Module 104 - Internal Dose Control

DOE-HDBK-1113-98

Radiological Safety Traning for Uranium Facilities

Module 104 - Internal Dose Control

IV.

MODULE 104 - Internal Dose Control

Objectives

EO6

Identify t he modes of entry int o the bod y for uran ium.

EO7

Describe the measures taken to control intakes of uranium, including special radiological

surveys and techniques, instruments, and release of materials.

Internal Exposure to Uranium

As discussed in Module 101, the primary biological hazard is the potential for uranium to be

taken into the body. This exposure may result in heavy metal poisoning, including kidney

damage (for acute exposures), or an increased cancer risk (for chronic exposures). Uranium may

enter the body through inhalation, ingestion, absorption through the skin, or injection into the

bloodstream, such as from contamination of an open wound.

The most common route of entry is inhalation, but much of the material inhaled does not stay in

the lungs. The lungs and related air passages constantly work to remove all the dust we breathe,

including dust that contains uranium. The dust expelled from the lungs but not exhaled is

swallowed, so some of the inhaled uranium ends up in the digestive tract.

The amount of uranium retained in the lungs depends a great deal on the size of the particle

breathed. The smallest particles tend to be exhaled or absorbed into the bloodstream, while the

largest part icles are us ually removed bef ore they reach the lung. Uraniu m retained in th e lungs

may remain there or be absorbed into the bloodstream. Part of the uranium passing through the

digestive tract may also be absorbed in the bloodstream. Uranium in the bloodstream is either

transferred to various organs or excreted via the urine.

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