A method for determining acceptable residual radioactive contamination levels

Determining acceptable residual contamination levels for unrestricted public use of decommissioned nuclear facilities must be done in a manner that assures public safety. The method that we propose for determining these levels is based on a comparison of a calculated maximum annual dose received by a maximum-exposed individual with an established annual dose limit. When internal exposure from inhalation or ingestion is the dominant dose contributor, the maximum annual dose may not occur in the first year following the onset of exposure. Thus, a first-year dose equivalent will not predict the most restrictive contamination level. An alternative method might be to calculate the 50-year committed dose equivalent from residual contamination; however, there are no recognized standards limiting the 50-year committed dose equivalent. Therefore, neither the first-year dose equivalent nor the 50-year committed dose equivalent is appropriate for determining acceptable residual radioactive contamination levels. Our method, using the calculated maximum annual dose, results in residual contamination levels based on an annual dose that is compatible with existing standards. Equations, which help define the calculation of annual doses during continuing exposure, are presented in the paper. These equations and existing radiation exposure pathway models have been programmed into a computer code to help us further investigate and demonstrate the usefulness of calculated maximum annual doses. 18 refs