ML23129A092
| ML23129A092 | |
| Person / Time | |
|---|---|
| Issue date: | 04/18/2023 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | |
| References | |
| NRC-2367 | |
| Download: ML23129A092 (1) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
Advisory Committee on Reactor Safeguards Kairos Power Licensing Subcommittee Docket Number: (n/a)
Location: teleconference Date: Tuesday, April 18, 2023 Work Order No.: NRC-2367 Pages 1-130 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1716 14th Street, N.W.
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 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 5 (ACRS) 6 + + + + +
7 KAIROS POWER LICENSING SUBCOMMITTEE 8 + + + + +
9 TUESDAY 10 APRIL 18, 2023 11 + + + + +
12 The Subcommittee met via hybrid in-person 13 and Video Teleconference, at 1:00 p.m. EDT, David 14 Petti, Chairman, presiding.
15 COMMITTEE MEMBERS:
16 DAVID PETTI, Chair 17 RONALD G. BALLINGER, Member 18 CHARLES H. BROWN, JR., Member 19 VICKI BIER, Member 20 VESNA DIMITRIJEVIC, Member 21 GREGORY HALNON, Member 22 WALT KIRCHNER, Member 23 JOSE MARCH-LEUBA, Member 24 JOY L. REMPE, Member 25 MATTHEW SUNSERI, Member 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 ACRS CONSULTANT:
2 DENNIS BLEY 3 STEPHEN SCHULTZ 4
5 DESIGNATED FEDERAL OFFICIAL:
6 WEIDONG WANG 7 LARRY BURKHART 8
9 ALSO PRESENT:
10 ODUNAYO "AYO" AYEGBUSI, NRR 11 BENJAMIN BEASLEY, NRR 12 ANDREW BIELEN, RES 13 MATTHEW DENMAN, Kairos Power 14 KIERAN DOLAN, Kairos Power 15 TIMOTHY DRZEWIECKI, Kairos Power 16 JORDAN HAGAMAN, Kairos Power 17 MICHELLE HART, NRR 18 BRANDON HAUGH, Kairos Power 19 EDWARD HELVENSTON, NRR 20 MATTHEW HISER, NRR 21 DREW PEEBLES, Kairos Power 22 JEFFREY SCHMIDT, NRR 23 KENNETH CHARLES WAGNER, Kairos Power 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
3 1 CONTENTS 2 Page 3 ACRS Chairman Introductory Remarks 4 4 NRC Staff Introductory Remarks N/A 5 Hermes PSAR Section 12.9 6 6 Hermes SE Section 12.9 15 7 Hermes Chapter 12 Memo N/A 8 Hermes PSAR Chapter 13 - Maximum 23 9 Hypothetical Accident 10 Hermes SE Chapter 13 - Maximum 54 11 Hypothetical Accident 12 Hermes PSAR Chapter 13 - Other Sections 68 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 1:00 p.m.
3 CHAIR PETTI: Okay. This meeting will now 4 come to order. This is a meeting of the Kairos Power 5 Licensing Subcommittee of the Advisory Committee on 6 Reactor Safeguards. I'm David Petti, Chairman of 7 today's subcommittee meeting.
8 ACRS members in attendance are Charles 9 Brown, Jose March-Leuba, Joy Rempe, Matt Sunseri, Ron 10 Ballinger, Walt Kirchner, Vesna Dimitrijevic, Vicki 11 Bier, and Greg Halnon. Our consultants, Dennis Bley 12 and Steve Schultz, are also present. Weidong Wang of 13 the ACRS staff is the Designated Federal Official of 14 this meeting.
15 During today's meeting, the subcommittee 16 will continue its review of the staff safety 17 evaluation on the Kairos Power Hermes Non-Power 18 Reactor Preliminary Safety Analysis. The subcommittee 19 will hear presentations by and hold discussions with 20 the NRC staff, Kairos Power representatives, and other 21 interested persons regarding this matter.
22 A part of presentations by the applicant 23 and the NRC staff may be closed in order to discuss 24 information that is proprietary to the licensee and 25 its contractors, pursuant to 5 USC 552(b)(c)(4).
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5 1 Attendance at the meeting that deals with such 2 information will be limited to the NRC staff and its 3 consultants, Kairos Power, and those individuals and 4 organizations who have entered in an appropriate 5 confidentiality agreement with them. Consequently, we 6 will need to confirm that we have only eligible 7 observers and participants in the closed part of the 8 meeting.
9 The rules for participation in all ACRS 10 meetings including today's were announced in the 11 Federal Register on June 13th, 2019. The ACRS section 12 of the U.S. NRC public website provides our charter, 13 bylaws, agendas, letter reports, and full transcripts 14 of all full and subcommittee meetings, including 15 slides presented there. The meeting notice and the 16 agenda for this meeting were posted there. We have 17 received no written statements or requests to make an 18 oral statement from the public.
19 The subcommittee will gather information, 20 analyze relevant issues and facts, and formulate 21 proposed positions and actions, as appropriate, for 22 deliberation by the full Committee. A transcript of 23 the meeting is being kept and will be made available.
24 Today's meeting is being held in-person and 25 over Microsoft Teams for ACRS staff and members, NRC 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 staff, and the applicant. There's also a telephone 2 bridge line and a Microsoft Teams link allowing 3 participation of the public. In addressing the 4 subcommittee, participants should first identify 5 themselves and speak with sufficient clarity and 6 volume so that they may be readily heard. When not 7 speaking, we request that participants mute their 8 computer microphone or phone by pressing *6.
9 We'll now proceed with the meeting. Ed, do 10 you want to say something to kick us off?
11 MR. HELVENSTON: I have no introductory 12 remarks for the staff, so I think we'll turn it over 13 to Kairos for the presentation on Section 12.9, 14 Quality Assurance.
15 MR. HAGAMAN: Thank you. Good afternoon.
16 My name is Jordan Hagaman. I'm the Director of 17 Reliability Engineering and Quality Assurance and 18 Kairos Power. Today, we're talking about Section 12.9 19 of the PSAR. For a broader context, Chapter 12, in 20 general, describes all the plans for conduct of 21 operations at Hermes. This includes facility 22 operating, emergency planning, security plan, QA plan, 23 operator training, requalifications, startup, and 24 environmental reports.
25 CHAIR PETTI: We don't see any slides.
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7 1 MR. HAGAMAN: Okay. Let me pause there and 2 see.
3 CHAIR PETTI: This is interesting. Those 4 that have computers in the room see them, but we're 5 not getting them on our screens. So let's pause a 6 minute.
7 PARTICIPANT: I think there may have been 8 two different schedulers. There was one that said, it 9 said placeholder or something. It's possible that 10 we're in the wrong --
11 CHAIR PETTI: Well, except that this is 12 where the court reporter is and this is where -- let's 13 see. Any of the ACRS virtual members online? Matt, 14 Vesna, Walt?
15 MEMBER SUNSERI: Yes, this is Matt. I see 16 the slides.
17 MEMBER DIMITRIJEVIC: Yes.
18 CHAIR PETTI: Okay. So I think we're in 19 the right place.
20 MEMBER KIRCHNER: Yes, I do, too. This is 21 Walt.
22 (Long pause.)
23 MR. HAGAMAN: All right. Once again, my 24 name is Jordan Hagaman. And the main thing I wanted 25 to point out at the title slide is we're looking 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
8 1 Section 12.9, which is just one small part of Chapter 2 12, which describes all of the conduct of operations 3 for the Hermes plant.
4 So with that, we can jump to the next 5 slide. 10 CFR 50.34 requires construction permit 6 applicants to provide a QA program description to be 7 used to design, build, and operate the structure 8 systems and components for the reactor. We started 9 with NUREG 1537, which pointed us to guidance in Reg 10 Guide 2.5 and ANS 15.8, which was used to develop the 11 format and content of the quality assurance program 12 description for the Hermes non-power reactor. This is 13 provided in full as an appendix to Chapter 12.
14 On the applicability of this QA standard, 15 ANS 15.8 describes that the type of QA program 16 appropriate to a research and test reactor is 17 different than the type of QA program applied to 18 commercial power reactors. The front matter of the 19 standard describes the characteristics that are 20 different between non-power and commercial power 21 reactors that affect the type of QA program 22 recommended. The key of these characteristics could 23 be summarized as the relative simplicity of the safety 24 case for research and test reactors, which is 25 fundamentally different than the safety cases for 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 larger commercial power reactors. The safety 2 characteristic of research and test reactors could 3 also be applied to Hermes.
4 We'll discuss later today in the Chapter 13 5 presentation about the preliminary safety analysis 6 prepared for Hermes that shows very large margins to 7 Part 100 dose consequence limits. This is the key 8 metric for a simplified safety case, helping us to 9 establish that the Hermes safety profile is similar to 10 that of other research and test reactors.
11 We can go the next slide. The Hermes 12 quality assurance program description applies to 13 design phase, construction phase, and operations phase 14 activities affecting quality for safety-related 15 structures, systems, and components. I'd like to 16 briefly expand on that to help describe the 17 applicability of the program. We've discussed the 18 Hermes definition of safety related in previous 19 subcommittee meetings. That definition of safety 20 related is repeated in the Hermes QAPD for 21 consistency. To summarize, it includes all SSCs that 22 are responsible for at least one of three things: the 23 first one being SSCs responsible for the integrity of 24 the vessel, maintaining coolant above the core; the 25 second being SSCs responsible for reactivity shutdown 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 capability; and the third is SSCs that provide 2 capability to prevent or mitigate accident 3 consequences beyond Part 100 limits.
4 As far as program applicability is 5 concerned, there's a table in Chapter 3 of the PSAR.
6 That's Table 3.6-1. This table lists all of the SSCs 7 for Hermes and notes both safety classification and 8 quality program applicability. You'll note that all 9 SSCs designated as safety related are also listed as 10 quality related. Therefore, the requirements of the 11 Hermes QA program apply to those SSCs.
12 Examples of the safety-related SSCs are the 13 reactor vessel, the reactivity shutdown elements, the 14 decay heat removal system, the reactor protection 15 system. Quality-affecting activities associated with 16 those SSCs include the final design, fabrication, 17 construction and testing.
18 We can go to the next slide, please. All 19 right. As mentioned in the previous slide, the Hermes 20 quality assurance program description describes 21 requirements for design, construction, and operations 22 phase activities affecting quality. However, at the 23 CP stage, only the design and construction portions of 24 the QAPD were subject to review. As a result, the 25 requirements for facility operations do not appear on 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 this slide, but we do look forward to discussing those 2 requirements during the review for the operating 3 license.
4 Also not listed here is the 19th 5 requirement in the design and construction section of 6 ANS 15.8. Requirement 19 is custom for research and 7 test reactors. That's for experimental equipment.
8 The Hermes demonstration reactor is not being designed 9 or licensed for experiments. Rather, the project 10 mission is to demonstrate the construction and 11 operation of a Kairos FHR and to demonstrate delivery 12 of low-cost nuclear heat. Without formal defined 13 experiments, Requirement 19 for experimental equipment 14 does not apply. What does apply are the traditional 15 18 QA criteria that we're familiar with. The 16 requirements described in ANS 15.8 are, more or less, 17 directly accepted into the Hermes quality assurance 18 program with only editorial changes.
19 And with that, that's the end of my 20 prepared remarks.
21 MEMBER HALNON: Hey, Jordan, this is Greg 22 Halnon. Did I hear you right that there's only two of 23 the criteria that are in play right now, and it's the 24 design and what was the other one?
25 MR. HAGAMAN: Design and construction were 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 the ones that are subject to review during the 2 construction permit stage.
3 MEMBER HALNON: Okay. So I understand your 4 point on, you know, they'll be more operationally 5 phased. I'm interested in the corrective action 6 portion. How, if that's not in -- do you have a 7 corrective action program now that will just carry 8 over to the operation phase, it's just not subject to 9 review right now, or are you waiting to put that in 10 place later on?
11 MR. HAGAMAN: So the third from the bottom 12 on the right-hand, the corrective action program, 13 Requirement 16, is part of the design and construction 14 phase.
15 MEMBER HALNON: Okay. Thanks.
16 CHAIR PETTI: Members, any other questions?
17 MEMBER BALLINGER: Yes, I have a --
18 CHAIR PETTI: Go ahead.
19 MEMBER BALLINGER: -- I guess it's a 20 theoretical question. So it's not designed for 21 experiments. So you build this thing and you start 22 operating it, and you find out that something doesn't 23 work and that not work would translate into the FHR.
24 Are you saying that you cannot, because of the 25 restrictions, you cannot do an experiment or what 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 would be called an experiment with this plant to solve 2 a problem which you've discovered that will translate 3 into the FHR?
4 MR. HAGAMAN: So we would expect anything 5 that gets implemented in terms of modifications for 6 the Hermes plant to be subject to the same reasonable 7 assurance that it's going to perform a safety function 8 as any of the originally-designed SSCs. So we will 9 have that reasonable assurance before we put those 10 SSCs into service, so they wouldn't be considered an 11 experiment. They'll be just the same as any other SSC 12 that was part of the original design.
13 CHAIR PETTI: But I think Ron's question 14 was a little different. Let's say you find, you know, 15 something doesn't go as planned, not just related 16 necessarily to SSCs, but something where, in order to 17 fix it, you might have to go outside your tech spec 18 and have to change the tech spec. There's a process 19 for that, I would think, right, so that you could do 20 that?
21 MR. HAGAMAN: That should fall under our 22 normal 50.59 process.
23 MEMBER BALLINGER: Yes, okay.
24 CHAIR PETTI: Any other questions, members?
25 MEMBER REMPE: The staff talk about 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
14 1 but, if you explore Ron's question, I thought we kind 2 of discussed this a while back. If the reactivity 3 coefficients are as anticipated or you want to try and 4 better understand some instabilities you see, there 5 are tech specs and you are going to have to try and 6 get more data. It seems like that, you know, with an 7 operating plant, the staff would be cognizant of that 8 ahead of time. The applicant knows they have to 9 discuss this with the staff, the staff would say, yes, 10 okay, you're going to be doing some sort of test.
11 It's the whole reactor is sort of an experiment, and 12 they have to communicate it to the staff, and the 13 staff would have some process in place ahead of time 14 before the licensee would be able to do that test with 15 the entire reactor. And I thought the staff had told 16 us at that time in whatever chapter it was that, yes, 17 they need to do that and that will be clear.
18 MR. HELVENSTON: Yes, I think when we talk 19 about there not being experiments, you know, we sort 20 of mean in the traditional sense where, you know, 21 they're not necessarily doing some of the, you know, 22 sample irradiations, radiography, isotope production, 23 things like that that you'd associate with a 24 traditional operating non-power reactor. But in a 25 sense, like you said, it really is the reactor itself 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 would be considered somewhat of an experiment. And we 2 expect Kairos, Your Honor, in the operating license 3 phase to have startup plans and sort of, you know, 4 procedures in place to look at, as they're starting 5 up, in a phase approached and taking observations and 6 learning as they go, and, you know, that could still 7 inform the future operations of the facility.
8 And, certainly, you know, the NRC has, you 9 know, the regulations have processes in place, like 10 the 50.59, the license amendment process, you know, if 11 there needs to be some change to how the reactor is 12 operated or some system based on the operational 13 experience that's been collected up to that point.
14 MEMBER REMPE: Thank you.
15 CHAIR PETTI: Okay. Then did the staff 16 have any slides on QA? Thank you. Go ahead.
17 MR. HELVENSTON: Are you sharing the 18 slides, Ben? You can go ahead to the next slide.
19 So I'll just start off like we did on, I 20 think, the previous meeting, just go into the agenda 21 and a couple of the highlighted level items that apply 22 to all the sections we're going to be presenting over 23 the next couple of days, you know, to avoid having to 24 do this at the beginning of each section again. So 25 I'll just briefly go over, we'll start out with 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
16 1 presentation on PSAR Section 12.9 on quality 2 assurance. Also, later this afternoon, we'll provide 3 a presentation on the sections of the PSAR of the 4 Chapter 13. They're specific to the maximum 5 hypothetical accident. And then I believe tomorrow 6 morning we'll follow that up with a discussion of the 7 remaining sections of Chapter 13 on the postulated 8 bounded events.
9 In terms of the agenda for each chapter of 10 the staff's presentation, that will be pretty similar.
11 We'll start with an overview of the chapter and the 12 relevant PDCs, if there are any; any topical reports; 13 what we did for our technical evaluation; and then the 14 staff's findings and conclusions.
15 Next slide. So in terms of the reg basis 16 that we looked at in our review of these chapters, the 17 three regulations that are in common for every section 18 we looked at is 50.34(a), 50.35, and 50.40, as well as 19 the guidance in NUREG 1537, Part 2, which provides the 20 review plan and the acceptance criteria for the 21 application. In some of the subsequent presentations, 22 there may be some additional regulations and guidance 23 that are applicable to that specific section that 24 we'll go into detail on the following presentations.
25 So with that, I'll turn it over to Ayo who 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 will present on the NRC staff's review of PSAR Section 2 12.9 on quality assurance.
3 MR. AYEGBUSI: Thanks, Ed. So good 4 afternoon. My name is Ayo Ayegbusi. Can you hear me?
5 All right. Like I said, good afternoon. My name is 6 -- is this better? All right. My name is Ayo 7 Ayegbusi, and I am a reactor operations engineer in 8 the Quality Assurance and Vendor Branch in NRR. My 9 presentation today will discuss the staff's review of 10 the quality assurance section in the Kairos Hermes 11 PSAR.
12 Next slide, please. All right. So in 13 Section 12.9 of the PSAR, Kairos states that its 14 quality assurance program is based on Reg Guide 2.5 15 which endorses ANS 15.8, which is the quality 16 assurance program requirements for research reactors.
17 The Kairos Hermes QAPD is described in Appendix B of 18 PSAR Chapter 12. So that's just background 19 information, some of which Kairos has covered.
20 Next slide, please. In addition to the 21 regulations and guidance mentioned earlier during the 22 common regulatory basis that Ed covered, the staff 23 specifically reviewed the Kairos Hermes QAPD against 24 the ANS 15.8 standard.
25 Next slide, please. So for the staff's NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
18 1 evaluation, the staff evaluated Sections 1 and 2 of 2 the QAPD because those two sections directly apply to 3 the construction permit application. As Kairos 4 mentioned, those sections cover design and 5 construction.
6 The staff's evaluation found that Kairos 7 followed the ANS 15.8 standards closely. My many 8 slides will cover areas where Kairos deviated from the 9 ANS 15.8 standard. However, the staff did not 10 evaluate Section 3 of the QAPD because it covers 11 facility operations, which, at this point, is not 12 relevant to issuing a construction permit.
13 Next slide, please. The first deviation 14 from the ANS 15.8 standard is that Kairos proposed an 15 alternate definition for safety related to match what 16 is used in PSAR Chapter 3. The staff found this 17 proposal acceptable because it's consistent with the 18 Hermes design and the safety related definition in the 19 ANS 15.8 standard. At this point, my understanding is 20 that ACRS has been given a draft copy of our safety 21 evaluation. That does not include our evaluation in 22 what we found here, but we will be revising that 23 safety evaluation to discuss our findings as far as it 24 relates to the safety related definition that Kairos 25 proposed.
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19 1 The next deviation from ANS 15.8 standard 2 is that the QAPD did not include a section for 3 experimental equipment. Kairos already covered that.
4 Again, the staff found this acceptable because the 5 PSAR states that no experiments will be carried out, 6 and I'm paraphrasing that.
7 The next deviation from the ANS 15.8 8 standard is that the QAPD did not include Section 4 9 and 5 from the standard, namely applicability to 10 existing facilities and decommissioning respectively.
11 In this case, the staff found this acceptable because 12 the QAPD will not utilize an existing facility, and 13 decommissioning plans are not required for the 14 construction permit application. And I --
15 MEMBER HALNON: This is Greg, just real 16 quick. You paraphrased to say that they're not going 17 to do experiments. Is the demarcation between 18 experiment and test clear enough such that we're not 19 going to be arguing on whether it's an experiment or 20 a test? Because it's like a 50.59 experiment test and 21 modification, so is that clear enough in the 22 regulation for them to be able to ascertain that no 23 experiments will be done?
24 MR. AYEGBUSI: So like I mentioned earlier, 25 because I hear you mentioned regulation, our 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
20 1 was based on the ANS 15.8 standard, which is what 2 we've endorsed, right. Section 2.19 has to do with, 3 I forget the title, but it has to do with experiments, 4 right. I think it's experimental equipment, equipment 5 for experiments. And so that's focused on 6 experiments, right. It doesn't address testing.
7 So to your question for testing, I would 8 have to defer to Ed. What he said earlier is they 9 would have to address it --
10 MEMBER HALNON: It's not a real fine point.
11 I'm just curious because, at least in the operating 12 reactor world, in light water, we always had that 13 struggle internally. When we did test procedures, 14 someone said is this experimental or not, and we never 15 really found a good demarcation of where that line was 16 between a test and experiment. Now, it may be in the 17 test reactor world it's much more clear, and that's 18 what I was kind of getting to, if that's more clear in 19 the test reactor world, or the research reactor, I'm 20 sorry.
21 MR. AYEGBUSI: Honestly, I would have to 22 defer to the other technical staff because this 23 section really focuses on quality assurance, so, in 24 essence, the quality of the activities of the design 25 and construction of the plant so --
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21 1 MEMBER HALNON: Okay. Well, you said they 2 were clearly within 2.9, and I'm satisfied with that.
3 But maybe at another time I'll have that philosophical 4 discussion. Maybe there's some hard information 5 somewhere we can get to.
6 MR. AYEGBUSI: Okay. Next slide, please.
7 I already spoke to this slide, so I'm going to go on 8 to the next slide, please.
9 So the staff's safety evaluation 10 recommended that the construction permit should 11 include a condition for the quality assurance program.
12 The condition requires that the QA program is 13 implemented, as described in the PSAR, and any changes 14 that reduce the commitments in the QAPD are submitted 15 to NRC for approval prior to implementation.
16 Next slide, please. So in conclusion, the 17 staff found the preliminary design information to be 18 consistent with the applicable criteria in NUREG 1537.
19 The staff concluded that the information in Section 20 12.9 and Appendix 12(b) of the PSAR is sufficient for 21 the issuance of a construction permit. Lastly, the 22 staff concluded that reviews related to the conduct of 23 operations and decommissioning can be left at the 24 operating license application phase.
25 Next slide, please. So that concludes my 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 presentation. Thank you. And are there any 2 questions?
3 MR. SCHULTZ: I presume that Kairos has 4 accepted the recommended change that you indicated in 5 terms of changes to the QA program that can be made 6 without NRC approval and then submitted 90 days prior 7 or subsequent? On the previous slide it was 8 described.
