PURPOSE: To prevent the deformation due to deliquescence by the pellets, by means of storing a waste pellet of radioactive solid as a main component of Na2SO4 in a sealed vessel.

CONSTITUTION: After produced pellets 4 by a glanulator 3 being filled in a metallic vessel 12, the metallic vessel is made into a sealed vessel 14 by means of compressing an upper disk 13 with an exhaust port on the metallic vessel 12, and this is stored in a long term within a storage 15. After the inner part of the vessel being made to a vacuum by means of reducing air by using a vacuum pump 16 from the exhaust port of the uper disk of the sealed vessel 14 in which the radioactivity of the pellet was enough attenuated, asphalt 8 is poured into the vessel by a asphalt pouring device 17. The obtained pellet by such means and a filling vessel 8 of saphalt are contained in a final solidifying vessel lined with cement 10, and the final solidfying body 19 is formed by means of pouring asphalt 8 in the space.