ML25051A167
| ML25051A167 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 02/20/2025 |
| From: | Shaver M NuScale |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| Shared Package | |
| ML25051A166 | List: |
| References | |
| RAIO-179692 | |
| Download: ML25051A167 (1) | |
Text
RAIO-179692 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com February 20, 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) response to the referenced NRC Request for Additional Information (RAI).
The enclosure to this letter contains NuScale's response to the following RAI question from NRC RAI-10298 R1:
XPC.LTR-6 is the proprietary version of the NuScale response to NRC RAI No. 033 (RAI-10298 R1, Question XPC.LTR-6). NuScale requests that the proprietary version be withheld from public disclosure in accordance with the requirements of 10 CFR § 2.390. The enclosed affidavit (Enclosure 3) supports this request. Enclosure 2 is the nonproprietary version of the NuScale response.
This letter makes no regulatory commitments and no revisions to any existing regulatory commitments.
If you have any questions, please contact Amanda Bode at 541-452-7971 or at abode@nuscalepower.com.
I declare under penalty of perjury that the foregoing is true and correct. Executed on February 20, 2025.
Sincerely, Mark W. Shaver Director, Regulatory Affairs NuScale Power, LLC
RAIO-179692 Page 2 of 2 02/20/2025 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 NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR-6, Proprietary :
NuScale Response to NRC Request for Additional Information RAI-10298 R1, Question XPC.LTR-6, Nonproprietary :
Affidavit of Mark W. Shaver, AF-179693
RAIO-179692 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-6, Proprietary
RAIO-179692 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-6, Nonproprietary
Response to Request for Additional Information Docket: 052000050 RAI No.: 10298 Date of RAI Issue: 10/31/2024 NRC Question No.: XPC.LTR-6 Issue Table 4-17 in the XPC LTR states that the fuel decay heat source used in the methodology is biased high or low based on the direction of conservatism for the acceptance criterion.
The topical report does not state how the methodology biases the decay heat source low, except to state (( 2(a),(c) Lower decay heat would result in a faster cooldown after a non-LOCA event during the eight-hour DHRS cooldown period. When ECCS actuates at eight hours, this would result in less steam condensate flow to the boron baskets and mixing tubes and reduce flow through the RRVs needed to get boron into the core. This situation has not been addressed in the topical report methodology. Additionally, the analysis of core reactivity after a non-LOCA transient assumes (( }} 2(a),(c) However, operation at reduced power or a short maintenance shutdown could result in higher core xenon with a reduced core boron concentration to offset peak xenon. This situation has not been addressed in the topical report methodology. Information Requested a) Update the topical report to state how the methodology biases the decay heat source low. b) Provide an evaluation of the impacts on reduced decay heat from (1) plant operation at reduced power operation and (2) a plant restart after a maintenance outage. Discuss the impact NuScale Nonproprietary NuScale Nonproprietary
of a maintenance outage of one to three weeks on decay heat after restart and impact on the methodology analyses. Revise the SDAA and/or topical report. Additionally, evaluate the impact on the methodology analyses of a non-LOCA transient with initial conditions of peak xenon and reduced core boron concentration before end-of-cycle. Revise the SDAA and/or topical report accordingly. c) Revise the SDAA and/or topical report to include the methodology for how the decay heat source is determined when biased low, and the methodology, analysis and results for the impact on criticality during extended passive cooling of (1) reduced decay heat conditions and (2) peak xenon and the corresponding reduced initial boron near end-of-cycle conditions. The methodology for how xenon transients are analyzed needs to be provided or a guaranteed minimum boron concentration must be provided regardless of plant operation down powers (cycle capacity factor). The revisions need to justify the assumed operational paradigm that any transients initialized at partial power are from short term deviations from full power operation (short term down powers or short duration shutdowns) and how this will be assured in the design (identification of the operational restrictions and how they are enforced). The revisions need to include the operational restrictions and limits for shutdowns or downpowers near end-of-cycle that are used to ensure decay heat levels are sufficient to maintain subcriticality. NuScale Response: In response to audit item A-XPC.LTR-6, NuScale addressed low-biased decay heat resulting from postulated reactor shutdowns or reduced-power operations before events analyzed in the boron transport analysis. The audit response explains that the boron mass from the emergency core cooling system (ECCS) supplemental boron (ESB) required to maintain subcriticality in the boron dilution analysis is a function of initial reactor coolant system (RCS) boron concentration and decay heat level. A higher initial RCS boron concentration requires less supplemental boron to maintain subcriticality. A higher decay heat level results in more condensation in containment following the transition to ECCS cooling to dissolve and transport supplemental boron. With sufficiently high initial RCS boron concentration, the core may remain subcritical with reduced, or even neglected, decay heat. NuScale Nonproprietary NuScale Nonproprietary
