ML25058A345

LLC, Response to NRC Request for Additional Information No. 030 (RAI-10269 R1) on the NuScale Standard Design Approval Application

ML25058A345
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Site:	05200050
Issue date:	02/27/2025
From:	Shaver M NuScale
To:	Office of Nuclear Reactor Regulation, Document Control Desk
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RAIO-179450 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com February 27, 2025 Docket No.52-050 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738

SUBJECT:

NuScale Power, LLC Response to NRC Request for Additional Information No. 030 (RAI-10269 R1) on the NuScale Standard Design Approval Application

REFERENCE:

NRC Letter to NuScale, Request for Additional Information No. 030 (RAI-10269-R1), dated October 04, 2024 The purpose of this letter is to provide the NuScale Power, LLC (NuScale) response to the referenced NRC Request for Additional Information (RAI).

The enclosure to this letter contain NuScale's response to the following RAI question from NRC RAI-10269 R1:

4.3-28 is the proprietary version of the NuScale response to NRC RAI No. 030 (RAI-10269 R1, Question 4.3-28). NuScale requests that the proprietary version be withheld from public disclosure in accordance with the requirements of 10 CFR § 2.390. The enclosed affidavit (Enclosure 3) supports this request. Enclosure 2 is the nonproprietary version of the NuScale response.

This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.

If you have any questions, please contact Amanda Bode at 541-452-7971 or at abode@nuscalepower.com.

I declare under penalty of perjury that the foregoing is true and correct. Executed on February 27, 2025.

Sincerely, Mark W. Shaver Director, Regulatory Affairs NuScale Power, LLC

RAIO-179450 Page 2 of 2 02/27/2025 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Distribution:

Mahmoud Jardaneh, Chief New Reactor Licensing Branch, NRC Getachew Tesfaye, Senior Project Manager, NRC Stacy Joseph, Senior Project Manager, NRC NuScale Response to NRC Request for Additional Information RAI-10269 R1, Question 4.3-28, Proprietary :

NuScale Response to NRC Request for Additional Information RAI-10269 R1, Question 4.3-28, Nonproprietary :

Affidavit of Mark W. Shaver, AF-179451

RAIO-179450 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com NuScale Response to NRC Request for Additional Information RAI-10269 R1, Question 4.3-28, Proprietary

RAIO-179450 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com NuScale Response to NRC Request for Additional Information RAI-10269 R1, Question 4.3-28, Nonproprietary

Response to Request for Additional Information Docket: 052000050 RAI No.: 10269 Date of RAI Issue: 10/04/2024 NRC Question No.: 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.

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 NuScale Nonproprietary NuScale Nonproprietary

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.

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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].

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 FZ [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 NuScale Nonproprietary NuScale Nonproprietary

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.

NuScale Response:

Executive Summary The NRC staff requests NuScale to add a limiting condition of operation (LCO) for the heat flux hot channel factor (FQ) to the Final Safety Analysis Report (FSAR) Part 4, Technical Specification 3.2, Power Distribution Limits. However, during the audit of the Standard Design Approval Application (SDAA), NuScale provided background information to conclude that the hot channel heat flux factor, FQ, does not meet the threshold to require an LCO based on 10 CFR 50.36(c)(2)(ii)(B), Criterion 2, which is the same conclusion reached for the US600 in the Design Certification Application (DCA).

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NuScale does not use FQ as a direct initial condition in safety analysis applications that assume the failure of or challenges the integrity of a fission product barrier. For the loss of coolant accident (LOCA) scenario, current operating pressurized water reactors (PWRs), which include a total peaking factor Technical Specification, are typically limited by peak centerline fuel temperature, whereas NuScales dominant figures of merit during a LOCA is minimum critical heat flux ratio (MCHFR) and collapsed liquid level. As described in TR-0516-49422-P, Loss-of-Coolant Accident Evaluation Model, MCHFR is a surrogate to prevent fuel melt (i.e., peak centerline fuel temperature) or cladding failure (i.e., peak cladding temperature), thus, evaluating MCHFR is conservative for the NuScale design.

The NRC staff requested NuScale to postulate axial power profile scenarios that are more conservative than the approved methodologies in TR-0915-17564-P-A, Subchannel Analysis Methodology, Revision 2 and TR-108601-P-A Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, Revision

4. This response corroborates NuScales determination that the axial power peaking shapes used in safety analysis are bounding of the extreme, unphysical axial offset cases proposed by the NRC staff. Because the NuScale MCHFR and peak linear heat generation rate are evaluated using axial power shapes with a conservative method approved by the NRC, monitoring axial offset (AO) with LCO 3.2.2 is sufficient to capture local power peaking effects without an LCO for FQ.

In this request for additional information (RAI) response, NuScale provides the applicable regulatory requirements, a description of how core power distribution is controlled for a NuScale Power Module (NPM) core design, NuScale precedence, industry applicability, and a summary of the related audit question A-4.3-28. Additional sensitivity cases align with NuScales conclusions that the established NPM core power distribution LCOs are appropriate.

Regulatory Requirements 10 CFR 50.36(c)(2)(ii)(B) outlines the criteria for determining whether an LCO is required for a system or parameter. An LCO is the lowest functional capability or performance of equipment that is required for safe operation of a plant. Specifically, 10 CFR 50.36(c)(2)(ii)(B) Criterion 2 states the following:

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.

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The intent of 10 CFR 50.36(c)(2)(ii)(B) is to ensure that systems or parameters critical to mitigating accident consequences are maintained within their specified limits.

NuScale Core Design and Power Distribution Controls NuScales NPM core design is smaller, axially and radially, than a typical PWR. The NPM core contains 37 PWR assemblies with an active fuel height of 6.5 feet, leading to a height-to-diameter ratio of approximately 1. Additional core parameter comparisons of the NPM core to other PWR designs are provided in FSAR Table 4.4-1. An advantage to having a smaller core is tightly coupled neutronics, so power does not shift locally in one region without impacts to the rest of the core that can be detected.

