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{{#Wiki_filter:Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
 
==Title:==
Advisory Committee on Reactor Safeguards Docket Number:    (n/a)
Location:        teleconference Date:            Wednesday, September 8, 2021 Work Order No.:  NRC-1635                          Pages 1-57 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W., Suite 200 Washington, D.C. 20009 (202) 234-4433
 
1 1
2 3
4                              DISCLAIMER 5
6 7  UNITED STATES NUCLEAR REGULATORY COMMISSIONS 8        ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 9
10 11          The contents of this transcript of the 12 proceeding of the United States Nuclear Regulatory 13 Commission Advisory Committee on Reactor Safeguards, 14 as reported herein, is a record of the discussions 15 recorded at the meeting.
16 17          This transcript has not been reviewed, 18 corrected, and edited, and it may contain 19 inaccuracies.
20 21 22 23 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                    UNITED STATES OF AMERICA 2                  NUCLEAR REGULATORY COMMISSION 3                                + + + + +
4                            688TH MEETING 5            ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 6                                    (ACRS) 7                                + + + + +
8                              OPEN MEETING 9                                + + + + +
10                                WEDNESDAY 11                          SEPTEMBER 8, 2021 12                                + + + + +
13                  The Advisory Committee met via Video-14 Teleconference, at 8:30 a.m. EDT, Matthew W. Sunseri, 15 Chairman, presiding.
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
 
2 1 COMMITTEE MEMBERS:
2            MATTHEW W. SUNSERI, Chairman 3            JOY L. REMPE, Vice Chairman 4            WALTER L. KIRCHNER, Member-at-large 5            RONALD G. BALLINGER, Member 6            VICKI BIER, Member 7            DENNIS BLEY, Member 8            CHARLES H. BROWN, JR. Member 9            VESNA B. DIMITRIJEVIC, Member 10            GREG HALNON, Member 11            JOSE MARCH-LEUBA, Member 12            DAVID A. PETTI, Member 13 ACRS CONSULTANT:
14            STEPHEN SCHULTZ 15 DESIGNATED FEDERAL OFFICIAL:
16            WEIDONG WANG 17 ALSO PRESENT:
18            BLAISE COLLIN, Kairos Power 19            DARRELL GARDNER, Kairos Power 20            BRANDON HAUGH, Kairos Power 21            DUKE KENNEDY, NRR 22            SCOTT MOORE, Executive Director, ACRS 23            RICHARD RIVERA, Kairos Power 24            JEFFREY SCHMIDT, NRR 25            JAMES TOMKINS, Kairos Power 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 1                                CONTENTS 2
3 Call to Order . . . . . . . . . . . . . . . . . .                              4 4 Opening Remarks by the ACRS Chairman                      . . . . . .          5 5 Kairos Topical Report on Fuel Performance . . . .                              8 6            Remarks from the Subcommittee Chairman                    . .      8 7            Presentation by Kairos Power                . . . . . . . 10 8            Presentation by NRC Staff . . . . . . . . . 42 9 Public Comments (None)            . . . . . . . . . . . . . 56 10 Committee Comments (None) . . . . . . . . . . . . 56 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
 
