.g., tensile). effects on SCC growth rates. Acceptance other corrosion criteria for powder (virgin and recycled) should processes that may consider oxide content.

be active in the environment.

Fatigue refers to Medium While fatigue Limited data are

• Without adequate post-processing, surface the initiation and can be a concern and available in the literature roughness is known to be a greater issue with L-propagation of lead to component on the fatigue life of L- DED materials and can reduce fatigue life.

cracks due to cyclic failure, other post- DED materials

• Fatigue properties also depend on post-loading with or processing steps such compared to processing heat treatment and component without as surface finishing, conventionally porosity.

environmental residual stress manufactured materials.

• Limited data suggest high-cycle fatigue life may effects playing a reduction, and HIP heat be reduced compared to that of conventional Fatigue significant role in treatments can be used 316L stainless steel, while low-cycle fatigue life the process. to improve fatigue is comparable to that of conventional 316L (Fatigue) susceptibility in many stainless steel.

applications.

• Stress-relieved (without annealing heat treatment) 316L L-DED stainless steel shows anisotropic fatigue strength and preferential crack growth directions due to the columnar microstructure.

• Data in representative environments are important to support fatigue calculations,

Difference NRC Ranking of Significance (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability including for environmentally assisted fatigue, in L-DED materials.

Irradiation effects High Irradiation effects Very limited data exist

• Data in representative environments are refer to the impact are highly relevant to on irradiation effects, important to demonstrate that irradiation effects of neutron address for irradiated particularly neutron will not be significantly greater in L-DED irradiation on reactor internals irradiation, on the materials than in forged materials.

various aspects of components in behavior of 316L L-DED

• Post-processing with appropriate parameters material properties light-water reactors, stainless steel materials. would be expected to make material properties Irradiation Effects and performance, which can lead to and performance more similar to those of including, but not premature component conventional forged materials.

(SCC and IASCC, limited to, loss of failures. Local material

• Current studies point to reduced Irradiation-fracture toughness, characteristics irradiation-induced defects in L-DED Assisted IASCC, and void (i.e., grain boundary components compared to those produced with Degradation) swelling. chemistry and conventional manufacturing. However, the microstructure) may understanding is very limited, and research is amplify differences with ongoing. Additional research is likely needed to conventional materials understand performance differences.

not apparent in other tests (e.g., tensile).

High-temperature High Very limited data exist

• For high-temperature operating environments aging effects refer High-temperature, on high-temperature, (as discussed in ASME Boiler and Pressure to any time-dependent aging time-dependent aging Vessel Code,Section III, Division 5), data in time-dependent effects are of high effects for 316L representative environments are important to aging mechanisms importance to stainless steel L-DED demonstrate that high-temperature, time-relevant to elevated component integrity for materials. dependent aging effects in L-DED materials will High-temperatures (as the elevated operating be equivalent to or acceptable when compared Temperature, discussed in temperatures expected to those in forged materials.

Time-Dependent American Society for many advanced

• Post-processing with appropriate parameters Aging Effects of Mechanical reactor designs. would be expected to make material properties (e.g., Creep and Engineers (ASME) and performance more similar to those of Creep-Fatigue)

Boiler and conventional forged materials.

Pressure Vessel Code,Section III, Division 5),

including creep and creep-fatigue.

Difference NRC Ranking of Significance (Corresponding Definition Knowledge/ Key Technical Information Importance ORNL Gaps)1 Manageability Weld integrity High Welds can be a The NRC is not aware of

• Data in representative environments are refers to the location of degradation any significant data on important to demonstrate that welds with L-DED properties and and may behave weld integrity for 316L L- base materials will perform similarly to those Weld Integrity performance of the significantly differently DED stainless steel with conventionally manufactured base weld and with L-DED materials. materials. materials.

surrounding heat-affected zone.

Weldability refers Medium Weldability is The NRC is not aware of

• Very limited information has been published on to the ability to a concern but should any significant data on the results of using traditional joining methods successfully weld a not greatly impact the weldability of 316L on L-DED components.

material to another component L-DED stainless steel

• Higher oxygen content, residual stress, and component without performance as long as materials. Existing microstructural segregation may affect the Weldability/

unacceptable satisfactory welds welding standards to optimal parameters for welding on 316L L-DED Joining defects. passing ASME Boiler demonstrate weldability stainless steel compared to on conventional and Pressure Vessel and accept final 316L stainless steel.

(Weldability)

Code requirements can manufactured welds are

• Weldability should be demonstrated for L-DED be made. expected to remain materials, but the existing welding standards applicable for L-DED and demonstration processes should be components. sufficient.

Note 1: Section 3.4 of the ORNL TLR discusses the corresponding ORNL gaps.