Reactive transport modeling of uranium 238 and radium 226 in groundwater of the Konigstein uranium mine, Germany

Knowledge of the transport behavior of radionuclides in groundwater is need ed for both groundwater protection and remediation of abandoned uranium min es and milling sites. Dispersion, diffusion, mixing, recharge to the aquife r, and chemical interactions, as well as radioactive decay, should be taken into account to obtain reliable predictions on transport of primordial nuc lides in groundwater. This paper demonstrates the need for carrying out reh abilitation strategies before closure of the Konigstein in-situ leaching ur anium mine near Dresden, Germany. Column experiments on drilling cores with uranium-enriched tap water provided data about the exchange behavior of ur anium. Uranium breakthrough was observed after more than 20 pore volumes. T his strong retardation is due to the exchange of positively charged uranium ions. The code TReAC is a 1-D, 2-D, and 3-D reactive transport code that w as modified to take into account the radioactive decay of uranium and the m ost important daughter nuclides, and to include double-porosity flow. TReAC satisfactorily simulated the breakthrough curves of the column experiments and provided a first approximation of exchange parameters. Groundwater flo w in the region of the Konigstein mine was simulated using the FLOWPATH cod e. Reactive transport behavior was simulated with TReAC in one dimension al ong a 6000-m path line. Results show that uranium migration is relatively s low, but that due to decay of uranium, the concentration of radium along th e flow path increases. Results are highly sensitive to the influence of dou ble-porosity flow.