ML25183A354
| ML25183A354 | |
| Person / Time | |
|---|---|
| Issue date: | 06/30/2025 |
| From: | Jeffrey Poehler NRC/RES/DE |
| To: | |
| Jeff Poehler 3014158353 | |
| Shared Package | |
| ML25183A340 | List: |
| References | |
| Download: ML25183A354 (1) | |
Text
1 2
3 4
5 6
7 8
9 10 11 12 13 14 15 16 17 18 19 A
B C
J K
L M
N O
P Q
R S
T U
V W
X Y
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 AZ BA Dave Rudland Jeff Poehler On Yee Average ImportanceUncertaintyKnowledge ImportanceUncertaintyKnowledge ImportanceUncertaintyKnowledge Recommendation ID title of recommendation Scope, objectives, and/or topic modifications Score Score Score Rationale Score Score Score Rationale Score Score 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 1
Ensure that characterization techniques such as TEM, FIM, APT and PAS, continue to evolve.
L L
PK These characterization techniques are important for fundamental research in the behavior of irradiation effects, but from a practical perspective, phenomenological or mechanistic based models lag in comparison to empirical models L
L K
The state of development of characterization techniques does not have a direct impact on safety. There have been great strides in improving these techniques over the last 50+
years. However, this is not an area where NRC would likely sponsor research.
L M/L PK the evolvement of these methods would be scientific - but from a regulatory perspective would be difficult to near impossible to require.
Given the current circumstances -
enforcing anything before the current test requirements would be near impossible 1.0 1.2 1.7 0.194444 1.0000 1.1667 1.6517 0.194444 1
2 1
1 2
2 Materials evaluated should be representative of operating reactor materials under high dose conditions.
H L
K As much as practicable, data from real materials under realistic conditions are needed for understanding the fundamental issues M
L K
This goes without saying. The statement is too general to base any research recommendations. This statement is also redundant with RPV-12.
M M
K/PK PSSP. Do we need more??
How is this different than RPV-12?
Also - somewhat related to RPV capsule/specimen testing 2.3 1.0 1.2 0.166667 2.3333 1.0000 1.1667 0.388889 2
2 3
3 2
3 Harvesting of reactor pressure vessel support materials could be beneficial for improving embrittlement predictions for these materials.
M M
PK While it would be beneficial, the practical apects of this work are really not known.
Many of the supports are redundant and not typically flawed, so it may be aof little use.
H H
PK This is a relatively low knowledge area - low flux/fluence and low temperature irradiation. Also, I ranked importance high because structural integrity evaluations of RPV supports probably do not take embrittlement into account.
However, my personal uncertainty on this topic is high.
M M
PK An area of interest - and of review in SLRAs knowledge/data from harvested materials - can help confirm/alter positions. But this is not needed to proceed with NRC reviews.
2.3 2.3 2.0 0.388889 2.3333 2.3333 2.0150 0.388889 3
4 Develop improved physics-based models for embrittlement M
M K
It would be extremely useful to have an accruate physics based model, but this has been attempted for years, and has had limited sucess.
L M
PK I ranked this low for importance because I don't believe physics-based models are necessary for accurate prediction of embrittlement. An example is E900-15, an empirically fit ETC which performs better than EONY which is partially physics-based. I think it is more important that the industry/NRC generate more high-fluence data and data covering other areas of sparse data to feed into development of improved ETCs.
L M/L PK the evolvement of these models would be scientific - but from a regulatory perspective would be difficult to near impossible to reuquire.
Given the current circumstances -
enforcing anything before the current frameowrk seems near impossible 1.3 1.8 1.7 0.305556 1.3333 1.8333 1.6667 0.388889 4
5 t
M M
PK Not sure how much more data is needed for a material that might be less susepctible to embrittlement M
M PK I think the concern for the low-copper, low -phosphorus materials would be Ni-Mn-Si precipitates, which have not been demonstrated to be a significant contributor to embrittlement in steels used in US LWRs. I agree that M/L M/L PK Existing Domestic Fleet - how much is really considered "low-copper" may be more of an issue for new reactors - or later vintage plants (so only a subset) 1.8 1.8 2.0 0.305556 1.8333 1.8333 2.0000 0.388889 5
6 Investigate phosphorus segregation levels with respect to intergranular failure L
M UK I'm not sure I see the practical applciation of such work M
M PK recuse =- dont know enough about this to make any judgement 1.3 1.7 2.0 0.277778 1.3333 1.6667 2.0150 0.222222 6
7 Improve existing embrittlement trend curves, such as ASTM E 900, and incorporate improvements into regulatory guidance H
M K
Necessary to correct the non-conservative predictions in embrittlement in RG1.99 H
L PK I think improving ETC's is one of the most important areas for future research related to RPV integrity. Improving ETCs would be beneficial to reducenonconservatism in the existing ETC (RG 1.99) at fluences greater that 6E19.
M M
K/PK Subject is related to the SECY-22-0019 Importance - Medium because the impacts/benefit would limited to subset of US plants
.. PWRs with projected "high" fluence.
With operation to 100 years or more - this would still be ~2/3 the fleet..
