A model has been developed which relates the surface density (liter/ft2, kg/ft2) for enriched uranium and plutonium in a storage facility with its physical size. Calculations indicate that the allowable surface density for a small storage facility can be significantly increased over that for a large facility. A much higher total loading can be achieved for a given floor area by grouping several small adjacent storage rooms, each separated by a 1-ft-thick concrete wall, into a larger structure. This type of approach would need to be weighed against the added cost of 12-in.-thick interior concrete walls necessary to provide neutron isolation between adjacent rooms for a practical plant design.