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 scintillat ion 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 microsco py (SEM), were performed on samples thought to contain colloidal parti cles to determine particle composition and the nature of their associa tion with radioactive material. Several different types of particles r anging in size from 0.02 to 20 mu m were identified within the leachat e including crystalline calcium hydroxide particles, rounded siliceous grains, angular weathered soil, and spherical particles apparently co mposed of an organic polymer. The primary radioactive material associa ted with these particles was Sr-90. About 2% of the total Sr-90 activi ty in the leachate is associated with colloidal particles. This inform ation indicates that colloidal particles play a role in radioactive ma terial transport through lysimeter soils. (C) 1998 Elsevier Science Lt d. All rights reserved.