Development of Labyrinth-type sealing devices for prototype fast breeder reactor subassemblies

Abstract

A sodium-cooled, 500-MW(electric) prototype fast breeder reactor (PFBR) is under construction in Kalpakkam, India. The PFBR core houses various subassemblies that are supported vertically inside the core by the sleeves provided in the grid plate. A small radial gap exists between the grid plate sleeve and the foot to facilitate easy handling of subassemblies. It is natural that there will be some leakage flow through this radial gap into the hot and cold pools of the PFBR. To minimize this leakage flow, top and bottom labyrinths are provided on the foot of the subassemblies. The total leak flow rate permitted from the top labyrinth is 195 kg/s, whereas the leak flow rate allowed through the bottom labyrinth is 436 kg/s. Labyrinth-type sealing devices have been developed by carrying out experimental studies. Based on various parametric studies, the labyrinth geometry was optimized. It was found that apart from the clearance between the foot and sleeve, important parameters affecting pressure drop are groove profile, groove pitch, groove-depth-to-width ratio, etc. Taking into account the outcome of these studies, helical square grooved labyrinths have been designed and manufactured for PFBR. This paper presents the details of the similarity criteria followed, experimental methodology applied, and results obtained from the experiments along with their transposability to reactor conditions.