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Deep Underground Disposal of the Actinide-Loaded Radioactive Wastes

#1326


Evaluation of Geological and Geochemical Conditions for Deep Underground Disposal of the Actinide-Loaded Radioactive Wastes

Tech Area / Field

  • ENV-RWT/Radioactive Waste Treatment/Environment

Status
8 Project completed

Registration date
04.08.1998

Completion date
07.02.2006

Senior Project Manager
Novozhilov V V

Leading Institute
IGEM (Geology & Mineralogy), Russia, Moscow

Supporting institutes

  • Khlopin Radium Institute, Russia, St Petersburg\nInstitute of Geochemistry and Analytical Chemistry, Russia, Moscow

Collaborators

  • Geological Survey of Japan, Japan, Tsukuba\nRadioactive Waste Management Center, Japan, Tokyo\nUniversity of Tokyo / Department of Quantum Engineering and Systems Science, Japan, Tokyo

Project summary

The purpose of this project is to study processes affecting migration of the long-lived actinides (U, Pu, Np, Am) from the deep underground high-level nuclear waste (HLW) repository. The prolonged half-live and high radiotoxicity of actinides imply that they should be isolated from the biosphere over time-scales of nґ(104 – 105) years. For substantiation of the possibility of an efficient isolation of the actinide-loaded HLW over such an extended time, the behavior of actinides should be studied under HLW repository conditions. The main process that can lead to actinides escape from the underground repository to the accessible environment is groundwater-borne migration. The proposed Project is focused on theoretical and experimental studies of the main geological, hydrogeological and physicochemical conditions affecting actinide transport by groundwater from the actinide-loaded HLW repository.

In the proposed studies will be employed:


· Experimental techniques for determination of uranium and of transuranium elements (TRU) solubility in the aqueous solutions of different composition.
· Methods of geochemical (computer) simulation of uranium behavior in aqueous solutions under conditions of variable temperature, pH and Eh of the liquid phase and composition of the solid mineral phases.
· Observations over natural analogues represented by the processes of uranium groundwater-borne migration in the present-day and paleohydrogeochemical conditions.
· Methods of numerical simulation of convective groundwater-borne migration of the long-lived radionuclides.

The projected activities include:


· Compilation from the published literature and reports and critical review of the available data on uranium migration in the subsurface hydrosphere, including data on uranium content in the present-day groundwaters, reconstruction of the processes responsible for accumulation and destruction of uranium ore bodies in the sandstone roll-front uranium deposits, formation of “positive” (uranium influx) and “negative” (uranium efflux) geochemical aureoles, etc.
· Physicochemical (computer) simulation of uranium behavior in aqueous solutions under conditions of varying solution composition and temperatures up to 150 ºC with consideration of the impact of the water-rock interaction on uranium migration and specification of the hydrogeochemical conditions responsible for uranium precipitation (“geochemical barriers”).
· Substantiation of a concept on the “optimal” geological environment for disposal of actinide-loaded HLW according to the requirement of minimal uranium mobility and correspondingly of the minimal leaching rate of uraninite matrix.
· Bench tests on determination of solubility of transuranic actinides (Pu, Np, Am) with evaluation of solubility dependence on groundwater U-saturation.
· Generalization of experimental data from the published literature and that obtained from the current research on the actinides solubility in the aqueous solutions under conditions simulating groundwater composition in the “optimal” HLW repository.
· Mathematical modeling of the long-lived radionuclides migration driven by groundwater forced and free thermal convection.


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