Internal Dosimetry - STD-1128-98master0123

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

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INTERNAL DOSIMETRY

Internal dosimetry is an essential part of a quality health physics program at every facility where

plutonium is handled or processed. The purpose of an internal dosimetry program is to monitor

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

conduct internal dose assessments from bioassay measurement data.

It is DOE policy that facilities are 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, if they occur at all, are negligible to the extent

achievable with state-of-the-art technology. In spite of excellent design and operation policies,

inadvertent intakes of radioactive material can occur as a result of equipment malfunction, failure to

follow procedures, or the unanticipated presence of radioactive material.

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

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 plutonium-

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 have been 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

start 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. For plutonium

and americium intakes, the bioassay data necessary for final dose assessment may require long

periods of time (many months) to obtain. 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.

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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 internal dose equivalents to organs and tissues of concern can be

estimated by using fundamental dosimetry principles, by various intake-to-dose conversion factors,

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