ML24054A096
| ML24054A096 | |
| Person / Time | |
|---|---|
| Site: | 99902100 |
| Issue date: | 02/23/2024 |
| From: | Stephanie Devlin-Gill NRC/NRR/DANU/UAL1 |
| To: | Jessup W NRC/NRR/DANU/UAL1 |
| References | |
| EPID L-2023-TOP-0057 | |
| Download: ML24054A096 (1) | |
Text
OFFICIAL USE ONLY PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION DISCUSSION TOPICS FOR THE FEBRUARY 8, 2024, CLOSED MEETING REGARDING THE TERRAPOWER, LLC STABILITY METHODOLOGY TOPICAL REPORT, REVISION 0 (EPID: L-2023-TOP-0057)
The purpose of this document is to provide discussion topics for the February 8, 2024, closed meeting regarding the U.S. Nuclear Regulatory Commission (NRC) staffs review of TerraPower, LLC (TerraPower) Stability Methodology Topical Report [(TR)], Revision 0, (Agencywide Documents Access and Management System (ADAMS) Accession No.: ML23334A238; non-public). The NRC staff is performing a completeness determination review to assess whether there is sufficient technical information in scope and depth to allow the NRC staff to perform its detailed technical review of the TR. The TR is intended to demonstrate how the Natrium design conforms with Natrium Principal Design Criterion 12, Suppression of reactor power oscillations.
In accordance with Office of Nuclear Reactor Regulation, Office Instruction LIC-109, Revision 3, Acceptance Review Procedures for Licensing Basis Changes (ML20036C829), the NRC staff conducted a preliminary assessment of the TR and determined that TerraPowers approach to performing reactor stability analysis for the Natrium design appears conceptually reasonable insofar as it aligns with prior sodium fast reactor stability analysis methods and produces similar figures of merit concerning stable core performance. However, the NRC staff has preliminarily observed that the TR is missing key details concerning the derivation of some key functions that are an integral part of the stability analysis, and that additional justification may be required for some modeling simplifications and uncertainty treatments. Relative to these issues, the NRC staff would like to discuss the following topics with TerraPower to assist in its ongoing completeness determination:
- 1. The NRC staff observes that TerraPowers predicted stability analysis results for the Fermi 1 benchmark, described in TR Section 6.0, Fermi-1 Benchmark Calculation and listed in TR Table 6-5, Nyquist Summary, indicate significant deviations between measured and predicted behavior, which warrants further discussion to establish whether the benchmark can be considered meaningful or a different benchmark could be considered. For the Fermi 1 benchmark, consideration could be given to the comparisons of both the zero-power transfer function (ZPTF) with no reactivity feedback and the full power transfer function (FPTF) with reactivity feedback to further identify the source of the deviations between measured and predicted data. The NRC staff observes that the Fermi 1 validation for zero power without reactivity feedback is in better agreement with measured data (~0.5%
standard deviation) (Reference 1, page 80).
- 2. The validation absolute errors and standard deviation in TR Table 6-5 are high. Specifically, considering the aggregate of comparisons between measured and predicted values, an average absolute error of ((
)). The NRC staff would like to discuss whether additional justification could be provided to support the existing information or if consideration could be given to using different validation methods or different facilities validating data sets (Reference 2).
- 3. The TR does not describe the neutronics governing equations in the time and frequency domains. Section 5.1.1, Full Power Transfer Function Calculation, of the TR describes the calculation of the FPTF. The FPTF equation and information describing how this equation
OFFICIAL USE ONLY PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 2
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION was derived from time domain kinetic equations are important (see the example below) but are missing in the TR. The NRC staff would like to discuss whether additional information is available that describes the derivation of the FPTF so that the NRC staff can confirm and verify the results provided in the TR Table 6-2, Example Gain and Phase Shift, in the TR.
The ZPTF is given in the TR as ((
)). The ZPTF can be calculated using the physical parameters in the TR Table 6-2. The FPTF is given in Eqs. (5-12) through (5-14) in the TR. To calculate the FPTF, the feedback transfer function, H(), ((
)), the FPTF in TR Table 6-2 cannot be reviewed. The NRC staff notes that one example which TerraPower could consider are the equations in Reference 3 for calculation of FPTF.
- 4. Additional detail will be needed concerning the treatment of various reactivity feedback mechanisms:
- a. The NRC staff would like to discuss any available additional information regarding the effects included in the ((
)) and the justification for why it adequately accounts for any multidimensional effects.
- b. The NRC staff would like to discuss how TerraPower has accounted for ((
)). (Note: For both items a, above, and b, TerraPower may consider performing sensitivity analyses to demonstrate the adequacy of the treatment of these parameters; see page 208 to 209 of Reference 4).
- 5. The NRC staff would like to discuss the prospect of TerraPower providing a total reactivity governing equation that describes the overall combination of temperature feedback (e.g.,
linear, quadratic, or weighting). As an example, refer to the total reactivity feedback for Molten Salt Reactor Experiment Facility from page 92 of Reference 5.
REFERENCES
[1] A. E. Klickman, et. al., Enrico Fermi Atomic Power Plant Nuclear Test Series, Oscillator Tests in the Enrico Fermi Reactor, APDA-NtS-11, dated August 1967.
[2] Ling Zou at al. SAM Code Validation using the Compact Integral Effects Test (CIET)
Experimental Data, ANL/NSE-19/11, Argonne National Laboratory, dated June 2019.
[3] Antonio Cammi et al., Transfer Function Modeling of Zero-Power Dynamics of Circulating Fuel Reactors, [DOI: 10.1115/1.4002880], Journal of Engineering for Gas Turbines and Power, Vol. 133, dated May 2011.
[4] Toshio SANDA et. al., Transfer Function Measurements in JOYO by Pile Oscillator Method, Journal of Nuclear Science and Technology, 20[3], pp. 199-212, dated March 1983.
[5] Vikram Singh, Study of The Dynamic Behavior of Molten-Salt Reactors, Thesis, University of Tennessee, 2019.