ML25324A407
| ML25324A407 | |
| Person / Time | |
|---|---|
| Site: | Kemmerer File:TerraPower icon.png |
| Issue date: | 11/05/2025 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| Download: ML25324A407 (1) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards Open Session Docket Number:
(n/a)
Location:
teleconference Date:
Wednesday, November 5, 2025 Work Order No.:
NRC-n/a Pages 1-73 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W.
Washington, D.C. 20009 (202) 234-4433
NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
(202) 234-4433 WASHINGTON, D.C. 20005-3701 www.nealrgross.com 1
1 2
3 DISCLAIMER 4
5 6
UNITED STATES NUCLEAR REGULATORY COMMISSIONS 7
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 8
9 10 The contents of this transcript of the 11 proceeding of the United States Nuclear Regulatory 12 Commission Advisory Committee on Reactor Safeguards, 13 as reported herein, is a record of the discussions 14 recorded at the meeting.
15 16 This transcript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.
19 20 21 22 23
1 UNITED STATES OF AMERICA 1
NUCLEAR REGULATORY COMMISSION 2
+ + + + +
3 730TH MEETING 4
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 5
(ACRS) 6
+ + + + +
7 OPEN SESSION 8
+ + + + +
9 WEDNESDAY, NOVEMBER 5, 2025 10
+ + + + +
11 The Committee met via Video-12 Teleconference, at 8:30 a.m. EST, Walter Kirchner, 13 Chair, presiding.
14 MEMBERS PRESENT:
15 WALTER L. KIRCHNER, Chair 16 GREGORY H. HALNON, Vice Chair 17 VICKI M. BIER, Member 18 VESNA B. DIMITRIJEVIC, Member 19 CRAIG D. HARRINGTON, Member 20 ROBERT P. MARTIN, Member 21 SCOTT P. PALMTAG, Member 22 DAVID A. PETTI, Member 23 THOMAS E. ROBERTS, Member 24 MATTHEW W. SUNSERI, Member 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
2 DESIGNATED FEDERAL OFFICIAL:
3 ALSO PRESENT:
4 JOSH BORROMEO, NRR 5
EDWIN LYMAN, Public Participant 6
7 8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
3 P-R-O-C-E-E-D-I-N-G-S 1
8:30 a.m.
2 CHAIR KIRCHNER: Good morning, the meeting 3
will now come to order. This is the first day of the 4
730th meeting of the Advisory Committee on Reactor 5
Safeguards, ACRS. I am Walt Kirchner, Chairman of the 6
ACRS.
7 Due to the continued lapse in 8
appropriations for government funding, this meeting is 9
being conducted virtually. In addition, the ACRS is 10 authorized to perform only those activities that have 11 been designated by the Agency as high priority.
12 Consequently, we have made some adjustments to the 13 meeting agenda that was published in the Federal 14 Register on October 1st, 2025. I will mention these 15 changes later in my opening remarks.
16 ACRS members participating virtually are 17 Vicki Bier, Vesna Dimitrijevic, Gregory Halnon, Craig 18 Harrington, Robert Martin, Scott Palmtag, Dave Petti, 19 Tom Roberts and Matt Sunseri. If I have missed 20 anyone, please speak up now. I note that we have a 21 quorum for today's meeting.
22 Larry Burkhart of the ACRS staff is the 23 Designated Federal Officer for this morning's full 24 Committee meeting. No member conflicts of interest 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
4 were identified for this morning.
1 The ACRS was established by the Atomic 2
Energy Act and is governed by the Federal Advisory 3
Committee Act, FACA. Under the Atomic Energy Act, 4
ACRS shall advise the Nuclear Regulatory Commission on 5
the hazards of proposed and existing reactor 6
facilities and the adequacy of proposed safety 7
standards.
8 Following Executive Order 14300, the 9
Committee has narrowed its focus to only those 10 activities necessary to fulfill its statutory 11 obligations. As a result, the ACRS is prioritizing 12 the review and reporting of new reactor facilities and 13 proposed safety standards with particular attention to 14 issues that are unique, novel and noteworthy. The 15 Committee will consider other nuclear safety matters 16 at the direction of the Commission.
17 Please note that the ACRS speaks only 18 through its published letter reports. All member 19 comments should be regarded as only the individual 20 opinion of that member and not a Committee position.
21 Information about ACRS activities, such as letters, 22 rules for meeting participation and transcripts, are 23 on the NRC public website and can be found by 24 searching About Us, ACRS on the NRC's home page.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
5 The ACRS, consistent with the Agency's 1
value of public transparency and regulation of nuclear 2
facilities, provides opportunity for public input and 3
comment during our proceedings. We have received 4
several written statements from members of the public 5
for a topic that was on the published agenda, the 6
Palisades Steam Generator Operational Assessment; 7
however, due to the lapse in appropriations, this 8
topic will no longer be addressed in this meeting.
9 The ACRS will capture these written statements in a 10 summary report and the certified minutes from this 11 meeting.
12 Another topic that was removed from the 13 original agenda is the Westinghouse Topical Report on 14 the Adaption of the FULL SPECTRUM LOCA Evaluation 15 Methodology to perform analyses of cladding rupture 16 for high burnup fuel. At this time, we are not 17 certain whether these topics will be rescheduled by 18 the ACRS at a later date. If they are rescheduled, 19 they will be posted on our public website.
20 Therefore, the only topics that remain on 21 this meeting's agenda are the Kemmerer Construction 22 Permit Application letter report and our Planning and 23 Procedures, P&P, Session. Discussions during the 24 Planning and Procedures Session will be limited to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
6 higher priority activities. There were no written 1
statements or requests to make an oral statement from 2
the public on the two topics I mentioned, any further 3
written statements may be forwarded to today's 4
Designated Federal Officer. And we have also set 5
aside time this morning for public comments.
6 Just another note about possible changes 7
to the agenda, due to the removal of the two topics I 8
just discussed, the Planning and Procedures Session 9
may be moved from Friday to tomorrow, Thursday.
10 A transcript of the meeting is being kept 11 and will be posted on our website. When addressing 12 the Committee, the participants should first identify 13 themselves and speak with sufficient clarity and 14 volume so that they may be readily heard. If you are 15 not speaking, please mute your computer on Teams. If 16 you are participating by phone, press star six to mute 17 your phone and star five to raise your hand on Teams.
18 The Teams chat feature is only for 19 communicating IT issues or brief meeting logistical 20 topics. Please do not use it for comments or 21 questions on the topics under discussion by the 22 Committee.
23 Finally, if you have any feedback for the 24 ACRS about today's meeting, we encourage you to fill 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
7 out the Public Meeting Feedback form on the NRC's 1
website.
2 Before proceeding, I would like to this 3
opportunity to acknowledge the service of one of our 4
colleagues, Member Vesna Dimitrijevic, who is 5
completing her second term this month. This will be 6
her last ACRS meeting. Vesna, your keen insights, 7
collegial interactions with members and staff and 8
especially your contributions in the PRA area where 9
you have been an expert practitioner now for many 10 years, going back to studying under Norm Rasmussen at 11 MIT, your contributions have materially helped this 12 Committee complete its work. Your views on PRA and 13 overall reactor safety are much valued and we will 14 miss you professionally and personally.
15 In particular, I will miss your long 16 distance commentary on matters before the Committee.
17 Very often you get us refocused on the substantive 18 safety matters at hand. So on behalf of the 19 Committee, Vesna, thank you very much.
20 At this point, if any of my colleagues 21 would like to make a comment, please go ahead.
22 All right, hearing none, during today's 23 meeting, the Committee will consider the Kemmerer 24 Construction Permit Application Review. And so with 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
8 that, I'll turn the Committee's deliberations over to 1
our TerraPower Subcommittee Chairman, Tom Roberts.
2 Tom, go ahead.
3 MEMBER ROBERTS: Thank you, Mr. Chairman.
4 Good morning, as Walt said, I'm going to summarize the 5
subcommittee review of the safety aspects of the 6
construction permit application for TerraPower Natrium 7
Reactor at a site in Kemmerer, Wyoming.
8 This application was accepted for review 9
by the NRC staff in May of 2024 and they intend to 10 complete the review by the end of this month. The 11 ACRS review is part of the process of NRC review of a 12 construction permit application as required by the 13 Atomic Energy Act. We focused our review on aspects 14 of the application that affect safety and are unique, 15 novel or noteworthy. Sandra, can you bring up the 16 next slide? Thank you.
17 The reactor that is proposed to be 18 constructed in Kemmerer is called a Natrium reactor.
19 It's an 840 megawatt thermal sodium fast reactor.
20 When thinking about what might be unique, novel or 21 noteworthy about it, the U.S. has experience in sodium 22 fast reactors which is leveraged by the Natrium 23 design, but much of this experience such as EBR-II, 24 the Fast Flux Test Facility, the PRISM design, are 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
9 more than 30 years old. This reactor is also the 1
first non-light water reactor power reactor to submit 2
a construction permit application, the first to use a 3
licensing modernization project as the basis for the 4
safety case and the first to use the 10 CFR 50.160 new 5
emergency planning rule for small modular reactors and 6
other new technologies.
7 We had a fairly large field of areas that 8
we could screen as novel, noteworthy or unique that 9
were worthy of review. So Sandra, next slide.
10 Back in July and September, we reviewed a 11 potential list of areas that we would define as 12 unique, novel or noteworthy and worthy of focus in our 13 review. When we looked through the documents, the 14 safety documents, the Preliminary Safety Analysis 15 Report and the Topical Reports, we came up with four 16 major areas that we thought were worthy of our focus 17 in the review. Three of them are what are generally 18 called fundamental safety functions and that's control 19 of heat generation or control of the reactivity or 20 power control for the plant.
21 Control of the heat removal, a fundamental 22 safety function, which is removal of heat once the 23 reactor has been shut down and still a significant 24 amount of decay heat that needs to be accommodated 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
10 over the next days, weeks and months.
1 For the third fundamental safety function, 2
it's retention of radionuclides which is usually known 3
as containment or in this case called a functional 4
containment. In those three areas, we had more 5
detailed sub-focus areas that I'll talk about in a 6
couple of minutes, but those were the three 7
fundamental safety functions we chose to review.