There are three potential modes of neutronically-induced power oscillations that are possible in traditional PWRs: azimuthal, radial, and axial. Azimuthal oscillations are not likely due to the inherent symmetry of the NPM core loading pattern and symmetry in control rod assembly (CRA) location and allowable movements. The NPM core is inherently stable with regards to power oscillations due to the overall negative reactivity coefficients at power. Xenon induced power distribution oscillations are evaluated for axial and radial stability. As shown in FSAR Table 4.3-6, xenon oscillations are stable for the NPM core design because the stability index is less than zero. Because the NPM core has fewer degrees of freedom for developing locally peaked conditions due to the small core size and neutronic stability, bounding axial power shapes are developed and analyzed in conjunction with bounding FH for the NPM core without need for explicit FQ considerations.

NuScale controls and monitors core power distribution with LCOs on two important parameters:

enthalpy rise hot channel factor (FH) and the AO window (LCO 3.2.1 and LCO 3.2.2, respectively).

FH is defined as the ratio of the maximum integrated rod power to the average rod power of the core. The purpose of the FH limiting condition of operation is to set limits on core power density to ensure fuel design criteria are met and accident analysis assumptions remain valid.

Controlling power distribution prevents local conditions in the fuel rods or coolant channels from threatening fuel clad integrity during normal operation and analyzed postulated accidents. Limits on FH preclude core power distributions that would result in exceeding specified acceptable fuel design limits (SAFDLs). The technical specification FH values are conservatively used in safety analysis calculations.

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As described in FSAR Part 4, Section B.3.2 Power Distribution Limit Bases, LCO 3.2.1 on FH establishes limits on the power density at any location in the core. The limit on FH protects the fuel design criteria and accident analysis assumptions. The local conditions with respect to core power distributions are controlled as stated in the following Part 4 Section B.3.2 excerpts:

Control of the core power distribution with respect to these limits ensures that local conditions in the fuel rods and coolant channels do not challenge core integrity at any location during either normal operation or a postulated accident analyzed in the safety analyses.

Limits on FH preclude core power distributions that exceed fuel design SAFETY limits.

Because the limits on FH and axial offset protect the local conditions in the core, additional LCOs would be redundant.

Axial offset is defined as the ratio of the difference between the power in the top and bottom of the core to the total power in the core (FSAR Eq. 4.3-1). Axial offset is influenced by the following core-related parameters:

Regulating bank group position

Core power level

Axial burnup

Axial xenon distribution

Reactor coolant temperature

Boron concentration The AO window is a range that is established in the nuclear design process to confirm that operation within the AO window produces core peaking factors and axial power distributions that meet safety analysis fuel design limits. Limiting the AO ensures that the bounding axial distribution is not exceeded during normal operation or during xenon transients. Additionally, limits on AO restricts the core power distributions that are initial conditions in the analyses of anticipated operational occurrences (AOO), infrequent events, and design-basis accidents.

The axial peaking factor (FZ) is defined as the maximum relative power at any axial point in a fuel rod divided by the average power of the fuel rod. NuScales definition is different from the convention of some other fuel vendors where FZ is defined as the maximum relative power at any axial point in a fuel rod divided by the average core power. During the required cycle-specific safety analysis of each operating cycle, all operationally possible FZ values are NuScale Nonproprietary NuScale Nonproprietary

considered in the analysis of the AO window. The LCO on the AO window precludes the need for an LCO on FZ. NuScale analyzes approximately 5,000 axial power shapes in a cycle-specific multi-dimensional parametric case-matrix to generate an AO window that is bounding of all operationally possible axial peaking factors within the analyzed operating ranges. The axial shapes analyzed for the AO window consider different powers from 20 to 100 percent, varying cycle exposure, and conservative flow and temperature assumptions.

While the same AO value may have varying maximum FZ values, a larger FZ magnitude will correspond to a reduction in FH. Therefore, using maximum FZ values from the possible axial shapes within the AO window, while also using the technical specification FH value, results in a conservative calculation of peak linear heat generation rate (PLHGR). FH restricts radial power peaking and AO considers operating conditions that restricts the severity of the axial power shape. Radial peaking (i.e., FH) and axial power profiles (i.e., AO and ultimately FZ) are the initial conditions used in safety analysis, so the limits that restrict these initial conditions are the appropriate technical specification LCOs.

The heat flux hot channel factor, FQ, is defined as the ratio of maximum local heat flux on the surface of the fuel rod to the average fuel rod heat flux. FQ is formulated as the product of FZ and FH for calculation of PLHGR. An LCO on the AO window to limit FZ and an LCO on FH precludes the need for an additional redundant LCO on FQ. As indicated in TR-0915-17564-P-A, Equation 4-2, FQ is not used as a direct input into the PLHGR calculation, but the maximum FZ value (along with the technical specification FH) is direct input in the PLHGR calculation. The PLHGR is directly correlated to the maximum FZ or axial power peaking value, whereas MCHFR calculations are heavily influenced by the axial power peaking shape. This conclusion is evident in the case study provided in this RAI in the section titled NuScale Core Power Distribution Sensitivity Case Study.

The methodology for axial power shape generation is NRC approved as noted in the safety evaluation report (SER) for TR-108601-P-A Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, Revision

4. Interpolation between powers, temperatures, and flows provides a complete spectrum of parameters to identify the operationally possible axial peaking extremes (within rounding errors).