4 1                    P R O C E E D I N G S 2                                                              8:31 a.m.
3                CHAIR SUNSERI: Good morning. The meeting 4 will now come to order.
5                This is the first day of the 688th meeting 6 of the Advisory Committee on Reactor Safeguards.                        I'm 7 Matthew Sunseri, the Chair of the ACRS.
8                I'll now call the roll to verify a quorum 9 and that communications are open.
10                Let's start with Ron Ballinger.
11                MEMBER BALLINGER:            Here.
12                CHAIR SUNSERI:          Vicki Bier?        Vicki, are 13 you there?    Unmute.
14                MEMBER BIER:        Sorry about that.          Yes, I'm 15 here.
16                CHAIR SUNSERI:          Okay.      Dennis Bley?
17                MEMBER BLEY:        Here.
18                CHAIR SUNSERI:          Charles Brown?
19                MEMBER BROWN:          I'm here.
20                CHAIR SUNSERI:          Vesna Dimitrijevic?
21                MEMBER DIMITRIJEVIC:                I'm here.
22                CHAIR SUNSERI:          Greg Halnon?
23                MEMBER HALNON:          Here.
24                CHAIR SUNSERI:          Walt Kirchner?
25                Walt is having some communication troubles 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 1 today.        I'm sure he'll be joining us as soon as he 2 can.
3                    Jose March-Leuba?
4                    MEMBER MARCH-LEUBA:              Here.
5                    MEMBER KIRCHNER:            Matt, I'm here.        Sorry.
6                    CHAIR SUNSERI:          Okay, good.      Great.        Got 7 you.
8                    Dave Petti?
9                    MEMBER PETTI:          Here.
10                    CHAIR SUNSERI:          Joy Rempe?
11                    MEMBER REMPE:          Here.
12                    CHAIR SUNSERI:          And myself.
13                    So,  we    have      all      members    present        and 14 communications were loud and clear.                        So, we have a 15 quorum.
16                    The ACRS was established by the Atomic 17 Energy Act and is governed by the Federal Advisory 18 Committee Act.            The ACRS section of the U.S. NRC 19 public website provides information about the history 20 of    the    ACRS  and    provides        documents      such    as      our 21 Charter,        Bylaws,      Federal        Register      notices        for 22 meetings, Letter Reports, and transcripts of all full 23 and      subcommittee      meetings,          including    all    slides 24 presented at the meetings. The Committee provides its 25 advice on safety matters to the Commission through its 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 1 publicly available Letter Reports.
2                    The Federal Register notice announcing 3 this meeting was published on August 16th, 2021, and 4 provided the agenda and instructions for interested 5 parties to provide written documents or requests and 6 opportunities to address the Committee.
7                    The Designated Federal Officer for this 8 meeting is Mr. Weidong Wang.
9                    During today's meeting, the Committee will 10 consider the following:
11                    The first topic is the Kairos Topical 12 Report        on  Fuel      Performance.                We'll    have        a 13 presentation,          and      then,      we      will    have    report 14 preparation activities.              And I do note that portions 15 of the Kairos session will be closed to discuss and 16 protect information designated as proprietary.
17                    And  then,      in    the      afternoon,    we      will 18 continue        preparations        for      our      briefing    to      the 19 Commission which is scheduled for October.
20                    The phone bridge line has been opened to 21 allow members of the public to listen in on the 22 presentation        and  Committee        discussions.          We    have 23 received no written comments or requests to make oral 24 statements        from  members        of      the    public  regarding 25 today's session.
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 1                    There will be an opportunity for public 2 comment, and we have set aside time in the agenda for 3 comments from members of the public attending or 4 listening to our meeting.                    Written comments may be 5 forwarded to Mr. Weidong Wang, the Designated Federal 6 Officer.
7                    A transcript of the open portions of the 8 meeting is being kept.                  So, it is requested that 9 speakers identify themselves and speak with sufficient 10 clarity and volume, so that they can be readily heard.
11 Additionally, participants should mute themselves when 12 not speaking.
13                    So, I just wanted to open by saying it's 14 been a while since we've gotten together.                          July was 15 our      last    Committee        meeting.              We  did    have        a 16 subcommittee          in  September.              So,      I do  appreciate 17 everyone getting back together here.
18                    And I want to acknowledge everybody's 19 patience for us and the early hour of this meeting.
20 We had intended that this meeting would be an in-21 person        meeting.      When      we    scheduled      it  as    such, 22 pandemic trends were looking beneficial to support in-23 person meetings, which we were greatly anticipating 24 and looking forward to.                  However, in light of the 25 public health trends, we could not in good conscience 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 1 schedule travel amongst the escalating rates of the 2 virus transmission.          So, we decided to postpone in-3 person meetings, not indefinitely, but we'll talk more 4 about this during our P&P session.                      But it's not 5 likely to get back together until December, even if 6 that is supported by the public health trends.
7                Anyway, that's all I wanted to say.                      So, 8 at this point in time, I will ask Member Petti if he 9 is ready to start the Kairos sessions, and turn it 10 over to Dave.
11                MEMBER PETTI:          Thank you, Mr. Chairman.
12                Let's see, would the senior staff like to 13 say something before we pass it over to Kairos?
14                MR. KENNEDY:        Yes.      Good morning.
15                This is Duke Kennedy.                  I'm the Acting 16 Chief of the Advanced Reactor Licensing Branch.                          So, 17 I will give some opening remarks.
18                So,  good      morning,          Mr. Chairman        and 19 Distinguished Members of the ACRS.                    It's my pleasure 20 to be here today to provide introductory remarks on 21 behalf of the Division of Advanced Reactors and Non-22 Power Production and Utilization Facilities in the 23 Office of Nuclear Reactor Regulation.
24                With me today is Mr. Jeffrey Schmidt of 25 the Advanced Reactor Technical Branch, who is the lead 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 1 technical        reviewer      and    will      provide    the      staff 2 presentation,        and    Mr. Richard          Rivera,  providing 3 project management support, and other members of DANU.
4                  The    staff        is        looking    forward          to 5 discussions with and feedback from the ACRS members 6 today on the Draft Safety Evaluation of the Kairos 7 Power Topical Report titled, "KP-FHR Fuel Performance 8 Methodology."          Staff        briefed        the  Kairos      Power 9 Licensing Subcommittee on this report on July 6th, 10 2021, as was mentioned.
11                  And as you will hear, this Topical Report 12 is important for Kairos' safety case and is related to 13 other Topical Reports, such as the Mechanistic Source 14 Term and Fuel Qualification Reports.
15                  We note that this meeting is the third 16 time staff and Kairos Power have had the opportunity 17 to brief the ACRS on Kairos Power Topical Reports, and 18 the staff appreciated the helpful comments from the 19 ACRS on Topical Reports covering reactor coolant, 20 scaling        methodology,      and    licensing        modernization, 21 project implementation, and the draft of the report 22 that's the subject of today's meeting.
23                  The staff looks forward to continuing to 24 work with the Chairman and the rest of the ACRS 25 members and staff as we complete the reviews of more 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 1 Kairos        Power  Topical      Reports        and  review    license 2 applications for facilities that will use the Kairos 3 Power design.
4                    We expect to receive a construction permit 5 application for the Kairos Power's Hermes Test Reactor 6 later this year.
7                    I'd like to highlight that the working 8 relationship between NRC staff and Kairos Power was 9 excellent.          Similar to previous reviews of Kairos 10 Power Topical Reports, the staff has used public 11 meetings        as  an    efficient          means      for  addressing 12 technical        issues    without        the      need  for  extensive 13 interactions via requests for additional information.
14                    Finally, I'd like to thank the technical 15 staff from the Advanced Reactor Technical Branch and 16 DANU for their efforts to produce a high-quality Draft 17 Safety Evaluation and the staff from the Office of 18 Research for their valuable support.
19                    That concludes my opening remarks, and I 20 guess we'll turn it over to Kairos Power.
21                    MR. TOMKINS:            Okay.        My name is James 22 Tomkins.          I'm Kairos Power licensing and focused 23 mainly on Fuel Topical Reports and Chapter 4 of the 24 PSAR.
25                    So, we have Blaise Collin, who is one of 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 1 our fuel performance experts, who will present an 2 overview of the Topical Report.
3                  So, Blaise, I think you're on?
4                  MR. COLLIN:        Yes, I am on.
5                  Good morning, everybody.
6                  MR. TOMKINS:        So, with that said, I will 7 turn it over to Blaise. He's going to present a high-8 level        overview  of    the    Fuel      Performance    Topical, 9 because we did cover it in pretty substantial detail 10 at the last meeting.            And this is a public meeting.
11                  So, Weidong, if you can set up Blaise, so 12 that he can share his screen?
13                  And,  Blaise,      go      ahead    and share      your 14 screen and take it away.
15                  MR. WANG:          Blaise        is  already      as      a 16 presenter.        So, he can share the screen.
17                  MR. TOMKINS:        Okay.
18                  MEMBER PETTI:        We don't see anything yet, 19 Blaise.
20                  MR. COLLIN:            Good morning, everybody, 21 again.
22                  Sorry for the technical blip.                  The team 23 has asked, when it actually starts, that I share my 24 screen.        I am not presenter anymore at the moment.
25 So, we ask the ACRS if they could make me one again.
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 1                CHAIR SUNSERI:          My screen shows you as a 2 presenter. This is Matt.
3                MR. COLLIN:        Okay.        Now it seems to be 4 working again. I'm not sure what you're seeing.                    Are 5 you seeing my presentation?
6                MEMBER PETTI:          There we go.      We can see 7 it.
8                MR. COLLIN: All right. Okay, here we go.
9                All  right.          Sorry      for  the  technical 10 difficulties.
11                Good  morning,        Mr.      Chairman,  and      good 12 morning, Members of the ACRS Committee.                Good morning 13 to the staff and the public listening in.
14                This will be an overview of our Fuel 15 Performance Methodology Topical Report.                  We already 16 had an extensive discussion about this Topical Report 17 with the ACRS Subcommittee in early July.                  This will 18 be a high-level public presentation in which we, 19 obviously, do not disclose any of our proprietary 20 material.
21                So, the Topical Report for October from 22 Kairos Power contains the following introduction.
23 Basically, it covers how we modeled the behavior of 24 TRISO fuel under our KP-FHR conditions, and also 25 discusses how we intend to perform verification and 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 1 validation, including answers on the quantification of 2 the fuel performance code which is named KP-BISON.
3 It's the Kairos Powers commercial version of the BISON 4 code developed at INL.                  And there's a consequence 5 section in the Topical Report that describes exactly 6 how we intend to perform fuel performance analysis 7 with KP-BISON.
8                    So, as many of you know, this is just a 9 slide presenting an overview of TRISO fuel behavior 10 when put under neutron flux. A TRISO particle is made 11 out of, in our case, a UCO kernel, which is uranium 12 oxycarbide fuel.              That kernel is surrounded by a 13 carbon        buffer  and    three      outer      coating  layers,        a 14 silicon          carbide    layer        sandwiched        between        two 15 pyrocarbon layers.
16                    So,    all      these        layers,    all      these 17 constituents have various behaviors. When under flux, 18 the kernel tends to swell outward. The buffer and the 19 PyC layers tend to shrink early during irradiation and 20 reverse to swelling when neutron fluence accumulates.
21 And the SiC layer, which is sandwiched here between 22 the two PyC layers, tends to have pretty much elastic 23 behavior.
24                    So, the whole purpose of, I mean, one of 25 the purposes of our fuel performance calculation is, 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 1 obviously, to ensure the integrity of the fuel when 2 put      under      the  KP-FHR        irradiation          conditions,        and 3 therefore, we need to calculate the elemental changes 4 of      all    these    coating        layers        and    calculate        the 5 associated stresses to these dimensional changes.
6                      Again, something that is pretty well known 7 by      the    TRISO    community,          historically,        and      more 8 recently with the development of the Advanced Gas 9 Reactor Program by their department of energy, the 10 fuel failure mechanisms have been identified for TRISO 11 fuel, in general, and UCO fuel, in particular.                              These 12 are listed on the slide.
13                      There    is    a  potential          pressure    vessel 14 failure          of    TRISO      particles          that    results      from 15 increasing internal pressure inside the particle, that 16 pressure coming from fission gas.                        And in the case of 17 UO2 fuel, it can also come from the formation of 18 carbon monoxide.
19                      As I mentioned earlier, the PyC layers 20 tend to shrink early during irradiation, and that 21 could, in particular, lead to the cracking of IPyC 22 layer.        That cracking can itself lead to a failure of 23 the      silicon      carbide        layer      by,      basically,      adding 24 additional stress on the silicon carbide layer.
25                      Another phenomena that exists between the 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 1 IPyC and the SiC is the potential debonding between 2 the two layers that will also put stress on the 3 silicon carbide layer, potentially, again, leading to 4 its failure.
5                There    are      other        phenomena      that      are 6 specific to UO2, like kernel migrations, where the 7 kernel would migrate towards the SiC layer because of 8 accumulation of carbon monoxide on one side of the 9 layer, the particle pushing the kernel in the other 10 direction. And once the kernel contacts the coating 11 layers, the outer coating layers, it could fail the 12 silicon (audio interference).
13                (Audio interference) attacked by fission 14 products that are, obviously, generated in the kernel 15 or by, in the case of UO2, it could be chemically 16 attacked by carbon monoxide, and that also could lead 17 to its failure when the thickness of the silicon 18 carbide layer gets too thin.
19                At very high temperature, the silicon 20 carbide layer might or would also decompose between 21 its constituent silicon, on the one side, and carbon, 22 on the other side.        That only occurs at temperatures 23 above about 2,000 degrees Celsius, so far out of reach 24 of KP-FHR temperatures.
25                And  finally,          a    more    recent    failure 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 1 mechanism        that  was      observed        by    post-irradiation 2 examination of FHR fuel is a fracture of the buffer 3 that could lead to cracking of the IPyC in case the 4 IPyC        doesn't    debond        from        the      buffer      during 5 irradiation.        And as we've seen cracking of the IPyC 6 layer could itself lead to failure of the silicon 7 carbide layer.
8                    So, these are about half a dozen failure 9 mechanisms that are well identified for TRISO fuel and 10 models for the relevant failure mechanisms relevant to 11 UCO fuel, which is the Kairos Power fuel, and relevant 12 to the irradiation conditions of KP-FHR.                          So, these 13 relevant        failure    mechanisms          were      developed        and 14 implemented in BISON and, by extension, in KP-BISON, 15 with the purpose being to predict potential failure of 16 the coating layers, including the SiC layer, and 17 potential subsequent release of fission products from 18 the particle into the fluoride coolant of the KP-FHR.
19                    MEMBER MARCH-LEUBA:              This is Jose March-20 Leuba.
21                    This    is      a    good        exposition      of      the 22 degradation mechanisms of the kernel.                          Do you also 23 consider        fabrication        problems        when    it  came      out 24 defective from the factory? How are those considered?
25                    MR. COLLIN:        Correct.          So, we do have a 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 1 fuel specification, and they're similar to the actual 2 specification of the AGR program. By fabrication, you 3 can have manufacturing defects.                      These defects have 4 specifications. So, for instance, you could fabricate 5 particles with defective layers.                          So, you know by 6 fabrication that some of your particles might have a 7 defective SiC layer or defective PyC layers or a 8 missing buffer.
9                    So, you have like a set of defects that 10 were identified by previous TRISO fuel fabricators, 11 including the AGR program. And all these defects have 12 upper        allowed    limits.            So,      when    we    run      our 13 calculations        for  (audio      interference)          release        of 14 fission products, we take into account that, purely by 15 fabrication, some of these particles are potentially 16 already defective.            So, it's sort of independent of 17 additional calculations made by KP-BISON.
18                    KP-BISON would, basically, tell you if you 19 put intact particles into flux, are they going to keep 20 their integrity or are some of these coating layers 21 failed?        But, in addition to these calculations, we 22 have already a small fraction of already-existing or 23 already defective particles, and that is accounted for 24 when      we  do  calculations          of    release    of    fission 25 products.
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18 1                  MEMBER MARCH-LEUBA:              And that fraction is 2 calculated based on sampling? I mean, it's on quality 3 control?        Previous experience?              Testing?
4                  MR. COLLIN:        So, at this moment, because 5 we do not have, well, Kairos has not produced TRISO 6 particles yet.        So, at this moment, we are using this 7 specification.        And so, we have, for each potential 8 defect, there is an upper limit on the allowable 9 fraction of defects.              And we're using these upper 10 bounding values for our calculations in the short 11 term.        So, it's short-term calculations.
12                  In  the      future,        once    the  fuel        is 13 fabricated, it will be characterized and all these 14 defects        will    be      measured          as    part    of        the 15 characterization process.                So, we will, potentially, 16 we will be able to replace the upper values from the 17 fuel specification by actual measured values from 18 actual fabrication.            And obviously, we expect these 19 values to be, these measured values to be smaller than 20 with the specification, and it's the point of the 21 specification        to  reject      every      lot  whose  measured 22 characteristics would be above specification.
23                  MEMBER MARCH-LEUBA: Okay. Thank you very 24 much.
25                  MR. COLLIN:        Sure.
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19 1                  MEMBER REMPE:          This is Joy.
2                  During our Subcommittee open meeting, we 3 talked about the fact that Kairos will still need to 4 get data to show or support any statements that say 5 the coolant is a separate and independent fission 6 product release barrier.              Because we don't have, or 7 Kairos doesn't have, data to try and characterize 8 whether there's any chemical attack by the coolant on 9 the various layers of the particle.
10                  How  will      Kairos      try      and  estimate          a 11 mechanistic      source    term      when      they    have  so      much 12 uncertainty in the timing and magnitude of the fission 13 products      released?        Because        there      could    be    some 14 chemical attack by the coolant on the various layers 15 of the particles.
16                  MR. COLLIN:        So, at this moment and at 17 this time, I guess we are assuming that there will 18 actually be no interaction between the coolant and the 19 TRISO particles.        So, like in our design, in our fuel 20 design, obviously, we do have -- in the pebble form, 21 there's a layer, there's an outer shell that keeps the 22 fuel itself or the TRISO particles separate from the 23 fluoride, from the coolant.
24                  And so, we are going to conduct tests --
25 so, these tests are actually already ongoing -- to 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 1 basically study the interaction between the fluoride 2 and the graphite and the pebble; check for potential 3 infiltration of the fluoride into the pebble.                        It is 4 my understanding at this point that we do not have 5 infiltration of the fluoride into the pebble, so that 6 the fluoride is not reaching the TRISO particles.
7                MEMBER REMPE:          So, discuss those tests a 8 little bit more here on the record.                      Are they high 9 temperature or at temperature and at characteristic 10 fluids conditions?
11                MR. COLLIN:        So, I would have to let our 12 test expert discuss these.            I don't know the details.
13                MEMBER PETTI:          Blaise, can I ask you a 14 question?
15                I  understand          that      a    white  paper        on 16 mechanistic source term has come in. And I don't know 17 that my colleagues know that, but I do.                    We will be 18 reviewing that.      Will there be more information in 19 that Topical Report on this sort of topic?
20                MEMBER REMPE:          And, in particular, will 21 there be experimental data to support it?                      Because, 22 yes, I am aware that that paper has come in.                    And I'm 23 just kind of wondering because, if you don't have data 24 to support it, I'm just thinking, then, you must have 25 to take into account a lot of uncertainties with 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 1 respect to timing and magnitude.
2                MR. TOMKINS:          Yes,      Joy,  this  is      Jim 3 Tomkins.
4                I think the question you're asking is 5 really more related to the Fuel Qualification Topical 6 Report, which you will be seeing at some point in the 7 near future.
8                MEMBER REMPE:            This Topical Report, in 9 tests -- it is not saying that it's proprietary --
10 indicates that you believe that the coolant is a 11 separate and independent barrier, right?
12                MR. TOMKINS:        Yes, it is.
13                MEMBER    REMPE:            So,    I  think    it's        a 14 legitimate    question,      if  you      believe      that  it's        a 15 separate and independent barrier, and then, the fact 16 that you're mentioning release of fission products 17 here, to ask. Again, this is a big uncertainty if you 18 don't have data to support the timing and magnitude of 19 the release.
20                And I know the staff has addressed this by 21 not making a finding at this time.                    But, again, when 22 we have a lot of uncertainties, and we start having 23 the staff review things with a lot of gaps in data, 24 then there will be re-reviews as you're planning --
25 this is like the first step in a multi-stage review, 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 1 correct?
2                MR. TOMKINS:        Correct.
3                MEMBER REMPE:          So, I        just am curious on 4 what the plan is.
5                MR. TOMKINS: And we have data in the fuel 6 qualification that indicates that infiltration at the 7 pressures we're at, it does not occur.
8                MEMBER REMPE: Okay. So, do you have data 9 that      also is  considering          radiation,      temperature, 10 pressure, all of these phenomena together?                    And it's 11 characteristic of your anticipated burnup that you 12 expect for the fuel?
13                MR. TOMKINS:        That I don't know.          I don't 14 know what --
15                MR. GARDNER: So, this is Darrell Gardner.
16 I apologize for jumping in.
17                I think we're getting off-topic.                        The 18 questions being asked really are specific to another 19 Topical Report that hasn't been presented and is still 20 under review by the staff. So, I think we acknowledge 21 the comment, but we're not prepared to have the 22 conversation about fuel qualification and the testing, 23 and all that, today at this meeting.
24                MEMBER REMPE:          Okay, I'll wait.            And I 25 want to discuss this same issue with the staff.
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23 1                  Thank you.
2                  MR. COLLIN:          So,      if    I can  just      add 3 something      to  close      the      discussion        in    a      way.
4 Obviously, development of any type of fuel performance 5 code, you have to go with some assumptions about what 6 you should model and what you can, basically, ignore 7 because of insignificant impact.
8                  In the case you mention, the assumption is 9 that the fluoride will not have any deleterious effect 10 on the TRISO particles, which, as we mentioned, is 11 something that is under test.                        Obviously, if the 12 findings contradict the assumption, we'll obviously 13 have to account for that potential interaction and 14 find a way to develop the appropriate model to include 15 and implement in KP-BISON.                But, at this point, we 16 don't have any reason to believe that this will be the 17 case.
18                  As you mentioned, this is a multi-step 19 process.        We're, basically, at step one of this 20 development of our fuel performance code.                      We do have 21 a lot of verification and validation still to be done, 22 and,        of  course,        in      the        future,      potential 23 implementation of new models, depending on findings on 24 our fuel qualification tests.
25                  So, I guess I'll go ahead and discuss our 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 1 fuel performance code KP-BISON.                    So, Kairos Power, 2 which is on the left side of this slide, we decided to 3 go with UCO TRISO fuel in the fluoride salt-cooled, 4 High-Temperature Reactor.
5                On the other hand, INL, Idaho National 6 Laboratory, with its own funding early on, and then, 7 with support from the MOOSE program, has been working 8 on the development of a high fuel performance code 9 called BISON. And it was our understanding at Kairos 10 Power that there were like a lot of benefits to use 11 BISON as our fuel performance code.
12                So, we developed this collaboration with 13 INL to implement UCO TRISO models in BISON and, like 14 I mentioned earlier, get our own commercial version of 15 the code that's being called KP-BISON to run our fuel 16 performance calculations.            So, a few more words about 17 KP-BISON. As mentioned, it was chosen by Kairos Power 18 for its fuel performance code.
19                BISON sits on the MOOSE framework that 20 also has a lot of other "animals" under its framework.
21 There's like computation of benefits from using BISON 22 because of the link to MOOSE.                      We also leverage 23 extensive developments made by INL and NEAMS, not only 24 for TRISO fuel, but for fuel performance in general.
25 The code is pretty robust.
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25 1                  So, what we worked on with INL, it's a 2 conversion between Kairos and INL. So, we, basically, 3 wrote the BISON code to like almost, I would call that 4 state of the art in terms of TRISO fuel modeling. So, 5 it's      quite  a  bit    of    the    plan      where  we    imported 6 existing TRISO models into BISON.                      A lot of that work 7 has been done through an FOA award.                            So, it's a 8 collaboration; this FOA is a collaboration between 9 Kairos Power and a couple of National Labs on various 10 modeling and simulation aspects, including one on fuel 11 performance that we are working on with INL.
12                  And    obviously,          one      of  the    important 13 benefits of the using BISON as our fuel performance 14 tool is the ongoing support from the BISON team at 15 INL.        There's a group of half a dozen INL engineers 16 that are really on top of things and really helping 17 develop this TRISO modeling in BISON to, again, like 18 a state-of-the-art status.
19                  So, how does this all work?                Well, it's a 20 modeling code.        So, there's not many surprises here.
21 On      the    one  hand,        we    have        the  geometry        show 22 characteristics of the TRISO fuel, as we mentioned 23 earlier when discussing fuel properties.                        Because of 24 fabrication,        all    the      fuel      properties      will      have 25 distributions. All the properties are computed around 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 1 no known values, but they have tails extending on both 2 sides of their nominal values.
3                    We  have        our      KP-FHR        with    its        own 4 irradiation conditions, and KP-BISON takes these as 5 inputs,        and  together        with    some      of  the    material 6 properties        implemented        in    the      code  --    material 7 properties being, for instance, some of, I know we 8 mentioned like a swelling of the kernel, shrinkage of 9 the PyC layers.          So, these are material properties 10 that      are  ones  which      have      correlations        that      are 11 implemented in the code.
12                    So,    the        geometry,          the    irradiation 13 conditions, they feel into some of these material 14 properties,        and  with      all    these      input  parameters, 15 KP-BISON calculates intermediate results, such as the 16 fuel temperature or temperature in the kernel or in 17 the coating layers, the pressure coming from the 18 fission gas, the displacements of the coating layers, 19 and the stress or stresses that are induced by these 20 displacements.
21                    And all these intermediate results serve 22 the purpose of calculating the two figures of merit of 23 KP-BISON which are the probability of failure of the 24 outer        coating  layers      and    the    release    of    fission 25 products that can be directly from intact particles or 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 1 that could be enhanced by failure of some of the 2 coating layers.        So, that's the overall philosophy of 3 these KP-BISON calculations.
4                    As  I    mentioned            earlier,    the      fuel 5 properties or the fuel that is used by Kairos is 6 similar to the fuel developed by the AGR program.
7 Specifically, it is similar to, there's the same or 8 very close specification, so similar to the AGR-2 UCO 9 fuel and the AGR-5/6/7 fuel.
10                    The AGR-2 UCO fuel is discussed in a 11 Pre-Topical Report.              That's compilation of results 12 from AGR-1 and AGR-2 PIE that was issued, presented to 13 the staff, obviously, and issued in 2020.
14                    The AGR-5/6/7 is the latest portion of the 15 AGR irradiation program.                The fuel is now out of the 16 reactor and awaiting PIE.                  And obviously, a lot of 17 information        from    the      AGR-5/6/7          PIE  will    become 18 available in the upcoming years.
19                    So, it's just important to note that we 20 are relying on the fuel that proved to be robust and 21 showed        very  good      performance            during  the        AGR 22 irradiation tests.
23                    So, that's two properties are, obviously, 24 one big part of the KP-BISON input parameters.                              The 25 other inputs are the material properties and the 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 1 physical model.        So, these two tables summarize, on 2 the      one  hand,  the      material        properties    that      are 3 included in KP-BISON for all the constituents of the 4 TRISO particle.          So, there's the swelling of the 5 kernel.        We  have    elastic        properties.        We      have 6 properties that depend on the irradiation level, so, 7 basically, on a fast neutron fluence.                      Obviously, 8 thermal properties, and for the purpose of fission 9 product release, we also have diffusion coefficients 10 for a handful of isotopes and for each of the TRISO 11 constituents as well.
12                  And obviously, to capture the physical 13 behavior of the fuel, we rely on a few physical 14 models.        Some of these are very basic, like heat 15 equation,      something      you    would        find in  any      fuel 16 performance code.
17                  We're looking at things like fission gas 18 release and the pressure that fission gas will create 19 inside a particle, but we also have things that are 20 more particular to TRISO fuel like penetration of 21 palladium into the silicon carbide layers, meaning the 22 migration of palladium from the kernel into the SiC 23 and corrosion of that layer that could lead to its 24 failure.
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29 1 at      something      called        release-rate-over-birth-rate 2 ratio, which is just basically a measure of the 3 release of these short-lived fission gases over their 4 production rate.
5                  And finally, as I mentioned, we're doing 6 fission product release calculations, and we model 7 fission product transport through these kernel or 8 TRISO constituents using fission diffusions.
9                  So, all this makes, all these models and 10 properties implemented in KP-BISON -- so, the existing 11 database,        if  you    will,      is      pretty    well-suited        to 12 studying and modeling behavior of UCO TRISO fuel in 13 the KP-FHR.        So, we feel that we have a good tool to 14 now perform our fuel performance calculations in the 15 KP-FHR.
16                  So,    that      slide        shows    our  V&V,        so 17 verification and validation, plan.                        We really rely 18 heavily on these two existing benchmarks. One is from 19 the IAEA.        It's a benchmark that was already executed 20 by some of, at the time, some of the participating 21 countries.
22                  And our purpose is to go through, again, 23 all      of    these  benchmark        cases      that  cover    normal 24 operation or operational transients and, also, some of 25 the expected behavior under accident conditions.                              It 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 1 mixes verification and validation cases.                      And like I 2 said, it's been already run by a lot of different 3 codes.        So, it's a very good starting point to make 4 sure that all the TRISO models have been currently 5 implemented in BISON.
6                    A  more      recent        benchmark      from        the 7 Generation IV International Forum focuses on a couple 8 of, again, more recent experiments; namely, AGR-1, 9 AGR-2, and the European Commission test, HFR-EU1bs.
10 We will also use this benchmark to verify and validate 11 KP-BISON.
12                    And  in      addition        to      the AGR    tests, 13 including in this benchmark, we also intend to extend 14 our ow V&V to what we refer to as INL benchmark.
15 Basically, it means that we want to use even more AGR 16 data to test KP-BISON, specifically, under conditions 17 that      are  more  relevant      to      or    KP-FHR  irradiation 18 conditions.
19                    So, basically, we want to basically select 20 data that are closer to the KP-FHR envelope.                        We also 21 want to use the AGR data to look at separate effects, 22 looking        at  things      like      swelling        of the    buffer 23 -- swelling of the kernel, I'm sorry, or shrinkage of 24 the buffer; looking at cracking of the IPyC.                        Yes, so 25 we will use select data from the AGR PIE to look at 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 1 separate effects and check that KP-BISON is able to 2 reproduce the PIE data.
3                And actually, we'll rely on other existing 4 data published from German tests or, more recently, 5 tests on the HTR-PM Chinese reactor.                  So, basically, 6 like the irradiation tests they did on their fuel 7 prior to, obviously, inserting in the HTR-PM core.
8                So, a lot of different things that cover 9 -- we're trying to basically cover and use most of the 10 existing data on TRISO fuel.                  It's still a small, 11 TRISO is still a small world when compared to light-12 water reactor fuel, but we're trying to be exhaustive 13 in the data that we can use to perform the V&V of 14 KP-BISON.
15                MEMBER REMPE:          So, this is Joy.
16                I was just wondering about when you plan 17 to do a peer review.        Because isn't that required for 18 -- I assume this would be considered a newly developed 19 method, and the staff is going to require peer reviews 20 as part of a PRA of a newly developed method.                    And is 21 that in your plan?          Because I didn't recall seeing 22 that in your Topical Report.
23                MR. COLLIN:        I'm not sure I understand 24 what you mean by "new."
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32 1 been around for a while, you're adding new models to 2 it. And so, for your code, I believe, if you're going 3 to be using something that supports a PRA, which I 4 believe you're going to use the licensee modernization 5 process with your design, right?                    And so, the staff 6 usually requires newly developed methods to have a 7 peer review.      And where will that be in your code 8 development process, before or after you do the V&V?
9                MR. COLLIN:            I might let some of my 10 licensing colleagues answer that question.                      We have 11 not -- well, at least as far as I know, I have not 12 gotten into that type of discussion with the rest of 13 the Kairos team yet.        Now we're early in our V&V.                So, 14 right now, we're mostly focused on doing that V&V.
15 But Darrell or Jim, maybe you have an answer.
16                MR. TOMKINS:        Blaise, maybe Brandon can.
17                Brandon, can you address that?
18                MR. HAUGH:        Sure, I can do that.
19                Hi. This is Brandon Haugh, the Director 20 of Modeling Simulation at Kairos Power.                    Hopefully, 21 you can hear me okay.
22                So, Joy, to answer your question, I'll do 23 it in two parts.
24                So, we will go through a commercial grade 25 dedication activity for BISON and KP-BISON when we get 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 1 to that point.      So, that will be at the end or near 2 the end of our verification and validation process.
3 So, that will meet our quality assurance requirements 4 to make sure that the code performs as it's supposed 5 to.
6                When it comes to the peer review, I would 7 leave that to the PRA model, when we get to the 8 application of the licensing modernization project.
9 It wouldn't necessarily be BISON itself.                It would be 10 an application within the PRA, whether that's Level 1, 11 2, or 3, and how it's used, determining frequency and 12 consequences.
13                So,    we      haven't          committed    to        the 14 application of the licensing modernization project for 15 the Hermes Test Reactor. That's what we're focused on 16 now.
17                While this report, methodology, could be 18 applied to both, our nearer-term horizon is the non-19 power test reactor.          So, we'll be applying it in a 20 more deterministic fashion.
21                MEMBER REMPE: So, if you're just going to 22 focus for the near term on Hermes, do you really need 23 NRC approval? I mean, that's going to be built on the 24 Oak Ridge site, right?
25                MR. HAUGH:        No, it --
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34 1                  MEMBER REMPE:            So, it's not a powered 2 reactor.        So,  why    worry      about        all  these    safety 3 evaluations?
4                  MR. HAUGH:      Well, the reactor is not on a 5 DOE site. It's outside of that. So, we are licensing 6 that with the NRC.          While it is a non-power reactor, 7 we still need appropriate methods to ensure that we 8 meet the top-level regulatory requirements.                        And fuel 9 performance, since it's a fission product barrier, is 10 one of those.
11                  MEMBER REMPE:            Okay.        Well, we'll just 12 have to see how this goes.                Thank you.
13                  MR. HAUGH:        Uh-hum.
14                  MR. COLLIN:        All right.            So, back to the 15 presentation.        So, yes, this slide shows like a high-16 level        -- it's  a    high-level          flow      chart  of      fuel 17 performance analysis and methodology.                        As mentioned 18 earlier, what we're trying to do, basically, is from 19 our irradiation input parameters, which are fission 20 rate        density,    fast      fission          fluence,      and        the 21 temperature of the coolant, these are inputs to the 22 code.
23                  Our code performs thermal analyses, so 24 looking at the temperatures of all the coating layers 25 and of the kernel, performs a stress analysis and 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 1 calculates the stress in the coating layers.                  And the 2 stresses inform about potential failure of the coating 3 layers.        And    the      temperatures          inform        the 4 diffusivities,      so    the      values        of  the  diffusion 5 coefficients in the various layers, and that leads to 6 calculation of the fission product really. So, we say 7 there's like more to each of these boxes, but for a 8 public presentation, that's the high-level methodology 9 for KP-BISON analysis.
10                So, I already mentioned the fact that, 11 during quantification, all of the fuel properties will 12 be distributed around a nominal value and extend on 13 both sides of these nominal values, for the average 14 values during quantification.
15                So, basically, each property will have 16 statistical variations because of this process.                        And 17 we know from experience that particles that are in the 18 tails of these distributions are usually more likely 19 to fail. That is, for instance, when the thickness of 20 your silicon carbon layer gets too thin, it might not 21 be able to sustain the internal pressure from the 22 fission gas, if it's too thin.                So, it's more likely 23 to fail.
24                So,  we      have      to      account  for      these 25 statistical variations when assessing the probability 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 1 of failure of the fuel.                So, this table here shows 2 just a summary of all of the fuel properties that will 3 have a distribution around these new values.                        And as 4 mentioned in these bullets, part of the methodology is 5 to treat the fuel statistically, so it captures (audio 6 interference) the rise of failure probability.
7                  And this is done in KP-BISON by using 8 Monte Carlo modeling, where we, basically, sample 9 through these distributions for -- each particle is 10 sampled        through    the      distribution          of  its      fuel 11 properties.        So we can, for each particle, more 12 accurately determine if it fails or if it stays intact 13 during irradiation.
14                  That's    sort      of,      again,    a  high-level 15 summary of that Monte Carlo calculation scheme where 16 we sample the fuel properties. We let KP-BISON do its 17 -- like with the sampled particles, look at the 18 potential, you know, the particular performance of 19 that particle under KP-FHR irradiation conditions.
20 Basically, does it fail or does it stay intact?
21                  We sample many, many particles to get 22 something representative of the KP-FHR core and, also, 23 representative of the distributions of these fuel 24 properties.        And when the loop is over, we just 25 compute        the  statistics          of      all    these    sampled 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 1 calculations and come up with the overall failure 2 probability for that sample and, again, the potential 3 or subsequent fission product release.
4                  So, we have, obviously, discussed this 5 scheme in greater details with the Subcommittee in 6 July. Again, this is a high-level flow chart for this 7 public meeting.
8                  As I mentioned, part of V&V is uncertainty 9 quantification.        In general, when talking about fuel 10 performance modeling, and, in particular, for UCO, 11 uncertainty can be found in these four inputs to the 12 code:
13                  Your operating conditions. So, that would 14 be in our case the fission rate density, the neutron 15 flux, the temperature of coolant.                      All of these can 16 have      uncertainties    that      for      KP-BISON      would      come 17 from -- these are inputs that come from neutronation 18 and thermal-hydraulic codes.                    So, these codes have 19 their own uncertainties, and we, obviously, have to 20 account for the fact that all these inputs to KP-BISON 21 come with their own uncertainties.
22                  Uncertainties can also be found on the 23 material properties.            So, I think kernel swelling, 24 shrinkage      of  the  carbon        layers.          So,  all    these 25 material properties are known within a degree of 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 1 uncertainty.        And since they impact the potential or 2 the interior of the coating layer, we also have to 3 account for their potential uncertainty when running 4 KP-BISON.
5                  Some of the physical models that we use 6 are also subject to uncertainty.                        They would, for 7 instance, include diffusivities that are used to model 8 fission product transport.                    So, again, we have to 9 understand what the impact of the uncertainties on 10 these physical models, what impact they have on the 11 results calculated by KP-BISON.
12                  And finally, as already mentioned, we do 13 have uncertainties on the fuel properties that come 14 from        these  statistical          variations        during        the 15 quantification process.
16                  So, that's a lot of different parameters.
17 I think at some point we tallied up to about 60 18 different input parameters to KP-BISON.                        We already 19 know from previous codes or evolution of programs that 20 some of these input parameters have a large impact on 21 fuel performance.            And since some of them have a 22 negligible        impact,      it's      our      goal    to  run      some 23 sensitivity        studies        to    particularly          assess        the 24 relative impact of all these input parameters to the 25 code.
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39 1                  And  again,        we      find      these  two      FOMs 2 throughout the presentation.                  We are concerned about 3 the      probability    of    failure        of    the    fuel  and      the 4 potential release of fission products that would be 5 enhanced by failure of some of the coating layers.
6                  So, we give a methodology for uncertainty 7 quantification. This methodology is proprietary. So, 8 we will not discuss it in detail during the open 9 session of this meeting.            It's already been discussed 10 in early July with the Subcommittee.
11                  We feel that methodology provides us with 12 a conservative way of calculating of failure of the 13 fuel      and release    of      fission        products.      So,      the 14 methodology includes the calculation of one-sided 15 95/95 tolerance limits on these two figures of merit.
16 And we think that these tolerance limits, the way they 17 are      calculated    and    the    way      the    methodology        for 18 uncertainty quantification has been developed, we feel 19 that these are conservative tolerance limits that 20 will, then, show that we do have like a conservative 21 way of calculating the performance of the fuel in our 22 KP-FHR cores.
23                  And I think that's the end of it.
24                  MEMBER PETTI:          Members, any questions?
25                  MEMBER HALNON:          This is Greg Halnon.
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40 1                    A  quick      question        on    the  uncertainty 2 calculations.            Since      the      plant      is  not    really 3 physically          built      or      designed          yet,    from        my 4 understanding, how did you ensure that the operating 5 conditions that you chose were bounding in the fact 6 that,        since  there's      an    input        to    the  model      for 7 uncertainties -- I guess what I'm trying to get to is, 8 how did you define the operating conditions, such that 9 you bounded all the necessary fuel parameters that may 10 result from operating transients and other things that 11 may happen, based on human interactions?
12                    MR. COLLIN: So, I will, unfortunately, to 13 answer this question during this public session.                              The 14 treatment of operating conditions is a large, like 15 important part of our methodology.
16                    MEMBER    HALNON:            Okay.        Well,    we      can 17 talk --
18                    MR. COLLIN:        Yes, we can discuss; I can 19 answer that question once we hit the closed session, 20 if you --
21                    MEMBER HALNON:          Sure.      Yes.
22                    MR. TOMKINS:          And I might add, I mean, 23 Greg, we haven't made a final determination of the 24 operating condition uncertainties because it does 25 depend on the instruments we use in the plant and 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 1 things like that.          So, that isn't done yet.
2                    MEMBER HALNON:          Okay.      Well, that may be 3 the answer to the question.
4                    MR. TOMKINS:        Yes, yes.
5                    MEMBER HALNON: We can talk in more detail 6 later on.
7                    MR. COLLIN:        Yes, we do have -- they're 8 still TBD.        Again, they do not depend on -- they're, 9 you know, outside of -- well, I guess what I'm trying 10 to      say    is  like  these      are      things    that  are      not 11 controlled by KP-BISON. These are inputs to the code.
12 The code will take whatever is given to it.                              But, 13 right now, we have the way around to, again, make sure 14 that        we    run  conservative              evaluation    of      this 15 uncertainty.          But, yes, we can discuss it in more 16 detail.
17                    MEMBER HALNON:          Okay.      Yes, let's discuss 18 the relationship between the inputs and how you chose 19 the operating conditions to provide those inputs.                              I 20 think that's my question.                So, we'll talk more.
21                    MR. COLLIN:        Sure.
22                    MEMBER PETTI:          Okay.        If there's no more 23 questions, does staff have their presentation?
24                    MR. SCHMIDT:        Yes, I do.
25                    MEMBER PETTI:          Thanks, Jeff.
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42 1                  MR. SCHMIDT:          I'll log in here.
2                  Can people see this?
3                  MEMBER PETTI:          Yes.
4                  MR. SCHMIDT:          All right.          Great.
5                  Good morning, everyone.                  My name is Jeff 6 Schmidt, and I'm a Senior Reactor Systems Engineer in 7 the Advanced Reactor Technical Branch II, the Division 8 of Advanced Reactors and Non-Power Production and 9 Utilization        Facilities,        or    better      known    as    DANU.
10 We're        going  to    be      discussing          the  KP-FHR      Fuel 11 Performance Methodology Revision 3.
12                  Kairos requested approval of the Fuel 13 Performance        Methodology        Revision        3. The  Topical 14 Report is applicable to the Kairos UCO TRISO fuel for 15 the FHR non-power reactor, which has been identified 16 as Hermes earlier, and the power reactor. So, this is 17 kind of a dual-use Topical Report.                          I think that's 18 already been addressed.
19                  The TR itself identifies several open 20 items to be addressed in subsequent revisions.                          We've 21 talked about that already.                  That is a staged review.
22 So, there are some known.                    Kairos identified open 23 items, and some staff identified open items in the 24 limitation section of the SE.
25                  The    staff        review          focused      on      the 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 1 calculational framework, which is composed of UCO 2 TRISO fuel failure mechanisms, which Blaise went into 3 in some detail; uncertainty parameters and associated 4 methodology; determination of the upper tolerance 5 limits for the figures of merits of in-service failed 6 fuel fractions and fission product release. TRISO 7 being one of the important barriers to fission product 8 release,        these  outputs        from      the    fuel  performance 9 analysis        fell  into      the    mechanistic          source      term 10 methodology, which is a separate Topical Report.
11                  The    regulatory            basis,      Kairos      wants 12 flexibility so far in the licensing path.                        So, you'll 13 see that 10 CFR 50.34(a) and (b) are also listed, and 14 the          corresponding          regulations            for        design 15 certification,        combined        license        application,          and 16 standard design approvals.
17                  As mentioned, the TRISO particle is the 18 primary fission product barrier.                      So, 10 CFR 100.11, 19 "Determination of exclusion area, low population zone 20 and      population    center        distance,"          is  an  important 21 regulatory basis.
22                  And then, Kairos has a PDC 10, "Reactor 23 Design," which has been approved by staff, which, 24 basically, limits the release of TRISO, well, of 25 fission products during normal operations and AOOs.
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44 1                    Portions      of    the      Topical      Report        not 2 addressed by the Safety Evaluation, and there's a 3 number here.          So, the PIRT in Section 2.3; Section 4 2.4,        "Fission    Product        Transport,"          and    all      the 5 subsections        of  2.4;      Section        3,    "Fuel    Modeling, 6 Material Properties, and Physical Models"; Section 7 4.1.1,        "Verification      and    Validation";        Section        5, 8 "KP-BISON Code, and all subsections; Topical Report 9 (audio interference), "Defeating Coefficients for Key 10 Fission Product Modeling KP-BISON"; Section 6.4.2, 11 "TRISO and Pebble Models, including potential pebble 12 behavior and material uncertainties that could affect 13 TRISO particle failure fractions," and Section 6.3, 14 "Fission Product Release," as it pertains to fuel-15 pebble mechanical and chemical interactions with a 16 salt      environment    and      possible        wear,    which    (audio 17 interference) could be outside the scope of this 18 Topical Report.
19                    And I know there was a question on the 20 salt environment, and those type of questions are 21 being        addressed  by    the    Kairos        Fuel    Qualification 22 Topical Report.
23                    So, the staff made no findings in these 24 areas,          primarily    because          of    verification          and 25 validation and quantitative uncertainty analysis was 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 1 not provided in Revision 3.
2                  As was mentioned --
3                  MEMBER MARCH-LEUBA:                Jeff?
4                  MR. SCHMIDT:          Yes?
5                  MEMBER MARCH-LEUBA:                Yes, this is Jose.
6                  MR. SCHMIDT:          Okay.
7                  MEMBER MARCH-LEUBA:                This petition from 8 the staff, they are going to provide that in Revision 9 4 in the near future?                  Or is it going to be a 10 supplement?      Or both?
11                  MR. SCHMIDT:          Yes, I don't know.            Maybe 12 Kairos can speak to that.              I mean, my conceptual idea 13 was a Revision 4, but --
14                  MEMBER MARCH-LEUBA:                Yes, that's what I 15 was thinking because, if we issue Revision 3 as an 16 approved Topical Report, and it doesn't get superseded 17 by    a    Revision  4,    then    there        are  holes  in      this 18 approach.
19                  MR. SCHMIDT:          Yes.        Yes. So, I guess I 20 envisioned it as a Revision 4 which would supersede 21 this revision in its entirety.
22                  MEMBER MARCH-LEUBA:                Correct.
23                  MEMBER REMPE:          So, Jeff, this is Joy.
24                  MR. SCHMIDT:          Hi, Joy.
25                  MEMBER REMPE:          I guess I'm not sure from 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 1 what I've heard from Kairos.              So, it would be good to 2 hear from them because it sounded like they're going 3 to have a multi-stage review process, and you might 4 end up with six or seven of these iterations.                      And to 5 preclude -- I mean, I hope that it will all come in 6 Rev. 4 -- but to preclude having a lot of these 7 iterations    for  all      these      design        developers,        I'm 8 wondering if the staff needs to start thinking about 9 some guidance.
10                And I know I mentioned this during the 11 Subcommittee meeting on, what's the minimum set of 12 requirements for a first-step review?                    And will you 13 limit it to two or three, or can they come in 10 14 times, and then, say, "Well, we have 10 SEs from the 15 staff," or something? I just am kind of wondering how 16 many iterations there are going to be.
17                MR. SCHMIDT:          Do you want me to try to 18 handle that or do you want Kairos --
19                MR. TOMKINS: Can I address that? This is 20 Jim Tomkins. Can you hear me?
21                MEMBER REMPE:          Sure.        I'm interested in 22 Kairos' response, but I'm also interested in the 23 bigger picture for all of the design developers that 24 are coming through here.
25                MR. TOMKINS:        So, first off, it is a two-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 1 step process.        So, it's not going to be an eight-step 2 process.          And so, we're going to close these open 3 items, either with a revision to the Topical Report or 4 a separate Technical Report or possibly as part of the 5 FSAR.          We're not committing to any one of those 6 approaches at this point in time.
7                    But we're going to get an SER that says, 8 "Here's the open items."                  And we think any one of 9 those three methods is a viable way to close the open 10 items.
11                    MEMBER REMPE:        So, this is on the record, 12 and, I mean, you've got a couple of these or several 13 of these Topical Reports, and they're all kind of a 14 multi-stage review process.                    And I guess maybe I've 15 missed something, but this is the first time where 16 I've heard you say on the record, "No, we're just 17 going to have a two-step process," which gives me a 18 lot or relief, frankly.                So, we can, actually, put 19 this in our letter, that this is the first step of a 20 two-step process, is what the licensee told us on the 21 record?
22                    MR. TOMKINS:        Yes.      We might want to have 23 Darrell --
24                    MR. GARDNER:        This is --
25                    MR. TOMKINS:        Yes.
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48 1                  MR. GARDNER:            Yes,      this  is    Darrell 2 Gardner.
3                  I would argue that that's not what we 4 said.        What we said was that we recognize that, when 5 this SE is issued, it will have open items that we're 6 obligated to address as part of a future licensing 7 action, which would an FSAR or a PSAR, as the case may 8 be, or a Design Certification or a COL. So, all those 9 avenues are available in terms of licensing actions.
10 And those licensing actions could not be completed, 11 absent us addressing these open items.                      That's --
12                  MEMBER REMPE: Well, I guess I'm confused.
13 You're saying you may not even submit another Topical 14 Report?        You may just wait until the PSAR?
15                  MR. GARDNER:          I'm      saying  that    is      an 16 acceptable licensing option.                  There's no regulations 17 that require any Topical Reports be submitted at all.
18                  MEMBER REMPE:        Okay.        So, there will be a 19 lot more required in the FSAR and PSAR if that's your 20 approach.        And so, I guess we --
21                  MR. GARDNER: (Audio interference). I get 22 it.
23                  MEMBER REMPE: -- maybe should think about 24 documenting        this    in      our    letter;      that,  clearly, 25 something else has to be done, but it's unclear 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 1 whether it will come as a Topical Report or as the 2 final FSAR.
3                  MR. GARDNER:        I guess the question would 4 be    of    the Committee      is,    is    there      a  reason      that 5 decision has to be made as part of this review?
6                  MEMBER    REMPE:            No,    but,    again,        I'm 7 concerned,        not  just      with      Kairos        and  what    you're 8 planning on doing.            You're right on that.                But I am 9 wondering what is going to happen here with all of the 10 design developers and whether the staff needs to think 11 about some guidance for this process.                        Because there 12 have been --
13                  MR. GARDNER:        Sure, I understand --
14                  MEMBER REMPE:          -- some doubts in all of 15 your Topical Reports.
16                  MR. GARDNER:        I understand that, and I'd 17 like to just take the opportunity to go on the record.
18 We've had an extensive dialog with both the staff, the 19 management        team,    and      the    Commission,        about        our 20 licensing approach and our licensing strategies.                                I 21 would say we've had feedback that was very positive in 22 our approach that's consistent with a way to innovate.
23                  MEMBER REMPE:            But you can understand 24 that, again, our concern is safety, but sometimes we 25 have design developers who come in who complain about 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
 
