Localization of cesium radioaerosols on granulated materials from the water vapor-air medium

The paper deals with localization of ¹³⁷Cs¹³¹I radioaerosols and products of their oxidative hydrolysis from the water vapor-air medium with various filtering elements: granulated sorbents based on silica gel and their combination with a helical filtering element (HFE) and TRUMEM metallic membrane filter (pore size ～2.0 μm). The degree of localization of ¹³⁷Cs¹³¹I aerosols was studied in relation to the air flow temperature, water vapor content, linear flow velocity in the sorption column, and amount of ¹³⁷Cs¹³¹I aerosols delivered to the filtration system. Localization of ¹³⁷Cs₂MoO₄ radioaerosols on the granulated sorbents was also studied.     

Conversion of I<Subscript>2</Subscript> into ionic species on composite materials in the NPP primary coolant

The conversion of I₂ into its ionic species in aqueous solutions, including the simulated primary coolant, at 20, 40, and 60°C on the solid phase of composite materials prepared by modification of KU-2 cation exchanger containing d elements was studied. These materials are capable of converting I₂ into its ionic species to 99% both in distilled water and in a solution corresponding in its composition to the aqueous primary coolant of NPP with WWER-type reactors. Practically complete conversion of I₂ (to more than 95.0%) is attained in 15 min. AV-18 anion exchanger is capable of sorbing I₂ in the form of I₃⁻ from aqueous solution with the distribution coefficients K _d >10³ ml g⁻¹ upon 24-h contact of the solid and liquid phases at V/m = 100.     

Kinetics of aerosol formation in gas flows

Discrete and continual versions of the rate equation for the size distribution function of primary aerosol particles were formulated. With the CsI aerosol as example, it was shown that coarsening of primary aerosol particles can be described in terms of both discrete and continual models. This conclusion is based on the results of experiments performed by the procedure that makes it possible to reveal primary particles against the background of their aggregates, ensures complete transfer of primary particles from the aerosol volume to the collector, and allows determination of their size on the collector by electron microscopy. Under the examined conditions, the size distribution of primary particles is described by an exponential function.     

Removal of volatile radioactive iodine compounds from water vapor–air medium

Sorption of CH₃ ¹³¹I and ¹³¹I₂ from water vapor–air medium onto SiO₂–C (2 wt %) composite material and a mixture of SKT-3I with SiO₂–Cu⁰ (10 wt %) was studied. SKT-3I shows high performance in sorption of ¹³¹I₂ and CH₃ ¹³¹I. The degree of localization of ¹³¹I₂ and CH₃ ¹³¹I exceeds 99.99% at ~60°С and gas phase–sorbent contact time τ of ~0.45 s. The degree of sorption of ¹³¹I₂ and CH₃ ¹³¹I onto the SiO₂–C (2 wt %) composite material under similar conditions does not exceed ~87 and ~8%, respectively. Experiments on ¹³¹I₂ and CH₃ ¹³¹I sorption onto mechanical mixtures of SiO₂–Cu⁰ and SKT-3I in the weight ratio varied from 1: 4 to 1: 1 showed that the degree of the ¹³¹I₂ and CH₃ ¹³¹I sorption at ~60°С and τ ~0.45 s exceeded 99.95 and 99.0%, respectively. The scheme of layer-by-layer arrangement of SiO₂–Cu⁰ and SKT-3I in the column was examined. It shows promise for use in AUI-1500VM filters in ventilation systems of nuclear power plants.     

Oxidative Hydrolysis in Water Vapor-Air Phase of CsI Radioaerosols Produced by CsI Sublimation from Metallic Surface

Behavior of CsI radioaerosols produced by CsI sublimation from a platinum support in argon, air, and water vapor-air mixture was studied. During 10-12 min of the vaporization at 900-1570 K, CsI radioaerosols undergo oxidative hydrolysis with atmospheric oxygen and water vapor to form CsOH aerosols and I₂. The cesium-to-iodine ratio determined in various fractions shows that oxidation of CsI in argon is minimal and is caused by the presence of oxygen and water traces. Oxidative hydrolysis of CsI strongly increases with increasing water vapor content in the vapor-gas flow. The degree of oxidative hydrolysis of CsI in the gas flow depends not only on the content of water vapor and oxygen but also on the initial CsI/O₂ molar ratio.     

Sorption of CH3131I from Steam-Gas Phase on Modified Ag-Containing Zeolites

Sorption of CH₃ ¹³¹I from the steam-gas phase on Ag-containing zeolites modified with acetylene was studied. The radioiodine adsorption in a column depends on the silver concentration in the sorbent, humidity of the steam-gas flow, and the temperature. The modified sorbents AgX-m containing 30-57% silver efficiently localize CH3I at the humidity up to 80% and sorption temperature from 120 to 195°C. Under these conditions the decontamination factor of a gas flow with respect to CH₃ ¹³¹I at 7.5-cm height of the sorbent bed and a 0.2 s gas-sorbent contact time exceeds 99.99%. The sorption properties of the modified Ag-containing sorbents are better that those of the nonmodified sorbents and known Ag-substituted zeolites.     