8 The last category is a little different 9
than the fundamental safety functions. It's really a 10 catch all given the use of the licensing modernization 11 project, the unique aspects of this plant design, 12 called the sufficiency of the overall safety case.
13 For example, the LMP approach is very much centered on 14 a probabilistic risk assessment and so we wanted to 15 take a look at that and then see if the overall safety 16 case, at least at the stage of the construction 17 permit, would be sufficient.
18 Then, we noted at the time, that other 19 areas may arise as a result of subcommittee 20 discussions, so I'll mention that briefly as we go on.
21 Sandra, next slide.
22 We had two subcommittee meetings. They 23 were both multi-day subcommittee meetings. One was 24 two days early in the month of October when we focused 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
11 mainly on the overall plant design and the 1
implementation of the licensing modernization project 2
approach for licensing and safety justification.
3 Then, two weeks later, we had a meeting that focused 4
mainly on structures, systems and components, where 5
the aspects of the plant design that implement the 6
safety aspect, and we also had some follow-up during 7
that week on some of the open discussion items from 8
the previous meeting.
9 Those two meetings worked, I thought, very 10 well to address the focus areas and at the end of the 11 second subcommittee meeting, we went through the 12 detailed focus areas and I'm going to go through them 13 again for the full Committee just to review how we 14 resolved the areas that we identified as focus areas.
15 Sandra, if you can go the next slide. Thank you.
16 The first fundamental safety function was 17 the control of heat generation. We identified three 18 specific areas under that heading that we thought were 19 worth poking into. One is sensitivity of reactivity 20 events. There is a long history with sodium fast 21 reactors that because of the potential for significant 22 reactivity excursion caused by either boiling of 23 sodium or core geometry changes, you could have 24 potential consequences that could affect the reactor 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
12 vessel integrity or the integrity of containment 1
potentially depending on the magnitude of that 2
excursion.
3 The plan for Natrium was to not consider 4
that in the safety basis and so we wanted to 5
understand why. We poked at that in some detail and 6
we found that there were some significant aspects of 7
the plant design that were either different than 8
previous generations of these reactors or were 9
accounted for based on more knowledge or upgraded 10 models of various phenomena. For example, the design 11 uses a metallic fuel as opposed to an oxidized fuel.
12 The metallic fuel has characteristics that the 13 Applicant and the NRC staff explained make it very 14 unlikely that even if you had a situation with core 15 melt and a reactivity potential rearrangement of fuel, 16 the likelihood of a reactivity excursion is very low 17 just because of the physical and the chemical 18 properties of the metal fuel. We go into that in a 19 little bit more detail in the draft letter that we'll 20 read in later this morning.
21 The second major aspect is that the 22 likelihood of events, because of the safety features 23 that were included in this plant make it very, very 24 unlikely to even get to the point where you're in the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
13 range of having the fuel melt that could lead to core 1
geometry changes. The Applicant evaluated some 2
scenarios that were very, very unlikely and at least 3
as of yet, they have yet to come up with a scenario 4
that would even come to that. So when you combine 5
those two arguments, it's a strong argument to not 6
bias the design for these events that are somewhat 7
hypothetical in nature.
8 The second area that we looked at in this 9
category was the claim of two means of rod insertion 10 but all the means of rod insertion were driven by the 11 same reactor protective system. While the design had 12 been evolved since the Preliminary Safety Analysis 13 Report was first written, the Applicant had added a 14 second diverse means to insert rods, so that was an 15 excellent response to that concern. That concern 16 really no longer exists.
17 Finally, the limitations on rate of rod-18 based reactivity insertion. The design includes non-19 safety interlocks to limit the rate that the rods can 20 insert reactivity to bounds that are covered in the 21 analysis and we wondered why those were non-safety, 22 given the importance of limited reactivity insertion 23 rate. During the progression of the NRC staff review, 24 the staff and the Applicant identified a need to 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
14 reassess the safety classification of these interlocks 1
and so the Applicant will re-look at that as part of 2
the analyses that go into the operating license 3
submittal. Again, that's an issue that's identified 4
and being worked, so again, that was resolved. Next 5
slide.
6 The next fundamental safety function that 7
we focused on was the heat removal safety function and 8
we identified two areas. One is the reliability of 9
passive cooling. The design is passive, relies on 10 natural circulation heat transfer so when you lose 11 electrical power, the coolant circulates naturally, 12 transfers heat through various boundaries to get out 13 to the ultimate heat sink which is the environment.
14 There are two diverse means of removing decay heat, 15 but they both rely on a combination of air flow and 16 natural circulation. We discussed that and the 17 Applicant has a plan to get the data they need and 18 further advance the design going into the operating 19 license. We didn't see any show stoppers from the 20 actions that the Applicant identified that they 21 planned to pursue during the time between now and the 22 operating license.
23 The other one was the transition from 24 forced circulation to natural circulation. The 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
15 Preliminary Safety Analysis Report defined the pump 1
coastdown as a required safety feature that by 2
coasting down the pump speed relatively gradually, you 3
could transition to natural circulation. That raised 4
the question of what if you had a pump failure that 5
precluded the ability to coast down, like a seizure of 6
the pump rod or that type of thing. The Applicant 7
identified that they were looking at, in the design of 8
the pump, enough capability in the pump such as gaps 9
around the rotor to maintain the transition even if 10 the pump were to stop rotating more suddenly. That 11 was identified in a report that was issued as a 12 supplement to the Preliminary Safety Analysis Report 13 and that was issued in the last month or two. Again, 14 based on staff questions and their own advancement of 15 the design, they were working on that. So, we thought 16 that resolved our question there. Next slide.
17 The retention of radionuclides fundamental 18 safety function is usually known as containment. This 19 design is the first sodium fast reactor to use the 20 functional containment strategy that was approved by 21 the NRC back in the 2019 time frame. We wanted to 22 understand because the functional containment concept 23 really came from different technologies, such as high-24 temperature gas reactors, we wanted to understand how 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
16 to apply the sodium fast reactor. So we poked at that 1
pretty hard. We actually looked at that in some 2
previous Topical Report reviews and then we looked at 3
it again at both of the meetings. We concluded a 4
number of things. One, is the licensing modernization 5
project methodology leverages the mechanism of source 6
term concept that evaluates based on events that are 7
deemed to be likely enough to be included, which also 8
includes assessment of the so-called cliff-edge 9
effects that I'll get to in a minute, where events 10 that aren't expected to happen but still because if 11 they did happen they would change the safety 12 performance significantly. There is a wide range of 13 events that are looked at to determine what is 14 required for containment.
15 By the time the Applicant got through that 16 process, they ended up with a containment that looked 17 a lot like prior SFR containments. When you look at 18 it, it has boundaries, barriers that are defined, that 19 are tested, that have safety classifications, although 20 they may be somewhat different than they would be 21 under the previous regime, where you would define what 22 the boundaries are and don't base them strictly on 23 analysis. But one important point is they ended up at 24 about the same place as they would have if they had 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
17 followed precedent and just designed a containment 1
that met historic characteristics of sodium fast 2
reactor containments, so that was point number one.
3 Now, point number two was looking at the 4
overall design, the reason why the LMP process came up 5
with such low risk in terms of the number of scenarios 6
and the types of scenarios that would challenge a 7
containment, was because of safety enhancements that 8
the Applicant made in the design compared to prior 9
generation SFRs. We've got in the draft letter a list 10 of some of those features, but there are significant 11 enhancements, such as redundant means of passive decay 12 heat removal, the characteristics of the metal fuel 13 that have benefits such as low amounts of stored 14 energy and, as I mentioned a couple of slides ago, 15 less of a likelihood of reaching a condition that has 16 a higher reactivity than the original core.
17 Just going through the safety 18 enhancements, it seemed reasonable that the LMP 19 produced results that supported the containment 20 design. They appear to be reasonable and they will be 21 fully validated during the operating license. We 22 ended up concluding that the approach to the 23 functional containment was reasonable for the stage of 24 design that they're at and there is confidence that 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
18 the Applicant will able to get there and finish the 1
justification as part of the operating license phase.
2 The other area on radionuclide retention 3
that we have focused on was the sodium fires. The 4
Preliminary Safety Analysis Report wasn't really clear 5
on things like guard pipes or guard vessels or those 6
types of things to have double containment to keep 7
sodium from interacting with air that could 8
potentially lead to a significant chemical explosion 9
or fire. The staff and the Applicant have been also 10 working on the same question and since we started the 11 review, there was a section added to chapter 8 of the 12 Preliminary Safety Analysis Report to more fully 13 explain their strategy and to better explain the 14 double containment that they plan to have for any area 15 that's at risk of these types of interactions. And so 16 it appeared to us that the Applicant was working on 17 the right things and there is more work to go before 18 the operating license submittal, but again it looked 19 like they had given enough to support the safety at 20 the construction permit level. Next slide.
21 The last category that we identified for 22 focus was the sufficiency of the overall safety case.
23 We focused on cliff-edge effects. If you look at the 24 LMP process, there are some relatively general 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
19 requirements in the LMP process documents to consider 1
the potential for cliff-edge effects for scenarios 2
that don't screen in based on expected frequency of 3
occurrence, but if they were to occur because of basic 4
uncertainties and the ability to define all the 5
scenarios that can
- occur, that they would 6
significantly change the outcomes of the event to the 7
extent that it would affect safety. So the Applicant 8
is required to assess those but the LMP process 9
documents are a bit light on how, so we wanted to hear 10 from the Applicant on how they're handling that.
11 And the next focus area, I'll cover the 12 two together, which was related but a little bit 13 different so we had to call it out as a separate sub-14 focus, is the Applicant defined a subset of events 15 that they called other quantified events. They were 16 events that were included that were below the 17 frequency thresholds that the LMP process required to 18 be considered as licensing basis events. But it 19 wasn't entirely clear what their criteria were for 20 them and so we wanted to understand better what those 21 were. Those two had really the same discussion and 22 resolution in the subcommittee meeting.
