Some casks can only be used for storage and others can be used for both storage and transport (dual purpose). The former consist of a cylindrical capsule of various layers of stainless steel and carbon steel that ensure the confinement of the material and contains a rack with a neutron absorbent for housing the fuel. During storage, these capsules are placed in a concrete module which also provides structural protection. For transport, the capsule must be transferred to another module designed to meet transport requirements.

Dual purpose casks consist fundamentally of a steel vessel with a welded bottom and two bolted upper covers to contain the material and with an inside neutron absorbing rack to maintain sub-criticality, allowing the protection of the structure and the dissipation of heat from the fuel assemblies.