Low-Level Waste Data Base Development Research Articles

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.

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 the Field Lysimeter Investigation: Low-Level Waste Data Base Development Program) were examined to determine if radiocolloid particles were present. Radiometric analyses were performed on 1.0 1 volumes of leachate. Samples of these leachates were passed through polycarbonate filters with pore diameters from 0.01 μm to 0.40 μm. One set of filters was analyzed to determine if radioactive material was trapped on their surfaces. A second set of filters was analyzed with a scanning electron microscope and energy dispersive x-ray analysis. Three radionuclides, Sr-90, Cs-137, and Co-60, were measured at 33.7 33.7 ± 0.52, 0.20 ± 0.03, and 0.13 ± 0.03 Bq/L, respectively, in the sand filled lysimeter leachate. Only Sr-90 at a concentration of 8.58 ± 0.37 Bq/l was measured in the soil filled lysimeter leachate. Amorphous particles < 0.20 μm in diameter were observed on the filters used with the sand filled lysimeter leachate. X-ray dispersive analysis was used to quantify the fractions of high atomic number materials present in these particles. 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 ⩽ 0.20 μm in diameter composed primarily of Si, and spherical particles about 0.2 μm 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 activity of beta emiting radionuclides detected on the filters was observed to increase as filter pore sizes decreased. This observation provides evidence of the presence of radiocolloids. It also indicates that a minor radiocolloid transport mechanism may be occurring within these lysimeters.

Radiation degradation in organic ion exchange resins

The EPICOR-II Resin/Liner Investigation: Low-Level Waste Data Base Development Program, funded by the U.S. Nuclear Regulatory Commission, studied the degradation effects in EPICOR-II organic ion exchange resins caused by internal radiation. Results of the third sampling analysis of ion exchange resins from prefilters PF-8 and PF-20 are compared with baseline data from tests performed on unirradiated resins and with results from the first and second samplings to determine if degradation has occurred because of the high internal radiation dose. Those results are also compared to findings of other researchers.