ML25183A349
| ML25183A349 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/2025 |
| From: | Jeffrey Poehler NRC/RES/DE |
| To: | |
| JEFF POEHLER 3014158353 | |
| Shared Package | |
| ML25183A340 | List: |
| References | |
| Download: ML25183A349 (1) | |
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Z AA AB AC AD AE AF AG AH AI AJ AK AL AM AN AO AP AQ AR AS AT AU AV AW AX AY Panelist 1 Panelist 2 Panelist 3 Average Recommendation ID title of recommendation Scope, objectives, and/or topic modifications Score Rationale Score Rationale Score Rationale Score Rationale Score Rationale Score Rationale Score Rationale Score Rationale Score Rationale Importanc e (avg)
Uncertaint y (avg)
Knowled ge (avg) error bars Import Uncert.
Know error More research could be used to gain knowledge on a topic expected to be important to safety More research could reduce uncertainty and clarify topic importance More research could improve knowledge but topic not expected to be safety significant Topic expected to have safety significance but likely could be addressed without additional research Topic may have safety significance but sufficient knowledge exists to manage Topic not expected to have safety significance and sufficient knowledge exists H/M/L H/M/L K/PK/UK H/M/L H/M/L K/PK/UK H/M/L H/M/L K/PK/UK FAT-1 Evaluate effects of water chemistry additions (e.g., KOH, NMCA, DO) on EAF M
Water chemistry effects have been long studied. There is some uncertainty, however, if HWC retains its effectiveness over very long operating times. wEPRI has been studiyng replacement of LiOH with KOH but fatigue was not part of their studies. Threshold effects may also be a bigger concern long-term. Biggest issue with limited data is NMCA for C/LAS which requires low DO which is counter to FAC DO requirements. PB components are generally protected by LBB and fatigue typically results in leakage.
H uncertainty of common water chemistry effects on fatigue is generally low; slight increase due to possible saturation effects.
Wouldn't expect KOH to cause significant effects. Long-term effects on threshold EAF factors are probably biggest unknowns PK Knowledge is generally good except for long-term water chemistry effects. Might also be a concern near thresold stress intensity factors.
M Experience has shown environmental effects in laboratory environments are more severe than in actual reactor environment H
Based on the studies on environmental effect of fatigue, it is still not a well understood phenomon UK Little is known based on my knowledge M
Experience has shown environmental effects in laboratory environments are more severe than in actual reactor environment M
Environmental fatigue studies appear to be focused on DO, strain rate, Temperature, and Sulphur content. It appears that it is still not a well understood phenomon for KOH addition.
PK Some knowledge is available. The knowledge needs to be enhanced for LTO. Further, effects of KOH addition are not known.
2.0 2.0 2.3 0.333333 2.0000 2.0000 2.2833 0.333333 2
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2 FAT-2 Evaluate the effects of irradiation on fatigue lives M
This is little data on irradiation effects, making this more interesting. However, HCF data near threshold has shown that threshold increases due to strength elevation. I think that this phenomenon is well studied and only concern is with LCF; only internals components affected.
M While there's not much data, I don't expect the safety significance of this issue to be too high since it only affects internals, which are nominally not significantly loaded, especially in fatigue UK While there's some data on this phenomena, it's limited and only typically near the endurance limit H
Failure of components such as core support structures has high safety significance M
Licensees have been collecting specimens in reactor surveillance capsules and have studied the specimens; effect on +80 years may be informed by in-reactor performance for 60 years.
K Licensees have knowledge from decades of in reactor specimen collection H
Failure of components such as core support structures has high safety significance H
Data from reactor surveillance capsules in current fleet provides some information on radiation effects. Projection of this data for
+80 years may have uncertainties further compounded by its effect on fatigue.
PK Knowledge from decades of in reactor specimen collections for radation effects is available. But knowledge on LTO operation and effects on fatigue are not well known.
2.7 2.3 2.0 0.388889 2.6667 2.3333 2.0250 0.388889 2
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2 FAT-3 Understand the fatigue characteristics of AM materials and effect of important attributes (e.g., surface finish, orientation, processing variables).
