ML21076A416
| ML21076A416 | |
| Person / Time | |
|---|---|
| Issue date: | 03/17/2021 |
| From: | Hossein Esmaili NRC/RES/DSA/FSTB |
| To: | Hayes M NRC/NRR/DANU/UART |
| Kyriazidis L | |
| Shared Package | |
| ML21076A417 | List: |
| References | |
| Download: ML21076A416 (4) | |
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MEMORANDUM TO:
Michelle Hayes, Chief Advanced Reactor Technical Branch Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation FROM:
Hossein Esmaili, Chief Fuel and Source Term Code Development Branch Division of Systems Analysis Office of Nuclear Regulatory Research
SUBJECT:
METALLIC FUEL ASSESSMENT IN FAST In accordance with the Advanced Reactor Program - Summary of Integrated Schedule and Regulatory Activities (US NRC, 2021), staff from the Fuel and Source Term Code Development Branch (FSCB) have prepared a technical assessment report for completing the FAST code assessment for metallic fuel milestone. This memorandum identifies the overall conclusions from the metallic fuel assessment report.
The work continues the assessment of NRCs fuel performance code FAST for modeling sodium fast reactor fuels (i.e., sodium bonded metallic fuels). This assessment report adds to FASTs existing metallic fuel assessment cases by modeling EBR-IIs X441 experiment. The assessment report discusses the current material properties used in the fuel performance codes FAST and BISON for SFR fuel types, discusses key phenomena important to modeling, compares the simulation results to experimental results, and discusses future improvements to that should be implemented to FAST to improve its current capabilities.
Summary of the Assessment Work The main conclusions from this report are as follows:
FAST and BISON both have capabilities needed to model sodium fast reactor metallic
fuel rods. The assessment work has identified improvements that could be made to enhance code capabilities.
Improvements to FASTs fuel thermal conductivity model are underway as comparisons
to models in literature revealed FASTs model was overpredicting measured values. The effects of sodium infiltration and porosity on fuel thermal conductivity will also be investigated.
CONTACT: Lucas Kyriazidis, RES/DSA 301-415-7834 March 17, 2021 Signed by Esmaili, Hossein on 03/17/21
M. Hayes 2
The current fission gas release model implemented in FAST overpredicts low to medium
burnup fuels, found in the literature and does not account for transient effects. Efforts are underway to investigate a more mechanistic FGR model which may improve the ability to model transients and low to medium burnup fuels. Overpredictions in FGR causes an overestimation in rod internal pressure, leading to predictions cladding strains that may be overly conservative.
The assessment revealed that assuming isotropic fuel swelling may not be appropriate,
as comparing the simulation results to published literature revealed a significant overprediction in axial fuel swelling. Metallic fuels prefer to radially swell, and the assumption of isotropic swelling caused a late prediction of gap closure which subsequently affects strain estimates. Efforts are underway to investigate how current data can support development of an anisotropic fuel swelling model.
FAST assumes no fuel-clad slippage when in contact and any fuel axial expansion in the
fuel is transmitted directly to the cladding. As FAST currently assumes isotropic swelling and it is known the metallic fuels prefer to radially swell, this resulted in a significant overprediction in cladding elongation.
Future Work The assessment work has identified key improvements that FAST should undergo to prepare for confirmatory calculations. Near-term improvements include implementation of a new thermal conductivity model, development and implementation of an anisotropic fuel swelling model, and implementation of a more mechanistic FGR model.
The NRC is also considering if improvements to the mechanical modeling of the fuel and cladding should be made. This includes investigating the effects of modeling fuel deformation and creep, slippage between fuel and cladding after contact and modeling fuel-cladding chemical interaction.
Lastly, future work will include expanding the metallic fuel database in FAST. The FAST team has identified another key assessment case (i.e., FFTF IFR-1 experiment). In addition, the FAST team will continue to collaborate with the BISON team with the goal of building a common metallic fuel database.
This memorandum will complete the Strategy 2 Volume 2 (US NRC, 2020) FAST code assessment for metallic fuel milestone (US NRC, 2021).
M. Hayes 3
References US NRC. (2020). NRC Non-LWR Vision and Strategy, Volume 2 - Fuel Performance Analysis for Non-LWRs. ML20030A177.
US NRC. (2021, March 9). US NRC Public Site. Retrieved from Advanced Reactors Details -
Summary of Integrated Schedule and Regulatory Activities:
https://www.nrc.gov/reactors/new-reactors/advanced/details.html#visionstrat
ML21076A417; Memo ML21076A416 OFFICE RES/DSA/FSCB RES/DSA/FSCB NAME LKyriazidis HEsmaili DATE Mar 17, 2021 Mar 17, 2021