ML24264A000
| ML24264A000 | |
| Person / Time | |
|---|---|
| Site: | 99902078 |
| Issue date: | 09/19/2024 |
| From: | NRC |
| To: | NRC/NRR/DNRL/NRLB |
| References | |
| Download: ML24264A000 (6) | |
Text
From:
Getachew Tesfaye Sent:
Thursday, September 19, 2024 10:46 PM To:
Request for Additional Information Cc:
Getachew Tesfaye; Mahmoud -MJ-Jardaneh; Griffith, Thomas; Osborn, Jim; NuScale-SDA-720RAIsPEm Resource
Subject:
NuScale SDAA Section 6.3 - Request for Additional Information No. 036 (RAI-10350-R1)
Attachments:
SECTION 6.3 - RAI-10350-R1-FINAL.pdf Attached please find NRC staffs request for additional information (RAI) concerning the review of NuScale Standard Design Approval Application for its US460 standard plant design (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23306A033).
Please submit your technically correct and complete response by the agreed upon date to the NRC Document Control Desk.
If you have any questions, please do not hesitate to contact me.
Thank you, Getachew Tesfaye (He/Him)
Senior Project Manager NRC/NRR/DNRL/NRLB 301-415-8013
Hearing Identifier:
NuScale_SDA720_RAI_Public Email Number:
38 Mail Envelope Properties (BY5PR09MB56825782AA8C34377E9662498C6C2)
Subject:
NuScale SDAA Section 6.3 - Request for Additional Information No. 036 (RAI-10350-R1)
Sent Date:
9/19/2024 10:45:42 PM Received Date:
9/19/2024 10:45:47 PM From:
Getachew Tesfaye Created By:
Getachew.Tesfaye@nrc.gov Recipients:
"Getachew Tesfaye" <Getachew.Tesfaye@nrc.gov>
Tracking Status: None "Mahmoud -MJ-Jardaneh" <Mahmoud.Jardaneh@nrc.gov>
Tracking Status: None "Griffith, Thomas" <tgriffith@nuscalepower.com>
Tracking Status: None "Osborn, Jim" <josborn@nuscalepower.com>
Tracking Status: None "NuScale-SDA-720RAIsPEm Resource" <NuScale-SDA-720RAIsPEm.Resource@nrc.gov>
Tracking Status: None "Request for Additional Information" <RAI@nuscalepower.com>
Tracking Status: None Post Office:
BY5PR09MB5682.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 584 9/19/2024 10:45:47 PM SECTION 6.3 - RAI-10350-R1-FINAL.pdf 173977 Options Priority:
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1 REQUEST FOR ADDITIONAL INFORMATION No. 036 (RAI-10350-R1)
BY THE OFFICE OF NUCLEAR REACTOR REGULATION NUSCALE STANDARD DESIGN APPROVAL APPLICATION DOCKET NO. 05200050 CHAPTER 6, ENGINEERED SAFETY FEATURES SECTION 6.3, EMERGENCY CORE COOLING SYSTEM ISSUE DATE: 09/19/2024
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Background===
By letter dated October 31, 2023, NuScale Power, LLC (NuScale or the applicant) submitted Part 2, Final Safety Analysis Report (FSAR), Chapter 6, Engineering Safety Features, Revision 1 (Agencywide Documents Access and Management System Accession No. ML23304A345), of the NuScale Standard Design Approval Application (SDAA) for its US460 standard plant design. The applicant submitted the US460 standard plant SDAA in accordance with the requirements of Title 10 Code of Federal Regulations (10 CFR) Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants, Subpart E, Standard Design Approvals. The NRC staff has reviewed the information in Chapter 6 of the SDAA, and other Chapters as necessary, and determined that additional information is required to complete its review.
Regulatory Basis General Design Criterion (GDC) 1, Quality standards and records, requires that structures, systems, and components important to safety shall be designed, fabricated, erected, and tested to quality standards commensurate with the importance of the safety functions to be performed. Where generally recognized codes and standards are used, they shall be identified and evaluated to determine their applicability, adequacy, and sufficiency and shall be supplemented or modified as necessary to assure a quality product in keeping with the required safety function.
