Comparison of Measured and Modeled Radionuclide Air Concentrations in the Environment Following Emissions from the Hanford Site

K. Rhoads1; B.G. Fritz1; L.H. Staven1; L.P. Diediker2; and D.L. Dyekman3 (1Pacific Northwest National Laboratory; 2Duratek Federal Services Hanford; 3Fluor Hanford, Inc.)

Department of Energy facilities are required by regulation to report radioactive air emissions and the resulting dose to a maximally exposed individual on an annual basis. The reported air emissions include those from monitored sources such as stacks, as well as potential emissions from diffuse or fugitive sources that cannot be measured directly. The correlation between measured air concentrations at offsite environmental sampling stations, and downwind air concentrations estimated using measured stack emissions with standard atmospheric dispersion models, has been used at the Hanford Site as an indicator of potential diffuse or fugitive radionuclide emissions. The purpose of this study is to investigate the level of conservative bias in the calculated stack doses and in estimated potential emissions from non-stack sources. The current study uses an approach similar to that employed for the annual compliance reports - atmospheric modeling is used to estimate downwind radionuclide concentrations resulting from stack emissions, and the results are compared to air concentrations measured at onsite and offsite environmental sampling stations. The study focuses on I-129 emissions from an inactive Hanford facility where stack emissions are continuously monitored. The conservative approach used for annual compliance reporting has also estimated potential I-129 emissions from diffuse or fugitive sources in recent years. Initial results using facility-specific atmospheric modeling parameters indicate good agreement between estimated air concentrations and ambient air concentrations of I-129 measured at some downwind air monitoring stations. Therefore, it is likely that the approach used in annual compliance reports to model emissions from stacks and potential emissions from diffuse or fugitive sources overestimates the contribution from non-stack sources. *Work Supported by the U.S. Department of Energy under contract DE-AC05-76RL01830

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