These operational parameters, such as temperature, flow, and radial peaking, have separate LCOs to ensure they remain within analyzed operating ranges. Cycle exposure is also a dimension in the multi-dimensional parametric case-matrix. Because SIMULATE5 is a best-estimate core simulator, phenomena such as fuel densification and expansion, and other material composition changes that occur as a function of fuel exposure, are inherently included NuScale Nonproprietary NuScale Nonproprietary

in the multi-dimensional case-matrix. So, the sampling of cycle exposure, allowed operating conditions, and allowed equipment configurations all impact the local conditions in the core, in turn impacting the power shape and power peaking through the cycle. Sampling multi-dimensional parametric case-matrix captures possible local power peaking that could be experienced during the defined operational cycle (which consists of a specific loading pattern, allowed operating conditions, and allowed equipment configurations).

Interpolation between the sampling of the multi-dimensional parametric case-matrix is appropriate given the fundamental physics involved. Axial power shape is constrained by geometry (e.g., geometric buckling) and U-235 distribution. For typical NPM core average axial power shapes, the axial power shape transitions from a middle-peaked chopped-cosine in beginning of cycle to a square shape at end of cycle. Fuel design and loading is confirmed during low power physics testing at the beginning of each cycle and AO is continuously monitored with the online core monitoring system throughout operation. The multi-dimensional parametric case-matrix identifies possible extreme axial peaking values (within rounding errors) given the operational and physics constraints. No phenomena exist that would make the interpolation approach between the multi-dimensional evaluated points invalid.

The axial U-235 distribution is a reflection of exposure distribution. Because exposure is an integrated power parameter, exposure values begin at relatively small magnitudes. Normalized axial exposure distributions near beginning of life are more curved and larger peaked. The axial power shapes gradually flatten in the center of the assembly, becoming less center peaked with exposure. However, an un-normalized distribution plotted in absolute units of GWd/MTU on the same plot as an end-of-life assembly will appear to be almost uniform compared to the much larger exposures in the axial middle of a highly exposed assembly. By the end of cycle, there is much less U-235 throughout the middle of the core, with increasing concentrations at the top and bottom of the core as shown on the left side of Figure 1. The right side of Figure 1 shows axial distributions as function of cycle exposure. In summary, the axial power peaking distribution is constrained by geometry and the U-235 distribution, and the multi-dimensional parametric case-matrix evaluation of the operating domain for a given cycle captures the range of operationally possible axial peaking (FZ) values.

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((2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

NuScale Core Power Distribution Sensitivity Case Study In response to in-person meetings the week of December 6, 2024 and subsequent virtual meetings, the NRC staff requested specified sensitivity case comparisons to verify that the NuScale NPM-20 core design is not sensitive regarding linear heat generation rate and total power peaking. Specifically, the NRC staff requested the following information: LHGR Information:

For the limiting Manual Peaking 5% point that is inside the AO window, provide the LHGR value for the peak node in the power shape. This point was created by manually changing the axial peaking to increase the power to a node(s) by 5%.

Provide the LHGR value for the peak node in the power shape before the manual change to the axial peaking for the limiting Manual Peaking 5% point that is inside the AO window. This will be referred to as Pre-Manual Peaking point.

Provide the value for the total power of the fuel pin containing the Manual Peaking 5% point as well as the total power of the fuel pin containing the Pre-Manual Peaking point.

Set the total power for the Pre-Manual Peaking point hot pin to be equal to the total power in the Manual Peaking 5% point hot pin by changing the Fdh for the Pre-Manual Peaking point pin. This will be referred to as Pre-Manual Peaking Fdh point.

Set the total power for the Pre-Manual Peaking point fuel pin to the power corresponding to the Max Fdh used in MCHFR transient analyses (i.e. the Pre-Manual Peaking point pin should have a Fdh of 1.5 according to the presentation). This will be referred to as Pre-Manual Peaking Fdh limit point. Provide the LHGR value for the peak node in the power shape and provide the value for the total power for the Pre-Manual Peaking Fdh limit point pin.

Provide the LHGR value for the peak node in the power shape and provide the value for the total power for the pin for the limiting points for Shape FQ, Asymmetric Single Rod, Symmetric PDILs for the nominal AO. MCHFR Analysis Information NuScale Nonproprietary NuScale Nonproprietary

Perform the limiting MCHFR FSAR analysis using the Pre-Manual Peaking point as the input for the hot assembly. Provide the transient analysis MCHFR, peak pin power and peak node LHGR.

Perform the limiting MCHFR FSAR analysis using the Pre-Manual Peaking Fdh point as the input for the hot assembly. Provide the transient analysis MCHFR, peak pin power and peak node LHGR.

Perform the limiting MCHFR FSAR analysis using the Manual Peaking 5% point as the input for the hot assembly. Provide the transient analysis MCHFR, peak pin power and peak node LHGR.

Perform the limiting MCHFR FSAR analysis using the Pre-Manual Peaking Fdh limit point as the input for the hot assembly. Provide the transient analysis MCHFR, peak pin power and peak node LHGR. To summarize, the NRC staff requested comparisons of the Pre-Manual Peaking case to cases where the total peaking was manually increased by 5 percent and cases where FH is at the the limit. (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Table 1: Core Power Distribution - Maximum FQ (( }}2(a),(c) In Table 2, the FQ values provided are the calculated product of FH and FZ. ((

}}2(a),(c)

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((

}}2(a),(c)

Manually manipulating the peaking by 5 percent has ((

}}2(a),(c)

With the recognition that FH is more important to MCHFR than maximum FQ, the nominally expected axial power shapes that are generated with the NRC-approved power shapes methodology in TR-0915-17564-P-A appropriately captures the limiting power distribution, including xenon transients, that can occur in the NuScale core when operated within allowable technical specifications. ((

}}2(a),(c)

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(( }}2(a),(c) The FQ values used in Chapter 15 safety analyses (calculated using NuScales approved axial power shapes methodology) (( }}2(a),(c) for positive and negative axial offset power shapes in Figure

2. Note that the artificial increase in peaking was performed on an axial power shape that was already at an unphysical distribution at the edge of a forced axial offset, than the nominal case data points, as indicated by the higher FQ values.