Following a downpower or shutdown, the decay heat level is dependent on power history and rate of power ascension. A power history with higher cumulative power operation results in higher decay heat levels. A slower rate of power ascension allows decay heat levels to build up as power is increased, as opposed to a lag in the buildup of decay heat after a faster rate of power ascension. For most of the operating cycle, the initial RCS boron concentration in the analysis is adequate to offset a reduction in the assumed decay heat level due to variations in power history. For reactor shutdowns or extended downpowers near the end of cycle (EOC), operational limits on RCS boron concentration can be used to ensure decay heat levels are sufficient to maintain subcriticality in the boron dilution analysis. As part of the audit response, NuScale performed an analysis using decay heats from an array of core operational histories (i.e., reactor shutdowns and downpowers) to demonstrate boron concentration limits can be used to maintain subcriticality margin in the boron transport analysis. As a result of the analysis, NuScale revised topical report TR-124587-P, Extended Passive Cooling and Reactivity Control Methodology, to specify the following:
low-biased decay heat used in the boron dilution analyses is evaluated to account for reactor shutdowns and reduced power operation before event initiation
operational limits on RCS boron concentration can be used to ensure results of the boron transport calculations demonstrate subcriticality is maintained
the boron dilution analysis includes power histories that capture the effect of short-term xenon transients prior to reactor trip In response to this request for additional information (RAI) question (XPC.LTR-6), a markup to TR-124587-P provides additional clarification on how decay heat is biased low and how the effects of xenon transients are addressed in the boron transport methodology. Calculation EC-132087, Revision 2, NPM-20 Boron Transport Analysis, implements this methodology, as described below. EC-132087, Revision 2, is provided in the electronic reading room with this response for NRC staff review. A markup to Section 15.0 of the Final Safety Analysis Report incorporates EC-132087, Revision 2 and is provided in the electronic reading room with this response for NRC staff review. The boron transport calculation in EC-132087, Revision 2, evaluates an array of postulated power maneuvers prior to event initiation to evaluate subcriticality during extended passive cooling with reduced decay heat levels. Decay heat calculations used in the boron transport calculation are performed using the Oak Ridge Isotope Generation (ORIGEN) computer code to generate decay heat curves for a range of power maneuvering scenarios. The range of scenarios follow a general sequence that changes reactor power as follows: NuScale Nonproprietary NuScale Nonproprietary
1. Reactor power is reduced to a range of powers 2. Reactor power is held at the reduced power for a range of durations 3. Reactor power is increased over a range of times 4. Reactor power is increased to a range of final power levels 5. A reactor trip is initiated Table 1, Table 2, and Table 3 of this response describe the power maneuvers considered in the decay heat calculations. Table 1 and Table 2 contain power maneuvers with long-duration down powers that significantly reduce core decay heat compared to operation at nominal full power before the event. The shutdown durations in Table 1 and Table 2 bound the maintenance outage duration of 1 to 3 weeks referred to in the RAI question. Table 3 contains power maneuvers with short-duration down powers and rapid power ascents. These short-duration power maneuvers capture transients where xenon concentrations at the end of the maneuver are higher than equilibrium xenon concentrations; including at least one case where the xenon concentration is 24 percent higher than the equilibrium value. The higher xenon concentrations result in lower initial RCS boron concentrations at event initiation compared to equilibrium values at the same operating conditions. Table 1: Analyzed Power Maneuvers - Full Power Ascent Cases (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
Table 2: Analyzed Power Maneuvers - Partial Power Ascent Cases (( }}2(a),(c) Table 3: Analyzed Power Maneuvers - Short-Duration Cases (( }}2(a),(c) NuScale Nonproprietary NuScale Nonproprietary
The array of postulated power maneuvers results in hundreds of unique depletion histories. ((
}}2(a),(c) The boron dilution calculation uses these conservative decay heat curves as inputs.
