ML25016A300
| ML25016A300 | |
| Person / Time | |
|---|---|
| Site: | 05200050 |
| Issue date: | 01/16/2025 |
| From: | Shaver M NuScale |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| Shared Package | |
| ML25016A298 | List: |
| References | |
| RAIO-178483 | |
| Download: ML25016A300 (1) | |
Text
RAIO-178483 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com January 16, 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. 008 (RAI-10081 R1) on the NuScale Standard Design Approval Application
REFERENCE:
NRC Letter to NuScale, Request for Additional Information No. 008 (RAI-10081 R1), dated October 31, 2023 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-10081 R1:
6.3-1 is the proprietary version of the NuScale Response to NRC RAI No. 008 (RAI-10081 R1, Question 6.3-1). 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. 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 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 16, 2025.
Sincerely, Mark W. Shaver Director, Regulatory Affairs NuScale Power, LLC
RAIO-178483 Page 2 of 2 01/16/2025 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-10081 R1, Question 6.3-1, Proprietary Version : NuScale Response to NRC Request for Additional Information RAI-10081 R1, Question 6.3-1, Nonproprietary Version : Affidavit of Mark W. Shaver, AF-178484
RAIO-178483 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-10081 R1, Question 6.3-1, Proprietary Version
RAIO-178483 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-10081 R1, Question 6.3-1, Nonproprietary Version
Response to Request for Additional Information Docket: 052000050 RAI No.: 10081 Date of RAI Issue: 10/31/2023 NRC Question No.: 6.3-1 Regulatory Basis 10 CFR 52.137(a)(2) states a standard design application must include [a] description and analysis of the SSCs of the facility, with emphasis upon performance requirements, the bases, with technical justification, upon which the requirements have been established, and the evaluations required to show that safety functions will be accomplished. Additionally, 10 CFR 52.137(a)(4) states a standard design application must include [a]n analysis and evaluation of the design and performance of SSC with the objective of assessing the risk to public health and safety resulting from operation of the facility and including determination of the margins of safety during normal operations and transient conditions anticipated during the life of the facility, and the adequacy of SSCs provided for the prevention of accidents and the mitigation of the consequences of accidents.
Issue The NPM-20 emergency core cooling system (ECCS) relies on the actuation of the decay heat removal system (DHRS) to remove a portion of decay heat by condensing steam from the reactor primary coolant system. During the long-term cooling period following an anticipated operational occurrence (AOO) or postulated design basis accident, the DHRS system is actuated to remove core decay heat and other sensible heat by condensing reactor coolant system (RCS) steam. The primary side steam generated from the reactor core contains combustible gases, hydrogen, and oxygen, which are generated via radiolysis of water. After the steam condenses, the combustible gas may accumulate in the RCS. Over time, the accumulated gases may reach the combustion threshold concentration in localized subcompartments inside containment, which includes subcompartments in the RCS that could cause loss of containment integrity or loss of appropriate mitigating features for design basis events given that the design basis events can last beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This could result in severe degradation of the RCS, DHRS, and ECCS and prevent them from performing their safety functions and satisfying associated regulatory requirements, such as General Design Criteria NuScale Nonproprietary NuScale Nonproprietary
10, 15, 34, 35, and 10 CFR 50.46.
It is necessary to preclude local concentrations of combustible gases collecting in areas where unintended combustion or detonation could cause loss of containment integrity or loss of appropriate mitigating features. Operating reactors have addressed combustible gas control for design basis and beyond design basis severe accidents in accordance with 10 CFR 50.44, and its regulatory progression, through analyses, intrinsic design capabilities, installation of mitigative features, and reliance on operator actions to purge and vent. NuScales NPM-20 design and approach to design basis event mitigation with no reliance on operator actions differs significantly from active operating reactors. Therefore, additional information is needed for the staff to evaluate standard design approval application (SDAA) Sections 6.3, 15.0.5, 15.6.5, Extended Passive Cooling and Reactivity Control Methodology Topical Report, and Loss-of-Coolant Accident Evaluation Model Topical Report regarding the potential for combustible gas generation and accumulation in the RCS.