NuScales axial power shape methodology, combined with existing technical specifications for FH and AO window, is conservative for safety analysis evaluations and precludes the need for a technical specification on FQ. NuScale Nonproprietary NuScale Nonproprietary

Table 2: Core Power Distribution Sensitivity Cases - Limiting Increase in Steam Flow Transient (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) NuScale Precedence In the NuScale Design Certification Application SER for FSAR Chapter 4 (ML20205L411), the NRC staff states in Section 4.3.4.9, Technical Specifications, that the NRC staff agrees that FQ does not need an LCO because FQ is not relied on for power distribution verification or for input into TR-0516-49422-P-A, Loss-of-Coolant Accident Evaluation Model. Additionally, in the SER for Chapter 4, Section 4.3.4.1, Power Distributions, the NRC staff concluded the following. Based on the information discussed in this section and the analytical methods discussed in SER Section 4.3.4.7, the NRC staff finds the power distributions acceptable because (1) the safety analyses apply a conservatively bounding power distribution when evaluating thermal-margin, (2) the applicant used an approved core design methodology to perform analyses that demonstrate operation within the bounding power distributions used in the safety analyses, and (3) operation within the bounding power NuScale Nonproprietary NuScale Nonproprietary

distributions used in the safety analyses is verified in accordance with GTS 3.2.1 and GTS 3.2.2. The finding provided above remains applicable to the NuScale NPM-20 design because safety analyses apply a conservatively bounding core power distribution and operation within the core power distribution is verified with the LCOs on FH and the AO window. The NRC-approved methodology in which the bounding power distribution is developed remains unchanged from the DCA. In RAI-10269, the NRC states that NuScale cannot include the same basis as the DCA for not including an LCO for FQ because of the increased linear heat generation rate between the NPM-160 and NPM-20 design. The average linear heat generation rate for the DCA was 2.5 kw/ft with a peak LHGR of 5.0 kw/ft. The SDA linear heat generation rate increased to 3.9 kw/ft with a peak LHGR of 7.5 kw/ft. However, the average LHGR for a typical PWR is approximately 5-7 kw/ft, with peak LHGRs upwards of 14 kw/ft. While the linear heat generation rate for the NPM-20 design increased, it is still significantly below (~70% average LHGR, ~50% peak LHGR) that of a typical PWR. Industry Practice and Applicability This section provides industry research conclusions on PWR standard technical specifications with comparisons to the NuScale design. NUREG-1431 Standard Technical Specifications Westinghouse Plants - Revision 5, Volume 2 (ML#21259A159) In the Westinghouse standard technical specifications (NUREG-1431), FQ(Z) is defined as a measure of the peak fuel pellet power. The LCO on FQ(Z) precludes the following: a. During a large break LOCA, the peak cladding temperature must not exceed 2200 F. b. During a loss of forced reactor coolant flow accident, there must be at least 95% probability at the 95% confidence level (the 95/95 DNB criterion) that the hot fuel rod in the core does not experience a departure from nucleate boiling (DNB) condition. c. During an ejected rod accident, the energy deposition to the fuel must not exceed 280 cal/gm. d. The control rods must be capable of shutting down the reactor with a minimum required SDM with the highest worth control rod stuck fully withdrawn. NuScale Nonproprietary NuScale Nonproprietary

The LCOs for NuScale that satisfy the same criterion above are: a. Not Applicable. b. LCO 3.2.1 Enthalpy Rise Hot Channel Factor and LCO 3.2.2 Axial Offset. c. LCO 3.2.1 Enthalpy Rise Hot Channel Factor, LCO 3.2.2 Axial Offset, LCO 3.1.4 Rod Group Alignment Limits, LCO 3.1.5 Shutdown Bank Insertion Limits, and LCO 3.1.6 Regulating Bank Insertion Limits. d. LCO 3.1.1 Shutdown Margin. Additionally, NUREG-1431 states the following for assumed accident analysis initial conditions. Limits on FQ(Z) ensure that the value of the initial total peaking factor assumed in the accident analyses remains valid. Other criteria must also be met (e.g., maximum cladding oxidation, maximum hydrogen generation, coolable geometry, and long term cooling). However, the peak cladding temperature is typically most limiting. For the NuScale design, peak cladding temperature is not the limiting figure of merit for LOCA analysis, but critical heat flux (CHF) is. The limits on FH and AO provide margin to CHF. NUREG-2194 Standard Technical Specifications Westinghouse Advanced Passive 1000 (AP1000) Plants - Revision 1, Volume 2 (ML#24026A234) NUREG-2194 states that peak cladding temperature is typically most limiting, therefore, the limit is placed on FQ(z) to ensure accident analysis assumptions are valid. Additionally, FQ is only used when the AP1000 monitoring system is functional. When the online monitoring system is not monitoring the specified parameters, the power distribution is limited by the LCOs on axial flux difference, quadrant power tilt ratio, and control bank insertion limits. The NuScale design is limited by minimum critical heat flux ratio, not linear heat generation rate, and there is sufficient margin to fuel centerline temperature limits that is protected by monitoring CHF. Bounding axial shapes, confirmed on a cycle-specific basis, are used as input into the subchannel analysis that evaluates both MCHFR and fuel centerline melt acceptance criteria. NUREG-1430 Standard Technical Specifications Babcock and Wilcox Plants - Revision 5, Volume 2 (ML#21272A370) NuScale Nonproprietary NuScale Nonproprietary

