ML25009A006

LLC, Responses to NRC Request for Additional Information No. 039 (RAI-10359 R1) on the NuScale Standard Design Approval Application

ML25009A006
Person / Time
Site:	05200050, 99902078
Issue date:	01/09/2025
From:	Shaver M NuScale
To:	Office of Nuclear Reactor Regulation, Document Control Desk
Shared Package
ML25009A005	List: ML25009A006
References
RAIO-177783
Download: ML25009A006 (1)

Text

RAIO-177783 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com January 09, 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 Responses to NRC Request for Additional Information No. 039 (RAI-10359 R1) on the NuScale Standard Design Approval Application

REFERENCE:

NRC Letter to NuScale, Request for Additional Information No. 039 (RAI-10359 R1), dated October 16, 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 enclosures to this letter contain NuScale's response to the following RAI question from NRC RAI-10359 R1:

6.2.1-1 is the proprietary version of the NuScale responses to NRC RAI No. 039 (RAI-10359 R1, Question 6.2.1-1). 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.

RAIO-177783 Page 2 of 2 01/09/2025 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com If you have any questions, please contact Jim Osborn at 541-360-0693 or at josborn@nuscalepower.com.

I declare under penalty of perjury that the foregoing is true and correct. Executed on January 09, 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-10359 R1, Question 6.2.1-1, Proprietary Version : NuScale Response to NRC Request for Additional Information RAI-10359 R1, Question 6.2.1-1, Nonproprietary Version : Affidavit of Mark W. Shaver, AF-177784

RAIO-177783 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-10359 R1, Question 6.2.1-1, Proprietary Version

RAIO-177783 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-10359 R1, Question 6.2.1-1, Nonproprietary Version

Response to Request for Additional Information Docket: 052000050 RAI No.: 10359 Date of RAI Issue: 10/16/2024 NRC Question No.: 6.2.1-1 Regulatory Basis

• GDC 16, Containment Design, as it relates to the reactor containment and associated systems being designed to assure that containment design conditions important to safety are not exceeded for as long as postulated accident conditions require.

• GDC 38, Containment Heat Removal, as it relates to the containment heat removal system(s) (CHRS) function to rapidly reduce the containment pressure and temperature following any LOCA and maintain them at acceptably low levels.

• GDC 50, Containment Design Basis, as it relates to the reactor containment structure and associated heat removal system(s) being designed so that the containment structure and its internal compartments can accommodate the calculated pressure and temperature conditions resulting from any LOCA without exceeding the design leakage rate and with sufficient margin.

Issues (a) The LOCA EM LTR, Revision 3, Section 9.6.1, presents the impact of three containment vessel (CNV)-reactor pressure vessel (RPV) nodalization schemes, summarized in Table 9-7, on the NPM-20 LOCA figures of merit (FOMs) for the reactor coolant system (RCS) injection line and high point vent line breaks, with no DHRS operation credited. No nodalization sensitivity results are presented for the limiting containment design basis accident (DBA), i.e.,

RCS discharge line (DL) break. (( 2(a),(c) As opposed to US600, the US460 design relies on DHRS operation for the containment DBA mitigation, which would lead to an increasing level of CNV pressurization sensitivity to DHRS performance as the break size becomes smaller and the ECCS actuation is delayed. Therefore, NuScale Nonproprietary NuScale Nonproprietary

during the audit, the staff requested information about the containment vessel and reactor pool nodalization sensitivity and natural convection modeling assumptions for the US460 design. The staff had requested the information as the reactor pool heat up and thermal stratification could degrade the DHRS capacity as the DBA progresses, which would potentially lead to a higher CNV pressurization under delayed ECCS actuation, especially for small break LOCA. (( }} 2(a),(c). NuScale provided no information for the US460 containment and pool nodalization sensitivity to address the staff concerns about the DHRS performance degradation due to pool heat up and thermal stratification and its impact on containment pressurization accompanied by delayed ECCS actuation, especially toward the smaller break end of the spectrum. None of the information provided in the audit or available in the SDAA supports a bounding minimum DHRS capacity for the limiting containment analyses. The staff needs additional information to ensure that there is no CNV response that could potentially challenge the limiting CNV design basis event for the NPM-20 containment design. (b) During the audit, the staff also requested NuScale to provide the description and assumptions made for the reactor pool bay corresponding to an individual NPM, and the nodal implementation of the natural convection correlation on the CNV external surface. (( }} 2(a),(c) (c) The staff compared the wall condensation and interphase heat and mass transfer correlations between the LOCA EM TR, Revision 2 and Revision 3. (( }} 2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