M I don't view the safety significance of this issue to be high, especially in near term because I don't expect many safety related components to be AM, although it's research that I believe is important. For safety related applications, most of the fatigue issues come from unmachined surfaces, near surface porosity, and anisotropic effects. Most of these contributing factors can be controlled.
M although data is still limited in this area, I don't believe that the lack of such data should impede its use PK some effects, like surface roughness are no different for AM or conventional materials.
Anisotropy or near surface effects are somewhat unique M
Depending on AM material application and the extent of application, the safety significance can be high.
H AM materials are not well understood UK Reliability of AM materials are not well understood and there is no known reactor application experience M
Depending AM material application and the extent of application, the safety significance can be high.
M Ue of AM materials is a relatively new field. The fatigue behavior of AM materials is not well understood.
PK Development of AM materials in Nuclear applications is in the infant stage.The ASME Section III has very limited information on fatigue.
The knowledge of impacts on LTO operation does not exist.
2.0 2.3 2.3 0.388889 2.0000 2.3333 2.3333 0.388889 FAT-4 Develop appropriate codes and standards for the use of AM materials in new designs and replacement parts.
ranking importance w.r.t fatigue requirements needed in AM C&Ss L
While C&S is important, I believe that the current requirements should largely be applicable to AM components. Only some process-related considerations will need to be addressed and qualification programs can address unique issues.
M This will affect a relatively small number of future AM components; i.e., those governed by Code.
Expectation is that by the time this is needed, there will be sufficient information to justify Code provisions PK I believe that the current Code fatigue requirements cover > 80%
of all relevant issues.
M Certain applications may have high safety signficance H
Not much code requirements have been published UK Limited research has been done; particularly long term operation research is needed.
M Certain applications may have high safety signficance M
Very little information is available on AM materials.
UK Research and Codes & standards development for AM materials are needed.
1.7 2.3 2.7 0.388889 1.6667 2.3333 2.6417 0.388889 FAT-5 Develop fatigue prediction and assessment methods for AM-manufactured safety-significant nuclear components M
The importance of this topic is slightly elevated compared to FAT-3 since the focus is on safety-significant components.
Otherwise reponse is similar to FAT-3 topic.
M lack of data shouldn't impede use assuming that proper qualification program is followed and that the application is appropriately justified UK There is no experience or knowledge associated with nuclear AM-manufactured safety related components because they don't exist to date. However, the technical framework and knowledge associated with convensional materials is generally applicable.
H Certain applications may have high safety signficance H
ASME BPV Code fatigue curve did not consider AM material PK Limited prediction method for AM materials M
Certain applications may have high safety signficance M
Very little information is available on fatigue prediction and assessment methods for AM materials.
UK Method for AM materials for design and prediction during LTO operation does not exist.
2.3 2.3 2.7 0.388889 2.3333 2.3333 2.6667 0.388889 FAT-6 Develop field-implementable methods to gather dynamic, field data on loading conditions.
Instrumentation and modeling to transfer data into component loads/stresses; ease of installation, durability, realibility are important attributes.
M I think that this could be important work, especially for understanding actual component loads. I think such work, however, would largely be used to relax existing conservatisms so I don't view it as particularly safety significant. One strategy that could improve safety is if monitoring/inspection are used during life to confirm viability of fatigue life projections.
L techniques are generally available which could be used for this; the only challenge is making them robust for field applications in some cases.
PK There is pretty good knowledge of general plant conditions associated with fatigue loading; what's less known are specific reasons for plant-specific variations M
Field data can provide health of the safety signficant SSCs when fatigue effect is not well understood for >80 yrs L
There is decades of experience in gathering field data that has been done for reactors including startup testing K
There is decades of experience in gathering field data that has been done for reactors H
Field data can provide health of the safety signficant SSCs when fatigue effect is not well understood for >80 yrs M
Operating fleet have collected fatigue monitoring data using installed instrumentation (e.g.
