Characterization of Internal Hazards

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

is not required. As a matter of caution, some sites try to obtain baseline bioassays as soon as a pregnancy is

declared, with another baseline bioassay following the end of pregnancy. Some sites also offer to restrict

pregnant workers from jobs with relatively high potential for occupational intakes.

Minors and members of the public are limited by 10 CFR 835.207 and 10 CFR 835.208 to a TEDE of

0.1 rem/year. Minors are also limited to 10% of the occupational dose limits of 10 CFR 835.202(a)(3) and

(a)(4). Internal exposure monitoring is required if an intake is likely to result in 50% of that limit (0.05 rem)

from all radionuclide intakes in a year. Because bioassay monitoring is not likely to be sufficiently sensitive

to identify such intakes on a routine basis, enhanced workplace surveillance or restriction of access may be

required.

5.2 CHARACTERIZATION OF INTERNAL HAZARDS

Monitoring for uranium poses special problems for the following reasons.

Uranium presents both chemical and radiological toxicity risks, the relative importance of which

depends on its transportability from the lung.

Uranium usually exists in mixed transportability classes.

Small, recent intakes easily mask larger, older intakes because nearly 50% of the uranium going

to blood is cleared immediately through the urine.

An intake of class Y material potentially resulting in a CEDE of 0.1 rem generally cannot be

detected by routine bioassay monitoring. Monitoring of the workplace to document the working

environment and to provide immediate indication of an intake is essential.

Low-level chronic intakes are common, so the bioassay program must monitor for long-term

buildup as well as for potentia lly significant acute intakes.

Individual and temporal variability in the environmental background of uranium complicates

interpretation of urinalysis results.

Consequently, the proper bioassay monitoring program for uranium workers is best determined on a

case-by-case basis in consultation with an internal dosimetry specialist. As part of the program technical

basis, the uranium mixtures need to be determined. In addition, determinations should be made at the time

of identified incidents of potential intake. Methods for such determination may include radiochemical

analysis or chemistry followed by mass spectrometry.

Solubility is of major importance in uranium inhalation toxicology. Soluble uranium compounds

are absorbed and rapidly transported to kidney and bone, or excreted in urine. Because uranium damages

kidney tissues by the same mechanisms as other heavy metals, dissolved uranium is considered to be a

chemical toxicant. Dissolved uranium also deposits in bone and is retained for long periods of time, such

that sufficiently enriched uranium can deliver an accumulated radiation dose sufficient to be considered a

radiological hazard to bone (Morrow 1986).

Oxides of uranium tend to exhibit inhalation class Y behavior, slightly more soluble compounds are

assigned to class W, and soluble compounds are assigned to class D. Note that some compounds that

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