Development of a clogging probability model in simplified geometry for fast reactor flow blockage analysis

The occurrence of flow blockage accident in fuel assemblies is considered as one of the primary challenges to be addressed in liquid metal fast reactors. Flow blockage accidents are primarily caused by the accumulation of solid particles, such as corrosion products, wire spacer fragments, and chemical products between liquid metal and impurities like air or water. To better understand the mechanisms underlying the blockage formation, a project consisting of several series of simulated experiments is currently underway at Sun Yat-sen University and Harbin Engineering University. In the initial stage of the project, experimental study was conducted to investigate the influence of particle characteristics on the probability of clogging by discharging various solid particles into a reducer pipe. Preliminary experimental analyses revealed the formation of an arch structure at a specific location on the pipe. This arch structure causes the granular flow to cease, resulting in blockage. Based on the accumulated experimental database, in this study an empirical model is developed to predict the clogging probability, taking into account the above-mentioned influential parameters. The model demonstrates a reasonable agreement with experimental results within the current range of conditions, encompassing variations in the ratio between hopper outlet size and particle size, particle capacity, particle static friction coefficient, and particle release height. Although further extension of the empirical model is inevitably necessary under more realistic reactor conditions, such as incorporating realistic sub-channels, irregularly shaped particles, or a loop with a liquid phase, it is expected that the model will be beneficial for the improved design of sub-channels and safety analysis of fast reactors.