Long-Term Safety Assessment of a (Near-Surface) Short-Lived Radioactive Waste Repository in Lithuania

The paper presents the long-term safety assessment of the Maisiagala radioactive waste repository (Lithuania) using the advanced computer codes DUST, FEFLOW, and AMBER. The software DUST was employed for calculations of the one-dimensional leaching flux of radionuclides from the repository vault and subsequent transport in the unsaturated zone. Using the mass flux of radionuclides calculated in DUST as a source to the aquifer, the software FEFLOW was used for two-dimensional assessment of activity concentrations of radionuclides in groundwater. Using the groundwater concentrations calculated in FEFLOW, the code AMBER was used to calculate the dose over time at four hypothetical wells downstream from the repository. The well distances ranged from 150 to 1600 m.

When the hypothetical drinking water well is installed 150 m from the repository (close to the outside perimeter of the controlled area), the highest effective doses will arise from ³H, ³⁶Cl, and ²³⁹Pu. The doses determined by ³H and ³⁶Cl may exceed a dose limit of 1 mSv/yr for 50 to 230 yr after the closure of the facility (1989). The dose of ²³⁹Pu will remain almost constant for >60 000 yr after the closure, yet it will not exceed the dose limit value. According to previous studies, the intrusion scenario is much more critical compared to the groundwater exposure pathway in the case of ²³⁹Pu (as well as ²²⁶Ra).