An example of a dose assessment for the unrestricted release of material with small amounts of volumetric radioactive contamination

The Hanford 105 K Reactor Basin and Transfer Area roofing material unintentionally became slightly contaminated through unfiltered building roof exhausters. Rain water carried surface contamination through cracks in the aged roof to the underlying fibrous material. This process resulted in volumetric contamination of the roof. Each roof was sectioned into sampling areas depending on the potential for contamination and to perform ALARA analyses. The principal radionuclides of concern are 137Cs and 90Sr/90Y. The Westinghouse Hanford Company (WHC) volumetric release criteria for these radionuclides is 0.37 Bq g-1 (10 pCi g-1). Areas of the roof exceeding this release limit had a concentration, as determined by gamma spectroscopy, of 0.63 Bq g-1 (17 pCi g-1). 90Sr/90Y concentrations were conservatively assumed to be the same as 137Cs based on characterization studies. Trace amounts of 241Am and 60CO were also detected in a few areas. A dose assessment to determine potential impacts of this unrestricted material release was performed using the computer code RESRAD. The resultant dose was less than 10 nSv y-1 (0.001 mrem y-1). A cost/benefit analysis indicated a $17,000,000 per person-Sv ($170,000 per person-rem) averted savings which meets the ALARA criteria. A savings of $350,000 will be realized by the unrestricted release and burial of this material in the radiologically clean Hanford Central Landfill. The approval for this release came from DOE-HQ in accordance with DOE Order 5400.5 and was the first to be received by WHC