A radiological assessment of the 903 Pad, Mound, East Trenches and off-site areas at the Rocky Flats Plant

This thesis presents a radiological assessment of three contaminated areas at the Rocky Flats Plant in Colorado. The first area is located in Operable Unit 2 (OU 2) in the southeastern portion of the plant. The other two areas are located just off-site to the east. The goal of this thesis is to determine whether the U.S. Department of Energy (DOE) can release these areas to the public or whether it must remediate them, based on the requirements and procedures outlined in DOE Order 5400.5, "Radiation Protection of the Public and Environment." The methodology used to perform the assessment is based on DOE/CH/8901, "A Manual for Implementing Residual Radioactive Material Guidelines, A Supplement to U.S. Department of Energy Guidelines for Residual Radioactive Material at Formerly Utilized Sites Remedial Action Program and Surplus Facilities Management Program Sites." The calculations were made using Argonne National Laboratory's RESRAD computer model (Version 4.6) that uses the methodology in DOE/CH/8901. The critical pathways for radiation exposure are principally dust inhalation and soil ingestion. When the distribution coefficients are low, drinking-water ingestion can be also be a more serious exposure pathway, as can water-dependent plant and meat ingestion. The dose comes principally from Am-241. Under worst-case conditions, the dose to a receptor in the northern and southern off-site areas is under the base radiological dose limit (BRDL) of 100 mrem/yr. Thus, both of these areas may be released to the public. Under average (nominal) conditions at the on-site area, the dose to a receptor is 60 mrem/yr, which is under the limit. However, increasing the soil mass loading to its maximum value or reducing the distribution coefficient to its minimum value raises the dose above the limit. Under worst-case conditions, the dose is 3760 mrem/yr. Thus, the on-site area may require remdiation. The single radionuclide guideline for Am-241 is about 7.1 picocuries per gram (pCi/g) for low distribution coefficients and 0.83 pCi/g for the worst-case scenario. Reducing the soil concentrations of Am-241 below the guidelines reduces the dose below the limit for the respective conditions. More study is necessary.