Simulating Effects of Non-Isothermal Flow on Reactive Transport of Radionuclides Originating From an Underground Nuclear Test

In numerical simulation of radionuclide transport, a mechanistic reactive transport model can account for non-electrostatic surface complexation, ion exchange, and mineral dissolution/precipitation reactions. However, in radionuclide transport originating from an underground nuclear test, thermal effects must also be considered because heat accounts for the majority of energy released from the test. A large fraction of residual test heat is initially contained in a "puddle" of solidified melt glass and rubble containing much of the less-volatile radionuclides. Residual test heat induces thermal convection by reducing fluid density and viscosity. Residual test heat also increases glass dissolution rates and, consequently, the rate of release of certain radionuclides into pore fluids. We combine a transient streamline reactive transport simulation approach with a hydrothermal flow model to predict the combined three-dimensional effects of test heat and non-linear geochemistry on radionuclide transport within a scale of ~ 1 km. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.