ML25008A172

LLC Response to NRC Request for Additional Information No. 033 (RAI-10298 R1) on the NuScale Standard Design Approval Application

ML25008A172
Person / Time
Site:	99902078, 05200050
Issue date:	01/08/2025
From:	Shaver M NuScale
To:	Office of Nuclear Reactor Regulation, Document Control Desk
Shared Package
ML25008A171	List: ML25008A172
References
RAIO-177982
Download: ML25008A172 (1)

Text

RAIO-177982 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com January 08, 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. 033 (RAI-10298 R1) on the NuScale Standard Design Approval Application

REFERENCE:

NRC Letter to NuScale, Request for Additional Information No. 033 (RAI-10298 R1), dated October 31, 2024 The purpose of this letter is to provide the NuScale Power, LLC (NuScale) responses to the referenced NRC Request for Additional Information (RAI).

The enclosures to this letter contain the NuScale responses to the following RAI questions from NRC RAI-10298 R1:

XPC.LTR-1 XPC.LTR-18 XPC.LTR-28 Enclosures 1, 3, and 5 are the proprietary version of the NuScale Responses to NRC RAI No. 033 (RAI-10298 R1, Questions XPC.LTR.1, XPC.LTR-18, and XPC.LTR-28). NuScale requests that the proprietary versions be withheld from public disclosure in accordance with the requirements of 10 CFR § 2.390. Enclosure 5 has also been determined to contain Export Controlled Information. This information must be protected from disclosure per the requirement of 10 CFR § 810. The enclosed affidavit (Enclosure 7) supports this request., 4, and 6 are the nonproprietary version of the NuScale responses.

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.

RAIO-177982 Page 2 of 2 01/08/2025 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com I declare under penalty of perjury that the foregoing is true and correct. Executed on January 08, 2025.

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

Mahmoud Jardaneh, Chief New Reactor Licensing Branch, NRC Getachew Tesfaye, Senior Project Manager, NRC : NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR.1, Proprietary Version : NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR.1, Nonproprietary Version : NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR-18, Proprietary Version : NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR-18, Nonproprietary Version : NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR-28, Proprietary Version : NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR-28, Nonproprietary Version : Affidavit of Mark W. Shaver, AF-177983

RAIO-177982 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-10298 R1, Question XPC.LTR.1, Proprietary Version

RAIO-177982 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-10298 R1, Question XPC.LTR.1, Nonproprietary Version

Response to Request for Additional Information Docket: 052000050 RAI No.: 10298 Date of RAI Issue: 10/31/2024 NRC Question No.: XPC.LTR-1 Issue The TR-124587 methodology is missing key information related to testing and validation for the NRELAP5 code for the staff to make a finding of acceptability of the Evaluation Model.

Specifically, the topical report is missing:

a) A demonstration of how the effects of both the SG and DHRS being in operation, after ECCS is actuated, are adequately addressed for the duration of the long-term events, up to the full 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. There is no testing presented in the topical report to validate the models for events where the SG and DHRS are in operation for the long-term (72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />) after ECCS actuation. The uncertainty introduced by this unaddressed phenomenon has not been quantified, nor has it been shown how the uncertainty has been adequately addressed/included in the NRELAP5 analyses that use the topical report methodology.

b) Validation of the coarse ECCS long term cooling (LTC) model utilized for LTC calculations against LTC tests. (( 2(a),(c) The coarse ECCS LTC model needs an adequate validation basis for the parameters important to LTC calculations over a range of LTC conditions. The topical report figure 5-15 shows a comparison of the riser collapsed liquid level between the LOCA topical report model and the LTC coarse model. ((

}}

2(a),(c) Given that the limiting LTC event results show that the level above the top of active fuel (TAF) is small, the modeling uncertainty introduced by the coarse integral LTC topical report model needs to be addressed as part of the NuScale Nonproprietary NuScale Nonproprietary