The LCO on FQ(Z) for a Babcock and Wilcox (B&W) plant prevents power peaks that exceed that assumed in the LOCA analysis. The figure of merit typically most limiting to a B&W plant is peak cladding temperature reached during a LOCA. NuScales LOCA evaluation methodology does not include peak cladding temperature as a figure of merit because the NPM design is limited by critical heat flux. As stated previously, bounding axial shapes, confirmed on a cycle-specific basis, are used as input into the subchannel analysis that evaluates both MCHFR and fuel centerline melt acceptance criteria. NUREG-1432 Standard Technical Specifications Combustion Engineering Plants - Revision 5, Volume 2 (ML#21258A424) In NUREG-1432, Section 3.2 Power Distribution Limits, linear heat rate, total planar radial peaking factor (FXY), total integrated radial peaking factor (FrT), azimuthal power tilt (Tq), and axial shape index have LCOs to protect fuel thermal margin limits. Similar to the Westinghouse and B&W standard technical specifications, the Combustion Engineering LCOs on core power distributions are to ensure the peak cladding temperature remains below 2200 degrees Fahrenheit in the event of a LOCA. NuScale protects fuel thermal margin limits (MCHFR and fuel centerline melt) through the process described in this response. NuScale Nonproprietary NuScale Nonproprietary

Audit Phase A Review This section reviews the progression of the review of A-4.3-28 during the audit phase. The original A-4.3-28 question was asked on June 7, 2024. Subsequently, NuScale provided the first response on June 24, 2024 stating that the DCA precedence is applicable to the SDA. On July 31, 2024, the NRC staff provided feedback disagreeing that the DCA precedence is applicable to the SDA and that the NRC staff is moving forward with with drafting the RAI. During a clarification call on August 14, 2024, there was no resolution or clear path to move forward with A-4.3-28. NuScale took the initiative to plan an in-person meeting on Chapter 4 to try to work through some of the highly technical audit issues. The in-person meeting was held on September 5, 2024. During the meeting, it was not clarified what NuScale could provide to resolve this issue. On a call on September 11, 2024, NuScale committed to providing clear technical justification on how all possible Fz values are bounded by the AO window. NuScale then provided a revised response on September 27, 2024. On October 3, 2024, the NRC staff provided additional feedback and issued the final RAI on October 4, 2024. The following discussion is organized by NRC staff feedback and then the NuScale response to each portion of the feedback. Breaking down the feedback into smaller portions ensures all feedback from the NRC staff is taken into consideration during the development of the response to this RAI. NRC Staff Feedback - July 31, 2024 NuScale received feedback on the original NuScale audit response on July 31, 2024. The feedback to this response is identical to RAI-10269. FSAR Section 4.3.2.2.1 states that a limit on the heat flux hot channel factor (FQ), also referred to as total peaking factor, is used to ensure that SAFDLs are not exceeded. NuScale revised FSAR Section 4.3.2.2.1 to state that the parameters that are input into the peak linear heat generation rate, which is used to ensure peak cladding temperature is not exceeded, are FH and Fz. 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 NuScale Nonproprietary NuScale Nonproprietary

peak linear heat generation rate (PLHGR), remains within the assumed initial conditions of the safety analysis. As identified in the section titled Industry Practice and Applicability of this RAI response, the standard technical specifications for PWRs include such limits because peak cladding temperature is the dominant figure of merit in their respective LOCA analyses. NuScales figure of merits for LOCA analyses are CHF and collapsed liquid level. 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). Given the NPM-20 standard designs LHGR similar to 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. The section titled NuScale Precedence in this RAI response addresses the comparison of linear heat generation rates for the NPM-160 and NPM-20 compared to the linear heat generation rate of large operating PWRs. The NPM-20 still maintains a relatively low linear heat generation rate compared to the operating fleet. Linear heat generation rate is not a criterion for necessitating an LCO per 10 CFR 50.36(c)(2)(ii)(B), Criterion 2. Although FSAR Section 4.3.2.2.1 states that FQ is not used as an initial condition for any transient or design basis accident, as also noted by the applicant in its response to A 13, NRC staff notes that these 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 NuScales response to audit question A-4.3-28 stated 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. NuScale Nonproprietary NuScale Nonproprietary

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. NuScale revised FSAR Section 4.3.2.2.1 and Section 4.4.2.2 to clarify how peak linear heat generation rate is calculated using FZ and FH. In TR-0915-17564-P-A, Subchannel Analysis Methodology, Revision 2 (SAM) topical report, it is explicitly stated that the limitation on FH is a core operating limits report (COLR) value. 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. In the SAM topical report, Section 3.2 states the above quotation. However, Section 3.2 also states that the difference in minimum CHF ratio for axial profiles with the same AO is addressed in Section 3.10.8. Section 3.10.8 of the SAM topical report then discusses how the AO window is determined by using axial power shapes from scenarios that could occur for normal and anticipated operation. The set limits on FH, AO, and other operating limits are used as input into a large case-matrix of axial shapes used to find the bounding axial shapes for MCHFR analysis, as well as the limiting Fz for fuel performance analysis. 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 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. NuScale agrees with the definition the NRC staff provided for axial offset. However, NuScale did not intend to imply that axial offset measurement by itself is sufficient to capture local axial power peaking. The combination of axial offset monitoring and the robust cycle-specific NuScale Nonproprietary NuScale Nonproprietary