Information Requested Provide a quantitative analysis for the generation and transport of combustible gases within the RCS that demonstrates adequate performance of AOO and accident mitigating SSCs to accomplish their safety functions. A summary of pertinent portions of the analysis, including its results and conclusions, should be incorporated into the SDAA and associated topical reports.
NRC Feedback Provided 8/13/2024:
The RAI response should provide the following information:
- Demonstration that H2 gas will be rapidly drawn into the control rod drive mechanism pressure housing as part of startup procedures, including an explanation for how the quantity of stored hydrogen molecules will correspond to a number of hydrogen atoms greater than the minimum required to prevent O2 accumulation in the pressurizer vapor space during passive DHRS cooldown.
- Consistent with the assumptions in the analysis, prescribe in the FSAR that operating procedures will ensure that the CRDM pressure housings are filled at least with 50% hydrogen during startup.
- Explanation of the physical mechanism, and associated timeline, related to the assumption that H2 located in the CRDM pressure housings will become dissolved into the liquid water in the RPV and thus be available to recombine with dissolved oxygen generated by radiolysis, given the CRDM pressure housing interfaces with the pressurizer vapor space and the CRDM-stored hydrogen is in the gaseous state.
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- Address the release of dissolved radiolytic species into the pressurizer vapor space as a result of vaporization of liquid primary coolant at the liquid-vapor interface in the pressurizer during DHRS shutdown cooling.
NuScale Response:
Background
This Request for Additional Information (RAI) presents statements that NuScale finds to be incorrect or inaccurate and do not reflect the US460 design and function.
The RAI states that the NPM-20 emergency core cooling system (ECCS) relies on the actuation of the decay heat removal system (DHRS) to remove a portion of decay heat by condensing steam from the reactor primary coolant system.
The ECCS is an independent system and does not rely on the DHRS to actuate or operate. The ECCS provides core cooling capabilities in conjunction with containment heat removal function.
The containment heat removal function, including the steel wall of the containment vessel (CNV) provides for the direct (passive) transfer of containment heat (normal, transient, or accident conditions) to the ultimate heat sink. Separately, the DHRS removes decay heat. The DHRS heat removal function does not rely on actuating the ECCS. The DHRS provides secondary side reactor cooling for non-loss-of-coolant accident (LOCA) events when normal feedwater is not available and for LOCA events prior to ECCS actuation. There are two trains of decay heat removal equipment: one attached to each steam generator (SG) loop. Each decay heat removal train has a passive condenser submerged in the reactor pool. Notwithstanding the independence of ECCS and DHRS, both systems are credited for performing the function to remove primary system energy in specific events (e.g., small break LOCAs). Decay heat removal through DHRS is important in smaller LOCA events where the break flow does not remove decay heat. In the smaller LOCA design-basis event analysis, the DHRS removes decay heat to reduce primary fluid energy prior to ECCS actuation, which reduces the containment peak pressure response after ECCS actuation.
Additionally, the RAI states that accumulated gases may reach the combustion threshold concentration in localized subcompartments inside containment, which includes subcompartments in the RCS NuScale Nonproprietary NuScale Nonproprietary
The reactor coolant system (RCS) is not a subcompartment of the containment system (CNTS) and the RCS does not contain isolated subcompartments. The RCS includes the reactor pressure vessel (RPV) and integral pressurizer (PZR), the reactor vessel internals (RVI), the reactor safety valves (RSVs), RCS piping inside the CNV (RCS injection, RCS discharge, PZR spray supply, and RPV high-point degasification lines), the PZR control cabinet and the RCS instruments and cables, as stated in Standard Design Approval Application (SDAA) Section 5.2.
The CNTS includes the CNV, CNV supports, containment isolation valves, passive containment isolation barriers, and containment instruments, as stated in SDAA Section 6.2.1. Piping, supports, and components associated with the functional systems that communicate through the CNV boundary, although housed in the CNV and defined as part of the RCS, are not part of the CNTS.
