Internal Dose Measurements - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

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

concern.

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.