ML18247A093
| ML18247A093 | |
| Person / Time | |
|---|---|
| Issue date: | 08/24/2018 |
| From: | Michael Snodderly Advisory Committee on Reactor Safeguards |
| To: | |
| Snodderly M | |
| References | |
| NRC-3862 | |
| Download: ML18247A093 (88) | |
Text
Official Transcript of Proceedings NUCLEAR REGULATORY COMMISSION
Title:
ACRS NuScale Subcommittee - Open Session Docket Number:
N/A Location:
Rockville, Maryland Date:
August 24, 2018 Work Order No.:
NRC-3862 Pages 1-88 NEAL R. GROSS AND CO., INC.
Court Reporters and Transcribers 1323 Rhode Island Avenue, N.W.
Washington, D.C. 20005 (202) 234-4433
NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
(202) 234-4433 WASHINGTON, D.C. 20005-3701 www.nealrgross.com 1
1 2
3 DISCLAIMER 4
5 6
UNITED STATES NUCLEAR REGULATORY COMMISSIONS 7
ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 8
9 10 The contents of this transcript of the 11 proceeding of the United States Nuclear Regulatory 12 Commission Advisory Committee on Reactor Safeguards, 13 as reported herein, is a record of the discussions 14 recorded at the meeting.
15 16 This transcript has not been reviewed, 17 corrected, and edited, and it may contain 18 inaccuracies.
19 20 21 22 23
1 UNITED STATES OF AMERICA 1
NUCLEAR REGULATORY COMMISSION 2
+ + + + +
3 ADVISORY COMMITTEE ON REACTOR SAFEGUARDS 4
(ACRS) 5
+ + + + +
6 NUSCALE SUBCOMMITTEE 7
+ + + + +
8 OPEN SESSION 9
+ + + + +
10 FRIDAY 11 AUGUST 24, 2018 12
+ + + + +
13 ROCKVILLE, MARYLAND 14
+ + + + +
15 The Subcommittee met at the Nuclear 16 Regulatory Commission, Two White Flint North, Room 17 T2B1, 11545 Rockville Pike, at 8:30 a.m., Walter 18 Kirchner, Chairman, presiding.
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2 COMMITTEE MEMBERS:
1 WALTER L. KIRCHNER, Chairman 2
RONALD G. BALLINGER, Member 3
DENNIS C. BLEY, Member 4
CHARLES H. BROWN, JR. Member 5
MICHAEL L. CORRADINI, Member 6
JOSE MARCH-LEUBA, Member 7
JOY L. REMPE, Member 8
GORDON R. SKILLMAN, Member 9
MATTHEW SUNSERI, Member 10 11 DESIGNATED FEDERAL OFFICIAL:
12 MICHAEL SNODDERLY 13 14 15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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3 T-A-B-L-E O-F C-O-N-T-E-N-T-S 1
Opening Remarks 2
Walter Kirchner..............
4 3
Subchannel Analysis Methodology 4
NuScale Presentation...........
7 5
Staff Presentation
............ 16 6
Public Comment
................. 52 7
Closing of Meeting from Public Participation
.. 53 8
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4 P R O C E E D I N G S 1
8:33 a.m.
2 CHAIRMAN KIRCHNER: The meeting will come 3
to order. This is a meeting of the Advisory Committee 4
on Reactors Safeguards, NuScale Subcommittee. I am 5
Walt Kirchner, Chairman for today's Subcommittee 6
meeting.
7 Members in attendance today are Ron 8
Ballinger, Dennis, Bley, Gordon Skillman, Matt 9
Sunseri, Mike Corradini, Joy Rempe, Jose March-Leuba, 10 Charlie Brown. And Mike Snodderly is the Designated 11 Federal Official for this meeting. Thank you, Mike.
12 The Subcommittee will review the staff's 13 evaluation of Revision 1 to NuScale's topical report, 14 TR-0915-17564P, subchannel analysis methodology.
15 Today we have members of the NRC staff and NuScale to 16 brief the Subcommittee.
17 The ACRS was established by statute and is 18 governed by the Federal Advisory Committee Act, FACA.
19 That means that the Committee can only speak through 20 its published letter reports. We hold meetings to 21 gather information to support our deliberations.
22 Interested parties who wish to provide comments can 23 contact our office requesting time after the meeting 24 announcement is published in the Federal Register.
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5 That said, we've set aside ten minutes for 1
comments from members of the public attending or 2
listening to our meetings. Written comments are also 3
welcome.
4 The ACRS section of the US NRC public 5
website provides our charter, bylaws, letter reports, 6
and full transcripts of all full and subcommittee 7
meetings, including slides presented there. The rules 8
for participation in today's meeting were announced in 9
the Federal Register on August 13, 2018.
10 The meeting was announced as an 11 open/closed meeting. We plan to close the meeting 12 after the open portion to discuss proprietary 13 material, and presenters can defer questions that 14 should not be answered in the public session to that 15 time. No written statement or request for making an 16 oral statement to the Subcommittee has been received 17 from the public concerning this meeting.
18 A transcript of the meeting is being kept 19 and will be made available, as stated in the Federal 20 Register notice. Therefore, we request that the 21 participants in this meeting use the microphones 22 located throughout the meeting room when addressing 23 the Subcommittee. Participants should first identify 24 themselves and speak with sufficient clarity and 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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6 volume so that they can be readily heard.
1 We have a bridge line established for the 2
public to listen in to the meeting. To minimize 3
disturbance, the public line will be kept in a listen-4 in only mode. To avoid disturbance, I further request 5
that attendees put their electronic devices like 6
cellphones in the off or noise-free mode.
7 We'll now proceed with the meeting. And 8
shall I turn to NuScale first or the staff?
9 MEMBER SUNSERI: To Paul.
10 CHAIRMAN KIRCHNER: Okay, Paul, would you 11 please begin. Paul Infanger from NuScale.
12 MR. INFANGER: I'm Paul Infanger, I'm 13 Licensing Project Manager for Chapters 4 and 15, which 14 includes the Subchannel Topical Report. I've been 15 with NuScale for about three and a half years. Prior 16 to that, I worked on the Barakah Plant with the 17 Koreans.
18 And then before that, I was with UniStar 19 new plants with Calvert Cliffs COLA. And before that 20 I was licensing manager at a number of operating 21 plants for about 25 years.
22 My background, I went to Ohio State 23 University. I have degrees in physics and a master's 24 in nuclear engineering.
And appreciate the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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7 opportunity today to present technical information in 1
support of the staff. This is the third topical 2
report related to our core methodologies. So we had 3
the nuclear codes and methods and the CHF palpables 4
last month.
5 And so we'll have some presenters here 6
today. Immediately to my left is our lead presenter, 7
is Ken Rooks.
8 MR. ROOKS: My name is Ken Rooks, I've 9
been with NuScale for four and a half years in the 10 Core TH Group within the nuclear fuels organization.
11 Prior to NuScale, I was with AREVA, or former AREVA, 12 now Framatome, for four and a half years in their 13 fuels T/H organization. And prior to that I was 14 graduated from NC State in nuclear engineering.
15 MS. CALLAWAY: My name's Allyson Callaway, 16 I'm the Nuclear Analysis Supervisor. I've been with 17 NuScale doing nuclear analysis for the last eight 18 years.
19 CHAIRMAN KIRCHNER: Do you have other 20 NuScale people now on the line that you want to 21 introduce, or at least confirm they're on?
22 MS. CALLAWAY: Sure. Kenny, Anderson, are 23 you on the line?
24 MR. ANDERSON: Yes.
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8 MS. CALLAWAY: Okay, and Kenny Anderson, 1
who's also in the nuclear analysis field.
2 CHAIRMAN KIRCHNER: And what is Kenny's 3
role in NuScale's operation?
4 MS. CALLWAY: Nuclear analysis and core 5
thermohydraulics.
6 CHAIRMAN KIRCHNER: Thank you.
7 MR. ROOKS: All right, so Ken I will go 8
ahead and get started with the presentation.
9 All right, so today we're going to cover 10 in this session an overview of the topical report, an 11 overview of the safety analysis process, and then a 12 brief introduction to the NuScale SMR. Then we'll 13 discuss the VIPRE subchannel T/H code, and then the 14 additional qualification for NuScale conditions and 15 the overall methodology approach.
16 The purpose of the Subchannel Analysis 17 Topical Report is to obtain NRC approval to evaluate 18 the NuScale core using the VIPRE computer code for 19 steady state and transient analyses. We also 20 illustrate NuScale's use of VIPRE and its compliance 21 with the generic SER conditions. And also approval of 22 the conservative methodology for licensing 23 calculations.
24 So I understand we're --
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9 MEMBER CORRADINI: If I might, whoever's 1
on the line, you might want to mute it on your end.
2 That may reduce the crackling.
3 MR. ROOKS: Okay. To understand the 4
objective of subchannel analysis, I've kind of 5
presented a simplified flow chart of the safety 6
analysis process. The four components that generally 7
make up the safety analysis processes are nuclear 8
analysis, fuel performance, system transient analyses, 9
and subchannel analysis.
10 The safety analysis uses the design for 11 input and it's informed by testing, such as CHF.
12 Today we're going to be mostly focused on subchannel 13 analysis. As you can see, this portion's quite 14 integrated, with a lot of input lines that are feeding 15 into it. Nuclear analysis specifically is the core 16 design, core physics provided inputs, which is a topic 17 report that's nearing acceptance that you guys have 18 seen.
19 Fuel performance already has an approved 20 topic, which is the fuel thermal-mechanical methods.
21 And system transient analyses are specifically the 22 non-LOCA events for which the subchannel analyses are 23 applicable for that provide thermohydraulic boundary 24 conditions.