Regulation The RAI cites General Design Criteria (GDC) 10, 15, 34, 35, and 10 CFR 50.46. NuScale maintains the cited regulatory criterion are not applicable to the US460 design in a capacity related to combustible gas in the RCS.
General Design Criterion 10 requires the reactor core, associated coolant, control and protection systems to be designed with appropriate margin to ensure that specified acceptable fuel design limits (SAFDLs) are not exceeded during any condition of normal operation, including the effects of anticipated operational occurrences (AOOs). GDC 10 is intended to ensure that the fuel system is not damaged by exceeding specified fuel design limits and that anticipated reactivity transients will not result in exceeding the specified design limits. GDC 10 does not require evaluation of postulated combustible gases.
General Design Criterion 15 requires the RCS and associated auxiliary, control and protection systems to be designed with sufficient margin to assure that the design conditions of the reactor coolant pressure boundary (RCPB) are not exceeded during normal operations, including AOOs. Design transients, loading combinations, stress limits, and evaluation methods given by the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) are used in the design and fatigue analyses of RCPB components to support the conclusion that the integrity of the RCPB is maintained, thereby ensuring compliance with GDC 15.
General Design Criterion 34 requires a residual heat removal system that removes decay and other residual heat from the core at a rate such that SAFDLs are not exceeded and the design conditions of the RCPB are not exceeded. Similar to GDC 15, these conditions and NuScale Nonproprietary NuScale Nonproprietary
requirements are defined by the ASME BPVC and do not address combustion within the RCS.
Potential combustible gas accumulation in the RCS is not a source of decay or residual heat.
General Design Criterion 35 addresses emergency core cooling following a loss of reactor coolant. The staffs concern relates to combustible gas accumulation in the RCS under DHRS operation during AOOs and long-term cooling. As previously stated, the ECCS does not rely on the actuation of the DHRS. The DHRS is not an emergency core cooling system.
Regulation 10 CFR 50.46 addresses ECCS performance following a LOCA. Similar to the context of GDC 35, the ECCS operates in conjunction with the containment heat removal function and does not rely on the actuation of the DHRS to remove decay heat from the reactor.
Regulation 10 CFR 50.44 addresses combustible gas control in containments. This RAI explicitly addresses combustible gas accumulation in the RCS. Maintaining that the RCS is not a subcompartment of the CNTS, this regulation is not pertinent to combustible gas control within the RCS.
Discussion of Issue The RAI states that, accumulated gases may reach the combustion threshold concentration in localized subcompartments inside containment and it is necessary to preclude local concentrations of combustible gases collecting in areas where unintended combustion or detonation could cause loss of containment integrity or loss of appropriate mitigating features.
In direct response to the NRC staff inquiry specific to potential for combustible gas inside containment and the potential for resulting loss of containment integrity or mitigating features, the US460 design relies on the passive autocatalytic recombiner (PAR) to maintain an inert containment atmosphere following a design-basis event or severe accident; therefore, an analysis of the effects of combustion on containment integrity is not necessary. Regulation 10 CFR 50.44 defines an inert atmosphere as having an oxygen concentration below four percent.
The PAR is sized to limit oxygen concentrations to a level that does not support combustion (i.e., less than four percent). This results in an inert containment atmosphere. Therefore, the US460 design precludes a threat to the function of the RCS, DHRS, and ECCS resulting from exceeding the combustion threshold concentration inside containment.
NuScale agrees, as stated by the NRC in the RAI, that operating reactors have addressed combustible gas control for design basis and beyond design basis severe accidents in accordance with 10 CFR 50.44 and its regulatory progression, through analyses, intrinsic design NuScale Nonproprietary NuScale Nonproprietary
capabilities, installation of mitigative features, and reliance on operator actions to purge and vent. NuScale asserts that, similar to the operating fleet, using the PAR to maintain an inert containment atmosphere, the US460 design adequately addresses combustible gas control in containment in accordance with 10 CFR 50.44 requirements.
