Treatment methods and comparative risks of thorium removal from waste residues

摘要

This study was done to examine the risks of remediation and the effectiveness of removal methods for thorium and its associated radioactive decay products from various soils and wastes associated with DOE's Formerly Utilized Sites Remedial Action Program (FUSRAP). Removal of (sup 230)Th from uranium process residues would significantly reduce the buildup of (sup 226)Ra (half-life of 1600 years), and since (sup 230)Th concentrations at most of the important sites greatly exceed the (sup 226)Ra concentrations, such removal would reduce the accumulation of additional radiation risks associated with (sup 226)Ra and its products; and, if treatment also removed (sup 226)Ra, these risks could be mitigated even further. Removal of (sup 232)Th from thorium process residues would remove the source material for (sup 228)Ra, and since (sup 228)Ra has a half-life of 5.76 years, its control at FUSRAP sites could be done with land use controls for the 30--50 years required for (sup 228)Ra and the risks associated with its decay products to decay away. It must be recognized, however, that treatment methods invariably require workers to process residues and waste materials usually with bulk handling techniques. These processes expose workers to the radioactivity in the materials, therefore, workers would incur radiological risks in addition to industrial accident risks. An important question is whether the potential reduction of future radiological risks to members of the public justifies the risks that are incurred by remediation workers due to handling materials. This study examines, first, the effectiveness of treatment and then the risks that would be associated with remediation.