50 1 the cost for licensing.            And if it was an endless DO 2 loop, it could really increase the cost.                  But, again, 3 if you're just going to wait until the FSAR, that's 4 another situation. I just am trying to understand the 5 vision here.
6                MEMBER MARCH-LEUBA:                  Yes, and this is 7 Jose.
8                And I understand your position from a very 9 high level, point of view, but I cannot see how you 10 can validate a KP-BISON code in the FSAR. There is no 11 section of the FSAR that says, "Validation of Codes."
12 You have to validate it before you use them.                      That's 13 my opinion.
14                MR. GARDNER:        So, this is Darrell Gardner 15 again to say that, there are a number of open items.
16 I    mentioned  three      pathways        that    are  acceptable 17 licensing vehicles to address those open items.                          You 18 could use a combination. So, typically, validation is 19 not something you would see, but you could see that in 20 a Technical Report, while other open items might be 21 addressed directly in the FSAR.
22                MEMBER HALNON:          Yes, and that's to mean 23 that all the information in a study or uncertainty 24 analysis would be in the text of an FSAR, but you 25 would reference a report or some other thing that the 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 1 staff had reviewed during the process.                    I'm assuming 2 that's what you're meaning here. Because, from Jose's 3 perspective, we wouldn't put chapters and pages and 4 pages and pages of a study in there.                      It would be a 5 lot of reference --
6                MR. TOMKINS:        Right, because it would be 7 proprietary.
8                MEMBER      HALNON:                Incorporation          by 9 reference.      Right.
10                MR. TOMKINS:        Yes.
11                MEMBER HALNON: But the staff would review 12 those referenced reports as part of the approval 13 process for the application.
14                MR. TOMKINS:        Right.
15                MR. SCHMIDT:          This      is  Jeff  Schmidt.
16 Should I move on then?
17                MEMBER PETTI:          Yes, please do.
18                MR. SCHMIDT:        Thank you.
19                So, the staff review, the staff found that 20 the        UCO TRISO    particle          failure        mechanism          is 21 acceptable,      based      on    the        expected      operating 22 conditions, subject to Limitation and Condition 3, 23 based on the AGR program data and the EPRI TRISO 24 Topical Report.
25                Other    relevant        TRISO        particle    release 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 1 mechanisms, such as manufactured defect particles and 2 dispersed uranium, are included in the calculational 3 framework.
4                  Relevant      model      uncertainties,      such        as 5 particle        manufacturing          variability,        model,        and 6 physical      properties,        and    irradiation      conditions, 7 operating conditions, were adequately accounted for.
8                  Individual              uncertainties                were 9 conservatively combined to yield an upper tolerance 10 limit for the predicted failed particle fraction and 11 the fission product release from fully intact and in-12 service failed particles.
13                  The staff SER limitations and conditions.
14 NRC-approved fuel performance failure must be used to 15 determine in-service particle failure fraction and 16 fission product release. A subsequent TR, as has been 17 talked about, may include other means to determine 18 these figures of merit.
19                  UCO TRISO --
20                  MEMBER MARCH-LEUBA:                Can you give me an 21 example of these "other means"?                    What do you have in 22 mind?
23                  MR. SCHMIDT:          Let's see.        A subsequent 24 document may include other means.                    I guess what we're 25 really saying there is the revisions of the Topical 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 1 Report will -- so, there are options in the Topical 2 Report which you could input, instead of using an 3 approved fuel performance code, for example, you could 4 use directly, say, the AGR fuel failure fractions as 5 input.          You  could      use    experimentally-derived                or 6 experimentally-based inputs into the code.
7                    That was one of the options listed in the 8 Topical        Report,  but      the    details        weren't  provided 9 sufficient for the staff to make any finding in that 10 area.
11                    MEMBER MARCH-LEUBA:              Okay. Thanks.      Yes, 12 keep going.
13                    MR. SCHMIDT:        Yes.        So, Jose, that was, 14 let's say if you wanted to use the AGR fuel failure 15 fractions, for example, as input, experimentally-16 based.        Does that make sense?
17                    MEMBER MARCH-LEUBA: Yes, basically, what 18 you are saying is that TRISO is a very good fuel and 19 you can probably bound what can possibly be a worse 20 mechanism; you don't need to calculate it?
21                    MR. SCHMIDT:            Yes,      or  you  can      use 22 experimental data.
23                    MEMBER MARCH-LEUBA:              Yes, but that's what 24 I mean by "bounding."                  And it's probably a good 25 approach.        I'm not saying it's not.
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 1                    MR. SCHMIDT:        Yes.
2                    MEMBER MARCH-LEUBA:              I understand, but I 3 would code, though.
4                    MR. SCHMIDT:        Yes, so, I mean, the staff 5 is not agreeing or disagreeing. It's just saying that 6 that was presented in the Topical Report, but we would 7 need some information about it, how that was proposed 8 to be done.
9                    So,  the      UCO    TRISO        particle    failure 10 mechanism        must  be    reevaluated            if  the  operating 11 conditions are not bounded by the UCO TRISO EPRI-AR-1A 12 Topical Report.
13                    The  Kairos      Fuel      Qualification        Topical 14 Report will address expanding the EPRI TRISO operating 15 envelope.            Kairos      has    identified          in  the      Fuel 16 Qualification Topical Report that the particle power 17 density is not bounded, at least for the KP reactor.
18 It may be bounded the Hermes reactor that's still 19 under review, but I think they acknowledge that there 20 might        be  some  additional          work      needed    there      for 21 particle power.
22                    Federal Limitations and Conditions 4, 5, 23 6,    8,    10,  and  11    exist,        due    to    information        not 24 included in the TR Revision 3, but is expected in 25 subsequent revisions.
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55 1                The methodology can be used to evaluate 2 the figures of merit -- or cannot be used, I'm sorry 3 -- cannot be used to evaluate the figures of merit for 4 AOOs, design basis accidents, beyond design basis 5 events, as a methodology for combining these with 6 bounding quasi-steady-state operating conditions was 7 not provided.
8                Some aspects of pebble performance will be 9 addressed in another TR.          And that's really referring 10 to the Kairos Fuel Qualification Topical Report.
11                Staff conclusions.              The fuel performance 12 methodology of Revision 3 Topical Report provides an 13 acceptable methodology for determining conservative 14 UCO TRISO particle fission product release from in-15 service failed and intact particles, manufacturing 16 defects, and dispersed uranium.
17                Staff    approvals            are      subject    to      the 18 Limitations and Conditions of the SER.
19                That ends my presentation.                Are there any 20 questions?
21                (No response.)
22                MEMBER PETTI:          Thank you, Jeff.
23                Hearing no further questions.
24                So, I think were' done with this session, 25 Mr. Chairman.
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56 1                CHAIR SUNSERI:            All right.      Thank you, 2 Dave.
3                We can ask for public comments at this 4 point in time.
5                And  because      we      are    using this      Teams 6 approach, it's my understanding that the public can 7 unmute their line by using *6, state their name, and 8 make their comment.
9                So, let's call for that then. So, members 10 of the public listening in, this is your opportunity 11 for making a comment.
12                If you are muted, unmute your line using 13 *6, state your name, and make your comment.
14                (No response.)
15                All right.        We are not hearing any.              So, 16 I mean, we will offer the same opportunity for direct 17 participants of the Teams line, just like we would be 18 doing if you were in the room.
19                So, any members that would like to make a 20 comment, please do so at this time.
21                (No response.)
22                All right.        Dave, it looks like we don't 23 have any comments.
24                So, at this point in time, we think we 25 would move into report preparation, which we needed to 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 1 at      least    start    in      a  closed        session,    it's        my 2 understanding.        Is that correct?
3                  MEMBER PETTI:          Correct.
4                  CHAIR SUNSERI:            All right.      So, let's do 5 this.        Let's take a 30-minute break.                We'll reconvene 6 at 10:30 Eastern time in closed session.
7                  (Whereupon, at 9:59 a.m., the open session 8 was concluded.)
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
 
