Effect of Rate-Limited Sorption on the Transport of Radionuclide Decay Chain

Experimental and theoretical studies have been undertaken to understand the transport ofradionuclides in subsurface environments because that the radionuclide transport in groundwater is one ofthe main pathway in the exposure scenarios for the intake of radionuclides. The radionuclide transport ingroundwater can be predicted using analytical models as well as numerical models. Despite their limitations,analytical or semi-analytical models are rapid and efficient tools for long-term predictions of radionuclidetransport as compared to time-marching numerical models which generally put severe demands oncomputational time. Transport processes of radionuclides generally involve a series of first-order sequentialdecay reactions. During migrations of radionuclides, mobile, toxic and harmful daughter products maysequentially form and move downstream with elevated concentrations. Solutions that accounts for only asingle-nuclide reactive transport do not permit transport behaviors of daughter species of radionuclide decaychain to be evaluated. Analytical or semi-analytical solutions for multiple nuclides transport equationscoupled with first-order sequential decay reactions can serve as fast and cost-effective tools for long-termpredictions of the transport of the predecessor and successor species of radionuclide decay chain. However,only few analytical solutions that were solved for coupled multiple radionuclides transport equations areavailable in literature. For mathematical convenience, most models currently used to simulate radionuclidedecay chain transport assume instantaneous equilibrium between contaminant in the dissolved and sorbedphases. Research has demonstrated that rate-limited sorption can have a profound effect upon the solutetransport in the subsurface environment. By making the equilibrium sorption assumption, the potentialeffects of rate-limited sorption/desorption are not considered and cannot be examined. In this project, wewill develop analytical model for radionuclide decay chain transport subject to rate-limited sorption. Thederived analytical model will be applied to investigate the effects of the rate-limited sorption on plumemigration of radionuclide decay chain. Ultimately, we will combine the derived analytical model and theRESidual RADioactivity (RESRAD) code to evaluate the rate-limited sorption on calculation of doses and risks