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Session Overview
8.05-1: Experimental & Numerical Studies - I
Tuesday, 17/Mar/2020:
11:15am - 12:45pm

Location: R-3014

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Pressure distribution in assemblies of 17×17 fuel rods

Ulrich Bieder, Clarisse Genrault


The pressure distribution within and between full cross-section fuel assemblies with generic but realistic mixing grids are analyzed by CFD using high performance computing (HPC). The reference fuel assembly consists of a bundle of 17×17 rods, including fuel rods, control rod guide tubes and a mixing grid with split type mixing vanes. The axial length of the analyzed domain spans approximately the distance between two consecutive mixing grids.

The shown results are based on the calculation procedure recently published by the authors in Annals of Nuclear Energy. The intra-assembly pressure field is analyzed by modelling one single assembly; inter-assembly pressure fields are analyzed by modelling a bundle of three horizontally aligned fuel assemblies (3×1 fuel assemblies), each build of 17×17 rods and a mixing grid. Only hydraulic effects of the mixing grids on the behavior of the flow are analyzed, power input and heat transfer are not considered.

The pressure distribution in three configurations of assemblies with 17×17 rods are compared: a single assembly test case and two multi-assembly (3×1) test cases. In the multi-assembly test cases, two water gaps separate the central assembly from the neighboring fuel assembles. These water gaps have a width of 3 mm and 7 mmm, respectively. Three vertically arranges fuel rods are considered In the first multi-assembly test case. In order to simulate deformed fuel assemblies, the fuel rods of the central assembly are inclines by about 2° in the second test case. The pressure distribution in the assemblies and the flow in the water gaps are discussed. Pressure loss coefficients are compared to correlations and hydraulic forces acting on the mixing grids and the fuel rods are presented.

Experimental Studies on the Turbulent Flow Steady-State Mixing Processes in the Large-Scale Test Facility

M. Budnikov1, A. Budnikov1, A. Barinov1, D. Patrushev1, S. Dmitriev2

1JSC OKBM; 2Nizhny Novgorod State Technical University

Extended Abstract

Over the last two decades, CFD codes are being actively introduced into the practices of solving applied problems and safety analyses in the nuclear power industry, which requires the CFD codes to be validated and verified.

Article describes series of experimental activities being accomplished by JSC “Afrikantov OKBM” jointly with NNSTU n.a. R.E. Alekseev. These studies are being conducted to validate the approaches to the selection of the grid discretization and turbulence models in order to describe mixing processes in reactor chambers with the use of CFD programs and to justify the feasibility of translating validation results from the model into the full-size object. Analogously to the test series in the FLOWMIX-R project, the experiments are conducted in the isothermal mode on a reactor pressure chamber model 400 mm in outside diameter, with the downcomer annulus 63.5 mm wide and 1,100 mm high. The experiments study mixing of a passive impurity with the use of conductometric mesh-type and rod-type pickups with the measurement rate on the order of 10,000 samples/second.

Dimensions and geometry of the experimental model do not ensure similarity to any of the reactor plants but rather are selected such that the relative impurity concentration at the chamber outlet be ~ 0.5, and the maximum simplicity be ensured for computational grids being generated.

Conductive and non-conductive bubbly flow in vertical pipes : Experimental works and its modelling using CFD

Guillem Monros-Andreu, Raul Martinez-Cuenca, Salvador Torro, Sergio Chiva

Universitat Jaume I

Multiphase flows occur in a vast amount of industrial applications; consequently, they have been intensively studied during last decades. For many reasons, the high-speed measurement of the main local parameters of the phases involved are of industrial and scientific interest. However, there are only few suitable measurement techniques. Measurement with multi- needle probes is a well-stablished method for the investigation of two-phase flows, but based on the conductivity difference of the phases

Local measurements of void fraction, interfacial area concentration (IAC), interfacial velocity, and Sauter mean diameter weremade using intrusive local probes. Two kind of Impedance multisensor needle probes have been used, the first one is a well-known multisensor conductivity probe and I has been used to measure the gas parameters distribution in conductive fluids. The other one is a novel capacitance based multi-needle probe system suited for local measurements even in non-conductive two-phase flows, like petroleum or another organic fluid. Liquid velocity and turbulence intensity were measured using laser Doppler anemometry (LDA).

An upward isothermal co-current gas-liquid flow in a vertical pipe (52 mm ID) has been experimental investigated. Different air-water flow configurations was investigated for a liquid velocity up to 1 m/s and a void fraction up to 15%. For each two-phase flow configuration 25 radial positions and 3 axial locations were measured by the conductivity probe methodology, and several radial profiles were measured with LDA at different axial positions. In order to test the capacitive proves, experiments have been carried out using air/silicone-oil mixture. Furthermore, high-velocity imaging analysis were used in order to validate the measurements. The results from the experiments assess both the measurement principle and signal processing methodology of the developed sensor.

The vertical pipe experiments has been modeled using CFD using an euler-euler approach, and the results has been validate with experiments performed.

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