9 MR. HELVENSTON: Yes. We have a proposed 10 recommended permit condition that's described on that 11 slide, but that is something that we would likely 12 verify with Kairos before that's finalized to make 13 sure they understand and are in agreement with that 14 condition.
15 MR. SCHULTZ: That sounds like a good idea.
16 Thank you.
17 CHAIR PETTI: Other comments, members?
18 Okay. Thank you. With that, we can go to the Chapter 19 12 memo. The Chapter 12 memo does not have a section 20 explicitly on Section 12.9, so I think, in expediency, 21 it's probably not worth, we've already seen the 22 Chapter 12 memo in March, so I think we can just keep 23 the schedule moving and move on to Chapter 13.
24 MEMBER SUNSERI: Dave, this is Matt.
25 You're correct. I mean, we did address the QA program NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
23 1 in that memo. We kind of got ahead a little bit, so 2 it's already been discussed and incorporated into the 3 memo.
4 CHAIR PETTI: Thank you. So let's move on 5 to Chapter 13 then. Kairos.
6 MR. DENMAN: Hello. My name is Dr. Matthew 7 Denman. I'm a reliability engineer at Kairos Power, 8 and it's my pleasure today to talk to you about the 9 Hermes Chapter 13 PSAR accident analysis.
10 Next slide. In 10 CFR 50.34(a)(4), it 11 requires a preliminary safety analysis to assess the 12 risk to public health and safety from the operation of 13 a facility and determination of the margins to safety.
14 In order to demonstrate compliance with 10 CFR 100.11 15 dose reference values, a maximum hypothetical accident 16 was developed that bounds the postulated events, and 17 this is analyzed for dose consequences by challenging 18 the performance of our functional containment. The 19 Hermes MHA approach is consistent with the guidance in 20 NUREG 1537. It's not a physical accident. It is 21 hypothetical in nature. It includes conservatisms 22 that maximize the source term and the release off-23 site, and it includes a postulated release of 24 radioactive material.
25 To ensure that postulated events are indeed 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 bound by the MHA, we developed a list of postulated 2 events that is comprehensive to ensure that any event 3 with potential significant radiological consequence 4 will be considered. Initiating events and scenarios 5 are grouped so that limiting cases for each group can 6 be qualitatively described in the construction permit 7 application. Quantitative results will be included at 8 OL. Acceptance criteria are provided for the 9 important figures of merit in each postulated event 10 group to ensure that the potential consequences of 11 that event group remain bound by the MHA as the design 12 progresses. Prevention of event initiators are also 13 justified in the PSAR.
14 Next slide.
15 MR. SCHULTZ: Matt, before you leave that 16 slide, this is Steve Schultz. You've indicated in 17 that last group of bullets that, when you go to the 18 operating license application, you're going to provide 19 the quantitative results. Is that going to be group 20 by group or by accident by accident? How are you 21 going to present those quantitative results?
22 MR. DENMAN: Thank you very much for that 23 question. The OL will present the results group by 24 group, but we will have internal analysis to justify 25 that our grouping or that the presented results 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
25 1 bounding of the group.
2 MR. SCHULTZ: Good. Thank you.
3 MR. DENMAN: Okay. So just another slide 4 to kind of conceptualize this relationship between the 5 dose limits, the maximum hypothetical accident, and 6 our postulated events, the MHA is constructed to be 7 extremely conservative and non-physical to 8 overestimate the potential off-site dose consequences, 9 ensure that we have sufficient margin to safety, and 10 ensure that reasonable design constraints will result 11 in a bounded postulated event.
12 If you look over at the qualitative figure 13 on the right, you'll see that we've got our 14 100.11(a)(1) and (2) dose reference values. That's a 15 mouthful. There's going to be a sufficient margin 16 between those reference values and where our MHA dose 17 is going to occur. Because of the hypothetical and 18 conservative assumptions that go into the MHA that 19 will not be included in the postulated events, you're 20 going to have a standoff of additional dose, and then 21 you'll have a range of doses or calculated doses where 22 the potential postulated events will arise, and these 23 will be due to our traditional design basis 24 conservatisms that go into both the thermal fluid 25 calculations and our mechanistic dose or source term 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 methodology. At the PSAR stage, only the MHA dose is 2 quantitatively evaluated, and this is the only event 3 that is needed to ensure that sufficient margin exists 4 to the 100.11 dose reference values.
5 MEMBER MARCH-LEUBA: Hi, this is Jose. You 6 say on the PSAR stage. Is there any other stage where 7 the dose would be for other postulated events?
8 MR. DENMAN: Thank you very much for that.
9 As was mentioned on the previous slide, we are 10 proposing a series of figures of merit which will, 11 assuming that we -- sorry, not assuming. We will 12 demonstrate that those figures of merit meet certain 13 acceptance criteria and that, by going to the figures 14 of merit NEPA acceptance criteria, that will map to a 15 dose less than the MHA.
16 MEMBER MARCH-LEUBA: So only the MHA will 17 be evaluated. The rest will have to do with figures 18 of merit?
19 MR. DENMAN: That is what we described.
20 MEMBER MARCH-LEUBA: Thanks.
21 MR. DENMAN: Okay. Next slide. So the 22 maximum hypothetical accident. I've got a couple of 23 slides on the overall narrative here. A key feature 24 of the maximum hypothetical accident is this time-25 temperature curve or curves. There's one for the fuel 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 and one for the coolant. What should be noted here is 2 that explicit system performance is not modeled. In 3 fact, the boxy nature of the time-temperature curves 4 are slightly intended to demonstrate that we're not 5 mechanistically modeling our system performance and 6 our temperature history. Instead, these temperature 7 curves are designed to ensure that a bounding 8 radionuclide release from our functional containment 9 will occur, so it's not just the high temperatures but 10 it's the extended and exaggerated time intervals over 11 which we're at these high temperatures will ensure 12 that the functional containment will be maximally 13 stressed and off-site doses will be conservatively 14 high.
15 MEMBER REMPE: Before you leave this slide, 16 could I ask a couple of questions? I struggled on 17 where to bring this up, but I think this temperature 18 plot is the best place to bring this up.
19 When I look at your various scenarios or 20 challenges and events you have, you have an event 21 where you have air ingress into your primary system, 22 and you note that the graphite oxidizes, as well as 23 the carbon matrix. And I don't see anywhere in the 24 PSAR or that topical report you generated or even in 25 the staff SE about combustible gas generation that 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 would occur when you oxidize the graphite CO with CO2.
2 And I'm wondering, I guess you haven't done it yet 3 because I'm guessing you're waiting, because you've 4 created this maximum hypothetical accident that's 5 going to bound all possible challenges, so I'm 6 guessing you didn't use your codes to evaluate how 7 much combustible gas got generated, and I don't think 8 there's any system that I've seen in your description 9 of what you're going to do with the combustible gas 10 that gets generated and I'm not sure you know how much 11 is. And I'm just thinking that somebody needs to 12 think about combustible gas generation, and maybe it's 13 a small amount, but anytime you get above 500 - 600 C, 14 which this plot has, that could be a problem, 15 especially when you get up to temperatures like 1,000 16 C or whatever, 850 or whatever.
17 And so, anyway, I'm just kind of thinking 18 that somebody needs to think about combustible gas 19 generation and if it could be an issue.
20 MR. HAUGH: Hi, Joy. This is Brandon 21 Haugh, Director of Modeling Simulation. Great point, 22 good question. We are considering that. It's, you 23 know, it requires a lot of, I'm going to say, design 24 fidelity to understand the predictability of that, but 25 we are creating models and, if we deem that's a risk, 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 we'll be able to understand how much is generated.
2 MEMBER REMPE: So you don't know, and you 3 might have to add a system or you might want to try 4 and have a primary system that can withstand the shock 5 of an ignition, a combustion event or something. It 6 just seems like somebody ought to do some scoping 7 calculations early on before you pour concrete and 8 start ordering components on this.
9 MR. HAUGH: It's great feedback. We have 10 done that and we are doing that.
11 MEMBER REMPE: So how much gas do you get 12 and where does it go, if you've already done that and 13 you don't think it's a problem?
14 MR. HAUGH: Well, it's highly dependent on 15 the chemistry and the temperatures in the system 16 because it re-oxidizes back to be non-combustible 17 depending on the situation. So it's very scenario-18 dependent on the amount of air ingress and the 19 temperature time history. So there's a good amount to 20 unpack there, and it's probably more than this 21 discussion is needed, but it will be covered at the 22 operating license application phase.
23 MEMBER REMPE: Okay. So, again, I'm just 24 one member, but I strongly recommend that the memo can 25 point this out and that our letter point this out 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 because this is something that I don't see in Appendix 2 A, and it's something I think people ought to make 3 sure gets addressed. And I'll stop there. Thank you.
4 CHAIR PETTI: So just another point, this 5 is, of course, a big deal in helium gas-cooled 6 reactors, and you have to go way back, but my 7 understanding is studies were done, I want to say by 8 Brookhaven, the CO that's generated is usually on the 9 lean side, so it's not combustible, at least that's 10 what they found in HTGRs. So it's probably worth you 11 guys trying to find that information, as well, and 12 understand that chemistry, as you think about the 13 chemistry.
14 MR. DENMAN: Thank you very much. One 15 other point I just want to clarify is that the time-16 temperature curves you're seeing here are bounding 17 temperatures for our fuel and our fuel covered by our 18 Flibe, right. So pebbles that are suspended above the 19 Flibe would, A, not expected to be at these 20 temperatures and, B, would be handled separately from 21 the MHA analysis.
22 MEMBER REMPE: Yes, but I don't have any 23 curves to show me what those temperatures are, I don't 24 have a risk assessment to show that the frequency of 25 such events is very low. So, again, I need 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
31 1 information. Of course, you can go ahead and pour 2 concrete, you can wait until the operating license; 3 but I think it definitely is something that everybody 4 needs to think about and have a good answer on.
5 MR. DENMAN: Understood. Thank you for 6 that comment.
7 MEMBER BALLINGER: This is Ron Ballinger.
8 You know, this curve puts you squarely at the upper 9 limit on the stainless steel, and so you're into 10 Division 5. But the best estimate for some of these 11 things is considerably lower. So with this bounding 12 calculation, you're definitely having to consider 13 creep; is that right?
14 MR. DENMAN: Well, first off thank you very 15 much for your question. I'll note two things. One, 16 the MHA is designed to maximize release of radioactive 17 material from our functional containment. It is not 18 an accident that is designed to analyze stress on 19 vessels or other components within the system. In 20 fact, our commitment on our vessel temperature in the 21 CPA is lower than the 816 ASME steel temperature 22 limit. We are using this higher temperature as the 23 stressor on our functional containment and then that 24 delta between where the temperatures actually are 25 going to wind up in our system and these evaluated 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 temperatures will play into why our MHA will end up 2 releasing more radionuclides than our postulated 3 events will.
4 MEMBER BALLINGER: Okay. Thanks.
5 CHAIR PETTI: So I view it as sort of an 6 artificial thing, right.
7 MEMBER BALLINGER: You could artificially 8 fail the --
9 CHAIR PETTI: Well, right, in this 10 hypothetical sense. But, yes, the few curves that are 11 in the appendix of the technical report I think shows 12 there's good margin there, and I actually noted that 13 in our letters. Keep going.
14 MR. DENMAN: Okay. Thank you. So for our 15 maximum hypothetical accident, we have radionuclides 16 that are postulated to diffuse from TRISO particles.
17 The distribution of TRISO particles included in the 18 MHA account for both manufacturing defects and 19 potential in-service failures prior to the transient 20 occurring.
21 Pre-transient diffusion of radionuclides 22 from kernels are hypothetically and conservatively not 23 modeled to maximize the fuel inventory available for 24 release during the MHA. Radionuclides are postulated 25 to evaporate and de-gas from the Flibe, as driven by 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 the conservative natural circulation boundary 2 conditions. No hold up of any gases are credited 3 within the Flibe portion of the functional 4 containment.
5 Tritium is conservatively assessed to 6 maximize both its initial inventory and its subsequent 7 release. The initial inventory of Tritium is 8 conservatively assessed and released. Tritium is 9 conservatively postulated to desorb from in-vessel 10 graphite as a function of temperature and 11 instantaneously release from both steel and Flibe.
12 CHAIR PETTI: Matt.
13 MR. DENMAN: Yes, sir.
14 CHAIR PETTI: The question on the tritium.
15 Did you include all the sources besides the Flibe?
16 Did you look at lithium impurity in graphite and 17 ternary fission sources? I'd like at the ternary 18 fission, and I scaled it. I don't think it's an 19 issue. I always am not sure on the lithium and 20 graphite.
21 MR. DENMAN: I agree with you. The ternary 22 fission is very insignificant and, in fact, that is 23 part of our fuel inventory that subsequently would 24 diffuse out through our grouping structures. The 25 lithium impurities in the graphite is considered.
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34 1 CHAIR PETTI: Okay. That's good. I mean, 2 in the old days, there used to be a lot of lithium in 3 graphite, and people got very worried about it. I 4 don't think it's a problem today. I think they're 5 just better quality graphite. But if you go and read 6 the old literature, you can get a little confused that 7 it's still a problem. I don't think it's as problem.
8 I'm glad you confirmed it. Thanks.
9 MR. DENMAN: Okay. And then --
10 MR. SCHULTZ: Matt, this is Steve Schultz.
11 It's not stated on this slide, but, in the 12 documentation, with regard to the TRISO particles, the 13 TRISO behavior during the accident, the release is 14 from diffusion only, and then it would be a different 15 release if the particles are failed before the 16 accident. But the particles do not fail during the 17 accident; is that correct?
18 MR. DENMAN: That is correct. The 19 diffusion is an effective diffusion term, so it, you 20 know, accounts for multiple different ways 21 radionuclides can move through the system and just 22 approximate it as a diffusivity. In-service failures 23 are pre-transient. We do not expect there to be a 24 statistically-significant fraction of in-transient 25 failures, as will be shown in our postulated events.
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35 1 Thus, the transient failures are not included in the 2 MHA.
3 MR. SCHULTZ: Okay. And you demonstrate 4 that statement regarding the events that are evaluated 5 will demonstrate that there isn't going to be particle 6 failure as a result in those events that we'll see 7 evaluated at the operating license stage?
8 MR. DENMAN: Correct.
9 CHAIR PETTI: So, Steve, if you look at the 10 database on TRISO, the failure rates under the 11 accidents that go up to 1600 degrees is like 10 to the 12 minus 5, and they're assuming 10 to the minus 3 order, 13 so it's down in the --
14 MR. SCHULTZ: Good. Thank you, Matt.
15 MR. DENMAN: Thank you. Okay. So going 16 through the methodology in a little bit more detail, 17 the Hermes MHA uses a methodology or methodologies 18 from the approved KP-FHR mechanistic source term 19 methodology topical report, KP-TR-12-P-A. The 20 concepts, the following concepts will directly 21 leverage the topical report. This includes our 22 radionuclide grouping and transport approaches for our 23 TRISO fuel and our Flibe coolant mass transfer 24 correlations for tritium into graphite reflectors and 25 pebbles. That's part of the inventory calculation.
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36 1 Gas face is not credited for confinement of 2 radionuclides that release from the Flibe free surface 3 and a two-hour hold up assumption for radionuclide 4 transporting through the reactor building is modeled.
5 Conservative unfiltered ground-level releases are 6 modeled to maximize off-site doses. So all of these 7 come directly from that topical report.
8 MR. SCHULTZ: Matt, Steve Schultz again.
9 The ground-level release assumption, is that based 10 upon the configuration that you expect from the 11 facility? In other words, that's where you would 12 expect to see the release? It's not apparent to me 13 that that maximizes off-site doses at ground-level 14 release versus an elevated release.
15 MR. DENMAN: Steve, thank you very much for 16 the question. The ground-level release is not 17 indicative of what we would expect a release to look 18 like from the facility. However, as part of the 19 topical report, we and the staff agreed that this was 20 a suitably conservative approach.
21 MR. SCHULTZ: Okay. Maybe the staff will 22 come in on that one in their presentation. Thank you.
23 MR. DENMAN: Okay. The following 24 additional non-physical conditions provide additional 25 hypothetical challenges to the functional containment 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 beyond which is described in our mechanistic source 2 topical report. The hypothetical time-temperature 3 histories are applied to the transient. You've 4 already seen a preview of that, and we'll go back and 5 show you a little bit more in subsequent slides. This 6 ensures that the MHA will bound the system 7 temperatures from postulated event groups. The pre-8 transient diffusion of radionuclides from the fuel and 9 the reactor core is negligible. This ensures that the 10 maximum inventory is available for release at the 11 initiation of the transient. A bounding vessel void 12 fraction is assumed to facilitate the release of low 13 volatile species in the vessel via our bubble burst 14 release model. And additional conservatisms in 15 tritium modeling are used to address limitations 16 associated with the tritium modeling in graphite as 17 described in our approved topical report.
18 CHAIR PETTI: What was that specific, the 19 tritium that was adjusted, if you will?
20 MR. DENMAN: So we have a couple of things.
21 May I table that to the next few slides --
22 CHAIR PETTI: Sure.
23 MR. DENMAN: -- and we'll talk a little bit 24 more when we get to the inventory discussion, as well 25 as the release discussion. I don't want to have 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
38 1 try to --
2 CHAIR PETTI: Yes, no problem.
3 MR. DENMAN: Thank you. Okay. So our 4 basic approach for the MHA is kind of three stages.
5 The first stage, we identify and account for all 6 sources of material at risk and all barriers that that 7 material is going to see as it releases through the 8 system. We're going to evaluate release fractions for 9 every combination of barrier radionuclide group and 10 time interval associated with the MHA, and then we're 11 going to use the RADTRAD and ARCON code to evaluate 12 our dose consequences at the exclusionary boundary and 13 the low population zone.
14 And then here we have kind of a graphical 15 representation. All of our MAR and fuel kernel is 16 first going to be held up in our TRISO fuel. Then 17 it's going to propagate into the Flibe into the gas 18 face. Circulating activity is going to start in the 19 Flibe but then can evaporate or de-gas into the gas 20 face. Our structural MAR is tritium and argon-41.
21 These are both gases, so, once they release from the 22 graphite, they bypass the Flibe and move directly into 23 the gas face.
24 Diving a little bit deeper into our sources 25 of material at risk, most of our material at risk in NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
39 1 our system is contained within the TRISO fuel. The 2 Serpent 2 code is used to evaluate fuel inventories 3 for our reactor. Pre-transient depletion of 4 radionuclides from the fuel is neglected in order to 5 maximize the inventory of available material at risk.
6 The circulating activity uses a bounding circulating 7 activity distribution of radionuclides. This is 8 expected to be controlled by technical specifications.
9 And, importantly, the circulating activity, because 10 this is a bounding value, is accommodating what we 11 expect to see from nominal release of radionuclides 12 from the TRISO fuel into the Flibe coolant. So any 13 radionuclides that would have nominally left the TRISO 14 fuel into the Flibe coolant during normal operations 15 are effectively being double-counted here because that 16 TRISO fuel assumes that there's no depletion of that 17 radionuclides.
18 Next slide. So we also have our structural 19 MAR. We'll focus on tritium first. The inventory 20 conservatively bounds the operating lifetime at a full 21 capacity factor with margin while accounting for 22 differential uptake rates of our pebbles and 23 reflector. The transfer from Flibe to structures, the 24 tritium is assumed to be born in the Flibe but 25 transferred to and absorbed into structures.
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40 1 Primarily, this is the graphite that's going to uptake 2 the tritium and store it up for release in the maximum 3 hypothetical accident.
4 Transport speciation is conservatively 5 assigned to tritium fluoride to maximize the tritium 6 absorption into our system, e.g. our graphite. And 7 then transfer from Flibe to structures is determined 8 by max transfer coefficients from our predicted Flibe 9 flow characteristics at steady state in our reactor.
10 When we talk about absorption within 11 structures, the tritium absorbs solely as a function 12 of mass transfer from the Flibe to structures, i.e.
13 there's no diffusion resistance. If it can transfer 14 in, it gets stored and locked up. And then retention 15 of that tritium is modeled without any steady-state 16 release mechanism, so this a perfect absorber of 17 graphite. It just sucks in tritium due to mass 18 transfer during the operation of the facility and then 19 this should maximize the quantity of tritium that then 20 would be available for release during the transfer.
21 CHAIR PETTI: So, Matt, just a question.
22 In reality, there will be partitioning between the 23 Flibe and the graphite, and the question is if, in 24 fact, you made the graphite less sorb to, so the 25 inventory was higher in the salt, doesn't it come out 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 of the salt easier than it comes out of the graphite?
2 So is that truly a conservative assumption to put it 3 all in the graphite? Wouldn't it be more conservative 4 to keep it in salt? Did you look at that sort of 5 stuff?
6 MR. DENMAN: Thank you very much for the 7 question. I would note that the quantity of tritium 8 that we end up absorbing into the graphite are orders 9 of magnitude higher than the quantity of tritium that 10 is expected to be circulating through the salt. We 11 did look at a lot of these sensitivities, and it was 12 much more conservative, given these set of boundary 13 conditions have as much tritium absorbed into the 14 salt. Also, due to our -- sorry. Not in the salt, in 15 the graphite.
16 Also, due to our highly-conservative 17 release models, the tritium in the graphite gets 18 released in a non-physical rapid rate. So even 19 though, yes, the graphite is going to hold it a little 20 bit more than the Flibe as we model the system in the 21 MHA, it's not that much more.
22 CHAIR PETTI: Okay.
23 MR. DENMAN: And we can talk a little bit 24 more about that as we get to the release models.
25 CHAIR PETTI: Okay. Thanks.
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42 1 MR. DENMAN: Not a problem. And thank you 2 for your question. Okay. So moving on -- no, no, 3 argon-41.
4 MR. PEEBLES: Before we move on from that, 5 we did have a correction to make. So, Kieran, are you 6 online?
7 MR. DOLAN: Yes, I'm here. Can you hear 8 me?
9 MR. PEEBLES: Yes. Can you provide a 10 correction to an earlier statement about lithium 11 impurities?
12 MR. DOLAN: Yes. So a couple of slides 13 ago, we were talking about which sources of tritium 14 are included for these calculations on tritium MAR for 15 the MHA. So in our initial analysis here, we are just 16 including the tritium sources produced by neutron 17 irradiation of Flibe, so the numbers fed to the MHA in 18 the current state do not include evaluations of 19 tritium produced by lithium impurities in the 20 graphite. We don't expect those to be significant 21 contributors to the overall tritium production or 22 tritium source term, but that is a detail we could 23 evaluate for source term tritium calculations in the 24 operating license application.
