Module 104 Internal Dose Control
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
particles are usually removed before they reach the
lung. Uranium retained in the 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 limiting. For
chronic exposures, chemical toxicity is more
limiting up to 1.3% enrichment. Beyond 1.3%, the
effective dose equivalent becomes limiting.
Highlight the internal
Internal Dose Measurements
used at your facility.
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.