Internal Dosimetry - doe-std-1136-20040103

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

5.0 INTERNAL DOSIMETRY

Internal dosimetry is an essential part of a comprehensive radiological control program at every

facility where uranium is handled or processed. The purpose of an internal dosimetry program is to

monitor workplace activities, assess accidental or inadvertent intakes of radioactive material, and

conduct internal dose assessments from bioassay measurement data.

DOE requires that facilities be designed, operated, and remediated to prevent intakes of radioactive

materials. Radiological controls for the workplace should ensure that radionuclides are contained and

handled properly, and that intakes are as low as reasonably achievable.

Experience has shown that the most common route for inadvertent uranium intake is inhalation. The

uranium may be in natural, enriched, or depleted form, or a combination thereof. Intakes can also occur by

accidental ingestion or by wound contamination. Surveillance programs should be designed to rapidly

detect a release in the event of a loss of radioactive material containment. Internal dosimetry programs

should be tailored to the needs of each uranium-handling facility so that inadvertent intakes are discovered

and quantified and workers' dose equivalents are determined by appropriate methods.

When workers are inadvertently exposed to radioactive material, appropriate corrective action should

be taken to ensure that control and containment are re-established. Prompt detection by routine workplace

monitoring practices is essential to regaining control after any contamination spread or loss of containment.

Prompt workplace indications of potential intake are also crucial to ensure timely initiation of special

bioassay monitoring for intake and dose assessment. An early assessment of the probable severity of an

intake and its corresponding dose, preferably within the first two hours of the intake, is needed for decisions

on dose reduction therapy and event reporting. Uranium is both a radiological and chemical hazard.

Because the total risk must be considered, both hazards must be considered. For uranium intakes, it may

take many months to obtain the bioassay data necessary for final dose assessment. Until such data become

available, ongoing preliminary assessments of intake and dose may be necessary to provide guidance for

the administrative and medical management of the workers.

5.1 INTERNAL DOSE EVALUATION PROGRAM

Internal doses are not directly measured but are estimated or calculated based on knowledge of the

material to which a worker may be exposed and its known or assumed biokinetic behavior. The common

approach to internal dosimetry is to calculate an occupational intake based on worker bioassay

measurements or workplace air-sample data and assumed breathing rates. Once an intake is calculated,

appropriate dose equivalents to organs and tissues of concern can be estimated by using fundamental

dosimetry principles, by various intake-to-dose conversion factors, which incorporate assumed biokinetic

models, or by an appropriate computer code. Intake-to-dose conversion factors can be found in Federal

Guidance Report No. 11 or ICRP Publication 30. Further discussion on intake and dose assessment is

provided in Section 5.8.

Participation in internal dose evaluation programs (which include routine bioassay programs) is

required for conditions identified in 10 CFR 835.402(c). The internal dose evaluation program must

address both general workplace conditions and individual intakes. Workplace conditions are monitored

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