25 CHAIR PETTI: I think you're right. It's 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 just worth confirming it when you get to the OL.
2 MR. DOLAN: Right.
3 MR. DENMAN: Thank you very much, Kieran.
4 My apologies on that misstatement. Okay. So for 5 argon-41 released, argon-41 is primarily produced via 6 neutron activation of argon-40 to argon-41, and we are 7 assuming that the inventory available for release from 8 our system consists of the argon-41 contained within 9 the graphite's closed porosity.
10 Okay. Next slide. For our release models, 11 we will talk first about our TRISO fuel. The time-12 temperature history for this fuel, and this fuel is in 13 the in-core fuel or, you know, submerged within the 14 Flibe, you can see the time-temperature history as 15 pointed out. It's, first, this higher dotted line, 16 and then it moves into the more solid darker line.
17 All of the fuel within the core is assumed to be at 18 this temperature simultaneously.
19 Transport through the TRISO layers are 20 modeled using fixed law of diffusion. The CORSOR 21 model is used for kernel diffusivity or diffusion of 22 radionuclides out of the kernel. And then the IAEA 23 correlations described in the construction permit 24 application are used for layered diffusivity or 25 movement of radionuclides through each of those NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
44 1 layers.
2 Diffusion, again, is driven by this 3 hypothetical temperature curve. Each layer and the 4 kernel all have the exact same temperature as 5 described this temperature curve. And transient 6 diffusion of fission products was shown, given the low 7 temperatures that we see in this hypothetical 8 temperature curve, even though they're bounding of our 9 postulated events, they're low for TRISO accident 10 analysis in general, is negligible if even a single 11 pick layer remains intact. Thus, the total release 12 from our fuel is really dominated by releases from 13 exposed kernels within the TRISO configuration.
14 Okay. Next slide. The --
15 MEMBER KIRCHNER: This is Walt Kirchner.
16 Could I ask, could you -- I'm not sure this is a 17 proprietary because you're using EPRI's spec. What's 18 your assumption on the exposed kernel fraction?
19 Because you're right. At these temperatures, that 20 would be the dominate source of uranium and/or fission 21 products.
22 MR. DENMAN: I'm not sure if that number is 23 proprietary. Let me look to my --
24 CHAIR PETTI: I hope not. It's in our 25 letter. It's been in our memos.
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45 1 MEMBER KIRCHNER: Yes. It's in the EPRI 2 spec, if that's what you're using.
3 MR. DENMAN: It's very close to that spec.
4 MEMBER KIRCHNER: Can you hazard a number?
5 CHAIR PETTI: Yes, aren't you assuming a 6 much higher number than EPRI?
7 MR. PEEBLES: So we can confirm that it's 8 not proprietary and then get back to you after the 9 break, if that works.
10 MR. DENMAN: I'd want to look up the exact 11 number. I don't have it right in front of me, but we 12 can get back to you.
13 Okay. So maximum hypothetical releases 14 from our Flibe coolant. The Flibe provides a 15 secondary functional containment barrier bounding, 16 this bounds the circulating activity or, sorry, Flibe 17 provides secondary functional containment barrier to 18 both the bounding circulating activity and our in-19 transient releases of fission products from TRISO.
20 There are two primary release pathways from 21 the Flibe. These include bubble burst as the initial 22 assumed conservative void fraction, bursts at the top 23 of our Flibe free surface, and then the evaporation, 24 which is driven by the time-temperature curve.
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46 1 bypass Flibe's functional containment as no credit is 2 given for gas retention within our Flibe in the MHA, 3 and highly-volatile noble metals who have a high-vapor 4 pressure or are modeled as having a high-vapor 5 pressure evaporate extremely quickly in our MHA.
6 Thus, they effectively have no hold up.
7 CHAIR PETTI: So, Matt, just to be clear 8 since most of those fission products aren't that 9 important, iodine is like a noble gas that follows 10 that pathway?
11 MR. DENMAN: Per our mechanistic source 12 term topical report, iodine is grouped as a salt-13 soluble fluoride.
14 CHAIR PETTI: Oh, okay. So it's like 15 cesium. It stays in the salt.
16 MR. DENMAN: Correct.
17 CHAIR PETTI: And then has -- okay.
18 MR. SCHULTZ: Matt, Steve Schultz. You 19 sort of mentioned this before, but, the bounding 20 circulating activity, you assume what is in technical 21 specifications for that value in the calculation?
22 MR. DENMAN: Yes. Thank you very much for 23 the question. The circulating activity is assumed to 24 be maintained via technical specifications, although 25 those values will not be provided until OL.
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47 1 MR. SCHULTZ: But in the numbers that you 2 provided in the MHA calculation, you depict a typical 3 number that might be used in the technical 4 specifications or just bounded it in some fashion?
5 MR. DENMAN: We bounded what we believe to 6 be, what would be in the circulating activity given 7 the state of the design as reflected in the PSAR.
8 MR. SCHULTZ: Okay. Thank you.
9 MEMBER KIRCHNER: This is Walt Kirchner.
10 You would then, Matthew, do the same thing with the 11 argon cover gas, right? Because on the previous 12 slide, you talked about argon-41 release that had been 13 trapped in structure, but the cover gas would be 14 activated, as well. So that would be controlled by 15 tech specs, and that would be added into the MHA?
16 MR. DENMAN: Yes.
17 MEMBER KIRCHNER: Thank you.
18 MR. DENMAN: Okay. So I think we can move 19 on to the next slide. For structural MAR, tritium is 20 assumed to be held within the graphite grains. No 21 hold up of tritium, and the Flibe instantly drops the 22 concentration of tritium outside the graphite grains 23 to zero. So, effectively, the grains are modeled as 24 a sphere. You have a constant flux of tritium that's 25 pushing more and more tritium into that graphite NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
48 1 grain. The flux drops to zero outside of the grain, 2 and now all of that tritium that was being forced into 3 the grain is now able to rapidly diffuse out of the 4 grain due to this immediate and non-physical 5 concentration gradient.
6 The MAR outside of the graphite grains are 7 instantly released at the start of the transient; and 8 within tens of hours, basically, all of the tritium 9 that is stored within these grains are modeled to be 10 released, which is non-physical and extremely 11 conservative.
12 Next slide. So then we can move on to our 13 gas and atmospheric transport. Once you have any 14 gases and evaporated materials that leave our 15 functional containment, they bypass the vessel head 16 and go directly into the reactor building. That's 17 what they're modeled to do. In reality, the vessel 18 head would contain these radionuclides, but they're 19 modeled to bypass the vessel head. And then they're 20 input into RADTRAD. RADTRAD has two depletion 21 mechanisms that we use for radionuclides that enter 22 the reactor building. That is radioactive decay and 23 aerosol settling through the Henry correlation. There 24 is a conservative two-hour hold-up assumption applied 25 to radionuclides that enter the reactor building, 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
49 1 after that two-hour hold-up assumption is applied, 2 they are released to the environment. This is where 3 ARCON 96 is used to calculate our dispersion 4 estimates, our chi over Qs. It inputs hourly 5 radiological data. It evaluates distances from the 6 reactor building to the exclusionary boundary in low-7 population zone, and it uses multiple approved values 8 from the KP-TR-12 topical report. And once all that 9 information is fed in, out is provided the time 10 average dispersion values which you can see on the 11 table.
12 Next slide.
13 MR. SCHULTZ: Matt, Matt, this is Steve.
14 I'm sorry. Are you finished here?
15 MR. DENMAN: Yes.
16 MR. SCHULTZ: If you didn't assume any 17 depletion mechanisms, how much would that affect your 18 answer for release in RADTRAD?
19 MR. DENMAN: Steve, thank you for your 20 question. I believe, as part of our methodology, we 21 always look at the release, we always calculate the 22 release fraction from the building. Those release 23 fractions are, the equation for the building release 24 fraction that we propose is in our mechanistic source 25 term topical report. I believe, and it's been a while 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 since I've looked at it, but it's roughly on the order 2 of a release fraction of 0.9-ish.
3 It's a little different for different 4 radionuclides. They have different decay rates.
5 Gases, obviously, don't settle. Our off-site releases 6 are heavily dominated by gases, but it's roughly on 7 the order of 0.9.
8 MR. SCHULTZ: That makes sense. Thank you.
9 MEMBER KIRCHNER: May I ask a question?
10 This is Walt again. Matthew, since you don't take 11 credit for confinement, when you look at the leakage 12 from the reactor building, I presume it would be at 13 the upper level, not the ground level. Did you look 14 at how that might impact your results?
15 MR. DENMAN: Thank you very much for your 16 question. Can I restate it, restate your question to 17 make sure I understand?
18 MEMBER KIRCHNER: Sure.
19 MR. DENMAN: You're asking, I believe 20 you're asking did we look at the delta between an 21 elevated release and a ground-level release to see 22 what the dispersion changes would --
23 MEMBER KIRCHNER: Yes, that's one part.
24 MR. DENMAN: -- or how that would impact 25 dispersion changes. Thank you for that question. No, 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 we did not model the difference between an elevated 2 release versus a ground-level release due to the 3 approval of the ground-level release being 4 conservative in our mechanistic source term topical 5 report.
6 MEMBER KIRCHNER: Okay. I can go back and 7 review again the mechanistic source term topical 8 report. But then a second question is do you have 9 separation. A two-hour hold up, that's based on, if 10 I remember correctly, that's based on civil 11 engineering code standards for unventilated building, 12 but you're dealing with hot, potentially hot gases or 13 at least a fairly warm environment, and you're dealing 14 with tritium. Does that factor into these analyses?
15 MR. DENMAN: Thank you very much for that 16 question. The two-hour hold up, again, is a parameter 17 that was approved within a mechanistic source term 18 topical report. It was actually pulled from NRC 19 guidance for design basis accident dose calculations 20 from fuel handling accidents in the spent fuel 21 building and releases in open containment. So if 22 you're doing, if you're moving fuel within the 23 containment of a light water reactor, you have the 24 doors open, and you have a release of radioactive 25 material and it's just allowed to migrate out of an 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 open building, that's where the two-hour hold-up 2 assumption came from, and that was the basis for our 3 argument within the approved source term topical 4 report.
5 MEMBER KIRCHNER: Okay. Thank you.
6 MEMBER HALNON: Just one other question.
7 This is Greg. The ARCON 96, did you do any 8 sensitivity runs on that based on different site 9 layouts? In other words, different buildings may be 10 in the way versus a clear path to the site boundary?
11 MR. DENMAN: Thank you very much for that 12 question. No, we did not do any calculations of a 13 torturous path of the plume through the building. We 14 used the straightest path from the exterior of our 15 building to the site boundary.
16 MEMBER HALNON: Do you feel like that's the 17 most conservative, given the potential wave effect of 18 different buildings that may be in the way that could 19 actually cause a redirection of different air flows?
20 MR. DENMAN: Yes, we believe that that is 21 the conservative path.
22 MEMBER HALNON: Okay. Thanks.
23 MR. DENMAN: Okay. So now to the results.
24 As is seen on this table, the dose results meet the 10 25 CFR 100.11 reference values at the EAB and LPZ 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
53 1 significant margin both for the exclusionary boundary, 2 whole-body dose, and thyroid, and the low-population 3 zone over 30 days.
4 Okay. Next slide. To conclude, the MHA 5 dose consequence results meet the site dose reference 6 values in 10 CFR 100.11(a)(1) and (2) at the EAB and 7 LPZ with significant margin, and the MHA dose is 8 bounding because it employs various non-physical 9 conditions that are beyond the expectations of design 10 basis calculations.
11 And with that, thank you very much for your 12 time, attention, and questions.
13 CHAIR PETTI: Members, any additional 14 questions?
15 MEMBER KIRCHNER: How are you going to 16 proceed, Dave? Are we going to hear from the staff on 17 MHA, or are we going to events next?
18 CHAIR PETTI: MHA first, I think.
19 MEMBER KIRCHNER: Okay.
20 CHAIR PETTI: And then tomorrow will be the 21 accident detail. So then why don't we hear from the 22 staff. Is it Michelle? Yes.
23 MS. HART: Good afternoon. I'm Michelle 24 Hart from the staff; I'll just say that.
25 (Laughter.)
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54 1 MS. HART: I forget who I work for. We're 2 here today to talk about the staff's review of the 3 preliminary analysis of the maximum hypothetical 4 accident for the Hermes PSAR.
5 Next slide, please. Okay. So Kairos just 6 provided a thorough description of the maximum 7 hypothetical accident assumptions, methods, and 8 consequence analysis, as described in the PSAR. As 9 they described, the MHA describes a hypothetical 10 radionuclide release intended to result in 11 consequences that are bounding for the postulated 12 events.
13 With respect to the MHA as bounding, PSAR 14 Section 13.2.2 described the postulated event 15 methodology and the figures of merit and acceptance 16 criteria that Kairos developed to provide assurance 17 that the MHA consequence analysis is bounding for 18 postulated events, and we'll be describing our 19 evaluation of that information at tomorrow's meeting.
20 There are a couple of referenced topical 21 reports that are relevant to the MHA analysis, and 22 that is the fuel qualification methodology and the 23 mechanistic source term methodology.
24 Next slide, please. We had a lot of 25 discussion about the MHA hypothetical temperature NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
55 1 versus time profile that is given to give bounding 2 radionuclide releases for the MHA. As Kairos had 3 described, it's not a specific scenario. It's not 4 physical. And because fission product release and 5 transport is mainly through diffusion driven by 6 temperature, it would maximize the releases. And 7 final determination of that temperature versus time 8 curve is conservative for the postulated events will 9 be done during the operating license review.
10 As Kairos has described, it assumes that 11 the safety related systems function as designed but 12 includes consideration of the single failure 13 criterion, even though it's not directly modeled in 14 the MHA analysis and there are no incremental fuel 15 particle coding failures from the transient.
16 Next slide, please. So for the consequence 17 analysis, they do refer to the accident source term 18 methodology that was in the approved topical report.
19 It models the system as sources of radioactive 20 material at risk of release or MAR and the barriers to 21 release. They apply a release fraction to each 22 barrier to eventually result in release to the 23 environment, and that's consistent with the 24 description of a functional containment. And they do 25 also model gravitational settling of Flibe aerosols in 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
56 1 the reactor building consistent with the approval in 2 the topical report.
3 Next slide, please. To go to a little bit 4 of our evaluation of the MHA source term modeling, as 5 we've described several times, that temperature-time 6 profile does drive the diffusion releases from fuel, 7 Flibe, and graphite. The MHA assumes conservative 8 fuel, Flibe, structural and cover gas releases. In 9 effect, the complete fuel inventory is available for 10 release into the Flibe. The bounding failed fuel 11 fractions by cohort are assumed. That's the different 12 particle layer of failures and bare particles, as 13 well. Flibe and cover gas radionuclide inventories 14 are set to technical specification values which will 15 be provided at the OL.
16 Except for the fuel transient releases, 17 tritium and argon-41 modeling, the MHA uses approved 18 mechanistic source term models from the topical 19 report. The fuel releases are modeled using accepted 20 methods, and the staff reviewed the fuel release 21 references to find those models acceptable.
22 The tritium modeling that they have in the 23 MHA resulted in higher total releases than would be 24 expected from the topical report methodology, and the 25 staff also evaluated the modeling assumptions for both 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 the tritium releases and argon-41 in the audit, and we 2 found them to be conservative.
3 Next slide, please. As noted before, the 4 mechanistic source term topical report methodology 5 will not be fully implemented until it's used by the 6 applicant in the operating license application FSAR.
7 And the staff will review the final implementation of 8 that topical report for the Hermes, including the 9 limitations and conditions in the topical report SE in 10 its review of the operating license application.
11 Staff presents its evaluation of the site 12 characteristic accident atmospheric dispersion factors 13 to the subcommittee on March 23rd.
14 Next slide, please. So to go into some of 15 the audit, some of the information that we audited.
16 We did look at the preliminary consequence analysis 17 and MHA source term information. So we did see their 18 calculation packages, output from codes, things like 19 that.
20 In the audit, we were able to confirm the 21 PSAR description of their MHA analysis. In those 22 calculation and reference reports supporting those 23 calculations, we were able to see how they determined 24 the initial radionuclide inventory and MAR sources, 25 including for fuel and Flibe, and those calculations NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
58 1 of tritium generation and argon-41 inventories, how 2 they modeled those in the graphite. We were able to 3 see the calculations estimating releases from the 4 graphite and the modeling of radionuclide transport 5 across barriers and the release fractions for those 6 barriers, as well.
7 We also were able to have an in-person 8 discussion with the staff that they could show us how 9 they went through that process using cesium as an 10 example, isotope, to show us how they could actually 11 put it into the RADTRAD code to generate the doses.
12 MR. BLEY: Michelle, Dennis Bley with a 13 question. It actually goes back a slide.
14 MS. HART: Okay.
15 MR. BLEY: But conservative is a word that 16 makes me a little nervous whenever I hear it. Can you 17 talk a little bit about what you found conservative?
18 Was it the results in the quantity released? Was it 19 the models? Was it the assumptions? Where did you 20 find the conservatism?
21 MS. HART: So the majority of the 22 conservatism that we really had and in the discussions 23 with the staff at Kairos was there was a lot of 24 conservative-leaning assumptions. They made bounding 25 assumptions. You know, we were able to see that they 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
59 1 had used appropriate models or models that we were 2 aware are appropriate for the use.
3 MR. BLEY: So if I understand you right, 4 given the assumptions, you think the modeling was 5 reasonable, but it's the assumptions that you found to 6 be conservative?
7 MS. HART: Do you want to add something to 8 that, Jeff?
9 MR. SCHMIDT: Yes. This is Jeff Schmidt 10 from the staff. So, you know, Matt kind of laid out 11 a bunch of conservatisms as he went through there. So 12 it's things like graphite being a perfect absorber and 13 then the release fractions from that graphite. Like, 14 they looked at different diffusivities to maximize 15 that release. Pebble release fractions were -- I hope 16 this isn't proprietary -- were near one at those 17 temperatures. So the mass transport of tritium into 18 the graphite was a conservative calculation. The fact 19 that the fuel inventory, nothing was allowed to leak 20 away while the coolant activity is also at its tech 21 spec value is a conservatism.
22 So I think it's hard to break out, like, 23 single -- there are multiple levels of conservatism in 24 this calculation. And I think a lot of those were 25 just covered.
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60 1 MR. BLEY: Okay. Thanks.
2 CHAIR PETTI: Michelle, do you remember 3 what isotopes dominated the dose?
4 MS. HART: So from what I remember, it was 5 mostly tritium and argon.
6 CHAIR PETTI: Okay. That's what I would 7 have expected. That's what my gut said.
8 MEMBER MARCH-LEUBA: If you went on the 9 blaming game and you have to blame somebody for how 10 low these numbers are, would you blame the fact that, 11 and, by blame, I mean the fact that the various 12 fractions of TRISO fuel has failed, and the fraction 13 that has not failed does not raise anything. Is that 14 why we're getting these ridiculously low numbers with 15 these conservative assumptions?
16 MS. HART: So I would say it's fair to 17 state that the TRISO particles are retaining the 18 majority of the fission products. Flibe does retain 19 some. Did we look at specific failure fractions and 20 did they provide sensitivity analysis on that? No, 21 not at this stage.
22 MEMBER MARCH-LEUBA: What gives me comfort 23 when I look at this design, it's not that they assume 24 various fraction of particles that are failed but that 25 they measure it when they operate by measuring 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
61 1 contamination in the activity of the Flibe.
2 MS. HART: Right.
3 MEMBER MARCH-LEUBA: So if we start 4 operating and suddenly we see a hundred times the 5 Flibe, we'll stop and we'll figure out what's going 6 on. So the fact that it's something that we're 7 measuring and we can know what it is is good.
8 MEMBER KIRCHNER: Jose, this is Walt. If 9 I could observe, at the time-temperature curve that 10 they're using for the TRISO fuel, the fuel meets the 11 spec. You're hardly challenging it. So as I think 12 Michelle answered, it's going to be tritium and argon 13 because you're not assuming the actual produced fuel 14 performs that well. That's the reason why the numbers 15 are so very, very low.
16 Now, as you said, if they have a batch of 17 fuel that turns out not to be up to spec, they'll see 18 it right away in the circulating inventory and in the 19 cover gas. You'll see that almost instantly if 20 there's a large, a much larger defect fraction for 21 kernels and particles that are either defective or 22 there's tramp uranium outside of the particles.
23 CHAIR PETTI: Those are not the most 24 difficult QC techniques. If you get bad fuel, you 25 know it in QC. It's pretty obvious. You know, you NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
62 1 get zero, and then you get integral, most of the time, 2 integral measurements of kernels. So, oh, that pebble 3 has three exposed kernels, that one has none. It's 4 very clear when you do the test.
5 MEMBER KIRCHNER: On that subject, I guess, 6 you're more familiar with this. It's been a long time 7 since I've looked at these equations for the TRISO 8 particle performance, but I would submit, at these 9 temperatures, you're not going to see much of an 10 impact, assuming, again, the fuel meets the spec.
11 CHAIR PETTI: These temperatures are so 12 much lower than you have in an HTGR that the diffusion 13 --
14 MEMBER KIRCHNER: From a calculational 15 standpoint, you're not going to see anything using the 16 approved equations, methods, for analyzing TRISO 17 performance.
18 MEMBER MARCH-LEUBA: The dose at the 19 perimeter of the plant is controlled by your 20 fabrication. You don't make any mistakes, and that's 21 easy to quality control. It's reliable.
22 CHAIR PETTI: And the fact that they assume 23 in-service failure, normal operation failure, a 24 hundred times with the AGR program demonstration.
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63 1 but we still haven't operated a reactor. Let's get a 2 couple of years of running it and see what happens.
3 MS. HART: All right. So the only other 4 thing I wanted to say about this is, because we did 5 have this extensive audit, there was no need for me to 6 do a consequence analysis, a confirmatory analysis.
7 Next slide, please. So our evaluation 8 findings were that we do find that the MHA serves as 9 a bounding hypothetical analysis for the Hermes 10 reactor. The combination of bounding conditions 11 analyzed are beyond what is assumed for postulated 12 events. The preliminary dose analysis for the MHA are 13 subsequently below the regulatory dose reference 14 values for test reactor siting in 10 CFR 100.11. And 15 because the assumptions of the MHA are bounding, 16 calculated doses would likely not be exceeded by any 17 accident considered credible and the staff will 18 confirm calculations as part of the OL application 19 review.
