Flask Fluid Flow Simulation Using CFD

BNFL and its subsidiary Company, PNTL, design and operate waterfilled L WR fuel transport flasks for the international transport of irradiated fuel. Although some 150 flasks are currently in operation, new flask designs are being developed. As part of the supporting R&D programme, Computational Fluid Dynamics (CFD) codes are being investigated as a means of predicting fluid movements and temperatures within the complex mternal geometry of flasks. The ability to simulate fluid flow is particularly important when convection heat transfer is significant. Although obviously relevant to water filled flasks, the technique is applicable to dry flask thermal assessments (where experience shows that convection heat transfer is often underestimated). Computational Fluid Dynamics has emerged in recent years as an important technique in engineering design and safety assessments. Cheaper computing and the development of general CFD codes allows complex engineering structures to be analysed. However, because of this complexity, it is essential that the application and associated modelling assumptions are critically reviewed. To assess the ability of a CFD code to model flask internals, the code PHOENICS has been used to model the fluid movements in a BNFL Excellox-type flask and the results compared with test data.