Experimental study on the mechanism of flow blockage formation in fast reactor

Various sources of solid particles might exist in the coolant flow of a liquid metal cooled fast reactor (e.g., through chemical interaction between the coolant and impurities, air, or water, through corrosion of structural materials, or from damaged/molten fuel). Such particles may cause flow blockage accidents in a fuel assembly, resulting in a reduction in coolant flow, which potentially causes a local temperature rise in the fuel cladding, cladding failure, and fuel melt. To understand the blockage formation mechanism, in this study, a series of simulated experiments was conducted by releasing different solid particles from a release device into a reducer pipe using gravity. Through detailed analyses, the influence of various experimental parameters (e.g., particle diameter, capacity, shape, and static friction coefficient, and the diameter and height of the particle release nozzle) on the blockage characteristics (i.e., blockage probability and position) was examined. Under the current range of experimental conditions, the blockage was significantly influenced by the aforementioned parameters. The ratio between the particle diameter and outlet size of the reducer pipe might be one of the determining factors governing the occurrence of blockage. Specifically, increasing the ratio enhanced blockage (i.e., larger probability and higher position within the reducer pipe). Increasing the particle size, particle capacity, particle static friction coefficient, and particle release nozzle diameter led to a rise in the blockage probability; however, increasing the particle release nozzle height had a downward influence on the blockage probability. Finally, blockage was more likely to occur in non-spherical particles case than that of spherical particles. This study provides a large experimental database to promote an understanding of the flow blockage mechanism and improve the validation process of fast reactor safety analysis codes.