Liquid - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

Radiological Safety Training for Uranium Facilities

Module 101 Properties of Uranium

2. Liquid

Uranium melts at 1133C, 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

the lungs.

4. Gas

Another form of uranium that is an inhalation hazard is the volatile UF6,

becoming a gas above 56C. 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