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10 MEMBER REMPE: Are you, you mentioned that 1
the neutronics analysis report has been reviewed.
2 What about the system transient analysis? Are you 3
planning to submit a report?
4 MR. ROOKS: That's a good question. It's 5
in review currently. By the staff.
6 MEMBER REMPE: Okay.
7 MR. ROOKS: So as mentioned, we'll focus 8
on the subchannel moving forward. The objective of 9
the subchannel analysis is to evaluate margin to 10 acceptance criteria. The specific criteria are 11 SAFDLs, which are specified acceptable fuel design 12 limits.
13 The fuel design limits evaluated using the 14 methods in this topical report are critical heat flux 15 and fuel center line melting, which correspond to the 16 overheating of cladding and fuel pellets in the 17 standard review plan of Chapter 4. Ultimately, the 18 results of the subchannel analysis are used as inputs 19 to the NuScale FSAR for Chapters 4 and 15.
20 So now a quick summary of the pertinent 21 NuScale reactor conditions. As you know, the NuScale 22 reactor is a natural circulation PWR, which implies 23 the system flow changes with thermal power level, flow 24 rates hydraulically driven by the density gradient 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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11 between the core and the steam generator.
1 This illustrates how NuScale is unique by 2
not having pumped driven core flow, but it's also 3
important to note that NuScale's not quite that 4
different from a traditional PWR. Our core is 5
operated to maintain the core average exit as 6
subcooled. These subcooled exit quality conditions 7
occur for normal conditions and all AOOs, for off-8 normal conditions.
9 These fluid conditions are very similar to 10 traditional large PWRs. Our hot channel exit slightly 11 saturating with an equilibrium quality greater than 12 zero, but that's due to our conservative methodology 13 that we're implemented.
14 MEMBER MARCH-LEUBA: Can you repeat that?
15 Go back to the hot channel quality is greater than 16 zero because?
17 MR. ROOKS: Because of our conservative 18 methodology, the way we modeled --
19 MEMBER MARCH-LEUBA: So it really is not, 20 you don't expect it to be greater than zero.
21 MR. ROOKS: That's correct.
22 MEMBER MARCH-LEUBA: But the calculations, 23 because of your uncertainty, conservative assumptions.
24 MR. ROOKS: That's correct. So NuScale is 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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12 using the VIPRE-01 subchannel analysis tool, which was 1
developed by EPRI. And it's maintained by Zachry.
2 It's a finite volume code capable of determining three 3
dimensional core flow and distribution for single and 4
two-phase conditions.
5 It uses the three equation homogenous 6
equilibrium model and has empirical models to 7
incorporate it for simple boiling and void quality 8
relationships.
9 From the picture you can see the 10 flexibility in the discritization (phonetic) the VIPRE 11 can handle, from modeling an entire core, which is 37 12 assemblies, all the way down to a single volume within 13 the subchannel. VIPER-01 has a strong user and 14 licensing base in the traditional PWR fleet.
15 MEMBER CORRADINI: Maybe it's a little bit 16 off topic, but are you aware of the number of 17 utilities that are using VIPRE as their subchannel 18 analysis tool?
19 MR. ROOKS: I'm not sure of the total 20 number, but I do know that Duke and Dominion are two 21 large ones that use it.
22 MEMBER CORRADINI: I knew about Dominion, 23 I didn't know about Duke. Okay, thank you.
24 MR. ROOKS: So as I mentioned, NuScale is 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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13 using the as-approved version of VIPRE, which is the 1
common base used throughout the industry. We've made 2
no changes to the main program, only incorporating 3
NuScale proprietary CHF correlations through a dynamic 4
link library.
5 VIPRE-01 is managed internally through 6
NuScale's Appendix B software QA program. VIPRE has 7
a generic SER that contains a list of several 8
conditional criteria which NuScale has demonstrated 9
compliance.
10 With NuScale using the generically 11 approved version of VIPRE, the robust qualification 12 performed by the original co-developers remains 13 applicable. In addition, NuScale performed additional 14 qualification to justify the applicability to NuScale 15 core conditions.
16 The additional qualification consisted of 17 code-to-code comparisons to a different NRC-approved 18
- code, additional experimental comparisons to 19 experiments not in the original SER test suite, and 20 then as well parametric and generalized sensitivity 21 studies.
22 These three additional techniques provided 23 a strong holistic basis that VIPRE was applicable for 24 NuScale applications.
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14 MEMBER BROWN: And we're going to see 1
those in the closed session?
2 MR. ROOKS: That's correct.
3 MEMBER BROWN: Okay.
4 MR. ROOKS: The analysis methodology we've 5
implemented is premised on the development of a 6
conservative base model using bounding axial power 7
shapes and general radial power distribution. We set 8
the nodalization to accurately capture the hot channel 9
local conditions for evaluating a conservative MCHFR.
10 The uncertainties on inputs are applied in 11 a deterministic manner, meaning the biases are applied 12 in a conservative direction. In addition, we have a 13 detailed analyst-completed checklist that's performed 14 on the analysis level that ensures the method was 15 incorporated correctly and the results are acceptable.
16 So in summary, NuScale had developed a 17 conservative subchannel analysis methodology for 18 evaluating steady state and transient conditions. The 19 topical report provides details about NuScale's use of 20 VIPRE and its compliance with all SER conditions, as 21 well as VIPRE's applicability to the NuScale design 22 and a deterministic methodology for, with supplemented 23 sensitivities.
24 The results using this NuScale subchannel 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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15 analysis methodology are used as inputs to the NuScale 1
final safety analysis report for Chapters 4 and 15.
2 CHAIRMAN KIRCHNER: Since we're in the 3
open session, can you just qualify what family of 4
transients that you used this for versus what you 5
would do the rest of Chapter 15 with?
6 MR. ROOKS: This would apply to heat-up 7
events and cool-down events or control rod reactivity 8
events. It's applicable to most NuScale Chapter 15 9
events, with the exception of LOCA.
10 CHAIRMAN KIRCHNER: Sure, okay, thank you.
11 MEMBER BROWN: So, okay, so if I reverse 12 it, except for LOCA, it's not only just AOOs, but a 13 number of the DBAs would be you'd be using VIPRE as 14 part of your analysis?
15 MR. ROOKS: That's correct.
16 CHAIRMAN KIRCHNER: Okay, at this point 17 then -- yeah, before we do, are there any questions 18 here in the open session? Or I assume people are 19 going to wait for the closed session.
20 MEMBER MARCH-LEUBA: You assume correctly.
21 CHAIRMAN KIRCHNER: Okay, yes, okay, Mike, 22 let's bring up the staff then. Thank you.
23 Okay, now we'll turn to the staff. Bruce.
24 PARTICIPANT: I don't think your mic's on.
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16 CHAIRMAN KIRCHNER: Just pull it closer, 1
please.
2 MR. BAVOL: Good morning, my name is Bruce 3
Bavol, I'm a project manager in the Office of New 4
Reactors. Today's presentation from the NRC is on the 5
subchannel analysis methodology. The NRC technical 6
reviewers that are involved with this morning's 7
presentation, the lead, Syed Haider, who's to my 8
right.
9 Also, we have Matt Thomas, who's on the 10 bridge line. Matt is currently on rotation as a 11 resident inspector at Watts Bar. He's found some time 12 to call in this morning, because Matt was a support in 13 the review of this presentation, or this topical 14 report.
15 And then to my left at the side desk, Tim 16 Drzwiecki, also was a support with this review and is 17 currently Acting Branch Chief and representing 18 Reactors Systems Branch this morning.
19 First, I'd like to point out that your 20 hard copy presentation has the first bullet there, it 21 should be the subchannel analysis Revision 1, not the 22 codes and methods. I changed it on a presentation.
23 February 15, 2017, Revision 1 was submitted for 24 review. In October of 2016, Revision 0 was submitted, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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17 but the change from Rev 0 to Rev 1 was a proprietary 1
update of information in the topical report. And so 2
staff is working with Revision 1.
3 The request for additional information, 4
there the following RAIs are listed there. They're 5
mentioned within the safety evaluation, and the 6
responses from NuScale are also, the ML numbers are 7
also listed.
8 There is, I believe, one confirmatory item 9
that we'll be looking for an update in Revision 2 of 10 the document when we complete this process of going 11 through ACRS.
12 We plan to go to full committee on 13 September 6. And staff plans a final safety 14 evaluation late October. And then the dash A we're 15 scheduled for early 2019.
16 MEMBER MARCH-LEUBA: How is that going to 17 work? Are we going to write a letter on a draft SER?
18 MEMBER CORRADINI: The intention is that 19 we're, they're asking for a letter from us based on 20 the documentation we have now.
21 MR. BAVOL: That's correct. So the 22 updates to that, for confirmatory reasons, will be 23 annotated in the safety evaluation as such. It'll 24 just be --
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18 MEMBER MARCH-LEUBA:
As long as 1
everybody's happy, I'm happy.
2 MEMBER CORRADINI: No, I think so far 3
we've had topical reports that have all the open items 4
closed. There have been confirmatory items.
5 MR. BAVOL: Right.
6 MEMBER CORRADINI: So we're in the same 7
situation here.
8 MR. BAVOL: That's correct. Okay, I'd 9
like to now turn it over to Syed to start the 10 presentation. And just let me know when you want to 11 shift your slides.
12 MR. HAIDER: Thank you, Bruce. Good 13 morning, my name is Syed Haider. I'm the lead 14 technical reviewer at NRO for the NuScale subchannel 15 analysis methodology topical report, Revision 1, that 16 was submitted in February 2017.
