Ambient environmental profile for the Savannah River Site

One of the steps that has been taken to expedite the radiation dose reconstruction process is the development of "site profiles." These reports, one of which has been prepared for each of the major U.S. Department of Energy nuclear sites, include detailed assessments of the dose rates at a given site due to on-site exposures. Presented in this paper is a summary of the development of the ambient environmental dose profile for the Savannah River Site (SRS) for specific time periods from 1951-2001. Internal doses were estimated based on the radionuclide concentrations in the atmosphere due to individual facility releases and the resuspension of radioactive materials from the soil. External doses were estimated on the basis of releases of noble gases and contributions from ambient background radiation, which had been elevated due to various on-site activities. Although the annual environmental reports for the SRS served as a major resource for this effort, considerable work was required to access these data in terms of the accompanying dose rates. This was due, for example, to the confounding effects of nuclear weapons testing, lack of spatial and radionuclide resolution, and insensitivity of sampling methods to radionuclides important to dose. To overcome these problems, methods were developed to use well-documented source terms from reports published by others, coupled with historical meteorological records, to estimate specific airborne concentrations for radionuclides such as 3H, 41Ar, 131I, 234U, 235U, 238U, 238Pu, 239Pu, and 240Pu. Airborne concentration calculations included spatial and release height considerations for source terms at eight different production facilities. The resulting estimates then were used to derive annual intakes based on an assumed individual breathing rate of 2,400 m3 y(-1). Annual intakes resulting from resuspension of radionuclides from soil were based on maximum soil concentrations located in appropriate areas. This being accomplished, the estimated intakes and ambient radiation exposures were used to estimate the dose rates to major body organs of interest at specific time intervals.