calculation of axial shapes results in a bounding treatment of operationally possible local axial power peaking values. NRC Staff Feedback - October 3, 2024 The feedback provided below from the NRC staff is in response to the NuScale response posted on September 27, 2024. The response and proposed FSAR markup do not substantiate that the measured AO is capable of detecting local power peaking at various core elevations. By definition, Axial Offset (AO) is the ratio of the gross power difference between top and bottom of the core power to the total core power. Without additional justification, it is unclear how the AO window established by calculations can ensure that the specific acceptable fuel damage limit will not be exceeded. Also, the staff notes that this approach is not consistent with the accepted industry practice. The ratio of the linear heat generation rate at an elevation over the average linear heat generation in the core, FQ, is a global factor that considers local power peaking under normal conditions, AOOs and LOCA. The sample power profiles presented in the response on 9/27/2024 appear to be calculated based on steady states. Although NuScale indicates that the LOCA analyses do not use FQ, transient conditions, such as xenon oscillation, uncontrolled control rod movement, may induce local power peaking in the core that must be detected and limited using FQ or other appropriate measurable parameters. Each portion of the feedback above is broken down with NuScale discussion. The response and proposed FSAR markup do not substantiate that the measured AO is capable of detecting local power peaking at various core elevations. By definition, Axial Offset (AO) is the ratio of the gross power difference between top and bottom of the core power to the total core power. NuScale agrees that AO is defined as the gross power difference between the core power located in the top and bottom of the core divided by total core power. However to mathematically have large absolute AO values (top or bottom), the maximum axial peaking factor must be relatively large as compared to the maximum axial peaking factor located in the opposite half of the core. However, axial power shape is highly constrained by geometric buckling and U-235 distribution. There is no realistic situation that can occur where a large axial peaking factor (Fz) can occur in the top of the core as well as in the bottom of the core (i.e., a hypothetical double humped shape) to produce a depressed AO value. Regardless, if a NuScale Nonproprietary NuScale Nonproprietary

double-humped shape was possible, it would be included in the analysis of possible operational configurations, with the the most limiting axial shapes used in bounding MCHFR analysis and the most extreme Fz values used in bounding fuel performance analysis. Without additional justification, it is unclear how the AO window established by calculations can ensure that the specific acceptable fuel damage limit will not be exceeded. The same methods for establishing the AO window, in conjunction with evaluation of temperatures, power, and burnup distributions, have been previously NRC-approved in the DCA for evaluating the minimum critical heat flux ratio and fuel centerline melt SAFDLs. This method relies upon capturing axial power peaking to evaluate CHFR and peak linear heat generation rate or pellet temperatures at all core elevations. Also, the staff notes that this approach is not consistent with the accepted industry practice. The ratio of the linear heat generation rate at an elevation over the average linear heat generation in the core, FQ, is a global factor that considers local power peaking under normal conditions, AOOs and LOCA. NuScale agrees that the approach is not consistent with the industry practice for large PWRs that have additional SAFDLs for LOCAs or DNB trips. However, this practice was approved in the DCA for the NPM-160 design, and therefore is consistent with accepted industry practice for NuScale modules. The sample power profiles presented in the response on 9/27/2024 appear to be calculated based on steady states. Although NuScale indicates that the LOCA analyses do not use FQ, transient conditions, such as xenon [transients], uncontrolled control rod movement, may induce local power peaking in the core that must be detected and limited using FQ or other appropriate measurable parameters. The sample profiles are steady-state axial power shapes considering possible scenarios that can occur for normal or anticipated operation (e.g., xenon transients) within or at the AO window limits. The profiles consider credible core configurations of cycle exposure, control rod configuration, xenon distribution, and core thermal-hydraulic conditions. This methodology is NRC approved as stated in the SER for TR-0915-17564-P-A, Revision 2, and was subsequently found acceptable during the review of the TR-108601-P-A, Revision 4. Therefore, the combination of an approved axial power shape method with bounding radial power distribution peaking (FH) is considered appropriate for evaluating the minimum critical heat flux ratio NuScale Nonproprietary NuScale Nonproprietary

SAFDL, because it conservatively captures the local power peaking in the core. For uncontrolled rod movement transients, approved methodology in TR-0915-17564 Revision 2 assures that the MCHFR and peak linear heat generation rate SAFDLs capture local power peaking appropriately. Evaluating axial power shapes that extend to the AO window with a forced axial offset condition (as compared to a realistic depletion shape) is a conservative method to capture the maximum axial peaking factor. For example, Figure 3 below shows the SIMULATE5 iteration search on AO to a specific target value (red) and compares that to axial power shapes generated from a large parametric spectrum of continuous load following scenarios using control rods only, boron only, various reduced power levels, various durations at the partial power condition, and with return to power methods that maximize axial peaking (blue). The blue dots in Figure 3 represent an extreme load following scheme that produces a range of FZ values for a given AO value, which are used for comparison purposes only. The red dots indicate the spread of FZ when using the iteration search to a target AO value, which is used in the approved methods discussed in this audit response. Using the SIMULATE5 target AO search compared to realistic depletion shapes for an extreme load follow core produces a conservative range of maximum Fz values, as expected, given that the SIMULATE5 target AO search creates unphysical xenon axial distributions. The purpose of providing Figure 3 is to show that the MCHFR and peak linear heat generation rate SAFDLs are evaluated using axial power shapes with an approved method and produces larger Fz values than would be seen even with extreme load following cycle depletion. Therefore, monitoring AO with LCO 3.2.2 is sufficient to capture local power peaking effects without an LCO for FZ or FQ. NuScale Nonproprietary NuScale Nonproprietary

Figure 3 Comparison of axial peaking from iterated and long-term depleted methods Impacts to FSAR Chapter 4 Subsection NRC Staff Feedback - October 3, 2024 of this RAI response references the use of SIMULATE5 for a targeted AO search when producing axial power shapes and providing comparisons of the targeted AO search to the resulting AO from extreme core load following scenarios. However, NuScale follows the approved methodology in TR-0915-17564-P-A, Subchannel Analysis Methodology, Revision 2 and TR-108601-P-A Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, Revision 4, for the creation of bounding axial power shapes and event-specific axial power shapes. The extreme load follow cases are provided for information only, and further supports that the NuScale approved methodology to determine bounding axial power shapes is conservative. NuScale does not credit any analyses based on load following and SDAA FSAR Chapter 4 only allows for baseload operations. Thus, Chapter 4 does not include the information regarding extreme load following as requested in feedback by NRC staff. The use of the heat flux hot channel factor, FQ, in FSAR Section 4.3 is clarified in the attached markup. Clarification was provided on how FH and FZ are used to calculate a maximum FQ. NuScale Nonproprietary NuScale Nonproprietary