validation of the model. The integrated model is highly sensitive to the coarse nodalization and should be accounted for in the uncertainty within the methodology in order to validate the model used for LTC calculations for figures of merit. Information Requested a) In the absence of test data, provide an evaluation that contains sensitivity analyses over various conditions of NRELAP5 and independent calculations to demonstrate that the system heat transfer behavior is similar to a first principles simplified conceptual model that evaluates the various heat transfer coefficients (slowly varying steady state heat removal) and that quantifies the sensitivity to the multiple heat transfer coefficients over a broad range. Provide sensitivity analyses over various conditions that quantify the sensitivity to the multiple heat transfer coefficients for the integrated NPM 20 response for long term cooling figures of merit. Alternately, provide additional sensitivity calculations that show progressively higher and lower sensitives to the heat transfer coefficient values for the minimum level case, maximum temperature case, minimum temperature case, and the boron transport thermal hydraulic cases. The results should either show that the responses are relatively insensitive over an extremely large range, or the uncertainty should be accounted for in the methodology results. Revise the topical report to include the results and summary. b) The nodalization has a noticeable impact on the calculation results for the LTC and adds uncertainty/bias that needs to be accounted for in the methodology for the validation. Provide the validation of the integrated coarse ECCS long term cooling model utilized for LTC calculations that accounts for the introduced bias/uncertainty due to the nodalization. The validation basis that accounts for the nodalization impacts for the coarse ECCS LTC model needs to have an adequate validation basis for the parameters important to LTC calculations over a range of LTC conditions including various different event types (LOCA and non-LOCA cases). If a sufficient validation basis that accounts for the introduced bias/uncertainty due to nodalization is not available, then develop and propose an appropriate penalty as part of the LTR. If updates to the methodology are made, revise the topical report and affected SDAA sections. NuScale Nonproprietary NuScale Nonproprietary

NuScale Response: NuScales response to audit question A-XPC.LTR-01 addresses this request for additional information. The original audit response was posted to the electronic reading room on April 21, 2023 and is provided below. NuScale voluntarily supplemented the original audit response and posted the supplemented audit response on March 14, 2024. The content of the March 14, 2024 response is included below within the section titled Response Supplement for Item b (March 14, 2024). NuScale posted a subsequent supplemented audit response on June 27, 2024 to address NRC feedback. The content of the June 27, 2024 response is included below within the section titled NuScale Response to NRC Feedback. On September 17, 2024, NuScale received additional feedback from the NRC on NuScales original and supplemental audit responses. NuScales response to the additional NRC feedback is presented at the end of the response, starting with the section labeled NuScale Response to Additional NRC Feedback. Original Response to Item a TR-124587-P, Revision 0, Extended Passive Cooling and Reactivity Control Methodology, Section 4.4.3.24, Steam Generator Shell-Side Heat Transfer, discusses steam generator (SG) shell side heat transfer. (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) Sensitivities are performed to vary the SG condensation heat transfer coefficient and evaluate the effect on total effective heat transfer coefficient, or total heat transfer capacity. The scope of sensitivity cases is shown in Table 1, Summary of Heat Transfer Resistance Sensitivity Calculation Ranges Evaluation, below. Table 1: Summary of Heat Transfer Resistance Sensitivity Calculation Ranges Evaluated (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Results of the Case 3 sensitivity calculations are shown in Figure 1, Effect of Varying Steam Generator Condensation Heat Transfer Coefficient on Total Thermal Resistance Fraction, and in Figure 2, Effect of Varying Steam Generator Condensation Heat Transfer Coefficient from Nominal Calculated, on Total Thermal Resistance Fraction of this response. ((

}}2(a),(c)

Based on the thermal resistance evaluation, the bottom-up assessment in TR-124587-P concluded that the NRELAP5 nominal model results for condensation heat transfer on the steam generator shell side are adequate for use in the extended emergency core cooling system (ECCS) and DHRS calculations. With respect to the DHRS heat transfer conditions, after energy is transferred from the shell side through the steam generator tubes to the inside, the DHRS response is independent of whether the shell-side heat transfer was due to liquid convection or vapor condensation. Therefore, DHRS heat transfer during long-term cooling (LTC) is evaluated as follows. TR-124587-P Section 4.4.3.26, DHRS Heat Transfer, discusses DHRS heat transfer during LTC. ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

((

}}2(a),(c)

TR-124587-P Table 4-17, Top-Down Assessment for Extended ECCS Phenomena, summarizes the top-down assessment for SG/DHRS operation during extended ECCS cooling. Considering the first-principles analysis of heat transfer resistances, the boiling/condensing heat transfer mechanism, and NRELAP5 validation bases for long-term ECCS heat transfer and SG/DHRS heat removal, it is concluded that the overall EM capability is adequate. NuScale Nonproprietary NuScale Nonproprietary

