COMPUTATIONAL FLUID DYNAMICS MODELING APPROACH TO EVALUATE VSC – 17 DRY STORAGE CASK THERMAL
A numerical simulation of flow and heat transfer in a ventilated concrete dry storage cask system–17 (VSC–17) is performed and results compared with experimental data to assess the validity of the computational approach. The measurements of steady state temperature distributions on the cask surface, concrete surface, air flow channels, and fuel canister guide are available. Numerical simulations were carried out for normal operating conditions, where both the inlet and outlet vents are open, and for off-normal condition when normal air circulation is interrupted because of blocked vents. Results include the flow and temperature pattern in the ventilated storage system. Computed results were compared with experimental data for axial temperature distribution along the fuel assembly and radial temperature distribution along the storage assembly system. The effect of the turbulence model on temperature distribution pattern was also studied. For all the simulated cases, the computed results showed a trend similar to the experimental observation but did not model exactly. Computed peak cladding temperature in all the simulation cases was slightly higher than the experimental data. Heat transfer results showed some variation due to difference in backfill gas. A study of different k-ε and k-ω turbulence models showed very little effect on temperature distribution.
CFD SIMULATIONS OF FUEL CLADDING AND BASKET SURFACE TEMPERATURES IN AN MPC RAIL CASK DURING NORMAL TRANSPORT
A two-dimensional finite volume model was constructed of a Multi-Purpose Canister (MPC) in a rail cask with twenty-one PWR assemblies inside. Steady state thermal simulations are performed for a range of fuel heat generation rates, for both nitrogen and helium cover gas, and different fuel cladding emissivities. Computational fluid dynamics (CFD) simulations are employed to calculate buoyancy induced motion in, and natural convection and radiation heat transfer across, all gas filled regions. The results are compared to stagnant-gas CFD (S-CFD) simulations, and to simulations that employ Effective Thermal Conductivities (ETC) in the fuel regions. The thermal resistance in two narrow gaps (between the fuel basket and its support brackets, and between the MPC and the transport over-pack), and between the cask outer surface and the environment, account for a significant faction of the total thermal resistance between the hottest fuel and the environment. Uncertainty in those resistances affects the conclusions of this work. The cask Thermal Dissipation Capacity (QTDC) is defined as the fuel heat generation rate that causes the fuel cladding to reach its allowed temperature limit. The QTDC is 27% larger when helium is the backfill gas than for nitrogen. The QTDC predicted by S-CFD is essentially the same as that predicted by CFD, and 3-6% higher than that predicted by ETC. A ten percent increase in cladding emissivity leads to less than a 1% increase in the TDC. The non-isothermal temperature profiles of the fuel basket surfaces determined in this work will be used as boundary conditions in future benchmark experiments that model natural convection/radiation heat transfer in the fuel region.
Numerically Predicting Horizontally Oriented Spent Fuel Rod Surface Temperatures
A comparison between numerical calculations with use of commercial thermal analysis software packages and experimental data simulating a horizontally oriented spent fuel rod array was performed. Twelve cases were analyzed using air and helium for the fill gas, with three different heat dissipation levels. The numerically predicted temperatures are higher than the experimental data for all levels of heat dissipation with air as the fill gas. The temperature differences are 4{degree}C and 23{degree}C for the low heat dissipation and high heat dissipation, respectively. The temperature predictions using helium as a fill gas are lower than the experimental data for the low and medium heat dissipation levels. The temperature predictions are 1{degree}C and 6{degree}C lower than the experimental data for the low and medium heat dissipation, respectively. For the high heat dissipation level, the temperature predictions are 16{degree}C higher than the experimental data. Differences between the predicted and experimental temperatures can be attributed to several factors. These factors include experimental uncertainty in the temperature and heat dissipation measurements, actual convection effects not included in the model, and axial heat flow in the experimental data. This work demonstrates that horizontally oriented spent fuel rod surface temperature predictions can be made using existingmore » commercial software packages. This work also shows that end effects, such as axial heat transfer through the spent fuel rods, will be increasingly important as the amount of dissipated heat increases.« less