ML21309A057
| ML21309A057 | |
| Person / Time | |
|---|---|
| Issue date: | 10/18/2021 |
| From: | NRC/NMSS/DREFS/RRPB |
| To: | |
| Schneider, Stewart | |
| References | |
| 20211318, NRC-1694, NRC-2021-0174 | |
| Download: ML21309A057 (69) | |
Text
Official Transcript of Proceedings
NUCLEAR REGULATORY COMMISSION
Title:
Public Meeting on Reactor Pressure Vessel Embrittlement Monitoring and Prediction in Long-term Operation
Docket Number: (n/a)
Location: teleconference
Date: Monday, October 18, 2021
Work Order No.: NRC-1694 Pages 1-67
NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W., Suite 200 Washington, D.C. 20009 (202) 234 -4433 1
UNITED STATES OF AMERICA
NUCLEAR REGULATORY COMMISSION
+ + + + +
PUBLIC MEETING ON REACTOR PRESSURE VESSEL
EMBRITTLEMENT MONITORING AND
PREDICTION IN LONG-TERM OPERATION
+ + + + +
MONDAY,
OCTOBER 18, 2021
+ + + + +
The public meeting took place via Video
Teleconference, at 1:00 p.m. EST, Joan Olmstead, NRC
Facilitator, presiding.
PRESENT:
JOAN OLMSTEAD, NRC Facilitator
SCOTT BURNELL, NRC Public Affairs Officer
ALLEN HISER, NRR Senior Technical Lead
ELLIOT LONG, Principal Technical Lead, EPRI
DAVID RUDLAND, NRR Senior Technical Lead
STEWART SCHNEIDER, NMSS Senior Project Manager
ROBERT TAYLOR, NRR Deputy Officer Director
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P R O C E E D I N G S
1:08 p.m.
MS. OLMSTEAD: Good afternoon. My name is
Joan Olmstead, I am a member of NRC's Facilitator's
Corps, and it's my pleasure to facilitate this
afternoon'smeeting. Slide two, please.
This is an information meeting with a
question-and-answer session. And the purpose of this
meeting held by the Nuclear Regulatory Commission, or
NRC, staff is to meet directly with individuals to
discuss regulatory and technical issues.
Attendees will have an opportunity to ask
questions of NRC staff and provide feedback about the
issues during the discussion and question-and-answer
period. However, the NRC is not actively soliciting
comments towards regulatory decisions at this meeting.
The public announcement for this meeting
can be found in the Agencywide Documents Access and
Management System, ADAMS, in the -- the number is
ML21280A267. The NRC staff presentation slides can be
found in ADAMS under the accession number ML21270A002.
So, thank you for attending this meeting.
We are early in our review process, and this exchange
of information of NRC staff evaluation of reactors
pressure vessel embrittlement in long-term operation
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is important to the NRC's review.
The NRC staff discussion will include
information related to the embrittlement trend curve
in Regulatory Guide 1.99 Rev 2, Radiation
Embrittlement of Reactor Vessel Materials. And in 10
CFR 50.61, Fracture Toughness Requirements for
Protection against Pressurized Thermal Shock Events.
And the surveillance requirements in 10 CFR Part 50,
Appendix H, Reactor Vessel Material Surveillance
Program Requirements.
This is an information-gathering meeting.
And by the NRC's definition this means primarily the
purpose of this meeting is to exchange information
with members of the public and other stakeholders.
The NRC staff will also answer process-related
questions if time permits.
I'd like to note that the NRC has
continued to operate in a largely work-at-home status,
so most participants in this meeting are working
remotely and individually calling in. We recognize
this configuration presents unique challenges and
continue to welcome comments about what is and what
isn'tworking and with this meeting format.
Prior to the close of the meeting, I'll provide
information on how you can provide your feedback on
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today's meeting, and your inputs helps us improve
future NRC public meetings.
The agenda for our meeting is fairly
straightforward. After a presentation by NRC staff,
we'll have a presentation from the Electric Power
Research Institute, EPRI, and we will then give the
public an opportunity to provide feedback and ask
questions of the NRC staff.
This meeting is scheduled from one to four
p.m. Eastern Time. And we'll try to allow as much
public input as possible, but we will generally try to
adhere to the meeting schedule. Today's call is meant
to be an exchange of information, and as always for
NRC public meetings,no regulatory decisions will be
made. Slide 4, please.
This slide notes speakers for this
afternoon's meeting. Robert Taylor, Deputy Office
Director for the Office of Nuclear Reactor Regulation,
will be giving opening remarks, followed by David
Rudland,NRR Senior Technical Lead for this project.
Allen Hiser and Stewart Schneider are senior NRC staff
that also support this activity.
And with that, I'll turn this over to
Robert. Robert.
MR. TAYLOR: Thanks, Joan. Can everyone
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hear me?
MS. OLMSTEAD: Yes, we can hear you.
MR. TAYLOR: Great. So I wanted to take
the opportunity and open up this meeting and set a
tone for the discussion that we're going to have
today. And I'm excited to see the number panel -- or
number of attendees who've shown up for the meeting
and expressed interest in this. And we look forward
to hearing perspectives and feedback during the
meeting.
So for those of you who don't me, my name
is Rob Taylor. I'm the Deputy Office Director for New
Reactors in the Office of Nuclear Reactor Regulation,
and I have the materials issues for operating plants
under my responsibility as well. So I want to welcome
everyone to today's meeting. This is an important
topic as the NRC applies risk-informed approaches to
its safety mission.
Today we will hear from the NRC staff
about their efforts associated with monitoring and
prediction of reactor pressure vessel embrittlement
during longterm operation of nuclear power plants.
The NRC staff is continuing a discussion of these
issues that were first presented in a May 2020 public
meeting.
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During today's meeting, staff will
describe a holistic risk-informed analysis they've
performed on these issues and the potential impact on
reactor pressure vessel integrity. I want to assure
everyone that the NRC has high confidence that
operating plants remain safe and currently the NRC
regulations provide reasonable assurance of adequate
protection against brittle fracture of the reactor
pressure vessel.
Nothing in this meeting should be
construed as undermining our continued confidence in
the safe operation of these facilities. Instead, as
with any proactive and scientific regulatory program,
we should continue to assess new information and
identify places where our regulatory programs may need
enhancement in the future.
As such, today's meeting is intended to
gather insights and perspectives on this topic, and we
are not making any regulatory decisions.
The staff is proactively considering risk-
informed options to address the combined effects of
both issues of what we discuss today to ensure
continued reasonable assurance of adequate protection
against brittle fracture of the reactor pressure
vessels during longterm operation. The staff is very
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interested to receive feedback from external
stakeholders regarding the NRC staff's approach taken
in a holistic risk-informed analysis.
Other potential efforts impact to plant
operations that should be considered and if now is the
appropriate time to pursue these issues. The NRC
staff sincerely appreciates the external stakeholder
interest in these topics. We're expecting a very
interesting and productive meeting.
So with that, Joan, I will turn it back
over to you.
MS. OLMSTEAD: Thank you, Robert. Slide
5, please. This slide provides logistic information
on today's meeting. Please log into both the Webex
and call in to the toll-free phone line. The audio is
only through this bridge line. This arrangement
allows us to minimize our bandwidth to have a more
stable meeting platform and to help conduct the
meeting's discussion and question-and-answer session.
If you're not on Webex and you'd like to
view the presentation slides, they are in the NRC's
ADAMS document database. And the session number for
the package containing today's slides is ML21270A002.
The session slide's ML number is also included in the
public meeting announcement.
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Today's call is on an operator-moderated
phone line. Participants will have their lines muted
until we reach the portion of the meeting where they
can provide feedback and ask questions of the NRC
staff. You'll be given instructions on how to
participate before the discussion and question-and-
answer session portion of this meeting.
As indicated in the agenda, we have
allocated substantial portion of this meeting for this
process. However, if participants would like to email
questions to our public affairs officer during the
staff's presentation, please email Mr. Scott Burnell
at scott.burnell@nrc.gov.
