Experiences from using the STAR-CD code for Pb/Bi-coolant flows

The influence from using different turbulence models for two types of calculations has been investigated. The standard k-ε, the RNG k-ε, the Chen k-ε, the Cubic k-ε, and the Quadratic k-ε turbulence models were examined for a pin bundle and a reactor vessel air-cooling system. It was investigated how the turbulence models affect the heat removal rate from the reactor vessel during a Total-Loss-Of-Power accident in an 80 MW (thermal) Pb/Bi-cooled Accelerator-Driven System. The temperature and velocity profiles in the boundary layer next to the reactor vessel wall were in all three cases modeled with a standard law for the wall function. It was concluded from these STAR-CD calculations that the choice of turbulence model affects the heat transfer rate very weakly for this type of problem. Thereafter, one calculation was run in which the turbulence equations were not solved and yet another one in which the Two-Layer model in the boundary layer was used together with a RNG k-ε turbulence model. These two latter showed reasonably similar results, however, they had about a 20 K lower maximum temperature at core outlet during the transient evolution than the calculations using the law of the wall function. This discrepancy was attributed to the different heat transfer modes used from the liquid to the wall. Earlier two computational fluid dynamics codes, STAR-CD and FLUENT, has been compared for the air-cooling of the reactor vessel. The results for a Total-Loss of Power accident for the 80 MW (thermal) ANSALDO design showed that the temperature peak from these codes differed about 10 K. Furthermore, in the European project called Preliminary Design Study of and Accelerator-Driven System the STAR-CD outcome appears to be in good agreement with other codes like RELAP5/PARCS, SIMMER-ADS, TRAC-M etc. In the pin bundle calculation a discrepancy of about 20% was found with regard to maximum turbulence dissipation and turbulence kinetic energy at core outlet of the Pb/Bi-coolant when different turbulence models were used. The maximum temperature difference at core outlet varies only by 0.8 K for the examined turbulence models. The computational fluid dynamics code STAR-CD was used for all calculations presented in this paper. (author)