Conclusion In this RAI response, NuScale provides evidence to conclude that a limiting condition of operation for FQ is not required because FQ does not meet the criteria in 10 CFR 50.36(c)(2)(ii) for requiring an LCO. FQ is implicitly monitored through LCOs for FH and AO, in combination with the robust axial shapes analysis that must be performed for each operating cycle in accordance with the methodology approved by the NRC in topical reports. Established LCOs on FH and the AO window ensure that core power distribution remains within safe operating limits, inherently accounting for variations of FQ without the need for a separate LCO. Additional information is provided on the development and use of bounding axial power shapes to corroborate NuScales confidence that the axial power peaking shapes used in safety analysis are bounding of extreme, unphysical axial offset cases. Bounding axial power shapes are developed in accordance with the approved methodologies in TR-0915-17564-P-A, Subchannel Analysis Methodology, Revision 2 and TR-108601-P-A Statistical Subchannel Analysis Methodology, Supplement 1 to TR-0915-17564-P-A, Revision 2, Subchannel Analysis Methodology, Revision 4. The conclusion that an LCO on FQ is not required is based on the described regulatory requirements, initial conditions for accident analyses and how NuScale monitors core power distribution, and NuScale and industry precedence discussed in this RAI response. NuScale Nonproprietary NuScale Nonproprietary

NuScale Final Safety Analysis Report Nuclear Design NuScale US460 SDAA 4.3-6 Draft Revision 2 requirements and the specific power history of an individual cycle. The fuel loading pattern and fuel shuffle pattern for the reference equilibrium cycle are shown in Figure 4.3-2 and Figure 4.3-3, respectively. The equilibrium cycle does not include axial enrichment zoning in the form of axial blankets. Table 4.3-1 and Table 4.3-2 summarize the reactor core design parameters used in the analysis. The plant operating modes are described in the technical specifications. 4.3.2.2 Power Distribution Power distribution calculations are discussed in the Nuclear Analysis Codes and Methods Qualification topical report (Reference 4.3-2). This report contains a discussion of power distribution uncertainty, including application and a means for updating the uncertainty values. Additional discussion of the power uncertainties used in thermal-hydraulic analysis is provided in Section 4.4. 4.3.2.2.1 Definitions Enthalpy Rise Hot Channel Factor, FH The maximum enthalpy rise hot channel factor, FH, is defined as the ratio of the maximum integrated fuel rod power to the average fuel rod power. The limit on FH is established to ensure the fuel design criteria are not exceeded and the accident analysis assumptions remain valid. This limit ensures the design-basis value for the CHF ratio is met for normal operation, AOOs, and infrequent events. The FH limit is representative of the coolant flow channel with the maximum enthalpy rise. This channel has the highest power input to the coolant and therefore the highest probability for CHF. Heat Flux Hot Channel Factor, FQ Audit Question A-16-13, Audit Question A-4.3-28 RAI 4.3-28 The heat flux hot channel factor (or total peaking factor), FQ, is the ratio of maximum local heat flux on the surface of a fuel rod to the average fuel rod heat flux. FQ is the product of axial peaking factor (FZ) and the enthalpy rise hot channel factor (FH). The maximum FQ is used to calculate the peak linear heat generation rate (LHGR). Maximizing FQ through the use of FZ and FH ensures the SAFDLs are not exceeded.The maximum FQ value is used to calculate the peak linear heat generation rate (LHGR). The maximum value of FQ is used to ensure the SAFDLs are not exceeded. Axial Peaking Factor, Fz The axial peaking factor, Fz, is the maximum relative power at any axial point in a fuel rod, divided by the average power of the fuel rod.

NuScale Final Safety Analysis Report Thermal and Hydraulic Design NuScale US460 SDAA 4.4-4 Draft Revision 2 Audit Question A-4.3-28 RAI 4.3-28 The total peaking factor (FQ) is used to calculate the PLHGR.In safety analyses, PLHGR is determined using enthalpy rise hot channel factor (FH) and maximum axial peaking factor value (FZ) allowable within the AO window. Reference 4.4-1 provides a discussion on the calculation of the PLHGR based on the average linear heat generation (LHGR) and FQ. 4.4.2.3 Core Coolant Flow Distribution The design uses natural circulation, and there is no active control of the core flow. The core inlet flow distribution is dependent upon the geometry of the RCS loop, including the lower core plate and bypass flow paths. The core bypass flow paths are discussed in Section 4.4.3.1. There are flow inlets for each of the fuel assemblies in the core, similar to currently licensed PWR fuel designs. Several inlet flow distributions are evaluated in Reference 4.4-2 to understand the effect on CHF. For up to a 10-percent inlet flow reduction to the limiting fuel assembly, there is an insignificant effect on the minimum critical heat flux ratio (MCHFR). Additionally, for a given radial power distribution, there is no sensitivity observed to the inlet flow distribution. A 520-percent reduction in the flow to the limiting fuel assembly is used in the subchannel analysis. Core inlet flow is calculated from the total RCS flow including flow measurement uncertainty and is reduced by the nominal bypass flow. The bypass flow uncertainty is statistically applied as described in Reference 4.4-2. 4.4.2.3.1 Core Coolant Temperature Distribution As discussed in Reference 4.4-1, the core inlet temperature distribution is a boundary condition input for steady-state and transient subchannel analysis that is dependent on nuclear steam supply system design geometry. In the helical coil SG design, the primary RCS flow is on the shell side and the secondary feedwater flow is through the tubes. The concentric geometry of the SGs relative to the core ensures symmetric coolant temperature distribution through the downcomer into the core inlet. A uniform core inlet temperature is used in the subchannel analysis for AOOs, IEs, and accidents. 4.4.2.3.2 Turbulent Mixing The turbulent mixing model within VIPRE-01 accounts for the exchange of enthalpy and momentum among adjacent subchannels caused by turbulent flow. The coefficient for turbulent mixing and the turbulent momentum factor are the two inputs needed for this model. This mixing model is incorporated into the VIPRE-01 energy and momentum equations, which is dependent on the amount of turbulent crossflow per unit length. The turbulent mixing coefficient is determined from thermal mixing tests and is fuel-design specific. The value for the turbulent momentum parameter is not

