PURPOSE: To store radioactive waste stably and efficiently at low costs by connecting a glass solidification body and a moored floating body, temporarily leaving the glass solidification body at the bottom of the deep sea, and storing the high-level radioactive waste while cooling the same.

CONSTITUTION: A glass solidification body 3 resulting from the solidification of high-level radioactive waste by glass is made floating on a sea surface 4 so that the body 3 can be collected Later. For instance, the body 3 is connected to a moored floating body 1 such as a buoy by a wire 2, suspended and fixed at a sea bottom 5 of sufficiently low temperatures. The sea water of low temperatures is warmed by the heat generated from the solidification body 3, and exchanged with the surrounding cold water. As a result of this, a convection is brought about and the solidification body 3 is cooled, so that the decay- treat of the radioactive nuclide is gradually removed. The cycle is repeated for 30-50 years until the waste conforms to the requirements in processing of stratum. The method eliminates a special equipment and remarkably reduce the cost and labor for maintenance and management, without bad influences given to the environment.