Nuclear metal or alloy particle preparation method and device; said device comprising: means to prepare a fluid mass of the metal or alloy by melting; means to put the fluid mass of the metal or metal alloy in the form of a molten metal or alloy stream; means to impart a centrifugal rotation movement to a quenching fluid and carry out the atomisation of the molten metal or metal alloy stream particles and the quick quenching of the particles; means to melt the nuclear metal or metal alloy in an inert gas atmosphere, and means to surround the molten metal or metal alloy stream by a neutral gas envelope until quenching.