Decay-series disequilibrium study of in-situ, long-term radionuclide transport in water-rock systems

Uranium and thorium-series disequilibrium in nature permits the determination of many in-situ physico-chemical, geologic and hydrologic variables that control the long-term migration of radionuclides in geologic systems. It also provides site-specific, natural analog information valuable to the assessment of geologic disposal of nuclear wastes. In this study, a model that relates the decay-series radioisotope distributions among solution, sorbed and solid phases in water-rock systems to processes of water transport, sorption-desorption, dissolution-precipitation, radioactive ingrowth-decay, and α recoil is discussed and applied to a basaltic aquifer at the Idaho National Engineering and Environmental Laboratory (INEEL), Idaho.