ML24233A295
| ML24233A295 | |
| Person / Time | |
|---|---|
| Site: | 99902100 |
| Issue date: | 12/12/2024 |
| From: | Brusselmans R NRC/NRR/DANU/UAL1 |
| To: | George Wilson TerraPower |
| References | |
| TP-LIC-RPT-0006, EPID L-2023-TOP-0057 | |
| Download: ML24233A295 (1) | |
Text
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION TERRAPOWER, LLC - AUDIT
SUMMARY
REPORT, TOPICAL REPORT TP-LIC-RPT-0006, STABILITY METHODOLOGY TOPICAL REPORT, REVISION 0 Applicant:
TerraPower, LLC Applicant Address:
15800 Northup Way, Bellevue, WA 98008 Plant Name:
Natrium Project No.:
99902100
1.0 BACKGROUND
By letter dated November 30, 2023, TerraPower, LLC (TerraPower) submitted topical report (TR) Stability Methodology Topical Report, Revision 0 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23334A239) to the U.S. Nuclear Regulatory Commission (NRC) staff. The TR contains an overview and description of the model developed to evaluate reactor stability for the Natrium sodium fast reactor design. On February 20, 2024, the NRC staff found that the material presented in the TR provides technical information in sufficient detail to enable the NRC staff to conduct a detailed technical review (ML23355A072).
2.0 AUDIT REGULATORY BASES Title 10 of the Code of Federal Regulations (10 CFR) 50.34(a)(3)(i) requires that an application for a construction permit include in its preliminary safety analysis report the principal design criteria (PDC) for the facility. The NRC staff considered the following proposed Natrium PDC from TR NATD-LIC-RPRT-0002 (ML24101A362) in its review of this TR:
Natrium PDC 10: Reactor design. The reactor core and associated coolant, control, and protection systems shall be designed with appropriate margin to assure that specified acceptable system radionuclide release design limits are not exceeded during any condition of normal operation, including the effects of anticipated operational occurrences.
Natrium PDC 12: Suppression of reactor power oscillations. The reactor core; associated structures; and associated coolant, control, and protection systems shall be designed to ensure that power oscillations that can result in conditions exceeding specified acceptable system radionuclide release design limits are not possible or can be reliably and readily detected and suppressed.
3.0 AUDIT PURPOSE AND OBJECTIVES The purpose of the audit was for the NRC staff to gain a more detailed understanding of TerraPowers stability methodology. A secondary purpose of the audit was to identify any information that would require docketing to support the NRC staffs safety evaluation.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 4.0 SCOPE OF THE AUDIT AND AUDIT ACTIVITIES The audit followed the guidance in the Office of Nuclear Reactor Regulations Office Instruction LIC-111, Regulatory Audits, Revision 1 (ML19226A274). The NRC staff provided its audit plan for the subject TR to TerraPower on April 24, 2024 (ML24103A220). The audit was conducted virtually from May 7, 2024, through July 16, 2024, using TerraPowers electronic reading room (ERR). Audit activities included virtual meetings to discuss questions, audit of submitted files, and code demonstrations via videoconference.
Members of the audit team included the NRC staff listed below:
Reed Anzalone, Senior Nuclear Engineer, Natrium Technical Lead Inseok Baek, Reactor Engineer Stephanie Devlin-Gill, Senior Project Manager, Natrium Ben Parks, Senior Technical Advisor, Audit Lead The participants from TerraPower for this audit were Patrick Donnelly and Matthew Presson and the following representatives from General Electric Vernova:
Jacob Bartel Gregory Dunn Timothy Enfinger Adam Gregory Nelson Scott Pfeffer Gabrielle Schreier The NRC staff did not acquire any documents during the audit. The NRC staff reviewed the following documents during the audit using TerraPowers ERR:
NAT-6006, Reactor Stability Analysis for Natrium Preliminary Safety Analysis Report and Construction Permit Application, Revision 0, November 2023.
DBR-0069924, Natrium Demonstration Stability - Fermi-I Benchmark Analysis - Design Notes, Revision 0.
008N1018, Data Qualification Evaluation Report: Fermi-I Stability Benchmark, Revision 0, October 2023.