Today's call is being recorded and will be
transcribed. The transcription will be made available
alongside with the published meeting summary. Given
the number of participants we expect on the call and
the format, I would ask that as a person speaks, they
introduce themselves each time they speak. I also ask
that the speakers limit their use of acronyms.
Your participation will be noticed in the
meeting summary if you provide your information
through Webex or the bridge line. Slide 6, please.
And now I'd like to introduce David
Rudland, NRR's Senior Technical Lead, to discuss the
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purpose of the meeting and provide NRC's presentation.
David.
MR. RUDLAND: Thanks. I'll do a sound
check to make that you can hear me okay.
MS. OLMSTEAD: Yes, I can hear you, David.
MR. RUDLAND: Okay, great. Yeah, as
introduced, my name is Dave Rudland, and I am a Senior
Technical Advisor for Materials in the Division of New
and Renewed Licenses in NRR. And I'm going to be
going through the slides today.
The purpose of our meeting this afternoon
is to continue the discussions we had, as Rob Taylor
pointed out in the May 2020 public meeting, on two RPV
embrittlement issues. The first being the
embrittlement trend curve in Regulatory Guide 1.99 Rev
2, which is also in 10 CFR 50.61. And it's, the
issues with that trend curve at high fluence where the
predictions appear to be in some circumstances under-
predictive of the measurements.
And the second issue is to talk about
Appendix H, the surveillance testing program. This is
10 CFR Part 50, Appendix H. And we'll be looking at
those issues and those circumstances where some
capsules have been delayed, leaving large gaps between
surveillance tests.
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We talked about the technical details at
that particular public meeting, so I'm not going to go
over those details again. I will talk about, briefly
talk about the issues but won't go into the details
that we did in that public meeting.
I will be discussing a holistic risk-
informed analysis that looks at both of these issues
together and its impact on vessel integrity. And
again, this is a risk-informed analysis that takes a
look at the complete issue.
As mentioned also this is going to be
mainly a technical discussion, and no regulatory
decisions will be made. We'll be talking about some
options that the staff is considering about how to
move forward, so of course we would like feedback not
only the analysis results that I'll be presenting, but
also on some of the options that we discuss later on
also. Next slide, please.
Before I get into the issues, I wanted to
kind of give a quick background on how the monitoring
prediction of embrittlement works. Within this
Regulatory Guide 1.99 and 10 CFR 50.61 there is an
embrittlement trend curve, and that trend curve
predicts changes in fracture toughness as a function
of fluence. The embrittlement is measured by a change
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in the transition temperature from a brittle fracture
to a ductile fracture.
As you can see in this -- in the left
illustration, there is a measure of embrittlement at
the beginning of life. The red curve demonstrates a
trend that is predicting an increase in embrittlement
with an increase in fluence.
In addition to that, surveillance capsule
testing provides monitoring to ensure the
embrittlement trend curve predicts the plant-specific
behavior properly. And the data left plot is
illustrating how the data would fall in the
embrittlement trend curve predicts the behavior
properly.
Within the regulations, a margin is added
to those predictions from the trend curve, producing
something called an adjusted reference temperature.
That adjusted reference temperature is then used in
the regulations such as 10 CFR 50 Appendix G to
predict the pressure temperature limits for normal
operation, which is shown in an illustration in the
right figure.
You can see illustrated pressure-
temperature curves for 40, 60, and 80 years and how
those curves move to the right as the vessel becomes
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more brittle. And what that does is that shortens the
window, it reduces the size of the operating window
for a plant to cool down. All right, next slide,
please.
So the idea scenario for these two working
together is that you have ETC that provides accurate
or conservative predictions of embrittlement and
surveillance data that covers all operating periods.
Because Appendix H lists that that is type of data
should be pulled periodically throughout the life of
reactor.
However, you can have certain
circumstances where you may end up with uncertainty in
those predictions. For instance, as illustrated on
the left figure again, you can have an embrittlement
trend curve that may under-predict the measurements.
As you can see, the orange and pink data illustrate
that the red curve under-predicts that behavior. That
could have a source of some uncertainty.
Or, as illustrated in the picture on the
right, you may have limited data or no data at high
fluence, in which the uncertainty is even larger in
how well the embrittlement trend curve predicts the
actual embrittlement state of that particular
material.
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And so each one of these conditions could
have uncertainty and could add to the issues with the
embrittlement trend curves. Next slide, please.
Illustrating that a different way, as you
can see at the top figures, if we have reasonably
periodic measurement of embrittlement and an accurate
embrittlement trend curve, then you have an expected
amount of uncertainty, which is illustrated in the
upperrighthand figure by the blue dashed lines.
And our margins and regulations are based
on the amount of expected uncertainty. However, like
I mentioned, if you have missing data or, and/or an
embrittlement trend curve that may under-predict the
behavior, you could have an increased amount of
uncertainty.
And with that increase amount of
uncertainty, we are not sure that we understand what
the impacts of that uncertainty are on future
predictions of embrittlement. And so this holistic
analysis was needed to really understand what the
impacts of that uncertainty -- impacts for that
uncertainty are on the behavior of the vessel. Next
slide, please.
So our current perspectives on this
potential issue. As Rob pointed out, we have high
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confidence that the current operating plants remain
safe and that all of our current and recent licensing
actions remain valid.
However, with some insufficient
embrittlement monitoring and under-predictions of the
embrittlement trend curve, we may have an impact on
the confidence in the integrity of the vessel in
longterm operations, in that safety margins and
performance monitoring may be impacted.
And what we feel right now is that we need
to do future work in order to determine which plants
are impacted by this potential issue. I'll go into
that a little bit more as we go through this
presentation. Next slide, please.
So I'm going to go into some details right
now about each of the issues, just briefly touching on
the issues before we go into the holistic analysis.
In May of 1988, the NRC published Regulatory Guide
1.99 Rev 2, which contained an improved embrittlement
trend curve that was fit on 177 surveillance data
points.
And then in June of '91, the NRC updated
10 CFR 50.61 to include that same embrittlement trend
curve that was in Regulatory Guide 1.99 Rev 2 to
address some issues that were being had with lower
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than measured predictions of the current -- of the
embrittlement trend curve that was in 10 CFR 50.61
prior to that update.
More recently, the embrittlement trend
curve was reevaluated for continued adequacy in 2014
and in more detail in 2019. Those evaluations are
public and the ADAMS accession numbers are shown on
this screen for more information. Next slide, please.
To go into some, a little detail about
what we're seeing with the embrittlement trend curve,
this plot illustrates that behavior. On the Y axis,
on the vertical axis, this is a measure of the
difference between the embrittlement predicted by
Regulatory Guide 1.99 Rev 2, the difference of that
value versus the measure value from surveillance data.
So a value of zero on this vertical axis
represents a perfect prediction of embrittlement from
that trend curve. The X axis is an increase in
fluence. And what you see is that you have a pretty
good prediction through most of the fluence history.
You have some scatter in the data. The
solid --I'm sorry, the dashed heavy lines represent
the standard deviation in the data, the scatter in the
data as expected by Regulatory Guide 1.99.
As you get higher and higher fluence, the
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scatter in the data becomes greater. And at 3E to the
19th fluence, the trends begin to deviate from that.
I should point out that the red points on this plot
are US data, US surveillance data, and the gray points
are from international data.
At about 6E to the 19th, the data becomes
statistically significant in that the deviation
becomes greater than that two standard deviation that
I mentioned. And by the time you get to about 1E to
the 20th neutrons per centimeter squared fluence, you
can have about up a minus 180 degrees Fahrenheit of
under-prediction of embrittlement.
And again, remember, in this case
embrittlement is being measured by a shift in the
transition temperature. I will go into some detail, a
little bit, of that temperature means and what the
significance of that temperature is in a few slides.
Next slide, please.
This is a plot for --the prior plot was
for base metals. This particular plot is for weld
metals. And you see a similar behavior. You have
good predictions at low fluence. However, as the
fluence gets larger, the scatter is getting -- the
scatter is getting bigger than what was predicted from
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However, at high fluence there's limited
data. And so you don't see the downward trend,
probably due to the lack of data at this particular
time. Okay, next slide, please.
