The experimental plateform in Chernobyl: an international research Polygon in the Exclusion Zone for soil and grounwater contamination

Titre du congrès :Nato Advanced Research Workshop "Hot Particles released from different Nuclear Sources" Ville du congrès :Yalta Date du congrès :07/05/2007

From 1999 to 2003 the Institute for Radioprotection and Nuclear Safety (IRSN), the Ukrainian Institute of Agricultural Radiology (UIAR) and the Institute of Geological Sciences at Kiev (IGS) set up an open-sky laboratory in the frame of the Chernobyl Pilot Site project (CPS project). This field site, situated about 2.5 kilomètres from the Chernobyl Nuclear Power Plant (ChNPP), is idéal for studying the transport of différent radionuclides from a source term through the unsaturated zone into the aquifer. In 1987, during site clean-up, a number of shallow trenches were dug and filled with soil contaminated with dispersed fuel parti clés and végétation débris from the dead Red Forest. The CPS project focused on one such a trench, trench number 22, to develop site characterisation techniques and to gather enough quantitative data to simulate the release and migration of différent radionuclides. The first project focused on characterising the source term, and modelling the observed strontium-90 pollution plume in the aquifer. This necessitated an integrated approach using fractionated solution of fuel particles in the trench, and transport of strontium-90 through the unsaturated zone and groundwater. The second part of the project (EPIC, Expérimental Platform In Chernobyl), which started in 2005, is directed towards more in-depth knowledge now that the site is well equipped and constantly monitored. We distinguish three main Unes of interest. A first Une investigates the unsaturated zone as it became clear that transport of radionuclides in the vadose zone plays an important rôle. Another part focuses on quantifying the effect of transient changes on chemical variability and on the transport of radionuclides in the aquifer. In order to achieve this goal, several sampling campaigns are carried out per year and results are compared to pressure readings and infiltration data. This may help explain the discrepancy found between steady state modelling results and observations. A third part détermines the concentration of plutonium and other Transuranium éléments (TUE) in groundwater. This investigation includes the analysis of filters for colloids or other possible transport mechanisms. The project, carried out by différent institutes with différent but complementary compétences, quantifies and visualises the complex pattern of reactive transport in a real and heterogeneous subsurface system.