Hydrodynamics of Turbulent Flow in a Fast Reactor Fuel Assemblies (Velocity Field and Microstructure of Turbulence)

Abstract

The article describes the factors under the influence of which the formation of thermohydraulic characteristics occurs in the fuel assemblies of the core of fast reactors with liquid metal cooling. It is shown that one of the most important factors is a complex multiply connected geometry of a stochastic nature, subject to deformation during the campaign under the influence of temperature irregularities and radiation effects. The paper presents and analyzes the results of experimental and computational studies of the velocity field and shear stress, the microstructure of turbulence, momentum transfer in the central and peripheral regions of fuel assemblies without and with displacers, as well as in the case of deformation of the lattice of rods. The intensification of turbulent momentum transfer in the channels in the azimuthal direction in the area of the gaps between the rods is demonstrated. The anisotropy coefficient of turbulent momentum transfer reaches 30-40 units. The performed analysis indicated a significant difference in the calculated in the framework of semi-empirical models of turbulent transfer and experimental dependences of the coefficients of turbulent transfer of momentum in the radial and azimuthal directions and the coefficients of anisotropy of turbulent transfer of momentum in rod bundles. The results of an open benchmark on the thermohydraulics of fuel assemblies showed that common commercial computational thermohydraulic codes only approximately describe the experimental data. It is shown that the intensification of turbulent momentum transfer in the channels of rod assemblies is due to the appearance of large-scale turbulent momentum transfer (secondary flows). The contribution of large-scale turbulent momentum transfer to the kinetic energy of turbulent pulsations, azimuthal turbulent shear stresses, and turbulent momentum transfer coefficients in rod assemblies is calculated. An empirical dependence of the coefficient of interchannel turbulent impulse exchange in bundles of smooth rods is obtained, on the basis of a semi-empirical model, data on interchannel turbulent impulse exchange in assemblies of smooth rods are generalized, and the intensification of interchannel turbulent exchange in close lattices of rods is explained. Data on hydraulic resistance in bundles of smooth rods are analyzed. The tasks of further research are discussed.

Thermohydraulic studies of alkali liquid metal coolants for justification of nuclear power facilities

“…Flow meters of different designs were developed to measure flow rates of liquid metals. Methodologies and a technique were developed later for measuring electromagnetically the liquid metal local flow rate (velocity) vectors in channels and fuel rod bundles, and measuring the coolant mixing characteristics in experiments in air with a small fraction of gaseous tracers added in the form of Freon or propane (Rachkov et al 2018, Sorokin et al 2021b.…”

“…The results of experimental studies into hydrodynamic turbulent characteristics in fuel assemblies in air using a Pitot tube have shown (Fig. 1a, b) that there is a local maximum observed in the distribution of tangential stresses along the wetted perimeter of the regular fuel lattice cell at the point with the greatest channel expansion, which can be explained by the secondary vortex impact (Sorokin et al 2021b).…”

Thermophysical Studies of Alkaline Liquid Metal Coolants. Izvestiya vuzov

“…Для измерения расходов жидких металлов со зданы расходомеры различных конструкций. Позднее были созданы методики и техни ка электромагнитного измерения векторов локальных расходов (скоростей) жидкого металла в каналах и пучках стержней, измерений характеристик перемешивания тепло носителей в опытах на воздухе с добавкой малой доли газообразных трассеров в виде фреона или пропана [5,6].…”

“…Распределения касательных напряжений на поверхности твэлов и скорости в поперечном сечении каналов в периферийной области модельной ТВС с вытеснителями в периферийных каналах при номинальной геометрии (а, б) и деформации решетки твэлов в периферийной области ТВС (в, г) Результаты экспериментальных исследований турбулентных гидродинамических ха рактеристик в сборках твэлов на воздухе с использованием трубки Пито показали (рис. 1а, б), что в распределении касательных напряжений вдоль смоченного периметра ячейки правильной решетки стержней наблюдается локальный максимум в месте наибольшего расширения канала, который можно объяснить воздействием вторичного вихря [5].…”

“…Распределение скорости по нормали к смочен ному периметру описывается универсальным законом, если для расчета динамической скорости использовать локальное значение касательного напряжения. Наблюдается значительная интенсификация турбулентных пульсаций скорости в периферийной об ласти пучка по сравнению с бесконечной решеткой [5].…”