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Biota Dose Assessment for the INL Site


The impact of environmental radioactivity at the INL Site on nonhuman biota is assessed using guidance provided by the U.S. Department of Energy (DOE) technical standard entitled A Graded Approach for Evaluating Radiation Doses to Aquatic and Terrestrial Biota (https://www.standards.doe.gov/standards-documents/1100/1153-astd-2019). The graded approach meets the requirements of DOE Order 458.1 “Radiation Protection of the Public and the Environment" (https://www.energy.gov/ehss/services/environment/radiation-protection-public-and-environment). DOE facilities are required to demonstrate in their Annual Site Environmental Reports that routine radioactive releases from their sites are protective of non-human receptors.

The RESRAD-BIOTA code (https://resrad.evs.anl.gov/codes/resrad-biota/) implements the U.S. Department of Energy's graded approach methodology for evaluating radiation doses to aquatic and terrestrial biota. It calculates absorbed radiation doses to various biota organisms, default or user-created, from contaminated environmental media, as well as derives Biota Concentration Guides (BCGs) in terms of medium concentration levels, corresponding to a specific biota absorbed dose limit.

The first step in the graded approach uses conservative default assumptions and maximum values for all currently available data. For example, for the INL Site evaluation maximum concentrations of radionuclides in soils and effluent ponds are used for the general screening level. The general screening level (Level 1 in RESRAD-Biota) provides generic limiting concentrations of radionuclides in environmental media, termed Biota Concentration Guides (BCGs). Each BCG is the environmental concentration of a given radionuclide in soil or water that, under assumptions of the model, would results in a dose rate less than 1 rad/d (10 mGy/d) to aquatic animals or terrestrial plants or 0.1 rad/d (10 mGy/d) to terrestrial animals. If the sum of the measured maximum environmental concentrations divided by the BCGs (the combined sum of the fractions) is less than one, no negative impact to plant or animal populations is expected. Additional analysis may be warranted if biota dose evaluations using the screening and analysis methods described to this point continue to indicate that there is a potential adverse impact from radiation to populations of biota (i.e., the BCGs are exceeded). The INL Site assessment have never exceeded the fraction of one using soil and water measurements.

At Levels 2 and 3, more site- and organism-specific input data are accepted to perform a more realistic dose calculation for comparison with a specified dose limit. Both external radiation and internal radiation are considered in the dose calculation. Screening calculations (Level 1) performed using INL Site media data do not indicate the need for more realistic, site-specific parameters in the model. However, waterfowl collected near effluent ponds at the INL Site have measurable concentrations of radionuclides associated with the effluent. Bats collected at INL Site facilities also have measurable radionuclide concentrations. The availability of these data allow Level 3 assessments for the Annual Site Environmental Report. The assessment shows that doses received by waterfowl and bats are less than the limit of 0.1 rad/d (10 mGy/d) for terrestrial animals. A Site-Specific Biota Dose Assessment which may involve collection of biota, analysis, and risk characterization is thus not warranted.
Screening Analysis
RESRAD BIOTA Levels of Analysis Corresponding to the Graded Approach

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