A 3D DEM study on particle–wall/particle friction in pebble bed reactor is carried out.
Characteristic values are defined to evaluate features of pebble flow pattern quantitatively.
Particle–wall friction is dominant to determine flow pattern in a specific pebble bed.
Friction effect of hopper part on flow field is more critical than that of cylinder part.
Three cases of 1:1 full scale practical pebble beds are simulated for demonstration.