20 Next slide, please. We did have to talk a 21 little bit about control room habitability. It was 22 really described in PSAR Section 7.4. They did not 23 provide a dose analysis or design details for control 24 room radiological habitability in the PSAR. However, 25 we expect that they will do some kind of analysis 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
64 1 show compliance with PDC-19. They did identify that 2 as the relevant design basis for control room 3 habitability design, and an additional description of 4 the control room habitability design and dose analysis 5 corresponding to the final design will be provided in 6 the OL application.
7 MEMBER MARCH-LEUBA: This is Jose. Maybe 8 because we have such a serious concern about the 9 assumptions in our numbers, but the release inside the 10 plant is very large. Everything goes in there. So 11 habitability with this conservative analysis may be an 12 issue that you exceed applicable doses. Doses for 13 tritium are really, really low, and that will apply 14 mostly to the reactor areas but they move to the 15 control room, too.
16 MS. HART: Yes, it is certainly something 17 that we have in our sights to evaluate in the OL 18 application when we do that in the shielding analysis 19 and any further --
20 MEMBER MARCH-LEUBA: Yes, the steady state 21 you can release in the normal operating because the 22 temperatures are so high that it's going to leak like 23 a sieve.
24 CHAIR PETTI: But the assumptions that 25 they've used are very cavalier, shall we say, because NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
65 1 it still meets the off-site dose. But when you start 2 talking about worker safety, they're going to need a 3 sharper pencil, and I'm sure they will. It will be 4 clean-up systems. It's probably going to be a very 5 different sort of look than what you see in the PSAR.
6 MEMBER KIRCHNER: And we talked a little 7 bit about that at the March meeting, as well.
8 CHAIR PETTI: Yes.
9 MS. HART: Next slide, please. And so, in 10 conclusion, the NRC staff does find the preliminary 11 design information and analysis are consistent with 12 the applicable criteria in NUREG 1537 and that we 13 conclude that the information on the MHA is sufficient 14 for the issuance of a CP, and any further information 15 can be reasonably left for OL application.
16 Are there any further questions?
17 MEMBER KIRCHNER: Michelle, this is Walt 18 Kirchner. I know we've got the groups of events that 19 were analyzed as part of Chapter 13 coming next or 20 coming tomorrow. When you, the staff, went through 21 the applicant's selection of events that they thought 22 were limiting, did you flag any in particular that you 23 would be concerned about and want to go back and re-24 examine whether or not they might, any of those 25 individual events might challenge this MHA assumption?
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66 1 Because, basically, as we've been discussing, this MHA 2 doesn't really involve any significant release from 3 the fuel.
4 MS. HART: Nor does it really look at 5 oxidation of exposed graphite. We kind of mostly were 6 thinking about doing comparisons to the salt spill and 7 the pebble handling system failure. I don't know, 8 Jeff, if you had some additional thought on that.
9 MR. SCHMIDT: Yes, this is Jeff Schmidt.
10 I just want to echo what Michelle said. So I did a 11 lot of the evaluations for what I would call the dose 12 accidents in Chapter 13 for the postulated events, and 13 she's right. Those are the ones I kind of were 14 constantly questioning whether the MHA would bound 15 those because I really didn't have a great engineering 16 feel for how much salt is spilled, what's the release 17 from the salt, what's the aerosol generation from the 18 salt spill. So, you know, I used some of their 19 illustrative examples in the appendices of KP-TR-018 20 to get some sense for it. I asked for some 21 temperature profiles, what was holding the heat in a 22 salt spill, how much would I heat up due to a salt 23 spill accident, for example, to threaten those 24 temperatures of the MHA.
25 So those are the accidents, the salt spill NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
67 1 and the PHHS event, were the ones I kind of focused 2 on.
3 MEMBER KIRCHNER: Okay. Those are the same 4 two that I have concerns about, the potential for any 5 of the pebbles to be exposed in the pebble handling 6 machine or system. Until we see the detailed design, 7 it's hard to know where the level will wind up in the 8 reactor vessel. Certainly, there's discussion from 9 the applicant of unmitigated air ingress. How much 10 graphite is exposed is going to be a design detail, I 11 suspect. Could it result in any of the pebbles being 12 uncovered by Flibe would be something of concern, as 13 well.
14 Okay. Thank you.
15 CHAIR PETTI: Any other questions, members?
16 Okay. Well, we're well ahead of schedule. I just 17 think we should keep pushing through. Are you ready 18 to talk about the other part of Chapter 13 today?
19 PARTICIPANT: Yes, we are.
20 CHAIR PETTI: Okay. We can do the break 21 early. I had it circled at 3:10. It's 2:40. Okay.
22 Then let's take a break until 3:00, and then we'll 23 come back and we'll start the other sections. Thank 24 you.
25 (Whereupon, the above-entitled matter went NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
68 1 off the record at 2:41 p.m. and then went back on the 2 record at 3:00 p.m.)
3 CHAIR PETTI: Okay. We're back and ready 4 to start with Kairos. Matthew.
5 MR. PEEBLES: This is Drew Peebles, Senior 6 Licensing Manager. Just before we get started, we 7 were talking about the exposed kernel fraction. We 8 did check, and that is marked as proprietary in the 9 topical report. But in our fuel qualification 10 methodology topical, KP-TR-011, it's Table 313, if 11 that helps. But I can say in the public session that 12 the fraction that we assumed is not less conservative 13 than the AGR 2 spec.
14 CHAIR PETTI: Okay. Yes, we had a side 15 discussion and came to the same conclusions. Thanks.
16 MR. PEEBLES: Okay. I'll turn it over to 17 Matt. Thank you.
18 MR. DENMAN: Okay. Well, thank you. So my 19 name is Matthew Denman once again, and thank you very 20 much for the opportunity to talk to you about Chapter 21 13 accident analysis focusing on postulated events.
22 You will see these next two slides are a 23 little bit of repeat from what you heard earlier 24 today. We were expecting to give these tomorrow 25 morning, and we wanted to provide context again. But NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
69 1 just as a refresher, 10 CFR 50.34(a)(4) does require 2 a preliminary safety analysis to assess the risk of 3 public health and safety from operations of a 4 facility, including determination of margins to 5 safety. I won't go too far into the MHA again, other 6 than that this is, the MHA is supposed to bound 7 postulated events and it is analyzed for dose 8 compliance with 10 CFR 100.11.
9 The list of postulated events are 10 comprehensive to ensure that any event with a 11 potential for significant radiological consequences 12 has been considered. Initiating events and scenarios 13 are grouped so that the limiting case for each group 14 can be qualitatively described in the CPA, and 15 acceptance criteria are provided for important figures 16 of merit in each postulated event group to ensure that 17 potential consequences of that event group are bound 18 by the MHA as the design progresses. Additionally, 19 prevention of initiators are justified in the PSAR.
20 If we go to the next slide, again, this is 21 a conceptual slide to show the relationship between 22 the 100.11(a)(1) and (2) reference values. The MHA 23 and the potential postulated event doses where the MHA 24 demonstrates your margin to the reference value and 25 then the hypothetical natures and assumptions 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
70 1 boundary conditions and models within the MHA provide 2 that stand-off between the MHA doses and the potential 3 postulated event doses.
4 Next slide. So getting into the postulated 5 event analysis methodology, postulated events are 6 identified in Chapter 13 of the PSAR. Postulated 7 events include any potential upset of plant operations 8 within the design basis that causes an unplanned 9 transient to occur. Justification is provided for 10 those events excluded from the design basis. Figures 11 of merit are provided or, sorry, figures of merit 12 provide the means to measure and demonstrate the 13 resulting doses from postulated events are bound by 14 the doses of the MHA.
15 The preliminary methods and sample 16 calculations of postulated event groups are provided 17 in KP-TR-18, Rev 2. This methodology describes how 18 analyzed figures of merit for, how the figures of 19 merit for each postulated group are analyzed and how 20 acceptance criteria will ensure proper mapping between 21 the off-site dose consequences of the postulated 22 events and the MHA which bounds those events.
23 The final safety analysis results will be 24 provided with the operating license, including 25 verification and validation of the evaluation models NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
71 1 that will be used.
2 So for the next slide, I'm going to 3 transition to my colleague, Tim. Tim, please 4 introduce yourself.
5 MR. DRZEWIECKI: Thank you. This is Tim 6 Drzewiecki. I'm a safety analysis manager here at 7 Kairos Power. I'm going to spend a few minutes 8 talking about a postulated event analysis methodology.
9 So we do follow the steps that are outlined 10 on the in-depth process Reg Guide 1.203. Some of 11 those elements are discussed in our technical report 12 KP-TR-18. Postulated events with similar 13 characteristics are grouped into categories which is 14 consistent with NUREG 1537. Limiting event in each 15 category is then identified and, again, qualitatively 16 assessed from the event initiation until a safe state 17 is reached. That safe state is defined in the methods 18 for each event category as the point where the 19 transient figures of merit have been stabilized in a 20 safe condition and generally involves things like, you 21 know, some criticality and decay heat removal.
22 Next slide, please. As far as the inputs 23 for the postulated events analyses, these are actually 24 shown in Table 44 of KP-TR-18. There are 15 25 parameters in total. Some of them are biased in 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
72 1 conservative direction. Some are nominal. But 2 several are also varied over a range, and the bases 3 for these are described in that table.
4 Again, a range of values are assessed to 5 identify a limiting scenario for each postulated event 6 and key modeling uncertainties and initial conditions 7 are applied to the methods to ensure that the figures 8 of merit are conservatively predicted. And those 9 figures of merit again are shown in Table 13.11 of the 10 PSAR.
11 Next slide, please. So I was going to hit 12 a couple of events, and then I'm going to just kind of 13 walk through what a typical event is going to look 14 like in our reactor. So for the loss of forced 15 circulation, the limiting event here was a pump 16 seizure that would disable primary salt pump, and in 17 that event is we do see is a heat up of the system 18 which is then detected by the protection system. That 19 causes a trip early in this event.
20 And then other events that are predicted 21 here are things like a pump trip or a loss of normal 22 heat sink. The next category is the insertion of 23 excess reactivity. This is a control system or 24 operator error that causes an element to withdraw 25 continuously at the maximum speed, and this 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
73 1 detected by the protection system either by a high 2 flux or a high temperature. Events that also fall 3 under this category are errors in fuel loading, 4 reflector shifting, or venting of gas level. And, 5 last, a category I'm going to cover on this slide is 6 general challenges to normal operation. So this would 7 be any kind of challenge to operation that's not 8 covered by the other event categories. We think these 9 are bounded by the loss of poor circulation, and they 10 include things like spurious trips, operator errors, 11 and equipment failures.
12 So this next slide, I'm going to walk 13 through just a loss of forced circulation overheating 14 event. Now, those images that you see are actually 15 the same image or at least the image on the right.
16 That's adapted from a figure from KP-TR-18 just so who 17 the time scale a little more clearly because the one 18 on the right goes out to about 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and is on a 19 standard scale, as opposed to a semi-log scale.
20 So this event starts with a pump seizure or 21 a locked rotor. We do see the heat-up that occurs in 22 the first minute of this event at about 30 seconds, 23 and that would show up, on the left is one of those 24 peak lines there. We do see a reactor trip. And then 25 following that, there is a heat-up period in which 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
74 1 decay heat is higher than the heat that's being pulled 2 out by our DHRS, or decay heat removal system. That 3 heat-up period lasts for about 20 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br />, at which 4 point the heat removal from decay heat removal system 5 exceeds our decay heat loads and then we see a 6 decrease in the system temperature.
7 So if there's no questions, I'll hand it 8 back to my colleague, Matt.
9 MR. DENMAN: Well, thank you very much, 10 Tim. So I'm going to cover some of the postulated 11 events that really involve releases of radioactive 12 material outside of the vessel.
13 So the first event is the mishandling or 14 malfunction of the pebble handling and storage system.
15 The limiting event involves a break in the fuel 16 transfer line during removal of fuel from the core 17 that results in a spill of pebbles within the transfer 18 line into the surrounding room. The reactor 19 protection system detects this condition and initiates 20 a trip of the pebble handling and storage system to 21 prevent additional pebbles from moving into the pebble 22 transfer line. Grouped events include transfer line 23 breaks when pebbles are inserted into an empty core, 24 core at power, storage canisters, and mishandling fuel 25 outside of the reactor.
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75 1 MEMBER KIRCHNER: Matthew, this is Walt 2 Kirchner. Just quickly, you say the reactor 3 protection system detects this condition. What would 4 be the sensor for that? Gamma detection?
5 MR. DENMAN: Pressure.
6 MEMBER KIRCHNER: Well, you wouldn't detect 7 it on neutrons from your core flux monitoring system.
8 So is the idea that in the reactor cavity you would 9 have a sensor?
10 MR. DENMAN: So this would be a pressure-11 related trip on the cover gas system.
12 MEMBER KIRCHNER: Well, it's pretty low 13 pressure. Okay. Okay. Thank you.
14 MR. DENMAN: Okay. I will also note here 15 that the pebbles themselves do have a low decay heat 16 level and, thus, temperatures will be manageable.
17 The radioactive release material from a 18 subsystem or component, the limiting event is assumed 19 to be a seismic event that results in the failure of 20 all systems containing radioactive material that are 21 not qualified to maintain structural integrity during 22 a design basis earthquake. This is effectively a 23 common mode failure. Design requirements on the 24 amount of MAR for these structure systems and 25 components will be set to ensure that the amount 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
76 1 MAR that could be released is less than the MAR 2 derived from the maximum hypothetical accident 3 releases. And grouped events include releases from 4 the tritium management system, inert gas system, 5 chemistry control system, and inventory management 6 systems.
7 Next slide. Salt spills. So in this 8 scenario, a hypothetical double-ended guillotine break 9 occurs in the primary heat transport system hot leg 10 piping. The reactor protection system detects the 11 salt spill due to a low coolant level and initiates a 12 reactor trip. The grouped events for this scenario 13 include spurious draining of the primary heat 14 transport system, leaks from other Flibe-containing 15 systems, mechanical impact or collision of Flibe-16 bearing structure systems and components, and heat 17 rejection radiator tube breaks.
18 Finally, internal and external hazards are 19 considered. These include internal fires, internal 20 water flood, seismic events, high wind, toxic 21 releases, mechanical impacts or collisions, structure 22 systems and components, and external floods as 23 described in Chapter 2 of the PSAR. Events in this 24 category are bound or considered as initiators to 25 other event categories. A good example of this is 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
77 1 release of radioactive material from subsystems or 2 components that I talked about on the previous slide 3 where an external hazard provides that common mode for 4 release pathway for all of those.
5 So in conclusion, postulated events within 6 the design basis are identified and grouped by 7 characteristics and modeling approaches used to 8 evaluate these postulated events. Design features 9 which are credited with mitigating the effects of 10 postulated events are described. Figures of merit are 11 derived for the postulated events to provide surrogate 12 metrics which demonstrate that the resulting doses are 13 bound by the dose consequences of the maximum 14 hypothetical accident analysis. The acceptance 15 criteria for these figures of merit represent design 16 limits that ensure that the MHA will remain bounding.
17 And with that, I appreciate the ACRS for 18 their attention and questions. And thank you.
19 CHAIR PETTI: Matt, I had a question. It 20 wasn't clear to me in some of the events whether the 21 single failure criteria is applied or even has to be 22 applied in these events, particularly in core sort of 23 events.
24 MR. DRZEWIECKI: Yes, Dave, this is Tim 25 Drzewiecki. And, yes, we do apply single 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
78 1 criteria. We do, you know, account for a stuck rod, 2 as well. The single failure is generally associated 3 with our decay heat removal system. That's generally 4 seen to be our limiting single failure.
5 CHAIR PETTI: But let's look at the 6 reactivity event. Is there a delayed detection? You 7 say that the high flux is out, but then the higher 8 power gets you, shuts it down? What's the timing 9 there?
10 MR. DRZEWIECKI: The timing. So in terms, 11 those specific, you know, like, details, in terms of 12 what trip would come in then, those would have to be, 13 you know, looked at. But the one thing I do want to 14 highlight is in terms of our, you know, RPS is 15 designed to, you know, be single failure-proof or to 16 actually handle single failures. You know, that's 17 accordance with the standard that it's designed to.
18 CHAIR PETTI: So you think that the event 19 that's modeled in the appendix of the technical report 20 is still fairly reasonable once you get the final 21 design details? You're not going to see a greater 22 response, if you will.
23 MR. DRZEWIECKI: I can't speak to that 24 because our methods are still being developed. You 25 know, those calculations were based on preliminary 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
79 1 design information, so I think it's representative of 2 what we're going to see. But I can't say that it's 3 bounding. There are things in there that are very 4 conservative. For example, reactivity insertion.
5 Those are very conservative, so it could be bounding 6 but I can't commit to that.
7 MEMBER HALNON: This is Greg. Pardon me if 8 we've talked about this. The occupational dose with 9 the RBHVAC, I assume that you're assuming that, since 10 it's non-safety, it's essentially not there. Is that 11 another analysis another time, or is it factored into 12 this MHA?
13 MR. DENMAN: So occupational dose 14 evaluation will be provided at the OL.
15 MEMBER HALNON: And just surmising that 16 this MHA is going to exceed any occupational dose 17 allowables, what happens then? Do you have to come 18 back and re-look at the MHA, or do you have to design 19 something into the RBHVAC to control the environment 20 better?
21 MR. DENMAN: The MHA is intended to analyze 22 off-site doses, not occupational doses.
23 MEMBER HALNON: Okay. So that will be, 24 this will be unaffected by any inside dose, if you 25 will.
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80 1 MR. DENMAN: Correct.
2 MEMBER HALNON: Okay.
3 CHAIR PETTI: Any other questions, members?
4 MEMBER REMPE: To follow up, on page 47 out 5 of 99, you talk about the spilled pebbles, and you say 6 since the temperatures are high they'll react with the 7 air in the building to generate heat because it's an 8 exothermic reaction, and I just wondered do you know 9 what temperature they're at?
10 MR. DENMAN: Thank you very much for that 11 question. So the pebbles are, by the time they 12 actually make it out of the core and make it into the 13 cover gas space above the Flibe free surface, they're 14 going to be very, very, very close to the cover gas 15 temperature because the decay heat is so low and the 16 pebbles are fairly small. As they move through the 17 pebble handling and storage system, that trend is 18 going not follow. So as you get the temperatures in 19 the pebble transfer line, the temperatures of the 20 pebbles are going to start to decrease. And then in 21 a spill event, they're assumed to still be above the 22 400 C oxidation threshold temperature, but it's not 23 expected to be a rapid process, nor at a process where 24 you're likely going to see exothermic temperatures.
25 It will likely be endothermic. But, again, these are 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
81 1 all preliminary design information feeding into these 2 temperatures, and we'll have to look to OL to know for 3 sure and we will be ready to evaluate any condition 4 that we find.
5 MEMBER REMPE: So I think the answer is 6 that you're not exactly sure because you're modeling 7 hasn't progressed that far, right, is what the answer 8 is? Because I didn't hear a temperature really coming 9 out.
10 MR. DENMAN: Yes. So --
11 MEMBER REMPE: Okay. Thank you.
12 MR. DENMAN: Okay.
13 CHAIR PETTI: Okay. Hearing no more 14 comments, let's move to the staff. Jeff?
15 MR. SCHMIDT: Jeff Schmidt with staff.
16 I'll wait for my slides.
17 Okay. So we're going to talk about the 18 same things that Kairos just got done talking about, 19 postulated events in other sections.
20 Next slide, please.
21 Kairos, as we talked about, uses the MHA.
22 The MHA is supposed to bound the radiological release, 23 and there has been some reference to this PSAR Table 24 13.1-1, which I think is worth bringing up again, 25 because what that table is trying to communicate 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
82 1 that different events have different release pathways, 2 and you've got to control some of the variables or the 3 figures of merit in the table to ensure that the MHA 4 remains bounding.
5 I think we've said that multiple times, but 6 it's important to understand what the -- what the 7 purpose of that table is.
8 Postulated events considered are consistent 9 with those listed in 1537, as Tim just said. Though 10 there were some technology-specific events or event 11 sequences that are precluded by design, we'll talk 12 about two that the staff had additional questions on.
13 And, obviously, we've talked about these in 14 previous meetings. The Flibe interaction with water 15 or concrete are precluded by design, and that's listed 16 in that PSAR section.
17 Some technology-specific events such as 18 increased pebble packing fraction and the potential 19 reactivity insertion due to that have been evaluated, 20 at least to the design information available.
21 Next slide, please.
22 As we talked about, the postulated event 23 methodologies in KPTR-018 Rev 2. As Tim mentioned 24 also, KPTR-018 Table 4 has input parameters, which 25 kind of outline the overall methodology that's going 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
83 1 to be applied to the postulated events. It covers 2 things like initial power level, reactor coolant 3 temperatures.
4 We spent some time with Kairos flushing out 5 the details of that to ensure it was a very I think 6 thorough and consistent overall calculational 7 framework, relatively along the lines of, let's say, 8 like a NUREG-0800 Chapter 15 analysis.
9 FSAR analyses will consider the full range 10 of sensitivities based on the Table 4-4. KP-SAM and 11 KP-BISON have the capability to model postulated 12 events, corresponding fuel releases. We talked a 13 little bit about that in our previous meeting and the 14 capability of those codes. Just to remind everybody, 15 code verification and validation will be reviewed 16 prior to or as part of the OL application.
17 Next slide, please.
18 So I'm going to walk through each one of 19 the events kind of the way they're listed, the way --
20 I'm sorry, the way they're listed in the -- in the 21 PSAR. So the first one is insertion of excess 22 reactivity. Seems to continuously draw the highest 23 worth control rod at the maximum speed. Reactor trips 24 on high power or high temperature. Range of 25 reactivity insertion rates and initial core 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
84 1 levels will be evaluated at the OL.
2 So right now they've done the max -- like 3 a maximum reactivity insertion, but usually you look 4 at a different range of insertions because different 5 trips will pick up different reactivity insertion 6 rates.
7 Uncertainties will be quantified as part of 8 the OL application. Internal element injection is 9 precluded due to the low differential pressure between 10 the reactor and atmosphere, so that's a consideration 11 in, you know, what the events are for -- that are 12 considered as part of insertion of excess reactivity.
13 Temperatures stay below the MHA, 14 hypothetical temperature versus time curve, except for 15 the maximum reflector temperature, which slightly 16 exceeds the MHA-free surface and graphite temperature 17 limits for a short period of time.
18 Again, you know, it's important to stress 19 that these are preliminary calculations. At short 20 deviation was considered by the staff in that review 21 and thought to -- that the MHA was still going to be 22 bounding because it's a fairly short duration and a 23 relatively small deviation from the acceptance line.