FatiguePro) that includes number of cycles, realistic transient information, and stress data.
There is some uncertainty in using this data and projection for LTO.
PK Operating fleet have collected fatigue monitoring data using installed instrumentation (e.g.
FatiguePro) that includes number of cycles, realistic transient information, and stress data. The fatigue projections during LTO needs development.
2.3 1.3 1.7 0.222222 2.3333 1.3333 1.6667 0.222222 FAT-7 Explore novel sensors and monitoring techniques that can detect subtle changes in structural behavior affecting material resistance and are field-implementable techniques that would detect material changes before formation of an engineering flaw.
L While this is interesting research, I think that the technical readiness level associated with the topic is low, especially if fatigue precursor changes are being evaluated L
I don't view this research to be particularly safety significant except for applications where there is little residual life after the formation of a flaw. I think redesign is the proper approach in these cases however.
UK there's some knowledge in this area at a theoretical level but no effective field sensors are on the horizon as far as I know.
M Field data can provide health of safety signficant SSCs when fatigue effect is not well understood for >80 yrs M
Knowledge of existing sensors for reactor applications can aid the development of novel sensors PK Knowledge of existing sensors for reactor applications can aid the development of novel sensors M
Field data can provide health of safety signficant SSCs when fatigue effects are not well understood for >80 yrs M
Development of novel sensors need to consider the harsh environment. Redundancy is important as these are susceptible for failures or malfunctions.
PK Knowledge gained from existing sensors for reactor applications can aid the development of novel sensors 1.7 1.7 2.3 0.277778 1.6667 1.6667 2.3583 0.277778 FAT-8 Develop methods to validate and calibrate theoretical models with in-situ measurement information.
M methods to validate and calibrate models exist. The biggest challenge is to merge the model simplicity with the real world complexity associated with some fatigue locations. Long-term sensor reliability is potentially a concern if using more continuous in-situ measurement.
L I don't have significant uncertainty in my safety ranking. While I think research would be useful in this area, I don't think it will result in a safety issue if not completed.
PK There is general knowledge on how to validate models with in-situ data; what's missing is tailoring that knowledge to fatigue events.
M This is a typical process used to validate analytical models L
This validation process is typical and should not have high uncertainty K
There should be high knowledge of this validation process M
This is a typical process used to validate analytical models M
This validation process is typical and should not have high uncertainty PK Test data from limited component testing by EPRI in mid 90s and some ongoing tests overseas (
e.g. Japan, Korea) are available.
Correlating the component test data to lab testing small-specimen lab testing is needed.
2.0 1.3 1.7 0.222222 2.0000 1.3333 1.6417 0.222222 FAT-9 Adapt existing equipment health monitoring methods from the aerospace industry.
Research would mine lessons-learned from aerospace components that have some similarity to nuclear components to see if any techniques are applicable to nuclear.
L While the aircraft industry should be lauded for their approach to fatigue, I don't think that there are many transferable parameters given the differences in materials, geometries, maintanenace and operating spectrum; fatigue is their driving design concern where it's an ancillary concern for nuclear.
L I don't have significant uncertainty in my safety ranking. I don't think it will result in a safety issue if not completed.
PK While it's always good to glean information from an industry as generally successful in managing fatigue as the aircraft industry, I think that the easily transferable lessons have already been mined.
L Equipment health monitoring may not be directly applicable to the nuclear industry because of the different environments L
The health monitoring in the aerospace industry should be well documented, but proprietary nature may prevent the nuclear industry from adopting K
The experience associated with health monitoring within the aerospace industry should be fairly extensive M
Equipment health monitoring may not be directly applicable to the nuclear industry because of the different environments L
The health monitoring in the aerospace industry should be well documented but its adaptation for nuclear industry needs consideration PK The success of aerospace industry and its experiecne with fracture mechanics methodology in design coupled with prescribed inspection frequencies is well known. Adapatation of such knowledge for nuclear applications that involve higher temperature and higher pressures is needed.