Figure 1: Effect of Varying Steam Generator Condensation Heat Transfer Coefficient on Total Thermal Resistance Fraction (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 2: Effect of Varying Steam Generator Condensation Heat Transfer Coefficient from Nominal Calculated, on Total Thermal Resistance Fraction (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Table 2: (( }}2(a),(c) Evaluated Range of Decay Heat Removal System Pressure, Flow Rate (( }}2(a),(c) Original Response to Item b The ECCS long-term cooling model uses coarser nodalization compared to the models used for short-term non-LOCA or LOCA analyses in order to improve computational time. TR-124587-P Figure 5-11, Long-Term Cooling Model Nodalization Diagram, provides a noding diagram of the LTC model. This model applies nodalization similar to that used in the US600 Design Certification Application (DCA) long-term ECCS cooling analyses. As identified in the NRC-approved TR-0916-51299-P, Long-Term Cooling Methodology, Revision 3, the DCA long-term cooling model was derived from the coarser nodalized LOCA model, described in TR-0516-49422, Loss-of-Coolant Accident Evaluation Model, Revision 2, Section 9.6.1, Model Nodalization. The coarser model was selected to improve calculation performance over the NuScale Nonproprietary NuScale Nonproprietary

long-term, quasi-steady-state conditions where the fidelity of the finer model nodalization is not required. The NPM comparison results shown in TR-0516-49422 Section 9.6.1, TR-0916-51299 Section 4.3, Loss-of-Coolant Accident / Long-Term Cooling Consistency Evaluation, and TR-124587-P Section 5.2.2, Comparison of Simplified and Detailed Model Performance, give comparable results for the system level parameters such as reactor pressure vessel (RPV) and CNV pressure and level of interest during extended ECCS operation. More broadly, the adequacy of the NRELAP5 long-term cooling model used for the DCA is evaluated in TR-0916-51299 Revision 3, Sections 4.2, NRELAP5 Validation and Assessments for Long-Term Cooling, and Section 4.3 and associated NRC final safety evaluation report, 15 Transient and Accident Analysis, (ADAMS Accession No. ML20205L408), Section 15.6.5.2.4.1, Evaluation Model. In those evaluations, the approach to demonstrate LTC model adequacy uses (( }}2(a),(c) Similar to this approach, the adequacy of the NRELAP5 long-term cooling model used for the NuScale US460 standard design approval application is evaluated in TR-124587-P, Revision 0, Section 4.2, NLRELAP5 Assessment Basis for Extended Passive Cooling, and Section 5.2, NRELAP5 Models for Extended Passive Cooling. This evaluation uses (( }}2(a),(c) As described in TR-124587-P, the NRELAP5 long-term cooling model is demonstrated to be adequate using:

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

(( }}2(a),(c) Given the NRELAP5 code validation results and adequacy evaluations described above, the ECCS long-term cooling model has an adequate validation basis for the parameters important to LTC calculations over a range of LTC conditions. NuScale Nonproprietary NuScale Nonproprietary

Response Supplement for Item b (March 14, 2024) To further assess the adequacy of the coarser-nodalized NRELAP5 long term cooling model used in TR-124587-P, Revision 0, ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

Table 3: Major Sequence of Events (Liquid Space Break) (( }}2(a),(c) During the analyzed LTC phase, the base model versus coarse model FOM results are nearly indistinguishable. Table 4, Minimum and Maximum of Key Figures of Merit (Liquid Space Break) of this response compares the minimum and maximum values of key FOMs between the NIST-2 base and coarse NRELAP5 models. Figures 3 through 8 below show the RPV and CNV pressure and level comparisons. Table 4: Minimum and Maximum of Key Figures of Merit (Liquid Space Break) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 3: Liquid Space Break - Reactor Pressure Vessel and Containment Vessel System Pressure Comparisons (Full Duration) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 4: Liquid Space Break - Reactor Pressure Vessel and Containment Vessel System Pressure Comparisons (First 2000 Seconds) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 5: Liquid Space Break - Reactor Pressure Vessel Downcomer Collapsed Level (Full Duration) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 6: Liquid Space Break - Reactor Pressure Vessel Downcomer Collapsed Level (First 2000 Seconds) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 7: Liquid Space Break - Containment Vessel Collapsed Level (Full Duration) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 8: Liquid Space Break - Containment Vessel Collapsed Level (First 2000 Seconds) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

