Radiological Safety Training for Uranium Facilities
Module 104 Internal Dose Control
The enrichment of the uranium in its 235U isotope also plays a role in determining
whether the radiological or the chemical effects are the limiting factor. For acute
exposures, chemical toxicity is limiting up to 39% enrichment. Beyond 39%, the
effective dose equivalent becomes limiting. For chronic exposures, chemical
toxicity is more limiting up to 1.3% enrichment. Beyond 1.3%, the effective dose
equivalent becomes limiting.
Internal Dose Measurements
Once in the body, the presence of uranium can be detected using indirect
radioactivity measurements, direct radioactivity measurements, or both.
At one time, it was not possible to detect internal uptakes of uranium or certain
other radioactive materials at levels below the point at which the annual limit for
exposure (5 rem) was received. Any measurable intake of uranium was therefore
considered to be unacceptable. Improved analytical and calculational techniques
have now made it possible to measure uranium concentrations resulting in
exposures of about 10 mrem with a reasonable degree of accuracy. The estimation
of low-level internal exposure to uranium is no longer a matter for inordinate
1. Indirect or In Vitro Measurement
Bodily processes will, to some degree, eliminate uranium taken into the body.
How effective the body is at eliminating the uranium, and how long the process
takes, depends upon individual metabolism and the chemical form of the
uranium. For example, uranium hexafluoride contains uranium that is
chemically bound to fluorine and is more easily eliminated than uranium metal
or uranium dioxide.