1.3 1.0 1.7 0.166667 1.3333 1.0000 1.6667 0.166667 FAT-10 Tailor advanced data analytics tools to process large datasets and understand/predict equipment behavior during operation This one is focused on processing large datasets from plant monitoring programs to make life prediictions; could be AI/ML based.
M This one is interesting if existing plant data can be mined to identify telltale signals which imply that fatigue is occurring.
H While this is an intersting research topic, I recognize that the fatigue symptoms will be challenging to tease out of the larger, background signals. Also, fatigue precursors will likely be system specific making training AI/ML models hard PK Certainly experienced plant personnel can detect when vibrations or some other system fatigue precursors exist. The challenge is to tease out trends that are not as readily noted.
M Safety signficance may be application specific and depends on what components and systems are evaluated L
If the components being monitored and environments are similar, the uncertainty should be low.
K Processing data related to nuclear application should not novel. One issue may be storage for the large amount of data being collected M
Safety signficance may be application specific depending on the components and systems evaluated M
The uncertainty is medium because the use of AI for processing large data sets is relatively new.
UK Use of AI to process large data sets is an emerging technology.Adaptation of this emerging technology in processing data related to nuclear application needs development.
2.0 2.0 2.0 0.333333 2.0000 2.0000 2.0000 0.333333 FAT-11 Improve modeling and simulation tools by examining real world behavior, including unanticipated failure cases, to better predict and understand the impact of small design variations on fatigue behavior and identifying, quantifying and incorporating complex environmental and loading factors, and their interactions, that most significantly affect performance and reflect the conditions present in aging reactors Resonance effects are a good example of small differences having a big effect; worthwhile particularly for components with low fatigue life margin.
M Research to understand unanticipated failure cases is a good idea. The biggest challenge is to understand the effect of small design variations but they have been shown to be important wtih respect to fatigue. I am not rating this one higher because I generally don't believe the associated fatigue issues to be highly safety significant. Also, this is a complex topic, requiring integration of many different specialties which makes it difficult to develop a useful product H
I think that a better knowledge of plant-specific factors could potentially improve plant safety. I just think that it will be challenging to really understand the plethora of small differences among the plants which could impact fatigue life.
PK Biggest factors driving fatigue are typically pretty well known. More nuanced and plant-specific factors are less well-known.
M Safety signficance can low or high depending on situation.
H This seems to be a very comprehensive study that is comprised of many areas and disciplines PK Each area may have high knowledge but the interaction effects may make it challenging to reach a more definitive conclusion M
Safety signficance can low or high depending on situation.
H This is a complex issue UK knowledge on small variations in geometry during aging process, operational load cycle changes, and synergistic effects with flow induced acoustic resonances is limited.
2.0 3.0 2.3 0.5 2.0000 3.0000 2.3833 0.5 FAT-12 Develop total life fatigue methods to account for all stages of crack initiation and growth in a probabilistic manner.
L While Im not against doing research in this area, I am unclear how such research would benefit safety. There are already well known fatigue design and evaluation rules for known parameters and inputs. The challenge is with unknown attributes that can have a big effect (as discussed in prior write-ups).
I'm not sure how these attributes would be modeled probabilistically in a meaningful way L
It's not clear to me that having a probabilistic model will improve safety in any meaningful way.
PK There's generally good knowledge on the major fatigue drivers and material attributes. There's remains still less understanding on transferance to component level.
There's even less knowledge on developing supportable distributions to model component level behavior.
M While fatigue may be an important topic for >80-year reactor operation, developing a fatigue method in a probabilistic manner may not yield signficiant safety benefits.
L While there is higher probability of component fatigue and crack growth in >80-year reactor operation, the benefit of probabilistic prediction method may be limited.
PK There is a lot of knowledge of crack initation and growth, but effect of long term operation over 80 years may be limited.
