Radiocolloids in leachate from the NRC field lysimeter investigations

An investigation of colloidal particles has been completed on leachate samples collected from sand and soil-filled lysimeters (of the Field Lysimeter Investigation: Low-Level Waste Data Base Development Program) in which low-level radioactive waste forms were buried. An array of analytical techniques including: gamma spectroscopy, liquid scintillation spectrometry, gross alpha and beta particle proportional counting, energy dispersive X-ray analysis (EDX), neutron activation analysis (NAA), X-ray fluorescence analysis (XRF), proton induced X-ray emission analysis (PIXE), gravimetric analysis, and scanning electron microscopy (SEM), were performed on samples thought to contain colloidal particles to determine particle composition and the nature of their association with radioactive material. Several different types of particles ranging in size from 0.02 to 20 μm were identified within the leachate including crystalline calcium hydroxide particles, rounded siliceous grains, angular weathered soil, and spherical particles apparently composed of an organic polymer. The primary radioactive material associated with these particles was Sr-90. About 2% of the total Sr-90 activity in the leachate is associated with colloidal particles. This information indicates that colloidal particles play a role in radioactive material transport through lysimeter soils.