23 Basically, their approach is anything in 24 their PRA, any sequence of events they could think of, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
20 they included as another quantified event. That would 1
include cliff-edge effects, things that might test the 2
adequacy of defense-in-depth, those types of things 3
because they basically didn't screen anything out from 4
the standpoint of considering them as other quantified 5
events.
6 In terms of the criteria, their accepted 7
criteria was -- a little back of background, the 8
licensing modernization program uses a frequency-9 consequence curve that says that basically the less 10 frequent you think an event is, the more consequence 11 you could tolerate and there is a frequency cutoff 12 which is 5 times 10 to the minus 7 or 1 in 2 million 13 years. So, an event that is less frequent than 1 in 14 2 million years has no dose criterion. An event that 15 is right at that threshold, 1 in 2 million years has 16 a threshold of roughly 1,000 rem over 30 days at the 17 site boundary.
18 What the Applicant did was they took that 19 1,000 rem criterion for the cutoff frequency and 20 applied it to every OQE, every event. So, basically 21 any event they could think of, if it ends up being as 22 bad as what would be allowed at the frequency cutoff, 23 they will assess whether or not design changes are 24 warranted to improve defense-in-depth or make the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
21 frequency less, so make it less likely.
1 That seemed like a reasonable approach and 2
they also pointed out they hadn't found anything yet 3
that would have that kind of dose based on the nature 4
of their design and so there's more work yet to go to 5
confirm that, but thought it was a reasonable approach 6
to be thinking about it from that standpoint that no 7
matter what the perceived frequency is, they will look 8
at it and the dose consequence if it ends up being 9
what would be allowable within the space of a 10 licensing basis event, they will assess actions.
11 Again, we thought that covered that item.
12 The last item that we identified in our 13 initial list was the seismic design, just the 14 application of a seismic isolation system to the 15 entire reactor enclosure is new. Seismic interactions 16 can be important to reactivity control, if you move 17 around the metal fuel within the core that could 18 change the reactivity and so we wanted to make sure 19 that was looked at. In sum, the work done on the 20 seismic isolation system appears sound, there's more 21 work to go, but that work appears sound. All the 22 questions that we had on the seismic design were 23 answered so that seemed like it was, again, well under 24 way for the stage of a construction permit.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
22 I mentioned at the outset that we also 1
would consider any additional focus areas that came 2
out of the discussions and we found after the 3
subcommittee meetings, we had thorough presentations 4
from both the Applicant and the staff and we did not 5
identify additional focus areas based on what we heard 6
during the subcommittee meetings, so this ended up 7
being the complete list of what we focused on. Next 8
slide.
9 We concluded we had enough information to 10 proceed to a draft letter. We concluded that we did 11 not need to have presentations from the Applicant or 12 from the staff. They are probably online listening 13 and they'd certainly be free to correct anything I 14 said, but we didn't see a need to have any 15 presentations from them. I'd note at the end of this, 16 we're prepared to read the draft letter into the 17 record after we've had a chance for further 18 discussion.
19 So with that, I'd like to invite any 20 members of the subcommittee to make a comment or 21 correct what I said or add to it. Okay, hearing none, 22 I guess I offer if the Applicant or the NRC staff 23 wants to make a comment, there's no need to, but if 24 there's something you'd like to either correct or 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
23 amplify on the record, now would be a good time.
1 Josh?
2 MR. BORROMEO: Yeah, so this is Josh 3
Borromeo and I'm Chief of the Advanced Reactor 4
Licensing Branch in the Office of Nuclear Reactor 5
Regulation. I do just want to highlight my 6
appreciation for ACRS and their flexibility in 7
reviewing this review that we did for USO's 8
construction permit. I think it was efficient and 9
effective and I just wanted to highlight that in this 10 forum. Thank you.
11 MEMBER ROBERTS: Okay, thank you, Josh.
12 Okay, I'm not seeing any other requests to make a 13 comment, so with that, Mr. Chairman, I'll turn the 14 meeting back over to you.
15 CHAIR KIRCHNER: Thank you, Tom, for your 16 report. At this point, what I would like to propose 17 is that we take public comments. What I'm going to 18 ask people, I'd like to start with comments first on 19 the Kemmerer CPA application. If there are any 20 members of the public who would like to comment on 21 that, please raise your hand and we'll go through 22 those first and then I recognize that there were other 23 topics on our agenda and we'll give an opportunity for 24 short comments from the public on those other two 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
24 matters.
1 I see Ed Lyman's hand up. Ed, go ahead.
2 DR. LYMAN: Thank you. This is Edwin 3
Lyman from the Union of Concerned Scientists. I'd 4
just like to reiterate some of the comments that I 5
made during the subcommittee meetings. I guess I'm 6
disappointed that the Committee seems prepared to sign 7
off on some of the more safety significant aspects of 8
what I see as an unsafe design, in particular, the 9
issue of functional containment.
10 This is, again, an unprecedented feature 11 that's been before the Committee.
Given the 12 restrictions on the future ACRS deliberations, this 13 may be the only time that you're going to have the 14 opportunity to fully assess a functional containment 15 for any other subsequent design because it may not be 16 noteworthy or unique anymore. So you really need to 17 think very carefully about what you're doing at this 18 point. The key here is confirmation. What I see here 19 is a paper design of a novel reactor where many of the 20 features that are being discussed certainly have not 21 been tested to the point that they can be used to 22 validate any of the models that have been going into 23 calculating either probabilities or consequences of 24 the licensing basis events. Because of that, this is 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
25 essentially a prototype reactor.
1 The rules, unfortunately, have a gap in 2
that for construction permits, they don't have to 3
satisfy the requirements of the combined operating 4
license with regard to prototype demonstrations, but 5
I think that is a gap that is really a historical 6
problem. In fact, because this is essentially a 7
prototype reactor, it may warrant having additional 8
safety features that may not be needed for subsequent 9
units, but because it is a prototype, I think you'd 10 want to think very carefully about whether to 11 unequivocally sign off on the functional containment 12 and ask yourself one question. If, during the 13 operating license review, some of the assumptions are 14 not fully validated, would there really be a situation 15 where the staff would require a retrofit of a more 16 conventional containment? I think the answer is 17 pretty clearly no and because of that, this is a very 18 consequential decision at this point and, again, I 19 urge the Committee to think very carefully about what 20 you're doing, and in particular, the issue of 21 reactivity excursions.
22 I should note that most of the details of 23 the more severe events have really not been presented 24 to the public. Every time they come up, the Committee 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
26 has gone into a closed session and as a result, I'm 1
not persuaded that there are not the potential for 2
severe, fast-acting power excursions due to changes in 3
the state of the reactor that could potentially 4
overwhelm the so-called functional containment. As a 5
result, I'm not persuaded that this prototype reactor, 6
this experimental paper reactor, does not need 7
additional safety features like a full containment to 8
address the potential for these rapid power excursion 9
possibilities. And the fact that the preliminary 10 analyses at this point show that they're a low 11 probability, again, is not persuasive given the lack 12 of validation.
13 I'd also like to point out that even 14 though it's not within the Committee's purview, which 15 I think is unfortunate, the potential for sabotage 16 events is another factor that should be going into 17 this determination, but is simply not a part of this 18 discussion. But it really needs to be because again, 19 any of these low probability events could be induced 20 by sabotage attack and therefore, they may not be as 21 low probability as you think. I'll conclude my 22 remarks there. Thank you.
23 CHAIR KIRCHNER: Thank you, Ed. Any other 24 comments from the public participating? I'll start 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
27 again with Kemmerer CPA. Okay, seeing no hands 1
raised, we will turn now to public comments on the 2
other two topics that were previously on the agenda, 3
the Palisades Plant and the Westinghouse FULL SPECTRUM 4
LOCA TR. Let me ask you to keep your comments 5
succinct, concise and to the point. With that, I'll 6
open the floor for comments. Just raise your hand and 7
we'll recognize you in the order that we see you 8
expressing interest in making a comment. Okay, Larry, 9
as our Designated Federal Officer, I do not see any 10 hands raised.
11 MR. BURKHART: Yes, I agree, I agree.
12 CHAIR KIRCHNER: So, at this point then, 13 we'll close our public comment period and return to 14 our agenda. I think I noted, Vesna, are you there?
15 I think you joined us after we started.
16 MEMBER DIMITRIJEVIC: Yes, I'm here. I 17 had a problem on the one computer, so I switched to 18 the other one.
19 CHAIR KIRCHNER: Okay, well, while you 20 were --
21 MEMBER DIMITRIJEVIC: But I'm here.
22 CHAIR KIRCHNER: Okay, excellent. While 23 you were switching computers, I hope your ears were 24 ringing. So, let me just repeat again some comments 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
28 I made. And that is that we wanted to acknowledge 1
your service as you complete your second term on the 2
Committee and this will be your last meeting with us.
3 Your keen insights and collegial 4
interactions with members and staff, especially in 5
topics in the PRA area where you have been an expert 6
practitioner now for many years, going back to your 7
PhD work with Norm Rasmussen at
- MIT, your 8
contributions have significantly helped this Committee 9
complete its work. Your views on PRA and overall 10 reactor safety are much valued.
11 We will miss you professionally and 12 personally and, in particular, I will miss your long 13 distance commentary on matters before the Committee 14 very often getting us refocused on the substantive 15 safety matters at hand. So on behalf of the 16 Committee, thank you, Vesna.
17 MEMBER DIMITRIJEVIC: Well, thank you. I 18 will miss you guys too, thanks.
19 CHAIR KIRCHNER: Okay and with that now 20 we're going to turn back to Member Roberts, who will 21 have a letter report draft to read into the record.
22 Go ahead, Tom, I think we're ready for your reading.
23 MEMBER ROBERTS: Okay. Can you hear me?
24 CHAIR KIRCHNER: Yes.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
29 MEMBER ROBERTS: Okay, good. Okay, I'll 1
skip the very beginning part there.
Subject:
Report 2
on the safety aspects of the construction permit 3
application for TerraPower Natrium reactor at the 4
Kemmerer Power Station.
