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

¹ Institute of Geological Sciences, Gonchara Str. 55-b, Kiev 01054, Ukraine
² Institute for Nuclear Safety and Protection, BP. 6, 92266 Fontenay-aux-Roses cedex, France
³ Ukrainian Institute of Agricultural Radiology, Mashinostroiteley Str. 7, Chabany, Kiev Region 255205, Ukraine

Abstract

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 (K_d≈3 ml/g). Alluvial sediments comprising the middle part of the aquifer have notably higher sorption capacity (K_d≈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.