Each of this is being driven by the
fluence function within the embrittlement trend curve
in Regulatory Guide 1.99. The embrittlement is
predicted with that trend curve through a combination
of information from the material chemistry, as well as
the fluence. This equation that's at the top of the
chart shows that equation for predicting the
embrittlement.
CF is a chemistry factor that's a function
of nickel and copper. And then the fluence function
f is from the next part of the equation. And what's
plotted on this particular plot is that fluence
function as a function of fluence. And what you --
and what we see is about that about 3E to the 19, the
fluence function begins to -- the slope begins to
change and actually reaches a peak and begins to
decrease.
This point at which this inflection occurs
corresponds to the same fluence levels where the
under-prediction begins on Slide 12. It's unknown
right now whether or not the actual fluence function
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should follow that light blue line, or whether it
should increase slightly or decrease slightly. But we
know that following the dark blue line causes this,
some of this under-prediction to occur.
And the reason why this is there is
because at the time when this was developed, there was
a limited data. It was like I mentioned earlier, only
177 data points. And so when you extrapolate the
curve beyond the area in which we had data, that
behavior occurs. All right, next slide, please.
All right, so that's the main issues with
the embrittlement trend curve. I'm going to move now
to surveillance capsule. Appendix H from 10 CFR Part
50, as I mentioned earlier, requires periodic
monitoring of the changes in fracture toughness due to
neutron embrittlement. The regulation incorporates by
reference an ASTM standard, E185, that sets up the
testing surveillance schedule of details for a
program.
And these programs are typically about
three to five capsules. The capsules include material
property specimens that are placed inside the core,
closer to the core than the reactor vessel wall.
They're pulled at certain times and tested
to try to get a future behavior of embrittlement. The
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ASTM standard allows the last capsule, the final
capsule, to be pulled and tested at two times the
reactor pressure vessel design fluence.
Realizing that E185-82 was originally
really designed for 40- year lives, the last capsule --
I'm sorry, the second-to-last capsule was meant to be
tested at a fluence that was corresponding to about 40
years' life. And the last capsule therefore could be
tested at a much higher fluence.
And in fact, the ASTM standard allows for
holding and not testing that last capsule if you're
able to get the fluence, the correct fluence in the
first few capsules.
However, as we've moved to license renewal
and to subsequent license renewal, those particular
lives have changed from 40 years to 60 years and 80
years. And so that particular capsule continues to be
moved out.
In '97, the Commission made a finding
related to the Perry Plant that any time a staff
reviews a request to change a capsule withdrawal
schedule, it's limited to a verification or a
conformance kind of check to the ASTM standard. There
can't be a technical or safety check.
And because of the extended design lives,
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the change in the design fluence capsules and the
testing has been repeatedly delayed in some cases to
achieve to higher and higher fluence. Next slide,
please.
So as we went into license renewal, the
regulations --the staff decided the regulations did
not need to be changed, that the surveillance programs
could be addressed in the guidance. And the guidance
now provides flexibility to let the licensee
demonstrate adequate aging management.
Within the GALL reports, there are several
statements relating to these capsule programs. In
NUREG-1801 Rev 1, there's a statement that at least
one capsule with a projected neutron fluence equal to
or exceeding the 60- peak fluence needs to be tested --
needs to be tested.
In NUREG-2191, which is the GALL-SLR,
there's a similar statement that says withdrawal and
testing of at least one capsule with a neutron fluence
of the capsule between one and two times the peak
neutron fluence of interest at the end of the
subsequent period of operation need to be tested. And
it also specified that it's not acceptable to redirect
or postpone the withdrawal of testing to reach a
higher fluence level. Okay, next slide, please.
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What's happening in practice, however, is
that licensees are changing their capsule withdrawal
schedules prior to application. And this is only in
some cases. Prior to application for license renewal
or subsequent license renewal. And that change is
being evaluated under the current approach of
conformance, consistent with the Commission guidance
for earlier.
And then the current license basis
surveillance programs then are consistent with the
GALL program once they receive that conformance review
and approval. Next slide, please.
So this shows an example of one of those
cases. And in this particular figure, the Y axis
again is a measure of neutron fluence. The X axis is
the date at which a surveillance capsule was pulled
and tested. The black circled data points represent
one particular plant that has pulled four capsules.
And you can see theyears in which they were pulled.
Their last capsule was pulled around the
time of 2008 or so. Their fifth capsule was to be
tested at that first X, the orange X mark, which was
about 2009. And as you can see, it was moved a total
of four times, now to be tested somewhere around 2025.
There have been a lot of licensees that
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have delayed capsules. Some examples are shown on
this slide. But I do want to point out that not all
plants have delayed their withdrawal capsules. Many
have not,but some have.
And these changes have not been against
the guidance or the regulation. They have been moved
properly with the appropriate approvals. All right,
next slide, please. Hit one more time, please.
This is just another example to show of
the impact of this. This is this plot I showed
earlier of the difference between predicted and
measured embrittlement as a function of fluence. The
green lines on the plot show the four early
surveillance data points.
And what you can see is that all fourof
those fall within that range in which the
embrittlement trend curve does a good job at
predicting the embrittlement.
This particular plant's 60-year mark and
80-year mark are shown in blue. You can go one more
forward. And their fifth capsule is to be pulled in
2026, which is not until the 80- year mark, which is
about 1E to the 20th. Or they could have up to a
minus 180 degree under-prediction in their
embrittlement.
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And you can see here there's 25 years in
between when the last capsule was pulled and when the
next capsule is planned. Okay, next slide now. One
more time please.
This is a plot, again, a different way to
plot this. Embrittlement on the Y axis, on the
vertical axis, fluence on the horizontal axis. The
four data points I talked about earlier, you can see
how they are. One more time forward, please. If they
were to use Regulatory Guide 1.99 and only use the
material chemistry and the fluence, this was the
embrittlement trend that they would get, this orange
line.
The Regulatory Guide also allows them to
fit the data to adjust their embrittlement trend
curve. So if I take those four data points and I
adjust the embrittlement trend curve for those four
data points, I get the blue curve, which they can use.
So at 1E to the 20th, they have a embrittlement
measurement of about 230 degrees Fahrenheit.
If they were to test it and the tests were
to show the under-prediction that was suggested in the
previous slide, they could have about 150 degrees of
under-predicted fromtheir --from that blue line or
the adjusted embrittlement check.
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If I assume those two data points are
actual and I refit those using the procedures in
Regulatory Guide 1.99 Rev 2, I would get this yellow
line. Even with this yellow line, I still have under-
prediction of -- hit one more time please. I still
have an under-prediction of about 75 degrees, because
again, the fluence function does not properly predict
the behavior of the embrittlement.
Because of that flattening off and
decrease, the embrittlement trend -- or even when I
fit the data would not be an appropriate fit. In
actuality, the data would be a not credible because of
the differences between the data and embrittlement
trend curves, and the Regulatory Guide 1.99 would tell
them to go back and use the original curve, the orange
curve.
So there could be, even if we have the
data, there could still be issues with the
embrittlement trend predicting -- under-predicting the
actual behavior. Next slide, please.
So with those two issues that I talked
about, the under-prediction in embrittlement from
Regulatory Guide 1.99 and the same trend curve which
is in 50.61, and this issue with delaying the capsules
in Appendix H surveillance programs, the staff wanted
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to understand what the combined impacts were on
safety. And they used a risk-informed approach that
leveraged the five principles of risk-informed
decisionmaking.
And we wanted to make sure that not only
did we look at these five principles, but we kept in
mind the conditions in which this -- these issues were
of concern. And so we tried to choose a targeted
sample of plants to do this analysis on and use the
data that we had, but there was much plant-specific
information that was not available. And I'll talk a
little bit about that in terms of uncertainty here in
a couple of minutes. Next slide, please.
One of the main assumptions that we used
at the beginning was we wanted to compare the
embrittlement trend curve results from 1.99 to ASTM
E900-15 embrittlement trend curve. And we did that
because the staff found that this particular trend
curve provided the most accurate characterization of
the database of material.