Dear Chairman Wright,
during 5
the 730th meeting of the Advisory Committee for 6
Reactor Safeguards on November 5th through 7th, 2025, 7
we completed our review of the safety aspects of the 8
construction permit application for Unit 1 at the 9
Kemmerer Power Station and NRC staff's associated 10 Safety Evaluation Report with no open items.
11 Our TerraPower Design Centered 12 Subcommittee reviewed this matter during subcommittee 13 meetings on October 8th to 9th and October 21 to 23, 14 2025. During these meetings, we had the benefit of 15 discussions with NRC staff and representatives from 16 the Applicant, TerraPower, and there is a footnote 17 that explains that the construction permit application 18 was submitted by TerraPower, LLC on behalf of US SFR 19 Owner LLC or USO, a wholly owned subsidiary of 20 TerraPower. For simplicity, this letter report refers 21 to TerraPower as the Applicant -- so, just to avoid 22 some confusion with TerraPower or USO or whatever, we 23 wanted to use the same term throughout for clarity.
24 Going back, we also had the benefit of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
30 reference documents. This report fulfills the 1
requirements of Section 182(b) of the Atomic Energy 2
Act as amended. Footnote 2, just excerpts the portion 3
of Section 182(b) that that's referring to.
4 Okay, conclusions and recommendations.
5 One, the reactor design for the Kemmerer Power Station 6
is a TerraPower Natrium pool type metal fueled, sodium 7
cooled fast reactor, or SFR. The Natrium design 8
include safety advantages when compared to prior 9
generation SRFs, including two means of passive heat 10 removal, two diverse means of generating scram trips 11 and significant separation between the sodium and the 12 steam systems. The design does not require electrical 13 power or operator intervention to achieve a safe 14 shutdown.
15 Two, the Kemmerer CPA is the first 16 application for a power reactor to use the licensing 17 modernization project, or LMP, methodology that was 18 endorsed by the NRC staff in 2020. This methodology 19 focuses the safety case on those items most important 20 to overall risk with increased use of the 21 probabilistic risk assessment, PRA. We consider the 22 Applicant's implementation of this methodology to be 23 adequate for this stage of licensing and consistent 24 with the Commission's risk-informed performance-based 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
31 policy of advanced reactors.
1 Three, in their SER, the staff concludes 2
there is reasonable assurance that the proposed 3
facility can be constructed and operated at the 4
proposed location without undue risk to the health and 5
safety of the public. This conclusion is based on an 6
expectation that the Applicant will provide further 7
technical or design information required to complete 8
the safety analysis in the Final Safety Analysis 9
Report, or FSAR, prior to the operating license 10 review. We agree.
11 Four, this letter report identifies 12 several areas we will revisit during our review of the 13 OL application, including detailed justification on 14 the functional containment design and the consequences 15 of reactivity accidents, validation of the passive 16 cooling design, integration of the PRA and defense-in-17 depth assessments, and quantification of analytical 18 uncertainties. We encourage the Applicant and NRC 19 staff to address them prior to our OL review.
20 And then five, the construction permit for 21 Kemmerer Power Station Unit 1 should be issued.
22 Okay, background. The Kemmerer Power 23 Station consists of one TerraPower-designed Natrium 24 SFR rated to provide 840 megawatts thermal along with 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
32 required power conversion equipment to generate 336 1
megawatts electrical steady state and 500 megawatts 2
electrical peak electrical power. Key features of 3
this plant design include the following: a nuclear 4
island that includes the reactor core within a sodium 5
pool and an intermediate heat transfer system that 6
uses liquid sodium to transport heat from the sodium 7
pool to a sodium to molten salt heat exchanger. The 8
nuclear island also includes structures, systems and 9
components required to provide the fundamental safety 10 function and control of heat generation, reactivity 11 control, control of heat removal which is decay heat 12 removal, and retention of radionuclides, which is 13 containment.
14 An energy island that uses molten salt to 15 store and transfer heat for further use, such as a 16 steam generator or to power a turbine generator.
17 Because normal operation of fault conditions in the 18 energy island are not expected to affect reactor 19 safety, the Applicant has designated all SFCs in the 20 energy island as non-safety.
21 The Preliminary Safety Analysis Report, 22 also called PSAR, provided to support the construction 23 permit application, was prepared using the LMP 24 methodology. Footnote 3 is a reference to the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
33 documents that define what the LMP methodology is, 1
just to avoid having a five-line parenthetical here in 2
the text. This approach to safety justification is 3
based primarily on a PRA supported by hazards analysis 4
and supplemented by explicit assessment of safety 5
margins and defense-in-depth. The CPA is the first 6
application to be submitted to the NRC using the LMP 7
methodology.
8 Okay, discussion. Approach to our review.
9 Our review of the safety aspects of the Kemmerer CPA 10 was focused on areas that we identified as potentially 11 unique, novel or noteworthy in application.
12 Appendix 1 of this letter report is a 13 detailed list of those focus areas. They are 14 summarized as follows:
15 First major bullet, implementation of 16 fundamental safety functions. Then sub-bullet, 17 control of heat generation, for example, reactivity 18 control.
How are the unique reactivity 19 characteristics of fast spectrum reactors, such as the 20 potential for an increase in reactivity on core 21 geometry changes, accounted for and what design 22 features are included to mitigate them?
23 Control of heat removal, for example, 24 decay heat removal. How are the different passive 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
34 means of decay heat removal and their assumed 1
reliability validated?
2 Retention of radionuclides, such as 3
containment. The Natrium reactor is the first SFR to 4
use a
functional containment approach.
What 5
relaxations were made relative to the historical 6
approach to SFR containment and how are they 7
justified?
8 And second major bullet, adequacy of the 9
overall safety case. Does this first use of the LMP 10 methodology provide sufficient justification to issue 11 a construction permit?
12 Okay, next section, control of heat 13 generation, e.g., reactivity control. The Natrium 14 design uses active, passive and inherent means of 15 reactivity control to control heat generation. When 16 required by upset conditions such as plant transients, 17 control rods can be inserted into the reactor core.
18 Two control banks of diversified geometrical design 19 are inserted into the core by the control rod drive 20 system employing active and passive means. The scram 21 function results in passive gravity insertion of 22 control rods into the reactor core to control heat 23 generation. Gravity insertion will occur when 24 reactive trip breakers, or RTBs, open via either of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
35 two diverse systems: the reactor protective system, 1
which removes power to the RTB under a voltage trip 2
circuits based on any of several plant parameter 3
sensors; or two, as described by the Applicant, the 4
quote alternative shunt trip system that is not 5
detailed in the PSAR, but will use parameter sensors 6
and interfacing circuitry that are diverse from the 7
RPS to trip the reactor trip breakers using their 8
active shunt trip circuits.
9 In either case, the reactor trip breakers 10 remove power from scram system solenoid valves that 11 then open to vent scram pistons, delatching the 12 control rods and allowing them to drop due to gravity.
13 Next bullet. The drive line scram follow 14 function results in active insertion of the control 15 rods using the control rod drive motors when the RPS 16 or alternative shunt trip system generate a scram 17 signal. This feature provides defense-in-depth in 18 case control rods fail to delatch.
19 Inherent reactivity feedback 20 characteristics of the reactor core also substantially 21 contribute to the control of heat generation. As fuel 22 and coolant temperatures rise, the combined effects of 23 various physical and physics-based feedback mechanisms 24 result in net negative reactivity feedback within the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
36 core that reduces power. Their combined effect is a 1
safe and stable power level at which heat production 2
and heat removal are in balance and importantly, 3
provides a strong inherent response to counteract any 4
anticipated reactivity excursions.
5 Past SFR designs considered the 6
possibility that common cause failures could result in 7
loss of the active, passive, and inherent features 8
that act in control heat generation. Specifically, 9
they included consideration of a hypothetical core 10 disruptive accident, or HCDA, where an accident caused 11 by failure of the active and passive features was 12 postulated to relocate fissile material into a more 13 reactive configuration and thereby, also perturb the 14 inherent reactivity control features. An HCDA could 15 potentially lead to an energetic transient with 16 consequences such as pressure driven leakage of sodium 17 coolant from the reactor vessel into containment. And 18 the footnote is a reference to a report that explains 19 that phenomenon in more detail.
20 TerraPower and the NRC staff explain that 21 HCDAs will be shown to be incredible as part of the 22 Operating License Application and their consequence 23 will not be specifically considered as part of plant 24 design and safety analysis. The safety case is 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
37 expected to include one, design features that make 1
accidents that lead to potential for 2
melting/relocation of fuel extremely unlikely; and 3
two, characteristics of metal fuel that make energetic 4
reactivity transients unlikely even if fuel 5
melting/relocation were to occur, particularly when 6
compared to prior generations of sodium fast reactors 7
that use oxide fuel.
8 Appendix 2
of this letter report 9
summarizes the justification provided by the Applicant 10 and NRC staff. We plan to further evaluate this 11 justification when we review the Operating License 12 Application.
13 Part of the justification to exclude an 14 HCDA from the safety basis is analysis that is 15 expected to demonstrate that unprotected events, such 16 as rod withdrawal or loss of flow without scram will 17 not lead to fuel melt. These analyses assume certain 18 bounds on the severity of the unprotected transients, 19 specifically only one control rod is assumed withdrawn 20 and the loss of flow is assumed to be caused by de-21 energization of primary sodium pumps whose rotors then 22 coast down.
23 More severe transients are possible.
24 Withdrawal of more than one rod is precluded by a non-25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
38 safety rod withdrawal interlock, pump failures which 1
cause pump rotor stoppage without a coastdown will be 2
mitigated by a pump design that allows enough bypass 3
flow to establish natural circulation and prevent fuel 4
melt.
5 TerraPower intends to review the safety 6
classification of preventive controls, such as the rod 7
withdrawal interlock, prior to submitting any 8
Operating License Application. We agree this review 9
is warranted and believe the evaluation of a dual 10 locked rotator scenario to provide defense-in-depth 11 for such an unlikely transient will be an important 12 detail for the Operating License Application.