KP-NRC-2109-001 September 2, 2021                                                                  Project No. 99902069 US Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
 
==Subject:==
Kairos Power LLC Presentation Materials for Kairos Power Meeting with the Advisory Committee on Reactor Safeguards on Fuel Performance Methodology Topical Report This letter transmits presentation materials for the September 8, 2021 meeting with the Advisory Committee for Reactor Safeguards (ACRS) full committee. At the meeting, participants will discuss the KP-FHR Fuel Performance Methodology Topical Report (KP-TR-010) that was submitted to the Nuclear Regulatory Commission staff for review and approval. provides the non-proprietary presentation materials. Kairos Power authorizes the Nuclear Regulatory Commission to reproduce and distribute the submitted non-proprietary content, as necessary, to support the conduct of their regulatory responsibilities.
If you have any questions or need any additional information, please contact James Tomkins at tomkins@kairospower.com or (510) 808-5265, or Darrell Gardner at gardner@kairospower.com or (704)-769-1226.
Sincerely, Peter Hastings, PE Vice President, Regulatory Affairs and Quality
 
==Enclosures:==
: 1) Presentation Materials for the September 8, 2021 ACRS Meeting (Non-Proprietary)
Kairos Power LLC www.kairospower.com 707 W Tower Ave, Suite A                  5201 Hawking Dr SE, Unit A          2115 Rexford Rd, Suite 325 Alameda, CA 94501                          Albuquerque, NM 87106                    Charlotte, NC 28211
 
KP-NRC-2109-001 Page 2 xc (w/enclosure):
William Kennedy, Acting Chief, Advanced Reactor Licensing Branch Stewart Magruder, Project Manager, Advanced Reactor and Licensing Branch
 
KP-NRC-2109-001 Enclosure 1 Presentation Materials for the September 8, 2021 ACRS Meeting (Non-Proprietary)
 
KP-FHR Fuel Performance Methodology Topical Report KAIROS POWER ACRS FULL COMMITTEE MEETING SEPTEMBER 8, 2021 Copyright © 2021 Kairos Power LLC. All Rights Reserved.
No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
Topical Report Contents
* Introduction
* Fuel Behavior (including PIRT analysis)
* Fuel Modeling
* Verification and Validation / Uncertainty Quantification
* KP-BISON Code
* Fuel Performance Analysis Methodology 2
Copyright © 2021 Kairos Power LLC. All Rights Reserved.
2 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
UCO TRISO Fuel Behavior Coating Layer                      Irradiation Behavior                            Observation Kernel                  Swells outward                              Pushes buffer outward Buffer                  Shrinks inward                              Pulls IPyC inward if not debonded Shrink early during irradiation and then Swelling starts radially at moderate fast start swelling later in irradiation as fast IPyC / OPyC                                                          neutron fluence levels and tangentially at neutron fluence accumulates higher fast neutron fluence levels Dimensional changes are anisotropic PyC shrinkage provides compressive stress SiC                      Elastic behavior Fission gas pressure causes tensile stress Copyright © 2021 Kairos Power LLC. All Rights Reserved.
3 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
UCO TRISO Fuel Behavior - Failure Mechanisms Key failure mechanisms identified in TRISO fuel
* Pressure vessel failure of spherical or aspherical particles resulting in the failure of all three coating layers
* Cracking of the IPyC layer leading to SiC failure
* Partial debonding of the IPyC from the SiC leading to SiC failure
* Kernel migration towards the SiC layer and its subsequent failure
* Chemical attack of the SiC layer by fission products or CO leading to its failure
* Thermal decomposition of the SiC layer at high temperatures
* Buffer fracture leading to cracking of undebonded IPyC KP-BISON models failure mechanisms relevant to UCO fuel under KP-FHR irradiation conditions with the purpose of predicting the potential failure of the SiC layer and the release of fission products.
Copyright © 021 Kairos Power LLC. All Rights Reserved.
4 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
UCO TRISO Fuel Performance Modeling - KP-BISON UCO TRISO Model in BISON Engineering-scale nuclear fuel performance code Finite-element modeling of LWR, TRISO, and metal fuels in 1D-spherical, 2D-axisymmetric, and 3D geometries Fluoride Salt-Cooled High Fully-coupled thermodynamics and species Temperature Reactor (KP-FHR) diffusion equations UCO TRISO Fuel Steady and transient reactor operations Copyright © 2021 Kairos Power LLC. All Rights Reserved.
5 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
UCO TRISO Fuel Performance Modeling - KP-BISON KP-BISON was chosen as Fuel Performance Code by
* Computational benefits from the                              framework
* Leverage of extensive development effort by.                      and
* Level of development and maturity of                            code o Co-development KP-INL o FOA award DE-NE0008854 Modeling and Simulation Development Pathways to Accelerating KP-FHR Licensing
* Efficient support from development and maintenance team (BISON Team) at INL Copyright © 2021 Kairos Power LLC. All Rights Reserved.
6 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
KP-BISON - Inputs & Outputs Geometry radius, thickness, etc.
Fuel characteristics composition, densities, etc.
Variation in as-fabricated properties Fuel temperature, fission gas pressure, displacements, stress Figures of Merit (FOMs)
Failure probability Fission product release Material properties implemented in KP-BISON Irradiation conditions Fission rate density Fast fluence Coolant temperature Copyright © 021 Kairos Power LLC. All Rights Reserved.
7 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
KP-BISON - Fuel Properties Leverage of extensive DOE effort in the development and qualification of UCO TRISO fuel (AGR Program)
KP-FHR UCO TRISO fuel is similar to AGR UCO TRISO fuels
* AGR-2 -> UCO TRISO-Coated Particle Fuel Performance -
Topical Report EPRI-AR-1(NP)-A
* AGR-5/6/7 -> AGR Programs UCO TRISO fuel qualification and margin tests AGR-5/6/7 Test Train - Courtesy of AGR Program Copyright © 2021 Kairos Power LLC. All Rights Reserved.
8 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
KP-BISON - Material Properties & Physical Models TRISO Material Properties Constituents Swelling Elastic modulus Poissons ratio                                          Existing database of material properties Kernel Irradiation-induced creep                                      and physical models suited to modeling Buffer Poissons ratio in creep IPyC                                                                                        of TRISO fuel behavior and performance Irradiation-induced dimensional changes SiC Thermal conductivity OPyC Specific heat capacity Thermal expansion Diffusion coefficients Physical Models                                                              Description Heat Equation                                      Thermal state of the particle and temperature profile across the kernel and coating layers Fission yields                                    Generation of fission products Fission gas release                                Generation of internal pressure Internal gas pressure                              Stress state of the particle potentially leading to its failure Palladium penetration                              Corrosion of the SiC layer potentially leading to its failure Release rate over birth rate (R/B) ratio          Indicator of TRISO failure Fission product transport (Fickian diffusion)      Release of fission products to the coolant Copyright © 2021 Kairos Power LLC. All Rights Reserved.
9 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
Verification & Validation INL Benchmark                                                            IAEA CRP-6                                          Gen-IV International Data                                                          Benchmark                                      Benchmark
* Code-to-code comparison with PARFUME
* Fuel Performance Models During Normal
* TRISO Fuel Performance Models Under Accident o Representative cases of KP-FHR                                  Operation And Operational Transients            Conditions o Verification: cases 1-13                    o Select AGR-1, AGR-2, and HFR-EU1bis
* AGR-1 and AGR-2 PIE and AGR-5/6/7 R/B data                                                                                safety tests o Select data within KP-FHR envelope
* Fission Product Release Behavior Models Under    o Includes code-to-code comparison during o Separate effects                                                Accident Conditions                                  normal operation o Verification: cases 1-5
* Additional PIE or R/B data                                              o Validation: cases 6-11 o German, Chinese, etc.
Copyright © 2021 Kairos Power LLC. All Rights Reserved.
10 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
Fuel Performance Analysis Methodology For each TRISO particle
* Irradiation input parameters
* Thermo-mechanical analysis of the TRISO coating layers
* Evaluation of the failure probability (stress) and fission product release (diffusivities)
Fission Rate Density Thermal Analysis                  Failure Probability Fast Neutron Fluence Stress Analysis              Fission Product Release Flibe Temperature Diffusivities Copyright © 2021 Kairos Power LLC. All Rights Reserved.
11 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
Statistical Treatment
* Particle-to-particle statistical variations in physical                            Property        Specified Mean Value dimensions and fuel properties (layer thickness, density,                  Kernel diameter (m)          425  10 etc.) that arise from the fuel fabrication process.                        Buffer thickness (m)        100  15 PyC thickness (m)              40  4 SiC thickness (m)              35  3
* Particles in the tails of the statistical distributions are more            Kernel density (g/cm3)          10.4 prone to failure.                                                          Buffer density (g/cm3)      1.05  0.10 PyC density (g/cm3)          1.90  0.05 statistical treatment of a large population of particles to                      SiC density (g/cm3)            3.19 C/U atomic ratio            0.40  0.10 compute its overall failure probability.                                            O/U atomic ratio            1.50  0.20 PyC BAF                        1.045 Monte Carlo computation scheme implemented in KP-BISON                            SiC aspect ratio                1.04 Copyright © 021 Kairos Power LLC. All Rights Reserved.
12 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
Monte Carlo Calculation Scheme Sampling Fuel Properties Sampling loop Fuel Performance Analysis of sampled particle Computation of statistics for all sampled particles Failure Probability Fission Product Release Copyright © 2021 Kairos Power LLC. All Rights Reserved.
13 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
Uncertainty Quantification Uncertainty exists in:
* Operating conditions (i.e., fission rate density, neutron flux, temperature)
* Material properties that define the mechanical state of the TRISO particles and, ultimately, the integrity of the coating layers
* Physical models that determine some of the physical quantities affecting material properties and fission product transport
* Fuel properties (geometrical dimension, density, etc.) that are tailored by fuel fabrication to obtain TRISO particles that adequately perform under irradiation sensitivity studies will be conducted to assess the quantitative impact of the variations of these input parameters to the probability of failure of the TRISO particles and subsequent release of fission products.
Copyright © 2021 Kairos Power LLC. All Rights Reserved.
14 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
Uncertainty Quantification Methodology A proprietary methodology was developed to ensure that the probability of failure of the TRISO particles and subsequent release of fission products are calculated conservatively.
In particular, the methodology derives one-sided 95/95 tolerance limits on the two FOMs.
Copyright © 2021 Kairos Power LLC. All Rights Reserved.
15 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
 
NRC Staff Evaluation of the KP-FHR Fuel Performance Methodology, Revision 3 Jeff Schmidt Senior Reactor Systems Engineer Advanced Reactor Technical Branch 2 Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation
 
Introduction
* Kairos requested approval of the KP-FHR Fuel Performance Methodology Topical Report (TR) Revision 3
* The topical report is applicable to a Kairos UCO TRISO fueled, FHR non-power or power reactor
* The TR identifies several open items to be addressed in a subsequent revision
* In addition to the Kairos identified open items, the staff identified additional items in the safety evaluation which need to be addressed in a subsequent revision(s)
* The staffs review focused on the calculational framework composed of,
      - UCO TRISO fuel failure mechanisms
      - Uncertainty parameters and associated methodology
      - Determination of the upper tolerance limits for the figures of merit (FOMs) of in-service failed fuel fraction and fission product release
* Outputs from fuel performance analysis are inputs to the mechanistic source term methodology Non-Proprietary September 8, 2021                                                                                    2 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report
 
Regulatory Basis
* Title 10 of the Code of Federal Regulations (10 CFR)
Sections 50.34(a), 50.34(b) and corresponding regulations for design certification applications, combined license applications and standard design approvals
* 10 CFR 100.11 Determination of exclusion area, low population zone and population center distance
* Kairos PDC 10 - Reactor design which has been approved by the staff (KP-TR-003-NP-A)
Non-Proprietary September 8, 2021                                                                          3 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report
 
Portions of the Topical Report Not Addressed by the Safety Evaluation
* The staff makes no finding on the following TR sections:
      - Section 2.3, Phenomena Identification and Ranking Tables
      - Section 2.4, Fission Product Transport and all the Section 2.4 subsections
      - Section 3, Fuel Modeling - Material Properties and Physical Models, and all Section 3 subsections
      - Sections 4.1.1; Verification; 4.1.2, Validation (and all 4.1.2 subsections); and 4.1.5, Validation, Verification and Uncertainty Quantification Results
      - Section 5, KP-BISON Code, and all Section 5 subsections
      - Topical report Table 3-8, Diffusion coefficients for Key Fission Products Modeled in KP-BISON
      - Section 6.4.2, TRISO and pebble models, including the potential pebble behavior and material uncertainties that could affect TRISO particle failure fractions
      - Section 6.3, Fission Product Release as it pertains to fuel pebble mechanical and chemical interactions with the salt environment, and possible wear which are stated by the vendor to be outside the scope of this tropical
* The staff made no findings in these areas primarily because no verification, validation and quantitative uncertainty analysis was provided in Revision 3 Non-Proprietary September 8, 2021                                                                                    4 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report
 
Staff Review
* The staff found the UCO TRISO particle failure mechanisms acceptable based on the expected operating conditions subject to Limitation and Condition 3 based on the AGR program data and the EPRI-AR-1-A topical report
* Other relevant TRISO particle release mechanisms such as manufactured defective particles and dispersed uranium are included in the calculational framework
* Relevant model uncertainties such as particle manufacturing variability, model and physical properties and irradiation conditions (operating conditions) were adequately accounted for
* The individual uncertainties were conservatively combined to yield an upper tolerance limit for the predicted failed particle fraction and the fission product release from fully intact and in-service failed particles Non-Proprietary September 8, 2021                                                                              5 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report
 
Staff SER Limitation and Conditions
* An NRC approved fuel performance code must be used to determine in-service particle failure faction and fission product release. A subsequent TR revision(s) may include other means to determine these FOMs.
* UCO TRISO particle failure mechanisms must be re-evaluated if operating conditions are not bounded by the UCO TRISO EPRI-AR-1-A TR. The Kairos Fuel Qualification TR will address expanding the EPRI TRISO operating envelope.
* Several Limitations and Conditions (4, 5, 6, 8, 10 and 11) exist due to information not included in TR Revision 3 but is expected in a subsequent revision(s).
* The methodology can not be used to evaluate the FOMs for AOOs, DBA and BDBE events as the methodology for combining these with the bounding quasi steady-state operating conditions was not provided.
* Some aspects of pebble performance will be addressed in another TR Non-Proprietary September 8, 2021                                                                                6 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report
 
Staff Conclusions
* The Fuel Performance Methodology, Revision 3, TR provides an acceptable methodology for determining a conservative UCO TRISO particle fission product release from in-service failed and intact particles, manufacturing defects, and dispersed uranium
* The Staff approvals are subject to the Limitations and Conditions of the SER.
Non-Proprietary September 8, 2021                                                                          7 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report
 
Acronyms/Definitions
* Topical Report (TR)
* Uranium Oxycarbide (UCO)
* Tristructural isotopic (TRISO)
* Figures of Merit (FOMs)
* Kairos Power Fluoride-Salt Cooled High Temperature Reactor (KP-FHR)
Non- Proprietary September 8, 2021                                                                                  8 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report}}

Latest revision as of 14:29, 18 January 2022

Transcript of the Advisory Committee on Reactor Safeguards 688th Full Committee Meeting, September 8, 2021, Pages 1-85 (Open)
ML21287A635
Person / Time
Issue date: 09/08/2021
From:
Advisory Committee on Reactor Safeguards
To:
Burkhart, L, ACRS
References
NRC-1635
Download: ML21287A635 (85)
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Text

Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION

Title:

Advisory Committee on Reactor Safeguards Docket Number: (n/a)

Location: teleconference Date: Wednesday, September 8, 2021 Work Order No.: NRC-1635 Pages 1-57 NEAL R. GROSS AND CO., INC.