24 Staff scoping analysis yielded similar 25 results, as we show in the following slides. So we're 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
85 1 going to have -- at the end of this presentation, 2 we're going to go through some of the scoping analyses 3 that were performed by the staff, and basically go 4 through a comparison of their calculations to our 5 calculations. Andy Bielen will be handling that.
6 The staff has reasonable assurance that the 7 MHA dose bounds that of the insertion of excess 8 reactivity because of conservatisms in the MHA 9 analysis. As we talked about, there's a number of 10 conservatisms in the MHA analysis. There is no real 11 separate or different pathway to exposure here, say 12 like for the pebble handling system or the salt 13 system. So that was how we reached the conclusion 14 that the MHA was going to be bounding, just based on 15 the temperature profile that's used as part of the 16 MHA.
17 Next slide, please?
18 So the salt spill is the next postulated 19 event. This is a loss of coolant inventory resulting 20 in different release pathways in the MHA. As was 21 stated earlier, some safety-related systems work as 22 intended, assumes water or concrete interactions are 23 precluded by design. That's really referring to, you 24 know, the -- where the salt is spilled.
25 Methodology includes evaluating a range 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
86 1 break sizes and locations as part of the calculational 2 framework. As Matt described, their day-to-day, 3 double-ended guillotine break of the hot leg.
4 Release pathways, different from the MHA, 5 include radionuclide by the break, evaporation from 6 the spilled fuel pool, and oxidation of any exposed 7 graphite. And we've talked a little bit about that as 8 -- you know, right now we have preliminary estimates 9 of like the amount of salt spilled, but how much 10 graphite that is exposed during that transient the 11 staff is not sure of yet.
12 But that's one of the figures of merit that 13 has to be controlled, is that, you know, you have to 14 limit the oxidation such that, you know, oxidation 15 doesn't release or doesn't lead to, you know, 16 contributing to a release that's greater than the MHA.
17 Heat-up due to loss of inventory is 18 expected to be low. The staff asked for some 19 information on that during the audit, and bounded by 20 the MHA versus -- time versus temperature curve. So 21 the massive salt spilled, at least preliminary, is 22 fairly low to the total mass of the system. And a lot 23 of the heat of the system is tied up in the graphite, 24 so you would expect that the temperature increase due 25 to the -- to the loss of salt is pretty low.
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87 1 MR. HALNON: How does it get out into the 2 environment? It just infiltrates through the 3 building, or is there --
4 MR. SCHMIDT: Yeah. It just -- it spills 5 into an apartment or building and that just --
6 MR. HALNON: Is there any difference if the 7 RBHKC continues to operate and sucks it out and pushes 8 it out through --
9 MR. SCHMIDT: No.
10 MR. HALNON: -- point?
11 MR. SCHMIDT: No. We didn't look at that.
12 This just goes -- just goes into the reactor building 13 and out, part of that process, but --
14 MR. HALNON: Okay. Is that not a concern, 15 then, that it could be funneled and dragged out by an 16 operating fan and pushed out into -- with some 17 velocity?
18 MR. SCHMIDT: Yeah. That would -- I guess 19 that would have to be looked at as part of that. Its 20 failure -- I mean, that's a control system that would 21 lead potentially to a worse answer. But right now 22 these are more, I would think, qualitative evaluation 23 and not to that level of detail.
24 MR. HALNON: Okay.
25 MR. SCHMIDT: Methodologies for break air 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
88 1 salt generation and Flibe, vessel-free surface 2 evaporation. Methodologies are from the approved 3 mechanistic source term topical report. Salt spill 4 uses lower event-specific temperatures and, hence, 5 lower fuel wetted graphite surface, tritium, and lower 6 Flibe vessel preservice temperatures. That's just 7 basically saying that the MHA temperatures are 8 bounding this event.
9 Staff has reasonable assurance that the MHA 10 would bound a salt spill based on the minimal heat-up 11 in the low salt mass spilled. Quantitative dose 12 assessment comparison between the salt spill and the 13 MHA will be performed as part of the OL application.
14 Next slide?
15 The next event is loss of poor circulation.
16 This, as Tim pointed out, is seizure of the primary 17 salt pump, reactor trips on high outlook temperature, 18 uncertainties as -- with most of these accidents will 19 be quantified as part of the OL application.
20 Again, temperatures stay below the assumed 21 MHA, hypothetical time or temperature versus time 22 curve, except for the maximum reflector temperature 23 and upper plenum temperature, which slightly exceed 24 the free surface and graphite temperature limits for 25 a short period of time. The same argument goes again.
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89 1 The staff looked at some of the 2 conservatisms that are in these calculations, and 3 there are some significant conservatisms in these 4 calculations that could be refined such that, you 5 know, there is at least reasonable assurance that some 6 of these values could be brought down. But we'll --
7 that will be determined as part of the OL.
8 Staffing scoping analysis, again, we did 9 this event as well. It yielded similar results, as 10 Andy will go through in the following slides. Staff 11 has reasonable assurance the MHA does balance that --
12 balance that of the loss of poor circulation. Again, 13 this isn't really a different release path than the 14 MHA with effectively lower temperatures.
15 Next slide?
16 The pebble handling and storage system 17 event, as was described as a break in the pebble 18 handling system, it does have different release 19 pathways. Reactor protection system trips to stop the 20 pebble movement, as was described. Pebbles spill onto 21 the transfer room, and no active heat removal is 22 credited to limit the spilled pebbles temperature.
23 And I believe in the -- either the last 24 figure or the second-to-last figure in APTR-018 has 25 what the temperatures are for the pebbles. So that 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
90 1 available. And I can't remember -- it's one of the 2 last figures in their illustrative examples for salt 3 spill.
4 Release pathways, different from the MHAs.
5 We've talked about this is basically the mobilized 6 graphite dust that could come out as part -- that 7 accumulated in the pebble handling system and then is 8 expelled from the break, and then the pebble oxidation 9 -- as Dr. Kirchner was talking about, there's 10 assumption of spilled pebbles, and then any pebbles 11 that remain in the pebble handling system that may be 12 exposed to air.
13 We've had significant discussion with them 14 to include -- make sure that all of those pebbles were 15 included in the analysis, or will be included in the 16 analysis, I should say.
17 MEMBER REMPE: So I see the temperature 18 curve. Thank you. And it starts at xxx, and it just 19 drops down. So I'm guessing they don't consider 20 exothermic reactions if they start at xxx and they 21 have --
22 MR. SCHMIDT: Yeah. I think it stated 23 regime 1, if I remember correctly.
MEMBER REMPE: But I would think that you 24 would have some exothermic reactions.
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91 1 MR. SCHMIDT: It's very -- the oxidation at 2 those temperatures is fairly low.
3 CHAIR PETTI: Yeah. But notice -- this is 4 proprietary. We have to be careful.
5 MEMBER REMPE: Yeah. But I didn't say a 6 number. I just said it's going down. I mean, it's 7 CHAIR PETTI: No. You did mention a 8 number. You didn't mention what temperature scale, so 9 you're okay.
10 MEMBER REMPE: Okay.
11 CHAIR PETTI: But if you notice that 12 temperature scale, that's very low.
13 MEMBER REMPE: I've got documents that say 14 anytime you're above 500C that you can have oxidation.
15 CHAIR PETTI: Oh, you can -- oh, for sure 16 you can have oxidation.
17 MEMBER REMPE: Yeah.
18 CHAIR PETTI: But it's --
19 MEMBER REMPE: Yeah.
20 CHAIR PETTI: -- how much.
21 MEMBER REMPE: How much, but it can be 22 exothermic, too, is what I --
23 CHAIR PETTI: Well, it's always exothermic.
24 MEMBER REMPE: Right. So then does this 25 fit your --
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92 1 CHAIR PETTI: But there's a huge amount of 2 MEMBER REMPE: Yes. Again, we --
3 CHAIR PETTI: You'll see --
4 MEMBER REMPE: -- do you know if their 5 models considered the --
6 MR. SCHMIDT: There is an oxidation 7 correlation that's used, and I did look at it. I'm 8 not sure I remember it off the top of my head, but, 9 yeah, there is an oxidation model. Yeah.
10 MEMBER REMPE: And it considers the --
11 MR. SCHMIDT: It was an oxidation model 12 based on -- the Chinese had done a pebble matrix.
13 They created an A3-3-type pebble, and they had 14 developed a correlation that Kairos is referencing.
15 CHAIR PETTI: The U.S. has also done 16 measurements of matrix material. It's in the 17 literature.
18 MR. SCHMIDT: I was just referring to the 19 ones that they referenced.
20 CHAIR PETTI: Yeah.
21 MR. SCHMIDT: It seemed like an appropriate 22 reference over the appropriate temperature.
23 MEMBER REMPE: And so they are considering 24 the heat input from that oxidation?
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93 1 on basically mass loss. So whatever happens happens.
2 MEMBER REMPE: Okay. And then what about 3 the reflector surfaces, too, within a system and that 4 oxidation?
5 MR. SCHMIDT: That I think is part of the 6 graphite topical report, and the oxidation rate of the 7 graphite material is different than the ones I'm 8 referring to for the pebbles.
9 MEMBER REMPE: Okay. So, anyway, it's just 10 something that I thought --
11 MR. SCHMIDT: It's picked up in the 12 graphite --
13 MEMBER REMPE: -- and that -- again, the 14 answer may be there is not much combustible gas 15 generated, but I just --
16 MR. SCHMIDT: Yeah.
17 MEMBER REMPE: -- didn't see those words 18 anymore.
19 MR. SCHMIDT: You know, on this break, you 20 know, I don't -- I don't personally have a good handle 21 on how much structural graphite is exposed in this 22 type of --
23 CHAIR PETTI: Well, you should -- you 24 should look two figures earlier. There is the actual 25 oxidation.
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94 1 MEMBER REMPE: Okay. I see that.
2 CHAIR PETTI: So they are actually doing 3 that.
4 MEMBER REMPE: And is this for the pebbles, 5 or is this for -- so I'd have to go back and 6 CHAIR PETTI: This is for this accident, 7 pebble handling.
8 MEMBER REMPE: -- pebbles. But this isn't 9 the --
10 CHAIR PETTI: This could be for the 11 pebbles.
12 MEMBER REMPE: -- reflectors, though. This 13 is just the --
14 CHAIR PETTI: This is for pebble handling.
15 MEMBER REMPE: Just -- okay. But there is 16 also --
17 CHAIR PETTI: In the pebble handling event 18 MEMBER REMPE: Okay.
19 CHAIR PETTI: -- the pebbles that spill on 20 the floor.
21 MEMBER REMPE: Okay.
22 MR. SCHMIDT: Yeah. So, and the spilled 23 pebbles are assumed to be at their maximum burn up, 24 and, hence, maximum material at risk for the oxidation 25 calculation, and then the dust activation uses 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
95 1 same assumptions.
2 Next slide?
3 Is that -- oh, yeah. I'm just basically 4 saying I reviewed the pebble matrix oxidation and dust 5 generation calculations, or methodologies to be more 6 appropriate. The methodologies, I get those.
7 Fuel qualification topical report, so this 8 is an important tieback to the fuel qualification 9 topical report. You know, they're going to do tests 10 for their own specific pebble matrix material, and 11 that will inform how these calculations are done as 12 part of the OL, right?
13 So right now they're using this surrogate 14 A3-A that the Chinese had developed, but they're going 15 to do their own testing to come up with their own, to 16 see if that correlation is either still valid or needs 17 a different correlation.
18 And, again, another tieback to the fuel 19 qualification topical report, pebble wear will also be 20 looked at, right? There's an assumption of the wear 21 rate of these pebbles to generate that dust, right, 22 that's expelled as part of the pebble handling. And 23 I'm just referring back to they are doing tests to try 24 to, you know, quantify that dust generation rate.
25 And, again, the dust generation 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
96 1 resuspension from the break is already discussed and 2 approved in the mechanistic source from topical 3 report.
4 PHS event uses lower temperatures. Again, 5 I don't expect this to be really a temperature-driven 6 event. The loss of mass is expected to be low. The 7 salt, hence lower fuel wetted graphite surface 8 temperatures with lower tritium releases, lower Flibe, 9 vessel-free surface releases.
10 So, again, the concept is that the MHA 11 temperatures will easily bound the PHSS, but you have 12 to pick up these other figures of merit that have to 13 do with dust and oxidation.
14 A quantitative dose comparison between the 15 PHS event and the MHA will be performed at the OL 16 application. These will be specifically compared at 17 the OL application -- as part of the OL application.
18 Next slide?
19 This is a fairly simple thing that Matt was 20 discussing from Kairos. So this is a radioactive 21 release from a subsystem or component. The short 22 answer is that the materials at risk have to be 23 limited such that if there was, say, a single event, 24 say, speculated seismic event, that the non-protected 25 structures or non-safety-related structures, I should 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
97 1 say, will release, but that will still be bounded by 2 the MHA based on the quantities of material at risk in 3 these areas.
4 Next slide?
5 So general challenges to normal operation, 6 as was discussed, are caused by inadvertent operator 7 action, failure of a control system or 8 instrumentation. The reactor protection system will 9 sense to terminate the event, assuming setpoints are 10 reached. Events caused by operator action, control 11 system, instrument failures, are typically bounded by 12 events analyzed in Chapter 13 due to the use of 13 bounding assumptions and analyses.
14 Consequences caused by inadvertent operator 15 action, control system, or instrument failure will be 16 reviewed in more detail as part of the OL application.
17 Next slide?
18 Internal or external events. Again, these 19 are -- typically limiting internal events are 20 primarily just by Chapter 13. Kind of an aside to 21 that is the fire protection, which isn't really 22 addressed by Chapter 13. Programs are addressed as 23 part of PSAR Section 9.4 and will protect safety-24 related systems that perform event mitigation 25 function.
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98 1 Most external events are addressed by 2 designing SSCs commensurate with the hazard of the 3 applicable standard. Seismic-induced reactivity event 4 due to unique -- that's unique to the pebble bed, this 5 was kind of a -- this is a different, you know, 6 technology-specific accident that's, you know, driven 7 by an external hazard being a seismic event.
8 So there was -- Kairos did look at some of 9 the increase in pebble -- pebble packing fraction, 10 sorry, and associated reactivity increase. As we'll 11 discuss probably in the excess reactivity, this will 12 be I think easily bounded by the insertion of excess 13 reactivity event.
14 They did look at the change in moderation 15 near the reflector where it's a positive reactivity, 16 and then a corresponding negative reactivity insertion 17 towards the middle of the pebble bed. No final 18 numbers were generated, but there is a release 19 reported in the -- in the technical report.
20 But -- so there is a plus and a minus 21 component associated with this packing fraction 22 increase. I did a little research as far as relative 23 to high-temperature gas reactors, especially the 24 Chinese -- I think it's H-10, HT-10.
25 CHAIR PETTI: HRT-10.
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99 1 MR. SCHMIDT: HTR-10. Thank you. And one 2 of the -- you know, one of the reactivity increases 3 that you don't expect to see in this type of positive 4 buoyancy bed is slumping of the core relative to, say, 5 control rod insertion. Right? So if you were to 6 repack this thing, you would expect that since it's 7 positively buoyant to actually pack towards the top of 8 the core and not slumped towards the bottom.
9 So you're going to be moving the core 10 effectively in the direction of the control rods. You 11 know, there's a pretty big reactivity insertion 12 potentially, depending on where your rods are inserted 13 in a high-temperature gas reactor because the pebble 14 bed will slump on an increase in peaking factor, and 15 you'll effectively have less rod insertion as part of 16 that.
17 So there's like a two-part reactivity 18 insertion, one due to the slumping, due to the 19 increased packing fraction.
20 So that -- that situation should not occur 21 in the Kairos design. Therefore, I expect that the 22 excess reactivity event, which we'll talk about in 23 detail when we get to the following slides, will bound 24 this basic --
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100 1 what the packing fraction is? Was it the maximum 2 theoretical -- is it 0.1 percent, or is it 10 percent?
3 MR. SCHMIDT: Do you mean as far as --
4 MEMBER MARCH-LEUBA: With respect to the 5 with respect to the maximum theoretical you can put 6 the bolts on?
7 MR. SCHMIDT: So I want to say it's like 60 8 percent of .6 is -- is the number that I'm recalling.
9 But I'm not 100 percent sure on that.
10 MEMBER KIRCHNER: That's about right, Jeff.
11 This is Walt. Yeah.
12 MR. SCHMIDT: Okay.
13 MEMBER KIRCHNER: For a static pebble bed 14 reactor, that's about it. It depends also on the 15 diameter, because you have --
16 MR. SCHMIDT: Right.
17 MEMBER KIRCHNER: -- the edge effects on 18 the density of pebbles.
19 MEMBER MARCH-LEUBA: I'm not asking about 20 how much space there is for the Flibe. I'm saying 21 what you are talking about actually when you shake it 22 during the --
23 MR. SCHMIDT: Oh. How much --
24 MEMBER MARCH-LEUBA: -- and it compresses, 25 are you going to get more?
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101 1 MR. SCHMIDT: Right.
2 MEMBER MARCH-LEUBA: So what this -- with 3 respect to the maximum theoretical you could have 4 spheres.
5 MR. SCHMIDT: I don't remember that number.
6 I think it was actually in the article I read for a 7 high-temperature gas reactor, but I don't recall it.
8 And I don't know if I thought it was --
9 MEMBER MARCH-LEUBA: Because you --
10 MR. SCHMIDT: -- overly applicable to this.
11 MEMBER MARCH-LEUBA: -- you need the number 12 to know what the --
13 MR. SCHMIDT: Yeah, yeah. You do. You do.
14 You're right. You know, this -- like I said, I expect 15 the bed to actually move up, and it will densify to 16 some amount.
17 MEMBER MARCH-LEUBA: Because I --
18 MR. SCHMIDT: Yeah. Due to the shaking.
19 CHAIR PETTI: If it's the paper I think you 20 read, because there aren't that many out there --
21 MR. SCHMIDT: Yeah. No, it was hard to 22 find.
23 CHAIR PETTI: -- it was done by people I 24 know. I think they went -- they assumed it went to 25 maximum packing, which Ron says is .72.
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102 1 MR. SCHMIDT: Yeah. So that does seem --
2 that sounds familiar, the .72. But I'm --
3 MEMBER MARCH-LEUBA: .72 is the maximum 4 packing. So what is the normal operating --
5 MR. SCHMIDT: .6 roughly I think is --
6 MEMBER MARCH-LEUBA: Okay. So --
7 MEMBER BALLINGER: Basically, it's .74.
8 MR. SCHMIDT: .74, okay.
9 MEMBER MARCH-LEUBA: You just calculated 10 it?
11 (Off mic comment.)
12 MEMBER MARCH-LEUBA: So you calculated from 13 .6 to .7, so that's -- that's not the packing.
14 MR. SCHMIDT: Yeah. Again, I think we're 15 going to have -- my last bullet there is we're going 16 to have to look at this in detail at the OL. So I 17 think this will be one thing that will be revisited.
18 I was just looking for information that I could use 19 for a reasonable assurance finding that excess 20 reactivity would bound this event.
21 MEMBER MARCH-LEUBA: Just go with the 22 binding, the earthquakes takes it to the maximum 23 theoretical.
24 MR. SCHMIDT: Right.
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103 1 know what the normal is.
2 MR. SCHMIDT: Right. Right. But there is 3 -- yeah, right. You could do that, but there is 4 actually a negative reactivity insertion --
5 MEMBER MARCH-LEUBA: Into the control --
6 MR. SCHMIDT: -- due to Flibe -- well, the 7 Flibe -- let's just also -- the bed moving up relative 8 to the control rods, but you could also assume that 9 the controls rods are not -- that you're fully 10 withdrawn.
11 MEMBER MARCH-LEUBA: That's a good, handy 12 theoretical approach.
13 MR. SCHMIDT: Yeah. I think we'll address 14 that as part of the OL. How about that?
15 All right. Next slide, please.
16 Okay. So this is an area of -- so it's 17 prevented events, so these are events that are not 18 analyzed as part of the PSAR, and I'm going to --
19 there is a list in this PSAR Section 13.1.10. I'm not 20 going to go -- I didn't -- I'm not going to go through 21 all of the prevented events, but I will highlight two 22 that I thought were the most significant that the 23 staff passed RAIs on.
24 The first one was RAI-348, asks the basis 25 of why recriticality or unprotected events are 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
104 1 excluded from consideration. Kairos modified -- in 2 response to that RAI, Kairos modified PSAR Section 3 4.2.2.3 to further describe the shutdown element 4 testing to ensure the shutdown margin analysis remains 5 valid, and in part lower the probability of an 6 unprotected event.
7 So, as you recall from our previous 8 discussions, the shutdown rods go into the pebble bed.
9 So the staff was concerned that -- didn't have a lot 10 of experience, the insertion of rods into the pebble 11 bed and that they would sufficiently go in to both 12 meet the shutdown margin assumption and actually go 13 into the core enough to prevent the unprotected event.
14 So staff asked that -- what type of 15 qualification testing was going to be performed to 16 ensure that those two items were met, and Kairos 17 modified the PSAR section to address that.
18 The main thing the staff wanted to get out 19 of that is to ensure that if you were to insert all of 20 the control rods, would they successfully go into the 21 pebble bed to a sufficient depth to ensure shutdown 22 margin and prevent recriticality, because, you know, 23 as you cool down, right, you're going to add positive 24 reactivity to the system again, and you have to have 25 enough excess reactivity to maintain shutdown. 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
105 1 the other one was just to ensure that you didn't have 2 an unprotected event from a mechanical-induced 3 mechanism.
4 And then RAI-350 asked in part how 5 component integrity is ensured for the duration of an 6 air ingress event, including air ingress beyond the 7 heat rejection blower trip, and that was addressed in 8 SE Section 5.1.3.2.6, addresses the material 9 qualification testing after seven days.
10 And then there was discussion beyond what 11 happened -- what happens beyond seven days, and could 12 this system be placed in a safe state, because the air 13 for the air ingress event could -- might proceed 14 beyond seven days.
15 In the discussions with the Applicant, the 16 staff reached reasonable assurance finding that the 17 reactor could be placed in a safe state, protect 18 public health and safety.
19 And so now I'm going to turn it over to 20 Andy Bielen in Research, and he is going to go through 21 some of the scoping analysis.
22 MR. BIELEN: Hello? Can you hear me?
23 MR. SCHMIDT: Yeah, we can hear you.
24 MR. BIELEN: Okay. I'm going to make you 25 look at my face, because I did put on a jacket.
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106 1 (Laughter.)