Information Requested The RAI requests quantitative analysis for the generation and transport of combustible gases within the RCS that demonstrates adequate performance of AOO and accident-mitigating structures, systems, and components (SSCs) to accomplish their safety functions.
Notwithstanding the applicability of aforementioned regulatory criteria in this RAI, and pursuant to 10 CFR 52.137 requirements to provide information sufficient to permit understanding of the system designs, NuScale evaluated the potential for combustible gas accumulation in the RCS using a quantitative analysis.
Calculation EC-121960, Revision 2, NPM-20 Combustible Gas Management, ((2(a),(c) Calculation EC-121960, Revision 2, is provided in the Chapter 6 electronic reading room (eRR). An inert atmosphere in the RCS is maintained in one of two ways.
A critical hydrogen concentration suppresses the net accumulation of radiolytically produced hydrogen and oxygen inside the RPV.
Prior to reaching a combustible threshold, timed actuation of the ECCS vents combustible gases to containment, where the PAR recombines the oxygen. A critical hydrogen concentration is a condition that suppresses radiolytically produced oxygen using the dissolved hydrogen concentration present within the RCS. ((
}}2(a),(c)
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Section 5.2.3.2.1 of the SDAA discusses that a licensee will follow EPRI PWR guidelines. Combined Operating License (COL) Item 5.2-2 requires that an applicant referencing the SDAA develop and implement a Strategic Water Chemistry Plan, which adopts the latest version of the EPRI PWR Primary Water Chemistry Guidelines. ((
}}2(a),(c) A system with dissolved hydrogen greater than or equal to the critical hydrogen concentration suppresses the net accumulation of oxygen gas generated by radiolysis.
((
}}2(a),(c) This assessment concludes that a critical hydrogen concentration is maintained in the RCS throughout a DHRS cooldown.
((
}}2(a),(c) Prior to reaching a combustible threshold, an existing automatic eight-hour timer actuates ECCS, venting combustible gases to containment via the reactor vent valves, at which point the design utilizes the PAR to maintain an inert atmosphere. Report ER-E000-9003, Revision 6, Core-250B I&C Parameters and Analytical Limits, (( }}2(a),(c) NuScale provides ER-E000-9003, Revision 6, in the Chapter 6 eRR.
During normal operation, licensees routinely verify RCS chemistry conditions. FSAR Section 5.2.3 describes the conformance with RCS chemistry guidelines (i.e., fuel vendor guidelines and Electric Power Research Institute pressurized water reactor Primary Water Chemistry Guidelines). Section 5.2.3 states, Direct injection of high pressure gaseous hydrogen into the CVCS injection flow adds dissolved hydrogen to the reactor coolant. To bypass the 8-hour ECCS actuation, operators verify information such as preexisting RCS dissolved hydrogen sample data and RPV venting history to determine that the RPV contains sufficient hydrogen to maintain a critical hydrogen concentration in the RCS throughout DHRS cooldown. When conditions allow operators to bypass the eight-hour automatic timer, a critical hydrogen concentration suppresses the net accumulation of radiolytically produced oxygen. NuScale Nonproprietary NuScale Nonproprietary
SDAA Incorporation NuScale herewith provides a proposed markup of the SDAA, FSAR Section 5.4.3. This markup documents in the SDAA that the US460 design precludes the potential of a combustion event to occur in the RCS during DHRS cooldown. This is accomplished by either retaining a critical hydrogen concentration in the RPV, by suppressing the net accumulation of radiolysis gases, or by venting the combustible gases to the CNV using automatic actuation of the ECCS eight hours after reactor trip. NuScale proposes that, in lieu of the cited regulatory criterion in this RAI, NRC staff consider General Design Criteria 4 as the appropriate guiding regulation concerning the potential effects of unintended combustion or detonation of combustible gas on SSC. The subject of this RAI, similar to the intent of GDC 4, intends to protect SSC important to safety, designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation and postulated accidents. Conclusion The actuation and operation of ECCS does not rely directly on the DHRS. The RCS is not a subcompartment of the CNTS and does not contain isolated subcompartments. NuScale evaluated, through quantitative analysis, that the potential for generation and transport of combustible gases produced radiolytically within the RCS in the US460 design is mitigated by existing and passive intrinsic design capabilities. A combustible gas concentration in both the RCS and containment environments is precluded at all times by a critical hydrogen concentration or timed automatic actuation of ECCS valves in conjunction with the PAR. NuScale Nonproprietary NuScale Nonproprietary
