The discharge behavior of particles is important in many industrial applications,such as in the core of a pebble bed reactor,which uses a hopper bed filled with many large particles.In this work,a mixture composed of two particle types,freely discharged from a pebble bed,is simulated using the discreteelement method.One is a spherical pebble of diameter equal to that of the fuel pebble of the reactor.The other is a composite particle comprising three spherical pebbles bonded together.The included angle α of the three pebbles characterized the particle conformation,which may affect the discharge behavior of the mixture.The effects of volume fraction of the multi-sphere x (equivalent to the number fraction) on the discharge are also analyzed.Flow patts,number flow rate,discharge velocity,and mean force of the mixture are computed to help in revealing discharge features.The results show that increasing either α or x reduces the discharge flow rate.Fittings and correlations give a quantitative evaluation of the independent effects of α and x.The analysis of velocity and force explains the mechanism relevant to the main influencing factors α and x.The results are helpful in gaining a better understanding of the discharge feature of binary mixtures and in providing a quantitative evaluation of the discharge behavior of the reactor core,especially adverse failure conditions.