2 MR. BIELEN: Okay. So, yes, I'm Andy 3 Bielen. I'm in the Fuel and Source Term Branch of the 4 Office of Nuclear Regulatory Research. At DANU's 5 request we performed a series of scoping calculations 6 for the PSAR review.
7 So first I want to remind you that as part 8 of our non-LWR RADIS plan we have been over the last 9 several years doing some public demonstrations and 10 workshops of our ability to simulate the relevant 11 phenomena and characteristics of non-LWR systems.
12 Specifically, Volume 3 covers severe accidents and 13 source term analyses.
14 Within that suite of models that we've 15 developed is included the UC Berkeley Mark 1 design 16 which represents TRISO Pebble Fuel Molten Salt Cooled 17 FHR technology. Oak Ridge National Laboratory uses 18 scale suite to generate inventory and reactor physics 19 data, among other things, which is then provided to 20 the MELCOR severe accident source term code that 21 Sandia develops so we could model different accident 22 progressions.
23 Next slide, please. So it's nice that we 24 did these workshops for the past few years because 25 when DANU actually had an application in hand, they 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
107 1 asked us if we could provide any support, and we were 2 able to really go in and do some modifications to our 3 existing models to make it look more like Hermes and 4 then run some analyses that I think they found to be 5 useful in informing their engineering judgment.
6 One of the things I want to kind of point 7 out here is, as I mentioned, the original 8 demonstration workshops were very much in the severe 9 accident source term regime. We focused on the UCB 10 Mark 1 design as we understood it. We focused on 11 fission product release from the TRISO and into the 12 buildings and all these other sorts of things.
13 The focus was on beyond-design basis 14 events. We were explicitly doing elemental tracking, 15 radioisotopes and that sort of thing to figure out if 16 something went very, very, very wrong, where would all 17 this stuff end up.
18 In contrast to that, with respect to 19 Hermes, we were asked to do this. We were asked to 20 basically provide an independent verification of some 21 of the specific event evaluations that Kairos had 22 presented to ensure that the temperature stayed within 23 the MHA envelope that they've been describing over the 24 last few hours.
25 We wanted to do this with a very quick 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
108 1 turnaround to support the licensing schedule. We 2 wanted to keep this as quick and transparent as 3 possible. All of our information in the models was 4 informed by the PSAR information that was readily 5 available, or in the absence of specifics, engineering 6 judgment to the best that we could.
7 As I said, and as described in our meeting 8 back in March, we use scale to generate inventory, 9 decay heat, power shapes, and all these sorts of 10 things. Then we analyzed two classes of transients 11 from the Safety Analysis Technical Report.
12 Specifically, the insertion of excess radioactivity 13 scenario, and then a couple flavors of loss of for 14 circulation.
15 Okay. So to kind of walk through the 16 MELCOR modeling approach. So as you know, and you've 17 heard many, many times over the course of these 18 meetings, we are very much in preliminary space here 19 so we don't have a whole lot of detail design 20 information available to us.
21 We have focused our modeling efforts on 22 what we know in the primary system. The intermediate 23 loop and the DHRS are both represented basically by 24 boundary conditions at this point. We just don't have 25 any better information to build models based off of.
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109 1 In fact, some of the flow geometry and 2 structures at the top of the core specifically. I 3 don't think we have enough detailed information to 4 really know how everything is specifically arranged, 5 but we think we know enough to generate models that 6 can come to meaningful conclusions.
7 The pebble bed itself is modeled via porous 8 media approach. We have made the geometry and the 9 nodalization between the scale models and the MELCOR 10 models be consistent in order to simplify the mapping 11 process.
12 The reflector itself, I'll say that I think 13 it was judged that we just didn't have enough 14 information about what the flow splits looked like, 15 what was bypass, what was active core, so we just 16 neglected to model bypass at this stage. I think that 17 would be something that we would definitely revisit 18 when more detail was available.
19 Is there anything else I wanted to make 20 sure to mention at this point? I think that's pretty 21 much it. Again, the reflector, I think, that's 22 another thing where we don't have a whole lot of 23 specifics on what this thing looks like yet. It was 24 modeled approximately within the uncertainties that we 25 -- within the information we had available, but we 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
110 1 would certainly like to sharpen out pencils as far as 2 that goes.
3 One more point. Since the fluidic diodes 4 were relied upon to provide a natural circulation of 5 flow path under accident scenarios, we do explicitly 6 model those. You can kind of see that flow path there 7 at the top of the model underneath the primary salt 8 pump. The model is basically very simple. Kind of 9 check valve almost with a very high loss coefficient 10 in one direction and a very low one in the other 11 direction.
12 Okay. Specifically talking to the DHRS, so 13 the whole goal here is to basically be able to model 14 effectively the heat transfer from the core out to the 15 ultimate eat removal system in as much detail as we 16 need to. We start in the core and we work out way 17 through all the layers, through the pebble bed to the 18 reflector, through the reflector out through the 19 downcomer to the core vessel.
20 Then from the reactor vessel we allow 21 radiation and convection within that compartment to 22 transfer eat into these DHRS thimbles basically.
23 Then the DHRS model, you know, basically we have a 24 boundary condition that looks like 100 degree C model, 25 infinitely replenishable 100 degree C boiling water.
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111 1
2 Right? So when we want to model degraded 3 conditions within the DHRS itself, we can do that by 4 basically turning on and off heat transfer surfaces 5 based on the number of trains that we want to 6 evaluate.
7 Yeah, there are certain parameters within 8 this analysis, like when you're talking about 9 radiation heat transfer you have to worry about 10 emissivity and that's something that we have available 11 to us to do sensitivity analysis or calculations with.
12 Convective heat transfers is something else that we 13 have looked into. Then the specifics of the thermal 14 resistance within the DHRS itself.
15 Then just to kind of point out that we 16 basically took the Hermes system and plopped it into 17 the UCD1 building, right? We know that's not what the 18 real thing is going to look like. There's a lot of 19 kind of uncertainty or approximations made within the 20 specific dueling geometry itself, which is another 21 reason why we didn't go forth and do like specific 22 source term calculations because, you know, we know 23 the real thing is going to be different.
24 Okay. Next slide. Okay. So before I get 25 into describing the specifics of these simulations, I 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
112 1 wanted to point out first that these are simulating 2 basically three days of simulation time. Those 3 required about 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> of execution time to produce 4 these curves.
5 The MHA -- the temperature curves that are 6 provided by the MHA analysis are the solid lines on 7 this graph. You'll see the green solid line is what 8 the fuel temperature is allowed to get to. The red 9 solid line is what the stainless steel structures are 10 allowed to get to. The purple solid line is what the 11 reflector or the graphite structures are allowed to 12 experience.
13 Then the blue solid line is the flag 14 freezing temperature. The whole idea of this approach 15 is as long as your deterministic evaluation lies 16 within this envelope, then you can say that you have 17 met your dose requirements. And so our MELCOR models 18 have a couple different flavors of hot pebble, if you 19 will.
20 When you generate a peak fuel temperature 21 plot, you have to find some way to make like -- to 22 represent what the hottest part of the core is 23 including all the uncertainties that you want to put 24 on that hottest part of the core so you have 25 operational flexibility. We have basically 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
113 1 flavors of hot pebbles in our model.
2 The first one, the very fine dashes here, 3 you can see those are basically -- as far as the 4 MELCOR model is concerned, those are a pebble with 5 TRISO particles that have been bumped up to the very 6 top edge of the allowable power envelope from the AGR 7 sequence of tests.
8 Then we have another -- we noticed when we 9 ran the initial set of calculations that, hey, we 10 don't match initial peak temperature very well with 11 the applicant so we have another version of a hot 12 pebble where we just like turned the power up on that 13 pebble until we got something that was reasonably 14 comparable.
15 I think, you know, in retrospect maybe we 16 should have looked at some of the sensitivity co-17 efficients on the different heat transfer models that 18 we have available to us in MELCOR and done some 19 adjustments on that as well as power uncertainties.
20 You know, suffice it to say that we have some 21 treatment of this hot pebble in the MELCOR models.
22 Before I get into the specific results, 23 does that seem -- you know, are there any questions at 24 this point?
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114 1 just to make sure I'm understanding what you're 2 saying. There's like a green dash line with very 3 small dots and it only gets to about 1120C.
4 MR. BIELEN: Right.
5 MEMBER REMPE: And then you've got 6 something where you just arbitrarily jacked up the 7 power to 1380 or something like that? Is that what 8 you're telling me? And it's still below the 1400 9 something or other limit?
10 MR. BIELEN: Yes. I don't know if I would 11 use the word arbitrarily necessarily but, yes.
12 Essentially what we've done is we -- so we're not 13 doing any direct manipulation of the heat transfer 14 models themselves. Right? So the knob we're turning 15 is particle power.
16 The fine dashes are the -- or the dots 17 basically are what happens if we have a hot pebble 18 that bumps up the power with nominal heat transfer 19 coefficients, although this pebble has been placed in 20 the hottest location of the core.
21 Let me be clear about that. But what 22 happens when we bump the particle power of that pebble 23 up to the AGR limit? I don't remember specifically.
24 It's like 255 milliwatts per pebble or -- I can't 25 remember the specific number.
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115 1 MEMBER REMPE: So you kind of picked a peak 2 value that was in a representative range of values?
3 MR. BIELEN: Right. From the AGR test 4 basically. So we know that we have an envelope that 5 lives there and we can go and push a single pebble up 6 there. This is what the temperature looked like.
7 Now, clearly when you look at the applicant's 8 analysis, they have done some other manipulations that 9 I think are, you know, under the proprietary wall that 10 are getting their peak temperatures even higher than 11 that.
12 In lieu of going in and manipulating our 13 heat transfer mechanisms, what we've done is basically 14 just, yes, we have tuned the power of the peak pebble 15 to try to get a temperature that looks like what the 16 applicant has produced.
17 MEMBER REMPE: Okay. And I'm guessing you 18 don't have enough information yet to really see what 19 parameters are really important. For the future when 20 the real design comes in and you try and model it more 21 with the actual design details, do you know yet, you 22 know, this parameter is going to be really important 23 rather than the peak power of the pebble?
24 MR. BIELEN: Right, yeah. And I think, you 25 know, that is a good question. I think with robust --
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116 1 a little bit more robust kind of long-term planning of 2 the analysis we would provide to support DANU in this 3 particular case, we would be prepared to perform some 4 sensitivities up front and say, okay, well -- and look 5 at hot channel methodologies that are out there.
6 Ideally we would have access -- our model 7 developers would have access to the hot channel 8 methodology that Kairos is using and being able to 9 specifically adjust the different aspects of this heat 10 transfer that they are adjusting and see if we get 11 kind of simpatico affects on how your figures of merit 12 change as you change your model parameters.
13 MEMBER REMPE: Thank you.
14 MR. BIELEN: Sure. Okay.
15 Yes.
16 MEMBER KIRCHNER: This is Walt Kirchner.
17 Just one quick question. Did you assume one of the 18 DHSR trains down for this particular plot?
19 MR. BIELEN: I think the base case was one 20 DHSR train unavailable of the four.
21 K.C., you can step in if that's wrong.
22 MR. WAGNER: I think that's what the 23 applicant used, too.
24 APPLICANT: Yes, that's correct. We used 25 three.
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117 1 MR. BIELEN: Okay. Right. The analysis 2 that I'm going to present to you here is just very 3 base case as close to the technical report as we could 4 generate. There are a lot of additional work that we 5 did behind the scenes to kind of get a feel for the 6 importance of various systems' availabilities and 7 other parameters, but we can't really discuss that 8 here unfortunately.
9 So, okay. In terms of the reactivity 10 insertion event, as Kairos kind of discussed in their 11 part of the presentation here, you're reporting a lot 12 of reactivity and relatively quickly. Three dollars, 13 you know, in LWR space is like impossible and, you 14 know, not a thing that can even physically happen.
15 Three dollars in 100 seconds is a lot.
16 But basically 10 seconds into the 17 withdrawal, you end up tripping out on high power. As 18 an additional conservatism here they have a primary 19 salt pump trip and a flow coast down. You see here we 20 do get a fuel temperature increase initially due to 21 that power increase, which is pretty quickly stamped 22 out by the trip.
23 You can see the latent effects of that heat 24 leaving the fuel and getting into other parts of the 25 system as the transient progresses. Then you just 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
118 1 sort of sit there for a long time until the scenario 2 is terminated.
3 Again, we think that our results -- you 4 know, given all the uncertainty we have in the 5 specifics of the sand models versus the MO core 6 models, we think our agreement is, you know, pretty 7 reasonable. We feel fairly comfortable that what 8 Kairos has presented is reasonable.
9 I think I forgot to mention this, but the 10 reference results we're using are that little box on 11 the upper right. The PSAR results are the little box 12 on the upper right. The MELCOR calculations are the 13 big box.
14 Okay. Next slide. As Kairos has eluded 15 to, they have two flavors of loss of for circulation; 16 one for overheating trying to maximize temperatures, 17 and then one for over-cooling to try to see if they 18 can freeze the flood.
19 We looked at both those scenarios I'm going 20 to present here on this slide what the MELCOR results 21 were for the overheating scenario. You have a primary 22 salt pump trip that is actually a seizure so you have 23 a very rapid decrease in flow rate. You end up with 24 a trip over temperature. The temperature is coming up 25 during the transient.
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119 1 Then again, as soon as the reactor trips, 2 you have some kind of latent heat that leads the fuel.
3 Over the course of time it's transferred out through 4 all the heat transfer pathways in the system to the 5 DHRS.
6 Eventually your heat removal exceeds your 7 heat generation and then you start coming down in 8 temperature after about a day or so, or a little after 9 a day. Again, a case where you're clearly within DMHA 10 envelope. As the DMHA envelope is appropriately 11 defined, these transient scenarios would be pretty, 12 you know, within the acceptance criteria.
13 MR. SCHULTZ: Andrew, this is Steve 14 Schultz. The relative comparison between the results 15 that you've obtained and those that Kairos has 16 developed is encouraging thinking about moving forward 17 to the operating license analyses. Didn't you feel 18 that?
19 MR. BIELEN: Oh, yes. I mean, you know, we 20 were working on this project in close collaboration 21 with DANU. They are under a lot of time pressure to 22 get these reviews done quickly and efficiently.
23 I think Jeff can speak to this himself but, 24 you know, my impression throughout the whole course of 25 the project has been, hey, you know, by virtue of you 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
120 1 guys doing these things and us seeing some very 2 promising kind of agreement between different 3 completely independent methods doing the same sorts of 4 simulations.
5 It's a lot easier to say, okay, I have some 6 comfort here. We know that we're going to need to do 7 some more work when the OL comes in, but at least we 8 have -- it definitely cushioned that ability to get to 9 a reasonable assurance for a construction permit.
10 MR. SCHULTZ: That was impressive to me.
11 I really appreciate you showing us the detail.
12 MR. SCHMIDT: This is Jeff. I just want to 13 say my two piece here. I was amazed the general 14 trends of the curves were so similar. That was --
15 MEMBER MARCH-LEUBA: Also submission of 16 energy.
17 MR. SCHMIDT: Yeah, right, but there are 18 ways to screw that up, as you well know, Jose. I 19 don't know. I --
20 MR. BIELEN: Jose has never messed anything 21 up.
22 MR. SCHMIDT: Yes. I was encouraged by 23 the results; the shape of the curves, the times to 24 trip, the general trends of the curves. The fact 25 that, you know, even when we were pushing particle 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
121 1 powers to the edge of the AGR envelope, we still had 2 a lower temperature than the applicant.
3 That's kind of what I was referring to.
4 It's part of the audit that there were conservatism in 5 the applicant's calculations. This clearly helped 6 highlight some of those.
7 I can get some comfort in the fact that 8 there were conservatism. I generally was very 9 impressed with the likeness of the results based on 10 the information that we had available and the time 11 that researchers in Sandia had to do this.
12 MEMBER MARCH-LEUBA: I've seen the slide 13 you mentioned of the cooling and freezing. Could you 14 give us some thoughts on that?
15 MR. SCHMIDT: You know, the over-cooling 16 analysis in the PSAR is from the loss of poor 17 circulation and with four trains. We didn't put --
18 while we did it for comparison, we don't necessarily 19 think it's the limiting condition.
20 MEMBER MARCH-LEUBA: The important thing is 21 if it leads to a pathway for reuse, which is 22 different. I don't know.
23 MR. SCHMIDT: Right now the working 24 assumption is that freezing will be prevented. I just 25 wanted to point out that, you know, I didn't spend 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
122 1 much time talking about the over-cooling analysis in 2 the PSAR because I don't necessarily think it's the 3 limiting over-cooling event. While it is informative, 4 I think there could be other situations that may be 5 more limiting and that will have to just be flushed 6 out as part of the OL.
7 MEMBER MARCH-LEUBA: The thing is with 8 reactors we have to worry about a number of events.
9 Clear thing that we flag is freezing. You have to use 10 some thought and make sure that doesn't produce any 11 unexpected events.
12 MR. SCHMIDT: Yeah, as we discussed in the 13 decay heat removal, that is clearly on the mind of the 14 staff of like what scenarios after you were to say we 15 are to activate the system that you could get to, say, 16 a freeze within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
17 MEMBER MARCH-LEUBA: Is the bundling 18 condition 100 degrees C?
19 MR. SCHMIDT: Yeah, yeah. Right.
20 MEMBER MARCH-LEUBA: On the vessel?
21 MR. SCHMIDT: Well, on the decay heat 22 removal system, yeah. Right.
23 MEMBER MARCH-LEUBA: And the freezing 24 is --
25 MR. SCHMIDT: 450.
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123 1 MEMBER MARCH-LEUBA: 450?
2 MR. SCHMIDT: 459 C, I think.
3 MEMBER REMPE: When you finally get the OL 4 are you planning to do some sort of confirmatory dose 5 calculations? I mean, right now what I think I'm 6 reading is we're going to use the MHA and that's all 7 we're going to do for a dose calculation. Then we'll 8 do analyses and compare it to metrics. These are 9 being compared to those metrics. They are not dose 10 calculations. Are you going to --
11 MEMBER MARCH-LEUBA: You will do these 12 calculation versus the figure.
13 MEMBER REMPE: Right. Is that all staff is 14 going to do, too? Are you going to do confirmatory on 15 the MHA?
16 MR. SCHMIDT: I don't think it's been 17 decided. We have not laid out a path in detail where 18 we're going to go. This was just to inform our 19 reasonable assurance finding for the construction 20 permit.
21 MEMBER REMPE: Sure.
22 MR. SCHMIDT: And to reinforce what we 23 thought our engineering judgement was. Beyond that, 24 we're not committing to anything at this point other 25 than we have the models and capability to do it.
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124 1 MR. BIELEN: That's exactly right, Jeff.
2 The only thing I'll say about that right now is, first 3 of all, DANU is our customer and we aim to please our 4 customer, but we have the models and capabilities.
5 You know, I think a reasonable person would say, uh, 6 if you can do this thing, why don't you? That's all 7 I'll say about that at this point.
8 MEMBER REMPE: So then I'm going to mention 9 to you then you've got the capabilities in MELCOR to 10 look at oxidation of the pebbles and the reflector 11 graphic. I think you probably also have the ability 12 to predict Co and Co2 forms. Is that true? I'm not 13 sure actually. I shouldn't say I think. I don't know 14 what all models you put in for gas reactors.
15 MR. BIELEN: Yeah, we'll have to defer to 16 K.C. on this.
17 MR. WAGNER: Yes, we have empirical 18 correlation and the ratio of Co versus Co2's function 19 of temperature.
20 MEMBER REMPE: So you could do that type of 21 calculation, too.
22 MR. WAGNER: Yep.
23 MEMBER REMPE: Thank you.
24 MR. SCHMIDT: This is Jeff Schmidt. Do 25 you have more that you want to go through or are you 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
125 1 done?
2 MR. BIELEN: I mean, I'm prepared to 3 respond to any additional questions, but I think 4 that's my last slide.
5 MR. SCHMIDT: Let's go on to the next 6 slide then. I'm going to do this one. Overall staff 7 conclusions. The staff found that postulated event 8 methodologies can be used to predict conservative 9 event temperatures and dose releases. This is really 10 the calculational framework of some of the things I 11 talked about like dust generation, associated 12 activities associated with that dust generation, 13 oxidation and Oxidation correlations.
14 I has, I think, a very reasonable 15 framework. Staff reviewed PSAR Table 13.1-1, 16 Acceptance Criteria, and found these acceptable as 17 described in SE Section 13.2.2 because they account 18 for the physical phenomena and release pathways that 19 are not part of the MHA to ensure that the MHA remains 20 founding.
21 The OL application will provide dose 22 analysis for events honored by the MHA release, along 23 with the comparison to the acceptance criteria for the 24 figures of merit in PSAR Table 13.1-1.
25 Next slide. Because the figures of merit 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
126 1 and associated acceptance criteria ensure that the MHA 2 releases remain amnii, the staff has reasonable 3 assurance that the radiological consequences of the 4 postulated events will also meet regulatory 5 requirements of 10 CFR 100.11, and 10 CFR 50.34(a).
6 Staff concludes information in the Hermes 7 PSAR Chapter 13 is sufficient for the issuance of a 8 construction permit (CP) in accordance with 10 CFR 9 50.35 and 50.40. Further information can be 10 reasonably left to the OL application.
11 MEMBER REMPE: I'm sorry. I guess I 12 misunderstood. The third bullet, they will provide 13 dose analyses for events -- for each category events 14 even though it's down by MHA. I thought they said no, 15 we're just going to do the MHA and --
16 MR. SCHMIDT: Yeah. So my expectation is 17 like specific classes of events the limiting of that 18 will be compared to the MHA.
19 MEMBER REMPE: Will be compared with the 20 metrics. Here it says they will provide dose 21 analysis.
22 MR. SCHMIDT: Dose analysis.
23 MEMBER REMPE: Someone asked that today and 24 I thought they came back and said no, we're just going 25 to do the MHA.
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127 1 MEMBER MARCH-LEUBA: My understanding of 2 the answer was that they wouldn't.
3 MEMBER REMPE: That's what I thought, too, 4 but you are confident what you have here is true.
5 MR. SCHMIDT: As far as I'm aware, yes.
6 MEMBER REMPE: Is that documented enough in 7 the SE that we can be confident? That's why I was 8 pushing for the staff to do the dose analysis if they 9 are not going to.
