ML24278A018
| ML24278A018 | |
| Person / Time | |
|---|---|
| Site: | 99902078 |
| Issue date: | 10/04/2024 |
| From: | NRC |
| To: | NRC/NRR/DNRL/NRLB |
| References | |
| Download: ML24278A018 (5) | |
Text
From:
Stacy Joseph Sent:
Friday, October 4, 2024 8:35 AM To:
RAI@nuscalepower.com Cc:
Getachew Tesfaye; Mahmoud -MJ-Jardaneh; Griffith, Thomas; Bode, Amanda; NuScale-SDA-720DocsPEm Resource
Subject:
NuScale SDAA Section 4.3 - Request for Additional Information No. 30 (RAI-10269-R1)
Attachments:
Section 4.3 - RAI-10269-R1-FINAL.pdf Attached please find NRC staffs request for additional information (RAI) concerning the review of NuScale Standard Design Approval Application for its US460 standard plant design (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23306A033).
Please submit your technically correct and complete response by the agreed upon date to the NRC Document Control Desk.
If you have any questions, please do not hesitate to contact me.
Thank you, Stacy K. Joseph Senior Project Manager USNRC/NRR/DNRL/NRLB
Hearing Identifier:
NuScale_SDA720_Doc_Public Email Number:
15 Mail Envelope Properties (PH0PR09MB110406FF4851AF3A6769138DE8C722)
Subject:
NuScale SDAA Section 4.3 - Request for Additional Information No. 30 (RAI-10269-R1)
Sent Date:
10/4/2024 8:35:23 AM Received Date:
10/4/2024 8:35:26 AM From:
Stacy Joseph Created By:
stacy.joseph@nrc.gov Recipients:
"Getachew Tesfaye" <Getachew.Tesfaye@nrc.gov>
Tracking Status: None "Mahmoud -MJ-Jardaneh" <Mahmoud.Jardaneh@nrc.gov>
Tracking Status: None "Griffith, Thomas" <tgriffith@nuscalepower.com>
Tracking Status: None "Bode, Amanda" <abode@nuscalepower.com>
Tracking Status: None "NuScale-SDA-720DocsPEm Resource" <NuScale-SDA-720DocsPEm.Resource@nrc.gov>
Tracking Status: None "RAI@nuscalepower.com" <RAI@nuscalepower.com>
Tracking Status: None Post Office:
PH0PR09MB11040.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 536 10/4/2024 8:35:26 AM Section 4.3 - RAI-10269-R1-FINAL.pdf 312481 Options Priority:
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1 REQUEST FOR ADDITIONAL INFORMATION No. 030 (RAI-10269-R1)
BY THE OFFICE OF NUCLEAR REACTOR REGULATION NUSCALE STANDARD DESIGN APPROVAL APPLICATION DOCKET NO. 05200050 CHAPTER 4, REACTOR SECTION 4.3, NUCLEAR DESIGN ISSUE DATE: 10/04/2024
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Background===
By letter dated October 31, 2023, NuScale Power, LLC (NuScale or the applicant) submitted Revision 1 of its US460 standard plant design approval application (SDAA) (Agencywide Documents Access and Management System Accession No. ML23306A033). The applicant submitted the US460 standard plant (NPM-20) SDAA in accordance with the requirements of Title 10 Code of Federal Regulations (10 CFR) Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants, Subpart E, Standard Design Approvals. The NRC staff has reviewed the information in the Final Safety Analysis Report (FSAR) provided in SDAA Part 2, specifically information in Chapter 4, Reactor, (ML23304A355), Chapter 15, Transient and Accident Analysis, (ML23304A365), Chapter 16, Technical Specifications (ML23304A368) and associated TR-101310-NP, Revision 0, US460 Standard Design Approval Technical Specifications Development (ML23304A370), TR-0915-17564-P-A, Subchannel Analysis Methodology, Revision 2 (ML18305B221), and other FSAR Chapters as necessary. The staff has also reviewed the information in Volume 1, Specifications (ML23304A387) and Volume 2, Bases (ML23304A388) provided in SDAA Part 4, US460 Generic Technical Specifications. The NRC staff has determined that additional information is required to complete its review.