This database of material that I've shown
here was what ASTM used in making -- in developing
this particular embrittlement trend curve. And the
staff report where the staff did this evaluation is
shown below. The ML number for that is shown below.
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And what the data shows here is that -- is
that the predictions are good for most of the fluence
levels. Even the standard deviations seem relatively
reasonable if you don't see that dropoff in either the
base metals or the welds. So we wanted to use this as
a baseline. Next slide, please.
So the assumption that we used in the
analysis was we targeted a sample of 21 plants. We
focused on high fluence plants, because again, this
issue seems to be focused on fluences that were
greater than about 3E to the 19. But we included some
low copper plants or plants that weren't accessible to
embrittlement, and some BWRs to kind of round out the
sample of plants that we looked at.
And we -- from those samples and the data
we had, we determined the changes in this adjusted
reference temperature, or this transition temperature
shift from moving from (inaudible) --I'm sorry, can
everybody still hear me? I had a lot of static come
through the line.
MS. OLMSTEAD: Yes, I can hear you now.
MR. RUDLAND: Okay, all right, I'm sorry.
I don't know where that static came from.
And so we calculated what the switch in
adjusted reference temperature was from going from
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Regulatory Guide 1.99 Rev 2 to E900- 15. And we titled
that the embrittlement shift delta, and we used this
embrittlement shift delta to benchmark and to focus
our risk analyses. Can we go to the next slide,
please.
So what we found out from this is that
there is a tendency for the reference temperatures
that we're talking about to increase when switching
from Regulatory Guide 1.99 to ASTM E900-15. And we
say it's a tendency. It didn't happen in all cases,
but on average it seemed to -- the reference
temperature seemed to increase. And the base metals
were more likely to see that increase than the weld
metals.
Most of the cases only had a shift that
was about 50 degrees. There were some that had more
than 50 degrees, but not very many. And those that
did have a shift of more than 50 degrees tended to be
fluences that were around 6E to the 19. And I'll talk
about the impacts of that in one second.
But this range of ESDs, or the
embrittlement shift deltas, is what we assumed in the
risk study that I'll talk about here in a second.
Next slide.
So the staff did a variety of probablistic
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fracture mechanics analyses looking at these impacts.
They looked a variety of conditions, a variety of
transients. Looked at a variety of flaw sizes, both
1/4T flaws and small surface breaking flaws, to
determine if their -- determine what the impact was
going to be.
This particular plot is for a 103 per hour
cool down where the transient follows the PT curve.
If you could hit the next slide, please. So for this
particular plot, there is a -- there's two things.
There's the conditional probability of failure curves
and conditional probability of initiation.
And for the conditional probability of
failure, a 50-degree embrittlement shift delta gave
about two orders of magnitude, or two, or two and a
half orders of magnitude change in the conditional
probability of the failure.
At 150 degrees, if you hit the slide
again, please, there is about six order of magnitude
changes. So it's relatively a large change in
additional probabilities of failure for these
embrittlement shift deltas. But there's a lot of
uncertainties. The main one is the frequency of the
The frequency of following the PT curve
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during cool down is very low. And so what that is is
it's still a little bit uncertain. There's a lot of
plant fluence variations. We're unsure if these
analyses are bounding. There's a lot of plant-
specific considerations that need to be taken into
account.
And as always, we know that there are
administrative and operational controls in place
against violating PT limit curves and how much
protection do those --do those really give.
Details of this analysis, there's a
summary slide the next slide, but the details of this
analysis can be found in the reference that's shown at
the bottom of this slide. And the ML number is given
there.
So the summary of the results, if you go
to the next slide, illustrates that in most cases, the
conditional probability of failure was low or less
than 1E to the minus 6 from those conditions. And for
those conditions that were greater than 1E to the
minus6, there was some uncertainty.
But the staff felt that through-wall crack
frequency, which again is the conditional probability
of failure times the transient frequency, remains
below 1E to the minus 6. But we felt a bit
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uncomfortable because of these uncertainties.
There needed to be some additional
information that may be required to determine for at
high cool down rates it might be possible. And to
really understand what the event frequencies are, in
all cases, not just following the PT curve, will help
us to gain confidence that the risks are low. All
right, next slide, please.
We also looked at pressurized thermal
shock. That prior slide was for normal operations.
In pressurized thermal shock, again, 10 CFR 50.61 uses
the same embrittlement trend curve for as Reg Guide
1.99. And this RT-PTS that is calculated in that
regulation might be impacted.
There's a screening criteria which is
shown here of 270 degrees F for -- plates, forgings
and axial welds at 300 degrees F for circ welds might
be impacted. And actually if the embrittlement trend
curve was changed, some might actually pass this
screening environment.
However, for the sample that we took, for
the plant that we sampled, we calculated the through-
wall crack frequencies for pressurized thermal shock
with the corrected embrittlement, and it was less than
1E to minus 6 for all cases investigated. So the risk
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for pressurized thermal shock for these issues is
relatively low. All right, next slide.
So even though the risks are low, the
uncertainties are high, and the uncertainties are
increasing with time. And really taking care and
fixing these issues will help us maintain the --the
fundamental safety principles that went into
developing the regulations and the basis for plant
design and operation.
And really, safety margins that we need to
take a look at, as provided by the regulation, provide
reasonable assurance against brittle fracture. All
right, next slide.
I'm going to illustrate what I'm talking
about in this particular -- in this particular way.
This particular plot showed an illustration of a
pressure-temperature curve. The area to the right,
typical operating window, shows, excuse me, the area
in which typical plantscool down. So they'll start
at a high pressure, high temperature and decrease the
pressure and temperature to stay inside this window.
Next, please.
There is a structural limit, and that
structural limit is where if they -- if the particular
plant were to cool down too fast and not reduce
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pressure, they may pass that structural limit and have
a large chance of a brittle fracture. Hit, go again.
The orange curve demonstrates an accurate
PT curve, and that accurate PT curve provides
significant margin -- can you hit one more time,
please. Provides adequate margin between the
structural limit and the operating behavior. And you
notice there still is some gap between the PT curve
and the operating window, and that is usually due to
operational limits. Can you hit again, please.
And that adequate margin that we have
between the structural limit and the regulated PT
curve is directly proportional to each other. So that
the margin and the uncertainty are well aligned. One
more time, please.
However, if we use the current Reg Guide
1.99 and you have a condition where you are under-
predicted the behavior, you can have a PT curve that
shows -- that's shown like this. One more time,
please.
And while this line defines the operating
margin between the PT curve viewed in Reg Guide 1.99
and the operating window, you may actually have a
smaller operating window because the actual PT would
be the orange line. And the margin to structural
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failure -- hit one more time please. The margin is
actually reduced due to this under-prediction. And
that is going against typically how we develop
margins. You can hit more time please.
Typically as the margins -- as the
uncertainty increases, we like to have larger margins
since we -- since we're uncertain. But in this
particular case, the margin is decreasing while the
uncertainty is increasing.
And this increase in uncertainty and
reduction of margin is leading us to evaluate the
behaviors in these two --in both Appendix H and the
embrittlement trend curves in Reg Guide 1.99. Okay,
next slide, please.
And again, we also could talk about
performance monitoring. Appendix H, as I mentioned
earlier, allows for the periodic testing, which allows
us to make sure that an analysis remains valid and the
that the embrittlement trend curves properly predict
the plant-specific behavior, and to make sure that
there's no unexpected safety issues that may occur.
To delay capsule withdrawals or having an
extended period between capsule withdrawals represents
a lack of performance monitoring. Next slide, please.
So in summary, and the with the current
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state of knowledge, the generalized analysis suggests
that the overall risk of brittle fracture is low. The
uncertainty really is high, butit's increasing with
time, especially with the conditions that may be
occurring at high fluence with an under-prediction in
the Reg Guide trend curve and the delaying of
surveillance capsules.
In our particular analyses, though, the
plant-specific details really were not considered
because we didn't have a lot of information. We used
the information that we had. And so that adds to the
uncertainty that we had. And under certain
conditions, the safety margins may be impacted and are
probably decreasing as the uncertainty increases.
