Spent fuel storage

A space is formed underground by partitioning walls made of radiation shielding material, in which only a storage cell is contained. The storage cell comprises metal blocks made of a heat conductive material such as stainless steels. A great number of holes each having a predetermined diameter are vertically arranged to the metal block, and storage pits are constituted by the holes. Spent nuclear fuels are contained in a first columnar vessel and the first columnar vessel is further contained in a large second columnar vessel. Both of the first columnar vessel and the second columnar vessel are made of a durable metal material such as stainless steels. The second columnar vessel is inserted to the storage pit of the storage cell. With such a constitution, heat emitted from the second columnar vessel is transferred to the metal block by radiation and dissipated from the metal block. Accordingly, a heat dissipation efficiency can be increased. (I.N.)