Radiological characterization of waste drum contents and its implication for radiological protection measures

Full text: Nuclear Engineering Seibersdorf (NES) is responsible for collection, characterization, treatment, and interim storage of all radiological waste generated in Austria. Facilities for waste treatment at NES include an incinerator plant for burnable solid and liquid radiological wastes, a treatment facility for non-burnable liquid wastes, and a high-pressure compactor for non-burnable solid radiological wastes. All conditioned radiological waste transferred from the NES treatment facilities to interim storage is contained in 200-l waste drums as standard storage containers. Even though these standard waste drums cannot be distinguished by visual inspection, except for their unique labeling, their contents may differ significantly in physical parameters and activity distribution, depending on the mode of treatment necessary for the initial unconditioned waste packages. The range of differences in the drum contents spans from homogeneous activity distributions in a concrete matrix from ashes or sludges to discrete sources in discrete locations in a concrete slab to centered compacted pellets in a concrete casing. For reasons of efficiency, inspection and subsequent radiological protection measures are based on a screening system for external dose rate at the surface and at a distance of 1 m from the drum. However, the various activity distributions in the waste drums will give rise to differing dose rate distributions at these locations. This paper examines the dose rate distributions due to the various conditioning methods and radionuclides of interest, investigates the uncertainties for standard dose rate measurements from these distributions, and evaluates their impact on radiological protection measures taken by the storage facility staff. (author)