Radionuclide migration using a travel time transport approach and its application in risk analysis

Abstract

The travel time transport approach for radioactive elements undergoing sorption and decay is employed in assessing the potential health risk at possible locations of human receptors. The principal entity in approach presented is a travel time probability density function conditioned on the set of parameters used to describe different transport processes, like advection, dispersion, sorption, and decay. The importance of accounting for parameter uncertainty and possible correlation between them is described and demonstrated in the study of risk analysis at the Nevada Test Site (NTS), which is located in the southwestern part of the state of Nevada. Because of the lack of sorption, the migration of tritium is found to provide the largest health risk to the accessible environment. Inclusion of the sorption process indicates that the parameter uncertainty and especially negative correlation between the mean velocity and the sorption strength are important in evaluating the arrival time of radionuclides at the prespecified accessible environment. The results from the risk-based screening analysis suggest that tritium, which does not sorb and has a short effective half-life (both physical and biological), is responsible for about 90% of the total risk.