Computational fluid dynamic investigations and experimental validation of frozen seal sodium valve assembly of a fast reactor

Frozen seal sodium valves are used in fast reactors. To achieve sodium freezing, horizontal fins are attached to the outer surface of valve sheath. Adjacent fins form open-ended cavities and natural convection of air in these cavities is investigated using the PHOENICS code for various values of fin length, spacing and root temperature. It is seen that convective air does not penetrate deep into shallow cavities leading to poor heat transfer coefficient, offsetting the enhancement in surface area. Penetration depth of air is a function of aspect ratio and Rayleigh number based on fin spacing and is independent of fin length. Generalized correlations are derived for Nusselt number in terms of Rayleigh number and aspect ratio. Using these correlations, temperature distribution in entire valve assembly is predicted using the HEATING5 code, to select an optimum design. Experiments have been conducted on a model valve of selected design in the SILVERINA facility available at this centre. Measured stem temperature distribution is found to compare satisfactorily with HEATING5 predictions, validating the correlations derived from computational fluid dynamic studies and integrated thermal analysis methodology.