Modelling of Coupled Groundwater Flow and Radionuclide Transport in Crystalline Basement Using Feflow 5.0

Abstract

The strategy of radioactive waste management of Lithuania provides for evaluating the possibilities of disposal of spent nuclear fuel and long‐lived radioactive waste originated from Ignalina NPP in deep geological formations. The initial studies performed in Lithuania during 2001–2004 focused on screening of all potentially prospective geological formations as host formations. Since most information is available on crystalline basement, this formation was selected for the model case studies. Taking into account the assumptions (canister defect scenario proposed by Swedish experts and evaluated by LEI experts), groundwater flow and radionuclide (iodine‐129 as mobile and long‐lived one) transport modelling using computer code FEFLOW was performed according to geosphere conditions and parameters characteristic of the southern part of Lithuania (0,8×0,6×0,52 km far‐field block). The upward groundwater flow through defected canister located in tectonically damaged zone was simulated. The main results of calculations are the following: in the case of upward groundwater flow, the maximum I‐129 volumetric activity in single tectonic fracture above defected canister will not exceed 1 Bq/1, and in the active water exchange zone, it is close to 10−2 Bq/l. These figures show that doses obtained by human recipient via aquatic pathway should be below the dose constraint (0,2 mSv/y). More complicated scenarios and assumptions should be investigated in future studies.

Radionuclide and Heat Transport From Hypothetical SNF Canister in Crystalline Basement, Case of South-Eastern Lithuania / Radionuklidų Ir Šilumos Sklaida Iš Hipotetinio PBK Konteinerio Kristalinio Pamato Uolienose (Pietryčių Lietuvos Pavyzdys)

“…It is based on the physical conservation principles for mass, chemical species, linear momentum and energy in a transient and three-dimensional numerical analysis (Diersch 2002). Mathematical formulations of numerical analysis for present model domain are described in (Jakimavičiūtė-Maselienė et al 2006a, 2006b.…”

“…The geometrical discretization (Fig. 1) of model domain and used parameters values are presented in detail in (Jakimavičiūtė-Maselienė et al 2006a,. 2006b) and briefly summarized in Table 1.…”

“…1 and Tables 3-4. The boundary conditions for radionuclide transport are evaluated in (Jakimavičiūtė-Maselienė et al 2006a,. 2006b).…”

“…Later, the fuel enrichment was increased up to 2.8%. The initial studies of radionuclide transport from the SNF canister has already been performed (Brazauskaitė, Poškas 2005, 2006, 2007Jakimavičiūtė-Maselienė et al 2006a, 2006b. These publications describe the SNF disposal system concept, container properties, engineering barriers, the radionuclide transport and retardation processes in the near-field and far-field regions of SNF disposal system.…”

The Geoenvironmental Impact of Klaipėda Geothermal Plant / Klaipėdos Geoterminės Jėgainės Poveikis Geologinei Aplinkai / Воздействие Клайпедской Геотермальной Станции На Геологическую Среду

“…Mathematical principles and premises of FEFLOW software are given in detail in methodical recommendations provided by the author (Diersch 2002(Diersch , 2004. The software was successfully used for simulation of mass and heat transport problems (Sanner et al 2005;Jakimavičiūtė-Maselienė et al 2006).…”