Geochemically Based Safety Assessment

Abstract

ÃÃPerformance assessment (PA) for nuclear waste disposal based on transport processes frequently neglects significant safety factors by overestimation of radionuclide mobilization and underestimation of radionuclide retention processes. To include well understood geochemical knowledge into PA, the quasi-closed system approach (QCS) was developed. The QCS approach is described and applied to a LLW disposal in a German salt mine with respect to the disposed waste forms, geo-engineered barriers, and backfill strategies. The geochemical tools and the thermodynamic database for modelling highly concentrated salt systems are discussed. Applications are demonstrated which cover the long-term geochemical environment in the disposal caverns, the optimization of buffer materials, radionuclide retention, and the overall robustness of the approach. Also the effect of a potential solution exchange between different emplacement caverns is investigated. It is shown that the QCS approach provides essential data concerning the long-term geochemistry and related radionuclide concentrations to be used in PA and safety analysis.

Summary of Uranium Solubility Studies in Concrete Waste Forms and Vadose Zone Environments

“… At the DOE Fernald site in Ohio, uranium was found as an autunite-like phase, a schoepite-like phase, and an undefined uranyl-organic phase. MgCl brine ambient pH 7-10.5, 5-18 years equilibration 8E-09 -5E-07 (Kienzler et al 2010;Kienzler et al 2007) NaCl brine pH 11-12, 5-18 years equilibration 2E-09 -4E-07 U(VI) artificial cement pore water nitrogen pH 13.3 6E-06 (Wieland et al 2010)…”

Uranium, Mining and Hydrogeology

“…The implementation of geochemical processes in safety analyses using thermodynamic modeling has gained importance within the last years (Köster and Rudolph 1991;Kienzler et al 2007). There are still open questions with regard to reaction rates of geochemical processes , the requirements of quasi-closed systems for geochemical modeling (Kienzler et al 2007) and the quality of the thermodynamic data bases (Altmaier et al 2008).…”

Geochemically Based Safety Assessment

“…To be able to deal with geochemical aspects in PA, the quasi-closed system (QCS) approach was developed. [1][2][3][4] This concept can be used to determine source terms and to optimize the barrier system in an underground repository.…”