250°F is the maximum temperature to which a UF6 cylinder will be heated
The weight of a cubic foot of 250°F liquid UF6 is 203.3 lb.
The weight of a cubic foot of 80°F solid UF6 is 317.8 lb.
Allowance of 5% of certified minimum volume is made for ullage in cylinder.
When heated, uranium hexafluoride expands and undergoes a phase change from a solid to a liquid. Fill limits ensure that cylinders do not rupture by requiring a 5% void space when the cylinders are heated to the maximum temperature of 250°F.