For the steam space break, transient results for the major sequence of events in Table 5, Major Sequence of Events (Steam Space Break), of this response show the sequence timings match well, with the coarse model indicating flow reversal (i.e., beginning of LOCA Phase 2) about 7 seconds after the base case. Table 5: Major Sequence of Events (Steam Space Break) Event NRELAP5 Base [s] NRELAP5 Coarse [s] t(Coarse-Base) [s] (( }}2(a),(c) During the analyzed LTC phase, the base model versus coarse model FOM results are nearly indistinguishable. Table 6, Minimum and Maximum of Figures of Merit (Steam Space Break), of this response compares the minimum and maximum values of key FOMs between the NIST-2 base and coarse NRELAP5 models. Figures 9 through 14 show the RPV and CNV pressure and level comparisons. Table 6: Minimum and Maximum of Figures of Merit (Steam Space Break) Parameter NRELAP5 Base NRELAP5 Coarse Parameter (Coarse-Base) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 9: Steam Space Break - Reactor Pressure Vessel and Containment Vessel System Pressure Comparisons (Full Duration) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 10: Steam Space Break - Reactor Pressure Vessel and Containment Vessel System Pressure Comparisons (First 2000 Seconds) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 11: Steam Space Break - Reactor Pressure Vessel Downcomer Collapsed Level (Full Duration) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 12: Steam Space Break - Reactor Pressure Vessel Downcomer Collapsed Level (First 2000 Seconds) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 13: Steam Space Break - Containment Vessel Collapsed Level (Full Duration) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 14: Steam Space Break - Containment Vessel Collapsed Level (First 2000 Seconds) (( }}2(a),(c) In addition to the sequence of events and FOMs compared above, (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

NuScale Response to NRC Feedback On April 19, 2024, NuScale received written feedback from the NRC. The text of the NRC feedback is in italicized text, followed by NuScales response to the feedback. NRC Feedback on Item a The response did not provide the requested information. The audit item requested validation of the models for events where the SG and DHRS are in operation for the long-term (72 hours) after ECCS actuation. Instead NuScale provided results from ((

}}2(a),(c)

However, the staffs question was asked irrespective of whether or not other heat transfer mechanisms were potentially more significant. ((

}}2(a),(c) and therefore may not represent how the topical report NRELAP model is validated with respect to the calculation of the NPM 20 design response.

Given that the conditions and phenomena when the SGs are uncovered are unknown (no test data), it is unknown how the topical report NRELAP model (of the SG design) will respond with respect to the integrated NPM 20 design response including, but not limited to, heat transfer to the tubes (for example, but not limited to, condensation on the top SG tubes leading to unknown liquid layers on the mid to bottom sections of the SG tubes and other heat transfer mechanisms). In the absence of test data, the staff would have expected the evaluation to contain ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) The uncertainty introduced by this unaddressed phenomenon has not been quantified nor has it been shown how the uncertainty has been adequately addressed/included in the NRELAP analyses that use the topical report methodology. Topical markups are missing this information. Provide LTR markups as originally requested. NuScale Response to Feedback on Item a As described in NuScales audit response posted to the TR-124587 Audit electronic reading room on April 21, 2023, A-XPC.LTR-01 Audit Response, the XPC evaluation model adequately addresses the effects of extended DHRS operation after ECCS is actuated. Validation bases for NRELAP5 models of long-term ECCS heat transfer and SG/DHRS heat removal support the adequacy of the XPC evaluation model without additional testing. This conclusion is based on the following points.

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

(( }}2(a),(c) Based on NRC feedback provided to NuScale on April 19, 2024, NRELAP5 sensitivity analysis is provided with this response to further support this conclusion. During DHRS operation before ECCS actuation, there is primary liquid flow and convective heat transfer on the shell side of the SG tubes. During DHRS operation after ECCS actuation, there is vapor flow and condensation heat transfer on the shell side of the SG tubes because RCS level decreases below the SG tubes as a result of ECCS actuation. ((

}}2(a),(c) has a negligible impact on minimum riser collapsed liquid level (CLL) above top of active fuel (TAF), CNV pressure, and moderator temperature.

