PURPOSE: To easily and quickly execute melting of metallic uranium by giving magnetic field rotation in a nozzle to molten metallic uranium, injecting it into oxidizing atmosphere from the small holes thereof an dissolving the generated uranium oxide in acid dissolving solution.

CONSTITUTION: The metallic uranium US melting in a furnace 2 is continuously supplied into the nozzle 3 and allowed to flow down and at the same time, permanent magnets 15, 16 are rotated around the nozzle with a driving mechanism 17 and oxygen is fed into an oxidizing chamber 4 from an oxidizer tank 6. To the molten metallic uranium US in the nozzle 3, the rotating force around the nozzle axis is given with the rotating magnetic field generated with the permanent magnets 15, 16, and the molten metallic uranium US is injected into the oxidized chamber 4 from plural radially set small holes 3b at bottom part of the nozzle and splashed as drip-state to become the granular uranium oxide UO. This uranium UO is cooled with a cooling means 14 during passing through a communicating tube 13 and dropped down into the acid dissolving solution in a dissolving vessel 7 at a lower part to become the uranium dissolved liquid LL and at the time of becoming the prescribed concn., this is recovered into a tank 21 and sent to the following treatment process to make uranium dioxide.