A fissile storage container made of nonflammable materials utilizes a thick moderator such as water to enclose each storage unit in a container array. The internal moderator serves three basic functions: (a) it partially isolates adjacent storage units from one another in an array of units, thus permitting high vault loadings; (b) it substantially reduces the ambient dose rate in the storage area; (c) it reduces the temperature of the stored fissile material. The containers have been used in the storage of 3-kg plutonium metal cylinders. In this application, the ambient total dose rate (n+γ) is reduced by a factor of ∼8, and the cylinder temperature reduced ∼30°F over the corresponding temperature for storage in an unshielded metal container. Multiplication factor calculations show that a 5 × 5 × 5 array of the containers is well subcritical even with 27 containers in the center of the array double loaded.