Experimental substantiation of selection of fuel channel imitator for hydrodynamic model of nuclear reactor

Description is given of the methodology for experimental substantiation of hydrodynamic characteristics of imitators of fuel channels in the model of reactor unit with two-loop configuration. It is known from the experience of development of reactor units of different types that it is practically not feasible to select the channel to serve as the imitator with simple geometry for which the dependence of pressure drop due to hydraulic losses would be the same as the dependence for full-scale operating fuel channel containing fuel assemblies. Therefore, only approximate modeling of hydraulic losses in operational fuel channels with fuel assemblies and imitating channels within the limited range of Reynolds numbers can be discussed as well as inclusion of all coolant flow regimes within the reactor vessel predicted by design calculations.Selection of final geometry of imitating channels was made based on the following several basic assumptions of approximate modeling of flow path in the full-scale fuel channel with fuel assembly under nominal operational mode of the nuclear reactor using the channel with simplified geometry: (1) range of variation of coolant flow rates in the operational fuel channel with fuel assembly in nominal operational mode of the reactor is known from physical and from preliminary thermal physics calculation studies; (2) equality of Euler numbers for nominal coolant flow regimes in the reactor and for coolant flow in imitating channels. Experiments were conducted with three types of imitators and the most suitable among them was chosen as the result. The finally selected design of imitating channel included a pipe with high-quality of manufacturing, two diaphragms and a nozzle with configured using the method suggested by Vitoshinsky.