Calculated Substantiation of the Fixed-Bed Nuclear Reactor Core Thermal Reliability

The study is aimed at performing calculated substantiation of the thermal reliability of a pressurized water reactor (PWR) with spherical fuel elements, commonly known as a fixed-bed nuclear reactor, and determining the most advantageous design of the spherical packing from the view point of thermal hydraulics. Spherical fuel elements have a number of advantages over cylindrical fuel rods; in particular, they feature better retention of fission products, enhanced nuclear safety (due to a high melting temperature of ceramic materials), more intense heat transfer due to increased coolant flow turbulence, and a reduced influence of thermal cyclic loads on fuel elements. To confirm these statements, a thermohydraulic calculation of the KLT-40S type reactor with a modified intra-channel filling of fuel assemblies (FAs) consisting of spherical fuel elements was carried out. To determine the optimal spherical filling, two types of spherical packing were calculated, with three different diameters of spherical fuel elements. In the course of the calculation, solutions to the following issues were proposed: how to take into account the channels flow area variability, how to calculate the Reynolds number for channels of a given shape, what formulas should be used to determine the Nusselt number, and how to determine the hydraulic resistance in the channels. As a result of the calculation, data on the following main thermohydraulic characteristics have been obtained: surface heat flux density, heat transfer coefficient, maximum fuel temperature, and hydraulic losses. These results were compared with the results of calculations for cylindrical fuel rods. The obtained results demonstrate the advantage of spherical fuel elements over cylindrical fuel rods in a number of basic parameters, which gives prospects for further study of the use of spherical fuel elements in reactors of this type. The obtained study results can be applied in designing reactor plants of low and medium capacity, as well as in modernizing the existing reactor plants.

Compaction effects on permeability of spherical packing

Purpose The purpose of this paper is to investigate the evolution of the permeability of spherical packing during cold compaction by pore-scale modeling. Design/methodology/approach The discrete element method (DEM) is used to generate spherical packing structure under different compressive pressures and the Lattice Boltzmann method (LBM) is adopted to calculate the permeability of each spherical assembly. Findings It is found that the decrease of the porosity is the main reason of the reduction in permeability in the initial compression stage, but its influence becomes insufficient in the late compression stages. Besides, two empirical formulas are obtained, which describe the relation between the permeability and the equivalent mean diameter and the variation of normalized permeability with compressive pressure, respectively. Research limitations/implications In this study, the authors study the spherical particles and ignore the non-spherical effects. Besides, the classical contact model, the linear-spring-damping model, is used in DEM, so the plastic deformation cannot be considered. Originality/value The DEM and the LBM are well combined to study the compaction effects on permeability of spherical packing. Two simple expressions of the spherical packing structure with uniform diameter distribution are given for the first time.

Application of Polyhedral Spherical Packing Precipitation Technology in Water Plant Reform

On the basis of micro flocculation interception sedimentation technology, polyhedral spherical packing is used as intercepting material in sedimentation tank. The process utilizes the characteristics of polyhedral sphere to make flocs and water move relatively, and continuously change the direction of water flow to produce turbulent vortices. When water moves in a vorticity, solid particles move relative to the flow along the radial direction under the action of centrifugal inertia force, which provides for the radial collision of particles with different scales along the vortices. Under these conditions, the micro flocs collide and aggregate continuously as they pass through the blades, and the concentration of alum in the water is increased. Finally, the precipitation is removed under the action of gravity. The process is applied to the reconstruction of Miluo New City Waterworks, and the original inclined pipe sedimentation tank is retained and put into operation. The results show that the turbidity of effluent from polyhedral spherical sedimentation tank can reach below 2NTU, while that from inclined tube sedimentation tank is above 2NTU. The treatment effect of polyhedral sphere on low turbidity water is better than that of inclined tube, which provides a reference for the transformation of small and medium-sized water plants in rural areas. Keywords: Polyhedral sphere packing; Interception sedimentation; Technological transformation; Engineering application