13 Okay, next major heading is control of 14 heat removal, e.g., decay heat removal. The Natrium 15 design uses active and passive means to control heat 16 removal. Two diverse residual heat removal systems, 17 the intermediate air cooling system, IAC, and the 18 rapid air cooling system, or RAC, provide -- perform 19 these functions. The IAC system provides means that 20 are active and passive while the RAC system provides 21 passive means of removing decay heat.
22 The reliance of an active circulation of 23 sodium coolant to transfer heat to air is common in 24 both the IAC and RAC systems. The Operating License 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
39 Application is expected to have more information on 1
the technical bases to confirm effective natural 2
circulation flow and heat transfer from sodium to 3
air. For example, models of natural circulation 4
flow will need to be validated, as well as, heat 5
transfer from the core to the ultimate heat sink 6
through various interfaces, such as the reactor 7
vessel to guard vessel gap.
8 Additionally, both the IAC and RAC 9
systems rely on air flow through long passages that 10 could be blocked due to natural phenomena and means 11 to reliably keep such air passages open will need to 12 be demonstrated.
13 Okay, new heading, retention of 14 radionuclides, e.g., containment. The Natrium 15 design performs a fundamental safety function of 16 retaining radionuclides using a functional 17 containment strategy that employs diverse passive 18 barriers to ensure regulatory dose criteria and 19 quantitative health objectives are met. These 20 barriers begin in a radionuclide source and include 21 all structure systems and components between that 22 source and the environment.
23 The functional containment strategy 24 consists of: one, the safety-related, or SR, primary 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
40 functional containment boundary defined as the 1
minimum set of barriers encompassing the core and 2
primary systems that prevent a release of 3
radionuclides from exceeding regulatory limits; and 4
two, enveloping barriers defined as either a non-5 safety-related, NST, or non-safety-related with 6
special treatment, NSRST, structure systems and 7
components that provide a backup radionuclide 8
retention function to the primary functional 9
containment boundary it envelops.
10 Under LMP, the distinction between 11 primary and enveloping barriers and whether they are 12 designated as safety-related or not as established 13 through their relative safety significance.
14 In addition to the physical barriers, an 15 important inherent plant design feature supporting 16 the functional containment strategy is the high 17 boiling point of sodium relative to operational 18 coolant and fuel temperatures. This ensures that 19 the reactor core remains covered by sub-cold sodium 20 at near atmospheric pressure during licensing basis 21 events.
22 The low operating pressure of the 23 primary system and sodium cover gas ensures there is 24 no significant driving force to energetically 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
41 transport radionuclides away from the reactor.
1 The Natrium reactor is the first SFR 2
design to use a functional containment strategy.
3 TerraPower and the NRC staff stated that the 4
functional containment barriers described in the 5
piece are reflected to meet radiological dose 6
criteria for the mechanism or source term associated 7
with the full range of accident scenarios considered 8
under LMP. This includes assessment of the most 9
limiting design basis accident to support regulatory 10 requirements in 10 CFR 50 and the footnote quotes 11 the requirement, which is in sub-part 34 of 10 CFR 12 50.
13 Accident analyses to be performed in 14 support of the Operating License Application are 15 expected to confirm adequacy of the selected 16 barriers. The primary and enveloping physical 17 barriers that were selected to meet the LMP 18 frequency-consequence guidelines share many 19 similarities with prior SFR containment designs, 20 such as accredited physical barriers with leak rate 21 limits and planned testing through plant life to 22 confirm those limits continue to be met.
23 The principal differences from prior SFR 24 containments resulting from the functional 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
42 containment approach are higher leak rate limits 1
than prior designs and non-safety designations for 2
certain components of the enveloping barriers. When 3
compared to prior SFR designs, the Natrium reactor 4
has several safety enhancements as described in 5
Appendix 2 resulting in what is expected to be a net 6
reduction of risk despite these changes to 7
containment design. Therefore, it is reasonable to 8
expect that the functional containment approach can 9
be fully justified during the operating license 10 phase.
11 We expect to further review the 12 functional containment approach during our review of 13 the OL application with continued focus on the 14 adequacy of the supporting accident analyses and the 15 design and testing approaches as they compare to 16 traditional containment designs.
17 One of the primary goals of the 18 containment system for an SFR is to contain the 19 effects of a fire caused by chemical interaction of 20 sodium with air. The Natrium design has two 21 barriers between its sodium coolant and air, the 22 reactor vessel and guard vessel with sodium in the 23 core, the piping and guard piping or vessels for 24 risk significant parts of the intermediate sodium 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
43 loop, the piping and catch pads for non-risk 1
significant parts of the intermediate sodium loop 2
and guard piping or inert cells for parts of the 3
sodium processing system. These design choices 4
limit the risk of fire from a sodium air 5
interaction; however, given the difficulty in 6
fighting sodium fires, more details about sodium 7
fire progression models and the fire protection 8
program are needed to support the fire risk 9
assessment that will be performed as part of the 10 operating license.
11 Radionuclide retention during accident 12 conditions will also depend upon the sodium salt 13 heat exchanger being a reliable pressure boundary.
14 The sodium salt heat exchanger couples the nuclear 15 and energy islands. Ongoing R&D by TerraPower is 16 addressing materials, compatibility, reaction 17 energetics and leak detection and isolation methods.
18 The design concept is innovative but remains one of 19 the least material elements of the plant and 20 continued progress in these areas will be important 21 to the safety case at the OL stage.
22 New heading, adequacy of the overall 23 safety case. First up heading, application of LMP.
24 The Kemmerer CPA is the first application to use the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
44 LMP methodology. Implementation of this methodology 1
is consequently an important element in assessing 2
the adequacy of the safety case. The LMP 3
methodology is centered around use of a PRA to 4
select licensing basis events, LBEs, determine 5
appropriate safety classification of structures, 6
systems or components, SSCs, assign associated risk-7 informed special treatments and determine adequacy 8
of defense-in-depth.
9 While the LMP methodology is well 10 defined, its rigorous implementation may require 11 further development of processes and procedures.
12 The NRC staff stated they are evaluating this CPA 13 for lessons learned of potential clarifications with 14 associated NRC guidance. One area we observed was 15 TerraPower's approach to implementing the LMP 16 approach, the LMP guidance rather, for defense-in-17 depth. They used a methodical, quote, defense line, 18 end quote, approach where every group of licensing 19 basis events was assessed against the LMP five layer 20 defense-in-depth model to assure appropriate 21 independence and diversity in system design and 22 operation.
23 TerraPower stated that the linkage 24 between these defense lines, key safety functions 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
45 and quantifiable performance measures will continue 1
to develop through final design and the Operating 2
License Application. This will ensure traceability 3
from principal design criteria to assess 4
completeness of the PRA, defense-in-depth, and 5
assess for cliff-edge effects. We encourage 6
development of such approaches as they have the 7
potential to apply to the principal of defense-in-8 depth in a straightforward manner.
9 The LMP methodology uses a frequency-10 consequence curve that specifies acceptable dose 11 consequence limits that get larger with reducing 12 event frequency. For event sequences with a 13 frequency less than a 5 times 10 to the minus 7 per 14 year cutoff, LMP does not specify a dose limit, but 15 requires consideration of these very low frequency 16 sequences to assess for cliff-edge effects and 17 assure adequacy of defense-in-depth. The Kemmerer 18 construction permit application uses the term other 19 quantified events, or OQE, to refer to such events.
20 However, the PSAR is not consistent on the cliff-21 edge effects or what acceptance criteria are used 22 when assessing other quantified events.
23 During our subcommittee meetings in 24 October 2025, TerraPower explained that their review 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
46 for cliff-edge effects and defense-in-depth adequacy 1
will address in areas that meet either of two 2
conditions. One, the scenario has an estimated 3
frequency of occurrence of 1 times 10 to the minus 7 4
or greater with a 95 percent confidence level; and 5
two, any scenario regardless of frequency that has a 6
consequence of greater than 1,000 rem total 7
effective dose equivalent over 30 days in the 8
exclusion area or boundary.
9 The intent of evaluating the OQEs is to 10 determine if any low frequency events are 11 sufficiently consequential to consider additional 12 mitigation. TerraPower further stated they had not 13 yet encountered a scenario with a dose level high 14 enough to warrant this further evaluation, even 15 considering events such as unprotected reactivity 16 emissions and the losses of flow. We expect to 17 further review these conclusions as part of our 18 Operating License Application review.
19 Subheading, seismic isolation system.
20 One specific design feature considered to be novel 21 is the use of a seismic isolation system for the 22 reactor enclosure building. The design approach is 23 embedded in the reactor building substructure and 24 the seismic isolation system to support the reactor 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
47 and enhance protecting against seismic events.
1 TerraPower is following the general lead of the GE 2
PRISM design of the 1980s, which envisioned using 3
steel and rubber isolation devices to support the 4
reactor and provide seismic protection.
5 We observed that the interfaces between 6
SSE supported by the seismic isolation system and 7
those outside the system, such as connections to 8
intermediate heat transfer system piping, will 9
warrant special attention to ensure that the 10 relative deflections between components supported by 11 seismic constraints and those that are not are 12 appropriately addressed.
13 We also observed that phenomena such as 14 reactivity response and seismic forces may be 15 relatively new for an SFR design and their impacts 16 may not have been fully explored in the past. There 17 could be surprises once the Applicant gets into the 18 details and this should be thoroughly explored when 19 the OL application is submitted.
20 Last subheading, treatment of analytical 21 uncertainties. Some of the calculations required to 22 support the safety case are much more involved and 23 complex than for other reactor technologies and the 24 PSAR does not include discussion of the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
48 uncertainties for available margins. These analyses 1
will be refined as the design proceeds from the CP 2
stage to the OL stage. It will be important to 3
establish the margins to figures of merit that are 4
used to assess whether principal design criteria are 5
met. While in the end there may be sufficient 6
margin, the uncertainties associated with these 7
calculations need to be established and assessed for 8
acceptability at the OL stage.