NuScale Nonproprietary NuScale Nonproprietary

Table 7: NRELAP5 Sensitivity Results (( }}2(a),(c) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 15: NRELAP5 Sensitivity for Steam Generator Shell-Side Heat Transfer Coefficient - Containment Vessel Pressure (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 16: NRELAP5 Sensitivity for Steam Generator Shell-Side Heat Transfer Coefficient - Moderator Temperature (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 17: NRELAP5 Sensitivity for Steam Generator Shell-Side Heat Transfer Coefficient - Riser Collapsed Liquid Level above Top of Active Fuel (( }}2(a),(c) ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

((

}}2(a),(c)

The NRELAP5 sensitivity results described above further support the conclusion that the XPC evaluation model adequately addresses the effects of extended DHRS operation after ECCS is actuated. Validation bases for NRELAP5 models of long-term ECCS heat transfer and SG/DHRS heat removal support the adequacy of the XPC evaluation model. A markup of Section 4.4.3.24 of TR-124587-P is included with this response to include the justification provided by the NRELAP5 sensitivity analysis. NRC Feedback on Item b The response did not provide the requested information. The audit item requested validation of the coarse ECCS long term cooling model utilized for LTC calculations against long term cooling tests and adequate validation basis for the parameters important to LTC calculations over a range of LTC conditions. The original NuScale audit question response stated ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

Topical Report markups are missing that contain this information. Provide LTR markups as originally requested. NuScale Response to Feedback on Item b NuScale understands the feedback in the second paragraph of this response refers to ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

((

}}2(a),(c) to demonstrate the minimum level acceptance criterion is met. Markups to TR-124587 are provided with this response.

NuScale Response to Additional NRC Feedback During an audit meeting on September 17, 2024, NRC staff provided additional feedback on part a of this audit question. This revised audit response addresses the feedback by ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) The results of the expanded NRELAP5 sensitivity analysis further support the conclusion that the XPC evaluation model adequately addresses the effects of extended DHRS operation after ECCS is actuated. Validation bases for NRELAP5 models of long-term ECCS heat transfer and SG/DHRS heat removal support the adequacy of the XPC evaluation model. An updated markup of Section 4.4.3.24 of TR-124587-P is included with this response to include the justification provided by the expanded NRELAP5 sensitivity analysis. Table 8: Expanded NRELAP5 Sensitivity Results (( }}2(a),(c) (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 18: Expanded NRELAP5 Sensitivity for Steam Generator Shell-Side Heat Transfer Coefficient - Containment Vessel Pressure (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 19: Expanded NRELAP5 Sensitivity for Steam Generator Shell-Side Heat Transfer Coefficient - Moderator Temperature (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 20: Expanded NRELAP5 Sensitivity for Steam Generator Shell-Side Heat Transfer Coefficient - Riser Collapsed Liquid Level above Top of Active Fuel (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 21: Expanded NRELAP5 Sensitivity for Steam Generator Shell-Side Heat Transfer Coefficient - Integral Heat Removal from the Decay Heat Removal System (( }}2(a),(c) Impact on Topical Report: Topical Report TR-124587, Extended Passive Cooling and Reactivity Control Methodology, has been revised as described in the response above and as shown in the markup provided in this response. NuScale Nonproprietary NuScale Nonproprietary

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 133 4.4.3.24 Steam Generator Shell-Side Heat Transfer (( Audit Question A-XPC.LTR-1 }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 188 5.2 NRELAP5 Models for Extended Passive Cooling Audit Question A-XPC.LTR-1 The NRELAP5 XPC model input file is developed based on engineering drawings, calculations, and reference documents. These sources of information provide the numerical information necessary to develop a complete thermal-hydraulic simulation model of the NPM. For extended ECCS operation, the NPM model is adapted from the detailed NRELAP5 model as described in Section 5.2.1. Section 5.2.2 provides representative comparison results of the more detailed model developed for short-term LOCA calculations, and coarser model long-term ECCS model, to demonstrate that the coarser model is adequate for use in the boron transport methodologies described in Section 6.0 and Section 7.0, and for use in identifying potentially limiting minimum level transient cases. Cases identified as potentially limiting for minimum collapsed liquid level in the RPV riser are evaluated using the more detailed LOCA model to demonstrate the minimum level acceptance criterion is met. Figure 5-10 Representative Behavior of RCS Fluid Temperatures with Extended DHRS Operation and Riser Uncovery (( }}2(a),(c)

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 196 (( Audit Question A-XPC.LTR-1 Audit Question A-XPC.LTR-1 }}2(a),(c)

RAIO-177982 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-10298 R1, Question XPC.LTR-18, Proprietary Version