Response to NRC Feedback Provided 8/13/2024: Question: Demonstration that H2 gas will be rapidly drawn into the control rod drive mechanism pressure housing as part of startup procedures, including an explanation for how the quantity of stored hydrogen molecules will correspond to a number of hydrogen atoms greater than the minimum required to prevent O2 accumulation in the pressurizer vapor space during passive DHRS cooldown. The suppression of radiolytically produced oxygen is not dependent upon the rate at which hydrogen accumulates in the control rod rive mechanism (CRDM) pressure housings during module startup. The hydrogen concentration in the reactor coolant liquid suppresses radiolytically produced oxygen gas generation. Separately, in the startup process, nitrogen is initially used to establish pressure in the pressurizer. After initial pressurization is established, operators draw a steam bubble in the pressurizer to continue pressurizing. (( }}2(a),(c) However, the RCS must maintain dissolved hydrogen in accordance with the EPRI Guidelines, so hydrogen is periodically added to the RCS in a manner that allows this NuScale Nonproprietary NuScale Nonproprietary
equilibrium condition to occur while the RCS maintains compliance with the EPRI Guidelines. Hydrogen does not need to be rapidly drawn into the CRDM pressure housings. Rather, the RCS needs to maintain dissolved hydrogen in accordance with chemistry requirements and, as a result, hydrogen accumulates in the CRDM pressure housings. (( }}2(a),(c) Question: Consistent with the assumptions in the analysis, prescribe in the FSAR that operating procedures will ensure that the CRDM pressure housings are filled at least with 50% hydrogen during startup. The FSAR describes the startup process in sufficient detail to establish hydrogen as the dominant species in the CRDM pressure housings during power operation. Section 9.3.4 of the FSAR describes the chemical and volume control system during normal operation: During the heatup, operators draw a steam bubble in the pressurizer to replace the nitrogen gas used to pressurize the RCS. The RPV high point degasification line provides a vent path for the nitrogen to the LRWS along with some amount of vaporized reactor coolant. The above statement clarifies that nitrogen is used to establish initial RCS pressure, but the nitrogen is vented after the pressurizer steam bubble is drawn. Venting the initial startup nitrogen from the pressurizer assures hydrogen is the dominant gaseous species in the CRDM pressure housings. Section 9.3.4 states: For oxygen control during normal reactor operation, personnel introduce gaseous hydrogen from a compressed hydrogen source. Hydrogen addition quantities are verified by monitoring pressure of the compressed hydrogen source. The hydrogen injection pressure regulating valve ensures an appropriate rate of hydrogen addition. The above statement clarifies that dissolved hydrogen is added during operation as a routine part of maintaining normal operating conditions. Section 5.2.3.2.1 of the FSAR establishes compliance with the EPRI Primary Water Chemistry Guidelines. NuScale Nonproprietary NuScale Nonproprietary
The accumulation of gas in the CRDM pressure housings is proportional to operating pressure because the sequestered gas follows the ideal gas law (where-in molar quantity of a gas in a fixed volume at a fixed temperature is proportional to pressure). Full accumulation of hydrogen in the CRDM pressure housings can only be achieved at full operating pressure. At half of normal operating pressure, half accumulation can be achieved. The above statements from the SDAA demonstrate that the non-condensable gas in the pressurizer atmosphere will consist of hydrogen by the time the pressure of the RCS reaches half the operating pressure (1000 psia), thereby assuring the CRDM pressure housings are predominantly filled with hydrogen gas. Question: Explanation of the physical mechanism, and associated timeline, related to the assumption that H2 located in the CRDM pressure housings will become dissolved into the liquid water in the RPV and thus be available to recombine with dissolved oxygen generated by radiolysis, given the CRDM pressure housing interfaces with the pressurizer vapor space and the CRDM-stored hydrogen is in the gaseous state. The premise that the gas from the CRDMs must be transported through the pressurizer gas space, into the liquid, and then into the core as dissolved hydrogen is incorrect. The gas in the CRDMs does not need to find its way into the liquid phase to prevent radiolytic accumulation of oxygen gas. ((