9 We believe the following sources of 10 uncertainty should be addressed in the OL 11 application and subsequent Safety Evaluation Report:
12 Reactivity feedback coefficients depend on complex 13 calculations of the deformation of the fuel rods as 14 restrained by the core restraint system including 15 the effects of the lower grid plate. Moreover, 16 point kinetics may not capture the three dimensional 17 nature of the response of the core and 3D kinetics 18 may be necessary. The uncertainties associated with 19 these calculations and the margin to avoiding a net 20 positive reactivity coefficient should be 21 documented.
22 Calculations related to confirmation of 23 acceptable fuel integrity and safety-related 24 structural materials in general depend on detailed 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
49 thermomechanical analysis and the uncertainty and 1
the predicted response, stress, strain, creep 2
rupture, et cetera, that are not discussed in the 3
PSAR or referenced in Topical Reports. In 4
particular, analysis of the margin to the eutectic 5
melt, a key metric for fuel failure, is needed.
6 These values should be documented.
7 Summary. TerraPower has sufficiently 8
completed the early phases of risk-informed safety 9
case using the LMP approach to justify approval of 10 their construction permit for a Natrium sodium fast 11 reactor at a site in Kemmerer, Wyoming. This 12 application is supported by safety improvements 13 associated with the Natrium reactor design, which is 14 significant when compared to large light water 15 reactors and prior generation SFRs and can be 16 leveraged to support simplifications, such as use of 17 a functional containment approach in design and 18 analysis.
19 We look forward to reviewing the final 20 safety case when it is submitted with an application 21 for an operating license. The construction permit 22 should be issued. We are not requesting a formal 23 response from the staff to this letter. Sincerely, 24 Chairman.
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50 I'll take a short break there, page 1
through, there is enclosures and references I won't 2
read them. There are two appendices that were 3
mentioned in the body of the letter. And, yeah, 4
Sandra, if you go to the appendices, I'll start to 5
read the appendices.
6 Okay, Appendix 1, just a little 7
background. This is the document that we had 8
discussed in the July and September full Committee 9
meetings. And for the record, we wanted to capture 10 it so this was written before the review and so, you 11 know, obviously the review addressed many of these, 12 but again, just to capture for the record, this is 13 what we set out to review as the focus areas.
14 So, title is Unique, Novel, and 15 Noteworthy Elements. The focused ACRS review of the 16 TerraPower Natrium construction permit application.
17
Purpose:
This appendix lists elements of the 18 TerraPower Natrium construction permit application 19 that are unique, novel and/or noteworthy were 20 identified prior to the subcommittee review meetings 21 as areas of focus for the ACRS' review of this 22 construction permit application.
23 Background. The TerraPower Natrium 24 design is an 840 megawatt thermal sodium fast 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
51 reactor. While it leverages U.S. experience in 1
sodium fast reactors such as EBR-II, Fast Flux Test 2
Facility and the PRISM design, most experts more 3
than 30 years old, this reactor is also the first 4
non-light water power reactor to submit a 5
construction permit. The first to use the licensing 6
modernization project as the basis for its safety 7
case and the first to use the 10 CFR 50.160 8
immersive planning rule. Hence, there is a great 9
deal about this reactor construction permit 10 application that is unique, novel and/or noteworthy.
11 The challenge is to focus the ACRS 12 review of those items that were provided safety 13 assessment independent of that provided by the NRC 14 staff.
15 Discussion. The following four focus 16 areas for review are proposed. They are based on 17 the fundamental safety functions of controlled heat 18 generation, e.g., rapid rate control, controlling 19 heat removal, retention of radionuclides, e.g.,
20 containment and sophistication of the overall safety 21 case, e.g., use of the PRA-centered approach to 22 safety assessment.
23 Controlled heat generation, this is 24 largely set on with reactivity control. Aspects of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
52 reactivity control that are unique, novel and/or 1
noteworthy include: one, sensitive reactivity 2
events. Boiling of sodium can result in significant 3
reactivity excursion and reactivity of the core 4
called a hypothetical core disruptive accident.
5 While details are not included in the PSAR, the 6
Natrium safety case appears to be focused on showing 7
the sodium boiling or core derangement are so 8
unlikely as to not merit consideration in the safety 9
analyses.
10 Prior NRC assessments, such as the 1993 11 PRISM Preapplication Safety Evaluation Report, have 12 good assessments of such energetic reactivity 13 excursions even though they are considered to be 14 very unlikely. We should review the approach taken 15 by TerraPower.
16 Two: two means of rod insertion. The 17 PSAR takes credit for two groups of control rods 18 with different geometry in both passive gravity-19 driven and active rod drive motor driven rod 20 insertion to meet requirements for two means of 21 scram. In both cases, the two presumed diverse 22 means of insertion are controlled by the same 23 reactor protective system, we see adequacy of 24 reliance on the same RPS for diverse means of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
53 insertion.
1 Three: limitations of rate of rod-based 2
reactivity insertion. The PSAR notes a reactivity 3
insertion rate is limited by interlocks that assure 4
only one rod is withdrawn at a time and that limit 5
rod speed. These features are not described in 6
detail, nor are they listed as safety significant in 7
the PSAR. We could review the role of these 8
interlocks in a safety system.
9 Four: control of heat removal. This is 10 implemented with a combination of a purely passive 11 system and the second system that has both active 12 and passive modes. Aspects that are unique, novel 13 and/or noteworthy include: one, reliability of 14 passive cooling. The margin in natural circulation 15 heat transfer relative to decay heat removal needs 16 to be confirmed. For example, the purely passive 17 system, the reactor air cooling system, or RAC, 18 relies on an air flow path that may be subject to 19 clogging due to debris. From the PSAR, it does not 20 appear that this entire flow path can be clean. We 21 should review plans to address uncertainties in this 22 system including whether we consider air flow paths, 23 any change from analytical assumptions to be 24 sufficiently reliable to support the passive 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
54 function.
1 Two, transition from forced circulation 2
to natural circulation. The PSAR lists it's a 3
safety-related function of primary sodium pump 4
coastdown rate that is sufficiently slow to assure a 5
transition from forced circulation to natural 6
circulation through the reactor core. There is no 7
discussion of more extreme flow transients that 8
would occur with a mechanical failure of the pump, 9
such as on pump shaft shear or seizure of the 10 impeller. We should review the likelihood and 11 consequence of such a failure.
12 Retaining radionuclides. This is a 13 primary event of a functional containment and has 14 demonstrated analytically via a mechanism storage 15 term. Aspects of radionuclide retention that are 16 unique, novel and/or noteworthy include: one, first 17 application of a functional containment for an SFR.
18 As discussed in two prior Topical Report Reviews, a 19 functional containment approach has never been 20 applied for an SFR. The nature of functional 21 containment shares many similarities with prior SFR 22 containments with the differences being the safety 23 classification and the design leak rates. We should 24 review these differences to more fully understand 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
55 them and why they are acceptable including 1
consideration of the potential for energetic 2
reactivity events as described above under 3
controlled heat generation.
4 Two, sodium fires. One of the principal 5
goals of an SFR containment is to retain a slow 6
leakage characteristics in the case of a chemical 7
reaction involving sodium. The PSAR does not 8
explain how the assumed magnitude of sodium leakage 9
and containment would be determined for the 10 containment integrity analysis. Additionally, prior 11 designs, such as PRISM, make extensive use of guard 12 pipes to double contain sodium in case of leakage.
13 The Natrium PSAR does not discuss guard pipes in 14 chapter 7, but instead appears to rely on 15 strategically located catch pans. We should review 16 the plan to either limit the energy of a sodium fire 17 or design a functional containment for them.
18 Sufficiency of the overall safety case.
19 As noted earlier, the Natrium design is the first 20 commercial power non-light water reactor to submit 21 an application based on the PRA-centered LMP. The 22 LMP includes process steps to evaluate uncertainties 23 and include appropriate defense-in-depth to cover 24 such uncertainties including cliff-edge effects.
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56 Aspects of this approach that are unique, novel 1
and/or noteworthy include: one, cliff-edge effects.
2 Very little detail is provided in the PSAR on the 3
process used to ensure all relevant hazards are 4
identified. Additionally, the ASME standard and NEI 5
18-04 do not explain how the cliff-edge 6
determination and defense-in-depth assessments are 7
done for event sequences that do not screen in as 8
licensing basis events or are not modeled in the 9
PRA, i.e., completeness uncertainty. We should 10 review their process for hazard evaluation, LBE 11 selection and cliff-edge screening.
12 Two: role of other quantified events, 13 OQEs. LMP uses a frequency-consequence curve that 14 does not define a dose consequence criterion for 15 event of sequences with a frequency lower than 5 16 times 10 to the minus 7 per year. Natrium includes 17 such extremely unlikely scenarios, designated as 18 OQEs, to ensure the mechanism, source, term and 19 functional containment analyses are bounding when 20 considering uncertainties. It is unclear from the 21 PSAR what dose consequence criteria apply to OQEs.
22 We should evaluate the role of OQEs as part of 23 consequence acceptance criteria.
24 And three: seismic design. The Kemmerer 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
57 site is the first construction permit application 1
for a site west of the Mississippi River in some 2
time and resilience to earthquakes will be 3
particularly important to safety. The plant uses a 4
unique seismic isolation system for the reactor 5
enclosure system. We should review this and the 6
adequacy of the seismic design. And that's the end 7
of Appendix 1.
8 Okay Appendix 2? Yep, Appendix 2 is 9
Safety enhancements of the Natrium reactor design 10 relative to prior sodium-cooled fast reactors.
11 Purpose. This appendix enumerates some 12 of the safety enhancements in the Natrium design as 13 described by TerraPower and the NRC staff. The 14 licensing modernization process, LMP, methodology 15 leverages such safety enhancements to support the 16 approaches to the hypothetical core disruptive 17 accident, HCDA, and functional containment design 18 and the Natrium safety basis for Kemmerer Unit 1.
19 Background. As a risk-informed 20 methodology, LMP focuses on accident scenarios 21 determined via a probabilistic risk assessment, PRA, 22 and that gives source terms postulated events that 23 are deterministically judged to be bounding. Use of 24 a risk-informed approach can lead to differences in 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
58 safety design and analysis. For Natrium, this 1
approach resulted in two significant changes 2
relative to earlier SFR designs.