RAIO-177982 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-10298 R1, Question XPC.LTR-18, Nonproprietary Version

Response to Request for Additional Information Docket: 052000050 RAI No.: 10298 Date of RAI Issue: 10/31/2024 NRC Question No.: XPC.LTR-18 Issue During its audit (ML23067A300), the staff observed ((

}}

2(a),(c) Information Requested Provide basis information for whether the NRELAP5 SG-DHRS NPM nodalization in the long-term cooling phase ((

}}

2(a),(c) The staff also needs to understand the influence of thermal hydraulic boundary conditions on the DHRS performance, e.g., ECCS operation, riser uncovery and cooling pool heat-up. Provide supporting information that shows NuScale Nonproprietary NuScale Nonproprietary

whether (( }} 2(a),(c) Provide additional bases for the validation adequacy given that the information provided does not show good agreement for comparisons to test data response and phenomena (( }} 2(a),(c) oscillation phenomena that has been seen in the tests which is not in good agreement. Revise the XPC LTR to include the basis and justification information. NuScale Response: NuScales response to audit question A-NonLOCA.LTR-21 concludes: ... the cause of oscillations in ((

}}2(a),(c) do not have significant impact on DHRS heat transfer capacity.

The NRC provided written clarification of this audit question (i.e., A-XPC.LTR-18) on July 25, 2024. The audit question refers to concern about new oscillation phenomena ((

}}2(a),(c) and the written clarification refers to an unknown phenomenon. The audit question and clarification appear to not account for the extensive information previously provided by NuScale in the RSI-15 response, in audit responses, in the decay heat removal system (DHRS) deep dive, and in NuScale engineering work made available for audit in the electronic reading room that discuss phenomena observed from the NIST-2 Run 2 data. The measured test data indicates that (( 
}}2(a),(c)

These are known phenomena. NuScale has demonstrated in ((

}}2(a),(c) that condensate flow oscillations do not have a significant impact on DHRS heat transfer capacity. These results are consistent with understanding of the known NuScale Nonproprietary NuScale Nonproprietary

phenomena that drive heat removal in a closed loop isolation condenser. The conclusion is supported by information provided in NuScales responses to A-NonLOCA.LTR-21, A-NonLOCA.LTR-9, and RSI-15, including several engineering documents referenced in those responses. Given this conclusion and supporting information provided in previous responses, no additional information is provided in response to this request for additional information. Impact on Topical Report: There are no impacts to Topical Report TR-124587, Extended Passive Cooling and Reactivity Control Methodology, as a result of this response. NuScale Nonproprietary NuScale Nonproprietary

RAIO-177982 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-10298 R1, Question XPC.LTR-28, Proprietary Version

RAIO-177982 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-10298 R1, Question XPC.LTR-28, Nonproprietary Version

Response to Request for Additional Information Docket: 052000050 RAI No.: 10298 Date of RAI Issue: 10/31/2024 NRC Question No.: XPC.LTR-28 Issue XPC LTR Section 4.2.4 states that NRELAP5 ((

}}

2(a),(c) XPC LTR Section 4.2.3.5 states that ((

}}

2(a),(c) The staff notes that the methodology ((

}}

2(a),(c) does not support a finding that analysis assumptions compensate for code biases and uncertainties or are conservative. ((

}}

2(a),(c) As such, NRC staff does not have justification or basis to support the conclusion that using the topical report evaluation model adequately compensates for the differences between the data and the NRELAP5 results. NuScale Nonproprietary NuScale Nonproprietary

It is unclear to the staff how (( }} 2(a),(c) compensate and are conservative relative to code biases and uncertainties assessed through NIST-2 code-to-data comparisons. Information Requested Explicitly describe the XPC NRELAP5 pool modeling requirements and conservatisms used in the methodology. Provide justification and bases sufficient to demonstrate that conservative pool modeling ensures that the pool boundary conditions compensate and are conservative relative to code biases and uncertainties assessed through NIST-2 code-to-data comparisons and studies quantifying NRELAP5 sensitivity to uncertainties in NIST-2 conditions. Revise the XPC LTR to include the basis and justification. NuScale Response: Summary TR-124587-P, Extended Passive Cooling and Reactivity Control Methodology, Revision 0 describes reactor pool modeling requirements and conservatisms in Section 5.4, Initial Conditions and Biases. Pool level and temperature ((

}}2(a),(c) A markup of TR-124587 was provided during the audit, and is included with this response, to clarify this conservative modeling approach.