As I mentioned, delaying capsules
represents a lack of sufficient performance
monitoring. But most of these issues are focused on
plants or conditions where the fluences are excess of
6E to the 19 neutrons per centimeter squared. All
right, next slide, please.
So who is impacted? Using some data from
the MRP, we can estimate that at about 60 years, about
nine percent of the PWRs surpass the fluence level of
6E to the 19 neutrons per centimeter squared at the ID
surface. Andby 80 years it's about 34%.
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The differences between the columns to the
left and the columns to the right are the BWRs, which
really are not impacted by this because they are --
they operate and will operate through at least 80
years at a much lower fluence.
For those percentages of the -- of the
plants that I'm talking about, plant-specific details,
such as remaining material and other things, really
may contribute to which plants are impacted. And
again, more work is needed to determine how or if any
of those plants are truly impacted.
In terms of surveillance data, any plant
that has renewed its license that chooses to delay the
last capsule will be impacted. Those plants that are
in an integrated surveillance program will not, will
not be impacted. All right, next slide, please.
So what are our goals? Again, like I
mentioned early on, the staff feel that the
regulations are sufficient for a reasonable assurance
of adequate protection against brittle fracture. But
we want to make sure that as we move on into the
future -- as we move on into the future we continue to
have reasonable assurance.
So we want to provide remedies to the
identified solution --to the identified issues with
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the RPV surveillance requirements and the under-
predictions of embrittlement. We want to do that on a
risk-informed performance basis.
And we want to make sure that we don't
impact those plants that are not adversely affected.
The plants that have surveillance data that covers the
end of their license fluence level, and/or those that
may have a fluence that's less than 3E to the 19th --
3E to the 19th neutrons per centimeter squared. Next
slide, please.
So the staff is considering options, and
those options can range from a plant-specific action,
maybe a focused regulatory action, generic
communication, or possibly no action. So within this
discussion, we'd like to talk about these kinds of
things. If we can go to the next slide please.
Some of the things that we would like to
talk about are the options that I just mentioned of
whether or not the staff's approach that we took.
Looking at this thing holistically is appropriate,
seems to be appropriate. Are there other options that
we have not considered, or that we should consider?
Are there any other potential impacts to the plant
that need to be considered that we didn't consider
already? Unnecessary updates to PT limits is just one
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of those.
And is this the right time to pursue these
-- to purse these issues and to make a change on these
issues. I need to say again that the NRC is right now
is not actively soliciting any comments towards a
regulatory decision at this meeting. This is more of
a information-gathering session to understand people's
point of view. Okay, next slide, please.
Okay, so in summary, as I mentioned
earlier, the staff has high confidence that the
operating plants remain safe and that recent licensing
actions remain valid. The issues that I described
here may impact the staff's confidence in about ten
years that the integrity of the vessel for longterm
operation because of safety margins and performance
monitoring may be impacted.
We need to do further work, especially
plant-specific work, to determine which plants are
impacted, but we want to be proactive, and we want to
be able to assure continued reasonable assurance and
do that through a risk-informed, performance-based
solution.
We are considering options. Our desire
has been and will always be to try to focus that
solution on only those conditions that are impacted by
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this issue.
I think that's my last slide. There's no
next slide. Okay, so that's the end of my
presentation. I need to now turn the presentation
over to Elliot Long from EPRI. Elliot Long is a
Principal Technical Leader at EPRI. He will be making
a presentation on behalf of EPRI.
MS. OLMSTEAD: Thank you, David.
Operator, can you please unmute Elliot Long's line,
please.
OPERATOR: Elliot Long, your line is now
open.
MR. LONG: Hello, everyone, can you hear
me clearly?
MS. OLMSTEAD: Yes, we can.
MR. LONG: Excellent.
MS. OLMSTEAD: Elliot, I cannot hear you
now, though.
MR. LONG: (Simultaneous speaking.)
PARTICIPANT: Elliot's slides.
MR. LONG: On the --
MS. OLMSTEAD: Yes. All right, we see the
slides now. And can you put them on the slide view.
Okay. All right, that should work, Elliot. Thank
you.
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MR. LONG: Thank you all very much. As
was noted, I am Elliot Long. I am a Principal
Technical Leader with the Electric Power Research
Institute, and I'm going to make a presentation today
discussing some of the industry initiatives to help
generate highfluence data. So next slide, please.
As I noted, we have two ongoing industry
and EPRI MRP initiatives to generate additional
sources of high fluence capsule data. The first of
these is the Coordinated Reactor Vessel Surveillance
Program. And then the second is the PWR Supplemental
Surveillance Program, or PSSP.
I also want to revisit the conclusion made
by our colleague, my colleague Kim Hardin back in
November of 2019 at the ACRS meeting, and then talk
briefly about the potential impact of PT limit curve
as it regards to this current issue.
Before I move forward, you'll see the red
star. I don't have much about BWR units in this, it's
mostly a PWR discussion. However, the BWR units do
have an NRC-approved ISP, Integrated Surveillance
Program, through60 years of operation. In addition
to that, there is an implementation plan for
subsequent license renewal that has also been accepted
by NRC. I see the report title there.
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The second report does note that the
highest BWR units will not exceed the threshold for
fluence of 6 times 10 to the 19th during (inaudible)
an SLR time period. I just wanted to point that out
that we'll mostly be focusing on PWRs here. And I do
have some additional information on slide 12 in regard
to that fluencetopic. Next slide, please.
So we'll first talk about the CRVSP,
Coordinated Reactor Vessel Surveillance Program, as
documented in MRP-326, now Revision 1. Next slide.
The original intention of this program was
to optimize the remaining and existing US PWR
surveillance capsule withdrawal schedule to increase
the amount of high fluence data that can be generated
by the remaining capsule. This new data can then be
used to inform embrittlement trend correlations and
generate data from 60-plus years of operation.
The original revision from 2011 did just
that, wherein we reviewed every US plan, PWR plan,
surveillance capsule schedule and recommended changes
to maximize and optimize the high fluence data that
can be achieved by the current capsules that remain
through 2025. This year, the EPRI MRP did a revision
to this report, basically to review how we did, what
has happened, what's changed, what's left to do, and
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see if anything needs to be updated to continue moving
forward with plan.
The updates include checking the evaluated
capsule since 2011, revisiting future capsule pull
schedules, documenting updated capsule fluence values,
and then assessing the impact of closed or to-be
closed plants on the overall plan. Next slide.
As you can see, we have now tested 16 out
of the 30 CRVSP capsules. They're either already
tested or planned to be tested. The remaining 14,
there are 14 left of these, about half will not be
tested for a variety of reasons. Some due to plant
shutdown, some have been delayed beyond 2025.
In summary, as of this summer, we have 48
capsules in the US that have a tested fluence greater
than 3 times 10 to the 19th. Four of these are over
- 8. By 2025, those remaining seven CVRSP capsules will
also be tested at fluences greater than 3E 19, and two
of those will be over 8 times 10 to the 19th.
This report also did a first update to the
schedule for when the PSSP PWR Supplemental
Surveillance Program capsules will be withdrawn. The
first one will be Farley One, Capsule P, in the spring
of 2027. And then in the following fall of 2028,
Shearon Harris Capsule P will be ready.
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And that leads me into the next slide,
where we discuss the PSSP. So next slide again. This
program was developed to generate additional again
high fluence data that has a very similar objective to
the prior program, inform future ETC development
applicable to the RPVs at higher fluence.
This one was a targeted approach designed
to fill in the gaps of materials in the capsule
database.It also was designed to irradiate these
materials in commercial reactors since we were
generating data from commercial reactors and not from
test reactors.
The end game really says it all, we
fabricated two supplemental capsules and irradiated
them for ten years. That's the current status before
we withdrawal test and evaluate those materials.
These two capsules contain 288 Charpy Specimens from
27 unique plates, forgings, and welds.
The data will ultimately yield 24 new
transition temperature shift results, and then three
of the materials will shift just generate an upper
shelf energy.
You can see the fluence ranges at the
bottom. I will stress that all of the materials in
these capsules were from previously irradiated and
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tested surveillance capsules. So they were already
irradiated at a plant.
