Radioactive waste forms stabilized by ChemChar gasification: characterization and leaching behavior of cerium, thorium, protactinium, uranium, and neptunium

The uses of a thermally reductive gasification process in conjunction with vitrification and cementation for the long-term disposal of low level radioactive materials have been investigated. gamma-ray spectroscopy was used for analysis of carrier-free protactinium-233 and neptunium-239 and a stoichiometric amount of cerium (observed cerium-141) subsequent to gasification and leaching, up to 48 days. High resolution ICP-MS was used to analyze the cerium, thorium, and uranium from 46 to 438 days of leaching. Leaching procedures followed the guidance of ASTM Procedure C 1220-92, Standard Test Method for Static Leaching of Monolithic Waste Forms for Disposal of Radioactive Waste. The combination of the thermally reductive pretreatment, vitrification and cementation produced a highly non-leachable form suitable for long-term disposal of cerium, thorium, protactinium, uranium, and neptunium.     

Mechanistic study of the ChemChar Process using hexachlorobenzene as a surrogate for monitoring reaction products

The ChemChar Process, a non-incinerative thermolytic technology designed to destroy hazardous and non-hazardous wastes, was studied using the surrogate compound hexachlorobenzene (HCB). The process was varied from the conventional mode of operation, and thermal degradation products of HCB were collected in sampling trains. A mechanism of thermal destruction was proposed from experimental results and comparison to known mechanisms employing similar coal conversion technology.     

Feeding by a “nonfeeding” larva: uptake of dissolved amino acids from seawater by lecithotrophic larvae of the gastropod Haliotis rufescens

Larvae of the red abalone (Haliotis rufescens Swainson) are functionally incapable of capturing particulate foods. The aim of this study was to determine whether these larvae could acquire energy from seawater in the form of dissolved organic material. Trochophore and veliger larvae were shown to acquire energy by transporting dissolved organic material from seawater. Both larval stages took up all classes of amino acids tested. The influx of radiolabeled alanine represented the net substrate flux, as determined by direct chemical measurement for both trochophore and veliger larvae. Although veliger larvae have a transport system to take up taurine from seawater, a net efflux was observed for this amino acid. The release of taurine occurred independently of the presence of either taurine or other amino acids in the medium. Transported alanine was used in both anabolic and catabolic pathways. The percent of ¹⁴C-alanine in the trichloroacetic acid-insoluble fraction (macromolecules) of veliger larvae ranged from 21 to 56% of the total radioactivity in the larvae. No lipid biosynthesis was detected from ¹⁴C-labeled alanine. Veliger larvae catabolized 15 to 19% of the total alanine taken up and released it as ¹⁴CO₂. The metabolic rate (oxygen consumption) and the rate of amino acid uptake were both determined for the same group of veliger larvae. The percent contribution that the uptake of amino acids, from a total concentration of 1.6 M, made to the metabolic demand of abalone larvae ranged from 39 to 70%. Thus, these lecithotrophic larvae are not energetically independent of their environment, a result which differs from the current view of energy allocation to nonfeeding larvae.Please address all requests for reprints to Dr. Manahan at the University of Southern California     

Food availability and physiological state of sea urchin larvae (<Emphasis Type="Italic">Strongylocentrotus purpuratus</Emphasis>)

Food availability is highly variable in the ocean. Many species of marine invertebrates have a larval form that depends upon exogenous nutrients for growth, yet there are few biochemical and physiological indices for determining changes in the nutritional status of larvae. In this study, the effects of food availability on biochemical compositions and metabolic processes of larvae of the sea urchin, Strongylocentrotus purpuratus, were determined. Larvae were cultured under different food concentrations (fed-to-excess and unfed) and a suite of biological processes assayed, ranging from measurements at the level of the whole organism to that of specific molecules. These data were normalized to DNA content (an index of cell number) to allow comparisons of physiological rates in larvae of different sizes. Changes in the following were measured during larval growth: free amino acid pool, protein, lipid classes (cholesterol, free fatty acids, hydrocarbons, phospholipids, triacylglycerol), enzyme activities (Na⁺, K⁺-ATPase and citrate synthase), and respiration rates. In growing larvae, the two key components that showed differential cell-specific content relative to unfed larvae were glycine in the free amino acid pool and phospholipids. Additionally, several lipid classes were detectable only in fed larvae (cholesterols, free fatty acids, and hydrocarbons). While triacylglycerols were present in eggs and utilized during pre-feeding development, they were not re-accumulated at detectable levels in feeding larvae. Respiration rates, protein content, and enzyme activities were all similar on a cell-specific basis, showing that these variables did not provide useful indices of differences in physiological state between fed and unfed larvae. In contrast, measurements of the cell-specific content of glycine and certain lipid classes did provide useful indices of physiological state of larvae. Application of these indices could potentially allow for determinations of nutritional state of larvae in the ocean.     

Evaluation of a novel carbon adsorbent for fractionation and treatment of halogenated organic wastes

A carbon adsorbent obtained by a procedure analogous to reverse burn coal gasification is being evaluated in our laboratory. This low surface area carbon adsorbent shows considerable promise as a fractionation medium for a variety of organics. The performance of the adsorbent compares favorably to the highly specialized carbon adsorbents such as PX-21 (Amoco Corp.). The adsorbent also has considerable potential for treatment of wastes containing organochlorine compounds. The adsorbent shows good adsorption capacity and can hold as much as 50% (w/w basis) of organic sludge while maintaining a relatively dry, granular character. Furthermore, this waste-loaded adsorbent is amenable to highly efficient self-sustained thermal degradation. Degradation efficiencies approaching 99.99 percent have been achieved for such recalcitrant organics as polychlorinated biphenyls and tetrachlorodibenzo-p-dioxins.