17 I
would like to acknowledge the 18 contributions made to the review by Matt Thomas, my 19 colleague, who is also on the line, from the Reactor 20 Systems Branch. And Joe Kelly from the Office of 21 Research.
22 While Matt and I performed the topical 23 reviews and wrote the respective SER sections, Joe 24 performed all necessary VIPRE confirmatory analyses 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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19 that were needed to support the review. Last but not 1
least, thanks to Bruce for handling all of our 2
coordination with NuScale.
3 The staff conducted the review of the 4
NuScale subchannel analysis methodology topical report 5
per General Design Criterion 10 on reactor design from 6
10 CFR Part 50, Appendix A. The related regulatory 7
guidance is stipulated in NuScale design specific 8
standards, Sections 4.4 on thermal and hydraulic 9
design and 10 CFR 53.4.
10 The NuScale subchannel analysis 11 methodology uses the NRC approved VIPRE-01, dash the 12 01, subchannel thermal-hydraulic computer code, 13 Version MOD-02, to conduct the NuScale fuel design 14 subchannel safety analysis. The earlier VIPRE 15 version MOD-01 was approved by the NRC is 1986, which 16 the version MOD-02 that is used in the NuScale 17 methodology was approved in 1993.
18 The NRC approvals of VIPRE-01 MOD-01 and 19 MOD-02 code versions that were developed by EPRI are 20 documented through their respective NRC generic safety 21 evaluation reports. Note through the rest of the open 22 and closed sessions I will be referring to the NuScale 23 subchannel analysis methodology as an acronym, N-S-A-24 M, or NSAM.
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20 This slide also lists the four elements of 1
approval for the NuScale subchannel analysis 2
methodology, or NSAM, that NuScale applied for in the 3
topical report.
4 These four elements required the staff to 5
focus on that VIPRE-01 code's applicability to the 6
NuScale steady state and transient subchannel 7
analyses; how the methodology fulfills the NRC's 8
requirements, as specified in the generic SERs for 9
VIPRE-01 MOD-01 and MOD-02 versions; whether the 10 methodology is independent of any specific CHF 11 correlations; and whether the methodology for 12 treatment of uncertainties in the subchannel's 13 methodology is also appropriate.
14 So the two generic SERs that document the 15 NRC approval of VIPRE-01 versions MOD-01 and MOD-02 16 identify a total of nine conditions that an 17 application of VIPRE code has to meet. These nine 18 conditions that mainly deal with VIPRE modeling 19 assumptions and qualifications provided the technical 20 basis for the staff review of the NSAM topical report.
21 Out of the nine conditions, the first five 22 conditions belong to the 1986 MOD-01 SER. And the 23 later four conditions belong to the MOD-02 SER that 24 got approved in 1993. The review required the staff 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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21 to focus on several respects of the methodology 1
application and the treatment of uncertainties.
2 Even though generic VIPRE-01 3
qualifications for subchannel analyses had been 4
reviewed as a part of the original MOD-01 and MOD-02 5
approvals, the staff closely looked into certain areas 6
to ensure the VIPRE-01 licensing applicability to the 7
NuScale design.
8 These respects include questions about the 9
NSAM applicability range and any VIPRE-01 code 10 limitation applicable to the NuScale fuel design, 11 NuScale operating conditions, ensuring that the 12 current number criterion is met and numerical solution 13 is stable, inlet boundary condition consistency 14 between the system level and RELAP-5 and VIPRE-01 15 codes, verifying that the VIPRE predictions are not 16 made close to two-phase fluent stability, and 17 qualification of the VIPRE model and assumption, 18 especially the two-phase flow models used in NSAM.
19 In our review, the information the 20 analysis staff considered in addition to NSAM topical 21 report included the responses to RAIs 9080, 9086, 22 9099, and 9129, as well as the documents NuScale 23 provided for the auditor.
24 Now I'll summarize the applicability of 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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22 the nine MOD-01, MOD-02 SER conditions to the NSAM and 1
the how applicant met them.
2 Condition 1 requires that the application 3
of VIPRE-01 should be limited to PWR licensing 4
calculations that cover the heat transfer regimes up 5
to the critical heal flux. Any use of VIPRE-01 in 6
boiling water reactor calculations or post-CHF 7
calculations will require a separate analysis.
8 The applicant did not seek the VIPRE 9
approval for both CHF calculations, and rather limited 10 the NuScale VIPRE-01 application up to the point of 11 CHF.
12 MEMBER MARCH-LEUBA: Syed, has VIPRE been 13 approved for BWR after this SER was issued?
14 MR. HAIDER: Yes. I forgot to mention 15 that.
16 MEMBER MARCH-LEUBA: Okay.
17 MR. HAIDER: It's also worth mentioning 18 that Condition 1 is rooted in VIPRE version MOD-01.
19 That was not approved for BWR, while NuScale has 20 rather used the most recent version, MOD-02. That was 21 approved for PWR and BWR. However, the staff closely 22 reviewed the two-phase response of the NuScale boiling 23 transients.
24 In the closed session, I will present 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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23 additional information on the NuScale two-phase 1
operation conditions to show that Condition 1 is met, 2
and there are no staff concerns regarding the 3
NuScale's PWR, like two-phase flow attributes or VIPRE 4
codes limitation to handle the two-phase regimes 5
encountered.
6 MEMBER MARCH-LEUBA: Maybe I'll wait for 7
the closed session, but I don't 100% agree with what 8
you said about NuScale being a pressurized water 9
reactor all of the time. There is --
10 MR. HAIDER: I think let's wait until 11 closed session.
12 MEMBER MARCH-LEUBA: Maybe we should 13 discuss this in the closed session.
14 MR. HAIDER: Sure. Condition 2 mandated 15 the submittal of a separate topical report for the 16 staff review and approval for an unapproved CHF 17 correlation to be used in the VIPRE application. The 18 staff had to ensure that the methodology is applied 19 within the range of applicability of the CHF 20 correlation, including fuel assembly during design 21 pressure coolant mass velocity and quality.
22 NuScale submitted a separate topical 23 report for approval of the use of NuScale specific NSP 24 CHF correlation applicable to its new fuel STP 2 fuel 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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24 that is referenced in the NSAM topic report.
1 The applicant used VIPRE-01 to reduce the 2
experimental CHF data to calculate the local fluid 3
parameters to develop the CHF correlation and the 4
MCHFR for the NuScale fuel. The NSP 2 correlation has 5
been approved by the NRC.
6 The NSAM topical report also provides 7
assurance that only approved CHF correlations will be 8
used with VIPRE-01 MOD-02 for the NPM safety analyses 9
when the NSAM PR is referenced in the NuScale DCA.
10 In this regard, the staff has developed a 11 condition as a part of the present SER that requires 12 that an applicant referencing the NSAM topical report 13 in the safety analysis must also reference an approved 14 CHF correlation. So now it's a condition of the 15 current SER.
16 Based on the submittal of a separate TR 17 for the NuScale CHF correlation, and pursuant to the 18 SER condition use, NRC staff finds that the applicant 19 satisfied the generic VIPRE SER Condition 2. And this 20 discussion of the range of applicability of NSAM vis-21 a-vis the NSP 2 CHF correlation will be covered in the 22 closed session. That is also tied to the question 23 that you had raised.
24 Condition 3 asked for the specifications 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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25 for using specific modeling assumptions, choice of 1
two-phase flow models, heat transfer correlation, 2
input values of plant-specific data such as turbulent 3
mixing coefficient, two-phase slipper issue and loss 4
coefficient.
5 The applicant met Condition 3 by providing 6
sufficient information in the NSAM topical report, RAI 7
responses, and the audit documents about the factors 8
that are summarized in the present, on the present and 9
the next slides.
10 These factors typically belong to various 11 thermal-hydraulic input parameters, sensitivities, 12 uncertainties, penalties, heat transfer coefficients, 13 VIPRE model geometry and nodalization, and boundary 14 conditions. Some of them are described in detail by 15 the applicant in their presentation.
16 So the staff has presented some 17 confirmatory analyses that the staff performed about 18 the key sensitivities in the closed session to 19 demonstrate that the applicant has provided sufficient 20 information to justify the specific VIPRE models and 21 assumptions so that a Condition 2 is met by NuScale.
22 Next slide please.
23 Condition 4 requires that if a profile fit 24 a subcooled boiling model, which was developed based 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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26 on steady state data is used in boiling transient, 1
care should be taken in the time step sizing used for 2
transient analysis to avoid a Courant number less than 3
one. A defect is that NSAM indeed uses the existing 4
VIPRE-01 steady state support boiling correlations, so 5
this condition does apply to NSAM.
6 So a Courant number greater than one is 7
required for the convergence of the numerical solution 8
of the mass momentum and energy equations in a VIPRE 9
simulation of boiling transients while using subcooled 10 void correlation that is based on steady state data.
11 MEMBER MARCH-LEUBA: I guess this can be 12 discussed in the open session. That's a very 13 surprising condition, because most of us are used to 14 a Courant number less than one as the stability 15 condition. So you use Courant number greater than one 16 with an implicit method to offer them the solution and 17 converts to the steady state faster and more reliably.
18 And that I can understand.
19 Now, when you want to apply this 20 methodology to transients, where this overdamping is 21 giving you the wrong transient solution, and I realize 22 you didn't review VIPRE, that that was an old SER that 23 this came from. But this looks a little, something is 24 not kosher here.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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27 But using a highly damp implicit method, 1
you are not reducing the transient. So when you are 2
ejecting a control rod, you're not getting the proper 3
profile or whatever you're tracking in the subchannel.