Lanthanides and actinides among other groups of elements of the periodic table

The extent to which actinides (An) are similar to other elements of the periodic table is discussed. Actinides show certain similarity with transition metals in trends in variation of the stability of the highest and lowest oxidation states with increasing atomic number. Similarity between elements of the first half of the lanthanide (Ln) family and those of the second half of the An family is demonstrated. In the lowest oxidation states, An and Ln are analogs of alkali and alkaline-earth elements, and in the tetravalent state they start to exhibit noticeable similarity with d elements. The formation of Pu(VIII) is suggested on the basis of essentially similar volatility of oxides ot Os and Ru with that of Pu. Of particular interest are bivalent An and Ln ions with one d electron. Being analogs of bivalent elements, they form various types of clusters.     

Recovery of 137Cs, 90Sr, 90Y, and d-element ions from aqueous solutions with sorbents containing triethylenediamine

The possibility of using sorbents based on KSKG coarsely porous silica gel and containing triethylenediamine N(CH₂-CH₂)₃N (TEDA) for recovering ¹³⁷Cs, ⁹⁰Sr, ⁹⁰Y, and d-element ions (Cu²⁺, Ni²⁺) from aqueous solutions was examined. Both ⁹⁰Sr, ⁹⁰Y radionuclides and Cu²⁺, Ni²⁺ ions are sorbed on KSKG containing 0.01–6.72 wt % TEDA. However, on sorbents based on KSKG and containing complexes of Cu²⁺, Ni²⁺, and Zn²⁺ nitrates with TEDA, the ¹³⁷Cs, ⁹⁰Sr, and ⁹⁰Y radionuclides are not sorbed. The equilibrium in the systems with these sorbents is attained within 3 h. The sorption capacity for Cu²⁺ and Ni²⁺ strongly depends on the conditions of the sorbent synthesis. The capacity of the sorbents for Cu²⁺ varies from 63 to 320 mg of metal per gram of sorbent. For Ni²⁺, the sorption capacity is considerably lower (no more than 130 mg of Ni²⁺ per gram of sorbent). The distribution coefficients of ⁹⁰Sr and ⁹⁰Y are 300–700 ml g^?1 at the contact time of the solid and liquid phases of 96 h and V/m = 100 ml g^?1.     

Mechanism of UO<Subscript>2</Subscript>(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O decomposition under the action of microwave radiation: Part 2

Products of UO₂(NO₃)₂·6H₂O decomposition under the action of microwave radiation (MWR) were studied by thermal gravimetric analysis, X-ray phase analysis, IR spectroscopy, and electron microscopy. The results of physicochemical studies of these decomposition products were compared to the published data for various uranium compounds, including UO₂(NO₃)₂·6H₂O. Apart from gaseous products, the final products of decomposition of 2–10 g of UO₂(NO₃)₂·6H₂O under the action of MWR for 35 min (the maximal process temperature, 170–320°C, is attained in the first 2–5 min of irradiation) are uranyl hydroxonitrate UO₂(OH)NO₃ and uranium trioxide UO₃ or their hydrates. The results obtained are consistent with the mechanism suggested in our previous paper and involving the reactions (1) UO₂(NO₃)₂·6H₂O → UO₂(OH)NO₃ + 5H₂O + HNO₃ and (2) UO₂(OH)NO₃ → UO₃ + HNO_3. The physicochemical study confirms the conclusions on the composition of products of UO₂(NO₃)₂·6H₂O decomposition under the action of MWR, made previously on the basis of chemical studies. The only precursor of UO₃ in microwave treatment of UO₂(NO₃)₂·6H₂O is UO₂(OH)NO₃ (or its hydrates). This is the main difference between the courses of uranyl nitrate decomposition under the conditions of microwave and convection heating. In the latter case, uranyl nitrate and its hydrates also participate in the formation of UO₃.     

Sorption of Cs,Sr, and Y radionuclides on mixed layered double hydroxides of Mg,Al, and Nd from the aqueous phase

Sorption of ¹³⁷Cs, ⁹⁰Sr, and ⁹⁰Y radionuclides from aqueous solutions on the solid phase of layered double hydroxides (LDHs) of Mg, Al, and Nd was studied. Sorption of ¹³⁷Cs from 10⁻⁵ M aqueous CsNO₃ solutions on the LDH-Mg-Al-Nd solid phase is extremely weak. At the same time, ⁹⁰Sr and ⁹⁰Y are efficiently sorbed on the LDH-Mg-Al-Nd solid phase from 10⁻⁵ M aqueous Sr(NO₃)₂ solutions. After 5-min contact of the solid and liquid phases, K _d of ⁹⁰Sr and ⁹⁰Y exceeds 10³ ml g⁻¹. With an increase in the Nd content in LDHs of mixed composition, their sorption properties toward ⁹⁰Sr and ⁹⁰Y are enhanced.