NuScale Nonproprietary NuScale Nonproprietary

In response to this request for additional information, an additional NRELAP5 sensitivity analysis was performed on a previously-evaluated NIST-2 test. This sensitivity analysis quantitatively demonstrates the conservatism introduced by the reactor pool modeling approach specified in TR-124587-P. The sensitivity cases ((

}}2(a),(c) Therefore, the sensitivity results demonstrate conservatism in the reactor pool modeling approach specified in the extended passive cooling and reactivity control methodology topical report.

Details of the Sensitivity Analysis The NRELAP5 sensitivity calculations model Run 1 of the NIST-2 loss-of-coolant accident test ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) The plots are labeled with the prefixes shown in Table 1, Sensitivity Plot Prefixes and Descriptions, below. Table 1: Sensitivity Plot Prefixes and Descriptions Prefix Description (( }}2(a),(c) ((

}}2(a),(c) This behavior is consistent with expectations.

The sensitivity calculation results show ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

NRELAP5 will predict conservatively low system pressures, and therefore conservatively predict minimum RPV level. In contrast, (( }}2(a),(c) NRELAP5 will predict conservatively high system pressures. NuScale Nonproprietary NuScale Nonproprietary

Figure 1: Cooling Pool Conditions Sensitivity - Pressurizer Pressure (0 to 10,000 sec) (( }}2(a),(b),(c),ECI NuScale Nonproprietary NuScale Nonproprietary

Figure 2: Cooling Pool Conditions Sensitivity - Pressurizer Pressure (10,000 to 80,000 sec) (( }}2(a),(b),(c),ECI NuScale Nonproprietary NuScale Nonproprietary

Figure 3: Cooling Pool Conditions Sensitivity - Reactor Pressure Vessel Level (( }}2(a),(b),(c),ECI NuScale Nonproprietary NuScale Nonproprietary

Figure 4: Cooling Pool Conditions Sensitivity - Containment Vessel Pressure (0 to 10000 sec) (( }}2(a),(b),(c),ECI NuScale Nonproprietary NuScale Nonproprietary

Figure 5: Cooling Pool Conditions Sensitivity - Containment Vessel Pressure (10000 to 80000 sec) (( }}2(a),(b),(c),ECI NuScale Nonproprietary NuScale Nonproprietary

Figure 6: Cooling Pool Conditions Sensitivity - Containment Vessel Level (( }}2(a),(b),(c),ECI NuScale Nonproprietary NuScale Nonproprietary

Figure 7: Cooling Pool Conditions Sensitivity - Cooling Pool Vessel Liquid Temperature (( }}2(a),(b),(c),ECI NuScale Nonproprietary NuScale Nonproprietary

Figure 8: Cooling Pool Conditions Sensitivity - Cooling Pool Vessel Level (( }}2(a),(b),(c),ECI Impact on Topical Report: Topical Report TR-124587, Extended Passive Cooling and Reactivity Control Methodology, has been revised as described in the response above and as shown in the markup provided in this response. NuScale Nonproprietary NuScale Nonproprietary

Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 148 4.4.3.42 3D Flow, Mixing in Reactor Pool (( Audit Question A-XPC.LTR-28 }}2(a),(c) 4.4.4 EM Top-Down Assessment 4.4.4.1 NRELAP5 Top-Down Assessment for Extended ECCS Cooling Phenomena The first portion of the top-down assessment is focused on NRELAP5 prediction of extended ECCS cooling thermal-hydraulic phenomena. As the system analysis code, in the EM the calculation results are used to demonstrate margin in collapsed liquid level above the core and sustained decay heat removal. The code calculation results provide boundary condition input for boron transport analysis and subcriticality analysis. A summary of the NRELAP5 code governing equations and numerics is provided in the LOCA topical report (Reference 10.2.1) Section 6 and Section 8.3.

RAIO-177982 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-177983

AF-177983 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 Responses to NRC Request for Additional Information (RAI No. 10298 R1, Questions XPC.LTR.1, XPC.LTR-18, and XPC.LTR-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 responses to NRC Request for Additional Information RAI 10298 R1, Questions XPC.LTR.1, XPC.LTR-18, and XPC.LTR-28. The enclosures contain 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-177983 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 January 08, 2025. Mark W. Shaver}}