The boron transport calculation uses the conservative decay heat curves, with a 5 percent reduction applied for additional conservatism, as an input to perform subcriticality evaluations for reactor component cooling water line break and injection line break events. Previous analysis shows these events to be limiting for margin to subcriticality. The calculation uses analysis limits on initial RCS boron concentration as a function of integral downpower and power ascent rate. The limits ensure the initial RCS boron concentration is adequate to offset a reduction in decay heat due to variations in power history. The RCS boron concentration limits used in the boron transport calculation are shown in Figure 1 of this response. The limit in Figure 1 corresponds with a maximum power ascension rate limit of 25 MWt/hr. For power maneuvers with power ascent rates faster than 25 MWt/hr, the analysis uses a minimum RCS boron concentration limit of 300 ppm. The purpose of evaluating at 300 ppm is to demonstrate that above this concentration, operational history does not impact subcriticality conclusions. Therefore, power ascension limits and integral downpower do not need to be accounted for above that concentration. Operational limits specified in the core operating limits report and implemented by Technical Specification 3.5.4 ensure RCS initial conditions are within the bounds assumed in the boron transport analysis. Markups are provided in the electronic reading room with this RAI response that incorporate the analysis limits into the US460 Final Safety Analysis Report, and incorporate the operational limits into the US460 technical specifications. NuScale Nonproprietary NuScale Nonproprietary
Figure 1: Reactor Coolant System Boron Concentration Limit for Boron Transport Analysis In summary, as described in this RAI response above, the extended passive cooling and reactivity control methodology in TR-124587-P is updated to further clarify how decay heat is biased low and how xenon transients are analyzed in the boron transport analysis. EC-132087, Revision 2, implements the updated boron transport methodology and includes evaluations of reduced decay heat and xenon transients as a result of power maneuvering before event initiation. The calculation uses analysis limits on initial RCS boron concentration, which are implemented in the plant design through operational limits, to ensure the analysis demonstrates subcriticality is maintained for 72 hours after event initiation. Markups to the topical report, Final Safety Analysis Report, and technical specifications incorporate the methodology, analysis, and results described in this response. Impact on Topical Report: Topical Report TR-124587, Extended Passive Cooling and Reactivity Control Methodology, has NuScale Nonproprietary NuScale Nonproprietary
been revised as described in the response above and as shown in the markup provided in this response. Additional Information: Note this response references a proprietary version of the topical report that is marked as containing export controlled information (ECI). However, the extracted pages of the topical report that are attached to this response do not contain ECI as submitted herein. Notwithstanding, any proprietary information included in the response and the attachment hereto shall be withheld per 10 CFR 2.390. NuScale Nonproprietary NuScale Nonproprietary
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 118 4.4.3 Bottom-up Assessments for XPC Phenomena The high-ranked and medium-ranked phenomena identified by the XPC PIRT in Section 3.4 are assessed. The assessments are summarized in the following sections. The summaries describe the phenomena, the importance of the phenomena in parts of the EM calculation, and how the phenomena are addressed in the XPC evaluation method. 