4 Have you considered that maybe that condition of 5
Courant less than one was before a steady state, not 6
for transients?
7 MR. HAIDER: Okay, the staff kind of 8
expected this question. And I think they have a 9
detailed slide in the closed section. I'm sorry, the 10 staff expected this question, and there is material in 11 the closed session where we will be discussing this 12 particular issue.
13 CHAIRMAN KIRCHNER: Okay, but I think this 14 is a good point that Jose brought. Because I have to 15 admit, the first few times reading through the 16 material, I went like this -- for the record, I 17 scratched my head. And saying wait a minute, this is, 18 you're forcing a solution.
19 MEMBER MARCH-LEUBA: I thought it was a 20 typo.
21 CHAIRMAN KIRCHNER: I thought it was a 22 typo, and I kept revisiting this each time I tripped 23 over it. So we will look forward to your analysis of 24 this condition in the closed section.
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28 MR. HAIDER: Okay, the staff will offer 1
their thoughts.
2 CHAIRMAN KIRCHNER: Okay, thank you.
3 Again, for the record, this is counterintuitive.
4 MR. HAIDER: I think here I would just 5
like to say that the VIPRE uses an implicit scheme.
6 It is inherently--
7 CHAIRMAN KIRCHNER: You're drifting away 8
again.
9 MR. HAIDER: Sorry, the VIPRE uses an 10 implicit numerical scheme, which is inherently 11 instable. So this Courant number criterion emerged 12 out of the special uses of subcooled void correlation 13 under boiling transients. So it should not be looked 14 in the same light that is available in the open 15 literature about Courant number being less than one 16 being a condition for numerical stability.
17 MEMBER MARCH-LEUBA: I propose that we 18 wait.
19 CHAIRMAN KIRCHNER: We can wait, but no, 20 that's a good enough answer now for the record that, 21 why this is being done. And then we can revisit it in 22 the closed session. Okay, thank you.
23 MR. HAIDER: So VIPRE-01 MOD-01 SER 24 describes the quality control requirements. The 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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29 objective of these requirements, this requirement is 1
to ensure consistency in the development and 2
application of the VIPRE-01 code for safety analysis.
3 This essentially means that only an as-4 approved version of VIPRE-01 can be used in an 5
application, and any modification to VIPRE-01 is 6
implemented under Quality Control.
7 The applicant used the as-approved VIPRE-8 01 code, Version MOD-02, and no code modification was 9
made for NSAM applications. Besides, no QA issues or 10 additional Quality Control requirements were reported 11 in the VIPRE-01 MOD-02 SER, beyond what had already 12 been documented in the VIPRE-01 MOD-01 SER, the 13 earlier one.
14 So there were only enhancement made to 15 VIPRE-01 MOD-02 for NSAM application. That was the 16 implementation of the NuScale CHF correlation into 17 VIPRE-01 MOD-02 suite. This was done through a 18 dynamic link library, or the LL file, that allowed 19 using the user program CHF correlation without any 20 modification for the VIPRE-01 source code.
21 The staff has no QA concern about VIPRE-01 22 MOD-02 version use with the NSAM. Therefore, 23 Condition 5 has been met.
24 MEMBER MARCH-LEUBA: And did I understand 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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30 you correctly that the MOD-02 SER issued in 1993 1
approved it for BWR conditions?
2 MR. HAIDER: That's right.
3 MEMBER MARCH-LEUBA: So the Condition 1 4
was kind of moot after that point, the one that said 5
only applies for pressurized water reactors? Couple 6
of the slides before.
7 MR. HAIDER: That is the staff's 8
understanding, but we still studied, closely studied 9
the two-phase attributes and performed confirmatory 10 analysis.
11 MEMBER MARCH-LEUBA:
So MOD-02 is 12 acceptable for both generally subcooled operation and 13 also for relatively high quality conditions?
14 MR. HAIDER: Not the Courant number 15 condition, but the Condition 1. The Courant number 16 condition is Condition 4.
17 MEMBER MARCH-LEUBA: Not Courant, I'm 18 talking now a steady state void quality. If you go 19 back to slide number --
20 MEMBER CORRADINI: I think, if I read the 21 submittal by NuScale, although they're aware that 22 their MOD-02 of VIPRE can do it, they are not asking 23 for approval beyond CHF.
24 MR. HAIDER: That's true, that's true.
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31 That part of Condition 1 is met.
1 MEMBER MARCH-LEUBA: Yeah, but they're 2
asking for approval with 50% voids. Whereas, if you 3
go back to slide 6 please. It says, Condition for 4
more one -- now I can read more one, is that you have 5
to be on PWR conditions. But then you see MOD-02, 6
which is approved for boiling water reactor 7
conditions?
8 MR. HAIDER: Yeah, MOD-02 is also 9
applicable --
10 MEMBER MARCH-LEUBA: So this condition 11 really is not applicable to NuScale, because they used 12 MOD-02. It's not just that it's met, it's not 13 applicable.
14 MEMBER CORRADINI: I think it's, I guess 15 I'm reading it differently. They're basically, and 16 NuScale can correct me if I'm misunderstanding their 17 submittal, but as long they're below CHF, they're 18 going to use VIPRE. Once they get past CHF, they're 19 not relying upon VIPRE for their calculation.
20 I could have a void fraction much higher 21 than 50% and not be past CHF.
22 MEMBER MARCH-LEUBA: That's correct.
23 MEMBER CORRADINI: They're not linked.
24 MR. HAIDER: That's right, yeah, yeah.
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32 MEMBER CORRADINI: It's based on CHF 1
transition that they're not going to use VIPRE beyond.
2 MR. HAIDER: That's true.
3 MEMBER MARCH-LEUBA: Okay.
4 MR. HAIDER: That is true.
5 MEMBER REMPE: So again, stop me if I'm 6
getting into proprietary information, but several 7
times you as well as NuScale have said, We haven't 8
done anything to change VIPRE except for the CHF 9
correlation and how it's implemented.
10 If I read the technical report, it's 11 actually on page 65 of the PDF, but page 54, it talks 12 about that, how they do some comparisons with another 13 code related to thermal conductivity, and they may 14 calibrate VIPRE, if needed. Is that a change to the 15 code, or is that an input?
16 MR. HAIDER: See, the only --
17 MEMBER MARCH-LEUBA: That would be input 18 parameters.
19 MEMBER REMPE: It's an input parameter.
20 That's what I wanted to know, because I --
21 MEMBER MARCH-LEUBA: Well, you need to ask 22 them, but.
23 MEMBER REMPE: It is through input 24 parameters is how you calibrate the code. Because 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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33 that sure sounds like you're --
1 MEMBER CORRADINI: If you're going to 2
answer, go to a mic.
3 MR. GALIMOV: Azat Galimov, NuScale. If, 4
in case of the calibration, we actually tuned the 5
based model, and it's input parameter.
6 MEMBER REMPE: It is an input parameter, 7
thank you.
8 MR. HAIDER: Okay, and so we are done with 9
Condition 5. So with Condition 5, this concludes all 10 five conditions that were a part of 1986 SER for 11 VIPRE-01 MOD-01. Now I will present the four 12 additional conditions that were identified in the 1993 13 VIPRE-01 MOD-02 SER.
14 Condition 6 requires that the licensing 15 models used in VIPRE-01 MOD-02 should be qualified.
16 Besides, as is stipulated by some other conditions in 17 the two generic SERs for VIPRE MOD-01 and MOD-2, 18 NuScale needed to justify its two-phase modeling and 19 assumptions for using VIPRE over the range of expected 20 two-phase flow conditions expected in the design 21 application.
22 So there is also some overlap in the 23 conditions when it comes to qualifying various 24 modeling assumptions. It's like you would hear two-25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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34 phase in Condition 1, you'll also hear about two-phase 1
modeling assumptions in Number 6. So there is some 2
overlap, that should be recognized.
3 NSAM does not use the VIPRE user option to 4
specify a slip ratio as an input to the model.
5 Rather, VIPRE formulation is based on a three equation 6
compressible homogenous equilibrium model that solves 7
3D core flow and distributions through raw 8
temperatures and minimum critical heat flux ratio or 9
10 NSAM uses non-mechanistic empirical two-11 phase correlations to reflect subcooled boiling non-12 equilibrium and concurrent vapor liquid phase slip in 13 two-phase flow.
14 So this continues to the next page. The 15 homogenous equilibrium formulation may not be 16 sufficient to apply for cases with a large relative 17 phase velocities typical of transient boiling. Which 18 may raise convergence problems in transient boiling 19 calculations when using the subcooled boiling models 20 and bulk void correlations to account for the phase 21 slip.
22 The applicant also performed a sensitivity 23 study that is presented in the topical report, using 24 the drift flux model. The drift flux model calculates 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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35 the void fraction by using the physically more 1
realistic conservation of vapor mass generated by wall 2
superheat instead of defining the void simply as a 3
function of flow and quality with an empirical slip 4
formulation.
5 So drift flux model is physically more 6
realistic. The staff audited the applicant's drift 7
flux model sensitivity cases applicable to NuScale 8
conditions and confirmed that the use of drift flux 9
model had a negligible impact on void fractions and 10 CHFRs at any point along the hot channel.
11 MEMBER CORRADINI: Remind me, what did the 12 staff do to audit it? They used trace?
13 MR. HAIDER: The staff reviewed the 14 documents.
15 MEMBER CORRADINI: They didn't do a 16 calculation.
17 MR.
HAIDER:
They didn't do the 18 calculations.
