Laboratory Experiments to Assess the Potential for Colloid-Facilitated Plutonium Transport in Fractured Rock
Abstract
Experiments involving injections of Plutonium-doped inorganic colloids into saturated fractured volcanic cores from the Nevada Test Site (NTS) were conducted to assess the potential for colloid-facilitated groundwater transport of Pu from nuclear test cavities at the NTS. Pu(V) was pre-sorbed onto colloids of montmorillonite and silica, and Pu(IV) was sorbed onto clinoptilolite colloids in batch sorption tests in which the fraction of Pu adsorbed to the colloids was measured as a function of time. After three or more weeks of sorption, a portion of the Pu-colloid suspensions was injected as a finite pulse into one or more fractured cores along with tritiated water, which served as a conservative solute tracer. The fraction of Pu adsorbed to the colloids at the time of injection was determined from a batch measurement conducted at the same time. The responses of the tritiated water, Pu, and colloids from the fractured cores were independently measured using liquid scintillation counting for the radionuclides and high sensitivity liquid in-situ particle spectrometry for the colloids. Also, batch measurements of Pu desorption from the colloids were initiated at the time the fracture experiments were started using some of the suspension injected into the fractures as the starting material. We found that the ability of the colloids to facilitate Pu transport followed the order: clinoptilolite > montmorillonite > silica. This order corresponded to the order of strength of Pu sorption onto the minerals. Essentially none of the Pu that was sorbed to the clinoptilolite colloids desorbed in either the fractured cores or in the batch desorption tests. However, Pu desorption from the montmorillonite and silica colloids was greater in the fractured cores than in the batch tests, indicating that fracture minerals were able to successfully compete with these colloids for Pu sorption. In tests conducted in the same fractures, silica colloids were less attenuated than montmorillonite colloids, but the montmorillonite colloids facilitated the transport of Pu better than silica because the Pu sorbed more strongly to the montmorillonite.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.H41H..02R
- Keywords:
-
- 1806 Chemistry of fresh water;
- 1832 Groundwater transport