Court Reporters and Transcribers 1716 14th Street, N.W., Suite 200 Washington, D.C. 20009 (202) 234-4433

1 1

2 3

4 DISCLAIMER 5

6 7 UNITED STATES NUCLEAR REGULATORY COMMISSIONS 8 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 9

10 11 The contents of this transcript of the 12 proceeding of the United States Nuclear Regulatory 13 Commission Advisory Committee on Reactor Safeguards, 14 as reported herein, is a record of the discussions 15 recorded at the meeting.

16 17 This transcript has not been reviewed, 18 corrected, and edited, and it may contain 19 inaccuracies.

20 21 22 23 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 UNITED STATES OF AMERICA 2 NUCLEAR REGULATORY COMMISSION 3 + + + + +

4 688TH MEETING 5 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 6 (ACRS) 7 + + + + +

8 OPEN MEETING 9 + + + + +

10 WEDNESDAY 11 SEPTEMBER 8, 2021 12 + + + + +

13 The Advisory Committee met via Video-14 Teleconference, at 8:30 a.m. EDT, Matthew W. Sunseri, 15 Chairman, presiding.

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

2 1 COMMITTEE MEMBERS:

2 MATTHEW W. SUNSERI, Chairman 3 JOY L. REMPE, Vice Chairman 4 WALTER L. KIRCHNER, Member-at-large 5 RONALD G. BALLINGER, Member 6 VICKI BIER, Member 7 DENNIS BLEY, Member 8 CHARLES H. BROWN, JR. Member 9 VESNA B. DIMITRIJEVIC, Member 10 GREG HALNON, Member 11 JOSE MARCH-LEUBA, Member 12 DAVID A. PETTI, Member 13 ACRS CONSULTANT:

14 STEPHEN SCHULTZ 15 DESIGNATED FEDERAL OFFICIAL:

16 WEIDONG WANG 17 ALSO PRESENT:

18 BLAISE COLLIN, Kairos Power 19 DARRELL GARDNER, Kairos Power 20 BRANDON HAUGH, Kairos Power 21 DUKE KENNEDY, NRR 22 SCOTT MOORE, Executive Director, ACRS 23 RICHARD RIVERA, Kairos Power 24 JEFFREY SCHMIDT, NRR 25 JAMES TOMKINS, Kairos Power 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 1 CONTENTS 2

3 Call to Order . . . . . . . . . . . . . . . . . . 4 4 Opening Remarks by the ACRS Chairman . . . . . . 5 5 Kairos Topical Report on Fuel Performance . . . . 8 6 Remarks from the Subcommittee Chairman . . 8 7 Presentation by Kairos Power . . . . . . . 10 8 Presentation by NRC Staff . . . . . . . . . 42 9 Public Comments (None) . . . . . . . . . . . . . 56 10 Committee Comments (None) . . . . . . . . . . . . 56 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

4 1 P R O C E E D I N G S 2 8:31 a.m.

3 CHAIR SUNSERI: Good morning. The meeting 4 will now come to order.

5 This is the first day of the 688th meeting 6 of the Advisory Committee on Reactor Safeguards. I'm 7 Matthew Sunseri, the Chair of the ACRS.

8 I'll now call the roll to verify a quorum 9 and that communications are open.

10 Let's start with Ron Ballinger.

11 MEMBER BALLINGER: Here.

12 CHAIR SUNSERI: Vicki Bier? Vicki, are 13 you there? Unmute.

14 MEMBER BIER: Sorry about that. Yes, I'm 15 here.

16 CHAIR SUNSERI: Okay. Dennis Bley?

17 MEMBER BLEY: Here.

18 CHAIR SUNSERI: Charles Brown?

19 MEMBER BROWN: I'm here.

20 CHAIR SUNSERI: Vesna Dimitrijevic?

21 MEMBER DIMITRIJEVIC: I'm here.

22 CHAIR SUNSERI: Greg Halnon?

23 MEMBER HALNON: Here.

24 CHAIR SUNSERI: Walt Kirchner?

25 Walt is having some communication troubles 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 1 today. I'm sure he'll be joining us as soon as he 2 can.

3 Jose March-Leuba?

4 MEMBER MARCH-LEUBA: Here.

5 MEMBER KIRCHNER: Matt, I'm here. Sorry.

6 CHAIR SUNSERI: Okay, good. Great. Got 7 you.

8 Dave Petti?

9 MEMBER PETTI: Here.

10 CHAIR SUNSERI: Joy Rempe?

11 MEMBER REMPE: Here.

12 CHAIR SUNSERI: And myself.

13 So, we have all members present and 14 communications were loud and clear. So, we have a 15 quorum.

16 The ACRS was established by the Atomic 17 Energy Act and is governed by the Federal Advisory 18 Committee Act. The ACRS section of the U.S. NRC 19 public website provides information about the history 20 of the ACRS and provides documents such as our 21 Charter, Bylaws, Federal Register notices for 22 meetings, Letter Reports, and transcripts of all full 23 and subcommittee meetings, including all slides 24 presented at the meetings. The Committee provides its 25 advice on safety matters to the Commission through its 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 1 publicly available Letter Reports.

2 The Federal Register notice announcing 3 this meeting was published on August 16th, 2021, and 4 provided the agenda and instructions for interested 5 parties to provide written documents or requests and 6 opportunities to address the Committee.

7 The Designated Federal Officer for this 8 meeting is Mr. Weidong Wang.

9 During today's meeting, the Committee will 10 consider the following:

11 The first topic is the Kairos Topical 12 Report on Fuel Performance. We'll have a 13 presentation, and then, we will have report 14 preparation activities. And I do note that portions 15 of the Kairos session will be closed to discuss and 16 protect information designated as proprietary.

17 And then, in the afternoon, we will 18 continue preparations for our briefing to the 19 Commission which is scheduled for October.

20 The phone bridge line has been opened to 21 allow members of the public to listen in on the 22 presentation and Committee discussions. We have 23 received no written comments or requests to make oral 24 statements from members of the public regarding 25 today's session.

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 1 There will be an opportunity for public 2 comment, and we have set aside time in the agenda for 3 comments from members of the public attending or 4 listening to our meeting. Written comments may be 5 forwarded to Mr. Weidong Wang, the Designated Federal 6 Officer.

7 A transcript of the open portions of the 8 meeting is being kept. So, it is requested that 9 speakers identify themselves and speak with sufficient 10 clarity and volume, so that they can be readily heard.

11 Additionally, participants should mute themselves when 12 not speaking.

13 So, I just wanted to open by saying it's 14 been a while since we've gotten together. July was 15 our last Committee meeting. We did have a 16 subcommittee in September. So, I do appreciate 17 everyone getting back together here.

18 And I want to acknowledge everybody's 19 patience for us and the early hour of this meeting.

20 We had intended that this meeting would be an in-21 person meeting. When we scheduled it as such, 22 pandemic trends were looking beneficial to support in-23 person meetings, which we were greatly anticipating 24 and looking forward to. However, in light of the 25 public health trends, we could not in good conscience 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 1 schedule travel amongst the escalating rates of the 2 virus transmission. So, we decided to postpone in-3 person meetings, not indefinitely, but we'll talk more 4 about this during our P&P session. But it's not 5 likely to get back together until December, even if 6 that is supported by the public health trends.

7 Anyway, that's all I wanted to say. So, 8 at this point in time, I will ask Member Petti if he 9 is ready to start the Kairos sessions, and turn it 10 over to Dave.

11 MEMBER PETTI: Thank you, Mr. Chairman.

12 Let's see, would the senior staff like to 13 say something before we pass it over to Kairos?

14 MR. KENNEDY: Yes. Good morning.

15 This is Duke Kennedy. I'm the Acting 16 Chief of the Advanced Reactor Licensing Branch. So, 17 I will give some opening remarks.

18 So, good morning, Mr. Chairman and 19 Distinguished Members of the ACRS. It's my pleasure 20 to be here today to provide introductory remarks on 21 behalf of the Division of Advanced Reactors and Non-22 Power Production and Utilization Facilities in the 23 Office of Nuclear Reactor Regulation.

24 With me today is Mr. Jeffrey Schmidt of 25 the Advanced Reactor Technical Branch, who is the lead 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 1 technical reviewer and will provide the staff 2 presentation, and Mr. Richard Rivera, providing 3 project management support, and other members of DANU.

4 The staff is looking forward to 5 discussions with and feedback from the ACRS members 6 today on the Draft Safety Evaluation of the Kairos 7 Power Topical Report titled, "KP-FHR Fuel Performance 8 Methodology." Staff briefed the Kairos Power 9 Licensing Subcommittee on this report on July 6th, 10 2021, as was mentioned.

11 And as you will hear, this Topical Report 12 is important for Kairos' safety case and is related to 13 other Topical Reports, such as the Mechanistic Source 14 Term and Fuel Qualification Reports.

15 We note that this meeting is the third 16 time staff and Kairos Power have had the opportunity 17 to brief the ACRS on Kairos Power Topical Reports, and 18 the staff appreciated the helpful comments from the 19 ACRS on Topical Reports covering reactor coolant, 20 scaling methodology, and licensing modernization, 21 project implementation, and the draft of the report 22 that's the subject of today's meeting.

23 The staff looks forward to continuing to 24 work with the Chairman and the rest of the ACRS 25 members and staff as we complete the reviews of more 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 1 Kairos Power Topical Reports and review license 2 applications for facilities that will use the Kairos 3 Power design.

4 We expect to receive a construction permit 5 application for the Kairos Power's Hermes Test Reactor 6 later this year.

7 I'd like to highlight that the working 8 relationship between NRC staff and Kairos Power was 9 excellent. Similar to previous reviews of Kairos 10 Power Topical Reports, the staff has used public 11 meetings as an efficient means for addressing 12 technical issues without the need for extensive 13 interactions via requests for additional information.

14 Finally, I'd like to thank the technical 15 staff from the Advanced Reactor Technical Branch and 16 DANU for their efforts to produce a high-quality Draft 17 Safety Evaluation and the staff from the Office of 18 Research for their valuable support.

19 That concludes my opening remarks, and I 20 guess we'll turn it over to Kairos Power.

21 MR. TOMKINS: Okay. My name is James 22 Tomkins. I'm Kairos Power licensing and focused 23 mainly on Fuel Topical Reports and Chapter 4 of the 24 PSAR.

25 So, we have Blaise Collin, who is one of 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 1 our fuel performance experts, who will present an 2 overview of the Topical Report.

3 So, Blaise, I think you're on?

4 MR. COLLIN: Yes, I am on.

5 Good morning, everybody.

6 MR. TOMKINS: So, with that said, I will 7 turn it over to Blaise. He's going to present a high-8 level overview of the Fuel Performance Topical, 9 because we did cover it in pretty substantial detail 10 at the last meeting. And this is a public meeting.

11 So, Weidong, if you can set up Blaise, so 12 that he can share his screen?

13 And, Blaise, go ahead and share your 14 screen and take it away.

15 MR. WANG: Blaise is already as a 16 presenter. So, he can share the screen.

17 MR. TOMKINS: Okay.

18 MEMBER PETTI: We don't see anything yet, 19 Blaise.

20 MR. COLLIN: Good morning, everybody, 21 again.

22 Sorry for the technical blip. The team 23 has asked, when it actually starts, that I share my 24 screen. I am not presenter anymore at the moment.

25 So, we ask the ACRS if they could make me one again.

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12 1 CHAIR SUNSERI: My screen shows you as a 2 presenter. This is Matt.

3 MR. COLLIN: Okay. Now it seems to be 4 working again. I'm not sure what you're seeing. Are 5 you seeing my presentation?

6 MEMBER PETTI: There we go. We can see 7 it.

8 MR. COLLIN: All right. Okay, here we go.

9 All right. Sorry for the technical 10 difficulties.

11 Good morning, Mr. Chairman, and good 12 morning, Members of the ACRS Committee. Good morning 13 to the staff and the public listening in.

14 This will be an overview of our Fuel 15 Performance Methodology Topical Report. We already 16 had an extensive discussion about this Topical Report 17 with the ACRS Subcommittee in early July. This will 18 be a high-level public presentation in which we, 19 obviously, do not disclose any of our proprietary 20 material.

21 So, the Topical Report for October from 22 Kairos Power contains the following introduction.

23 Basically, it covers how we modeled the behavior of 24 TRISO fuel under our KP-FHR conditions, and also 25 discusses how we intend to perform verification and 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 1 validation, including answers on the quantification of 2 the fuel performance code which is named KP-BISON.

3 It's the Kairos Powers commercial version of the BISON 4 code developed at INL. And there's a consequence 5 section in the Topical Report that describes exactly 6 how we intend to perform fuel performance analysis 7 with KP-BISON.

8 So, as many of you know, this is just a 9 slide presenting an overview of TRISO fuel behavior 10 when put under neutron flux. A TRISO particle is made 11 out of, in our case, a UCO kernel, which is uranium 12 oxycarbide fuel. That kernel is surrounded by a 13 carbon buffer and three outer coating layers, a 14 silicon carbide layer sandwiched between two 15 pyrocarbon layers.

16 So, all these layers, all these 17 constituents have various behaviors. When under flux, 18 the kernel tends to swell outward. The buffer and the 19 PyC layers tend to shrink early during irradiation and 20 reverse to swelling when neutron fluence accumulates.

21 And the SiC layer, which is sandwiched here between 22 the two PyC layers, tends to have pretty much elastic 23 behavior.

24 So, the whole purpose of, I mean, one of 25 the purposes of our fuel performance calculation is, 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 1 obviously, to ensure the integrity of the fuel when 2 put under the KP-FHR irradiation conditions, and 3 therefore, we need to calculate the elemental changes 4 of all these coating layers and calculate the 5 associated stresses to these dimensional changes.

6 Again, something that is pretty well known 7 by the TRISO community, historically, and more 8 recently with the development of the Advanced Gas 9 Reactor Program by their department of energy, the 10 fuel failure mechanisms have been identified for TRISO 11 fuel, in general, and UCO fuel, in particular. These 12 are listed on the slide.

13 There is a potential pressure vessel 14 failure of TRISO particles that results from 15 increasing internal pressure inside the particle, that 16 pressure coming from fission gas. And in the case of 17 UO2 fuel, it can also come from the formation of 18 carbon monoxide.

19 As I mentioned earlier, the PyC layers 20 tend to shrink early during irradiation, and that 21 could, in particular, lead to the cracking of IPyC 22 layer. That cracking can itself lead to a failure of 23 the silicon carbide layer by, basically, adding 24 additional stress on the silicon carbide layer.

25 Another phenomena that exists between the 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 1 IPyC and the SiC is the potential debonding between 2 the two layers that will also put stress on the 3 silicon carbide layer, potentially, again, leading to 4 its failure.

5 There are other phenomena that are 6 specific to UO2, like kernel migrations, where the 7 kernel would migrate towards the SiC layer because of 8 accumulation of carbon monoxide on one side of the 9 layer, the particle pushing the kernel in the other 10 direction. And once the kernel contacts the coating 11 layers, the outer coating layers, it could fail the 12 silicon (audio interference).

13 (Audio interference) attacked by fission 14 products that are, obviously, generated in the kernel 15 or by, in the case of UO2, it could be chemically 16 attacked by carbon monoxide, and that also could lead 17 to its failure when the thickness of the silicon 18 carbide layer gets too thin.

19 At very high temperature, the silicon 20 carbide layer might or would also decompose between 21 its constituent silicon, on the one side, and carbon, 22 on the other side. That only occurs at temperatures 23 above about 2,000 degrees Celsius, so far out of reach 24 of KP-FHR temperatures.

25 And finally, a more recent failure 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 1 mechanism that was observed by post-irradiation 2 examination of FHR fuel is a fracture of the buffer 3 that could lead to cracking of the IPyC in case the 4 IPyC doesn't debond from the buffer during 5 irradiation. And as we've seen cracking of the IPyC 6 layer could itself lead to failure of the silicon 7 carbide layer.

8 So, these are about half a dozen failure 9 mechanisms that are well identified for TRISO fuel and 10 models for the relevant failure mechanisms relevant to 11 UCO fuel, which is the Kairos Power fuel, and relevant 12 to the irradiation conditions of KP-FHR. So, these 13 relevant failure mechanisms were developed and 14 implemented in BISON and, by extension, in KP-BISON, 15 with the purpose being to predict potential failure of 16 the coating layers, including the SiC layer, and 17 potential subsequent release of fission products from 18 the particle into the fluoride coolant of the KP-FHR.

19 MEMBER MARCH-LEUBA: This is Jose March-20 Leuba.

21 This is a good exposition of the 22 degradation mechanisms of the kernel. Do you also 23 consider fabrication problems when it came out 24 defective from the factory? How are those considered?

