Hydraulic design of primary sodium header of a fast spectrum reactor by computational and experimental studies

Computational fluid dynamics (CFD) investigations of flow and pressure distributions in the primary sodium header of fast reactor have been carried out. The focus of the study is to quantify the magnitude of swirl superimposed on main flow and assess its influence on pressure loss in the header and flow mal-distribution among the primary pipes. From compact layout considerations, a spherical shape has been chosen for the header. The static pressure loss coefficient for the basic ‘header-primary pipe’ assembly without any internals is determined to be 7.2. With suitable internal baffles and a central cone this value is reduced to 1.22. The loss coefficients predicted by CFD studies have been validated by conducting experiments on 1:3 scale air models. Following this, an integrated CFD study of header coupled with sodium pump including impeller and diffuser has been carried out. It is seen that the diffuser induces a strong swirl in the fluid entering the header. Due to this swirl, the total pressure loss coefficient in the header-pipe assembly increases by a factor of two, when compared to that without the swirl. The swirl also leads to flow mal-distribution among the two primary pipes to the extent of ±9% from the mean value. This flow mal-distribution is an important input for safety analysis of the reactor for the event of ‘one primary pipe rupture’.