PURPOSE: To stick sodium on inert powder and vaporize it, and to improve removal efficiency by burying the reactor core constituent element where sodium sticks in the inert powder, fluidifying it with inert gas, and holding them at specific temperature and carrying out processing.

CONSTITUTION: The reactor core instrument 21 which is already used is embed ded perpendicularly in the inert powder 23 in a container 22. Then the lower 25 of a gas circulation circuit 24 is driven to supply the inert gas from the lower part of the container 22 through a dispersion plate 26 and the powder 23 is fluidified, the inert gas is jetted from a gas nozzle installed at the lower end of the element 21 to hold the inside of the container 22 at 300W600°C. Then part of the sodium which sticks on and is absorbed by the element 21 inert powder particles is vaporized and recovered in the inert gas at held temper ature of 100W600°C. Further, the inert powder particle which absorbs the sodium by sticking are taken partially out of the lower part of the container 22 and the sticking absorbed sodium is separated centrifugally by a centrifugal separa tion 30 in a liquid state and recovered.