3 One: prior SFR designs considered the 4
potential for an HCDA which is a hypothetical severe 5
event in an SFR characterized by a rapid, 6
uncontrolled increase in reactor power and 7
subsequent rearrangement of fuel into a more 8
reactive configuration. This could lead to a power 9
surge and an energy release that might challenge the 10 reactor containment. Such actions may be triggered 11 by a loss of coolant flow or a transient overpower 12 event, especially if the reactor fails to shutdown 13 automatically, known as unprotected events. For 14 Natrium, TerraPower does not include an HCDA in 15 their safety basis since it is not deemed to be 16 credible per the LMP risk-informed process.
17 Two: prior SFR designs included a 18 containment structure or set of structures with 19 characteristics specified by principal design 20 criteria that define low leakage barriers and safety 21 classifications. For Natrium, TerraPower designed a 22 functional containment that includes the barriers 23 shown to be needed by a mechanistic source term 24 analysis.
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59 Discussion. The Natrium reactor design 1
incorporates several important features that support 2
the LMP-based design decisions discussed above. And 3
bulletized list, a large sodium pool with a high 4
degree of thermal inertia, metal fuel which 5
significantly reduces the amount of stored energy 6
available for interaction between the fuel and the 7
coolant when compared to oxidized fuels previously 8
used, no addition of plutonium in the fuel, which 9
reduces the magnitude of the void reactivity worth 10 compared to other SFR fuel systems.
11 Two independent and diverse shutdown 12 mechanisms, gravity scram and motor-driven driveline 13 scram follow, each controlled by independent and 14 diverse trip systems, reactor protection system and 15 alternative shunt trip system, each of these 16 shutdown mechanisms inserts two diversely designed 17 sets of control rods.
18 Two independent decay heat removal 19 systems, the reactor air cooling system is passive 20 and is always on and the intermediate air cooling 21 system can operate in active and passive modes.
22 Two primary mechanical sodium pumps 23 whose design enables the transition from forced to 24 natural convection of sodium with timing pump 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
60 coastdown.
1 Functional containment as supported by 2
improved understanding of fission product release 3
from metallic fuel and its associated transport in 4
sodium in the cover gas.
5 Separation of the energy island from the 6
nuclear island, which essentially eliminates the 7
potential for sodium water interaction. There is 8
potential for sodium salt interaction in the salt 9
heat exchanger, but TerraPower plans to prevent or 10 mitigate this interaction as described in chapter 13 11 of the Preliminary Safety Analysis Report.
12 Protection to be demonstrated for most 13 unprotected scenarios. The Applicant plans to 14 demonstrate that an unprotected reactivity addition 15 transient caused by unintended withdrawal of one 16 control rod and an unprotected loss of flow caused 17 by loss of power to the primary sodium pumps will 18 not lead to fuel melt or boiling of sodium.
19 Additional preventive features.
20 Unprotected transients complicated by failures such 21 as unintended withdrawal of multiple control rods or 22 locked rotor failures of both primary sodium pumps 23 would be required to possibly lead to fuel melt or 24 boiling of sodium. The Applicant intends to add 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
61 defense-in-depth features such as rod withdrawal 1
interlocks and bypass flow in the sodium pumps to 2
mitigate locked rotor conditions to further lower 3
the likelihood of such outcomes.
4 And last bullet, reduce potential for 5
severe accidents to lead to an energetic reactivity 6
transient. Specifically, as discussed in reference 7
national laboratory documents, and there are two 8
footnoted reports, certain thermal and physical 9
properties of metal fuel make it unlikely that fuel 10 melt will lead to a reactivity addition, 11 particularly when compared to earlier designs that 12 use oxide fuel.
13 Conclusion. These features result in 14 the robust implementation of the key safety 15 functions in the plant. They demonstrably influence 16 plant safety by either reducing the frequency of 17 postulated events or reduce the associated 18 consequences. Thus, a significant reduction in the 19 overall risk profile of the plant is expected when 20 compared to previous SFR designs. It is reasonable 21 to expect that these safety improvements can be 22 leveraged in the Operating License Application to 23 fully justify the TerraPower conclusions that an 24 HCDA is not credible and that a functional 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
62 containment strategy driven by robust mechanistic 1
source term analysis is technically sound.
2 And that is the end of the letter. I 3
guess, Mr. Chairman, I'll turn it back to you.
4 CHAIR KIRCHNER: Thank you, Tom. Okay, 5
at this juncture, I would propose that we take high 6
level comments from members before we get into line 7
by line review and deliberation about the details of 8
the letter report. And I see Matt's hand up, so 9
I'll turn first to Matt and then Dave Petti.
10 MEMBER SUNSERI: Thank you, Walt. Can 11 we go to recommendation -- or conclusion number 12 three at the top of the report? Okay, you know, I 13 know we're talking about the staff's SER. Their 14 conclusion that reasonable assurance that the 15 proposed facility can be constructed and operated at 16 the proposed location without undue risk to health 17 and safety of the public, the last words in this 18 paragraph is, we agree, and I don't think we should 19 be agreeing with the statement that it can be 20 operated at the proposed location without undue 21 risk.
22 I know there's this caveated sentence in 23 here that says the conclusion based on the 24 application, but, you know, we have plenty of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
63 examples throughout our letter report where there 1
has not been sufficient information to say that 2
there's reasonable assurance they can be operated, 3
so we either need to separate those two topics or 4
you all tell me that I'm wrong on this. But anyway, 5
I have some proposed wording that we can get to when 6
we get there, but -- and I know why the staff has 7
written it that way because they have some guidance, 8
but we don't have to agree with the staff and their 9
guidance. That's my comment.
10 CHAIR KIRCHNER: Thank you, Matt.
11 MEMBER ROBERTS: Yeah, if I could 12 respond.
13 CHAIR KIRCHNER: Okay, Tom.
14 MEMBER ROBERTS: The requirements for 15 10 CFR 50.35 pretty much define the scope of a 16 construction permit is what's in this paragraph that 17 there is a judgment being made about the ability to 18 operate the plant if the, you know, Applicant 19 follows through on all the commitments that are 20 defined in the construction permit application.
21 That is what it says and our conclusion number five 22 is the construction permit should be issued and so 23 that essentially is us agreeing with that because 24 that is what a construction permit is. So, I don't 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
64 know if the words we agree are necessarily needed at 1
the end of three, if that's -- you know, I 2
understand the comment that you can certainly take 3
that first sentence in isolation and say that's 4
premature. We don't have to be on record as 5
agreeing with that statement here in three, but I 6
think when we say in five that we agree the CP 7
should be issued, we are agreeing with that, because 8
that's what a CP is.
9 (Simultaneous speaking.)
10 MEMBER SUNSERI: I would support just 11 taking the we agree out of three. That would be 12 fine with me.
13 MEMBER ROBERTS: Yeah, I'm okay with 14 that too because that -- it's implied by five, so I 15 don't think we need to say that so I'm okay with 16 that.
17 MEMBER SUNSERI: Thank you.
18 CHAIR KIRCHNER: Thank you, Matt. I 19 think Dave Petti was next.
20 MEMBER PETTI: My comment is just 21 something to consider with Tom reading the letter 22 and then the two appendices back to back, there 23 seemed to be a lot of repetitiveness and I 24 understand, you know, Appendix 1 was written before 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
65 the review. It's just something I think that when 1
we get into the editing of the letter, we should 2
keep in mind if there's a way to make it less 3
repetitive.
4 CHAIR KIRCHNER: Okay.
5 MEMBER ROBERTS: Dave, when we get 6
there, we can certainly discuss that line by line, 7
but I think because if there was a desire to capture 8
what we agreed to in the September meeting for the 9
record, then taking things out because they were 10 discussed in the letter is almost abating the need 11 for the appendix because by definition everything in 12 that appendix we covered in the meeting and then we 13 covered in the letter. We can discuss 14 strategically. There is an option we discussed at 15 the September P&P meeting is to put that appendix in 16 the Summary Report of that meeting and leave it out 17 entirely. We could do that.
18 MEMBER PETTI: Okay.
19 MEMBER ROBERTS: But I would think that 20 we need to decide as a committee if we want to 21 capture for the record what we agreed to in the 22 September P&P meeting.
23 MEMBER PETTI: Yeah.
24 CHAIR KIRCHNER: Dave, my sense is it's 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
66 more a reference almost than -- yes, it's redundant 1
and I'm glad to see that the letter is consistent 2
with it, but it's more reference material than -- as 3
long as the letter stands alone, we can debate how 4
we capture that. I think the important point we 5
need to make is that that list of unique, novel and 6
noteworthy is the Committee's list, developed by the 7
Committee going into our review and maybe we can 8
capture that somehow in the introduction to that 9
attachment, to that appendix.
10 MEMBER PETTI: Yeah. Okay.
11 CHAIR KIRCHNER: I saw Vicki's hand and 12 then Bob.
13 MEMBER BIER: These are kind of ultra-14 high level comments that I don't think directly 15 relate to anything in the letter, but just a couple 16 of concerns that I have about the whole process, the 17 way it seems to be unfolding. When I look back at 18 the transcript from the earlier subcommittee 19 meetings and, you know, Bob commented, I think, at 20 one point that the review of the PRA, at least in 21 the material we saw from staff, he described it as a 22 two-finger compliance check.
23 As a PRA person, there is not very much 24 meat for me to get my hands into at this stage and, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
67 you know, especially if we are relying more on PRA 1
to say yes, things are safe, it seems a little odd 2
to be, you know, accepting the PRA results without 3
evaluating all the nitty gritty of how they got 4
there.
5 The other kind of high level concern I 6
have is with postponing things like the seismic PRA.
7 You know, I understand there's a lot that cannot be 8
done at the CP stage, like if you don't know where 9
the pipe hangers are going to be then it's kind of 10 hard to do a seismic PRA on, you know, a conceptual 11 design, but the construction permit is the place 12 where we approve the site. And if we are approving 13 the site without being able to look in detail at the 14 seismic implications of that site, it just seems a 15 little odd. So, like I said, those are just 16 concerns I have about the process. I don't think 17 they necessarily translate into any verbiage that 18 belongs in the letter, but I just wanted to get 19 those on the record. Thank you.
