Theoretical Considerations and Uncertainties

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

radioactive materials taken into the body. To facilitate control of intake in the work place, standard-setting

authorities have calculated derived air concentration (DAC) and annual limit on intake (ALI) which are

designed to limit resultant dose to internal organs. Operational hazards are directly controlled by the

observance of DAC and ALI values.

The ICRP and the NCRP are independent, non-governmental organizations which set standards and

guidance for control of radiation hazards. Governmental agencies implement these recommendations by

establishing Federal policy for the protection of workers.

Formal rules for air monitoring for DOE facilities are provided in 10 CFR Part 835. Efforts have been

made to keep these rules consistent with ICRP Publication 60 (ICRP 1991a), NCRP Report 91 (NCRP

1987a), and Federal Guidance Report 11 (EPA 1988a). The RCS detailed guidance on the best practices

currently available in the area of radiological control. More specific guidance is given in DOE G 441.1-8,

Air Monitoring Guide, and technical standards such as this one.

Limits of chemical exposure also need to be observed, especially for materials of low specific activity,

such as depleted uranium or non-radioactive materials. The threshold limit value time-weighted average

(TWA) for natural uranium is 0.2 mg m-3 (ACGIH 1993). TWA is the chemical analog of DAC. In the case

of reactor fuel uranium, enriched to about 3%, this corresponds to 4 x 10-10 microCi mL-1, which is

comparable to the DAC for soluble forms of uranium. However, the OSHA Permissible Exposure Limit for

soluble uranium is 0.05 mg m-3 , which is more restrictive than the DAC. Soluble forms of such materials

can be monitored directly by routine urinalysis, or indirectly by BZS and PAS. Internal deposits of

insoluble forms may only be estimated by BZS and PAS, as with asbestos, for example.

4.1.4 Theoretical Considerations and Uncertainties

A discussion of the theoretical aspects of air contamination monitoring, and inherent uncertainties,

should be useful in placing air monitoring programs in their proper perspective. In general, air sampling

should not be the primary measurement of internal dose, except when bioassay information is unavailable

or unobtainable. Evaluation of worker exposure potential in terms of DAC-hours, however, may be a

legitimate control measure and may demonstrate compliance with federal directives.

Airborne Concentration

An appropriate air-sampling method should provide samples which accurately represent the average

airborne concentration of radioactive materials present in the work place, but should not be used as a

measurement of individual exposures, except in unusual circumstances. If air activity data must be used for

exposure records, these samples should be collected from the breathing zones of the workers, or by using

an established conversion factor for the existing sampler configuration. In contaminated areas subject to

significant temporal and spatial variations in the activity concentrations, only personal air samples or

virtually continuous samples collected from within the breathing zone of workers can provide reliable

breathing zone concentration measurements.

A restricted area, having good ventilation and point sources of contamination, will have substantial

variations in the activity concentrations observed at different locations, particularly if the movements of the

workers cause resuspension of the activity. The worker often spends time closer to the source of

contaminant dispersion than is the location of the nearest BZS. Several researchers have investigated the

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