H There is higher probability of component fatigue and crack growth in >80-year reactor operation; therefore, safety signficance of fatigue failure goes up relative to other failure events H
The probability of component fatigue and crack growth in >80-year reactor operation (LTO) is certainly higher PK There is a lot of knowledge of crack initiation used in design (Section III CUF approach for design) and crack growth approach used during operation (Sction XI), but total life fatigue method to account for all stages of long term operation over 80 years along with probabilistic manner is limited.
2.0 1.7 2.0 0.277778 2.0000 1.6667 2.0500 0.277778 FAT-13 Develop a risk-informed approach to fatigue management which integrates direct measurements, analytics, and uncertainties.
Similar to FAT-12, except that component risk would be more directly considered, and plant operating data would be expressly used as basis for fatigue management.
H I think this topic is the most ripe for research because it potentially integrates all of the important considerations together. The goal is not to develop a probabilistic model but to use insights from all available information sources, coupled with failure consequences, to identify locations that are most risk-significant to fatigue. Those locatioins can then be managed accordingly M
This is a common practice now in other areas of nuclear and it's generally a sound philosophy.
The challenge is to tailor specifically to fatigue issues and address plant-specific effects.
This challenge increases the likelihood that research will not be successful.
PK A lot of the individual causal factors are known. The biggest challenge is to develop a framework to properly integrate and weight this information appropriately and address plant-specific issues.
L The risk-informed integrated approach is an improvement from exisitng monitoring combined with conservative assumptions; however, significant safety improvement may not be guarranteed M
Measurement and prediction are being done commonly; however, the integration of the methods with risk-informed approach may have some uncertainty PK Knowledge of individual methods is high, but combined measurement and analytical approach may be less known L
The risk-informed integrated approach is an improvement from exisitng monitoring combined with conservative assumptions; however, significant safety improvement may not be guarranteed M
Direct Measurements and analysis of large data using AI is quite new for fatigue applications. There is additional uncertainty with risk-informed approach.
PK Knowledge on combined measurement and analytical approach is very limited.
1.7 2.0 2.0 0.333333 1.6667 2.0000 1.9750 0.333333 FAT-14 Research the effects of flexible plant operation on fatigue and understand implications of changing power levels and other operational parameters on equipment longevity and safety Fundamental question is if existing requirements are sufficient or if more research is needed to understand implications.
M I believe that some work on this has been done as EPRI did a study on the effects of flexible power operation on plants. Also, the French do load following and other than thermal sleeve issues, which may be linked to load following, I am unaware of other issues. However, I do believe that some more work would be beneficial if this is something that we decide to allow. If not, research should not be supported.
M I have uncertainty associated with the fact that this will actually happen in the US. It's not something the NRC currently allows and I haven't heard industry expressing much interest recently.
However, as renewables continue to come online, it makes flexible operations more likely. I do think that depending on how the plants are cycled that new fatigue challenges could arise in different locations then seen previously.
PK Prominent fatigue locations and associated causal factors are pretty well understood now. The biggest knowledge gap will be the potential for new flow and/or temperature cycling phenomena if the plants are cycled through different power modes when placed offline.
M Changing power levels will have effect of fatigue, but its effect on safety signficance needs to be quantified L
It is resonable or fairly certain that changing power level have an effect on the safety importance K
The effect of changing power level on fatigue is fairly well known, but it needs to be quantified and documented M
Changing power levels will have effect of fatuge, but its effect on safety signficance needs to be quantified M
Future needs for flexible plant operation to support the scenarios of changing energy demands during daily operation. Flexible plant operation affects fatigue.
PK The effect of changing power level on fatigue cycles compared with those used in the initial design needs to be quantified and documented 2.0 1.7 1.7 0.277778 2.0000 1.6667 1.6917 0.277778 Importance Uncertainty Knowledge Importance Uncertainty Knowledge Importance Uncertainty Knowledge Importance Knowledge Fatigue 1
2 4
5 10 7
13 6
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High Low Known Unknown 14 12 3
11 Importance Knowledge Heat Map High Low Known Unknown Higher Potential Safety Signicance and Less Higher Potential Safety Signicance but More Lower Potential Safety Signicance and More Lower Potential Safety Signicance but Less