A Theoretical Approach to Modeling Ionizing Radiation Migration and Dose in Aquatic Environments Using Monte Carlo Simulation

This analysis focuses on estimating the migration of ionizing radiation and calculating potential doses for external radiation exposure from a Cs-137 source in the water column and sediments of large reservoirs or lakes. A Monte Carlo-based modeling approach is described and an adjoint transport equation incorporated with Monte Carlo-based modeling as well as a numerical integration method is used to estimate radionuclide migration and dose distributions. The adjoint transport equation is solved incorporating the Monte Carlo method and the results are compared to the results of the numerical iteration methods for a geometrically simplistic environment. The adjoint transport equation incorporated with the Monte Carlo method provides results that demonstrate that the dose estimates are comparable to numeric integration. However, incorporating Monte Carlo modeling also provides a way to bound the uncertainties associated with numerical solutions that estimate radiation field characteristics. The Monte Carlo method is computationally efficient for calculating ionizing radiation migration and potential dose, and can be used on more complex geometries than the applied numerical integration method. The Monte Carlo method can be used to support risk assessments that more accurately bound uncertainties.