10 MR. SCHMIDT: It's not our responsibility to 11 do the dose analysis.
12 MEMBER REMPE: Yeah, I know, but --
13 MR. SCHMIDT: I think it basically says in 14 the SE that they -- I would have to go back.
15 MEMBER REMPE: Let's ask the applicant 16 again but Jose came away with the same response.
17 MEMBER MARCH-LEUBA: SE is bounding. You 18 can put an additional condition but --
19 MR. SCHMIDT: The SE does not --
20 MEMBER MARCH-LEUBA: -- the oil --
21 MR. SCHMIDT: That's true. The SR -- the 22 PSAR in this case dictates.
23 MEMBER MARCH-LEUBA: All the staff can do 24 is wait for the applicant to make up their mind and 25 then decide whether --
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128 1 MEMBER REMPE: So we don't necessarily 2 believe this third bullet. I think I heard you say 3 I'm not sure.
4 MR. SCHMIDT: I mean, that's my 5 expectation.
6 MEMBER REMPE: Is that expectation 7 documented in your SE?
8 MR. SCHMIDT: That I would have to go back 9 and see if it's clearly documented.
10 MEMBER REMPE: can we just ask the 11 applicant to clarify because Jose and I kind of came 12 away with a different response.
13 MEMBER MARCH-LEUBA: Let's be realistic.
14 The II process is a work in progress.
15 MR. SCHMIDT: I mean, we can ask our --
16 MEMBER REMPE: Jose, I thought he asked 17 them that and they said something different.
18 MR. SCHMIDT: He did. He did. My bullet 19 is likely different than the response earlier.
20 MEMBER REMPE: Okay. Do we want to clarify 21 it or let it go?
22 MEMBER MARCH-LEUBA: It's clear that the 23 applicant doesn't have to commit now to do anything.
24 MEMBER REMPE: Okay.
25 MEMBER MARCH-LEUBA: Just provide a --
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129 1 MEMBER REMPE: Okay. We're both puzzled at 2 the difference, I guess.
3 MR. SCHMIDT: Okay. I thought so.
4 MEMBER REMPE: I'm sorry, what?
5 MR. SCHMIDT: He was giving me guidance 6 reminding me what's in our SE. We believe it's in our 7 SE.
8 MEMBER REMPE: Good. Okay.
9 MEMBER KIRCHNER: This is Walt. I believe 10 it's in your SE. It's my understanding that your last 11 bullet is correct.
12 MEMBER REMPE: I would like to see what --
13 point me to the place. I've got the SE here and it 14 would help.
15 MR. SCHMIDT: It's listed in the Appendix 16 A.
17 MEMBER REMPE: So it's in Appendix A?
18 That's great. Okay.
19 CHAIR PETTI: Is that it?
20 MR. SCHMIDT: It is.
21 CHAIR PETTI: So, members, any questions?
22 With that, the presentations are done. I think at 23 this point we probably should go to public comments 24 and then we can talk about next steps after that.
25 MEMBER MARCH-LEUBA: The memo is -- 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
130 1 discussion needs to be transcribed.
2 CHAIR PETTI: Right.
3 MEMBER MARCH-LEUBA: The public comments 4 also.
5 CHAIR PETTI: Okay. Any member of the 6 public that has a comment, please unmute yourself, 7 identify who you are, and state your comments.
8 Okay. Not hearing any, I think we are done 9 with presentations. We have to decide whether you 10 would like -- we will go off the record, court 11 reporter.
12 (Whereupon, the above-entitled matter went 13 off the record at 4:20 p.m.)
14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1716 14th STREET, N.W., SUITE 200 (202) 234-4433 WASHINGTON, D.C. 20009-4309 www.nealrgross.com
KP-NRC-2304-004 April 11, 2023 Docket No. 50-7513 US Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Kairos Power LLC Presentation Materials for Kairos Power Briefing to the Advisory Committee on Reactor Safeguards, Kairos Power Subcommittee on Hermes Preliminary Safety Analysis Report Section 12.9 and Chapter 13
References:
Letter, Kairos Power LLC to Document Control Desk, Submittal of the Preliminary Safety Analysis Report for the Kairos Power Fluoride Salt-Cooled, High Temperature Non-Power Reactor (Hermes), Revision 2, February 24, 2023 (ML23055A673)
This letter transmits the presentation slides for the April 18-19, 2023 briefing for the Advisory Committee for Reactor Safeguards (ACRS), Kairos Power Subcommittee. During the April 18 meeting, participants will discuss Hermes Preliminary Safety Analysis Report (PSAR) Section 12.9 and Chapter 13.
During the April 19 meeting, participants will have additional discussion on Hermes PSAR Chapter 13. provides the non-proprietary slides for the April 18, 2023 briefing. Enclosure 2 provides the non-proprietary slides for the April 19, 2023 briefing. Kairos Power authorizes the Nuclear Regulatory Commission to reproduce and distribute the submitted content, as necessary, to support the conduct of their regulatory responsibilities.
If you have any questions or need additional information, please contact Rachel Haigh at haigh@kairospower.com or (704) 412-5920, or Darrell Gardner at gardner@kairospower.com or (704) 769-1226.
Sincerely, Peter Hastings, PE Vice President, Regulatory Affairs and Quality 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-2304-004 Page 2
Enclosures:
- 1) Presentation Slides for the April 18, 2023 ACRS Kairos Power Subcommittee Meeting (Non-Proprietary)
- 2) Presentation Slides for the April 19, 2023 ACRS Kairos Power Subcommittee Meeting (Non-Proprietary) xc (w/enclosure):
William Jessup, Chief, NRR Advanced Reactor Licensing Branch Benjamin Beasley, Project Manager, NRR Advanced Reactor Licensing Branch Edward Helvenston, Project Manager, NRR Advanced Reactor and Licensing Branch Samuel Cuadrado de Jesus, Project Manager, NRR Advanced Reactor Licensing Branch Matthew Hiser, Project Manager, NRR Advanced Reactor Licensing Branch Weidong Wang, Senior Staff Engineer, Advisory Committee for Reactor Safeguards
KP-NRC-2304-004 Enclosure 1 Presentation Slides for the April 18, 2023 ACRS Kairos Power Subcommittee Meeting (Non-Proprietary)
Hermes PSAR 12.9 Quality Assurance J O R D A N H A G A M A N - D I R E C TO R O F R E L I A B I L I T Y E N G I N E E R I N G A N D Q UA L I T Y A S S U R A N C E ACRS KAIROS POWER SUBCOMMITTEE MEETING APRIL 18, 2023 Copyright © 2023 Kairos Power LLC. All Rights Reserved.
1 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
12.9 Quality Assurance
- 10 CFR 50.34 (a)(7) A description of the quality assurance program to be applied to the design, fabrication, construction, and testing of the structures, systems, and components of the facility.
- The Quality Assurance Program Description (QAPD) for the design, construction, and operation of the Hermes reactor is based on ANSI/ANS 15.8-1995 (R2005), Quality Assurance Program Requirements for Research Reactors Endorsed by NRC Regulatory Guide 2.5, Quality Assurance Program Requirements for Research and Test Reactors (RG 2.5)
Copyright © 2023 Kairos Power LLC. All Rights Reserved.
2 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Quality Assurance Program Description
- The Hermes QAPD applies to design-phase, construction-phase, and operations-phase activities affecting the quality and performance of safety-related structures, systems, and components (SSCs).
Technical aspects are considered when determining program applicability including, as appropriate, the SSCs design safety function.
Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Quality Assurance Program Description
- The Hermes QAPD includes discussion of eighteen design, construction, and modifications program elements:
Organization Inspections Quality Assurance Program Test Control Design Control Control of Measuring and Test Equipment Procurement Document Control Handling, Storage, and Shipping Procedures, Instructions, and Drawings Inspection, Test, and Operating Status Document Control Control of Non-Conforming Items and Services Control of Purchased Items and Services Corrective Actions Identification and Control of Items Quality Records Control of Special Processes Assessments Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Hermes PSAR Chapter 13 Accident Analysis DR . M AT T HEW DE N M AN - DI ST INGU ISHED E N G INEER, R E L I ABI LITY ACRS K A I RO S P OW E R S U BCO M M I T TEE M E E TING APRIL 18, 2023 Copyright © 2023 Kairos Power LLC. All Rights Reserved.
1 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Safety Case Summary
- 10 CFR 50.34(a)(4) requires a preliminary safety analysis to assess the risk to public health and safety from operation of the facility, including determination of the margins of safety
- To demonstrate compliance with 10 CFR 100.11 dose reference values, a Maximum Hypothetical Accident (MHA) that bounds the postulated events is analyzed for dose consequences by challenging the performance of functional containment The Hermes MHA approach is consistent with guidance in NUREG-1537 The Hermes MHA is not physical The Hermes MHA includes conservatisms that maximize source term The Hermes MHA includes a postulated release of radionuclides
- To ensure that the postulated events are bounded by the MHA:
The list of postulated events is comprehensive to ensure that any event with the potential for significant radiological consequences has been considered Initiating events and scenarios are grouped, so that a limiting case for each group can be qualitatively described in CPA (quantitative results will be provided with OLA)
Acceptance criteria are provided for the important figures of merit in each postulated event group to ensure that the potential consequences of that event group remain bounded by the MHA as the design progresses Prevention of an event initiator is justified in the PSAR Copyright © 2023 Kairos Power LLC. All Rights Reserved.
2 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Relationship between Dose Limits, the Maximum Hypothetical Accident, and Postulated Events
- The Maximum Hypothetical Accident (MHA) 100.11(a)(1-2) Reference Values is constructed to:
Be conservatively non-physical to overestimate Margin potential off-site dose consequences To EAB/LPZ Dose (relative)
Provide confidence that sufficient safety margin Dose Ref.
exists Values Ensure that reasonable design constraints will result in bounded postulated event doses MHA Dose Hypothetical Conservatism
- At the PSAR stage, only the MHA dose is:
Quantitatively evaluated Needed to ensure that sufficient margin exists to Design Basis 10 CFR 100.11 dose reference values Potential Postulated Event Doses Conservatism Copyright © 2023 Kairos Power LLC. All Rights Reserved.
3 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Maximum Hypothetical Accident: Narrative (1 of 2)
The shutdown and heat removal systems are assumed to perform their safety functions but are not modeled. Instead, hypothetical temperature curves are used to conservatively drive radionuclide movement through the functional containment. Individual release pathways are discussed on the next slide.
Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Maximum Hypothetical Accident: Narrative (2 of 2)
- Radionuclides are postulated to diffuse from TRISO particles The distribution of TRISO particles account for both manufacturing defects and in-service failures Pre-transient diffusion of radionuclides from the fuel kernels are hypothetically and conservatively not modeled to maximize fuel inventory for release
- Radionuclides are postulated to evaporate and degas from the Flibe driven by conservative natural convection boundary conditions. No holdup of gases in Flibe is credited.
- Tritium is conservatively assessed to maximize both its inventory and release The initial inventory of tritium is conservatively assessed The release of tritium is conservatively postulated to:
desorb from in-vessel graphite as a function of temperature instantaneously release from both steel and Flibe
- The Ar-41 inventory that is held up by closed graphite pores is instantaneously released Copyright © 2023 Kairos Power LLC. All Rights Reserved.
5 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
MHA: Methodology (1 of 3)
The Hermes MHA uses the methodology from the approved KP-FHR Mechanistic Source Term Methodology Topical (KP-TR-012-P-A). The following concepts directly leverage the topical report:
- Radionuclide grouping and transport approaches for the TRISO Fuel and Flibe coolant
- Mass transfer correlations for tritium into graphite reflectors and pebbles
- The gas space is not credited for confinement of the radionuclides that release from the Flibe free-surface
- Two-hour holdup assumptions for radionuclides transporting through the reactor building
- Conservative, unfiltered, ground level releases are modeled to maximize offsite doses Copyright © 2023 Kairos Power LLC. All Rights Reserved.
6 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
MHA: Methodology (2 of 3)
The following non-physical conditions provide additional hypothetical challenges to the functional containment (beyond what is described in KP-TR-012-P-A):
- Prescribed hypothetical temperature histories are applied to the transient. This ensures that the MHA will bound the system temperatures from the postulated event groups.
- Pre-transient diffusion of radionuclides from the fuel in the reactor core is neglected.
This ensures that the maximum inventory is available for release at the initiation of the transient.
- A bounding vessel void fraction is assumed to facilitate the release of low volatility species in the vessel via bubble burst.
- Additional conservatism in tritium modeling to address limitations associated with tritium modeling in graphite is described in KP-TR-012-P-A.
Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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MHA: Methodology (3 of 3)
- 1. Identify and account for the sources of material at risk (MAR) and the barriers to release
- 2. Evaluate release fractions for every combination of barrier, radionuclide group, and time interval
- 3. RADTRAD and ARCON evaluate dose consequences at the exclusion area boundary (EAB) and the low population zone (LPZ)
Three sources of MAR and associated release barriers Fuel kernels Legend: Circulating Structural MAR activity Sources Tritium Argon-41 TRISO layers Barriers Flibe Graphite grains Graphite pores for non-Flibe tritium Gas space Copyright © 2023 Kairos Power LLC. All Rights Reserved.
8 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Maximum Hypothetical Accident:
Sources of MAR (1 of 2)
- 1. TRISO Fuel Serpent 2 evaluation provides fuel inventory Pre-transient depletion of radionuclides from the fuel is neglected to maximize inventory available for release
- 2. Circulating Activity Bounding value of circulating activity is assumed in the analysis Expected to be a variable controlled by technical specification Copyright © 2023 Kairos Power LLC. All Rights Reserved.
9 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Maximum Hypothetical Accident:
Sources of MAR (2 of 2)
- 3. Structural (steel, reflector, pebbles)
Tritium The inventory conservatively bounds the operating lifetime at full capacity factor with margin while accounting for differential uptake rates for pebbles and reflector Transfer from Flibe to structures Born in the Flibe but transferred to and sorbed in structures (primarily graphite)
Transport speciation is conservatively assigned as tritium fluoride to maximize tritium sorption Transfer from Flibe to structures determined by mass transfer coefficients from Flibe flow characteristics Sorption within structures Sorbed solely as a function of mass transfer from the Flibe to structures (i.e., no diffusion resistance)
Retained without modeling steady state release mechanisms (i.e., perfect absorber)
Argon-41 Produced via neutron activation of Ar-40 to Ar-41 The inventory available for release consists of Ar-41 contained within the graphites closed porosity Copyright © 2023 Kairos Power LLC. All Rights Reserved.
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Maximum Hypothetical Accident:
Release models for the TRISO Fuel
- Transport through TRISO fuel layers is modeled using Ficks laws of diffusion Fuel Fuel The CORSOR model is used for kernel diffusion IAEA correlations are used for layer diffusion
- Diffusion is driven by the fuels hypothetical temperature curve
- Transient diffusion of fission products:
Is negligible if even a single PyC layer remains intact Total releases are thus dominated by releases from exposed kernels Fuel Particle
< 1 mm diameter Copyright © 2023 Kairos Power LLC. All Rights Reserved.
11 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Maximum Hypothetical Accident:
Release models for the Flibe Coolant
- Flibe provides a secondary functional containment barrier to:
Bounding circulating activity In-transient release of fission products from TRISO
- Two release mechanisms are modeled for Flibe Impurities Bubble burst Evaporation
- Certain radionuclide groups bypass the Flibes functional containment No credit for gas retention High volatility noble metals evaporate near instantaneously Copyright © 2023 Kairos Power LLC. All Rights Reserved.
12 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Maximum Hypothetical Accident:
Release models for the Structural MAR
- Tritium in graphite grains No-holdup of tritium in the Flibe instantly drops the concentration of tritium outside of graphite grains drops to zero Tritium rapidly diffuses out of the graphite grain due to the non-physical concentration gradient
- MAR outside of graphite grains (e.g., steel, pores) are instantly released at the start of the transient Pebbles Reflectors Copyright © 2023 Kairos Power LLC. All Rights Reserved.
13 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Maximum Hypothetical Accident:
Release models for the Gas/Atmospheric Transport
- RADTRAD:
Input: Mobilized material-at-risk activities Source RADTRAD Depletion mechanisms Radioactive decay Conservative and Prescriptive Values ARCON96 Aerosol settling (i.e., Henry correlation)
Environment Leakage rates (two-hour holdup) Reactor Building Reactor Building to Environment
- ARCON96:
Inputs ARCON96 Hourly Meteorological Data Distance from the reactor building to the following areas:
Exclusion area boundary Low population zone Approved values from KP-TR-012 Outputs Time averaged dispersion values Copyright © 2023 Kairos Power LLC. All Rights Reserved.
14 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Maximum Hypothetical Accident:
Dose Consequences Dose results meet 10 CFR 100.11 reference values at the EAB and LPZ with significant margin Whole Body Dose (rem) Thyroid Dose (rem)
Location and Duration 10 CFR 100 MHA Result 10 CFR 100 MHA Result Exclusion Area Boundary (First 2 hrs at 250m) 25 0.227 300 0.235 Low Population Zone 25 0.059 300 0.081 (30 days at 800m)
Copyright © 2023 Kairos Power LLC. All Rights Reserved.
15 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Summary
- The MHA dose consequence results meet the site dose reference values in 10 CFR 100.11(a)(1-2) at the EAB and LPZ with significant margin
- The MHA dose is bounding because it employs non-physical conditions that are beyond the design basis Copyright © 2023 Kairos Power LLC. All Rights Reserved.
16 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
KP-NRC-2304-004 Enclosure 2 Presentation Slides for the April 19, 2023 ACRS Kairos Power Subcommittee Meeting (Non-Proprietary)
Hermes PSAR Chapter 13 Accident Analysis DR. MAT THEW DENMAN - DISTINGUISHED ENGINEER, RELIABILITY DR. TIMOTHY DRZEWIECKI - MANAGER, SAFETY ANALYSIS ACRS KAIROS POWER SUBCOMMIT TEE MEETING APRIL 19, 2023 Copyright © 2023 Kairos Power LLC. All Rights Reserved.
17 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Safety Case Summary
- 10 CFR 50.34(a)(4) requires a preliminary safety analysis to assess the risk to public health and safety from operation of the facility, including determination of the margins of safety
- To demonstrate compliance with 10 CFR 100.11 dose reference values, a Maximum Hypothetical Accident (MHA) that bounds the postulated events is analyzed for dose consequences by challenging the performance of functional containment The Hermes MHA approach is consistent with guidance in NUREG-1537 The Hermes MHA is not physical The Hermes MHA includes conservatisms that maximize source term The Hermes MHA includes a postulated release of radionuclides
- To ensure that the postulated events are bounded by the MHA:
The list of postulated events is comprehensive to ensure that any event with the potential for significant radiological consequences has been considered Initiating events and scenarios are grouped, so that a limiting case for each group can be qualitatively described in CPA (quantitative results will be provided with OLA)
Acceptance criteria are provided for the important figures of merit in each postulated event group to ensure the potential consequences of that event group remain bounded by the MHA as the design progresses Prevention of an event initiator is justified in the PSAR Copyright © 2023 Kairos Power LLC. All Rights Reserved.
18 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Relationship between Dose Limits, the Maximum Hypothetical Accident, and Postulated Events
- The Maximum Hypothetical Accident (MHA) 100.11(a)(1-2) Reference Values is constructed to:
Be conservatively non-physical to overestimate Margin potential off-site dose consequences To EAB/LPZ Dose (relative)
Provide confidence that sufficient Dose Ref.
safety margin exists Values Ensure that reasonable design constraints will result in bounded postulated event doses MHA Dose Hypothetical Conservatism
- In PSAR Chapter 13, the MHA dose is:
Quantitatively evaluated Ensures that sufficient margin exists to 10 CFR Design Basis 100.11 dose reference values Potential Postulated Event Doses Conservatism Copyright © 2023 Kairos Power LLC. All Rights Reserved.
19 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Postulated Event Analysis Methodology
- Postulated events are identified in Chapter 13 of the PSAR Postulated events include any potential upset to plant operations, within the plant design basis, that causes an unplanned transient to occur Justification is provided for those events excluded from the design basis (Prevented Events, PSAR Section 13.1.10)
- Figures of merit provide the means to measure and demonstrate that the resulting dose of a postulated event is bounded by the dose consequences of the MHA
- The preliminary methods and sample calculations of the postulated event groups are provided in KP-TR-018, Rev. 2. The methodology describes:
How to analyze figures of merit for each postulated event group How the acceptance criteria ensure that the off-site dose consequences of postulated events are bounded by the MHA
- The final safety analysis results will be provided with the Operating License Application (including verification and validation of the evaluation models used)
Copyright © 2023 Kairos Power LLC. All Rights Reserved.
20 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Postulated Event Analysis Methodology (cont.)
- The evaluation model development activities for the postulated events follow a process similar to the Evaluation Model Development and Assessment Process (EMDAP) from Reg. Guide 1.203
- Postulated events with similar characteristics and modeling approaches are grouped into categories, consistent with NUREG-1537
- The limiting event for each event category is identified and qualitatively assessed from event initiation until a safe state is reached
- The safe state is defined in the methods for each category of events as a point where the transient figures of merit have stabilized in a safe condition Copyright © 2023 Kairos Power LLC. All Rights Reserved.
21 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Input Parameters for Postulated Event Analysis
- Input parameters considered for postulated event analysis include a range of values to be evaluated for the final design (Table 4-4 of KP-TR-018)
- A range of values are assessed to identify the limiting scenario for each postulated event
- Key model uncertainties and initial conditions are conservatively applied to the methods to ensure figures of merit are conservatively predicted Copyright © 2023 Kairos Power LLC. All Rights Reserved.
22 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Limiting Postulated Events (1 of 3)
- Loss of Forced Circulation Pump seizure disables the primary salt pump Reactor protection system detects high coolant temperature and initiates a reactor trip Grouped events include locked rotor and loss of normal heat sink
- Insertion of Excess Reactivity Control system or operator error causes highest worth control element to withdraw continuously at the maximum control element drive speed Reactor protection system detects the reactivity insertion due to a high neutron flux or high coolant temperature and initiates a reactor trip Grouped events include fuel loading error, reflector shifting, and venting of gas bubbles
- General Challenges to Normal Operation Includes challenges to normal operation not covered by another event category that require automatic or manual shutdown of the reactor Bounded by the limiting loss of forced circulation postulated event Grouped events include spurious trips, operator errors, and equipment failures Copyright © 2023 Kairos Power LLC. All Rights Reserved.
23 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Sample Transient Analysis - Loss of Forced Circulation (Overheating)
KP-TR-018, Figure A4-1 Adapted from KP-TR-018, Figure A4-1
- Loss of forced circulation initiated by pump seizure/locked rotor
- Reactor trip on high plenum temperature reached ~30 seconds into event
- A second peak occurs ~20 hours into event followed by monotonic temperature decrease Copyright © 2023 Kairos Power LLC. All Rights Reserved.
