ML25021A217
| ML25021A217 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 01/21/2025 |
| From: | Shaver M NuScale |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| Shared Package | |
| ML25021A216 | List: |
| References | |
| RAIO-177641 | |
| Download: ML25021A217 (1) | |
Text
RAIO-177641 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com January 21, 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. 037 (RAI-10357 R1) on the NuScale Standard Design Approval Application
REFERENCE:
NRC Letter to NuScale, Request for Additional Information No. 037 (RAI-10357 R1), dated October 17, 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 contains the NuScale response to the following RAI question from NRC RAI-10357 R1:
15.0.5-5 is the proprietary version of the NuScale Response to NRC RAI No. 037 (RAI-10357 R1, Question 15.0.5-5). 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 January 21, 2025.
Sincerely, Mark W. Shaver Director, Regulatory Affairs NuScale Power, LLC
RAIO-177641 Page 2 of 2 01/21/2025 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-10357 R1, Question 15.0.5-5, Proprietary Version : NuScale Response to NRC Request for Additional Information RAI-10357 R1, Question 15.0.5-5, Nonproprietary Version : Affidavit of Mark W. Shaver, AF-177642
RAIO-177641 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-10357 R1, Question 15.0.5-5, Proprietary Version
RAIO-177641 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-10357 R1, Question 15.0.5-5, Nonproprietary Version
Response to Request for Additional Information Docket: 052000050 RAI No.: 10357 Date of RAI Issue: 10/17/2024 NRC Question No.: 15.0.5-5 Issue FSAR Section 15.0.5 is missing a summary and results of evaluations for extended DHRS cooling up to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> (prior to ECCS actuation) that demonstrate subcriticality is maintained (1) at EOC conditions, (2) and over a range of powers. In addition, the evaluations need to consider boron transport when the upper riser holes are uncovered. The moderator temperature during extended DHRS cooling (without ECCS actuation) can fall below the temperature used for shutdown margin, meaning that the SDM calculations do not ensure subcriticality with the highest worth CRA fully withdrawn A key aspect of demonstrating subcriticality before ECCS actuation is that the boron concentration in the downcomer remains above the critical boron concentration when boron redistribution effects are maximized. In addition, subcriticality needs to be demonstrated for conditions where boron redistribution effects are less important and moderator temperature effects are maximized.
Information Requested Revise FSAR Section 15.0.5 to include a summary of evaluations for extended DHRS cooling up to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> (prior to ECCS actuation) sufficient to demonstrate subcriticality in the scenarios described above.
NuScale Response:
As previously described in NuScales responses to audit questions A-XPC.LTR-32 and A-15.0.5-5, TR-124587, Revision 0, Extended Passive Cooling and Reactivity Control Methodology (including associated audit response markups) and FSAR Section 15.0.5, Extended Passive Cooling for Decay and Residual Heat Removal, address the scenarios NuScale Nonproprietary NuScale Nonproprietary
described in this request for additional information (RAI) question. Responses to the specific NRC statements and requests in this RAI question are provided by first identifying the NRC statement or request in indented, italicized text, followed by the NuScale response in un-indented, regular text.
FSAR Section 15.0.5 is missing a summary and results of evaluations for extended DHRS cooling up to 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> (prior to ECCS actuation) that demonstrate subcriticality is maintained (1) at EOC conditions, (2) and over a range of powers.