(( }} 2(a),(c) Information Requested (a) NuScale is requested to provide the LOCA FOM results for both the CNV and reactor pool nodalization sensitivities, or demonstrate that the containment thermal-hydraulic response is not sensitive to the CNV and reactor pool nodalizations, (( }} 2(a),(c) The staff requests the analyzed containment transient results for 72 hours to ensure that the CNV pressure that is reduced to half within 24 hours would be maintained at acceptably low level (as required by GDC 38) despite the reactor pool heat up and DHRS performance degradation. (b) The staff requests a justification for the natural convection modeling of the CNV and DHRS by using an overall average heat transfer coefficient based on the surface height, for pool nodalization to be conservative with respect to the containment pressurization and DHRS capacity. Please justify this approach compared to accounting for natural convection from the CNV and DHRS to the pool driven by the local natural heat transfer coefficient for each node based on the local wall and local bulk pool temperatures. (c) (( }} 2(a),(c) NuScale Response: Executive Summary During a clarification call on October 8th, the NRC staff clarified that a sensitivity study evaluating the reactor pool at a high temperature may be used to address Item a regarding pool nodalization. The staff also indicated a high reactor pool temperature may be used to address the thermal stratification concerns raised in Item b. The reactor pool temperature sensitivity evaluates elevated pool temperatures near the decay heat removal system (DHRS) tubes to address concerns about pool thermal stratification near NuScale Nonproprietary NuScale Nonproprietary

the DHRS, and to further demonstrate that large break loss of coolant accidents (LOCAs) are more limiting with respect to peak containment pressure. The reactor pool temperature sensitivity results demonstrate that the limiting peak containment pressure response is not sensitive to reactor pool thermal stratification effects and therefore not sensitive to reactor pool nodalization. The results also demonstrate that the existing analysis results for peak containment pressure and temperature are more limiting, and thermal stratification does not prevent DHRS from performing its function to remove energy from the NuScale Power Module. The containment vessel (CNV) lower head has a minimal contribution to heat transfer to the reactor pool. The majority of heat transfer occurs due to condensation in the upper CNV shell region. Additionally, the lower CNV head represents a small fraction of the overall CNV surface area. Therefore, heat transfer from the lower CNV head to the reactor pool has a minor effect on the CNV pressure response and the specific convective heat transfer correlation used to model it is not safety significant. Items a and b Section 9.7 of the Loss-of-Coolant Accident (LOCA) Evaluation Model topical report, TR-0516-49022, Revision 3, presents sample results for the NPM-20 containment pressure response. Section 9.7.1 identifies that sensitivity analyses evaluate the effect of ((

}}2(a),(c) As described in the Request for Additional Information (RAI), the NRC staff concerns about the pool nodalization are related to thermal stratification of the reactor pool and its impact on the performance of the decay heat removal system (DHRS) prior to emergency core cooling system (ECCS) actuation, particularly for smaller breaks.

Regarding the LOCA break spectrum, Section 5.6.1 of the LOCA topical report states, ((

}}2(a),(c) To address the concerns identified in Items a and b of this RAI, and confirm the conservatism of the containment response analysis methodology as described in the LOCA topical report, NuScale performed a set of sensitivity calculations.

NuScale Nonproprietary NuScale Nonproprietary

Sensitivity Approach ((

}}2(a),(c) Therefore, the model input bounds the effects of thermal stratification that could develop around the DHRS condensers during a small LOCA event progression. (( 
}}2(a),(c)

((

}}2(a),(c)

((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

((

}}2(a),(c)

Sensitivity Results Table 1 summarizes the results of the sensitivity calculations, with results of cases performed in accordance with the methodology in Section 5.6 of the LOCA topical report. Figure 1 and Figure 2 show the peak CNV pressure results for the DL break and HPV break cases, respectively. Peak containment pressure and temperature results of the smaller break sensitivity cases are non-limiting compared to the results performed in accordance with the methodology. For the largest break sizes, differences in peak containment pressure and temperature are insignificant compared to the margin to the acceptance criteria. ((

}}2(a),(c)

NuScale performed the sensitivity calculations for sufficient time to demonstrate that, for the limiting cases the peak containment pressure, each case falls below 50 percent of peak containment pressure within one to two hours after ECCS actuation. For the larger breaks, ECCS actuation occurs in the first few minutes of the event while ECCS actuation occurs later in the smaller breaks. However, the peak pressure response to smaller breaks with delayed ECCS actuation is less than 50 percent of the peak containment pressure of the limiting breaks. ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

((

}}2(a),(c) Therefore, these sensitivity calculation results support the conclusion that the containment response analysis methodology is appropriate to evaluate the maximum containment pressure and temperature response, and demonstrate that the CNV pressure reduces to less than 50 percent of the peak within 24 hours of event initiation. The reactor pool temperature sensitivity calculations, and particularly the 100 percent HPV break case, provide additional demonstration that containment pressure will not rebound when considering the effects of pool heatup. Containment pressure remains below 50 percent of peak pressure.