4.4.3.1 Fuel Decay Heat Source and Distribution RAI XPC.LTR-6 (( }}2(a),(c) NRELAP5 includes appropriate decay heat and point kinetics models. It also includes the option for the user to specify the decay heat source as a tabulated input. These models and user input options are assessed and determined to be adequate. Audit Question A-XPC.LTR-6 (( RAI XPC.LTR-6 }}2(a),(c) 4.4.3.2 Core Heat Removal (( }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 221 5.4.4 Calculation Biases for Boron Transport Analysis - Sensitivities Audit Question A-XPC.LTR-32 Table 5-6 summarizes the key initial and boundary condition biases applied or evaluated for the extended ECCS cooling cases, including non-LOCA events that transition from DHRS to ECCS cooling as identified in Section 5.3.1. For these initiating events, the transient response is evaluated for at least 12 hours or until quasi-steady conditions are reached. Statepoint evaluations with the same biasing factors are performed to assess later time periods, out to 72 hours. RAI XPC.LTR-6 Table 5-6 Initial and Boundary Condition Biases Evaluated for Extended ECCS Cooling Cases Evaluated for Boron Transport - Sensitivities Key Parameter Bias Basis for Bias / Comment (( Single failures Power availability Normal control system response Operator action Decay heat Initial RCS Temperature }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 257 (( RAI XPC.LTR-6 }}2(a),(c) RAI XPC.LTR-6 (( }}2(a),(c) Audit Question A-XPC.LTR-26 RAI XPC.LTR-6 (( }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 271 (( }}2(a),(c) 6.3 Critical Boron Concentration Audit Question A-XPC.LTR-6 The change in core reactivity during XPC is primarily dependent on the moderator temperature coefficient (MTC), along with the temperature change of the moderator, and the buildup and decay of the xenon concentrationisotopes in the core after shutdown. These factors are contingent upon the core burnupoperating history, power level, CRA configuration, axial offset, and core thermal-hydraulic conditions. Reactivity calculations are performed for beginning of cycle (BOC), middle of cycle (MOC), and end of cycle (EOC) conditionsa range of operating histories. Calculations at EOCwith low initial boron concentrations corresponding with end of cycle (EOC) conditions are limiting compared to BOC and MOC due to the large negative MTC present at EOC. Core reactivity is evaluated over a range of moderator temperatures that are sufficiently low to bound the lowest possible temperatures expected during the cooldown, considering the minimum pool temperature operating range. As summarized in Section 4.1, the reactivity calculations are performed using the CMS5 software code suite. CASMO5 is used to generate explicit cross-section libraries for the core design. The cross-section libraries are applicable for temperatures below the minimum core moderator temperature during extended passive cooling (e.g., libraries are generated that are applicable for temperatures as low as 68 degrees F). Audit Question A-XPC.LTR-6, Audit Question A-XPAC.LTR-20 SIMULATE5 calculations are performed to evaluate core reactivity for core configurations and conditions present after reactor shutdown and moderator cooldown from extended DHRS or ECCS cooling. Although SIMULATE5 is a static code, it has the capability to evaluate reactivity changes due to transitory xenoncore isotopics after shutdown. RAI XPC.LTR-6 (( }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 272 (( Audit Question A-XPC.LTR-6 Audit Question A-XPC.LTR-6 Audit Question A-XPC.LTR-22 Audit Question A-XPC.LTR-6 Audit Question A-XPC.LTR-6 Audit Question A-XPC.LTR-6 }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 284 Audit Question A-XPC.LTR-6 RAI XPC.LTR-6 Figure 6-10 Transient Boron Concentrations for Dilution Sensitivity (( }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 285 Audit Question A-XPC.LTR-6 RAI XPC.LTR-6 Figure 6-11 Transient Boron Mass for Dilution Sensitivity (( }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 291 7.4 Assess Margin to Boron Precipitation The boron concentration results in the module determined from the boron transport calculations are compared to the appropriate boron solubility limits to demonstrate that the core boron concentration remains below the solubility limit for at least 72 hours after event initiation. 7.5 Representative Results RAI XPC.LTR-6 Representative results of an IORV-RVVhigh point vent line break outside containment using the boron precipitation methodology are provided in Figure 7-3 and Figure 7-4. Figure 7-3 shows the transient boron concentration in each mixing volume plotted along with the boron precipitation limit. Figure 7-4 shows the boron mass in each mixing volume. (( }}2(a),(c) Figure 7-2 Boric Acid, Boron Solubility Limit as a Function of Temperature (( }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 292 (( }}2(a),(c) There is significant margin between the maximum concentration and the solubility limit. RAI XPC.LTR-6 Figure 7-3 Transient Boron Concentrations for Example Precipitation Evaluation (( }}2(a),(c)