Criticality analyses at end of cycle for the most limiting cooldown effects of decay heat removal system (DHRS) cooling are bounded by ((2(a),(c) Limiting events that transition from DHRS to ECCS cooling at 8 hours are presented in final safety analysis report (FSAR) Section 15.0.5.3.1. These events are analyzed at the end of cycle (EOC) from 100 percent power conditions. ((
}}2(a),(c) is evaluated in the analysis of these events, as described in Section 2.2.11 of EC-132087, Revision 0, NPM-20 Boron Transport Analysis. The initial power for the limiting case is provided in FSAR Table 15.0-22. (( }}2(a),(c) The response to RAI XPC.LTR-6 provides the methodology for quantitative analysis of events with reduced power histories before the event. The analysis of events that transition from DHRS to ECCS cooling at 8 hours demonstrate that subcriticality is maintained, with the highest worth control rod stuck out, without additional boron during the 8-hour DHRS cooling period because the effects of xenon result in excess negative reactivity during this time. These results are shown in FSAR Figure 15.0-7, Boron Transport Analysis Concentrations - High Point Vent Lines Break Case, and FSAR Figure 15.0-9, Boron Transport Analysis Concentrations - Reactor Component Cooling Water Line Break Case. As shown in FSAR Table 15.0-22, these calculations are performed assuming low-biased decay heat and cold-biased pool temperature conditions to maximize cooldown conditions during the 8 hours of DHRS operation. Therefore, FSAR Section 15.0.5 provides a summary and results of evaluations for extended DHRS cooling up to 8 hours (prior to ECCS actuation) that demonstrate subcriticality is maintained at an EOC condition. (( }}2(a),(c)
NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c) In addition, the evaluations need to consider boron transport when the upper riser holes are uncovered. As described in FSAR Section 15.0.5.2.1, Riser Flow Characteristics, the upper riser hole flow paths are designed so that at least one elevation of upper riser flow paths remains covered by fluid in the riser during extended DHRS operation. Therefore, contrary to the assertion in the RAI question, the evaluations of subcriticality during DHRS cooling do not need to consider boron transport when all upper riser holes are uncovered because the design of the NuScale Power Module precludes this scenario. The moderator temperature during extended DHRS cooling (without ECCS actuation) can fall below the temperature used for shutdown margin, meaning that the SDM calculations do not ensure subcriticality with the highest worth CRA fully withdrawn As previously described in NuScales response to audit question A-15.0.5-5, the evaluations and results described above demonstrate the subcriticality acceptance criterion of the extended passive cooling and reactivity control methodology are met with the highest worth control rod assembly fully withdrawn. These evaluations are performed separate from, and have different acceptance criteria than, the shutdown margin calculations referred to in the RAI question. A key aspect of demonstrating subcriticality before ECCS actuation is that the boron concentration in the downcomer remains above the critical boron concentration when boron redistribution effects are maximized. In addition, subcriticality needs to be demonstrated for conditions where boron redistribution effects are less important and moderator temperature effects are maximized. Boron concentration in the downcomer before ECCS actuation is addressed in FSAR Section 15.0.5.2.2. Specifically, this section states, in part: The upper riser flow paths provide borated water from the riser to mix with the condensate in the downcomer. Calculations demonstrate that primary coolant flow through the riser flow paths exceeds condensation generation and the downcomer concentration remains higher than the critical concentration. The downcomer concentration remains above the critical concentration prior to ECCS actuation, including NuScale Nonproprietary NuScale Nonproprietary
accounting for the highest-worth control rod assembly stuck out of the core. Whether the module remains on DHRS cooling or ECCS actuates, the core remains subcritical. Therefore, the criteria for extended passive cooling for 72 hours with DHRS are met. Subcriticality is also demonstrated for conditions where boron distribution effects are less important (i.e., end of cycle) and moderator temperature effects are maximized. This demonstration is provided in FSAR Figure 15.0-7, Figure 15.0-9, and the corresponding descriptions in FSAR Section 15.0.5.3.1. Revise FSAR Section 15.0.5 to include a summary of evaluations for extended DHRS cooling up to 8 hours (prior to ECCS actuation) sufficient to demonstrate subcriticality in the scenarios described above. As described above, FSAR Section 15.0.5 includes summaries of evaluations for extended DHRS cooling up to 8 hours (prior to ECCS actuation) to demonstrate subcriticality in the scenarios described in the RAI question.
Boron concentration in the downcomer before ECCS actuation is addressed in FSAR Section 15.0.5.2.2. A markup to the FSAR is included with this response to clarify the conditions evaluated for this scenario.
