The Atlantic Richfield Company has developed the concept of storing spent fuel in dry caissons. Cooling is passive; safety and safeguard features appear promising. The capacity of a caisson to dissipate heat depends on site-specific soil characteristics and on the diameter of the caisson. It is estimated that ∼2 kW can be dissipated in the length of one fuel element. Fuel elements can be stacked with little effect on temperature. A spacing of ∼7.5 m (25 ft) between caissons appears reasonable. Business planning indicates a cost of ∼0.2 mill/kWh for a 15-yr storage period.