}}2(a),(c)
((
}}2(a),(c)
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Question: Address the release of dissolved radiolytic species into the pressurizer vapor space as a result of vaporization of liquid primary coolant at the liquid-vapor interface in the pressurizer during DHRS shutdown cooling. With sufficient dissolved hydrogen content, the net accumulation of radiolytically produced gases does not occur, as the net production of radiolysis products is rapidly suppressed due to the presence of dissolved hydrogen. Second, the question appears to premise that there is on-going vaporization within the RPV. ((
}}2(a),(c)
Finally, vaporization or condensation do not affect Henrys law equilibrium. Transport of hydrogen across the phase boundary is dictated by Henrys law equilibrium. If net condensation or net vaporization is occurring at the phase boundary (net condensation happens during long term DHRS operation because the liquid phase is being preferentially cooled through the steam generator) such that some hydrogen is dissolved or vaporized, then other molecular transport phenomena at the interface will compensate such that the system approaches Henrys law equilibrium for hydrogen. Addressing Additional NRC Feedback from December 9 Clarification Call H2 and O2 Transport The NRC staff questioned whether, during ECCS operation, non-condensable gases (NCGs) may accumulate in the steam generator region. Specifically, the staff feedback states: NuScale Nonproprietary NuScale Nonproprietary
(( }}2(a),(c) (( }}2(a),(c) The following analogies to operating plant conditions are considered: 1. Pressurized water reactors operate with pressurizer spray constantly applying liquid droplets to the vapor space. Despite the constant addition of pressurizer spray, non-condensable gases accumulate in the upper pressurizer vapor space. The non-condensable gases are periodically vented from the pressurizer so that pressure control is maintained. 2. Pressurized water reactors include containment spray for heat removal in the containment vessel during accidents. There are also recombiners or igniters as required in containment to address the requirements of 10 CFR 50.44. The utilization of containment spray does not result in the accumulation of NCGs lower in the containment vessel, such that the discrete components to recombine hydrogen or ignite hydrogen in a controlled manner would not perform their function. NuScale Nonproprietary NuScale Nonproprietary
((
}}2(a),(c)
The Froude number represents the ratio of inertial forces to gravitational and buoyant forces. ((
}}2(a),(c)
Hydrogen within the RCS during Shutdown The NRC staff questioned the potential depletion of dissolved hydrogen in reactor coolant during DHRS operation. ((
}}2(a),(c)
Operating plant experience in PWRs indicates that radiolysis is not a significant loss mechanism for dissolved hydrogen. The most significant hydrogen loss mechanism for operating PWRs is diffusion through the steam generator tubes. Electric Power Research Institute prediction models for the hydrogen loss due to diffusion account for the majority of hydrogen loss measured in operating plants, while radiolysis is not included in hydrogen loss prediction models. Radiolysis of water generates both reactive oxygen and hydrogen compounds at similar rates. The generation of hydrogen compounds is slightly less than the generation of oxygen compounds. Thus, while dissolved hydrogen is temporarily consumed by reactions with the radiolytically produced oxygen compounds (which suppresses the net generation of molecular oxygen), the consumed hydrogen is replenished by the radiolytically produced hydrogen. Therefore, hydrogen loss due to radiolysis is not a significant contributor, and NuScale NuScale Nonproprietary NuScale Nonproprietary
