Application of vadose zone approach for prediction of radionuclide transfer from near-surface disposal facility

Abstract

About 100 000 m3 of solid conditioned Low and Intermediate Level Waste, generated during operation and decommissioning of the Ignalina nuclear power plant, are to be disposed of in a near-surface repository.In this study a computer code FEFLOW 5.0 was applied for simulating the transport of the most mobile radionuclides (3H, 14C, 59Ni and 94Nb) within moisture through an unsaturated vault of the near-surface repository in Stabatiškė Site. HYDRUS-1D analysis was used to assess the radionuclide transport in the repository and to estimate initial activity concentrations of radionuclides transported from the cemented waste. Radionuclide release from the vaults in the unsaturated conditions after closure of the repository and consequent contaminant plume transport has been assessed taking into account site-specific natural and engineering conditions and based on a normal evolution scenario.The highest value of 14C activity concentration (about 3.3·108 Bq/m3) in the moisture of soils below engineering barriers is predicted after about 7300 years after repository closure. The predicted maximum activity concentrations of the others modeled mobile radionuclide 3H (after 100 years after repository closure), 94Nb (after 300 000 years) and 59Ni (after 173 000 years) at the groundwater table are 1.1·105, 3.7·104 and 2.4·106 Bq/m3, respectively.