Neptunium Retardation with Tuffs and Groundwaters from Yucca Mountain

by I. R. Triay, Los Alamos Natl Lab, Los Alamos, United States,
B. A. Robinson, Los Alamos Natl Lab, Los Alamos, United States,
R. M. Lopez, Los Alamos Natl Lab, Los Alamos, United States,
A. J. Mitchell, Los Alamos Natl Lab, Los Alamos, United States,
C. M. Overly, Los Alamos Natl Lab, Los Alamos, United States,



Document Type: Proceeding Paper

Part of: High Level Radioactive Waste Management 1993

Abstract: The retardation of neptunium was studied using batch sorption and column techniques. Pure mineral separates, tuffs and groundwaters from Yucca Mountain were used for these experiments. Our results indicate that Np sorption increases rapidly as the pH of the water increases in cases where surface complexation is thought to be the dominant sorption mechanism. Oxide minerals (such as hematite) sorb Np strongly; therefore, these minerals even at trace levels in Yucca Mountain tuffs can result in significant Np retardation. Neptunium in groundwaters from Yucca Mountain exhibited a significant amount of sorption onto quartz. Neptunium sorption onto quartz is important because of the large quantity of silica in the tuffs. Elution of neptunium solutions in groundwater through columns made of crushed tuff yielded sorption coefficients that agree with the sorption obtained using batch sorption techniques. Agreement between batch and column experiments indicates a neptunium sorption mechanism that is linear, reversible, and instantaneous.

Subject Headings: Sorption | Radioactive wastes | Groundwater | Columns | Minerals | Waste storage | Waste disposal | pH

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