NuScale Nonproprietary NuScale Nonproprietary

Table 1. Summary of Reactor Pool Temperature Sensitivity Results (( }}2(a),(c) The reactor pool temperature sensitivity is unrealistically conservative. For example, it includes the combination of:

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

(( }}2(a),(c) Sensitivity Conclusions Despite the conservatism, the results shown in Table 1 support the following conclusions: 1. Nodalization of the reactor pool has an insignificant impact on the peak containment pressure response. Nodalization of the reactor pool is bounded by this sensitivity because the initial pool temperature is set at an unrealistically high value. The largest breaks remain limiting for maximum containment pressure and temperature response, compared to smaller breaks. 2. The DHRS can perform its safety function to remove decay heat even if the reactor pool becomes thermally stratified during a small LOCA event progression. In this unrealistically conservative sensitivity, peak containment pressure and temperature are maintained within design limits. The NuScale Design Specific Review Standard (DSRS) Section 6.2.1.1.A, Containment, acceptance criterion 2 states: To satisfy the requirements of GDC 38 to rapidly reduce the containment pressure, the containment pressure should be reduced to less than 50 percent of the peak calculated pressure for the design-basis LOCA within 24 hours after the postulated accident. If analysis shows that the calculated containment pressure may not be reduced to 50 percent of the peak calculated pressure within 24 hours, the organization responsible for the review of DSRS Section 15.0.3 should be notified. The reactor pool temperature sensitivity provides additional assurance that the US460 standard design satisfies the DSRS acceptance criterion even if the reactor pool becomes thermally stratified during a small break LOCA. After ECCS actuation and after heat transfer through the CNV wall exceeds decay heat, CNV pressure decreases and remains below 50 percent of the peak value. ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) The maximum temperature long-term cooling results presented in FSAR Section 15.0 further demonstrate that CNV pressure remains below 50 percent of the peak value in the long-term. The maximum temperature cases (( }}2(a),(c) The long-term cooling maximum temperature results presented in FSAR Section 15.0 provide additional demonstration that the US460 standard design satisfies relevant provisions of GDC

38. The long-term pressure and temperature conditions are not sensitive to the initial break size or location. The long-term pressure and temperature conditions are sensitive to decay heat and the pool boundary conditions. Figure 3 shows the containment pressure response for the current NPM-20 maximum temperature case analysis. This case simulates an inadvertent ECCS actuation coincident with a loss of AC and DC power supply, with low pool level and high pool temperature boundary conditions. This case is selected for maximum temperature analysis because ((

}}2(a),(c) The containment pressure results do not show a rebound in containment pressure following peak containment pressure: 1. As shown in Figure 3, prior to 24 hours, containment pressure decreases from its peak and pressure does not rebound during the first 24 hours. In this calculation simulating the first 24 hours, (( }}2(a),(c) 2. Beyond 24 hours, containment pressure continues to decrease (( }}2(a),(c) The long-term maximum temperature case demonstrates that containment pressure rapidly decreases following peak containment pressure, and that there is no significant rebound in containment pressure during periods prior to or beyond 24 hours. This is consistent with the reactor pool temperature sensitivity results discussed above. Both analyses demonstrate that the design meets the GDC 38 requirement to rapidly reduce the CNV pressure and maintain the CNV pressure at acceptably low levels. NuScale Nonproprietary NuScale Nonproprietary

Justification of Natural Convection Modeling of the CNV and DHRS Part b of the RAI requested additional justification for the natural convection modeling of the CNV and DHRS. (( }}2(a),(c) The sensitivity cases provided in this RAI response demonstrate that the modeling approach is sufficient to account for the DHRS performance during LOCA events, considering effects of reactor pool heat up and thermal stratification. 2. (( }}2(a),(c) 3. (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) 4. (( }}2(a),(c) 5. With respect to maintaining long-term heat removal through the CNV wall, the CNV wall is relatively thick metal and Section 8.2.8 of the LOCA topical report summarizes (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

(( }}2(a),(c) 6. (( }}2(a),(c) Therefore, effects of pool heatup or uncertainty in the outside surface wall heat transfer coefficient are not significant to demonstrating adequate and sustained CNV heat transfer. NuScale Nonproprietary NuScale Nonproprietary

Figure 1 - Discharge Line Break Sensitivity Calculation Results, Containment Pressure (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 2 - High Point Vent LIne Break Sensitivity Calculation Results, Containment Pressure (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 3 - Emergency Core Cooling System Extended Passive Cooling Maximum Temperature Results, Containment Pressure NuScale Nonproprietary NuScale Nonproprietary

Figure 4 - NPM-160 CNV to Pool Heat Transfer Resistance Contribution as a function of Containment Pressure at Pool Temperature of 70 degree F (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary

Figure 5 - NPM-20 CNV to Pool Heat Transfer Resistance Contributionas a function of Containment Pressure at Pool Temperature of 65 degree F (( }}2(a),(c) Item c The NRC staff has expressed concern that NuScale applies the ((

}}2(a),(c)

NuScale Nonproprietary NuScale Nonproprietary

((

}}2(a),(c) Therefore, it is concluded that heat transfer from the lower CNV head to the reactor pool has a minor effect on the CNV pressure response and (( 
}}2(a),(c) is not safety-significant.

NuScales response to audit item A-6.2.1-8 provides background and historical information on the utilization of the Churchill-Chu correlation. Impact on US460 SDAA: There are no impacts to US460 SDAA as a result of this response. NuScale Nonproprietary NuScale Nonproprietary

RAIO-177783 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-177784

AF-177784 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. 10359 R1, Question 6.2.1-1) 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 10359 R1, Question 6.2.1-1. 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-177784 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 09, 2025. Mark W. Shaver}}