Measurement of Pressure Drop in a Full-Scale Fuel Assembly of a Liquid Metal Reactor

An experimental study has been carried out to measure the pressure drop in a 271-pin fuel assembly of a liquid metal reactor. The rod pitch to rod diameter ratio~ P/D! of the fuel assembly is 1.2 and the wire lead length to rod diameter ratio~H/D! is 24.84. Measurements are made for five different sections in a fuel assembly; inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. A series of water experiments have been conducted changing flow rate and water temperature. It is shown that the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly are much larger than those in other regions. The measured pressure drop data in a wire-wrapped fuel assembly region is compared with the existing four correlations. It is shown that the correlation proposed by Cheng and Todreas fits best with the present experimental data among the four correlations considered@DOI: 10.1115/1.1565076# The liquid metal reactor core consists of several fuel assemblies contained in a hexagonal shaped duct. There is no flow exchange between ducts. In order to efficiently extract the heat generated in a fuel assembly, it is important to distribute the flow rate among the fuel assemblies and to maintain the temperature distribution properly. The distribution of coolant flow rate in each fuel assembly is determined by the heat generation in each fuel assembly after the required whole coolant flow rate is determined to meet the reactor power. The reactor core is divided into a certain number of groups that have the same coolant flow rate, and then the temperature distribution of the fuel assembly is calculated and the coolant flow rate in each group is adjusted to have the same degree of peak temperature in the fuel rod. Then, the orifice in the bottom region of the fuel assembly is designed following the pressure drop of the fuel assembly. Thus, the information of pressure drop in a fuel assembly is very important in the thermal hydraulic design of the reactor core. The individual fuel assembly consists of inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. The primary objective of the present study is to measure the pressure drops in these regions for the design of Korea Advanced Liquid Metal Reactor ~KALIMER!. A series of experiments are conducted to measure the pressure drops in these regions. The relative magnitude of pressure drops in these regions is investigated from the measured data. As will be shown later, the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly is much larger than the pressure drops in other regions. The design of the inlet orifice for KALIMER is not determined yet and the inlet orifice used in the present measurement is only a tentative design. Thus, the primary emphasis of the present study is placed on the analysis of pressure drop in the wire-wrapped fuel assembly. In order to maintain a proper spacing between fuel pins and promote the coolant mixing, several types of spacers are proposed. Among the various spacers the helical-type wire-spacers are widely used in the liquid metal reactor ~LMR! and are adopted in the design of KALIMER. However, the existence of spacers between fuel pins causes the increase of hydraulic resistance,