19 MEMBER CORRADINI: Did they ask, I guess, 20 well, I'll ask this one. Did you ask NuScale to do 21 some sensitivities for them to look at the effect? In 22 other words, you can put in a phase, you can put in a 23 slip velocity to verify that it has a small effect.
24 Was the audit based on NuScale calculations that staff 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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36 asked to have additional calculations done?
1 MR. HAIDER: The staff did not ask for 2
additional calculations.
3 MEMBER CORRADINI: Just looking at what 4
was given.
5 MR. HAIDER: Looking at what was given, 6
but for a range of transients, so.
7 The applicant's use the drift flux model 8
to justify its VIPRE-01 two-phase modeling assumptions 9
is appropriate. The staff believes that the Condition 10 6 has been met, but will provide further supporting 11 information in the closed session about the staff's 12 sensitivities studies of the VIPRE two-phase modeling.
13 So Condition 7 from the generic VIPRE-01 14 MOD-02 SER requires the applicant to declare any 15 possible use of the GEXL Correlation with the proposed 16 subchannel analysis methodology. The GEXL Correlation 17 in the only correlation having the NRC approval for 18 using critical power ration CPR calculations for a 19 core containment fuel. This is just one of the 20 conditions.
21 NSAM TR, topical report, states the 22 NuScale does not perform CPR calculations for BWR fuel 23 with VIPRE-01. That essentially means that NuScale 24 will not use the GEXL Correlation with the NSAM VIPRE-25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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37 01 application. In addition, the present SER 1
condition bounds NSAM to use only the CHF correlations 2
that are approved by the NuScale, for NuScale 3
application, and GEXL is not one of them. So clearly 4
Condition 7 is met.
5 VIPRE-01 manual identified limitations for 6
VIPRE code Condition 8 requires that users submit 7
information certifying that the code is not being used 8
in violation of these limitations. The VIPRE 9
conservation equations are based on homogenous 10 equilibrium formulation, which is not sufficient to 11 apply to cases with large relative phase velocities.
12 Their countercurrent flows are conditions under which 13 the flow regimes may change radically.
14 VIPRE should not be applied to situations 15 that in damp conditions such as low flow boil-off and 16 overflow phase separation involving a sharp liquid 17 vapor interface for a countercurrent flow.
18 The applicant has provided sufficient 19 information in the topical report, as well as the 20 audit documents, and has appropriately addressed the 21 staff's concerns expressed in RAI 9080 and its 22 supplement about VIPRE-01 code limitations for a 23 NuScale application.
24 RAI 9080 details, and its resolution will 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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38 also be discussed in the closed session, will 1
demonstrate that an NSAM VIPRE application is not 2
susceptible to code limitations, and Condition 8 has 3
been met.
4 The generic NRC acceptance of VIPRE-01 5
MOD-01 did not endorse procedures and users of the 6
VIPRE-01 code described in the code manual. So the 7
users are advised that the suggested imports and 8
procedures are only for best estimate.
9 So the user is expected to justify the 10 import selection for licensing applications.
11 Condition 9 about import selections, uncertainties, 12 and sensitivity analyses is fairly generic and 13 overlaps with several other conditions. However, I 14 would like to report two confirmatory analyses the 15 staff performed to look into the import selection and 16 sensitivity studies about the VIPRE code.
17 One such aspect was inlet flow boundary 18 condition consistency between the system level code 19 and the RELAP 5, and VIPRE-01 application in NSAM.
20 The other was potential two-phase flow instability in 21 VIPRE predictions.
The staff checked to a
22 confirmatory analysis that I will be presenting.
23 So more details will be provided during 24 the closed session to demonstrate consistency between 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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39 the VIPRE and RELAP outputs. The staff also performed 1
a sensitivity study to establish that VIPRE did not 2
show any potential for two-phase instability, so 3
Condition 9 has been met with supporting information.
4 CHAIRMAN KIRCHNER: Doesn't the conclusion 5
on two-phase flow instability require some caveat 6
about a range of transient or operating conditions and 7
pressures?
8 MR. HAIDER: Yes, it does.
9 CHAIRMAN KIRCHNER: You just can't say 10 point blank doesn't show any potential for two-phase 11 instability.
12 MR. HAIDER: We conducted the confirmatory 13 analysis for the limiting case for the rod --
14 MEMBER MARCH-LEUBA: Can I suggest that we 15 wait for this discussion for today's closed session?
16 CHAIRMAN KIRCHNER: Speak up so that we 17 heard you last statement. Just finish your, repeat 18 your last statement.
19 MR. HAIDER: Okay, the staff performed the 20 confirmatory study for the limiting case of 21 misoperation, which was to take the single rod 22 withdrawal.
23 CHAIRMAN KIRCHNER: Okay, so that was the 24 two-phase flow instability confirmatory calculation 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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40 you did.
1 MR. HAIDER: That's right, that's right.
2 CHAIRMAN KIRCHNER: My only caveat here is 3
that this reads as a much broader validation of the 4
code for two-phase flow applications than is intended 5
in the actual -- we'll hear what the applicant 6
intends. But as I understand it, there are limits as 7
to drawing that conclusion.
8 MR. DRZEWIECKI: This is Tim from the 9
staff. I just wanted to clarify. The staff's SER 10 makes no findings about the stability of the design 11 based on those calculations. Both are just there just 12 for, you know, illustration purposes only.
13 But there was no findings associated with 14 this methodology in terms of stability. That's a 15 separate topical report that's in our review.
16 CHAIRMAN KIRCHNER: Okay.
17 MEMBER MARCH-LEUBA: I just want to put on 18 the record that I want to talk about this in the 19 closed session, because I disagree with most of the 20 conclusions and the analysis itself.
21 CHAIRMAN KIRCHNER: Okay. Please go on.
22 MR. HAIDER: So as I mentioned early, 23 okay, so as I mentioned early in the backdrop of the 24 CHF discussion, the staff had formulated a position 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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41 the part of the present the staff CR that an applicant 1
referencing the NSAM topical report in a safety 2
analysis must also reference an approved CHF 3
correlation.
4 Again, the objective of this SER condition 5
is to ensure that only NRC-approved correlations are 6
used with NSAM.
7 MEMBER MARCH-LEUBA: Is your intent that 8
the CHF correlation be developed with VIPRE? I mean, 9
you collect experimental data. You should analyze it 10 with VIPRE to be able to use it on VIPRE, or can you 11 analyze it with something else? You know what I mean?
12 You would, depending on -- because VIPRE uses an 13 number of approximations through the condition for the 14 channel on the electrically heated bundle test. You 15 should really -- with tool you're planning to use for 16 the analysis in the real reactor. Is that the intent 17 of the condition?
18 MR. HAIDER: As a matter of fact, the 19 applicant did ensure that they used consistent model 20 and consistent code origin, both in the CHF 21 development and NSAM.
22 MEMBER MARCH-LEUBA: Yeah, but was that 23 the likely coincidence? In my opinion, the condition 24 should specify that.
Because VIPRE is an 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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42 approximation. I mean it's not, it's close to our 1
best estimate call, but it's not our best estimate 2
call. It uses slip voids and it uses a number of 3
conservative assumptions.
4 The condition should probably be that the 5
CHF correlation you want to use on VIPRE had to be 6
developed using VIPRE on the experimental data.
7 MR. DRZEWIECKI: This is Tim from the 8
staff, I just want to clarify that. Okay, so as far 9
as the NSP-2 and the NSP-4 CHF correlations, which 10 were developed with VIPRE, staff's SER there does have 11 a condition that those CHF correlations with those 12 limits have to be used using this methodology. Which 13 is, you know, which is VIPRE-01 with certain models 14 frozen and certain parameters frozen. So yes, I agree 15 with you completely.
16 MEMBER MARCH-LEUBA: Yeah, what I'm saying 17 is the language in this condition should include, I 18 know you put the condition on the NSP-4 TR. It should 19 be on this TR for completeness.
20 MEMBER REMPE: I second what's he saying, 21 because if someone else could come in, the applicant 22 could come in with a different correlation in the 23 future. And I think he's right.
24 MR. HAIDER: Yeah, so far the staff has 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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43 not reconciled this condition with the condition in 1
the CFHR SER.
2 MEMBER REMPE: But in the future, NuScale 3
may have a different fuel and come up with a different 4
CHF correlation that was not generated with VIPRE.
5 And so for legal purposes you need to do that, I 6
think. He's right.
7 MEMBER MARCH-LEUBA: Don't be surprised if 8
our letter says that you should put that in your 9
condition.
10 MR. DRZEWIECKI: Okay.
11 MEMBER MARCH-LEUBA: And that's my 12 opinion, not the ACRS opinion.
13 MR. DRZEWEICKI: Okay, just so that we're 14 clear, you would like staff to make this condition a 15 little tighter to make sure that that says that it has 16 to use the CHF correlation that was developed using 17 this precise methodology.
18 MEMBER MARCH-LEUBA: If I was writing, I 19 would say, If the CHF correlation was not developed 20 using VIPRE, its applicability has to be reviewed by 21 the staff.
22 MR. DRZEWIECKI: Okay.
23 CHAIRMAN KIRCHNER: And a caution here, 24 because these are opinions of individual members, not 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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44 the opinion of the Committee writ large.
1 MEMBER REMPE: Yes.
2 CHAIRMAN KIRCHNER: So.
3 MR. HAIDER: The staff would also like to 4
clarify that NSAM TR uses several example values of 5
input parameters and includes the subchannel analysis 6
just to demonstrate the NSAM application to perform 7
subchannel analyses and enhance the understanding of 8
the analytical methods. The staff SER does not 9
approve the use of any specific example where new 10 inputs or reserves presented in the topical report.
