A system based on the continuous measurement (20) of the diameter of a cylindrical object (1) moving, laid down, on a belt conveyor (10) allows dimensional compliance of the latter object to be checked.The measurement system (20) may be coupled with a sorting system based on ejection out of the conveyor (10) by projecting a gas through a transverse nozzle (42).By means of the system according to the invention, it is possible to continuously determine whether a nuclear fuel pellet (1), in particular after rectification (2), has to be rejected or not.