Radionuclide Release in Geothermal Aquifers - the Role of Alpha Recoil

The concentration of Ra-226, Ra-228 and Ra-224 in geothermal brines is caused to a high extent by -recoil processes at the mineral/fluid interface in the aquifer. A Monte Carlo code for the prediction of the activity concentrations and the isotope ratios was developed and tested on single and multi component systems, respectively. The simulations consider the chemical behaviour of released recoil nuclei in the solution as well as the statistical character of the recoil process. Analytical data of Radium isotopes in a geothermal fluid of the North German Basin were well reproduced by this model. Highly radioactive fracture fillings in the granite of Soultz-sous-Forets could be excluded as a source of the Radium concentration in the associated brine.