Environmental simulation test for radionuclide migration under wet-dry cycle condition in aerated zone

Influence of discontinuous water flow based on repeated cycle of rainfall and evaporation (wet-dry cycle condition) on the migration behavior of 60Co, 85Sr and 137Cs in a sandy soil layer has been demonstratively investigated by using the equipment of environmental simulation test for radionuclide migration, in order to establish a reliable evaluation method of the radionuclide migration in natural barrier, in relation to the safety assessment on shallow land disposal of low-level radioactive waste. Migration velocity of cationic 85Sr, concentrations of particulate 60Co and 137Cs in the deeper soil layer, pH and ion concentration dissolved in the soil layer under the wet-dry cycle condition became larger than those under the continuous flow condition. Increase of the migration velocity of cationic 85Sr under the wet-dry cycle condition was attributed to that the concentration of Ca2+, by which the sorption ability of 85Sr onto soils was reduced, increased in interstitial water during an interruption period of water flow. On the other hand, the migration velocity of cationic 60Co and 137Cs was not affected by the wet-dry cycle condition. Increase of the concentration of particulate 60Co and 137Cs under the wet-dry cycle condition was probably caused from that movable {60Co(OH)2}n and 137Cs fixed on fine soil particles were produced during the interruption period. (author)