2.7 1.7 1.5 0.277778 2.6667 1.6667 1.5150 0.277778 7
8 Improve direct fracture toughness methodologies H
M K
Using actual fracture toughness data instead of Charpy energy will allow a more accruate prediction of embrittlement behavior and actual toughness response.
M H
PK I think improving DFT methodologies would be beneficial, but these methodologies are also becoming well accepted by regulators and industry.
Personally, I have high t i t h th th t
M/L L
K/PK IBR in ASME - viable uses and Robinson SLRA is the first test case for SLR - still under review - but use of RTT0 -
applicant demonstarted 50.61 is met for weld material PWROG t
ill d
2.2 2.0 1.5 0.333333 2.1667 2.0000 1.5000 0.222222 8
9 Update existing regulations and guidance, such as RG 1.162, to account for new findings related to nickel-manganese clusters and other factors affecting embrittlement.
L H
PK I'm not sure the industry will use this reg and gudiance, so not sure the worth of these efforts. I think late bloomng phases may occur but not in the fluence levels well above any reasoanble lifetime L
H PK Ni-Mn-Si precipitates, e.g. late-blooming phases, have not been demonstrated to be a significant factor in the transition temperature shift of LAS materials used in US operating LWRs. Therefore, I assigned an importance rank of L. I do think that the knowledge base on these precipitates could be improved.
I don't think we are at a point where we know enough to know whether we should modify regulatory guidance.
L L
PK Annealing of RPV would be a last ditch effort as a means to address/manage embrittlement
- From a regulatory perspective, thermal annealing the RPV would not be a widely used, or practical option.
Possible for individual plants if there was a business case There are more viable options (some require proactive planning) - (e.g., RTT0, flux reduction, fuel loading, 50.61a)
- before undertaking thermal annealing 1.0 2.3 2.0 0.388889 1.0000 2.3333 1.9850 0.166667 9
10 Studies of re-embrittlement after annealing to support long-term operation beyond 80 years are needed to support use of annealing for mitigation of embrittlement beyond 80 years L
L pk I'm not sure the industry will use this reg and gudiance, so not sure the worth of these efforts L
M PK I assigned this low importance because I don't see a compelling case that annealing will be necessary, especially given the evolution of analytical techniques such as direct fracture toughness, which will help to recapture some operating margin by more accurately quantifying embrittlement.
L L
PK Annealing of RPV would be a last ditch effort as a means to address/manage embrittlement
- From a regulatory perspective, thermal annealing the RPV would not be a widely used, or practical option.
Possible for individual plants if there was a business case There are more viable options (some require proactive planning) - (e.g., RTT0, flux reduction, fuel loading, 50.61a)
- before undertaking thermal annealing 1.0 1.3 2.0 0.222222 1.0000 1.3333 2.0000 0.333333 10 11 Additional research is recommended on the use of annealing to support LTO beyond 80 years, including determining whether annealing would be beneficial, and which type(s) of annealing should be pursued.
M M
pk Based on my commetns above, I thik we should investigate if annealing would be used, or at least what are the major roadblocks L
M PK See comment on RPV-10.
L L
PK Annealing of RPV would be a last ditch effort as a means to address/manage embrittlement
- From a regulatory perspective, thermal annealing the RPV would not be a widely used, or practical option.
Possible for individual plants if there was a business case There are more viable options (some require proactive planning)
(e g RTT0 flux 1.3 1.7 2.0 0.277778 1.3333 1.6667 2.0250 0.5 11 12 Additional surveillance testing is needed to generate high-fluence embrittlement data. This could involve either testing existing high-fluence specimens, installing new capsules/specimens for high-fluence irradiation, or both H
L K
Since the models we have are emperical based, and we have seen with RG1.99 going beyond the data that were used int eh development can lead to undesireable consequences. I think high fluence data is needed H
L PK This is pretty obvious and goes hand-in-hand with developing improved ETCs. The EPRI CRVSP and PSSP programs are partially addressing this recommendation. However, further efforts would probably be beneficial.
M M
K/PK PSSP. Do we need more??
How is this different than RPV-2?
Also - somewhat related to RPV capsule/specimen testing 2.7 1.3 1.5 0.222222 2.6667 1.3333 1.5000 0.277778 12 13 There is a need to ensure that there are sufficient surveillance specimens to monitor embrittlement during long-term operation H
L K
Since the models we have are emperical based, and we have seen with RG1.99 going beyond the data that were used in the development can lead to undesireable consequences. I think high fluence data is needed M
L PK It's not clear if this recommendation is referring to specific plants or the operating LWR fleet as a whole. If the fleet as a whole, RPV-13 is redundant with RPV-12.
L L
K Reconstitution of specimens has been implemented plant-specifically and for the BWR fleet Proven practice to support limited specimens Biggest challenge is not research - But with licensee's proactively planning the re-2.0 1.0 1.3 0.166667 2.0000 1.0000 1.3333 0.333333 13 1.0 1.0 1.0 1.0 1
2 3
4 5
6 7
8 910 11 12 13 Importance Knowledge High Low Known Unknown 1
2 3
4 5
6 7
8 9
10 11 12 13 2
2 Importance Knowledge Session 1 - RPV High Low Known Unknown