RAIO-179450 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Affidavit of Mark W. Shaver, AF-179451

AF-179451 Page 1 of 2

NuScale Power, LLC AFFIDAVIT of Mark W. Shaver I, Mark W. Shaver, state as follows: (1) I am the Director of Regulatory Affairs of NuScale Power, LLC (NuScale), and as such, I have been specifically delegated the function of reviewing the information described in this Affidavit that NuScale seeks to have withheld from public disclosure, and am authorized to apply for its withholding on behalf of NuScale. (2) I am knowledgeable of the criteria and procedures used by NuScale in designating information as a trade secret, privileged, or as confidential commercial or financial information. This request to withhold information from public disclosure is driven by one or more of the following: (a) The information requested to be withheld reveals distinguishing aspects of a process (or component, structure, tool, method, etc.) whose use by NuScale competitors, without a license from NuScale, would constitute a competitive economic disadvantage to NuScale. (b) The information requested to be withheld consists of supporting data, including test data, relative to a process (or component, structure, tool, method, etc.), and the application of the data secures a competitive economic advantage, as described more fully in paragraph 3 of this Affidavit. (c) Use by a competitor of the information requested to be withheld would reduce the competitors expenditure of resources, or improve its competitive position, in the design, manufacture, shipment, installation, assurance of quality, or licensing of a similar product. (d) The information requested to be withheld reveals cost or price information, production capabilities, budget levels, or commercial strategies of NuScale. (e) The information requested to be withheld consists of patentable ideas. (3) Public disclosure of the information sought to be withheld is likely to cause substantial harm to NuScales competitive position and foreclose or reduce the availability of profit-making opportunities. The accompanying Request for Additional Information response reveals distinguishing aspects about the response by which NuScale develops its NuScale Power, LLC Response to NRC Request for Additional Information (RAI No. 10269 R1, Question 4.3-28) on the NuScale Standard Design Approval Application. NuScale has performed significant research and evaluation to develop a basis for this response and has invested significant resources, including the expenditure of a considerable sum of money. The precise financial value of the information is difficult to quantify, but it is a key element of the design basis for a NuScale plant and, therefore, has substantial value to NuScale. If the information were disclosed to the public, NuScales competitors would have access to the information without purchasing the right to use it or having been required to undertake a similar expenditure of resources. Such disclosure would constitute a misappropriation of NuScales intellectual property, and would deprive NuScale of the opportunity to exercise its competitive advantage to seek an adequate return on its investment. (4) The information sought to be withheld is in the enclosed response to NRC Request for Additional Information RAI No. 10269 R1, Question 4.3-28. The enclosure contains the designation Proprietary at the top of each page containing proprietary information. The information considered by NuScale to be proprietary is identified within double braces, (( }} in the document.

AF-179451 Page 2 of 2 (5) The basis for proposing that the information be withheld is that NuScale treats the information as a trade secret, privileged, or as confidential commercial or financial information. NuScale relies upon the exemption from disclosure set forth in the Freedom of Information Act (FOIA), 5 USC § 552(b)(4), as well as exemptions applicable to the NRC under 10 CFR §§ 2.390(a)(4) and 9.17(a)(4). (6) Pursuant to the provisions set forth in 10 CFR § 2.390(b)(4), the following is provided for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld: (a) The information sought to be withheld is owned and has been held in confidence by NuScale. (b) The information is of a sort customarily held in confidence by NuScale and, to the best of my knowledge and belief, consistently has been held in confidence by NuScale. The procedure for approval of external release of such information typically requires review by the staff manager, project manager, chief technology officer or other equivalent authority, or the manager of the cognizant marketing function (or his delegate), for technical content, competitive effect, and determination of the accuracy of the proprietary designation. Disclosures outside NuScale are limited to regulatory bodies, customers and potential customers and their agents, suppliers, licensees, and others with a legitimate need for the information, and then only in accordance with appropriate regulatory provisions or contractual agreements to maintain confidentiality. (c) The information is being transmitted to and received by the NRC in confidence. (d) No public disclosure of the information has been made, and it is not available in public sources. All disclosures to third parties, including any required transmittals to NRC, have been made, or must be made, pursuant to regulatory provisions or contractual agreements that provide for maintenance of the information in confidence. (e) Public disclosure of the information is likely to cause substantial harm to the competitive position of NuScale, taking into account the value of the information to NuScale, the amount of effort and money expended by NuScale in developing the information, and the difficulty others would have in acquiring or duplicating the information. The information sought to be withheld is part of NuScales technology that provides NuScale with a competitive advantage over other firms in the industry. NuScale has invested significant human and financial capital in developing this technology and NuScale believes it would be difficult for others to duplicate the technology without access to the information sought to be withheld. I declare under penalty of perjury that the foregoing is true and correct. Executed on February 27, 2025. Mark W. Shaver}}