Fractional composition of partly hydrolysed polyvinyl acetate and its compatibility with hydroxypropyl methylcellulose in aqueous solutions

Fractionation of partly hydrolysed polyvinyl acetate (PVA) was performed by warming of its aqueous solutions. The following properties of the obtained fractions were determined: viscosity, molecular weight and molecular weight distribution, surface tension, and absorbance in the IR range. The blockiness of the polymer molecules, characterized by their behaviour towards iodine-containing systems such as I₂,-H₃BO₃ and I₂,-KI, was estimated. Fractionation of the aqueous solutions of PVA by warming is based mainly on the different internal molecular structure of the separated products, i.e. on the length of the vinyl acetate blocks in the PVA molecules and, to a lesser extent, on the degree of hydrolysis and the degree of polymerization. The more blocklike are the PVA molecules, the less compatible are the polymers in the PVA-hydroxypropyl methylcellulose (HPMC)-water system. At phase separation in this sytem the PVA molecules which are not compatible with HPMC are, in the first place, those of the highest blockiness.     

Radiation-Chemical Behavior of TBP in Hydrocarbon and Chlorohydrocarbon Diluents under Conditions of Reprocessing of Spent Fuel from Nuclear Power Plants

Experiments were performed for comparative assessment of the effect of ionizing radiation on the service characteristics of 30% TBP solutions in various diluents: hexachlorobutadiene (HCBD), mixtures of n-paraffins (RED diluent), and fraction of naphthenic hydrocarbons (RZh diluent). The following main parameters were chosen for comparative assessment of the quality of irradiated extractant solutions: composition and behavior of diluent radiolysis products, effect of diluents on the TBP radiolysis, and aggregative stability of emulsions in the main operations of the extraction cycle. The service life of the extraction mixtures was estimated from variation of the above parameters with the irradiation dose. Principles for choosing solvents with increased service life under irradiation were substantiated.     

Beyond-design-basis regimes of uranium stripping and of carbonate regeneration of the solvent

Beyond-design-basis regimes of centrifugal contactors for U stripping and of mixer–settlers for carbonate regeneration of the solvent, 30% TBP in Isopar M, were studied from the viewpoint of the influence of incomplete uranium stripping on the phase stability of the extraction system in the step of the carbonate scrubbing of the solvent. Dynamic relationship between these two operations was determined. A mathematical model of uranium stripping at stepwise–20% deviation from the nominal value was developed and verified; it was shown that the beyond-design-basis regime develops in such apparatuses within 4 h at the total trial time longer than 8 h. The mathematical relationships obtained were used in the development of software for calculating transient processes that occur when the stream parameters in the course of carbonate regeneration of the solvent change. The beyond-design-basis regime of the solvent regeneration was found to have two regions: region of stoichiometric excess of carbonate ions over uranyl ions with the risk of precipitation and region of excess of uranyl ions over carbonate ions with acidification of the unit and uranium breakthrough with the recycled solvent. The conditions of the tests performed correspond to the second region.     

Interaction of thorium and plutonium with pertechnetic acid in the course of extraction from nitric acid solutions with tributyl phosphate in diluent and its mathematical description

Databases on the coextraction of Th or Pu with Tc into 30% TBP in hydrocarbon diluent at 25°С are presented. The coextraction leads to mutual enhancement of the extraction of all the elements. The interactions in the system are described within the framework of a new approach to modeling, using the previously suggested and additional equations of concurrently occurring chemical reactions. The apparent equilibrium constants of these reactions are calculated.     

Current-induced resonance in ferromagnet-antiferromagnet junctions

The response of a ferromagnet-antiferromagnet junction to a high-frequency magnetic field is calculated as a function of the spin-polarized current density through the junction. Conditions are chosen under which the response is zero in absence of such a current. It is shown that increasing in the current density leads to proportional increase in the resonance frequency and resonant absorption. A principal possibility is indicated of using ferromagnet-antiferromagnet junction as a terahertz radiation detector.     

Ways of technetium and neptunium localization in extraction reprocessing of spent nuclear fuel from nuclear power plants

Possible ways of Tc and Np localization within the framework of the first extraction cycle of the Purex process are considered. Experimental data are presented on Tc localization in the high-level raffinate as applied to the RT-1 flowsheet, in the zirconium-tritium strip, and in the Pu-Np product or in the scrub from the unit of the barrier reductive scrubbing of the uranium solvent product as applied to six-unit extraction scheme in the design of the Experimental and Demonstration Center. For the latter case, the possibility of Np localization before and after Pu stripping was also examined.     

Effect of salting-out agents on nitric acid distribution between liquid and vapor in the course of evaporation of nitric acid radioactive waste

The database on the influence of concentrations of salting-out agents with different cation valence (Li⁺, Na⁺, K⁺, Cs⁺, NH₄⁺, Mg2+, Ca²⁺, Cu²⁺, Zn²⁺, Al³⁺, Fe³⁺, La³⁺, Pu⁴⁺, UO₂²⁺ nitrates) and of H₂SO₄ on the HNO₃ distribution between liquid and vapor at atmospheric pressure was verified and expanded by performing equilibrium evaporation experiments in an evaporator without reflux with circulation of the bottoms. This equilibrium can be described by the equation \(\log {\kern 1pt} {\alpha _H} = - 2.35 + 2\log \;{X_{\Sigma N{O_3}}}\) (where \({X_{\Sigma N{O_3}}}\) is the total concentration of nitrate ions in aqueous solution), taking into account partial binding of water due to hydration of the salting-out agent and apparent hydrolysis of polyvalent cations, and also incomplete dissociation of sulfuric acid. The suggested model is valid at \({X_{\Sigma N{O_3}}}\) from 3 to 16 M (azeotrope); at \({X_{\Sigma N{O_3}}}{\text{ < }}\;3\), Raoult’s law is observed (α_H = const), which is confirmed by a number of examples. In this model, the additivity of the properties of the salting- out agents, taking into account the concentration of “free” water, is assumed, which allows calculation of the composition of the bottoms and distillate when evaporating waste of any composition from radiochemical plants.     

Peer Reviewed: An Economic Perspective on Outdoor Residential Pesticide Use

Pesticides.     

Solubility and coprecipitation of barium and strontium nitrates in HNO<Subscript>3</Subscript> solutions and multicomponent systems

The solubility of Ba(NO₃)₂ and Sr(NO₃)₂ in HNO₃ solutions at 25–95°C is characterized by the power dependence on the total concentration of the nitrate ion with the exponent for Ba(NO₃)₂ equal to −2 in ∼9 M HNO₃ and −6 in more concentrated acid solutions. The latter exponent is also characteristic of the more soluble Sr(NO₃)₂ throughout the examined range of HNO₃ concentrations. In strongly acidic solutions, Ba(NO₃)₂ coprecipitates with Sr(NO₃)₂. The solubility curve for Ba(NO₃)₂ in NH₄(Na)NO₃ solutions suggests formation of a double salt, whereas in UO₂(NO₃)₂ solutions the dependence is the same as in HNO₃ solutions.