25 MR. COLLIN: Correct. So, we do have a 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 1 fuel specification, and they're similar to the actual 2 specification of the AGR program. By fabrication, you 3 can have manufacturing defects. These defects have 4 specifications. So, for instance, you could fabricate 5 particles with defective layers. So, you know by 6 fabrication that some of your particles might have a 7 defective SiC layer or defective PyC layers or a 8 missing buffer.

9 So, you have like a set of defects that 10 were identified by previous TRISO fuel fabricators, 11 including the AGR program. And all these defects have 12 upper allowed limits. So, when we run our 13 calculations for (audio interference) release of 14 fission products, we take into account that, purely by 15 fabrication, some of these particles are potentially 16 already defective. So, it's sort of independent of 17 additional calculations made by KP-BISON.

18 KP-BISON would, basically, tell you if you 19 put intact particles into flux, are they going to keep 20 their integrity or are some of these coating layers 21 failed? But, in addition to these calculations, we 22 have already a small fraction of already-existing or 23 already defective particles, and that is accounted for 24 when we do calculations of release of fission 25 products.

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18 1 MEMBER MARCH-LEUBA: And that fraction is 2 calculated based on sampling? I mean, it's on quality 3 control? Previous experience? Testing?

4 MR. COLLIN: So, at this moment, because 5 we do not have, well, Kairos has not produced TRISO 6 particles yet. So, at this moment, we are using this 7 specification. And so, we have, for each potential 8 defect, there is an upper limit on the allowable 9 fraction of defects. And we're using these upper 10 bounding values for our calculations in the short 11 term. So, it's short-term calculations.

12 In the future, once the fuel is 13 fabricated, it will be characterized and all these 14 defects will be measured as part of the 15 characterization process. So, we will, potentially, 16 we will be able to replace the upper values from the 17 fuel specification by actual measured values from 18 actual fabrication. And obviously, we expect these 19 values to be, these measured values to be smaller than 20 with the specification, and it's the point of the 21 specification to reject every lot whose measured 22 characteristics would be above specification.

23 MEMBER MARCH-LEUBA: Okay. Thank you very 24 much.

25 MR. COLLIN: Sure.

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19 1 MEMBER REMPE: This is Joy.

2 During our Subcommittee open meeting, we 3 talked about the fact that Kairos will still need to 4 get data to show or support any statements that say 5 the coolant is a separate and independent fission 6 product release barrier. Because we don't have, or 7 Kairos doesn't have, data to try and characterize 8 whether there's any chemical attack by the coolant on 9 the various layers of the particle.

10 How will Kairos try and estimate a 11 mechanistic source term when they have so much 12 uncertainty in the timing and magnitude of the fission 13 products released? Because there could be some 14 chemical attack by the coolant on the various layers 15 of the particles.

16 MR. COLLIN: So, at this moment and at 17 this time, I guess we are assuming that there will 18 actually be no interaction between the coolant and the 19 TRISO particles. So, like in our design, in our fuel 20 design, obviously, we do have -- in the pebble form, 21 there's a layer, there's an outer shell that keeps the 22 fuel itself or the TRISO particles separate from the 23 fluoride, from the coolant.

24 And so, we are going to conduct tests --

25 so, these tests are actually already ongoing -- to 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 1 basically study the interaction between the fluoride 2 and the graphite and the pebble; check for potential 3 infiltration of the fluoride into the pebble. It is 4 my understanding at this point that we do not have 5 infiltration of the fluoride into the pebble, so that 6 the fluoride is not reaching the TRISO particles.

7 MEMBER REMPE: So, discuss those tests a 8 little bit more here on the record. Are they high 9 temperature or at temperature and at characteristic 10 fluids conditions?

11 MR. COLLIN: So, I would have to let our 12 test expert discuss these. I don't know the details.

13 MEMBER PETTI: Blaise, can I ask you a 14 question?

15 I understand that a white paper on 16 mechanistic source term has come in. And I don't know 17 that my colleagues know that, but I do. We will be 18 reviewing that. Will there be more information in 19 that Topical Report on this sort of topic?

20 MEMBER REMPE: And, in particular, will 21 there be experimental data to support it? Because, 22 yes, I am aware that that paper has come in. And I'm 23 just kind of wondering because, if you don't have data 24 to support it, I'm just thinking, then, you must have 25 to take into account a lot of uncertainties with 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 1 respect to timing and magnitude.

2 MR. TOMKINS: Yes, Joy, this is Jim 3 Tomkins.

4 I think the question you're asking is 5 really more related to the Fuel Qualification Topical 6 Report, which you will be seeing at some point in the 7 near future.

8 MEMBER REMPE: This Topical Report, in 9 tests -- it is not saying that it's proprietary --

10 indicates that you believe that the coolant is a 11 separate and independent barrier, right?

12 MR. TOMKINS: Yes, it is.

13 MEMBER REMPE: So, I think it's a 14 legitimate question, if you believe that it's a 15 separate and independent barrier, and then, the fact 16 that you're mentioning release of fission products 17 here, to ask. Again, this is a big uncertainty if you 18 don't have data to support the timing and magnitude of 19 the release.

20 And I know the staff has addressed this by 21 not making a finding at this time. But, again, when 22 we have a lot of uncertainties, and we start having 23 the staff review things with a lot of gaps in data, 24 then there will be re-reviews as you're planning --

25 this is like the first step in a multi-stage review, 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 1 correct?

2 MR. TOMKINS: Correct.

3 MEMBER REMPE: So, I just am curious on 4 what the plan is.

5 MR. TOMKINS: And we have data in the fuel 6 qualification that indicates that infiltration at the 7 pressures we're at, it does not occur.

8 MEMBER REMPE: Okay. So, do you have data 9 that also is considering radiation, temperature, 10 pressure, all of these phenomena together? And it's 11 characteristic of your anticipated burnup that you 12 expect for the fuel?

13 MR. TOMKINS: That I don't know. I don't 14 know what --

15 MR. GARDNER: So, this is Darrell Gardner.

16 I apologize for jumping in.

17 I think we're getting off-topic. The 18 questions being asked really are specific to another 19 Topical Report that hasn't been presented and is still 20 under review by the staff. So, I think we acknowledge 21 the comment, but we're not prepared to have the 22 conversation about fuel qualification and the testing, 23 and all that, today at this meeting.

24 MEMBER REMPE: Okay, I'll wait. And I 25 want to discuss this same issue with the staff.

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23 1 Thank you.

2 MR. COLLIN: So, if I can just add 3 something to close the discussion in a way.

4 Obviously, development of any type of fuel performance 5 code, you have to go with some assumptions about what 6 you should model and what you can, basically, ignore 7 because of insignificant impact.

8 In the case you mention, the assumption is 9 that the fluoride will not have any deleterious effect 10 on the TRISO particles, which, as we mentioned, is 11 something that is under test. Obviously, if the 12 findings contradict the assumption, we'll obviously 13 have to account for that potential interaction and 14 find a way to develop the appropriate model to include 15 and implement in KP-BISON. But, at this point, we 16 don't have any reason to believe that this will be the 17 case.

18 As you mentioned, this is a multi-step 19 process. We're, basically, at step one of this 20 development of our fuel performance code. We do have 21 a lot of verification and validation still to be done, 22 and, of course, in the future, potential 23 implementation of new models, depending on findings on 24 our fuel qualification tests.

25 So, I guess I'll go ahead and discuss our 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 1 fuel performance code KP-BISON. So, Kairos Power, 2 which is on the left side of this slide, we decided to 3 go with UCO TRISO fuel in the fluoride salt-cooled, 4 High-Temperature Reactor.

5 On the other hand, INL, Idaho National 6 Laboratory, with its own funding early on, and then, 7 with support from the MOOSE program, has been working 8 on the development of a high fuel performance code 9 called BISON. And it was our understanding at Kairos 10 Power that there were like a lot of benefits to use 11 BISON as our fuel performance code.

12 So, we developed this collaboration with 13 INL to implement UCO TRISO models in BISON and, like 14 I mentioned earlier, get our own commercial version of 15 the code that's being called KP-BISON to run our fuel 16 performance calculations. So, a few more words about 17 KP-BISON. As mentioned, it was chosen by Kairos Power 18 for its fuel performance code.

19 BISON sits on the MOOSE framework that 20 also has a lot of other "animals" under its framework.

21 There's like computation of benefits from using BISON 22 because of the link to MOOSE. We also leverage 23 extensive developments made by INL and NEAMS, not only 24 for TRISO fuel, but for fuel performance in general.

25 The code is pretty robust.

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25 1 So, what we worked on with INL, it's a 2 conversion between Kairos and INL. So, we, basically, 3 wrote the BISON code to like almost, I would call that 4 state of the art in terms of TRISO fuel modeling. So, 5 it's quite a bit of the plan where we imported 6 existing TRISO models into BISON. A lot of that work 7 has been done through an FOA award. So, it's a 8 collaboration; this FOA is a collaboration between 9 Kairos Power and a couple of National Labs on various 10 modeling and simulation aspects, including one on fuel 11 performance that we are working on with INL.

12 And obviously, one of the important 13 benefits of the using BISON as our fuel performance 14 tool is the ongoing support from the BISON team at 15 INL. There's a group of half a dozen INL engineers 16 that are really on top of things and really helping 17 develop this TRISO modeling in BISON to, again, like 18 a state-of-the-art status.

19 So, how does this all work? Well, it's a 20 modeling code. So, there's not many surprises here.

21 On the one hand, we have the geometry show 22 characteristics of the TRISO fuel, as we mentioned 23 earlier when discussing fuel properties. Because of 24 fabrication, all the fuel properties will have 25 distributions. All the properties are computed around 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 1 no known values, but they have tails extending on both 2 sides of their nominal values.

3 We have our KP-FHR with its own 4 irradiation conditions, and KP-BISON takes these as 5 inputs, and together with some of the material 6 properties implemented in the code -- material 7 properties being, for instance, some of, I know we 8 mentioned like a swelling of the kernel, shrinkage of 9 the PyC layers. So, these are material properties 10 that are ones which have correlations that are 11 implemented in the code.

12 So, the geometry, the irradiation 13 conditions, they feel into some of these material 14 properties, and with all these input parameters, 15 KP-BISON calculates intermediate results, such as the 16 fuel temperature or temperature in the kernel or in 17 the coating layers, the pressure coming from the 18 fission gas, the displacements of the coating layers, 19 and the stress or stresses that are induced by these 20 displacements.

21 And all these intermediate results serve 22 the purpose of calculating the two figures of merit of 23 KP-BISON which are the probability of failure of the 24 outer coating layers and the release of fission 25 products that can be directly from intact particles or 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 1 that could be enhanced by failure of some of the 2 coating layers. So, that's the overall philosophy of 3 these KP-BISON calculations.

4 As I mentioned earlier, the fuel 5 properties or the fuel that is used by Kairos is 6 similar to the fuel developed by the AGR program.

7 Specifically, it is similar to, there's the same or 8 very close specification, so similar to the AGR-2 UCO 9 fuel and the AGR-5/6/7 fuel.

10 The AGR-2 UCO fuel is discussed in a 11 Pre-Topical Report. That's compilation of results 12 from AGR-1 and AGR-2 PIE that was issued, presented to 13 the staff, obviously, and issued in 2020.

14 The AGR-5/6/7 is the latest portion of the 15 AGR irradiation program. The fuel is now out of the 16 reactor and awaiting PIE. And obviously, a lot of 17 information from the AGR-5/6/7 PIE will become 18 available in the upcoming years.

19 So, it's just important to note that we 20 are relying on the fuel that proved to be robust and 21 showed very good performance during the AGR 22 irradiation tests.

23 So, that's two properties are, obviously, 24 one big part of the KP-BISON input parameters. The 25 other inputs are the material properties and the 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 1 physical model. So, these two tables summarize, on 2 the one hand, the material properties that are 3 included in KP-BISON for all the constituents of the 4 TRISO particle. So, there's the swelling of the 5 kernel. We have elastic properties. We have 6 properties that depend on the irradiation level, so, 7 basically, on a fast neutron fluence. Obviously, 8 thermal properties, and for the purpose of fission 9 product release, we also have diffusion coefficients 10 for a handful of isotopes and for each of the TRISO 11 constituents as well.

12 And obviously, to capture the physical 13 behavior of the fuel, we rely on a few physical 14 models. Some of these are very basic, like heat 15 equation, something you would find in any fuel 16 performance code.

17 We're looking at things like fission gas 18 release and the pressure that fission gas will create 19 inside a particle, but we also have things that are 20 more particular to TRISO fuel like penetration of 21 palladium into the silicon carbide layers, meaning the 22 migration of palladium from the kernel into the SiC 23 and corrosion of that layer that could lead to its 24 failure.

25 For short-lived fission gas, we're looking 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 1 at something called release-rate-over-birth-rate 2 ratio, which is just basically a measure of the 3 release of these short-lived fission gases over their 4 production rate.

5 And finally, as I mentioned, we're doing 6 fission product release calculations, and we model 7 fission product transport through these kernel or 8 TRISO constituents using fission diffusions.

9 So, all this makes, all these models and 10 properties implemented in KP-BISON -- so, the existing 11 database, if you will, is pretty well-suited to 12 studying and modeling behavior of UCO TRISO fuel in 13 the KP-FHR. So, we feel that we have a good tool to 14 now perform our fuel performance calculations in the 15 KP-FHR.

16 So, that slide shows our V&V, so 17 verification and validation, plan. We really rely 18 heavily on these two existing benchmarks. One is from 19 the IAEA. It's a benchmark that was already executed 20 by some of, at the time, some of the participating 21 countries.

22 And our purpose is to go through, again, 23 all of these benchmark cases that cover normal 24 operation or operational transients and, also, some of 25 the expected behavior under accident conditions. It 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 1 mixes verification and validation cases. And like I 2 said, it's been already run by a lot of different 3 codes. So, it's a very good starting point to make 4 sure that all the TRISO models have been currently 5 implemented in BISON.

6 A more recent benchmark from the 7 Generation IV International Forum focuses on a couple 8 of, again, more recent experiments; namely, AGR-1, 9 AGR-2, and the European Commission test, HFR-EU1bs.

10 We will also use this benchmark to verify and validate 11 KP-BISON.

12 And in addition to the AGR tests, 13 including in this benchmark, we also intend to extend 14 our ow V&V to what we refer to as INL benchmark.

15 Basically, it means that we want to use even more AGR 16 data to test KP-BISON, specifically, under conditions 17 that are more relevant to or KP-FHR irradiation 18 conditions.

19 So, basically, we want to basically select 20 data that are closer to the KP-FHR envelope. We also 21 want to use the AGR data to look at separate effects, 22 looking at things like swelling of the buffer 23 -- swelling of the kernel, I'm sorry, or shrinkage of 24 the buffer; looking at cracking of the IPyC. Yes, so 25 we will use select data from the AGR PIE to look at 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 1 separate effects and check that KP-BISON is able to 2 reproduce the PIE data.

3 And actually, we'll rely on other existing 4 data published from German tests or, more recently, 5 tests on the HTR-PM Chinese reactor. So, basically, 6 like the irradiation tests they did on their fuel 7 prior to, obviously, inserting in the HTR-PM core.

8 So, a lot of different things that cover 9 -- we're trying to basically cover and use most of the 10 existing data on TRISO fuel. It's still a small, 11 TRISO is still a small world when compared to light-12 water reactor fuel, but we're trying to be exhaustive 13 in the data that we can use to perform the V&V of 14 KP-BISON.

15 MEMBER REMPE: So, this is Joy.

16 I was just wondering about when you plan 17 to do a peer review. Because isn't that required for 18 -- I assume this would be considered a newly developed 19 method, and the staff is going to require peer reviews 20 as part of a PRA of a newly developed method. And is 21 that in your plan? Because I didn't recall seeing 22 that in your Topical Report.

23 MR. COLLIN: I'm not sure I understand 24 what you mean by "new."

25 MEMBER REMPE: Well, although BISON has 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 1 been around for a while, you're adding new models to 2 it. And so, for your code, I believe, if you're going 3 to be using something that supports a PRA, which I 4 believe you're going to use the licensee modernization 5 process with your design, right? And so, the staff 6 usually requires newly developed methods to have a 7 peer review. And where will that be in your code 8 development process, before or after you do the V&V?

9 MR. COLLIN: I might let some of my 10 licensing colleagues answer that question. We have 11 not -- well, at least as far as I know, I have not 12 gotten into that type of discussion with the rest of 13 the Kairos team yet. Now we're early in our V&V. So, 14 right now, we're mostly focused on doing that V&V.

15 But Darrell or Jim, maybe you have an answer.

16 MR. TOMKINS: Blaise, maybe Brandon can.

17 Brandon, can you address that?

18 MR. HAUGH: Sure, I can do that.

19 Hi. This is Brandon Haugh, the Director 20 of Modeling Simulation at Kairos Power. Hopefully, 21 you can hear me okay.

22 So, Joy, to answer your question, I'll do 23 it in two parts.

24 So, we will go through a commercial grade 25 dedication activity for BISON and KP-BISON when we get 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 1 to that point. So, that will be at the end or near 2 the end of our verification and validation process.

3 So, that will meet our quality assurance requirements 4 to make sure that the code performs as it's supposed 5 to.

6 When it comes to the peer review, I would 7 leave that to the PRA model, when we get to the 8 application of the licensing modernization project.

9 It wouldn't necessarily be BISON itself. It would be 10 an application within the PRA, whether that's Level 1, 11 2, or 3, and how it's used, determining frequency and 12 consequences.

13 So, we haven't committed to the 14 application of the licensing modernization project for 15 the Hermes Test Reactor. That's what we're focused on 16 now.

17 While this report, methodology, could be 18 applied to both, our nearer-term horizon is the non-19 power test reactor. So, we'll be applying it in a 20 more deterministic fashion.

21 MEMBER REMPE: So, if you're just going to 22 focus for the near term on Hermes, do you really need 23 NRC approval? I mean, that's going to be built on the 24 Oak Ridge site, right?

25 MR. HAUGH: No, it --

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34 1 MEMBER REMPE: So, it's not a powered 2 reactor. So, why worry about all these safety 3 evaluations?

4 MR. HAUGH: Well, the reactor is not on a 5 DOE site. It's outside of that. So, we are licensing 6 that with the NRC. While it is a non-power reactor, 7 we still need appropriate methods to ensure that we 8 meet the top-level regulatory requirements. And fuel 9 performance, since it's a fission product barrier, is 10 one of those.

11 MEMBER REMPE: Okay. Well, we'll just 12 have to see how this goes. Thank you.

13 MR. HAUGH: Uh-hum.

14 MR. COLLIN: All right. So, back to the 15 presentation. So, yes, this slide shows like a high-16 level -- it's a high-level flow chart of fuel 17 performance analysis and methodology. As mentioned 18 earlier, what we're trying to do, basically, is from 19 our irradiation input parameters, which are fission 20 rate density, fast fission fluence, and the 21 temperature of the coolant, these are inputs to the 22 code.