Subcriticality is demonstrated for conditions where boron distribution effects are less important (i.e., end of cycle) and moderator temperature effects are maximized. This demonstration is provided in FSAR Figure 15.0-7, Figure 15.0-9, and the corresponding descriptions in FSAR Section 15.0.5.3.1. A markup to the FSAR is included with this response to clarify this point. Impact on US460 SDAA: FSAR Section 15.0 has been revised as described in the response above and as shown in the markup provided in this response. NuScale Nonproprietary NuScale Nonproprietary
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-37 Draft Revision 2 downward trends in primary pressure and temperature are established during the short-term transient response, RCS pressure and temperatures remain acceptable and cooling continues for 72 hours. Therefore, the US460 standard design provides sufficient cooling via the DHRS for 72 hours. RAI 15.0.5-5 The upper riser flow paths provide borated water from the riser to mix with the condensate in the downcomer. Calculations evaluating a range of DHRS cooling conditions demonstrate that primary coolant flow through the riser flow paths exceeds condensation generation and the downcomer concentration remains higher than the critical concentration at beginning of cycle (BOC) and middle of cycle (MOC), where the potential for boron distribution effects before ECCS actuation is highest. These calculations include consideration of the effects of leakage and the uncovering of the uppermost riser holes. The downcomer concentration remains above the critical concentration prior to ECCS actuation, including accounting for the highest-worth control rod assembly stuck out of the core. Subcriticality is also demonstrated for conditions where boron distribution effects before ECCS actuation are less important (i.e., end of cycle (EOC)) and moderator temperature effects are maximized. This demonstration is provided in FSAR Figure 15.0-7, Figure 15.0-9, and the corresponding descriptions in this section. Whether the module remains on DHRS cooling or ECCS actuates, the core remains subcritical. Therefore, the criteria for extended passive cooling for 72 hours with DHRS are met. 15.0.5.3 Emergency Core Cooling System Extended Passive Cooling 15.0.5.3.1 Boron Transport during Emergency Core Cooling System Cooldown RAI 15.0.5-5 An ECCS cooldown occurs following a LOCA or inadvertent ECCS operation events or can occur following a non-LOCA event if required to maintain subcriticality. There are two factors that determine limiting cases for maintaining adequate boron concentration in the core to preclude criticality. The first is that an injection line break inside containment presents a continual flow path for boron to transport from the core and riser into containment. During ECCS cooling, this event is unique as it presents the only break where sustained liquid flow is from the RPV to the CNV. Other ECCS events result in increasing the concentration of boron in the RPV and are non-limiting for reactivity analysis during extended ECCS cooldown scenarios. The second factor is ensuring subcriticality for events that transition from DHRS cooling to ECCS cooling on the 8-hour timer. The transients that transition at 8 hours rapidly cool after ECCS actuation. The boron added from the ESB must be transfered into the core by recirculating liquid to offset the positive reactivity addition from decreasing temperature and xenon decay. This scenario is non-limiting for final boron concentration at the end of the analysis period, but can be limiting in the hours immediately following ECCS actuation. Events with slow-biased boron dissolution from the ESB, and events with fast-biased boron dissolution from the ESB are evaluated to determine limiting event
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-38 Draft Revision 2 progressions. A break on piping connected to the reactor component cooling water system is evaluated because steam generation and condensation in the CNV can dissolve the ESB boron oxide into the liquid below the CNV flange before ECCS actuation at 8 hours. These events are most limiting at end of cycle (EOC), when initial boron concentration is low. Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 Key input parameters and initial conditions used in the limiting reactor component cooling water pipe break boron transport case are provided in Table 15.0-22. The mass of reactor component cooling water added in the analysis is 6840 kg. Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 ESB parameters used in the boron transport analysis are selected to provide conservative calculations. These parameters include: high-biased mixing tube minor form losses, and nominal inner surface roughness mixing tube length conservatively modeled longer than actual design length mixing tube inlet elevation conservatively modeled lower than actual design elevation mixing tube outlet elevation conservatively modeled higher than actual design elevation Audit Item A-15.0.5-1 boron oxide pellets conservatively modeled as equilateral cylinders with 3/8 in. diameter, which is larger than the actual design diameter, for cases with slow-biased boron dissolution from the ESB Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 The condensate flow into the ESB dissolvers and containment mixing tubes, which is generated by the effective minimum CNV wall condensation area, is modeled in the boron transport and precipitation analyses as described in Reference 15.0-8. The temperature of the ESB condensate is modeled at the saturation temperature of the CNV vapor pressure. Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 RAI 15.0.5-1, RAI 15.0.5-6 Lower riser hole flow rates calculated by NRELAP5 are assessed as described in Reference 15.0-8 and. RAI 15.0.5-1, RAI 15.0.5-6 Results from low RPV pressure cases show that NRELAP5 calculates lower values of riser hole flow and is therefore more conservative than the alternate assessment calculation. NRELAP5 calculates a wide range of flow values, ranging from 0.1 kg/s to 6 kg/s. In contrast, the alternate assessment calculation range is relatively small, from 7 kg/s to 10.6 kg/s. Generally at lower pressures the long term cooling NRELAP5 model shows flow oscillations in the liquid space which tends to distribute the core thermal
NuScale Final Safety Analysis Report Transient and Accident Analyses NuScale US460 SDAA 15.0-39 Draft Revision 2 energy in both the forward and reverse directions as opposed to the alternate assessment calculation solution which assumes a forward flow heat balance energy solution. RAI 15.0.5-1, RAI 15.0.5-6 Results from high RPV pressure cases, with nominal loss coefficients, show that the alternate assessment calculation value is equal to or higher than the NRELAP5 value, implying that the NRELAP5 value is conservative. The NRELAP5 cases apply the nominal loss coefficient. Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 RAI 15.0.5-1, RAI 15.0.5-6 The lower riser hole flow rates calculated by NRELAP5 are determined to be acceptable for use in the boron transport and precipitation analyses because the use of the average riser hole flow from NRELAP5 increases the difference between the calculated core and downcomer boron concentrations during ECCS cooling. With this conservatively biased riser hole flow, the limiting boron transport analysis results demonstrate that the boron concentration in the RPV remains above the critical concentration. The parameters used for modeling riser holes in the extended passive cooling analyses include: RAI 15.0.5-1, RAI 15.0.5-6 total lower riser hole flow area of 7.07 sq in. with forward loss coefficient of 2.8 and reverse loss coefficient of 2.8. RAI 15.0.5-1, RAI 15.0.5-6 grouped upper riser hole flow area of 12 sq in. at each of the four upper riser hole elevations with forward loss coefficient of 5.75 and reverse loss coefficient of 4.75. elevation of riser holes groups are distributed to match the design within constraints of model nodalization forward and reverse losses are considered Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 RAI 15.0.5-5 The result for the limiting cases for the boron transport analysis are given in Table 15.0-18. Results for beginning of cycle (BOC) and middle of cycle (MOC) are also given for the injection line break for comparison. Figures 15.0-5 through Figure 15.0-10 show the boron concentrations and boron masses in the RPV and CNV for the limiting cases. The methodology for calculating boron transport is presented in Reference 15.0-8; calculation of the critical boron concentration accounts for the highest-worth control rod assembly remaining stuck out of the core. Audit Item A-15.0.5-1, Audit Item A-15.0.5-2 The margin to boron precipitation limits is evaluated. Key input parameters and initial conditions used in the limiting boron precipitation case are provided in Table 15.0-22.
RAIO-177641 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-177642
AF-177642 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. 10357 R1, Question 15.0.5-5) 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 10357 R1, Question 15.0.5-5. 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-177642 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 21, 2025. Mark W. Shaver}}