24 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Limiting Postulated Events (2 of 3)
- Mishandling or Malfunction of Pebble Handling and Storage System Break in a fuel transfer line during removal from the core results in a spill of pebbles within the transfer line to the room The reactor protection system detects this condition and initiates a pebble handling and storage system trip Grouped events include transfer line break when pebbles are inserted into empty core, core at power, storage canisters, and mishandling of fuel outside the reactor
- Radioactive Release from a Subsystem or Component Limiting event assumed to be a seismic event that results in a failure of all systems containing radioactive material that are not qualified to maintain structural integrity during a design basis earthquake Design requirement on the amount of MAR for SSCs to be below the amount of MAR derived from the MHA Grouped events include releases from the tritium management system, inert gas system, chemistry control system, and inventory management system Copyright © 2023 Kairos Power LLC. All Rights Reserved.
25 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Limiting Postulated Events (3 of 3)
- Salt Spills A hypothetical double-ended guillotine break occurs in the PHTS hot leg piping Reactor protection system detects the salt spill due to a low coolant level and initiates a reactor trip Grouped events include spurious draining of the PHTS, leaks from other Flibe containing systems, mechanical impact or collision of Flibe bearing SSCs, and HRR tube breaks
- Internal and External Hazard Events Internal and external events include internal fire, internal water flood, seismic event, high wind, toxic release, mechanical impact or collision with SSCs, and external flood as described in Chapter 2 Events in this category are bounded by or considered as initiators in other event categories Copyright © 2023 Kairos Power LLC. All Rights Reserved.
26 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
Summary Postulated events within the design basis are identified and grouped by characteristics and modeling approaches
- Design features which are credited with mitigating the effects of postulated events are described
- Figures of merit are derived for the postulated events to provide surrogate metrics which demonstrate that the resulting doses are bounded by the dose consequences of the MHA analysis
- The acceptance criteria for these figures of merit represent design limits that ensure the MHA is bounding Copyright © 2023 Kairos Power LLC. All Rights Reserved.
27 No Reproduction or Distribution Without Express Written Permission of Kairos Power LLC.
NRC Staff Review for PSAR Section 12.9 and Chapter 13 Briefing for the Advisory Committee on Reactor Safeguards April 18-19, 2023 Office of Nuclear Reactor Regulation
Agenda
- PSAR Section 12.9, Quality Assurance
- PSAR Chapter 13, Accident Analyses
- Maximum Hypothetical Accident (MHA) - PSAR Sections 13.1.1 and 13.2.1
- Postulated Events and Other Sections - PSAR Sections 13.1.2 to 13.1.10 and 13.2.2
- Common Agenda for Each Chapter
- Overview of PSAR Chapter and Principal Design Criteria (PDC)
- Referenced topical reports (if applicable)
- Staff technical evaluation
- Findings and conclusions 2
Common Regulatory Basis
- 10 CFR 50.34(a), Preliminary safety analysis report.
- 10 CFR 50.35, Issuance of construction permits.
- 10 CFR 50.40, Common standards.
- Guidance: NUREG-1537, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Part 2, Standard Review Plan and Acceptance Criteria.
3
NRC Staff Review for PSAR Section 12.9 Quality Assurance Briefing for the Advisory Committee on Reactor Safeguards April 18, 2023 By the Division of Reactor Oversight Office of Nuclear Reactor Regulation
Overview of PSAR Section 12.9, Quality Assurance
- PSAR Section 12.9, Quality Assurance states that the description of Kairos quality assurance (QA) program for the design, construction, and operation of Hermes is based on:
- Regulatory Guide (RG) 2.5, Quality Assurance Program Requirements for Research and Test Reactors, Revision 1, which endorses:
- American National Standards Institute/American Nuclear Society (ANSI/ANS) 15.8-1995, Quality Assurance Program Requirements for Research Reactors.
- Kairos provided its Quality Assurance Program Description (QAPD) as Appendix B to PSAR Chapter 12 (i.e., PSAR Appendix 12B).
5
Additional Regulatory Guidance
- NRC RG 2.5, Quality Assurance Program Requirements for Research and Test Reactors, Revision 1 endorses:
- ANSI/ANS 15.8-1995, Quality Assurance Program Requirements for Research Reactors.
6
Staff Evaluation
- Reviewed QAPD using the guidance in ANSI/ANS 15.8-1995, which is endorsed by NRC RG 2.5, Revision 1.
- Evaluated QAPD Section 1, Introduction, and Section 2, Design, Construction, and Modifications, for the issuance of a construction permit (CP) because those sections apply to Hermes design, fabrication, construction, and testing.
- Staff found Kairos followed ANSI/ANS 15.8-1995 in most sections. The following slides focus on areas where Kairos deviated from the standard.
- Did not evaluate QAPD Section 3, Facility Operations, because it would apply to Hermes operation and is therefore not relevant to the issuance of a CP.
7
Staff Evaluation
- Staff evaluation of QAPD sections not in accordance with ANSI/ANS 15.8-1995:
- Kairos proposed an alternate definition of safety-related to match the definition of safety-related in PSAR Chapter 3
- The staff found this to be acceptable
- PSAR Appendix 12B, Section 2.19 - Experimental Equipment:
- Kairos did not provide description of controls for experimental equipment
- PSAR Section 10.1 states that Hermes will not include special facilities dedicated to the conduct of reactor experiments or experimental programs.
- Based on this, the NRC staff finds it acceptable that the QAPD does not include controls for experimental equipment.
8
Staff Evaluation (continued)
- Staff evaluation of QAPD sections not in accordance with ANSI/ANS 15.8-1995:
- PSAR Appendix 12B, Section 4 - Applicability to Existing Facilities &
Section 5 - Decommissioning:
- ANSI/ANS-15.8-1995, Sections 4 and 5, are not applicable to the Hermes CP application
- Acceptable that the QAPD did not include this recommended information, because Kairos did not indicate that the QAPD will apply to any existing facilities, and because submission of decommissioning plans and associated quality assurance provisions is not required until a licensee applies for license termination after permanent cessation of operations.
9
Recommended Construction Permit Condition
- The staff recommends that the construction permit include the following condition:
- Kairos shall implement the QA program described, pursuant to 10 CFR 50.34(a)(7), in Chapter 12, Appendix B, of Revision 2 of the Hermes PSAR, including revisions to the QA program in accordance with the provisions below:
- Kairos may make changes to its previously accepted QA program description without prior NRC approval, provided the changes do not reduce the commitments in the QA program description as accepted by the NRC.
- Changes to the QA program description that do not reduce the commitments must be submitted to the NRC within 90 days.
- Changes to the QA program description that do reduce the commitments must be submitted to the NRC and receive NRC approval prior to implementation.
10
Conclusion
- NRC staff finds the preliminary design information is consistent with the applicable criteria in NUREG-1537
- The staff concludes information in Hermes PSAR Section 12.9 and Appendix 12B is sufficient for the issuance of a CP in accordance with 10 CFR 50.35 and 50.40
- Further information as may be required to complete the review of Kaiross QA program for the conduct of operations and decommissioning can be reasonably left for the OL application.
11
Questions?
NRC Staff Review for PSAR Section 13 Accident Analysis - Maximum Hypothetical Accident Briefing for the Advisory Committee on Reactor Safeguards April 18, 2023 By the Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation
Overview of PSAR 13 -
Maximum Hypothetical Accident (MHA)
- Preliminary analysis
- Consequences bounding for postulated events
- MHA event description and assumptions in PSAR Section 13.1.1
- MHA consequence analysis in PSAR Section 13.2.1
- PSAR Section 13.2.2 describes the postulated event methodology and assurance that the MHA consequence analysis is bounding for postulated events
- Staffs evaluation will be presented tomorrow 14
Referenced Topical Reports
- KP-TR-011-NP-A, Revision 1, Fuel Qualification Methodology for the Kairos Power Fluoride-Salt Cooled High Temperature Reactor (KP-FHR)
- KP-TR-012-NP-A, Revision 1, Mechanistic Source Term Methodology for the Kairos Power Fluoride SaltCooled HighTemperature Reactor 15
MHA Description and Assumptions
- PSAR Figure 13.2-1 MHA hypothetical temperature vs. time profile to give bounding radionuclide releases
- Not based on a specific scenario
- Fission product release and transport mainly through diffusion driven by temperature
- Final determination that temperature vs. time curve is conservative to postulated events at the OL review
- Assumes safety-related systems function as designed but includes consideration of the single failure criterion
- No incremental fuel particle coating failures from transient 16
MHA Consequence Analysis
- Accident source term methodology
- Model system as sources of radioactive material at risk of release (MAR) and barriers to release
- Apply release fraction to each barrier to eventually result in release to environment
- Consistent with functional containment
- Gravitational settling of Flibe aerosols in reactor building 17
MHA Source Term Modeling
- Radionuclide diffusion releases from fuel, Flibe, and graphite as a function of hypothetical temperature vs. time profile in PSAR Figure 13.2-1
- MHA assumes conservative fuel, Flibe, structural, and cover gas releases
- The complete fuel inventory is available for release into the Flibe
- Bounding failed fuel fractions by cohort are assumed
- Flibe and cover gas radionuclide inventories are set to technical specification values
- Except for fuel transient releases, tritium, and Argon-41, the MHA uses approved mechanistic source term (MST) models from KP-TR-012-P-A
- Fuel releases are modelled using accepted methods
- Staff reviewed the fuel release references and found the models acceptable
- Tritium modeling resulting in higher total releases
- Staff evaluated the modeling assumptions for Ar-41 and found them to be conservative
- Audit of Ar-41 calculation 18
Staff Evaluation - MHA Consequence Analysis
- Preliminary MHA dose analysis methods and assumptions are consistent with the approved MST methodology KP-TR-012-P-A
- Staff will review details of final implementation in OL
- Staff evaluation of the site-characteristic short-term atmospheric dispersion factors is discussed in SE Section 2.3 19
Staff Evaluation - MHA Consequence Analysis
- Staff audit of preliminary consequence analysis and MHA source term information
- Confirmed PSAR description of MHA analysis
- Kairos calculations and reference reports
- Initial radionuclide inventory/MAR sources
- Fuel, Flibe
- Tritium and Ar-41 inventories in graphite
- Releases from graphite
- Modeling of radionuclide transport across barriers/release fractions
- In-person discussion with Kairos staff showing example of how to take information from the MHA to develop the RADTRAD code input to calculate doses 20
Staff Evaluation Findings - MHA
- The MHA serves as a bounding hypothetical analysis for Hermes
- The combination of bounding conditions analyzed are beyond what is assumed for postulated events
- Preliminary dose results for MHA are substantially below the regulatory dose reference values for test reactor siting in 10 CFR 100.11
- Because assumptions of the MHA are bounding, calculated doses will likely not be exceeded by any accident considered credible
- Staff will confirm calculations as part of the OL application review 21
Staff Evaluation - Control Room Habitability
- SE Section 13.2.1 also includes staff evaluation of preliminary information on control room radiological habitability described in PSAR Section 7.4
- Identifies relevant design basis as PDC 19
- Additional description of the control room habitability design and dose analysis corresponding to the final detailed design will be provided in the OL application 22
Conclusion
- NRC staff finds the preliminary design information and analysis are consistent with the applicable criteria in NUREG-1537
- The staff concludes information in Hermes PSAR Chapter 13 on the MHA is sufficient for the issuance of a CP in accordance with 10 CFR 50.35 and 50.40 and further information can be reasonably left for the OL application 23
NRC Staff Review for PSAR Chapter 13 Accident Analysis - Postulated Events and Other Sections Briefing for the Advisory Committee on Reactor Safeguards April 19, 2023 Office of Nuclear Reactor Regulation and Office of Nuclear Regulatory Research
Overview of PSAR Chapter 13, Accident Analysis
- Kairos uses a Maximum Hypothetical Accident (MHA) approach to bound other postulated events
- Postulated events are bounded by the MHA radionuclide release
- Approach uses figure of merit and acceptance criteria in PSAR Table 13.1-1 to ensure MHA remain bounding if different radionuclide release pathways exist
- Postulated events considered are consistent with those listed in NUREG-1537
- Some technology-specific events or event sequences are precluded by design, such as Flibe interaction with concrete or water (e.g., decay heat removal system (DHRS) water leak)
- Some technology-specific events (e.g., increased pebble bed packing fraction) have been evaluated 25
Postulated Event Methodology - Generic Aspects
- Postulated event methodology is described in technical report KP-TR-018, Rev 2
- KPTR018, Table 4-4, Input Parameters for Postulated Events, identifies parameters and their ranges to be considered for all Chapter 13 events
- Examples: initial power level, reactor coolant temperature
- The NRC staff finds that KPTR018 specifies acceptable ranges for parameters to ensure the most limiting scenarios are analyzed
- FSAR analyses will consider a full range of sensitivities based on Table 4-4
- KP-SAM and KP-BISON have the capability to model postulated events and the corresponding fuel releases
- Code verification and validation will be reviewed prior to, or as part of, the OL application 26
PSAR Section 13.1.2, Insertion of Excess Reactivity Event
- PSAR analysis assumes continuous withdrawal of highest worth control element at the maximum speed
- Reactor trips on high power or high outlet temperature
- A range of reactivity insertion rates and initial core powers will be evaluated in the OL application
- Uncertainties will be quantified as part of the OL application
- Control element ejection is precluded due to the low differential pressure
- Temperatures stay below the assumed MHA hypothetical temperature vs. time curve except for the maximum reflector temperature, which slightly exceeds the MHA free surface and graphite temperature limits for a short period of time
- Staffs scoping analysis yielded similar results as will be shown in following slides
- The staff has reasonable assurance the MHA dose bounds that of the insertion of excess reactivity event because of conservatisms in the MHA analysis 27
PSAR Section 13.1.3, Salt Spill Event
- Salt spill is a loss of coolant inventory resulting in different release pathways than the MHA
- Assumes safety-related systems work as intended
- Assumes water or concentrate interactions are precluded by design
- Methodology includes evaluating a range of break sizes and locations
- Release pathways different from the MHA include radionuclides mobilized by the break, evaporation from the spilled pool, and oxidation of any exposed graphite
- Heat up due to the loss inventory is expected to be low and bounded by the assumed MHA temperature vs. time curve 28
PSAR Section 13.1.3, Salt Spill Event (continued)
- Methodologies for break aerosol generation and Flibe vessel free-surface evaporation methodologies are from the approved mechanistic source term (MST) topical report
- Salt spill uses lower, event-specific temperatures, hence lower fuel, wetted graphite surface tritium, and lower Flibe vessel free-surface releases
- Staff has reasonable assurance that MHA would bound the salt spill event based on the minimum heat up and low salt mass spilled
- A quantitative dose comparison between the salt spill event and MHA will be performed in the OL application 29
PSAR Section 13.1.4, Loss of Forced Circulation
- PSAR analysis assumes a primary salt pump seizure
- Reactor trips on high outlet temperature
- Uncertainties will be quantified as part of the OL application
- Temperatures stay below the assumed MHA hypothetical temperature vs. time curve except for the maximum reflector temperature and upper plenum temperature, which slightly exceed the MHA free surface and graphite temperature limits for a short period of time
- Staffs scoping analysis yielded similar results, as will be shown in following slides
- The staff has reasonable assurance the MHA dose bounds that of the loss of forced circulation 30
PSAR Section 13.1.5, Pebble Handling and Storage System (PHSS) Event
- PHSS event is a break in a pebble handing line resulting in different release pathways than the MHA
- Reactor protection system trips the PHSS to stop pebble movement
- Pebbles spill into the transfer line room and no active heat removal (i.e., room HVAC) is credited to limit spilled pebbles temperature
- Criticality is precluded by design and pebbles are assumed to remain intact
- Release pathways different from the MHA include radionuclides mobilized graphite dust from the break and pebble oxidation
- Spilled pebbles are assumed at their maximum burnup and hence pebble matrix material at risk is conservative for oxidation and dust activity determinations 31
PSAR Section 13.1.5, Pebble Handling and Storage System (PHSS) Event (continued)
- Staff reviewed methodologies for pebble matrix oxidation and dust generation rate and transport and found them acceptable
- Fuel Qualification (FQ) topical report (KP-TR-011) states pebble matrix oxidation tests will be performed to validate the PSAR assumed oxidation correlation
- FQ topical report states pebble wear against SS-316 will be tested to inform the PHSS dust generation rate
- MST topical report Section 7.3.3.2.2. evaluates the dust resuspension methodology
- PHSS event uses lower temperatures (event specific) temperatures hence lower fuel, wetted graphite surface tritium and lower Flibe vessel free-surface releases
- A quantitative dose comparison is between the PHSS event and MHA will be performed in the OL application 32
PSAR Section 13.1.6, Radioactive Release from a Subsystem or Component
- Radioactive material at risk of release (MAR) is limited such that the release, assuming no retention, is bounded by the MHA
- This includes all locations not qualified to maintain structural integrity during a postulated event (e.g., seismic event).
- Potential area with MAR limits include the tritium management system, inert gas system, chemistry control system (including filters), and inventory management system 33
PSAR Section 13.1.8, General Challenges to Normal Operation
- PSAR Section 13.1.8 addresses events caused by inadvertent operator action, failure of a control system or instrumentation
- The reactor protection system (RPS) will sense and terminate the event assuming the setpoints are reached
- Events caused by operator action, control system or instrument failures are typically bounded by the events analyzed in Chapter 13 due to the use of bounding assumptions and analysis
- Consequences caused by inadvertent operator action, control system or instrumentation failure will be reviewed in more detail as part of the OL application 34
PSAR Section 13.1.9, Internal or External Hazard Events
- Limiting internal events are primarily addressed by Chapter 13
- Fire protection systems and programs are addressed in PSAR Section 9.4 and will protect safety-related SSCs that perform event mitigation
- Most external events are addressed by designing SSCs commensurate with the hazard or applicable standard
- A seismic-induced reactivity event is unique to pebble bed reactors
- Potential increase in pebble packing fraction and associated reactivity increase expected to be bounded by the Chapter 13 insertion of excess reactivity event
- Reactivity insertion due to pebble bed slumping (i.e., elevation change of the active core) is not expected in a buoyant molten salt pebble bed
- Staff to review detailed seismic induced packing fraction reactivity analysis as part of the OL application review 35
PSAR Section 13.1.10, Prevented Events
- Prevented events are potential events which are prevented due to design features and hence are not evaluated
- Of the PSAR prevented events listed, the staff issued requests for additional information (RAI) on two of the prevented events
- RAI 348 (ML22227A180) asked the basis for why recriticality and unprotected events are excluded from consideration
- Kairos modified PSAR Section 4.2.2.3 to further describe the shutdown element insertion testing to ensure the shutdown margin analysis remains valid and, in part, to lower the probably of an unprotected event
- RAI 350 (ML22227A192) asked, in part, how component integrity is ensured for the duration of an air ingress event including air ingress beyond the heat rejection blower trip
- SE Section 5.1.3.2.6 addresses material qualification testing out to 7 days
- Beyond 7 days compensatory measures could reasonably to be established to ensure the final reactor state protects public health and safety 36
Staff Scoping Analysis of Hermes
- NRC developed several representative non-LWR systems models since 2020
- Part of Non-LWR Vision and Strategy, Volume 3 covering severe accidents/source term
- Included UC Berkeley Mark 1 design, representing TRISO pebble fueled/molten salt cooled FHR
- SCALE code suite used for inventory and reactor physics data generation (ORNL)
- MELCOR used for accident progression using SCALE-produced data (Sandia) 37
MELCOR Analysis Approach
- Original SCALE/MELCOR FHR work used the UCB Mark I design and focused on fission product release from TRISO and molten salt during beyond design basis events
- The UCB Mark I model was modified (January-March 2022) for the Kairos Hermes design and applied to select Chapter 13 postulated events
- Modifications based on PSAR information and engineering judgement
- SCALE-generated inventory and decay heat input
- Transients from technical report KP-TR-018: insertion of excess reactivity, loss of forced circulation 38
MELCOR Model Description
- Model focuses on primary system
- Intermediate loop and DHRS represented via boundary conditions
- Necessary given lack of detailed design info
- Detailed representation of flow paths within pebble bed
- Fluidic diodes represented as flow path with different forward and reverse loss coefficients 39
MELCOR DHRS Model Description
- Heat transfer between the reactor vessel (RV),
DHRS, and cavity wall
- Multi-surface radiation enclosure model
- Natural convection heat transfer from all surfaces
- Surface emissivities (variable - uncertainty parameter)
- Convective heat transfer coefficients (variable - uncertainty parameter)
- DHRS model
- 0, 6, 12, 18, or 24 DHRS thimbles DHRS
- Water (constant boundary condition at 100°C)
- Water to DHRS evaporator tube wall uses boiling heat transfer coefficient RV
- Thermal resistance between evaporator tube to thimble casing (variable - uncertainty parameter)
- Cavity wall
- Fire brick, steel liner, concrete wall
- No liner cooling 40 PSAR Schematic
MELCOR Results: Insertion of Excess Reactivity
- Withdrawal of control element inserts 3.02$* over 100 seconds
- Reactor trips on high power (120%)
at ~9 s, concurrent with PSP trip and flow coastdown
- Temperatures maintained within MHA envelope
- "$" is a unit of reactivity used in nuclear reactor analysis. MELCOR results as compared with PSAR 41 (upper right)
MELCOR Results: Loss of Forced Circulation
- Concurrent trip of primary and intermediate coolant pumps results in flow coastdown
- Two cases presented:
- Overheating
- Overcooling (Flibe freezing)
- Reactor trips on overtemperature
- System remains within MHA envelope MELCOR results for overheating case as 42 compared with PSAR (upper right)
Overall Staff Conclusions
- The staff found the postulated event methodologies can be used to predict conservative event temperatures and dose releases
- The staff reviewed PSAR Table 13.1-1, Acceptance Criteria for Figures of Merit and found these acceptable as described SE Section 13.2.2 because they account for physical phenomena and additional release pathways that are not part of the MHA to ensure the MHA remains bounding
- OL application will provide dose analyses for events bounded by the MHA release, along with a comparison to the acceptance criteria for the figures of merit in PSAR Table 13.1-1 43
Overall Staff Conclusions
- Because the figures of merit and associated acceptance criteria ensure that the MHA releases remain bounding, the staff has reasonable assurance that the radiological consequences of the postulated events will also meet regulatory requirements of 10 CFR 100.11 and 10 CFR 50.34(a)
- The staff concludes information in the Hermes PSAR Chapter 13 is sufficient for the issuance of a CP in accordance with 10 CFR 50.35 and 50.40 and further information can be reasonably left for the OL application 44