11 The staff would approve the specific input 12 values and ensuing reserves for the reactor core 13 design for this subsequent licensing submittal in DCA, 14 referencing the NSAM topical report. And the staff 15 will review these final design and planned specific 16 input values used in the subchannel analyses as a part 17 of the separate licensing submittals.
18 I'll elaborate further on the example 19 values during the closed session.
20 So here are the staff SER conclusions.
21 The NRC staff has reasonable assurance that the use of 22 the VIPRE-01 MOD-02 code with NSAM as described in the 23 topical report is appropriate for the NuScale fuel 24 thermal-hydraulic design and plant safety analyses, 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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45 provided that the present SER condition is met.
1 The staff also found that the sufficient 2
information has been presented for the requested 3
elements of approvals, so the staff concludes that 4
VIPRE-01 applies to the NuScale steady state and 5
transient subchannel analyses. NSAM fulfills the 6
NRC's requirements in the SERs for VIPRE-01 MOD-01 and 7
MOD-02.
8 NSAM is independent of any specific CHF 9
correlation and is used for NuScale applications with 10 an NRC-approved NuScale specific CHF correlation.
11 NSAM describes a methodology for the treatment of 12 uncertainties in the NuScale subchannel analysis that 13 is appropriate.
14 So this concludes the open part of my 15 presentation. And now the staff would like to invite 16 any further questions on the staff review of the 17 NuScale subchannel analysis methodology.
18 MEMBER REMPE: Am I misreading your 19 report? I liked the statements in the prior slide 20 because there are several examples where you say we 21 didn't approve the input value and we didn't approve 22 the methods for calculating the uncertainty associated 23 with it.
24 This last sub-bullet where you say they 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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46 described the methodology for treatment of 1
uncertainties and analysis that's appropriate seems 2
inconsistent with some of the things that I read in 3
your technical or topical report.
4 And we can into the details later, but I 5
guess I'm just wondering what that last sub-bullet 6
meant, because it seems like there's several cases 7
where you bring up areas where you're saying, hey, it 8
doesn't make sense what you've done here, or we 9
couldn't follow the logic, and so we don't approve it.
10 MR. HAIDER: There are several parameters 11 that were used in NSAM to produce the results and 12 conduct the sensitivity analysis. But those 13 parameters are fuel-specific, and they even sometimes 14 there are CHF-correlation-specific.
15 And they may change, and they should 16 ideally be reviewed where they are actually being 17 implemented in the safety analysis, like Chapter 15 18 review or Chapter 4 review. So their review will be 19 performed in the DCA, but their review--
20 MR. THOMAS: Syed?
21 MR. HAIDER: Yes, Matt? You want to?
22 MR. THOMAS: Let me ask a quick question.
23 This is Matt Thomas, Reactor Systems Branch. You 24 perhaps, I think we could probably discuss this in the 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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47 open portion right now.
1 MR. HAIDER: Okay.
2 MR. THOMAS: Considering it's coming 3
directly from the topical report. Can you point me to 4
a specific example where you see this inconsistency?
5 And that way we can try to work through it and clear 6
up what this even actually means on the slide.
7 MEMBER REMPE: Again, I hope I don't get 8
in trouble for things, but there was a concern about 9
the reflector and core barrel and guide tube 10 instrumentation tube IPLAS (phonetic) flow pin at 11 least that were selected. There was concern about the 12 axial power distribution that was selected.
13 Later in the closed section, you're going 14 to be talking about high impact parameters that had 15 more effect on the methodology. And when I look at 16 what the staff did, some of the concerns were 17 expressed about some of those parameters.
18 And again, I'll admit, maybe I'm just not 19 used to looking at staff SERs approving the 20 methodology. But it seemed like that this last sub-21 bullet, it's a bit of an overstatement of what was 22 concluded by the staff, if I look at the details.
23 MR. THOMAS: Okay, so let me try to 24 explain. So those certainty values that you allude 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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48 to, like the penalties bypass flow and things like 1
that, those are specific values that we are not 2
proving that are deemed as example values in the 3
topical report. Not approving.
4 MEMBER REMPE: Yeah, they clearly aren't, 5
I agree with you. They aren't approving that.
6 Likewise with the --
7 MR. THOMAS: Uncertainties in that the 8
applicant has used a deterministic method for applying 9
uncertainties.
10 MR. ROOKS: I think if I could jump in 11 here and help, maybe I can help. This last bullet I 12 think addresses uncertainty methodology in the actual 13 subchannel analysis, the method, not inputs.
14 So things like reconciling a systems code 15 input to inlet core flow rates or bypass is not an 16 uncertainty treatment within the subchannel 17 methodology. That's when I go to the systems analysis 18 and test the validity of the systems code meshing with 19 the subchannel analysis code that's looking at 20 detailed in-core phenomena.
21 MEMBER REMPE: Like that's also true with 22 the axial power distribution and how they've done --
23 MR. ROOKS: And I view axial power as an 24 input parameter.
25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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49 MEMBER REMPE: Okay. This is all fine 1
then.
2 MR. ROOKS: The methodology I think is 3
flexible about how it treats axial power. So I don't 4
see any limitation there.
5 MEMBER REMPE: Okay, that's fine --
6 MR. THOMAS: I would agree with those 7
statements.
8 MEMBER REMPE: Okay.
9 MR. THOMAS: And specifically for this 10 bullet point, it's referring to, that's right, the 11 methodology of the application of uncertainty 12 methodology, i.e., certainties and penalties by 13 biasing the actual parameter in a conservative 14 direction versus --
15 MEMBER REMPE: Okay, that's fine.
16 MR. THOMAS: Of applying uncertainties.
17 MEMBER REMPE: That's fine. I guess I got 18 confused because of all these conditions on using 19 VIPRE and how that there was a lot of concerns raised.
20 So thank you.
21 MR. THOMAS: Yes, understood, thank you.
22 MEMBER MARCH-LEUBA: I have a generic 23 comment. I am a little -- I realize that the approval 24 of this topical report is based on two old SERs, on 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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50 MOD-01 and MOD-02. And there are a series of 1
limitations and conditions from one and the other.
2 But when you go through that, it confuses a lot to me 3
what are we talking about. Are we talking about MOD-4 01 or MOD-02?
5 NuScale is requesting that we approve MOD-6 02 for their use, and the SER doesn't make that clear, 7
I don't think. I mean, by going through so much back 8
and forth between limitations for 01 and 02, it feels 9
as if you're approving both.
10 MR. HAIDER: Again, maybe this is a 11 regulatory documentation issue. Nowhere in the MOD-02 12 generic SER there is a statement that would say that, 13 that will state that the five conditions approved in 14 MOD-02 are superseded.
15 MEMBER MARCH-LEUBA: I'm just looking for 16 regulatory certainty. The SES you say NuScale should 17 use MOD-02 and forget about MOD-01. With this SER, 18 could they run calculations with MOD-01? Not that 19 they want to, but we are approving VIPRE MOD-02 for 20 use in NuScale.
21 MR. HAIDER: But to the best of my 22 knowledge, the five conditions from MOD-01 are also 23 applicable.
24 MEMBER MARCH-LEUBA:
And they are 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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51 applicable.
1 MR. HAIDER: To MOD-01.
2 MEMBER MARCH-LEUBA: Yeah, the limitation 3
conditions are applicable. You can make them 4
applicable and write the new SER. What I'm saying is 5
it's not clear what we are approving.
6 MR. HAIDER: But the staff agrees that 7
there is a nuance, that since MOD-01 was approved only 8
for BWR, while MOD-02 was approved for both BWR and 9
PWR. So the BWR aspect of Condition 1, how much of 10 that applies.
11 MEMBER MARCH-LEUBA: Yeah.
12 MR. HAIDER: So there is uncertainty about 13 that, but the staff tried to look into the two-phase 14 flow conditions that the --
15 MR. HAIDER: I just put my concern on the 16 record. I would like to see more, a clearer language 17 that NuScale plans to use MOD-02 and that's what we're 18 approving.
19 MEMBER CORRADINI: Can I ask the 20 applicant, what's the plan of NuScale? I assumed it 21 was to use MOD-02, which was an approved NRC standard 22 tool, with the limitation that you must use that 23 analysis technique to then develop your CHF 24 correlation, which then must be used in concert with 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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52 it. What is the applicant's --
1 MEMBER MARCH-LEUBA:
They're not 2
listening. That question is for you.
3 MEMBER CORRADINI: You guys hear the 4
question? Are you planning to use VIPRE MOD-01 or 5
MOD-02 in your analysis?
6 MR. GALIMOV: We installed only MOD-02, so 7
we're going to use only that version.
8 MEMBER CORRADINI: Only MOD-02.
9 CHAIRMAN KIRCHNER: Would you just 10 identify yourself.
11 MR. GALIMOV: Azat Galimov, NuScale.
12 MEMBER CORRADINI: But so your plans are 13 to use MOD-02.
14 MR.
GALIMOV:
- Yes, and in my 15 understanding, MOD-01 is not used by, probably 16 excluded from use from many vendors anyway.
17 MEMBER CORRADINI: Okay, thank you.
18 CHAIRMAN KIRCHNER: Okay, members, any 19 other questions at this point? Then let me turn to 20 the audience and see if there's anyone from the public 21 who wishes to make a statement, please come up and 22 identify yourself and make your comment.
23 Seeing no one, the bridge line is open.
24 OPERATOR: It's open.
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53 CHAIRMAN KIRCHNER: If there is anyone 1
from the public who wishes to make a comment, please 2
speak up, identify yourself, then make your comment.
