Hydraulics of Honeycomb Type Orifices for Flow Zoning in FBR.

摘要

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 Honey-comb 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.