Module 101 Properties of Uranium - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

Module 101 Properties of Uranium

Lesson Plan

Instructor's Notes

Gas

Provide a facility specific

Another form of uranium that is an inhalation hazard example of uranium in

is the volatile UF6, becoming a gas above 56C.

gaseous form.

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 radon escapes,

the subsequent daughters can accumulate in closed

or poorly ventilated areas.

In some situations, pressure from volatilized UF6 gas

can build up in small volumes such as a sealed

container or a pipe run between two valves. Line

breaks and leaks will cause a release of the UF6. As

the escaping UF6 gas cools, it becomes particulate,

which may have a suffocating effect on any nearby

workers.

Another reason for pressure buildup is alpha

particles emitted in radioactive decay eventually

becoming inert helium gas. The amount is only

significant for high specific activity forms of

uranium. For example, a sample of 99% uranium-

233 (233U) with 1% 232U creates approximately its

own volume of helium gas every year. Sealed

containers must include adequate gas space or be

fitted with pressure release valves. Once the

pressure is relieved, the low-pressure helium gas is

harmless.