While the audit plan had stated an audit exit meeting date of June 7, 2024, due to ongoing discussions for audit questions, the audit exit meeting was held on July 16, 2024, where the staff summarized the audit purpose, activities, and high-level results. On August 16, 2024, TerraPower submitted a revision to the subject TR, NAT-9393, Reactor Stability Topical Report, Revision 0 (ML24232A231), which is a result of the audit discussions between the NRC staff and TerraPower, as summarized below.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 5.0
SUMMARY
OF OBSERVATIONS As indicated in the NRC staffs audit plan, the audit was focused on specific inquiries pertaining to the content of the TR. The NRC staff reviewed information through the TerraPower ERR and held discussions with TerraPower to understand and resolve questions. The table below replicates the transmitted audit questions and summarizes the resolution of the questions.
Question Number Question Resolution of Question 1
TR section 2.3, Important Phenomena states, Phenomena relevant to the stability of the Natrium reactor were identified and ranked using a categorization of low, medium, and high importance, and all phenomena with an importance of medium or higher are identified as important phenomena and included in Table 2-2.
- a. Provide documentation showing the additional phenomena considered and ranked as low.
- b. Briefly describe how the ranking was accomplished.
TerraPower provided additional information about the phenomena identification and ranking process.
TerraPower stated that the individuals involved with the exercise have substantial experience and expertise with LWR stability evaluations and with sodium cooled reactors, and determined that there were no low ranked phenomena identified. Based on the additional clarification, the NRC staff determined that information provided in TR section 2.3 is adequate and docketing further information was not necessary.
2 TR chapter 3, Methodology Roadmap,
((
))
TerraPower proposed revisions to the TR that were responsive to the audit question.
3 Provide additional information to justify the uncertainty approach described in section 3.3.3.1, Description of Selected Approach.
TerraPower proposed revisions to the TR that were responsive to the audit question.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION Question Number Question Resolution of Question 4
TR chapters 4, Models, and 5, Technical Evaluation Process Description, provide descriptions of the models and stability evaluation process, respectively. TR chapter 6, Fermi-1 Benchmark Calculation, provides a comparison of the calculated stability performance of the Enrico Fermi Unit 1 (Fermi 1) reactor to measured data from stability tests at Fermi 1. TR chapter 7, Plant-Specific Application, provides an evaluation of Natrium stability at one statepoint. Provide calculation documentation (e.g., latest revisions of calculation notes or files) supporting the evaluations described in chapters 6 and 7, including:
- a. for chapter 6, material describing the treatment of experimental data;
- b. calculation of system reactivity coefficients and temperatures;
- c. calculation of the transfer functions; and
- d. description of the uncertainty analysis TerraPower provided the following reports in the ERR for the NRC staff to audit:
NAT-6006, DBR-0069924, and 008N1018.
The NRC staff audited the ZPTF and full power transfer function validations using the material provided in the ERR.
The NRC staff located an academic source ((
)) that provided independent verification for the Zero Power Transfer Function (ZPTF) referenced in TR chapter 6.
The NRC staff confirmed that TerraPower considered ((
)) reactivity in its methodology.
5 Provide additional information describing the assessment of Fermi 1 benchmarking results, including a justification that reasonable agreement was achieved and that appropriate differences between measured and calculated parameters have been identified (e.g., ((
)) as displayed in TR Figures 6-2, Transfer Function Gain Plot, and 6-3, Transfer Function Phase Shift Plot).
TerraPower proposed revisions to the TR that were responsive to the audit question.
6 As described in TR section 6.1.3,
((
)) a ((
)) is determined based on a comparison of measured to calculated values. Provide a justification for the application of this ((
))
to predicted Natrium results as described in TR section 7.2.1, Demonstration of Model Uncertainties Treatment.
TerraPower proposed revisions to the TR that were responsive to the audit question.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 6.0 REQUESTS FOR ADDITIONAL INFORMATION RESULTING FROM AUDIT As a result of the audit, the NRC staff did not identify any requests for additional information related to this TR. However, TerraPower submitted an update to its TR as a result of the audit.
7.0 OPEN ITEMS AND PROPOSED CLOSURE PATHS There are no open items resulting from this audit.