Models for the safe and economical storage of large quantities of plutonium or highly enriched uranium have been developed. The models cover a wide range of compositions from aqueous solutions, wet and dry oxides, to full density metals. The models all use the parameters of unit surface-to-volume ratio and array surface density to define the safe storage arrays. The models take account of unit shape, size, and composition, as well as vault size. Arrays containing a mixture of different units are easy to calculate by the model. Important accident situations, such as double batching and fissile solution spills, are considered.