A PRELIMINARY INVESTIGATION OF THE EXISTENCE OF RADIOCOLLOIDS IN LEACHATE FROM THE NRC FIELD LYSIMETER INVESTIGATIONS

Leachate samples collected from sand and soil-filled lysimeters (of th e Field Lysimeter Investigation: Low-Level Waste Data Base Development Program) were examined to determine if radiocolloid particles were pr esent. Radiometric analyses were performed on 1.0 l volumes of leachat e. Samples of these leachates were passed through polycarbonate filter s with pore diameters from 0.01 mu m to 0.40 mu m One set of filters w as analyzed to determine if radioactive material was trapped on their surfaces. A second set of filters was analyzed with a scanning electro n microscope and energy dispersive x-ray analysis. Three radionuclides , Sr-90, Cs-137, and Co-60, were measured at 33.7 +/- 0.52, 0.20 +/- 0 .03, and 0.13 +/- 0.03 Bq/L, respectively, in the sand filled lysimete r leachate. Only Sr-90 at a concentration of 8.58 +/- 0.37 Bq/l was me asured in the soil filled lysimeter leachate. Amorphous particles < 0. 20 mu m in diameter were observed on the filters used with the sand fi lled lysimeter leachate. X-ray dispersive analysis was used to quantif y the fractions of high atomic number materials present in these parti cles. Although stoichiometrically appropriate quantities of oxygen and perhaps carbon are also present, x-ray dispersive analysis indicated that these particles were composed of Si (9%), Ca (87%), and Mg (4%). Amorphous particles less than or equal to 0.20 mu m in diameter compos ed primarily of Si, and spherical particles about 0.2 mu m in diameter composed of low atomic number material, were observed on the filters used with the soil filled lysimeter leachate. Beta radiation emitting radioactive material was detected on the filters. The relative activit y of beta emiting radionuclides detected on the filters was observed t o increase as filter pore sizes decreased. This observation provides e vidence of the presence of radiocolloids. It also indicates that a min or radiocolloid transport mechanism may be occurring within these lysi meters.