Investigation into the Effect of Structural Elements of the Entrance Section of a Fuel Assembly in the RITM Reactor on the Coolant Hydrodynamics in a Fuel-Rod Bundle

Abstract

The results of experimental investigation into the coolant hydrodynamics within the entrance section of a fuel assembly in the core of the RITM reactor are presented. The investigation was aimed at capturing the effect of orifices and absorber grids of various designs on the development of the coolant flow in a fuel-rod bundle of a fuel assembly. To attain this goal, the experiments were performed in a scale model of the entrance section of the fuel assembly with all the structural elements of the standard assembly—from the throttle orifice to the second spacer grid. The spacing between model elements was increased by a scale factor equal to 5.8 relative to the standard spacing of their arrangement. The experiments were performed using two methods for investigating the coolant hydrodynamics: the pneumometric method and the tracer injection method. The studies were carried out at several cross-sections along the length of the model, and the studied region covered the entire cross-section of the model. The measurement sections were located considering the design features of the model. The hydraulic resistance coefficients (HRCs) of throttle orifices in fully open and maximally closed positions were experimentally determined. The features of the coolant flow at the inlet of the fuel assembly are visualized using maps of axial velocity distribution in the measurement sections as well as maps of injected tracer concentration distribution. A comparative analysis of the efficiency of application of two types of absorber grids was carried out. The experimental results were used to substantiate design solutions in modifying individual elements of the fuel assembly, as well as to confirm the reliability of new cores. In addition, the obtained experimental data can be used to validate the LOGOS CFD code developed in Russia.