Several factors that influence the design and capacity of a fissile metal storage vault are the size and shape of individual storage units, surface density, double batching of storage units, the effects of personnel upon storage array reactivity, and the possibility of water flooding of arrays. Calculations indicate that when the fissile material is elevated 12 in. or more above the concrete floor of the vault, keff is decreased 4 to 5% when 3 in. of water is upon the concrete floor. The effect of personnel reflection upon the reactivity of an array is a strong function of the mass of a fissile unit as well as the shape and orientation of this fissile unit with regard to the reflector. For example, when a heavy flat plate of metal is held edgewise against the reflector, the value of keff is 0.804. When the plate is held flat against the reflector, keff is 1.115. A considerable penalty on storage capacity will occur if controls cannot be developed to preclude the double batching and water flooding.