20 CHAIR KIRCHNER: Thank you, Vicki. Bob?
21 MEMBER MARTIN: Actually, I think there 22 is verbiage that can relate to Vicki's comment with 23 regard to the PRA. There's no reference to Reg 24 Guide 1.253, which, you know, very specifically 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
68 describes the framework or the expectation for the 1
level of detail the PRA at the construction permit 2
phase and the mention of PRA in the letter without 3
that context might imply that it's more than what it 4
is. So, all I'm suggesting is that we, one, I 5
notice the Reg Guide 1.253 is not in the reference 6
list, so it should be in the reference list; and 7
two, sprinkle in a couple places just mention, you 8
know, the context the PRA is within that Reg Guide 9
and not something else, like 171 or something like 10 that or 174. Anyway, that was really my only 11 comment.
12 MEMBER BIER: That's helpful, Bob, thank 13 you.
14 CHAIR KIRCHNER: Greg?
15 VICE CHAIR HALNON: Yep, there I am, 16 thank you. Just a couple items. One is when we get 17 into this a little more, I just question the need 18 for Appendix 1 overall. It kind of goes back to 19 Dave's discussion about repetitiveness. It's past 20 stuff, it's not necessarily, in my mind, relevant to 21 the letter, other than the fact that the letter kind 22 of goes through all the topics themselves, but we 23 can talk about that some more later.
24 Larry, I want to just make sure you get 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
69 the USO/TerraPower as the Applicant and NRC likes 1
it. We shorthand TerraPower and I think, Tom, you 2
had a footnote, but I couldn't see the footnote so 3
I'm not sure if that explains that or not.
4 Finally, the combination of three and 5
four conclusions gives me a little bit of pause in 6
the fact that it kind of goes back to what Matt was 7
talking about to some extent. The reasonable 8
assurance that the proposed facility can be operated 9
at the proposed location doesn't -- I don't know 10 that. I don't think I can agree that what we've 11 seen says that it can be operated at the proposed 12 location. It's not so much the proposed location, 13 it's the word operated. I mean it certainly can be 14 designed and constructed at the proposed location, 15 but the operations, there's so much more than just 16 the paper design that we've seen. So, a little bit 17 take pause at that word operated, I think that I 18 need to understand that a little bit better.
19 And then, when you get to four, it talks 20 about revisiting during the review of the operating 21 license. I'm not sure revisit is the right word for 22 it and I'm not sure that we can say that, you know, 23 the detailed justification of the functional 24 containment -- I think it's more detailed design of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
70 the proposed containment.
1 So, I'm a little bit -- maybe it's the 2
definite nature of the two that get to me a little 3
bit and I think that maybe some tweaks in the words 4
might be appropriate, but I'll think more on it, 5
Tom, I'm not sure what my resolution to my comment 6
is, which is I hate making comments without a 7
suggested resolution, but the bottom line is that I 8
think that we're a little bit too ahead of our skis 9
on the operations of it. I think that the revisit 10 word is a little bit too soft. That's my comment.
11 CHAIR KIRCHNER: Greg, I agree too. I 12 think number four could use some work going forward 13 and I think I kind of agree with you and Matt that 14 we need to be a little more careful. The things 15 that we feel need to be addressed are alluded to in 16 number four and based on the detailed design and 17 analysis that's presented at the OL phase, then one 18 perhaps can make the more definitive conclusion 19 about the operability, the safe operation of the 20 plant after it gets an operating license.
21 VICE CHAIR HALNON: Right.
22 MEMBER SUNSERI: Yeah, that was my point 23 exactly, I agree with both of you all.
24 CHAIR KIRCHNER: Larry, you have your 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
71 hand up.
1 MR. BURKHART: Yeah, I just recommend 2
the Committee consider the conclusions and 3
recommendations that were written for both Kairos 4
CPAs and it basically says we agree with the staff 5
that there is confidence the facility can be 6
constructed in accordance with the relevant 7
regulations and the design bases outlined in the 8
PSAR. Detailed design analysis and technology 9
qualification will be completed prior to the 10 operating license, OL, review, that's from the 11 Committee's letter for Kairos 2.
12 CHAIR KIRCHNER: Good, thank you. At 13 this point, we're coming up to the top of the hour, 14 if there are not --
15 (Simultaneous speaking.)
16 VICE CHAIR HALNON: Walt, you got Vesna 17 still has her hand up.
18 CHAIR KIRCHNER: Oh, I'm sorry, Vesna, I 19 didn't see the hand. Go ahead, Vesna.
20 MEMBER DIMITRIJEVIC: Okay, so one of 21 the things I have Larry just addressed, that we 22 should separate that operation and the, you know, 23 the letter but I have two very high level comments.
24 In this letter, we talk about the Natrium all the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
72 time and we never talk about Kemmerer Unit 1, so we 1
are reviewing design or we are -- you know, the NRC 2
talk in the SER only about KU1 which is the Natrium, 3
so if we are just talking about the Natrium design 4
and also these differentiate between the location 5
and design and things like that. So, maybe we 6
should clear up somewhere in the letter the Natrium 7
versus Kemmerer Unit 1, you know? When we have the 8
discussion, so this is very high level.
9 The second very high level is also I 10 remember that we agreed that when we talk about the 11 Committee conclusions and our work, we can say we 12 and, you know, that's perfectly fine instead of the 13 Committee, but I think when we talk about the 14 future, you know, we will review this in three, we 15 will do this for the future work we should just say 16 the Committee because there is a difference between 17 we now and we, you know, five years from now or 18 things like that. So, that was my other high level 19 comment and I gave it to Tom, but he said we use, we 20 like 30 times in the letter.
21 CHAIR KIRCHNER: Okay.
22 MEMBER DIMITRIJEVIC: Okay, those were 23 my high level comments.
24 CHAIR KIRCHNER: Noted, thank you.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
73 Yeah. Other member comments, high level comments at 1
this point? Okay, then at this point, I think we --
2 Larry, correct me if I'm wrong, we can release the 3
court reporter?
4 MR. BURKHART: Yes, I agree.
5 CHAIR KIRCHNER: Okay, so thank you for 6
your service today. I will not need your service 7
for the rest of this meeting so thank you. And then 8
I propose, we're at the top of the hour, I propose 9
we take a 15-minute break to 10:15 and we'll pick up 10 our letter review. We're recessed until 10:15 11 Eastern Time.
12 (Whereupon, the above-entitled matter 13 went off the record at 10:00 a.m.)
14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
ACRS Subcommittee Review of Kemmerer Construction Permit Application 1
Thomas Roberts, SC Meeting Chairman Advisory Committee on Reactor Safeguards (ACRS)
U.S. Nuclear Regulatory Commission
TerraPower Natrium Design
- The Natrium design is an 840 MWth sodium fast reactor.
- While it leverages U.S. experience in sodium fast reactors, such as EBR-II, Fast Flux Test Facility (FFTF) and the PRISM design, most of that experience is more than 30 years old.
- This reactor is also the first non-LWR power reactor to submit a CPA, the first to use the Licensing Modernization Project as the basis for its safety case, and the first to use the 10 CFR 50.160 emergency planning rule.
- Hence many aspects of this application are novel and/or noteworthy.
2
ACRS Focus Areas
- We selected four focus areas, three of which are defined as the fundamental safety functions, or FSFs:
- Control of Heat Generation FSF (e.g., reactivity control)
- Control of Heat Removal FSF (e.g., decay heat removal)
- Retention of Radionuclides FSF (e.g., functional containment)
- Sufficiency of the Overall safety case (e.g., PRA-centered LMP approach)
- Other areas may arise as a result of SC meeting discussions 3
Subcommittee Meetings
- The applicant and staff provided a comprehensive overview of the plant design and safety analyses as documented in the CPA.
- October 8-9: Overall Plant Design and implementation of LMP
- October 21-23: Structures, Systems, and Components
- These meetings satisfactorily addressed each of the focus areas, as discussed in the following slides.
4
Control of Heat Generation FSF
- Specific review areas include:
- Sensitivity to reactivity events - Potential for significant reactivity excursions caused by boiling of sodium and core geometry changes
- Two means of rod insertion - Reliance on the same reactor protection system to control presumably diverse means of rod insertion
- Limitations on rate of rod-based reactivity insertion - Reliance on non-safety interlocks to limit reactivity insertion rate 5
Control of Heat Removal FSF
- Specific focus areas include:
- Reliability of passive cooling - Margin in natural circulation heat transfer relative to decay heat removal needs
- Transition from forced circulation to natural circulation - Scenarios that lead to a rapid reduction in pump speed and may therefore not transition to natural circulation 6
Retention of Radionuclides FSF
- Specific focus areas include:
- First application of a functional containment for an SFR - The rationale for differences from prior SFR containments
- Sodium Fires - The plan to either limit the energy from chemical reactions involving sodium or design the functional containment for them.
7
Sufficiency of the Overall Safety Case
- Specific focus areas include:
- Cliff-edge effects - How the process for hazard evaluation, LBE selection, and cliff-edge screening adequately assess for cliff-edge effects and defense in depth.
- Role of Other Quantified Events (OQEs) - The role of extremely unlikely Natrium scenarios evaluated by the applicant to ensure analyses are bounding when considering uncertainties.
- Seismic design - The adequacy of the seismic design, since resilience to earthquakes will be particularly important to safety.
8
Conclusion
- The subcommittee has enough information to proceed to a draft letter report for deliberation by the Full Committee.
- We are prepared to read the draft letter into the record.
9
List of Acronyms
- CPA - Construction Permit Application
- EBR-II - Experimental Breeder Reactor - II
- FFTF - Fast Flux Test Facility
- FSF - Fundamental Safety Function
- LBE - Licensing Basis Event
- LMP - Licensing Modernization Project
- LWR - Light Water Reactor
- MWth - Megawatts, thermal
- OQE - Other Quantified Event
- PRISM - Power Reactor Innovative Small Module
- SC - Subcommittee
- SFR - Sodium Fast Reactor 10