3 Hearing none, let's then take a short 4
recess is the proper thing.
5 MR. SNODDERLY: When would you like to 6
come back?
7 CHAIRMAN KIRCHNER: Let's reconvene at 8
five minutes of ten.
9 MR. SNODDERLY: Five minutes of ten.
10 Okay, with the closed session.
11 CHAIRMAN KIRCHNER: With a closed session.
12 So we are recessed.
13 (Whereupon, the above-entitled matter went 14 off the record at 9:42 a.m.)
15 16 17 18 19 20 21 22 23 24 25 NEAL R. GROSS COURT REPORTERS AND TRANSCRIBERS 1323 RHODE ISLAND AVE., N.W.
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Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 NuScale Nonproprietary Subchannel Analysis Methodology TR-0915-17564 ACRS Presentation Kenneth Rooks ACRS Open Session - August 24, 2018
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 This material is based upon work supported by the Department of Energy under Award Number DE-NE0000633.
This report was prepared as an account of work sponsored by an agency of the United States (U.S.) Government. Neither the U.S.
Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the U.S.
Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the U.S.
Government or any agency thereof.
Acknowledgement & Disclaimer
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
Agenda
- Overview
- VIPRE-01 Subchannel T/H Code
- Qualification & Methodology Approach
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
Overview NuScale seeks approval for:
- VIPRE-01 use for steady-state and transient analysis
- Methodology fulfills requirements of VIPRE-01 generic safety evaluation report (SER) limitations
- Methodology application and treatment of uncertainties
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
Overview - Safety Analysis Design Nuclear Analysis (TR-0616-48793-P)
Fuel Performance (TR-0116-20825-P-A)
System Transient Analysis Subchannel Analysis Acceptance Criteria Testing (e.g. CHF)
(TR-0116-21012-P)
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
Overview - Subchannel Analysis
- Objective is to determine margin results for:
- Critical Heat Flux
- Fuel Centerline Melt
- Regulatory requirements
- General Design Criterion 10, 10 CFR 50 Appendix A
- SRP 4.2 - Fuel System Design
- SRP 4.4 - Thermal & Hydraulic Design Calculates critical information for FSAR Chapters 4 and 15
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
NuScale SMR
- Natural circulation PWR
system flow a function of power level
flow driven by density gradient between core and steam generator
- Core-average exit fluid conditions remain subcooled
- Hot channel exit quality greater than 0
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
VIPRE-01 Subchannel T-H Code Developed by EPRI and maintained by Zachry Finite-volume subchannel analysis code Solves 3-D core flow and enthalpy distributions, fuel rod temperatures, and MCHFR 3-equation homogeneous equilibrium model (HEM)
Empirical correlations for two-phase conditions Mature PWR licensing history 0
0
Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
NuScale Application
- NuScale using the industry-standard, as-approved version, no modifications to main program design-specific CHF correlations incorporated through dynamic link library (DLL) (NSP2 and NSP4 submitted in TR-0116-21012)
- Managed through NuScale software QA program
- Generic VIPRE-01 SER in EPRI-NP-2511-CCM-A conditional limitations for use NuScale meets SER conditions as demonstrated in topical report Leverages mature and robust basis for PWR analysis
PM-0818-61290 10 Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
VIPRE-01 Qualification
- Extensive qualification for PWRs previously performed as part of original approval
- To support SER conditions, NuScale performed additional qualification to ensure VIPRE-01 applicability code-to-code comparison with NRC-approved code additional experimental phenomena comparisons parametric and generalized input sensitivity studies VIPRE-01 applicable for NuScale conditions
PM-0818-61290 11 Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
Methodology Approach
- Conservative basemodel development generic cycle-independent radial power distribution bounding axial power shapes detailed radial and axial nodalization evaluations
- Input uncertainties are treated independently; no credit for statistical randomness
- Uncertainties are accounted for as model and acceptance criterion limit biases
- Detailed checklist to ensure compliance with method
PM-0818-61290 12 Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 T
Summary
- A conservative subchannel analysis method analyzing steady-state and transient conditions
- Topical report provides details and justification for:
- how NuScales use of VIPRE-01 satisfies all SER requirements
- applicability of VIPRE-01 to the NuScale reactor core
- deterministic methodology using VIPRE-01
- appropriate treatment of uncertainties
- Results from NuScale Subchannel Analysis Methodology application provide input to FSAR Chapters 4 and 15
PM-0818-61290 13 Copyright 2018 by NuScale Power, LLC.
Revision: 0 Template #: 0000-21727-F01 R4 Portland Office 6650 SW Redwood Lane, Suite 210 Portland, OR 97224 971.371.1592 Corvallis Office 1100 NE Circle Blvd., Suite 200 Corvallis, OR 97330 541.360.0500 Rockville Office 11333 Woodglen Ave., Suite 205 Rockville, MD 20852 301.770.0472 Charlotte Office 2815 Coliseum Centre Drive, Suite 230 Charlotte, NC 28217 980.349.4804 Richland Office 1933 Jadwin Ave., Suite 130 Richland, WA 99354 541.360.0500 Arlington Office 2300 Clarendon Blvd., Suite 1110 Arlington, VA 22201 London Office 1st Floor Portland House Bressenden Place London SW1E 5BH United Kingdom
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Presentation to the ACRS Subcommittee Staff Review of NuScale Topical Report TR-0915-17564, REVISION 1 SUBCHANNEL ANALYSIS METHODOLOGY Presenters:
Bruce Bavol - Project Manager, Office of New Reactors Syed Haider, Ph.D.- Reactor Systems Engineer, Office of New Reactors Matt Thomas - Reactor Systems Engineer, Office of New Reactors August 24, 2018 (Open Session)
Non-Proprietary 1
NRC Technical Review Areas/Contributors 2
Non-Proprietary Containment and Ventilation Branch NRO/DSRA/SCVB:
Reactor Systems NRO/DSRA/SRSB:
Jeffrey Schmidt Timothy Drzewiecki Matt Thomas
Staff Review Timeline TR-0915-17564, Subchannel Analysis Methodology NuScale submitted its Topical Report (TR) 0915 17564 P, Subchannel Analysis Methodology, Revision 1, on February 15, 2017 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML17046A333).
Staff issued the following request for additional information / NuScale provided response:
- RAI 9080 - 09/11/2017 (ML17254A439) / 11/09/2017 (ML17313B205) & S1 (ML18061A109)
- RAI 9086 - 09/09/2017 (ML17252A688) / 10/30/2017 (ML17299A973)
- RAI 9099 - 09/02/2017 (ML17251A368) / 09/13/2017 (ML17251A368)
- RAI 9129 - 11/17/2017 (ML17321A597) / 01/15/2018 (ML18015A012)
Staff plans to brief advisory committee on reactor safeguards (ACRS) full committee on September 6, 2018 Staff plans to issue its final SER in late October 2018.
Staff plans to publish the -A (approved) version of the TR in early 2019.
3 Non-Proprietary
Scope of the Staff Review (1/2)
Regulatory Basis General Design Criterion (GDC) 10, Reactor Design, in 10 CFR Part 50, Appendix A NuScale DSRS, Section 4.4, Thermal and Hydraulic Design 10 CFR 50.34, Contents of Applications; Technical Information NRC approved VIPRE-01 subchannel analysis code, version MOD-02 Elements of approval for the NuScale Subchannel Analysis Methodology (NSAM)
VIPRE-01 applies to the NuScale steady-state and transient subchannel analyses.
Methodology fulfills the NRCs requirements in the SERs for VIPRE-01, MOD-01 and MOD-02.
Methodology is independent of any specific CHF correlation and is used for NuScale.
applications if the methodology requirements are satisfied and if the NRC approves the CHF correlation.
Methodology for treatment of uncertainties in the NuScale subchannel methodology is appropriate.
4 Non-Proprietary
Scope of the Staff Review (2/2)
Technical basis for the NRC staff review Nine conditions in the generic SERs for VIPRE-01 MOD-01 and MOD-02 VIPRE-01 modelling assumptions and qualifications Areas requiring additional review NSAM applicability range and VIPRE-01 code limitations NuScale operating conditions Stability of the numerical scheme Inlet boundary condition consistency Two-phase flow instability verification Qualification of VIPRE-01 MOD-02 models and assumptions Information considered by NRC staff NuScale Topical Report, TR-0915-17564, Revision 1, Subchannel Analysis Methodology Responses to RAIs 9080, 9086, 9099, 9129 Audit documents 5
Non-Proprietary
- 1. Post CHF Application Limitation Summary of the VIPRE-01, MOD-01 SER Condition No. 1 Application of VIPRE-01 is limited to PWR licensing calculations with heat transfer regimes up to CHF. Any use of VIPRE-01 in boiling-water reactor (BWR) calculations or post-CHF calculations will require prior NRC review and approval.
Applicants Meeting the Condition in the NSAM Limits the VIPRE-01 code to PWRs up to CHF VIPRE approval not sought for post-CHF calculations.
NuScale is a PWR -- the BWR limitation not applicable.
NSAM meets the post-CHF application/BWR limitation on the use of the VIPRE-01 code for the NuScale design.
Condition 1 is met.
6 Non-Proprietary
- 2. CHF Correlation Requirement Summary of the VIPRE-01, MOD-01 SER Condition No. 2 Use of an unapproved CHF correlation will require the submittal of a separate TR for review and approval.
Application is within the range of applicability of the CHF correlation including fuel assembly geometry, spacer grid design, pressure, coolant mass velocity, quality, etc.,
Applicants Meeting the Condition in the NSAM A separate TR submitted/approved for the NuScale specific NSP2 CHF correlation.
