Radionuclide dispersion from a waste burial in the geosphere

Results are presented from the ongoing international study, namely Chernobyl Pilot Site Project, aimed at characterization and modeling of process controlling Sr releases from the shallow trench at Chernobyl NPP site containing nuclear fuel particles and subsequent radionuclide transport in the underlying eolian and alluvial sand aquifer. Microscopic analyses of fuel particles separated from waste have identified two families of particles: U–O and Zr-U-O (~25% and 75% of the number of particles respectively). The Zrcontaining particles exhibits low dissolution rate, therefore radionuclide inventory in source term available for migration is significantly less than estimated before. The Sr migration velocity in the eolian sand layer is estimated at 7% of real groundwater flow velocity (Kd 3 ml/g). Alluvial sediments comprising the middle part of the aquifer have notably higher sorption capacity (Kd 10 ml/g). Radioactivity balance calculations show that 4 7% of initial trench inventory of Sr has migrated by now to the geo-environment. Obtained results have important implications on safety assessment and remedial analyses of the radioactive waste dumps at ChNPP. In particular, local geological barriers and hydrogeological settings are shown to provide “natural containment” of contaminated groundwater essentially limiting offsite transport of Sr to the hydrographic network.