[en] The recovery and purification of plutonium involves interesting chemistry. Currently in use are several high temperature processes based on redox reactions. These processes include direct oxide reduction which uses calcium to reduce the oxide to the free metal and electrorefining which is used as a final purification step. The chemical research group at Rocky Flats is currently investigating the use of an aluminum/magnesium alloy to remove the ionic plutonium from the salts used in the above named processes. The results of this study along with an overview of pyrochemical plutonium processing chemistry will be presented

[en] Peat is relatively inexpensive material which possesses a native cation exchange capacity. Efforts to utilize peat have been hampered by its low permeability to water and its tendency to severely leach in water at pH 6. These disadvantages have been significantly minimized by treating the peat with a combination of concentrated sulfuric and phosphoric acids, resulting in a particulate material which is permeable to water and resistant to leaching. The acid treatment also increases the cation exchange capacity of the peat. This paper describes the results of both column and batch studies of the modified peat for use as an actinide adsorbent. 1 ref., 2 figs

[en] The H shaped catecholamides have been shown to be excellent actinide chelators. Decontamination factors as high as 145,000 have been mesured with the ligand absorbed onto a resin. Higher decontamination factors are inevitable once the ligands are bonded to a support so that all of the molecules will be available for chelation rather than just being smeared on the surface. Experiments are underway to evaluate backbone configurations' effect on plutonium bonding. Also, the methods necessary to measure the stability constants of the complexes are being developed. 4 figures, 1 table

[en] Peat is a relatively inexpensive material which possesses a native cation exchange capacity. Efforts to utilize peat have been hampered by its low permeability to water and its tendency to severely leach in water at pH 6. These disadvantages have been significantly minimized by treating the peat with a combination of concentrated sulfuric and phosphoric acids, resulting in a particulate material which is permeable to water and resistant to leaching. The acid treatment also increases the cation exchange capacity of the peat. This paper describes preliminary results of both column and batch studies of the modified peat for use as an actinide adsorbent

[en] The Waste Isolation Pilot Plant (WIPP) is a U.S. Department of Energy facility intended to store transuranic nuclear wastes. The conceptual model for WIPP dissolved concentrations is a description of the complex natural and artificial chemical conditions expected to influence dissolved actinide concentrations in the repository. By a set of physical and chemical assumptions regarding chemical kinetics, sorption substrates, and waste-brine interactions, the system was simplified to be amenable to mathematical description. The analysis indicated that an equilibrium thermodynamic model for describing actinide solubilities in brines would be tractable and scientifically supportable. This paper summarizes the conceptualization and modeling approach and the computational results as used in the WIPP application for certification of compliance with relevant regulations for nuclear waste repositories. The WIPP Site contains complex natural brines ranging from about sea water concentration to about ten times more concentrated than sea water. Data bases for predicting the solubility of AM(III) (as well as Pu(III) and Nd(III)), Th(IV), and Np(V) in these brines under potential repository conditions have been developed, focusing on chemical interactions with Na, K, Mg, Cl, S0₄ and C0₃ ions, and the organic acid anions acetate, citrate, ethylenediaminetetraacetate (EDTA), and oxalate. The laboratory and modeling effort augmented the Harvie et al. [1] parameterization of the Pitzer [2] activity coefficient model so that it could be applied to the actinides and oxidation states important to the WIPP system. (author)

[en] A backfill system has been designed for the Waste Isolation Pilot Plant (WIPP) which will control the chemical environment of the post-closure repository to a domain where the actinide solubility is within its lowest region. The actinide solubility is highly dependent on the chemical species which constitute the fluid, the resulting pH of the fluid, and the oxidation state of the actinide which is stable under the specific conditions. The use of magnesium oxide (MgO) has the backfill material not only controls the pH of the expected fluids, but also effectively removes carbonate from the system, which has a significant impact on actinide solubility. The backfill selection process, emplacement system design, and confirmatory experimental results are presented

[en] The conceptual model for WIPP dissolved concentrations is a description of the complex natural and artificial chemical conditions expected to influence dissolved actinide concentrations in the repository. By a set of physical and chemical assumptions regarding chemical kinetics, sorption substrates, and waste-brine interactions, the system was simplified to be amenable to mathematical description. The analysis indicated that an equilibrium thermodynamic model for describing actinide solubilities in brines would be tractable and scientifically supportable. This paper summarizes the conceptualization and modeling approach and the computational results as used in the WIPP application for certification of compliance with relevant regulations for nuclear waste repositories. The WIPP site contains complex natural brines ranging from sea water to 10x more concentrated than sea water. Data bases for predicting solubility of Am(III) (as well as Pu(III) and Nd(III)), Th(IV), and Np(V) in these brines under potential repository conditions have been developed, focusing on chemical interactions with Na, K, Mg, Cl, SO₄, and CO₃ ions, and the organic acid anions acetate, citrate, EDTA, and oxalate. The laboratory and modeling effort augmented the Harvie et al. parameterization of the Pitzer activity coefficient model so that it could be applied to the actinides and oxidation states important to the WIPP system

[en] The Waste Isolation Pilot Plant (WIPP), located in a salt bed in southern New Mexico, is designed by US Department of Energy to demonstrate the safe and permanent disposal of design-basis transuranic waste. WIPP performance assessment requires consideration of radionuclide release in brines in the event of inadvertent human intrusion. The mobility of radionuclides depends on chemical factors such as brine pmH (-log molality of H⁺) and CO₂ fugacity. According to current waste inventory estimates, a large quantity (∼ 10⁹ moles C) of organic materials will be emplaced in the WIPP. Those organic material will potentially be degraded by halophilic or halotolerant microorganisms in the presence of liquid water in the repository, especially if a large volume of brine is introduced into the repository by human intrusions. Organic material biodegradation will produce a large amount of CO₂, which will acidify the WIPP brine and thus significantly increase the mobility of actinides. This communication addresses (1) the rate of organic material biodegradation and the quantity of CO₂ to be possibly generated, (2) the effect of microbial CO₂ production on overall WIPP performance, and (3) the mechanism of using MgO to mitigate this effect

[en] The organic ligands acetate, lactate, oxalate and EDTA have been identified as components of wastes targeted for disposal in the Waste Isolation Pilot Plant (WIPP) located in Southeastern New Mexico. The presence of these ligands may increase dissolved actinide concentrations and impact chemical radiation during transport. The current work considers the complexation of Am(III), Th (IV) , Np(V), and U(V I) with two of the organic ligands, acetate and lactate, in Na CI media from dilute through high concentration. A thermodynamic model for actinide complexation with the organic ligands has been developed based on the Pitzer activity coefficient formalism and the Harvie-Moller-Weare, Felmy-Weare database for describing brine evaporites systems. The model was parameterized using first apparent stability constant data from the literature. Because of complexation of other metal ions (Fe, Mg, Ni, Pb, etc.) present in the WIPP disposal room with the organic ligands, preliminary results from model calculations indicate the organic ligands do not significantly increase dissolved actinide concentrations

[en] A backfill system has been designed for the WIPP which will control the chemical environment of the post-closure repository to a domain where the actinide solubility is within its lowest region. The actinide solubility is highly dependent on the chemical species which constitute the fluid, the resulting pH of the fluid, and oxidation state of the actinide which is stable under the specific conditions. The implementation of magnesium oxide (MgO) as the backfill material not only controls the pH of the expected fluids but also effectively removes the carbonate from the system, which has a significant impact for actinide solubility. The selection process, emplacement system, design, and confirmatory experimental results are presented