[en] Sodium cooled, 500 MWe Prototype Fast Breeder Reactor (PFBR) is under construction at Kalpakkam, India. The core of PFBR is divided into various zones such as fuel, blanket, reflector, storage etc., according to their function and flow requirement. The core subassemblies (SA) are supported vertically inside the core by the sleeves provided in the Grid plate (GP). The foot of the SA is located inside the GP sleeve and a small radial gap exists between sleeve and the foot. It is expected that there will be some leakage flow through this radial gap into hot and cold pools of PFBR. To minimize this leakage flow, labyrinth type sealing devices were developed by carrying out experimental study. This paper presents the details of the similarity criteria followed, experimental methodology and the results obtained from the experiments with their transposability to the reactor conditions. (author)