The Chernobyl pilot site project: Isolation and microscopic characterisation of fuel particles

A method of fuel particles separation from contaminated soil samples in heavy liquid was developed. Numerous particles have been isolated and characterised by Scanning Electron Microscopy. 14 years after Chernobyl accident 52% of Cs, 70% of Eu and Sr and 65% of Am still are associated with fuel particles. Hence the source term is mainly represented by fuel particles with a mean diameter of 4.17 µm. The source term consist of 2 types of particles: UO and ZrUO. Zr-U-O fuel particles account for 74% of the studied particles and showed much higher stability. Therefore the description of Chernobyl source term weathering requires 2 dissolution laws: a first one concerning UO particles with a higher dissolution constant and a second one with a low dissolution constant describing Zr-U-O dissolution

Strontium-90 transport parameters from source term to aquifer in the Chernobyl Pilot Site

Results are presented from multidisciplinary radiological and hydrogeological studies of process and parameters controlling 90Sr releases from the shallow trench containing nuclear fuel particles and subsequent radionuclide transport in the underlying eolian and alluvial sand aquifer at Chernobyl Pilot Site located at 2.5 km distance from the Chernobyl NPP. 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 fuel particles respectively). The Zr-containing particles exhibits low dissolution rate, therefore radionuclide inventory in source term available for migration is significantly less than estimated before. The 90Sr 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≈20 ml/g), and may represent essential natural sorption barrier to geo-migration. Radioactivity balance calculations show that 4 - 7% of initial trench inventory of 90Sr has migrated by now to the geological environment. Presented results have important implications on safety assessment and remedial analyses of the radioactive waste dumps at ChNPP