They were refabricated into new specimens
and are going back in to generate the higher fluence
levels shown there, 4.5 on 10 the 19th upward to 1.2
to the 20. So each individual component will have its
own unique fluence value. Next slide, please.
So as I said, the program fabricated two
supplemental capsules containing previously irradiated
and reconstituted PWR materials. The EPRI MRP
sponsored the fabrication and the host plans are shown
there.
Farley One went in in October of 2016. So
it'll have about 11 years, ten and a half of
irradiation. And then Shearon Harris has the second
one. It'll also have about a little under ten years
of irradiation in that vessel. The published report
was shown there in 2016. Please go to the next slide.
2027, the Farley Capsule P will be
withdrawn and Shearon Harris in 2028. You can see at
the right we took broken Charpy Specimens, the top
right image, machined one half of one side down to an
insert, so that middle piece is actually the material
of interest. We then welded end tabs of standard
material on either side both into the middle picture.
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Machined them flush and cut them to standard Charpy
size.
These are the materials, the 288 of the
bottom image there on the first caption, the first
figure, are in the capsule. They're going to be
evaluated starting into '27, 2027 and 2028. It'll
take a couple of years to get all that analysis done.
Hope to have the two capsule reports ready
towards the middle within 18 months of the withdrawal.
And then we'll spend the early part of the 2030s
evaluating the data and the impact on any future ETCs
for the existing ones or the need to develop new ones.
And then I showed just a picture on the
bottom right of what the capsule looks like seated in
its holder in the vessel. Go on to the next slide,
please.
Now I want to revisit what was discussed
at the November 2019 ACRS meeting that EPRI
participated in with my colleague Tim Hardin. I
summarized the conclusions and recommendations from
the final slide of that meeting on the right.
These conclusions have not changed from
EPRI's perspective. If a future revision to the Reg
Guide is implemented, E900-15 remains the preferred
ETC model as of today. That's consistent with the
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NRC's views as well.
It is understood that this, the target
fluence is 6 times 10 to the 19th. Below that, the
Reg Guide remains adequate for predicting
embrittlement.
And I do went to focus then if 6 times 10
to the 19th is the level and we're worried again about
PT limit curves, 10 CFR 50 Appendix G, the appropriate
metric is the 1/4T fluence. So I felt it appropriate
to determine when certain plant designs will see that
fluence level at the 1/4T. So go on to the next
slide, please.
This chart at the right shows the surface
fluence value needed to generate a 1/4T and 3/4T
fluence of 6 times 10 to the 19th using the
attenuations formulas in the current Reg Guide.
As you can see, the various designs of PWR
reactors in the US, the 2 and 3 loop WEC, B&W, the
various 4 loops, and some of CEs all have different
vessel thicknesses, ranging from a 62 inch thick
vessel up to an 11.2. The 1/4T fluence of 6 times 10
to 19th necessary and the surface fluence necessary to
hit that is listed under the 1/4T column.
So for instance, a WEC-4loop with a B&W
fabricated vessel needs a surface fluence of 9.99 E19
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to hit a 1/4T fluence of 6 times 10 to the 19th. So I
then looked at which plants have submitted for SLR and
what their SLR fluence would be. And thus far, only
one of the six PWRs would ever hit the necessary
surface fluence to achieve a 1/4T fluence of 6 times
10 to the 19th.
And even that one plant, plant A, is going
to take upwards of 65 EFPY (inaudible) are well into
the SLR operating period, well into the future before
that would occur.
You can also see from this chart a 3/4T,
which is governing for the heat-up limitations, it
seems like there would never be an issue. And in
things that will never be an issue as well, in the
bottom, BWR plants will never reach these fluence
levels as well in any reasonable timeframe. The BWR
SLR plant fluence is less than 5 times 10 to the 18th
neutrons per centimeters squared at the surface.
So I just wanted to summarize when this
could become an issue when you look at the 1/4T
fluence and the surface fluence necessary to hit that
value.
And that's all that I had for today.
Thank you.
MS. OLMSTEAD: Thank you, Mr. Long. Now
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Satira Labib from Duke Energy will make some
presentation. And I'll ask the Operator to unmute Mr.
Labib's line.
OPERATOR: Your line is now open.
MS. LABIB: Can you hear me?
MS. OLMSTEAD: Yes, we can.
MS. LABIB: Yes. I'm Satira Labib from
Duke Energy, Reactor Vessel Integrity Engineer. And
this is in regards to Slide 18 that mentioned Robinson
Nuclear Plant. So in 2011, Robinson made a commitment
to the NRC with withdraw their Capsule U when the
capsule reached the 80 year peak fluence value which
is 8E to the 19th. This commitment was made based on
recommendations listed in what Elliot just discussed,
MRP 326 to help the industry collect higher fluence
data.
RNP still intends to abide by this
commitment and withdraw Capsule U in 2024 when we
reach the aforementioned fluence value. This will
ensure that Robinson will have surveillance test data
available to cover the predicted level of vessel
fluence during the 80-year period and it should also
be noted that the projected 60-year fluence is below
the 6E to the 19th which is mentioned in this
presentation. And the value above which the under
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prediction of embrittlement is considered to be found
significant. That's my only comment.
Thank you.
MS. OLMSTEAD: Thank you very much, Ms.
Labib. And now I understand Mr. Paul Gunter from
Beyond Nuclear would like to make a presentation and I
will ask the operator to unmute his line.
OPERATOR: Paul, your line is now open.
MR. GUNTER: Hello, can you hear me?
MS. OLMSTEAD: Yes, we can.
MR. GUNTER: Thank you. I don't really
have a presentation per se, but you know, this is
quite a complex subject here. And I'm participating
mostly for my education and coming a little bit
farther up on the issue.
I understand that per usual I can ask
questions of the Nuclear Regulatory Commission, but I
wanted to start to see if I could ask a question of
EPRI. Is that permitted? If not, I could perhaps --
if EPRI can't answer, perhaps NRC could.
But on Slide 4 of EPRI's presentation,
there's a bullet point there update to the evaluation
includes, and I'm looking at the fourth point, their
analysis of closed or to be closed plants. And I'm
wondering with I could get a comment from either EPRI
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or from the Nuclear Regulatory Commission what
analysis we're talking about there or if, in fact,
there's another reference where I could go to get a
better understanding of this update. Because I didn't
hear the update in the presentation. So that's a
question.
MR. RUDLAND: Paul, this is Dave Rudland.
At this type of meeting, I believe we can ask
questions to EPRI, but they don't need to respond.
The questions should be directed towards the NRC.
And in fact, we have a section in a moment
to do a question and answer session. So if you wanted
to wait just a few seconds, we could do that. I
wanted to make sure you were finished with any
comments that you had or statements that you wanted to
make before we moved into the question and answer
section.
MR. GUNTER: Well, let me just say then to
cut to the chase here to get to that question. You
know, our main concern as an interested public
advocate for public safety and environment protection,
the subsequent license renewal proceedings are going
ahead right now and I understand that you're saying
that you're projecting loss of margin and offering
reasonable assurance. But the fact that clearly, you
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have a performance inadequacy that has been identified
and the -- but the public only has this shot at the
subsequent license renewal window which is closing.
And so while there is a concern that was
voiced in this meeting that the Agency has defined a
performance issue by delaying these capsules and
you're saying they've been delayed already 25 years,
but we don't really know -- you're still working on
your formula, so we don't really know how much longer
this delay is going to be, but at the same time, the
windows for the public due process are closing on age
management programs which include reactor pressure
vessel embrittlement and how your age management
programs are falling behind at present.
So I'm raising that as a concern that
you're providing yourself the luxury for the licensees
to proceed through the review process. It's a little
like paving the road as you travel, as you move right
through the public process. So I'm raising that as a
concern and that will conclude my comment.
MS. OLMSTEAD: Thank you very much, Mr.
Gunter. We appreciate your statement.
And this brings us to the discussion and
question and answer portion of this meeting. I'll ask
Glenna to show Slide 37 again from the NRC slide deck.