GDC 26, Reactivity control system redundancy and capability, requires that two independent reactivity control systems of different design principles shall be provided.
One of the systems shall use control rods, preferably including a positive means for inserting the rods, and shall be capable of reliably controlling reactivity changes to assure that under conditions of normal operation, including anticipated operational occurrences, and with appropriate margin for malfunctions such as stuck rods, specified acceptable fuel design limits are not exceeded. The second reactivity control system shall be capable of reliably controlling the rate of reactivity changes resulting from planned, normal power changes (including xenon burnout) to assure acceptable fuel design limits are not exceeded. One of the systems shall be capable of holding the reactor core subcritical under cold conditions.
GDC 27, Combined reactivity control systems capability, requires that the reactivity control systems shall be designed to have a combined capability, in conjunction with poison addition by the emergency core cooling system, of reliably controlling reactivity changes to assure that under postulated accident conditions and with appropriate margin for stuck rods the capability to cool the core is maintained.
GDC 37, Testing of emergency core cooling system, requires that the emergency core cooling system (ECCS) shall be designed to permit appropriate periodic pressure and
2 functional testing to assure (1) the structural and leaktight integrity of its components, (2) the operability and performance of the active components of the system, and (3) the operability of the system as a whole and, under conditions as close to design as practical, the performance of the full operational sequence that brings the system into operation, including operation of applicable portions of the protection system, the transfer between normal and emergency power sources, and the operation of the associated cooling water system.
10 CFR 52.79(a)(28) requires preoperational testing and initial operations.
10 CFR 52.47(b)(1) requires applications to contain the proposed inspections, tests, analyses, and acceptance criteria (ITAAC) that are necessary and sufficient to provide reasonable assurance that, if the inspections, tests, and analyses are performed and the acceptance criteria met, a plant that incorporates the design is built and will operate in accordance with its approval, the provisions of the Atomic Energy Act, and the NRC's regulations.
Question 6.3-7 Issue Description The NPM-20 SDA design relies on the key design aspects of the ECCS supplemental boron (ESB) feature to provide the appropriate long-term cooling response to AOOs and other design basis events. The integrated functionality of an NPM-20 ESB has not been tested and demonstrated. Performance of the full scale as-built ESB can be impacted by the geometry and functional arrangement of key components, variations in as-built parameters, and uncertainties associated with complex thermal-hydraulic phenomena, especially when considering the integrated system.
During an audit NuScale stated that proper ESB function is assured by boron dissolution separate effects testing; technical specification operability requirements; existing inspections, tests, analyses, and acceptance criteria (ITAAC); and conservatisms applied within the evaluation of ESB performance. The staff views these elements, and other system information provided in the FSAR, as pertinent to the establishment of performance requirements for the system and necessary to perform the safety analysis of the design, all of which are necessary to support a final safety determination of the standard design. However, this does not satisfy the additional requirements of an initial test program which are intended to provide assurance that the system operates in accordance with the design; validate, to the extent practical, the analytical models; and verify the correctness or conservatism of assumptions used to predict plant responses to anticipated transients and postulated accidents.
The ESB is a first-of-a-kind (FOAK) engineered safety feature. FOAK tests are used for new, unique, or special tests to verify design features reviewed by the NRC and set into operation for the first time. Integrated functional testing of the constructed ESB would provide assurance that the as-built system response conforms to the analytical predictions as noted above.
Information Requested The applicant is requested to modify an existing initial test program or ITAAC test, or develop a new test, to demonstrate acceptable performance of the as-built ESB based on predicted system response under expected test conditions to ensure the system as a whole meets fundamental design requirements of the safety analysis. The test should confirm the as-built
3 functionality of the ESB, including boron basket dissolution rates, condensate rail collection capability, mixing tube flow, lower containment boron concentration and mixing, and hopper loading sensor functionality.
