Three-parameter model for estimating atmospheric tritium dose at the Savannah River Site

The models used in the NRC approach to assess chronic atmospheric releases of radioactivity generate deterministic dose estimates by using standard assumptions about exposure conditions and environmental transport mechanisms. This approach has been used at the Savannah River Site since 1983. Total dose to off-site maximally exposed individuals at the SRS from atmospheric releases has been on the order of 1 microSv y(-1), three orders of magnitude lower than the applicable dose limit. When estimating atmospheric dose many parameters remain unchanged each time calculations are performed. These parameters, therefore, are essentially unimportant with regard to routine modeling. It is proposed, therefore, that transport and dosimetry models can be reduced to simple functions of a few parameters that essentially determine dose at all locations across the site. The three-parameter transport and dosimetry model developed in this work is useful for quick and easy estimates of chronic atmospheric tritium dose that are within a factor of 2 of estimates by more sophisticated models. The three parameters critical to estimating annual average concentration at the Savannah River Site are wind-direction frequency, downwind distance, and physical stack height. The model is bounded by physical stack heights between 10 and 61 m and downwind distances between 800 m (0.5 mi.) and 32 km (20 mi.) and should not be used outside its intended domain. It requires knowledge of wind-direction frequency, downwind distance, and physical stack height to estimate an Atmospheric Dose Factor (ADF; in units of microSv GBq(-1)) for the conversion of long-term release activity to maximum individual effective dose equivalent. This concept is being carried forward to the development of a reduced model for particulate emissions from SRS stacks.