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And that gives us some suggestions of discussion
topics for this session. And you can also ask other
questions of course.
Our operator will now give you information
on how to get into the queue for providing feedback
and asking questions for today's topics and we will
not be using the Webex chat or Q&A features, so please
enter the queue if you'd like to speak during this
meeting.
Operator?
OPERATOR: Thank you. We will now begin
the question and answer session. If you would like to
ask a question please press *1. Record your name
clearly when prompted. To withdraw your request,
please press *2.
MS. OLMSTEAD: And thank you very much.
And in an effort to ensure that we hear from as many
people as possible, we ask that participants limit
their feedback and questions to about three to five
minutes. After that, you can always reenter the queue
and speak again as time permits.
And first, I'd like to turn to Mr. Scott
for now to see if he received any questions from the
public by email during today's presentation.
MR. BURNELL: Thank you, Joan. To this
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point, I have not received any emails.
MS. OLMSTEAD: All right, well, thank you.
And now I'd like to ask the operator to see if
there's anyone in the phone queue that would liketo
ask a question.
Operator, first question, please.
OPERATOR: Thank you. Your first question
comes from Paul Gunter. You're line is open and you
may ask your question.
MR. GUNTER: Thank you. I'm just going to
repeat the question that in EPRI's presentation they
talk about how they're going to update their process
for this and they outline an analysis of closed or to
be closed plants and I'm wondering if EPRI could
eliminate that or if the NRC might provide some
comments. Thanks.
MR. HISER: Paul, this is Allen Hiser with
NRC. I'm not quite certain what the bullet on that
slide meant. I know that in many cases with plants
that are shutting down, both we and the industry have
looked at the surveillance capsules that are still
available for the plant to see if there would be value
in retrieving and testing those capsules. At this
point, NRC has not found too much value in those
capsules. I'm not sure if that's the full extent of
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the EPRI activity in this area or not.
MR. GUNTER: Well, I do know that -- can I
comment and follow up?
MR. HISER: Sure.
MR. GUNTER: I do know that -- EPRI
participated in a March 7th and 8th, 2017 workshop
with the Nuclear Regulatory Commission and other
industry and regulatory stakeholders that was looking
at harvesting of decommissioning nuclear power
stations with high priority on reactor pressure
vessels. And I'm wondering where that subject has
gone to, and if in fact, this is a reference to
harvesting.
MR. HISER: I don't know if it is or not.
I know that is one area that if there happened to be
a plant that was decommissioning that we would be
interested in obtaining specimens from the reactor
pressure vessel. The problem is that the fluences on
plants that would be decommissioning are not in the
range that we have identified potential issues at
present. If we had a vessel that had a fluence of 6
times 10 to the 19th, then we would probably be very
interested in it. But there are no opportunities for
that at this point.
MR. GUNTER: Would it also be able to
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provide some insights on how neutron embrittlement is
-- you know, the EMDA report referenced how neutron
bombardment can actually penetrate a vessel wall and
then bounce off the concrete on the other side and
cause embrittlement to be working from the outer wall
of the pressure vessel or welds, so that you could --
it just seems to me that there has been interest in
harvesting samples for a whole host of insights to do
with neutron embrittlement.
Would you not see any value for being able
to capture actual data on how neutron embrittlement
could be working its way by bouncing off the concrete
and then embrittling from the outer side of the vessel
inward?
MR. HISER: I know there were studies that
had been done looking at through-wall embrittlement
effects, and I would expect that some mechanism like
you mentioned would provide evidence, would have
provided evidence in those studies. I'm familiar with
one from the 1980s because I was one of the lead
reviewers or one of the lead technical staff on it.
So I'm not sure that there would be much additional
fruit that would be gained from pulling samples from
decommissioned reactors to assess that at this point.
It may be that at some point in the future
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as plants that are decommissioning have high fluences
on them, then at that point it may become more
interesting for us. But I think at this point, those
are some of the limitations.
MR. RUDLAND: This is Dave Rudland. In
terms of what we're trying to do in this effort,
especially with looking at the way the trend curves
predict, I also have to agree with Allen, I don't see
that it would add much to this particular study.
MS. OLMSTEAD: Well, thank you very much,
everyone, for that discussion. And I'd like to go on
next to our next person in the queue, please,
operator?
OPERATOR: Thank you. And that's from
Thomas Basso. Your line is open. You may ask your
question.
MR. BASSO: Thank you. This is Thomas
Basso. I'm with the Nuclear Energy Institute. I'm
the Senior Director of Engineering and Risk. And it's
kind of a comment and a question. So we do appreciate
and support the overall approach from the holistic
risk-informed analysis approach.
So my question probably to Dave Rudland is
do you have enough information for doing this from an
risk-informed approach or what else is needed to
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ensure from a risk-informed approach that we've come
up with the appropriate way of looking at this?
Is there more --you know, is there more
work that needs to be done from the risk community or
any outstanding concerns with the overall approach?
MR. RUDLAND: Thanks, Tom. Again, this is
Dave Rudland. I don't think there's anything that's
needed --anything additional that's needed from the
risk people. I think right now our biggest concern is
plant-specific details. I think a lot of our -- some
of our uncertainty, at least in analyses that we've
done so far has been generically based and plant-
specific information I think is the best way to try to
focus that.
As I mentioned in the presentation, we
don't really know how the plants are impacted at this
point because we haven't done enough work to determine
the individual plants are meeting the conditions that
we're talking about. So I think that's where we need
to focus our efforts, but I'm not -- I don't think
getting more information from the risk folks would
help us in this particular case.
MR. BASSO: In some of my earlier
experience at a plant that I used to work at, I know
that there's significant margin built into the
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operating procedures that address having adequate
margin. But obviously, the more data we get, the more
we can refine that margin, so appreciate the efforts,
sir. Thank you.
MS. OLMSTEAD: All right, thank you very
much. And operator, could we go to the next person in
the queue?
OPERATOR: Thank you. And that's from
Christopher Koehler. Your line is open. You may ask
your question.
MR. KOEHLER: Hi, can you hear me?
MS. OLMSTEAD: Yes, we can.
MR. KOEHLER: My question is specifically
related to -- I think it was the NRC's Slide 20 or so
where you showed the Reg Guide embrittlement trend
versus a best fit embrittlement trend and how a
licensee might react to --yes, that's the one.
And you stated that if the best fit was
based on non-credible surveillance capsule data, that
the Reg Guide directs the licensee to go back to the
Reg Guide generic embrittlement trend which I think is
inconsistent with how it's actually done in practice
in which case, and this is based on the work shop
slides that -- from post-Generic Letter 92- 01 was it,
where it indicated that if you have non-credible
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surveillance data, you should use the best fit
chemistry factor from that data and then also use the
full margin term on top of that. So I just wanted to
confirm what I heard and what you intended when you
said that.
MR. RUDLAND: This is Dave Rudland.
Thanks for your comment. I do appreciate that. If
you read the words of the Reg Guide, it doesn't make
you use the non-credible chemistry factor. It says to
go back to use the chemistry factor from --that you
derived from the chemistry. However, in many cases,
the chemistry factor for the non-credible fit, I
suppose, has been used. But the Reg Guide itself does
not -- does not make -- does not force you or does not
recommend that you use the non-credible chemistry
factor.
MR. HISER: Chris, this is Allen Hiser.
Just to amplify that, obviously the goal of the
embrittlement or the surveillance program and use of
embrittlement trend curve is to get the most accurate
prediction that you have. So if you have non-credible
data that are indicating a higher embrittlement than
use of the chemistry factor from the tables in the Reg
Guide, then we would hope that plants woulduse some
more accurate representation.
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So like Dave says, the Reg Guide doesn't
say that you shall use it, but I think that clearly is
within the engineering realm of wanting to provide the
most accurate prediction.
So the workshop slides I think are still -
- provide reasonable guidance on circumstances like
that.
MR. KOEHLER: Thank you.
MS. OLMSTEAD: Thank you, too. And now
I'll ask the operator for the next person in the
queue.
OPERATOR: Certainly. And again just
press *1 to ask a question. Our next question comes
from Steven Richter. Your line is open. You may ask
your question.