Question 4.3-28 Regulatory Basis 10 CFR 50.36(c)(2)(ii)(B) Criterion 2 requires that a technical specification limiting condition for operation (LCO) be established for a process variable, design feature, or operating restriction that is an initial condition of a design basis accident or transient analysis that either assumes the failure of or presents a challenge to the integrity of a fission product barrier.
General Design Criterion 10 requires the reactor core and associated coolant, control, and protection systems to be designed with appropriate margin to assure that specified acceptable fuel design limits (SAFDLs) are not exceeded during any condition of normal operation, including the effects of anticipated operational occurrences.
Issue FSAR Section 4.3.2.2.1 states that a limit on the heat flux hot channel factor (FQ), also referred to by NuScale as total peaking factor, is used to ensure that SAFDLs are not exceeded.
However, the currently proposed NuScale generic technical specifications (TS) do not include an LCO on FQ.
The NRC staff would rely on such an LCO to establish a finding that each NuScale Power Module (NPM) will be operated within the bounds of the safety analyses. The standard technical specifications (STS) for pressurized water reactors (PWRs) include limits on total power peaking (in addition to limits on axial power tilt, control rod insertion, and control rod alignment) to ensure that power distributions, and specifically peak linear heat generation rate (PLHGR), remains within the assumed initial conditions of the safety analysis.
2 During its review of the SDAA, the staff audited (ML23067A300) the engineering documentation for Nuclear Analysis Methodology, Cycle-Specific Nuclear Analysis, Revision 1, Fuel Centerline Melt Analysis, and Core-250B Parameters, Design and Operating Limits, Revision 1. The staff requested the applicant to provide the basis for not including an FQ limit in the generic TS for the NPM-20 design. In its responses to the staff audit questions about the SDAA basis for not establishing an LCO for FQ, NuScale referred back to the staffs findings in the NPM-160 design certification application (DCA) review. Specifically, NuScale stated that the basis provided in the response to RAI 9445, Question 16-42 during the NPM-160 DCA review, wherein the staff questioned exclusion of an LCO for FQ in the generic NPM-160 TS, is valid for the NPM-20 standard design.
The staff reviewed the response to RAI 9445, Question 16-42 (ML18163A417) and the safety evaluation report (SER) for the NPM-160 DCA (ML20205L411). The response to RAI 9445, Question 16-42 for the NPM-160 DCA states:
The heat flux hot channel factor (FQ) is used in the NuScale [NPM-160] design to calculate the peak linear heat generation rate to ensure that the specified acceptable fuel design limit for fuel centerline melting is not exceeded. The NuScale [NPM-160] design is characterized by a relatively low linear heat rate (kW/ft) compared to the PWR operating fleet and has substantial margin to fuel centerline melting at normal power levels. FQ is not used as an initial condition for any transient or design basis accident, including loss of coolant accident
[emphasis added]. As a result, a Limiting Condition for Operation for FQ is not needed in the NuScale design. FSAR Sections 4.3 and 4.4 are modified to clarify this point.
The staff notes that the NRCs approval of the generic TS for the NPM-160 design without an LCO for FQ was based on the consideration that the NPM-160 design has a relatively low linear heat generation rate (LHGR) compared to the PWR operating fleet.
In contrast, the LHGR specified in the SDAA for the NPM-20 standard design is significantly higher than that of the NPM-160 certified design and is much closer to the LHGRs of PWRs in the current operating fleet. Therefore, the staff cannot rely on the same basis for the NPM-20 design to determine that 10 CFR 50.36(c)(2)(ii)(B) Criterion 2 is met. The STS for operating PWRs (e.g., NUREG-1431, Revision 5, STS Westinghouse Plants) include LCOs protecting both peak local power density (such as FQ) and global axial power tilt (such as axial flux difference).
