Geologija / Geology
 ISSN 1392-110X ISSN 2029-056X (online) |
2006 m. Nr. 3 Modelling of radionuclide transport in crystalline basement for demonstration of spent nuclear fuel disposal feasibility (case of South-eastern Lithuania)
The Strategy of Radioactive Waste Management of Lithuania provides for evaluating the possibilities of disposal in a deep geological repository of spent nuclear fuel and long-lived radioactive waste originated from the Ignalina NPP. The initial feasibility studies performed in Lithuania during 2001–2004 focus on screening all potentially prospective rock types as a host medium for a repository. Since most information is available on crystalline basement and sedimentary cover of South-eastern Lithuania, this host medium was selected for model case studies. Taking into account the main assumptions (the canister defect scenario proposed by Swedish experts and evaluated by LEI experts) groundwater flow and radionuclide (iodine-129 as a mobile and long-lived one) transport modeling using FEFLOW computer code was performed to model the domain (approximately a 0.8 km long, 0.6 km wide and 0.52 km thick far-field block) of South-eastern Lithuania. The model domain comprises a Proterozoic–Archaean aquifer with an overlaying aquifer system of sedimentary cover. The upward groundwater flow through a defected canister located in a tectonically damaged zone was conservatively generated. The main results of calculations are the following: in case of upward groundwater flow, the maximum activity concentration of I-129 in the single longitudinal tectonic fracture above the defected canister will not exceed 10-4 Bq/l, and in the active water exchange zone it is close to 10-7 Bq/l. These figures show that doses obtained by a human recipient via the aquatic pathway should be below the dose limit (1 mSv/y). Location of the model domain in Southeastern Lithuania does not mean any reference to the site for a deep geological repository.
Keywords: spent nuclear fuel, geological repository, crystalline basement, groundwater, finite elements model |
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