Extended Passive Cooling and Reactivity Control Methodology TR-124587-NP Draft Revision 1 © Copyright 2024 by NuScale Power, LLC 293 RAI XPC.LTR-6 Figure 7-4 Transient Boron Mass for Example Precipitation Evaluation (( }}2(a),(c)
RAIO-179692 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-179693
AF-179693 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. 10298 R1, Question XPC.LTR-6) on the NuScale Standard Design Approval Application. NuScale has performed significant research and evaluation to develop a basis for this response and has invested significant resources, including the expenditure of a considerable sum of money. The precise financial value of the information is difficult to quantify, but it is a key element of the design basis for a NuScale plant and, therefore, has substantial value to NuScale. If the information were disclosed to the public, NuScales competitors would have access to the information without purchasing the right to use it or having been required to undertake a similar expenditure of resources. Such disclosure would constitute a misappropriation of NuScales intellectual property, and would deprive NuScale of the opportunity to exercise its competitive advantage to seek an adequate return on its investment. (4) The information sought to be withheld is in the enclosed response to NRC Request for Additional Information RAI No. 10298 R1, Question XPC.LTR-6. 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-179693 Page 2 of 2 (5) The basis for proposing that the information be withheld is that NuScale treats the information as a trade secret, privileged, or as confidential commercial or financial information. NuScale relies upon the exemption from disclosure set forth in the Freedom of Information Act (FOIA), 5 USC § 552(b)(4), as well as exemptions applicable to the NRC under 10 CFR §§ 2.390(a)(4) and 9.17(a)(4). (6) Pursuant to the provisions set forth in 10 CFR § 2.390(b)(4), the following is provided for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld: (a) The information sought to be withheld is owned and has been held in confidence by NuScale. (b) The information is of a sort customarily held in confidence by NuScale and, to the best of my knowledge and belief, consistently has been held in confidence by NuScale. The procedure for approval of external release of such information typically requires review by the staff manager, project manager, chief technology officer or other equivalent authority, or the manager of the cognizant marketing function (or his delegate), for technical content, competitive effect, and determination of the accuracy of the proprietary designation. Disclosures outside NuScale are limited to regulatory bodies, customers and potential customers and their agents, suppliers, licensees, and others with a legitimate need for the information, and then only in accordance with appropriate regulatory provisions or contractual agreements to maintain confidentiality. (c) The information is being transmitted to and received by the NRC in confidence. (d) No public disclosure of the information has been made, and it is not available in public sources. All disclosures to third parties, including any required transmittals to NRC, have been made, or must be made, pursuant to regulatory provisions or contractual agreements that provide for maintenance of the information in confidence. (e) Public disclosure of the information is likely to cause substantial harm to the competitive position of NuScale, taking into account the value of the information to NuScale, the amount of effort and money expended by NuScale in developing the information, and the difficulty others would have in acquiring or duplicating the information. The information sought to be withheld is part of NuScales technology that provides NuScale with a competitive advantage over other firms in the industry. NuScale has invested significant human and financial capital in developing this technology and NuScale believes it would be difficult for others to duplicate the technology without access to the information sought to be withheld. I declare under penalty of perjury that the foregoing is true and correct. Executed on February 20, 2025. Mark W. Shaver}}