The staff notes the bases for TS on power distribution limits for the AP1000 design (ML023400191) states that the purpose of the limits on the values of FQ(Z) is to limit the local (i.e., pellet) peak power density. The bases indicate that the peak LHGR (Z), which is proportional to FQ(Z), is continuously measured. The bases also indicate that the FQ(Z) is used not only for LOCA analysis but also for loss of forced reactor coolant flow accident and rod ejection accident analyses.
Given that the LHGR of the NPM-20 is much higher than that for the NPM-160, and closer to that of operating PWRs, the staff considers it necessary to establish a limit on FQ in an LCO subsection for heat flux hot channel factor in the SDA generic TS Section 3.2 to satisfy 10 CFR 50.36(c)(2)(ii)(B), Criterion 2. Specifically, Criterion 2 applies to A process variable, design feature, or operating restriction that is an initial condition of a design basis accident or transient analysis that either assumes the failure of or presents a challenge to the integrity of a fission product barrier [emphasis added].
3 Similar to the DCA RAI response quoted above, FSAR Section 4.3.2.2.1 states that FQ is not used as an initial condition for any transient or design basis accident. However, responses to questions during the audit of the SDAA design indicate that NuScales analyses make assumptions that are equivalent to using a peak linear heat generation rate relative to the core-average linear heat generation rate, i.e. FQ.
In addition, while NuScale stated through the NRC staff audit that generic TS LCO 3.2.2, Axial Offset, controls and monitors FZ, other sections of the FSAR and technical report appear to suggest that an additional TS limit is needed to ensure the peak linear heat generation rate remains within limits. Specifically, FSAR Section 4.4.2.2 states: The total peaking factor (FQ) is used to calculate the PLHGR. Reference 4.4-1 [NuScale Power, LLC, Subchannel Analysis Methodology, TR-0915-17564-P-A, Revision 2] provides a discussion on the calculation of the PLHGR based on the average linear heat generation rate (LHGR) and FQ.
Section 3.2 of TR-0915-17564-P-A, Subchannel Analysis Methodology, Revision 2, states that the core operating limits report (COLR) does not include a limit on axial peaking (Fz) because other limits on FQ and FH enforce a sufficiently flat power distribution. These other limits are not defined.
TR-0915-17564-P-A further states: Axial offset [AO] alone is not enough of an indicator for the axial power shape. Two axial power shapes with different peak
[core average axial peaking factor] values and peak locations can have the same AO percentage as long as each half of the core produces the same power. Therefore, the MCHFR for two axial power profiles with the same AO can be quite different.
The staff notes that FSAR Section 4.3.2.2.1 and SDA generic TS Section 1.1 define the AO as the ratio of the difference in power between the top half of the core and the bottom half of the core to the total core power. This definition of AO indicates that the axial offset window limit provides a gross axial power peaking measurement and cannot capture the local axial power peaking within the AO window because the difference in power between the top half of the core and the bottom half of the core is an aggregated parameter rather than a parameter that provides local power peaking.
During audit review, NuScale stated that it generated a large number of scenarios to examine the distribution of axial power peaking and the results show that the maximum peak powers are within the axial offset window and therefore the AO envelopes all local power peaking. The staff notes, however, that these sample cases were based on specific assumptions of the reactor operating conditions that may not necessarily cover the potential reactor loading variations and changes in operating conditions, and therefore insufficient to conclude generically that the AO window limit could capture local power peaking solely based on the maximum peak powers resulting from sample calculations within the axial offset window. The fuel geometry, e.g., fuel densification and expansion, as well as material composition changes along with fuel burnup, and local conditions in the core, will impact the power shape and power peaking through the cycle.
Information Requested The applicant is requested to establish an LCO subsection for FQ as a core power distribution initial condition parameter in generic TS Section 3.2, Power Distribution Limits, in SDAA Part 4, Generic Technical Specifications and Bases, with appropriate conforming updates to SDAA Part 2, FSAR Chapter 16, Technical Specifications; associated TR-101310-NP, US460 Standard Design Approval Technical Specifications Development; and SDAA Part 2, FSAR Sections 4.3 and 4.4.