Abstract: A container, termed a multi-element bottle, to receive irradiated nuclear fuel is housed within a flask for transport and both the bottle and flask contain water. Ullage space within the fuel chamber in the bottle and flask allow for thermal expansion under normal conditions. Additional ullage is provided as a safety measure in accident conditions involving fire and resulting rise in temperature with consequent increase in pressure within the bottle and the flask. The additional ullage space is provided by a closed chamber (10) at one end of the bottle, the chamber (10) being closed by a wall (11) which can collapse or rupture when the pressure exterior thereof exceeds a predetermined value. The normal ullage space within the fuel chamber (7) in the bottle can be increased by providing a further chamber (20) within the bottle between the fuel chamber (7) and the closed end chamber (10) having the collapsible wall with means (25) providing communication between the fuel chamber and the further chamber.