MR. RICHTER: Hello, this is Steve
Richter, Energy Northwest. This question is for David
Rudland. Going through your presentation, I didn't
notice, perhaps I missed it, any discussion on heat
affected zone material. Was there a reason it was
omitted? Were you considering it bounded or just not
for the purposes of this presentation? I saw the weld
material, the base material, but not heat affected
zone. Is that a concern?
MR. RUDLAND: I think the data that we
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showed was the data that was given as part of the
development of the ASTM E900 standard. Heat affected
zone data I believe is not required through Appendix H
any more.
MR. RICHTER: Okay. So that was the
reason you left it out. That's fine. Thank you.
MR. RUDLAND: Yes.
OPERATOR: At this time, I'm showing no
further questions.
MS. OLMSTEAD: All right, I'm going to
give a couple minutes. Please press *1 if you'd like
to get in the queue again, ask further questions, or
make any other statements or provide input for us.
I do notice somebody has just joined the
queue. Operator, can you introduce them, please?
OPERATOR: Jan, your line is open. You
may ask your question.
MS. BOUDART: Thank you. I am Jan Boudart
from Nuclear Energy Information Service. And I am
looking at a paper and I was going to have it ready
exactly when it was created, but it was kind of a long
time ago. And it was also a Japanese paper. So --
oh, I don't have a date on this paper. I apologize.
But it is created by Ino Hiromitsu and it is about a
plant in Japan that there was never any consideration
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of it being reopened after the Fukushima accident.
And the reason the Japanese did not consider
restarting this plant was embrittlement or one of the
reasons. And there is a graph in this paper showing
the computer predictions of embrittlement and the
actual capsules that were taken out of this plant.
The name of the plant is Genkai 1.
And the last capsule that was taken out
was so far above the predicted embrittlement that this
is one of the things that influenced TEPCO in deciding
not to reopen Genkai.
And so I just have a couple of comments
about this that I would like to clear up. Number one,
the Genkai graph is based on years, not on fluence.
And I think that there has to be a justification for
using fluence instead of years. And I wanted to point
out that the 19th power is 10 times greater than the
18th power so that a huge amount of time will elapse
from the time the fluence reaches the 18th power to
the time it reaches the 19th power.
And I'm questioning whether that enormous
increase in fluence would even occur in human history.
I mean I don't know how long it takes for the fluence
to reach these levels. And I was wondering if you
could give us some examples of fluences that have been
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reached in real time, I mean like when did such and
such a plant reach the 18th power? And when did such
and such a plant reach the 17th power? And how long
was the interval between reaching the 17th and the
18th? And how long does it take to get from one
exponent to the next higher exponent especially when
you're going from 18 to 19? Can someone estimate the
amount of time it would take to go from the 18th to
the 19th power? That's my question.
MR. HISER: This is Allen Hiser. I'll take
the first crack at it. The fluences depend on the
design of the reactor, how large the reactor vessel
is, how much water is between the core and the vessel.
So many BWR plants, which I'm assuming Genkai reactor
may be, would be on the order of 10 to the 18th at 40
years or 60 years of operation. BWRs also have a
variety of fluence levels. For example, just one that
I'm familiar with, the Turkey Point plants, at about
60 years, the fluence is about 6 times 10 to the 19th.
To go from 10 to the 18th to 10 to the 19th, there is
no set number of years. It's just a factor of ten in
the operation of the plant. So if a plant reached 10
to the 18th in 40 years, it would take them 400 years
to get to get to 10 to the 19th.
MS. BOUDART: Say that last part again,
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please, Mr. Hiser?
MR. HISER: It would be 10 times the
operating period to go from 10 times 10 to the 18th to
10 times 10 to the 19th.
MS. BOUDART: And has Turkey Point been
going for 60 years?
MR. HISER: They are about 50 years at
this point.
MS. BOUDART: And do you have a fluence
measure for them at 50 years?
MR. HISER: My guess is somewhere around 5
times 10 to the 19th.
MS. BOUDART: Five times 10 to the 19th?
Oh, yes, because the coefficient is something --
what's the coefficient? I didn't remember that. Nine
point something?
MR. HISER: Five times 10 to the 19th.
MS. BOUDART: Okay. Well, okay. So --
okay. And then I'm asking you to repeat again. You
said Turkey Point is 5 times 10 to the 19th for a long
time. How long -- I'm sorry to repeat this question.
Maybe you answered it and I didn't pick it up.
How long does it take a reactor like at
Turkey Point to go from 10 to the 18th to 10 to the
19th? I'm sorry, I know you said this, but I missed
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it.
MR. HISER: It would be -- let's see. It
probably was about year one that they were about 10
times 10 to the 18th, approximately.Then about year
10 when they would have been about 1 times 10 to the
19th. And these are guesstimates from recollection.
MS. BOUDART: Certainly, there were
capsules that were taken out -- oh, that would be a
different measurement though, the measurement of
brittleness, but not a measurement of fluence.
Okay, and then can you explain why you
have decided to go with fluence instead of time?
MR. HISER: Fluence is a measure of the
number of neutrons that have hit the reactor vessel
and so that correlates with the damage. If the
reactor is shut down for outages, it accumulates no
additional fluence. So it doesn't --
MS. BOUDART: Right.
MR. HISER: There's no real strong
correlation with time. It's really how much time the
plant operators.
MS. BOUDART: Okay. I appreciate your
answer. Thank you so much.
MR. HISER: Okay.
MS. OLMSTEAD: And thank you very much for
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your statement, Ms. Boudart.
And now I don't see anyone else in the
queue. I'll give people a few more minutes. Please
press *1 if you'd like to get in the queue and make a
statement or ask any questions.
Operator, do we have someone else in the
queue?
OPERATOR: We do. Michael Guthrie, your
line is open. You may ask your question.
MR. GUTHRIE: Hello. This is Michael
Guthrie with Dominion Energy. I have a question
regarding the value of 6 times 10 to the 19th that's
in the NRC presentation. Are you referring to inside
surface fluence or are you talking about 1/4 T fluence
as Elliot Long was referring to?
MR. RUDLAND: This is Dave Rudland. The
number that we were referring to was just the fluence
level in which the under prediction of the
embrittlement trend curve becomes statistically
significant, whether it occurs --no matter where it
occurs it's throughout the wall. We were just looking
at the point at which the prediction becomes non-
conservative. So if you're looking at PT curves, it
1/4 T. If you're looking at PTS, it's ID surface.
MR. GUTHRIE: Thank you. That clears it
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up.
MS. OLMSTEAD: And thank you. Operator,
is there anyone else in the queue?
OPERATOR: At this time, I'm showing no
further questions.
MS. OLMSTEAD: I'll give a couple more
minutes. Please press *1 if you'd like to get in the
queue to ask a question or make a statement. And if
we don't have anyone else showing up, I'll probably
start closing the meeting.
Operator, do we have anyone else in the
queue?
OPERATOR: At this time, I'm showing no
further questions.
MS. OLMSTEAD: All right, I'm just
checking on something and -- all right, it looks like
we don't have anyone else in the queue.
So please, Glenna, can you put up NRC
Slide 39?
All right, and as you can see on this
slide, to find more information about this meeting,
you can go to this website, regulations.gov and look
at the docket number, NRC-2021- 0174. Now the NRC will
post today's meeting summary and transcript within 30
days from today on the regulations.gov site.
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And please note that while the
regulations.gov's standard template mentions comments,
we will not be taking comments for this project at
this website.
Slide 40, please. I'd like to remind
everyone to fill out your meeting feedback forms
located at the NRC's recently held public meetings
webpage for this meeting's announcements. Your input
helps us improve future NRC public meetings.
Next slide, please. And these are some
contacts if you want to contact these people for more
information about this topic.
And thank you all for your attendance at
today's meeting. We very much appreciate your time
and feedback and we will carefully consider today's
discussion and look forward to engaging more with you
in the coming months. Thank you.
And that will end our meeting for today.
(Whereupon, the above-entitled matter went
off the record at 2:48 p.m.)
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