23 Our code performs thermal analyses, so 24 looking at the temperatures of all the coating layers 25 and of the kernel, performs a stress analysis and 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 1 calculates the stress in the coating layers. And the 2 stresses inform about potential failure of the coating 3 layers. And the temperatures inform the 4 diffusivities, so the values of the diffusion 5 coefficients in the various layers, and that leads to 6 calculation of the fission product really. So, we say 7 there's like more to each of these boxes, but for a 8 public presentation, that's the high-level methodology 9 for KP-BISON analysis.

10 So, I already mentioned the fact that, 11 during quantification, all of the fuel properties will 12 be distributed around a nominal value and extend on 13 both sides of these nominal values, for the average 14 values during quantification.

15 So, basically, each property will have 16 statistical variations because of this process. And 17 we know from experience that particles that are in the 18 tails of these distributions are usually more likely 19 to fail. That is, for instance, when the thickness of 20 your silicon carbon layer gets too thin, it might not 21 be able to sustain the internal pressure from the 22 fission gas, if it's too thin. So, it's more likely 23 to fail.

24 So, we have to account for these 25 statistical variations when assessing the probability 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 1 of failure of the fuel. So, this table here shows 2 just a summary of all of the fuel properties that will 3 have a distribution around these new values. And as 4 mentioned in these bullets, part of the methodology is 5 to treat the fuel statistically, so it captures (audio 6 interference) the rise of failure probability.

7 And this is done in KP-BISON by using 8 Monte Carlo modeling, where we, basically, sample 9 through these distributions for -- each particle is 10 sampled through the distribution of its fuel 11 properties. So we can, for each particle, more 12 accurately determine if it fails or if it stays intact 13 during irradiation.

14 That's sort of, again, a high-level 15 summary of that Monte Carlo calculation scheme where 16 we sample the fuel properties. We let KP-BISON do its 17 -- like with the sampled particles, look at the 18 potential, you know, the particular performance of 19 that particle under KP-FHR irradiation conditions.

20 Basically, does it fail or does it stay intact?

21 We sample many, many particles to get 22 something representative of the KP-FHR core and, also, 23 representative of the distributions of these fuel 24 properties. And when the loop is over, we just 25 compute the statistics of all these sampled 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 1 calculations and come up with the overall failure 2 probability for that sample and, again, the potential 3 or subsequent fission product release.

4 So, we have, obviously, discussed this 5 scheme in greater details with the Subcommittee in 6 July. Again, this is a high-level flow chart for this 7 public meeting.

8 As I mentioned, part of V&V is uncertainty 9 quantification. In general, when talking about fuel 10 performance modeling, and, in particular, for UCO, 11 uncertainty can be found in these four inputs to the 12 code:

13 Your operating conditions. So, that would 14 be in our case the fission rate density, the neutron 15 flux, the temperature of coolant. All of these can 16 have uncertainties that for KP-BISON would come 17 from -- these are inputs that come from neutronation 18 and thermal-hydraulic codes. So, these codes have 19 their own uncertainties, and we, obviously, have to 20 account for the fact that all these inputs to KP-BISON 21 come with their own uncertainties.

22 Uncertainties can also be found on the 23 material properties. So, I think kernel swelling, 24 shrinkage of the carbon layers. So, all these 25 material properties are known within a degree of 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 1 uncertainty. And since they impact the potential or 2 the interior of the coating layer, we also have to 3 account for their potential uncertainty when running 4 KP-BISON.

5 Some of the physical models that we use 6 are also subject to uncertainty. They would, for 7 instance, include diffusivities that are used to model 8 fission product transport. So, again, we have to 9 understand what the impact of the uncertainties on 10 these physical models, what impact they have on the 11 results calculated by KP-BISON.

12 And finally, as already mentioned, we do 13 have uncertainties on the fuel properties that come 14 from these statistical variations during the 15 quantification process.

16 So, that's a lot of different parameters.

17 I think at some point we tallied up to about 60 18 different input parameters to KP-BISON. We already 19 know from previous codes or evolution of programs that 20 some of these input parameters have a large impact on 21 fuel performance. And since some of them have a 22 negligible impact, it's our goal to run some 23 sensitivity studies to particularly assess the 24 relative impact of all these input parameters to the 25 code.

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39 1 And again, we find these two FOMs 2 throughout the presentation. We are concerned about 3 the probability of failure of the fuel and the 4 potential release of fission products that would be 5 enhanced by failure of some of the coating layers.

6 So, we give a methodology for uncertainty 7 quantification. This methodology is proprietary. So, 8 we will not discuss it in detail during the open 9 session of this meeting. It's already been discussed 10 in early July with the Subcommittee.

11 We feel that methodology provides us with 12 a conservative way of calculating of failure of the 13 fuel and release of fission products. So, the 14 methodology includes the calculation of one-sided 15 95/95 tolerance limits on these two figures of merit.

16 And we think that these tolerance limits, the way they 17 are calculated and the way the methodology for 18 uncertainty quantification has been developed, we feel 19 that these are conservative tolerance limits that 20 will, then, show that we do have like a conservative 21 way of calculating the performance of the fuel in our 22 KP-FHR cores.

23 And I think that's the end of it.

24 MEMBER PETTI: Members, any questions?

25 MEMBER HALNON: This is Greg Halnon.

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40 1 A quick question on the uncertainty 2 calculations. Since the plant is not really 3 physically built or designed yet, from my 4 understanding, how did you ensure that the operating 5 conditions that you chose were bounding in the fact 6 that, since there's an input to the model for 7 uncertainties -- I guess what I'm trying to get to is, 8 how did you define the operating conditions, such that 9 you bounded all the necessary fuel parameters that may 10 result from operating transients and other things that 11 may happen, based on human interactions?

12 MR. COLLIN: So, I will, unfortunately, to 13 answer this question during this public session. The 14 treatment of operating conditions is a large, like 15 important part of our methodology.

16 MEMBER HALNON: Okay. Well, we can 17 talk --

18 MR. COLLIN: Yes, we can discuss; I can 19 answer that question once we hit the closed session, 20 if you --

21 MEMBER HALNON: Sure. Yes.

22 MR. TOMKINS: And I might add, I mean, 23 Greg, we haven't made a final determination of the 24 operating condition uncertainties because it does 25 depend on the instruments we use in the plant and 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 1 things like that. So, that isn't done yet.

2 MEMBER HALNON: Okay. Well, that may be 3 the answer to the question.

4 MR. TOMKINS: Yes, yes.

5 MEMBER HALNON: We can talk in more detail 6 later on.

7 MR. COLLIN: Yes, we do have -- they're 8 still TBD. Again, they do not depend on -- they're, 9 you know, outside of -- well, I guess what I'm trying 10 to say is like these are things that are not 11 controlled by KP-BISON. These are inputs to the code.

12 The code will take whatever is given to it. But, 13 right now, we have the way around to, again, make sure 14 that we run conservative evaluation of this 15 uncertainty. But, yes, we can discuss it in more 16 detail.

17 MEMBER HALNON: Okay. Yes, let's discuss 18 the relationship between the inputs and how you chose 19 the operating conditions to provide those inputs. I 20 think that's my question. So, we'll talk more.

21 MR. COLLIN: Sure.

22 MEMBER PETTI: Okay. If there's no more 23 questions, does staff have their presentation?

24 MR. SCHMIDT: Yes, I do.

25 MEMBER PETTI: Thanks, Jeff.

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42 1 MR. SCHMIDT: I'll log in here.

2 Can people see this?

3 MEMBER PETTI: Yes.

4 MR. SCHMIDT: All right. Great.

5 Good morning, everyone. My name is Jeff 6 Schmidt, and I'm a Senior Reactor Systems Engineer in 7 the Advanced Reactor Technical Branch II, the Division 8 of Advanced Reactors and Non-Power Production and 9 Utilization Facilities, or better known as DANU.

10 We're going to be discussing the KP-FHR Fuel 11 Performance Methodology Revision 3.

12 Kairos requested approval of the Fuel 13 Performance Methodology Revision 3. The Topical 14 Report is applicable to the Kairos UCO TRISO fuel for 15 the FHR non-power reactor, which has been identified 16 as Hermes earlier, and the power reactor. So, this is 17 kind of a dual-use Topical Report. I think that's 18 already been addressed.

19 The TR itself identifies several open 20 items to be addressed in subsequent revisions. We've 21 talked about that already. That is a staged review.

22 So, there are some known. Kairos identified open 23 items, and some staff identified open items in the 24 limitation section of the SE.

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43 1 calculational framework, which is composed of UCO 2 TRISO fuel failure mechanisms, which Blaise went into 3 in some detail; uncertainty parameters and associated 4 methodology; determination of the upper tolerance 5 limits for the figures of merits of in-service failed 6 fuel fractions and fission product release. TRISO 7 being one of the important barriers to fission product 8 release, these outputs from the fuel performance 9 analysis fell into the mechanistic source term 10 methodology, which is a separate Topical Report.

11 The regulatory basis, Kairos wants 12 flexibility so far in the licensing path. So, you'll 13 see that 10 CFR 50.34(a) and (b) are also listed, and 14 the corresponding regulations for design 15 certification, combined license application, and 16 standard design approvals.

17 As mentioned, the TRISO particle is the 18 primary fission product barrier. So, 10 CFR 100.11, 19 "Determination of exclusion area, low population zone 20 and population center distance," is an important 21 regulatory basis.

22 And then, Kairos has a PDC 10, "Reactor 23 Design," which has been approved by staff, which, 24 basically, limits the release of TRISO, well, of 25 fission products during normal operations and AOOs.

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44 1 Portions of the Topical Report not 2 addressed by the Safety Evaluation, and there's a 3 number here. So, the PIRT in Section 2.3; Section 4 2.4, "Fission Product Transport," and all the 5 subsections of 2.4; Section 3, "Fuel Modeling, 6 Material Properties, and Physical Models"; Section 7 4.1.1, "Verification and Validation"; Section 5, 8 "KP-BISON Code, and all subsections; Topical Report 9 (audio interference), "Defeating Coefficients for Key 10 Fission Product Modeling KP-BISON"; Section 6.4.2, 11 "TRISO and Pebble Models, including potential pebble 12 behavior and material uncertainties that could affect 13 TRISO particle failure fractions," and Section 6.3, 14 "Fission Product Release," as it pertains to fuel-15 pebble mechanical and chemical interactions with a 16 salt environment and possible wear, which (audio 17 interference) could be outside the scope of this 18 Topical Report.

19 And I know there was a question on the 20 salt environment, and those type of questions are 21 being addressed by the Kairos Fuel Qualification 22 Topical Report.

23 So, the staff made no findings in these 24 areas, primarily because of verification and 25 validation and quantitative uncertainty analysis was 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 1 not provided in Revision 3.

2 As was mentioned --

3 MEMBER MARCH-LEUBA: Jeff?

4 MR. SCHMIDT: Yes?

5 MEMBER MARCH-LEUBA: Yes, this is Jose.

6 MR. SCHMIDT: Okay.

7 MEMBER MARCH-LEUBA: This petition from 8 the staff, they are going to provide that in Revision 9 4 in the near future? Or is it going to be a 10 supplement? Or both?

11 MR. SCHMIDT: Yes, I don't know. Maybe 12 Kairos can speak to that. I mean, my conceptual idea 13 was a Revision 4, but --

14 MEMBER MARCH-LEUBA: Yes, that's what I 15 was thinking because, if we issue Revision 3 as an 16 approved Topical Report, and it doesn't get superseded 17 by a Revision 4, then there are holes in this 18 approach.

19 MR. SCHMIDT: Yes. Yes. So, I guess I 20 envisioned it as a Revision 4 which would supersede 21 this revision in its entirety.

22 MEMBER MARCH-LEUBA: Correct.

23 MEMBER REMPE: So, Jeff, this is Joy.

24 MR. SCHMIDT: Hi, Joy.

25 MEMBER REMPE: I guess I'm not sure from 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 1 what I've heard from Kairos. So, it would be good to 2 hear from them because it sounded like they're going 3 to have a multi-stage review process, and you might 4 end up with six or seven of these iterations. And to 5 preclude -- I mean, I hope that it will all come in 6 Rev. 4 -- but to preclude having a lot of these 7 iterations for all these design developers, I'm 8 wondering if the staff needs to start thinking about 9 some guidance.

10 And I know I mentioned this during the 11 Subcommittee meeting on, what's the minimum set of 12 requirements for a first-step review? And will you 13 limit it to two or three, or can they come in 10 14 times, and then, say, "Well, we have 10 SEs from the 15 staff," or something? I just am kind of wondering how 16 many iterations there are going to be.

17 MR. SCHMIDT: Do you want me to try to 18 handle that or do you want Kairos --

19 MR. TOMKINS: Can I address that? This is 20 Jim Tomkins. Can you hear me?

21 MEMBER REMPE: Sure. I'm interested in 22 Kairos' response, but I'm also interested in the 23 bigger picture for all of the design developers that 24 are coming through here.

25 MR. TOMKINS: So, first off, it is a two-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 1 step process. So, it's not going to be an eight-step 2 process. And so, we're going to close these open 3 items, either with a revision to the Topical Report or 4 a separate Technical Report or possibly as part of the 5 FSAR. We're not committing to any one of those 6 approaches at this point in time.

7 But we're going to get an SER that says, 8 "Here's the open items." And we think any one of 9 those three methods is a viable way to close the open 10 items.

11 MEMBER REMPE: So, this is on the record, 12 and, I mean, you've got a couple of these or several 13 of these Topical Reports, and they're all kind of a 14 multi-stage review process. And I guess maybe I've 15 missed something, but this is the first time where 16 I've heard you say on the record, "No, we're just 17 going to have a two-step process," which gives me a 18 lot or relief, frankly. So, we can, actually, put 19 this in our letter, that this is the first step of a 20 two-step process, is what the licensee told us on the 21 record?

22 MR. TOMKINS: Yes. We might want to have 23 Darrell --

24 MR. GARDNER: This is --

25 MR. TOMKINS: Yes.

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48 1 MR. GARDNER: Yes, this is Darrell 2 Gardner.

3 I would argue that that's not what we 4 said. What we said was that we recognize that, when 5 this SE is issued, it will have open items that we're 6 obligated to address as part of a future licensing 7 action, which would an FSAR or a PSAR, as the case may 8 be, or a Design Certification or a COL. So, all those 9 avenues are available in terms of licensing actions.

10 And those licensing actions could not be completed, 11 absent us addressing these open items. That's --

12 MEMBER REMPE: Well, I guess I'm confused.

13 You're saying you may not even submit another Topical 14 Report? You may just wait until the PSAR?

15 MR. GARDNER: I'm saying that is an 16 acceptable licensing option. There's no regulations 17 that require any Topical Reports be submitted at all.

18 MEMBER REMPE: Okay. So, there will be a 19 lot more required in the FSAR and PSAR if that's your 20 approach. And so, I guess we --

21 MR. GARDNER: (Audio interference). I get 22 it.

23 MEMBER REMPE: -- maybe should think about 24 documenting this in our letter; that, clearly, 25 something else has to be done, but it's unclear 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 1 whether it will come as a Topical Report or as the 2 final FSAR.

3 MR. GARDNER: I guess the question would 4 be of the Committee is, is there a reason that 5 decision has to be made as part of this review?

6 MEMBER REMPE: No, but, again, I'm 7 concerned, not just with Kairos and what you're 8 planning on doing. You're right on that. But I am 9 wondering what is going to happen here with all of the 10 design developers and whether the staff needs to think 11 about some guidance for this process. Because there 12 have been --

13 MR. GARDNER: Sure, I understand --

14 MEMBER REMPE: -- some doubts in all of 15 your Topical Reports.

16 MR. GARDNER: I understand that, and I'd 17 like to just take the opportunity to go on the record.

18 We've had an extensive dialog with both the staff, the 19 management team, and the Commission, about our 20 licensing approach and our licensing strategies. I 21 would say we've had feedback that was very positive in 22 our approach that's consistent with a way to innovate.

23 MEMBER REMPE: But you can understand 24 that, again, our concern is safety, but sometimes we 25 have design developers who come in who complain about 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

50 1 the cost for licensing. And if it was an endless DO 2 loop, it could really increase the cost. But, again, 3 if you're just going to wait until the FSAR, that's 4 another situation. I just am trying to understand the 5 vision here.

6 MEMBER MARCH-LEUBA: Yes, and this is 7 Jose.

8 And I understand your position from a very 9 high level, point of view, but I cannot see how you 10 can validate a KP-BISON code in the FSAR. There is no 11 section of the FSAR that says, "Validation of Codes."

12 You have to validate it before you use them. That's 13 my opinion.

14 MR. GARDNER: So, this is Darrell Gardner 15 again to say that, there are a number of open items.

16 I mentioned three pathways that are acceptable 17 licensing vehicles to address those open items. You 18 could use a combination. So, typically, validation is 19 not something you would see, but you could see that in 20 a Technical Report, while other open items might be 21 addressed directly in the FSAR.

22 MEMBER HALNON: Yes, and that's to mean 23 that all the information in a study or uncertainty 24 analysis would be in the text of an FSAR, but you 25 would reference a report or some other thing that the 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 1 staff had reviewed during the process. I'm assuming 2 that's what you're meaning here. Because, from Jose's 3 perspective, we wouldn't put chapters and pages and 4 pages and pages of a study in there. It would be a 5 lot of reference --

6 MR. TOMKINS: Right, because it would be 7 proprietary.

8 MEMBER HALNON: Incorporation by 9 reference. Right.

10 MR. TOMKINS: Yes.

11 MEMBER HALNON: But the staff would review 12 those referenced reports as part of the approval 13 process for the application.

14 MR. TOMKINS: Right.

15 MR. SCHMIDT: This is Jeff Schmidt.

16 Should I move on then?

17 MEMBER PETTI: Yes, please do.

18 MR. SCHMIDT: Thank you.

19 So, the staff review, the staff found that 20 the UCO TRISO particle failure mechanism is 21 acceptable, based on the expected operating 22 conditions, subject to Limitation and Condition 3, 23 based on the AGR program data and the EPRI TRISO 24 Topical Report.

25 Other relevant TRISO particle release 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 1 mechanisms, such as manufactured defect particles and 2 dispersed uranium, are included in the calculational 3 framework.

4 Relevant model uncertainties, such as 5 particle manufacturing variability, model, and 6 physical properties, and irradiation conditions, 7 operating conditions, were adequately accounted for.

8 Individual uncertainties were 9 conservatively combined to yield an upper tolerance 10 limit for the predicted failed particle fraction and 11 the fission product release from fully intact and in-12 service failed particles.

13 The staff SER limitations and conditions.

14 NRC-approved fuel performance failure must be used to 15 determine in-service particle failure fraction and 16 fission product release. A subsequent TR, as has been 17 talked about, may include other means to determine 18 these figures of merit.

19 UCO TRISO --

20 MEMBER MARCH-LEUBA: Can you give me an 21 example of these "other means"? What do you have in 22 mind?

23 MR. SCHMIDT: Let's see. A subsequent 24 document may include other means. I guess what we're 25 really saying there is the revisions of the Topical 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 1 Report will -- so, there are options in the Topical 2 Report which you could input, instead of using an 3 approved fuel performance code, for example, you could 4 use directly, say, the AGR fuel failure fractions as 5 input. You could use experimentally-derived or 6 experimentally-based inputs into the code.

