American National Standard N13.39
Design of Internal Dosimetry Programs
Introduction
Internal dosimetry is the science of assessing the amount and
distribution of radionuclides in the body, and calculating resulting
radiation doses to internal organs or tissues over specific time
periods. Because the ionizing radiation energy deposited in a
particular organ from radionuclides incorporated in the body cannot be
measured directly, internal doses are estimated or inferred from in
vivo or in vitro bioassay or from air concentration measurements.
During work at nuclear facilities, the potential for intake of
radionuclides by ingestion, inhalation, wound, or absorption through
the skin often exists. Therefore, internal dosimetry programs are
instituted to monitor the type and magnitude of such intakes and
radiation dose associated with them.
Scope, Purpose, and Application
In the past, internal dosimetry standards have focused on providing
guidance for detection and dose assessment for specific radionuclides
or groups of radionuclides (e.g., tritium, uranium, and fission and
activation products). Frequently, however, these standards provided
conflicting or uneven treatment of the programmatic elements that are
basic to monitoring for and assessing the dose from any radionuclide.
Therefore, this standard was developed to provide uniform and
consistent guidance on programmatic issues that are universally
applicable to all radionuclides and all occupational intake pathways.
This
standard contains the essential elements of the internal dosimetry
component of a radiation protection program. It provides general
policies and the framework for the design and implementation of an
acceptable internal dosimetry program. The topics included herein are
definitions, organization, staffing and training, program
documentation, quality assurance, personnel participation, internal
dose assessment, incident response, and records and reports.
Other
than those examples necessary for clarification, this standard does not
address bioassay or internal dose assessment methodologies for specific
radionuclides.(a) It is intended that the development and
implementation of radionuclide-specific dosimetry programs be
consistent with the broad-scoped guidance provided herein.
By its very nature, internal dosimetry is a complex task with varying
degrees of difficulty, depending upon the radionuclide and the means by
which the radionuclide is metabolized. For some radionuclides, such as
tritium, it is relatively easy to monitor for and assess intakes that
result in small doses. For others, such as 239Pu, the task is
significantly more difficult. Therefore, while this standard provides
the minimal acceptable elements of an internal dosimetry program
regardless of the radionuclide, it should not be used to restrict the
level of excellence readily achievable for some radionuclides.
This standard provides guidance for programs where monitoring for
possible intakes by workers is part of the radiation protection
program. Engineered containment and administrative controls are used to
minimize the probability of an intake due to normal operations and
accident releases. Workplace surveillance practices identify that the
containment and administrative controls are effective. Routine bioassay
monitoring provides verification that radiological controls are being
maintained and work effectively. Special bioassay is performed in
response to indications of an abnormal condition that might have
resulted in an intake. This standard focuses on establishing intake
monitoring programs, identifying intakes, and assessing internal dose.
It does not address equally important aspects of radiation protection
involving minimizing intakes or implementing as
low-as-reasonably-achievable total dose control programs.
A graded approach is presented to account for programs involving only a
small risk of intake through programs with a risk of intake that might
result in an exposure above regulatory limits or even potential
radiation-induced health effects. Although most of the standard
addresses details relevant to programs with known or substantial risks
of intakes, it is recognized that one important purpose of internal
dosimetry programs is to document that workplace controls are adequate
and no recordable intakes are occurring. Therefore, some guidance is
provided for programs (or a part of a program) that would not be
expected to involve dose assessment.
(a) Also excluded is information on dosimetric quantities
and units, regulatory interactions, regulatory or administrative dose
limits, methods of and recommendations on decorporation therapy,
performance requirements for bioassay methodologies, bioassay
frequencies, and uncertainties in assessment results. The reader is
referred to the References for information on these and related topics.
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