considers this hydrogen loss mechanism to be insignificant over the design basis event time period. Hydrogen loss due to diffusion through the steam generator has been predicted in collaboration with industry experts. However, during DHRS operation, hydrogen loss due to diffusion is significantly reduced from the normal operational values due to reduced temperature and pressure. Operating experience within industry provides additional assurance that neither corrosion product interaction nor radiolytic depletion are significant loss mechanisms for hydrogen in the RCS during the design-basis event time period. Large pressurized water reactors are able to operate for days following a loss of the ability to add hydrogen to the coolant, and hydrogen is not depleted to a point where net radiolytic oxygen gas generation is not suppressed. Demonstration of Depressurization Time during DHRS Operation Figure 5-34 of the Extended Passive Cooling Topical Report shows a representative RCS pressure response to effective DHRS cooling. This figure is shown as Figure 1, below. The mintemp-dhrs curve reflects initial conditions of 100 percent power operation. The calculation is biased to rapidly cool the RCS (e.g., cold pool temperature is simulated) so they represent a rapid change in RCS pressure due to DHRS cooling. NuScale Nonproprietary NuScale Nonproprietary
Figure 1 - RCS Pressure Response during a Minimum Temperature DHRS Cooldown (( }}2(a),(c) Consideration of Energy Deposition due to the B-10 (n,) Reaction ((
}}2(a),(c)
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NuScale Final Safety Analysis Report Reactor Coolant System Component and Subsystem Design NuScale US460 SDAA 5.4-15 Draft Revision 2 General Design Criteria (GDC) 1, 2, and 4: The DHRS is Quality Group B and Class 2; design, fabrication, construction, testing, and inspections are in accordance with Section III of the ASME BPVC and in accordance with the Quality Assurance Program described in Chapter 17. The DHRS withstands the effects of natural phenomena without loss of capability to perform its safety function. The DHRS accommodates the effects of, and is compatible with, the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents. The design of the RXB structure, NPM operating bays, and location of the NPM within the operating bays provides protection from possible sources of externally or internally generated missiles. Section 3.6.2, Determination of Rupture Locations and Dynamic Effects Associated with the Postulated Rupture of Piping, describes protection of the DHRS from the external dynamic effects of pipe breaks. RAI 6.3-1 During normal operation at power, a critical hydrogen concentration is maintained in the RCS to suppress radiolytic oxygen production. The RPV maintains sufficient hydrogen to achieve a critical hydrogen concentration in the RCS throughout a DHRS cooldown, preventing the formation of oxygen gas and ensuring an inert atmosphere. RAI 6.3-1 It is possible for the critical hydrogen concentration to be removed through venting of the RPV. If this occurs, automatic ECCS actuation 8 hours after a reactor trip enables the passive autocatalytic recombiner located in containment to maintain inert conditions and prevent combustion. General Design Criterion 5: The DHRS does not share any active or passive components among individual NPMs necessary for performance of the DHRS safety functions. The NPMs share the reactor pool as the ultimate heat sink for removal of decay heat from the DHRS passive condensers. Chapters 1 and 3 describe the shared RXB and other structures, and Section 9.2.5, Ultimate Heat Sink, describes the reactor pool. The DHRS active components fail-safe on a loss of power. Therefore, shared power supplies among NPMs do not impact the capability of performing the DHRS safety functions. General Design Criterion 14: The DHRS connects to the secondary system and does not directly interface with the RCPB. Section 5.4.1 describes the SGs, and Section 6.2.4, Containment Isolation System, describes the CNTS components coupling the DHRS to the SGs. There are no other interfaces or shared components between the DHRS and the RCPB. Principal Design Criterion (PDC) 19: The DHRS initiates from the control room and is capable of safe shutdown of the reactor. The DHRS can also initiate from outside the main control room in the module protection system (MPS) equipment rooms within the RXB. PDC 34 and PDC 44: The DHRS is a passive design that utilizes two-phase natural circulation flow from the SGs to dissipate residual and decay core heat to
RAIO-178483 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-178484
AF-178484 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. 10081 R1, Question 6.3-1) 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 10081 R1, Question 6.3-1. 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-178484 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 16, 2025. Mark W. Shaver}}