Daniel I. Kaplan

Evaluation of a conceptual model for the subsurface transport of plutonium involving surface mediated reduction of Pu(V) to Pu(IV)

A conceptual model is proposed to explain the transport behavior of plutonium in laboratory columns packed with a sandy coastal soil from the U.S. Department of Energy (DOE)s Savannah River Site. The column transport experiments involved the introduction of a finite step input of plutonium, predominately in the +5 oxidation state, into the columns followed by elution with a low-carbonate solution of 0.02 M NaClO4 at pH 3, 5, and 8. Total plutonium concentrations were measured in the effluent as a function of time. These elution profiles suggest at least two distinct physical/chemical forms of plutonium, each with a different mobility. To explain the observed behavior, the following conceptual model was evaluated: [1] equilibrium partitioning of plutonium (V) and plutonium (IV) between the aqueous and sorbed phases as defined by pH-dependent, oxidation-state specific distribution coefficients and [2] kinetic reduction of plutonium (V) to plutonium (IV) in the sorbed phase. The conceptual model was applied to the column experiments through a one-dimensional advective/dispersive mathematical model, and predictions of the mathematical model were compared with the experimental data. Overall, the model was successful in predicting some of the major features observed in the experiments. It also yielded quantitative estimates of the rate constant for surface mediated reduction of plutonium (V) to plutonium (IV) that were of the same order (10(-4) to 10(-5) s(-1)) as those calculated from batch data both for this soil and for goethite.

Composite Analysis for Low-Level Waste Disposal in the 200 Area Plateau of the Hanford Site, Southeast Washington

A composite analysis of low-level radioactive waste disposal and other radioactive sources was recently completed for the Hanford Site in Southeast Washington State. Impacts from source release and environmental transportwere estimated for a 1 000-year period following Site closure in a multi-step process involving 1) estimation of radiological inventories and releases, 2) assessment of contaminant migration through the vadose zone, groundwater, and atmospheric pathways, 3) and estimation of doses. The analysis showed that most of the radionuclide inventory in past-practice liquid discharge sites and pre-1988 solid waste burial grounds on the 200 Area Plateau will be released in the first several hundred years following Hanford Site closure, well before projected releases from active and planned disposals of solid waste. The maximum predicted agricultural dose was less than 6 mrem/y in 2050 and declined thereafter. The maximum doses for the residential, industrial, and recreational scenarios, were 2.2, 0.7, and 0.04 mrem/y, respectively, and also declined after 2050.

Immobilization of Cesium-Contaminated Sediments Through the Addition of Illite Clays

Anna S. Knox—The University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, SC, 29802, USA, achlopecka@srel.edu. Telephone: (803) 725 2752, Fax: (803) 725 3309; Thomas G. Hinton—The University of Georgia, Savannah River Ecology Laboratory, Drawer E, Aiken, SC, 29802, USA, hinton@srel.edu, Telephone: (803) 725 5358, Fax (803) 725 3309; Daniel I. Kaplan—Westinghouse Savannah River Company, Aiken SC 29808, USA, daniel.kaplan@srs.gov, Telephone: (803) 725 2363, Fax (803) 725 3456; B. Thomas Butcher— Westinghouse Savannah River Company, Aiken SC 29808, USA, tom.butcher@srs.gov, Telephone: (803) 725 5810, Fax (803) 725 3456