As a result, organ-specific doses can vary significantly for different organs.

Organ absorbed doses for these many exposure pathways have been studied for decades and for most radionuclides. The absorbed dose to individual organs is well established and provided in a series of reports published by the International Commission on Radiological Protection (ICRP). ICRP recommendations address ingestion and inhalation scenarios.

U.S. Nuclear Regulatory Commission (USNRC) licensing activities for nuclear plants are based on the very simplistic dosimetry model reported in ICRP Publication 2 (1959). In this model, the concept of the critical organ is applied. The critical organ is defined as the organ, which can include the whole body, that is expected to receive the largest radiation dose. In contrast, current ICRP guidelines account for the exposure of all organs and tissues. Doses from intakes of radionuclides by individuals generally are much more accurately and comprehensively modeled under these guidelines.

Estimating the radiation exposure to individuals in the vicinity of a nuclear facility is a strong function of the type of facility, local conditions such as distances from effluent release points, and of course environmental conditions. Although there are wide variations in these conditions, estimating radiation exposures reduces to knowing effluent release patterns as a function of time, exposure pathways, and the quantity and type of radionuclide(s) released.

Some of this required information is quite complex. For example, to estimate radiation exposures from atmospheric release, one needs to know radionuclide quantities, concentrations, and release locations as a function of time, the local weather pattern also as a function of time, and any occupancy at appropriate locations surrounding the facility.

When the information discussed above is convolved with the aforementioned dosimetric models, individual and population absorbed doses can be estimated on an individual-by-individual basis. The reliability of these estimates will depend on the availability and quality of all the required input data.

I.1 EXTERNAL DOSES

External doses resulting from atmospheric releases of radioactive effluents consist of three components: (1) dose from airborne noble gases and fission (plus activation) products; (2) doses from radionuclides deposited on the ground or in water; and (3) dose due to direct exposure to radioactive material at the facility, including nitrogen-16 in turbine buildings (in boiling water reactor plants) and other radionuclides in stored wastes.



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