VIPRE-01 used to reduce the experimental CHF data to calculate the local fluid parameters to develop the NuScale specific CHF correlations/MCHFR.
NSAM TR provides assurance that only approved CHF correlations will be used with VIPRE-01 for the NuScale safety analyses supporting the NuScale DCA.
Submittal/approval of a separate TR for the NuScale specific CHF correlation met the present NSAM TR SER Condition 1. So, the generic VIPRE SER Condition 2 has been met.
Range of applicability of the NSAM is covered in the closed session.
7 Non-Proprietary
- 3. VIPRE-01 Models and Assumptions (1/2)
Summary of the VIPRE-01, MOD-01 SER Condition No. 3 Provide justifications for specific modeling assumptions, choice of two-phase flow models, heat transfer/CHF correlations, input values of plant specific data such as turbulent mixing coefficient, slip ratio, and grid loss coefficient, including defaults.
Applicants Meeting the Condition in the NSAM The applicant provided sufficient information on:
Turbulent mixing coefficient Grid spacer loss coefficient Heat transfer correlations Model geometry Radial and axial nodalizations Bypass flow Inlet flow/temperature distributions 8
Non-Proprietary
- 3. VIPRE-01 Models and Assumptions (2/2)
Applicants Meeting the Condition in the NSAM (cont.)
Radial and axial power distributions Rod and assembly bow penalties CHF correlation and DNBR limit Applicant provided sufficient information to justify the specific VIPRE models and assumptions.
Key sensitivities/confirmatory analyses are discussed in the closed session to demonstrate that Condition 3 has been met.
9 Non-Proprietary
- 4. Courant Number Criterion Summary of the VIPRE-01, MOD-01 SER Condition No. 4 If a profile fit subcooled boiling model, which was developed based on steady state data, is used in boiling transients, care should be taken in the time step size used for transient analysis to avoid the Courant number (NC ) less than 1.
Applicants Meeting the Condition in the NSAM A subcooled void correlation based on steady-state data is not suitable for modeling boiling transients in VIPRE with NC < 1. NC> 1 is required for the convergence of the numerical solution of the mass, momentum, and energy equations in VIPRE.
NSAM uses the VIPRE-01 steady-state subcooled boiling correlations.
NSAM TR presents results for three design-basis example transients. Transient time step selected on a case-by-case basis for the axial nodalization & coolant velocity, to ensure NC> 1.
Staff audit showed the condition was met throughout the transients.
Staff confirmatory calculations showed no numerical stability issues resulting from the transient time step selection for NC>1.
Condition No. 4 has been met.
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- 5. Quality Assurance Summary of the VIPRE-01, MOD-01 SER Condition No. 5 Quality control requirements, described in Section 2.6 of the VIPRE-01 MOD-01 SER, to ensure consistency in the development and application of the VIPRE-01 code for safety analysis.
Only an as-approved version of VIPRE-01 is used and any modification to VIPRE-01 is implemented under quality control.
Applicants Meeting the Condition in the NSAM No QA issues or additional quality control requirements reported in the VIPRE-01, MOD-02 SER (1993), beyond the VIPRE-01, MOD-01 SER (1986).
No modifications were made to VIPRE-01, MOD-02 for NSAM.
Implementing CHF correlation into VIPRE through a.DLL file allowed using the user-programmed CHF correlation without any VIPRE source code modification.
No QA concerns about the VIPRE-01, MOD-02 version use with NSAM.
Condition 5 has been met.
11 Non-Proprietary
- 6. Qualification of VIPRE-01 MOD-02 Models (1/2)
Summary of the VIPRE-01, MOD-02 SER Condition No. 1 The use of VIPRE-01 MOD-02 is contingent upon full qualification of the licensing models.
Besides, as stipulated by Condition 3 of the SER for VIPRE-01, MOD-01, and Conditions 6 and 8 of the SER for VIPRE-01, MOD-02, to support qualification of the modeling assumptions, NuScale needed to justify its two-phase modeling and the selected parameters for using VIPRE-01 for the design application over the range of expected two-phase flow conditions.
Applicants Meeting the Condition in the NSAM Slip ratio not used as a modeling assumption in NSAM - No slip ratio specified as a VIPRE input.
VIPRE formulation 3-equation incompressible, homogeneous equilibrium model (HEM)
Solves 3-D core flow field and enthalpy distribution, fuel rod temperatures, and MCHFR.
Non-mechanistic empirical two-phase correlations used to reflect subcooled boiling non-equilibrium and concurrent vapor/liquid phase slip in two-phase flow 12 Non-Proprietary
- 6. Qualification of VIPRE-01 MOD-02 Models (2/2)
Applicants Meeting the Condition in the NSAM The HEM formulation of VIPRE-01 using the subcooled boiling models and bulk void correlations to account for phase slip may not be sufficient for cases with large relative phase velocities.
Applicants drift flux model sensitivity study The drift flux model calculates the void fraction by using the physically realistic conservation of vapor mass generated by wall superheat instead of defining the void as a function of flow and quality with an empirical slip correlation.
Audited the applicants drift flux model sensitivity cases applicable to NuScale design conditions. The use of the drift flux model had a negligible impact on void fractions and CHFR at any point along the hot channel.
The applicants use of the drift flux model to justify its VIPRE-01 two-phase modeling assumptions is appropriate. Condition 6 has been met.
13 Non-Proprietary
- 7. GEXL Correlation Summary of the VIPRE-01, MOD-02 SER Condition No. 2 The GEXL correlation is the only correlation that currently has NRC approval for use in critical power ratio (CPR) calculations of a core containing GE fuels. However, use of the GEXL correlation for other vendors fuels or use of any other correlation requires a separate submittal for NRC review and approval.
Applicants Meeting the Condition in the NSAM This VIPRE-01, MOD-02 SER condition requires the applicant to declare any possible use of the GEXL correlation with the proposed subchannel analysis methodology.
NSAM TR states that NuScale does not perform CPR calculations for BWR fuel with VIPRE-01.
Condition 7 has been met as the above cited statement means that NuScale will not use the GEXL correlation with the NSAM VIPRE-01 applications.
14 Non-Proprietary
- 8. VIPRE-01 Code Limitations Summary of the VIPRE-01, MOD-02 SER Condition No. 3 VIPRE-01 manual identifies VIPRE code limitations. Each user, in its documentation for NRC approval, should certify that the code is not being used in violation of these limitations.
The VIPRE code should not be used to model cases with large relative phase velocities, countercurrent flow, or conditions under which the flow regime changes radically. VIPRE should not be applied to situations that entail conditions such as low-flow boil off, annular flow, phase separation involving a sharp liquid/vapor interface, or countercurrent flow.
Applicants Meeting the Condition in the NSAM The applicant provided sufficient information in the TR, and appropriately addressed the staffs concerns in RAI 9080 about VIPRE-01 code limitations for NuScale application.
RAI 9080 details will be discussed in the closed session to show that NSAM VIPRE-01 application is not prone to code limitations and Condition 8 is met.
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- 9. Input Selection, Uncertainties and Sensitivity Analyses Summary of the VIPRE-01, MOD-02 SER Condition No. 4 NRC acceptance of VIPRE-01 MOD-02 does not endorse procedures and uses of VIPRE described in the code manual. Each user is advised to note that values of input recommended by the code developers are for best-estimate use only and do not necessarily incorporate the conservatism appropriate for licensing type analysis. Therefore, the user is expected to justify or qualify the input selections for licensing applications.
Applicants Meeting the Condition in the NSAM The staff performed confirmatory analyses to look into the following two aspects of the NuScale VIPRE model:
Inlet flow boundary condition consistency Two-phase flow instability More details will be provided in the closed session to demonstrate consistency b/w VIPRE inlet flow BC and the system code output. VIPRE results did not show any potential for two-phase instability.
Condition 9 has been met.
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NSAM TR Conditions & Limitations Condition No. 1 An applicant referencing the NSAM topical report in a safety analysis must also reference an approved CHF correlation. The basis for this condition is provided in Section 4.1 of the staff SER of the NSAM topical report.
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NSAM TR Example Values The NSAM TR uses several example values of input parameters and includes the subchannel analysis results just to demonstrate the NSAM applicability to perform subchannel analyses, and enhance the understanding of the analytical methods. The staff SER does not approve the use of any specific example value inputs or results presented in the TR.
In various subsections of the SER, the staff has documented the review of various input parameters and the determination of the aspects that are approved.
The staff would approve specific input values and ensuing results for the reactor core design for the subsequent licensing submittals (e.g., DCAs) referencing the NSAM TR. The staff would review these final design-and plant-specific input values used in the subchannel analyses as a part of these separate licensing submittals.
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Staff SER Conclusions The NRC staff has reasonable assurance that the use of the VIPRE-01, MOD-02 code with the NSAM described in the TR is appropriate for the NuScale fuel thermal-hydraulic design and plant safety analyses, provided that the SER conditions and limitations are met.
Elements of Approval VIPRE-01 applies to the NuScale steady-state and transient subchannel analysis using the methodology presented.
NSAM fulfills the NRCs requirements in the SERs for VIPRE-01, MOD-01 and MOD-02.
NSAM is independent of any specific CHF correlation and is used for NuScale applications if the methodology requirements are satisfied and if the NRC approves the CHF correlation as confirmed by Condition 1 of this SER.
NSAM describes a methodology for treatment of uncertainties in the NuScale subchannel analysis that is appropriate.
19 Non-Proprietary
Questions/comments from members of the public before the closed session starts?
20 Non-Proprietary