Radiological Safety Training for Uranium Facilities
Module 101 Properties of Uranium
Uranium melts at 1133°°C, so molten uranium is unusual, except in a foundry.
It has often been observed that the radioactivity appears to increase when
uranium is melted. This is because radioactive decay products, such as radium
and thorium, float to the surface. The density of radium is 5 g/cm3, compared
with 19 g/cm3 for uranium; therefore, radium floats in molten uranium.
Uranium in contact or solution with water is common. The primary hazards
associated with a uranium solution are criticality (for enriched uranium) and
spills. Water decreases the quantity of enriched uranium required for criticality.
This topic will be discussed in Module 105 - Criticality Safety.
3. Airborne Powder
A spill of any radioactive solution is a concern. As the solution evaporates, it
leaves behind a radioactive residue, or powder, that can easily become airborne.
Airborne uranium may be inhaled and absorbed into the bloodstream through
Another form of uranium that is an inhalation hazard is the volatile UF6,
becoming a gas above 56°C. However, most uranium daughters are not volatile,
and so can accumulate in storage cylinders. When the volatile UF6 is extracted,
the nonvolatile daughters remain in the cylinder, resulting in the buildup of
residual radioactivity. However, in the case of uranium-232 (232U), uranium-
235 (235U), and uranium-238 (238U), each of these uranium isotopes has a
radon daughter. Radon is a gas at all but very low temperatures; therefore, if the