ML25071A020
| ML25071A020 | |
| Person / Time | |
|---|---|
| Site: | 99902100 |
| Issue date: | 03/12/2025 |
| From: | Reed Anzalone, Brusselmans R NRC/NRR/DANU/UAL1 |
| To: | |
| References | |
| Download: ML25071A020 (1) | |
Text
NRC Staff Review of the Topical Report Reactor Stability Methodology, Revision 0 Roel Brusselmans, Project Manager Reed Anzalone, Senior Nuclear Engineer Office of Nuclear Reactor Regulation Division of Advanced Reactors and Non-Power Production and Utilization Facilities
Agenda
- Review chronology
- Topical report (TR) purpose and review strategy
- Safety evaluation overview
- Conclusions
- Proposed Limitations and Conditions 2
Review Chronology
- June 29, 2023: Pre-Application Public Meeting (ML24012A067)
- November 23, 2023: Submittal of Stability Methodology Topical Report, Revision 0 (ML23334A239)
- February 20, 2024: TR accepted for review by the NRC staff (ML23355A078)
- May through July 2024: Audit conducted (ML24233A292)
- August 16, 2024: Revision to the TR submitted (ML24232A231)
- January 31, 2025: NRC staffs draft safety evaluation issued (ML24324A218)
Related TerraPower submittal:
- March 28, 2024: TerraPower submitted, on behalf of US SFR Owner, LLC, a construction permit application for the Kemmerer Power Station Unit 1 (ML24088A059).
3
TR Purpose and Review Strategy
- Purpose of TR:
- To describe the methodology used to characterize Natrium reactor stability. TerraPower states,
[n]uclear reactor stability analysis, as approached by this TR, is the study of a reactors oscillatory power response to reactivity perturbations. Ensuring a stable (i.e., non-diverging) oscillatory reactor power response helps preclude controllability issues and limits the potential of failing to maintain design limits.
- Review strategy
- Evaluate theoretical underpinning and prior uses of similar analytic methods
- Evaluate treatment of uncertainties
- Review demonstration of analytic methods and uncertainty treatment
- Evaluate operating reactor benchmark 4
Safety Evaluation Overview
- Regulatory evaluation
- Summary of TR
- Technical evaluation
- Operating domain and frequency domain
- Uncertainty treatment
- Fermi 1 benchmark evaluation
- Limitations and conditions
- Conclusions 5
Regulations and Review Scope
- The TR provides methods to demonstrate that the Natrium reactor is stable in all conditions of normal operation, including anticipated operational occurrences.
- Detect and suppress solutions for unstable conditions are not within the scope of NRC staff review.
6 Principal Design Criterion 12: 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 radionuclide release design limits (SARRDLs) are not possible or can be reliably and readily detected and suppressed.
Relevant Natrium Design Features
- Pool-type sodium-cooled, fast reactor
- Operates at near-atmospheric pressure
- Metallic fuel
- Fuel is chemically compatible with coolant
- Low fuel operating temperature gives substantial margin to coolant boiling
- Tightly coupled neutronic performance
- Key reactivity phenomena act core-wide 7
Conclusions The NRC staff concludes that the TR provides an acceptable methodology for assessing the stability characteristics of the Natrium reactor based on the following considerations:
- 1. The TR proposes an acceptable means to characterize and discretize the power-to-flow operating domain, including characteristics to indicate when a more detailed discretization would be necessary.
- 2. An applicant implementing the methodology will justify the selection of analyzed frequencies at each statepoint.
- 3. The TR methodology reflects a theoretical approach that has been used to evaluate stability in similar reactor system designs;
- 4. The TR methodology includes an acceptable means to characterize input and model uncertainty, and to justify these means; and
- 5. The TR includes an acceptable evaluation of a benchmarking exercise comparing its analytic methods to stability experiments in the Fermi 1 reactor.
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Proposed Limitations and Conditions 1.
Inputs provided to the methodology calculated by other methodologies are to capture the higher-fidelity behavior of the identified important phenomena in a manner consistent with their incorporation into this methodology.
2.
The topical report develops a ((
)) for the purpose of describing how such a ((
)) may be obtained and for the purpose of describing how such a (( )) is subsequently applied as part of the methodologys calculation steps. In application, a ((
)) must be developed and appropriately justified for the use described in this methodology. Any applied ((
)) must be reviewed and approved by the NRC.
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Acknowledgments
- RES/DSA - Peter Yarsky
- NRR/DANU - Ben Parks; Inseok Baek 10