The staff observes that such a test may only be needed for the first module, given its purpose to confirm the performance of a first-of-a-kind safety system and verify the conservatism in the safety analyses. In addition, as noted above, appropriate data gathering could be integrated into a test that is already planned to assess plant transient response.
Question 6.3-9 Issue Description FSAR Section 6.3.2.2.1 states two ESB dissolvers add boron to the ECCS recirculating coolant for reactivity control and the ESB dissolvers are fed by hoppers during the startup process.
During the audit, NuScale stated that this information was addressed as part of the staffs FSAR Chapter 16 review resulting in corresponding changes to LCO 3.5.4 and the cycle-specific core operating limits report (COLR). However, the safety analysis is based on certain non-cycle-specific key parameters and analytical limits for the ESB dissolvers. For example, the staff understands that there are maximum and minimum ranges for pellet diameter, as well as a standard pellet shape (i.e., equilateral cylinder). These are important parameters that need to be included in the FSAR.
Additionally, the FSAR does not include a description of the loading evolution prior to startup or explain how confirmation of establishing initial conditions will be accomplished. For example, FSAR Table 6.3-5 identifies the presence of dissolver basket indication; however, no other information of the loading sensors is provided in the FSAR.
Information Requested The staff requests the FSAR to be updated to provide design information sufficiently detailed for the reader to understand the system design and its relationship to the safety analysis to make the necessary finding. This information should include: 1) a description of pellet form (i.e.,
limitations on range of sizes and its shape); 2) a description of the loading/reloading process, including the plant conditions assumed during this evolution; 3) how proper quantity of boron pellets added to the hopper is determined; and 4) a description of instrumentation and sensors utilized by plant personnel to confirm proper remote transport of the boron pellets from the hopper to the dissolver basket.
Question 6.3-10 Issue Description FSAR Section 6.3.2.2 states operators may manually bypass the automatic actuation of ECCS after reactor trip upon confirmation of subcriticality at cold conditions and that sufficient hydrogen concentration will be maintained in the reactor coolant system (RCS) throughout DHRS cooldown to preclude radiolytic generation of combustible gases. FSAR Chapter 7 specifies the actuation delay is 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. However, it is not clear how these criteria will be determined by the control room operator and what information available in the control room will be used by the operator when determining whether it is acceptable to bypass the ECCS timer.
NuScale stated in the audit that the expected operational requirements for the manual bypass of
4 the 8-hour ECCS timer (i.e., block the ECCS actuation due to the 8-hour timer) include confirming subcriticality at cold conditions [defined as 200°F] and the detailed steps are expected to include confirmation of control rod insertion.
Information Requested NuScale is requested to clarify if all cycle-specific core designs will ensure the reactor remains subcritical under cold conditions when all control rods are inserted, and if so, prescribe this in the FSAR. If not, NuScale is requested to describe the criteria and information available to the control room operators at the time of a reactor trip that will be used to objectively determine sufficient shutdown margin under cold conditions such that it is appropriate to bypass the 8-hour ECCS actuation delay. Corresponding updates to the FSAR should be provided.
Question 6.3-11 Issue Description FSAR Table 6.3-4 specifies the supplemental boron lower mixing tube and dissolver Quality Group classification as "N/A." During the audit, NuScale stated that the components of the ESB are not pressure retaining and are not considered in the scope of the ASME BPV Code. The staff understands the basis for this explanation. The ESB, however, is a safety-related feature of the ECCS and is therefore considered important to safety in the context of GDC 1 and subject to the regulatory positions described in RG 1.26. Specifically, RG 1.26 states "systems or portions of systems important to safety that are designed for (1) reactor shutdown or (2) residual heat removal" should be classified as Quality Group B.
Information Requested In lieu of applying a generally recognized code or standard (e.g., the ASME BPV Code) to the ESB components, NuScale is requested to describe the design rules or augmented quality provisions that are assigned to the ESB components to ensure they are designed and constructed such that they will be capable of performing their safety-related functions and satisfy the requirements of GDC 1.