7 That was one of the options listed in the 8 Topical Report, but the details weren't provided 9 sufficient for the staff to make any finding in that 10 area.

11 MEMBER MARCH-LEUBA: Okay. Thanks. Yes, 12 keep going.

13 MR. SCHMIDT: Yes. So, Jose, that was, 14 let's say if you wanted to use the AGR fuel failure 15 fractions, for example, as input, experimentally-16 based. Does that make sense?

17 MEMBER MARCH-LEUBA: Yes, basically, what 18 you are saying is that TRISO is a very good fuel and 19 you can probably bound what can possibly be a worse 20 mechanism; you don't need to calculate it?

21 MR. SCHMIDT: Yes, or you can use 22 experimental data.

23 MEMBER MARCH-LEUBA: Yes, but that's what 24 I mean by "bounding." And it's probably a good 25 approach. I'm not saying it's not.

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54 1 MR. SCHMIDT: Yes.

2 MEMBER MARCH-LEUBA: I understand, but I 3 would code, though.

4 MR. SCHMIDT: Yes, so, I mean, the staff 5 is not agreeing or disagreeing. It's just saying that 6 that was presented in the Topical Report, but we would 7 need some information about it, how that was proposed 8 to be done.

9 So, the UCO TRISO particle failure 10 mechanism must be reevaluated if the operating 11 conditions are not bounded by the UCO TRISO EPRI-AR-1A 12 Topical Report.

13 The Kairos Fuel Qualification Topical 14 Report will address expanding the EPRI TRISO operating 15 envelope. Kairos has identified in the Fuel 16 Qualification Topical Report that the particle power 17 density is not bounded, at least for the KP reactor.

18 It may be bounded the Hermes reactor that's still 19 under review, but I think they acknowledge that there 20 might be some additional work needed there for 21 particle power.

22 Federal Limitations and Conditions 4, 5, 23 6, 8, 10, and 11 exist, due to information not 24 included in the TR Revision 3, but is expected in 25 subsequent revisions.

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55 1 The methodology can be used to evaluate 2 the figures of merit -- or cannot be used, I'm sorry 3 -- cannot be used to evaluate the figures of merit for 4 AOOs, design basis accidents, beyond design basis 5 events, as a methodology for combining these with 6 bounding quasi-steady-state operating conditions was 7 not provided.

8 Some aspects of pebble performance will be 9 addressed in another TR. And that's really referring 10 to the Kairos Fuel Qualification Topical Report.

11 Staff conclusions. The fuel performance 12 methodology of Revision 3 Topical Report provides an 13 acceptable methodology for determining conservative 14 UCO TRISO particle fission product release from in-15 service failed and intact particles, manufacturing 16 defects, and dispersed uranium.

17 Staff approvals are subject to the 18 Limitations and Conditions of the SER.

19 That ends my presentation. Are there any 20 questions?

21 (No response.)

22 MEMBER PETTI: Thank you, Jeff.

23 Hearing no further questions.

24 So, I think were' done with this session, 25 Mr. Chairman.

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56 1 CHAIR SUNSERI: All right. Thank you, 2 Dave.

3 We can ask for public comments at this 4 point in time.

5 And because we are using this Teams 6 approach, it's my understanding that the public can 7 unmute their line by using *6, state their name, and 8 make their comment.

9 So, let's call for that then. So, members 10 of the public listening in, this is your opportunity 11 for making a comment.

12 If you are muted, unmute your line using 13 *6, state your name, and make your comment.

14 (No response.)

15 All right. We are not hearing any. So, 16 I mean, we will offer the same opportunity for direct 17 participants of the Teams line, just like we would be 18 doing if you were in the room.

19 So, any members that would like to make a 20 comment, please do so at this time.

21 (No response.)

22 All right. Dave, it looks like we don't 23 have any comments.

24 So, at this point in time, we think we 25 would move into report preparation, which we needed to 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 1 at least start in a closed session, it's my 2 understanding. Is that correct?

3 MEMBER PETTI: Correct.

4 CHAIR SUNSERI: All right. So, let's do 5 this. Let's take a 30-minute break. We'll reconvene 6 at 10:30 Eastern time in closed session.

7 (Whereupon, at 9:59 a.m., the open session 8 was concluded.)

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

KP-NRC-2109-001 September 2, 2021 Project No. 99902069 US Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Kairos Power LLC Presentation Materials for Kairos Power Meeting with the Advisory Committee on Reactor Safeguards on Fuel Performance Methodology Topical Report This letter transmits presentation materials for the September 8, 2021 meeting with the Advisory Committee for Reactor Safeguards (ACRS) full committee. At the meeting, participants will discuss the KP-FHR Fuel Performance Methodology Topical Report (KP-TR-010) that was submitted to the Nuclear Regulatory Commission staff for review and approval. provides the non-proprietary presentation materials. Kairos Power authorizes the Nuclear Regulatory Commission to reproduce and distribute the submitted non-proprietary content, as necessary, to support the conduct of their regulatory responsibilities.

If you have any questions or need any additional information, please contact James Tomkins at tomkins@kairospower.com or (510) 808-5265, or Darrell Gardner at gardner@kairospower.com or (704)-769-1226.

Sincerely, Peter Hastings, PE Vice President, Regulatory Affairs and Quality

Enclosures:

1) Presentation Materials for the September 8, 2021 ACRS Meeting (Non-Proprietary)

Kairos Power LLC www.kairospower.com 707 W Tower Ave, Suite A 5201 Hawking Dr SE, Unit A 2115 Rexford Rd, Suite 325 Alameda, CA 94501 Albuquerque, NM 87106 Charlotte, NC 28211

KP-NRC-2109-001 Page 2 xc (w/enclosure):

William Kennedy, Acting Chief, Advanced Reactor Licensing Branch Stewart Magruder, Project Manager, Advanced Reactor and Licensing Branch

KP-NRC-2109-001 Enclosure 1 Presentation Materials for the September 8, 2021 ACRS Meeting (Non-Proprietary)

KP-FHR Fuel Performance Methodology Topical Report KAIROS POWER ACRS FULL COMMITTEE MEETING SEPTEMBER 8, 2021 Copyright © 2021 Kairos Power LLC. All Rights Reserved.

No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

Topical Report Contents

  • Introduction
  • Fuel Behavior (including PIRT analysis)
  • Fuel Modeling
  • Verification and Validation / Uncertainty Quantification
  • KP-BISON Code
  • Fuel Performance Analysis Methodology 2

Copyright © 2021 Kairos Power LLC. All Rights Reserved.

2 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

UCO TRISO Fuel Behavior Coating Layer Irradiation Behavior Observation Kernel Swells outward Pushes buffer outward Buffer Shrinks inward Pulls IPyC inward if not debonded Shrink early during irradiation and then Swelling starts radially at moderate fast start swelling later in irradiation as fast IPyC / OPyC neutron fluence levels and tangentially at neutron fluence accumulates higher fast neutron fluence levels Dimensional changes are anisotropic PyC shrinkage provides compressive stress SiC Elastic behavior Fission gas pressure causes tensile stress Copyright © 2021 Kairos Power LLC. All Rights Reserved.

3 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

UCO TRISO Fuel Behavior - Failure Mechanisms Key failure mechanisms identified in TRISO fuel

  • Pressure vessel failure of spherical or aspherical particles resulting in the failure of all three coating layers
  • Cracking of the IPyC layer leading to SiC failure
  • Partial debonding of the IPyC from the SiC leading to SiC failure
  • Kernel migration towards the SiC layer and its subsequent failure
  • Chemical attack of the SiC layer by fission products or CO leading to its failure
  • Thermal decomposition of the SiC layer at high temperatures
  • Buffer fracture leading to cracking of undebonded IPyC KP-BISON models failure mechanisms relevant to UCO fuel under KP-FHR irradiation conditions with the purpose of predicting the potential failure of the SiC layer and the release of fission products.

Copyright © 021 Kairos Power LLC. All Rights Reserved.

4 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

UCO TRISO Fuel Performance Modeling - KP-BISON UCO TRISO Model in BISON Engineering-scale nuclear fuel performance code Finite-element modeling of LWR, TRISO, and metal fuels in 1D-spherical, 2D-axisymmetric, and 3D geometries Fluoride Salt-Cooled High Fully-coupled thermodynamics and species Temperature Reactor (KP-FHR) diffusion equations UCO TRISO Fuel Steady and transient reactor operations Copyright © 2021 Kairos Power LLC. All Rights Reserved.

5 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

UCO TRISO Fuel Performance Modeling - KP-BISON KP-BISON was chosen as Fuel Performance Code by

  • Computational benefits from the framework
  • Leverage of extensive development effort by. and
  • Level of development and maturity of code o Co-development KP-INL o FOA award DE-NE0008854 Modeling and Simulation Development Pathways to Accelerating KP-FHR Licensing
  • Efficient support from development and maintenance team (BISON Team) at INL Copyright © 2021 Kairos Power LLC. All Rights Reserved.

6 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

KP-BISON - Inputs & Outputs Geometry radius, thickness, etc.

Fuel characteristics composition, densities, etc.

Variation in as-fabricated properties Fuel temperature, fission gas pressure, displacements, stress Figures of Merit (FOMs)

Failure probability Fission product release Material properties implemented in KP-BISON Irradiation conditions Fission rate density Fast fluence Coolant temperature Copyright © 021 Kairos Power LLC. All Rights Reserved.

7 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

KP-BISON - Fuel Properties Leverage of extensive DOE effort in the development and qualification of UCO TRISO fuel (AGR Program)

KP-FHR UCO TRISO fuel is similar to AGR UCO TRISO fuels

  • AGR-2 -> UCO TRISO-Coated Particle Fuel Performance -

Topical Report EPRI-AR-1(NP)-A

  • AGR-5/6/7 -> AGR Programs UCO TRISO fuel qualification and margin tests AGR-5/6/7 Test Train - Courtesy of AGR Program Copyright © 2021 Kairos Power LLC. All Rights Reserved.

8 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

KP-BISON - Material Properties & Physical Models TRISO Material Properties Constituents Swelling Elastic modulus Poissons ratio Existing database of material properties Kernel Irradiation-induced creep and physical models suited to modeling Buffer Poissons ratio in creep IPyC of TRISO fuel behavior and performance Irradiation-induced dimensional changes SiC Thermal conductivity OPyC Specific heat capacity Thermal expansion Diffusion coefficients Physical Models Description Heat Equation Thermal state of the particle and temperature profile across the kernel and coating layers Fission yields Generation of fission products Fission gas release Generation of internal pressure Internal gas pressure Stress state of the particle potentially leading to its failure Palladium penetration Corrosion of the SiC layer potentially leading to its failure Release rate over birth rate (R/B) ratio Indicator of TRISO failure Fission product transport (Fickian diffusion) Release of fission products to the coolant Copyright © 2021 Kairos Power LLC. All Rights Reserved.

9 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

Verification & Validation INL Benchmark IAEA CRP-6 Gen-IV International Data Benchmark Benchmark

  • Code-to-code comparison with PARFUME
  • Fuel Performance Models During Normal
  • TRISO Fuel Performance Models Under Accident o Representative cases of KP-FHR Operation And Operational Transients Conditions o Verification: cases 1-13 o Select AGR-1, AGR-2, and HFR-EU1bis
  • AGR-1 and AGR-2 PIE and AGR-5/6/7 R/B data safety tests o Select data within KP-FHR envelope
  • Fission Product Release Behavior Models Under o Includes code-to-code comparison during o Separate effects Accident Conditions normal operation o Verification: cases 1-5
  • Additional PIE or R/B data o Validation: cases 6-11 o German, Chinese, etc.

Copyright © 2021 Kairos Power LLC. All Rights Reserved.

10 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

Fuel Performance Analysis Methodology For each TRISO particle

  • Irradiation input parameters
  • Thermo-mechanical analysis of the TRISO coating layers
  • Evaluation of the failure probability (stress) and fission product release (diffusivities)

Fission Rate Density Thermal Analysis Failure Probability Fast Neutron Fluence Stress Analysis Fission Product Release Flibe Temperature Diffusivities Copyright © 2021 Kairos Power LLC. All Rights Reserved.

11 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

Statistical Treatment

  • Particle-to-particle statistical variations in physical Property Specified Mean Value dimensions and fuel properties (layer thickness, density, Kernel diameter (m) 425 10 etc.) that arise from the fuel fabrication process. Buffer thickness (m) 100 15 PyC thickness (m) 40 4 SiC thickness (m) 35 3
  • Particles in the tails of the statistical distributions are more Kernel density (g/cm3) 10.4 prone to failure. Buffer density (g/cm3) 1.05 0.10 PyC density (g/cm3) 1.90 0.05 statistical treatment of a large population of particles to SiC density (g/cm3) 3.19 C/U atomic ratio 0.40 0.10 compute its overall failure probability. O/U atomic ratio 1.50 0.20 PyC BAF 1.045 Monte Carlo computation scheme implemented in KP-BISON SiC aspect ratio 1.04 Copyright © 021 Kairos Power LLC. All Rights Reserved.

12 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

Monte Carlo Calculation Scheme Sampling Fuel Properties Sampling loop Fuel Performance Analysis of sampled particle Computation of statistics for all sampled particles Failure Probability Fission Product Release Copyright © 2021 Kairos Power LLC. All Rights Reserved.

13 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

Uncertainty Quantification Uncertainty exists in:

  • Operating conditions (i.e., fission rate density, neutron flux, temperature)
  • Material properties that define the mechanical state of the TRISO particles and, ultimately, the integrity of the coating layers
  • Physical models that determine some of the physical quantities affecting material properties and fission product transport
  • Fuel properties (geometrical dimension, density, etc.) that are tailored by fuel fabrication to obtain TRISO particles that adequately perform under irradiation sensitivity studies will be conducted to assess the quantitative impact of the variations of these input parameters to the probability of failure of the TRISO particles and subsequent release of fission products.

Copyright © 2021 Kairos Power LLC. All Rights Reserved.

14 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

Uncertainty Quantification Methodology A proprietary methodology was developed to ensure that the probability of failure of the TRISO particles and subsequent release of fission products are calculated conservatively.

In particular, the methodology derives one-sided 95/95 tolerance limits on the two FOMs.

Copyright © 2021 Kairos Power LLC. All Rights Reserved.

15 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.

NRC Staff Evaluation of the KP-FHR Fuel Performance Methodology, Revision 3 Jeff Schmidt Senior Reactor Systems Engineer Advanced Reactor Technical Branch 2 Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation

Introduction

  • Kairos requested approval of the KP-FHR Fuel Performance Methodology Topical Report (TR) Revision 3
  • The topical report is applicable to a Kairos UCO TRISO fueled, FHR non-power or power reactor
  • The TR identifies several open items to be addressed in a subsequent revision
  • In addition to the Kairos identified open items, the staff identified additional items in the safety evaluation which need to be addressed in a subsequent revision(s)
  • The staffs review focused on the calculational framework composed of,

- UCO TRISO fuel failure mechanisms

- Uncertainty parameters and associated methodology

- Determination of the upper tolerance limits for the figures of merit (FOMs) of in-service failed fuel fraction and fission product release

  • Outputs from fuel performance analysis are inputs to the mechanistic source term methodology Non-Proprietary September 8, 2021 2 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report

Regulatory Basis

  • Title 10 of the Code of Federal Regulations (10 CFR)

Sections 50.34(a), 50.34(b) and corresponding regulations for design certification applications, combined license applications and standard design approvals

  • 10 CFR 100.11 Determination of exclusion area, low population zone and population center distance
  • Kairos PDC 10 - Reactor design which has been approved by the staff (KP-TR-003-NP-A)

Non-Proprietary September 8, 2021 3 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report

Portions of the Topical Report Not Addressed by the Safety Evaluation

  • The staff makes no finding on the following TR sections:

- Section 2.3, Phenomena Identification and Ranking Tables

- Section 2.4, Fission Product Transport and all the Section 2.4 subsections

- Section 3, Fuel Modeling - Material Properties and Physical Models, and all Section 3 subsections

- Sections 4.1.1; Verification; 4.1.2, Validation (and all 4.1.2 subsections); and 4.1.5, Validation, Verification and Uncertainty Quantification Results

- Section 5, KP-BISON Code, and all Section 5 subsections

- Topical report Table 3-8, Diffusion coefficients for Key Fission Products Modeled in KP-BISON

- Section 6.4.2, TRISO and pebble models, including the potential pebble behavior and material uncertainties that could affect TRISO particle failure fractions

- Section 6.3, Fission Product Release as it pertains to fuel pebble mechanical and chemical interactions with the salt environment, and possible wear which are stated by the vendor to be outside the scope of this tropical

  • The staff made no findings in these areas primarily because no verification, validation and quantitative uncertainty analysis was provided in Revision 3 Non-Proprietary September 8, 2021 4 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report

Staff Review

  • The staff found the UCO TRISO particle failure mechanisms acceptable based on the expected operating conditions subject to Limitation and Condition 3 based on the AGR program data and the EPRI-AR-1-A topical report
  • Other relevant TRISO particle release mechanisms such as manufactured defective particles and dispersed uranium are included in the calculational framework
  • Relevant model uncertainties such as particle manufacturing variability, model and physical properties and irradiation conditions (operating conditions) were adequately accounted for
  • The individual uncertainties were conservatively combined to yield an upper tolerance limit for the predicted failed particle fraction and the fission product release from fully intact and in-service failed particles Non-Proprietary September 8, 2021 5 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report

Staff SER Limitation and Conditions

  • An NRC approved fuel performance code must be used to determine in-service particle failure faction and fission product release. A subsequent TR revision(s) may include other means to determine these FOMs.
  • UCO TRISO particle failure mechanisms must be re-evaluated if operating conditions are not bounded by the UCO TRISO EPRI-AR-1-A TR. The Kairos Fuel Qualification TR will address expanding the EPRI TRISO operating envelope.
  • Several Limitations and Conditions (4, 5, 6, 8, 10 and 11) exist due to information not included in TR Revision 3 but is expected in a subsequent revision(s).
  • The methodology can not be used to evaluate the FOMs for AOOs, DBA and BDBE events as the methodology for combining these with the bounding quasi steady-state operating conditions was not provided.
  • Some aspects of pebble performance will be addressed in another TR Non-Proprietary September 8, 2021 6 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report

Staff Conclusions

  • The Fuel Performance Methodology, Revision 3, TR provides an acceptable methodology for determining a conservative UCO TRISO particle fission product release from in-service failed and intact particles, manufacturing defects, and dispersed uranium
  • The Staff approvals are subject to the Limitations and Conditions of the SER.

Non-Proprietary September 8, 2021 7 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report

Acronyms/Definitions

  • Topical Report (TR)
  • Tristructural isotopic (TRISO)
  • Figures of Merit (FOMs)
  • Kairos Power Fluoride-Salt Cooled High Temperature Reactor (KP-FHR)

Non- Proprietary September 8, 2021 8 ACRS Presentation on the Kairos Power, LLC Reactor Coolant Topical Report

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