          G. K. PANDEY, D. RAMDASU, P.ANUP KUMAR, M. THIRUMALAI, G. PADMAKUMAR, V. PRAKASH, C. ANANDBABU, P.KALYANASUNDARAM, G. VAIDYANATHAN Indira Gandhi Centre for Atomic Research, Department of Atomic Energy Kalapakkam, Tamilnadu INDIA gkpandey@igcar.gov.in   The construction of Prototype Fast Breeder Reactor (PFBR) has commenced at Kalpakkam, INDIA. PFBR is a sodium cooled pool type reactor. PFBR core subassemblies (SA) are supported vertically inside the sleeves provided in the Grid plate (GP). The GP acts as a coolant header through which flow is distributed among the SA to remove fission heat. Since the power profile of the reactor core is not uniform, it is necessary to distribute the coolant flow to each subassembly according to their power levels. PFBR core is divided into 15 zones such as fuel, blanket, reflector, storage etc according to their respective power levels. To achieve the maximum temperature of sodium at core outlet, it is essential to feed the subassemblies with a flow proportional to the power generation. The flow zoning in the different SA’s of the reactor core is achieved by installing pressure dropping devices in the foot of the subassembly. Orifices having Honey7comb type geometry were developed to meet the flow zoning requirements of Fuel zone. The requirement for one such fuel zone VI is to achieve a pressure drop of 27.69 m Na at rated flow condition without any cavitation. Hydraulics of these orifices is important in achieving the required pressure drop without cavitation. The pressure drop across these orifice geometries depends mainly on geometrical factors and Reynolds number (Re) of the flow. Experiments were carried out on full scale model using water as simulant. Re and Eu (Euler number) similitude was followed. Cavitation test were carried out to find the incipient cavitation index and were compared to operating Cavitation index to find the suitability. Cavitation test were also bench marked with a standard orifice nozzle to validate test procedure. This paper presents the details of the similarity criteria followed, experimental methodology, instrumentation involved and the results obtained from the experiments with their transposability to the reactor conditions.  Fast breeder reactor, Similarity, Subassemblies, Flow zoning device, Reynolds number, Cavitation   A 500 MWe capacity sodium cooled fast breeder reactor (PFBR) is currently under construction at Kalpakkam, India. The heart of the reactor is the core where heat is generated from nuclear fission. This heat is transported by primary sodium and transfers the heat to the secondary sodium in the Intermediate Heat Exchanger. Finally the secondary sodium exchanges heat to water in the steam generator leading to production of superheated steam to generate power [1]. Heat transport circuit of PFBR is presented in Fig. 1. The power spectrum across the core of a nuclear reactor is not uniform. The core consists of different regions viz., fuel, blanket, storage etc. Each region is divided into number of zones based on the power produced and each zone consists of a number of subassemblies mounted vertically on the grid plate. To achieve the maximum temperature of sodium at core outlet, it is essential to feed the subassemblies with a flow proportional to the power generation. Flow through each zone is varied with maximum at central zones, to get uniform outlet temperature and is called flow zoning. Fig.1: Heat transport circuit of PFBR Since coolant for all fuel subassemblies which has similar geometries are fed by a common primary sodium pump, flow zoning is achieved by installing different pressure drop devices in the foot of these subassemblies. In the fuel region there are seven zones. Zone1 does not RECENT ADVANCES in NETWORKING, VLSI and SIGNAL PROCESSING ISSN: 1790-5117 225 ISBN: 978-960-474-162-5