ML18346A528
| ML18346A528 | |
| Person / Time | |
|---|---|
| Issue date: | 12/12/2018 |
| From: | Jorge Solis Office of Nuclear Material Safety and Safeguards |
| To: | Haile Lindsay NRC/NMSS/DSFM/IOB |
| Lindsay H | |
| Shared Package | |
| ML18338A059 | List: |
| References | |
| Download: ML18346A528 (11) | |
Text
Thermal Analysis of Dry Storage Casks: Verification, Validation, and Uncertainty Quantification Jorge Solís United State Nuclear Regulatory Commission Rockville, Maryland December 12, 2018
Agenda
- Introduction
- Ongoing Verification and Validation (V&V) Efforts
- V&V Results
- Additional Guidelines
- Summary 12/12/2018 2
Introduction Thermal reviews for dry casks are performed in accordance with 10 CFR Part 72 and the Standard Review Plan (SRP) for Spent Fuel Dry Storage Systems at a General License Facility (NUREG-1536)
Per 10 CFR 72, the spent fuel cladding must be protected during storage against degradation that leads to gross ruptures
- One of the ways that cladding is protected is by keeping the peak cladding temperature (PCT) below 400°C Cask vendors use CFD methods to perform thermal analysis
- Applicants for CoCs regularly request increases in cask heat loads which often result in reduced margin to cladding temperature limits For proper use of CFD methods CFD models are assessed for accuracy by NRC staff, including verification, validation, and quantification of uncertainties 12/12/2018 3
Ongoing V&V Efforts
- Validation: Procedure to test if the model accurately represents reality
- Verification: Procedure to test if the code solves the equations accurately
- Uncertainty: A potential deficiency that is due to lack of knowledge
- NRCs ongoing V&V efforts include the analysis of a dry cask simulator (DCS) which mimics conditions for aboveground and belowground configurations of vertical ventilated dry cask systems with canisters
- The NRC used the DCS experiments in order to validate assumptions in CFD calculations for ventilated spent fuel cask thermal design analyses
- NRC also performed the analysis of the TN-32B cask using data from DOEs high burnup fuel demonstration program 12/12/2018 4
V&V of a DCS Model DCS testing successfully completed for several configurations:
Over 40 unique data sets collected
- 14 each for aboveground and belowground configurations
- 13 additional data sets for cross-wind testing Comparisons with CFD simulations show favorable agreement Within validation uncertainty (simulation + experimental) for all cases for PCT and air flow rate (air)
Additional steady state temperature profiles comparisons for assembly wall, basket, pressure vessel canister, and overpack also show good agreement The solution method is not complete without:
Validation Solution Verification Uncertainty Quantification 12/12/2018 5
V&V of TN-32B Model
- The analysis shows predicted results are very sensitive to the input uncertainty (especially air and helium gaps)
- The analysis predicts the location where maximum temperature was measured. Also, the analysis compared very well with measured profiles including uncertainty bands
- Overall, considering all input assumptions in the analysis, CFD predictions show favorable agreement (provided complete information on uncertainty is used in the analysis)
- A lesson learned from this analysis is that quantification of uncertainty is paramount for any type of licensing analysis, especially when small margins to material temperature limits are predicted
- These results cannot be generalized because they are specific to the TN-32B 12/12/2018 cask
V&V Results
- The analysis results from both the DCS and TN-32B CFD models showed that by applying best practice guidelines, CFD methods can accurately predict PCTs
- The analyses also showed that, in order to predict accurate PCTs, quantification of uncertainties is necessary
- Based on these V&V efforts, the NRC concluded that in order to apply CFD methods and reduce margins to material temperature limits, cask vendors should perform V&V of their CFD models and quantify associated uncertainties 12/12/2018 7
Uncertainty Quantification
- Thermal analyses with very small margin have been submitted that do not provide modeling and application uncertainty
- To obtain accurate thermal results, CFD simulations should include a determination of modeling and application uncertainty (claimed conservatisms should be quantified)
- The modeling (i.e., turbulence, radiation heat transfer, porous media, etc.) and application uncertainty (i.e.,
boundary conditions) can only be determined through adequate model validation and sensitivity analysis 12/12/2018 8
Additional Guidelines Guidance will be revised/added based on the following reports:
- CFD best practice guidelines for dry cask applications (NUREG-2152)
- Impact of variation in environmental conditions (NUREG-2174)
- Performing validation using data from the BWR and PWR assembly zirc fire programs performed in Sandia National Laboratories (temperature and induced mass flow rate) (NUREG-2208)
- Thermal-hydraulic experiments using a dry cask simulator (NUREG/CR-7250) 12/12/20187 9
Additional Guidelines
- Verification, validation and uncertainty quantification of a CFD model using TN-32B cask data (NUREG report available in 2019)
- Verification, validation and uncertainty quantification of a CFD model using dry cask simulator data (NUREG report available in 2019)
NRC uses the ASME V&V 20 (Standard for Verification and Validation in Computational Fluid Dynamics and Heat Transfer) guidelines for dry cask applications 12/12/20187 10
Summary
- NRCs ongoing V&V efforts include the analyses of a dry cask simulator (DCS) and the TN-32B cask
- Comparisons of predicted vs measured PCTs from both models showed favorable agreement (within experimental uncertainty)
- Additionally, comparisons of predicted vs measured air mass flow rate showed favorable agreement (within experimental uncertainty) for a DCS
- Margins can only be claimed (and reduced if one choses to do so) by performing an adequate V&V with UQ (uncertainty quantification)
- As a result of additional experiments and validation studies, CFD BPG (NUREG-2152) and SRPs are being revised accordingly 12/12/2018 11