Mineral Surface Processes Responsible for the Decreased Retardation (or Enhanced Mobilization) of 137 Cs from HWL Tank Discharges Page: 4 of 13
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Experimental research will determine how the sorption chemistry of Cs on Hanford vadose
zone sediments changes after contact with solutions characteristic of high-level tank wastes
(HLW). Our central hypothesis is that the high ionic-strength of tank wastes (i.e., > 5 mol/L
NaNO3) will suppress all surface-exchange reactions of Cs, except those to the highly selective
frayed edge sites (FES) of the micaceous fraction. We further speculate that the concentrations,
ion selectivity, and structural aspects of the FES will change after contact with the harsh chemical
conditions of HLW and these changes will be manifest in the macroscopic sorption behavior of
Cs. We believe that migration predictions of Cs can be improved substantially if such changes are
understood and quantified.
The research will integrate studies of ion-exchange thermodynamics on the FES, with high
resolution surface microscopies and spectroscopy to probe the structure of FES in Hanford
sediments and to describe how the chemical environment of sorbed Cs changes when HLW
supernatants promote silica dissolution and aluminum precipitation. Newly available atomic-force
microscopies and high-resolution electron-beam microscopies afford previously unavailable
opportunities to visualize and characterize FES. Our overall goal is to provide knowledge that
will improve transport calculations of Cs in the tank-farm environment. Specifically, the research
" Identify how the macroscopic sorption behavior of Cs on the micaceous fraction of the
Hanford sediments changes after contact with simulants of HLW tank supernatants over a
range of relevant chemical ([OH], [Na], [Al], [K, NH4]) and temperature conditions
(23 -80 C).
" Reconcile observed changes in sorption chemistry with microscopic and molecular
changes in adsorption-site distribution, chemistry, mineralogy, and morphology/structure
of the micaceous sorbent fraction.
" Integrate mass-action-solution-exchange measurements with changes in the structure/site
distribution of the micaceous-sorbent fraction to yield a multi-component/site-exchange
model relevant to high ionic strength and hydroxide concentrations for prediction of
environmental Cs sorption.
Environmental Management Concerns
- Single Shell Tanks (SST's) containing high level wastes have leaked supernate containing
large amounts of radioactive 137Cs (106 Ci) and other co-contaminants into the Hanford
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Zachara, John M.; Bertsch, Paul M. & Serne, Jeffrey R. Mineral Surface Processes Responsible for the Decreased Retardation (or Enhanced Mobilization) of 137 Cs from HWL Tank Discharges, report, June 1, 1999; Richland, Washington. (digital.library.unt.edu/ark:/67531/metadc787551/m1/4/: accessed July 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.