A simulation of radiolysis of chloride solutions containing ferrous ion

ABSTRACT

To investigate the effect of dissolved species from steels on the radiolysis processes of Cl^?, radiolysis simulations of solutions containing both Cl^? and Fe²⁺ were carried out. The results showed that the generation of radiolytic products (H₂O₂, O₂ and H₂) increased mainly by the addition of Fe²⁺, and the concentrations of H₂O₂ and O₂ increased with increasing dose rate. Moreover, radiolysis of Fe²⁺ solutions also induced noticeable pH drop due to the hydrolysis of Fe³⁺. This pH drop enhanced the reactivity of Cl^? with ^?OH, which induced additional generation of H₂O₂ and O₂. These results show that low concentrations of Cl^? (1 × 10^?3 mol/dm³ = 35 mg/kg) in the presence of Fe²⁺ could influence the generation of H₂O₂ and O₂ during water radiolysis. On the other hand, it is considered that these effects of Fe²⁺ and Cl^? on water radiolysis are less important for corrosion of steels due to the low concentrations of H₂O₂ and O₂ generated if the concentrations of these additives and dose rate are sufficiently low. The other process, such as dissolution of iron enhanced by FeOOH, might predominantly induce corrosion under the conditions of solutions with low concentrations of H₂O₂ and O₂.     

Ion Exchange Separation for Decontamination of Centrifuge Enrichment Plant

Ion exchange separation of uranyl ion (UO²⁺ ₂) from metal cations has been carried out by the columnar operation using ion exchange resins in 0.1 mol/dm³ sulfuric acid medium. Uranyl ion was adsorbed in an anion exchange resin and the rest metal cations, Fe(III), Al(III), Cr(III), Ni(II) and Cu(II) ions, were adsorbed in a cation exchange resin in this system. Desorption of uranyl ion and metal cations adsorbed in the resins were tested by 2 mol/dm³ sulfuric acid solution. Desorbed elements were confirmed to be precipitated by appropriate alkaline solutions. On the basis of the results obtained, a concept was made on a decontamination system for uranium-contaminated waste solution from centrifuge enrichment plant.     

New Proposal for a Gas Centrifuge Rotating Differentially, (II)

Dry oxidation of spent ion exchange resin is one of the most effective methods to reduce radioactive waste volume and also to make the final waste form more stable. Thermo-gravimetric measurements were performed using cation exchange resins with or without Fe in either an ionized or unionized form to clarify the effect of metallic impurities on the resin oxidation.

The presence of an ionized Fe resulted in a considerable increase in the reaction rate constant, indicating that the Fe functioned as a catalyst. On the other hand, the unionized Fe showed no catalytic activity. Measurement of EPMA revealed that the ionized Fe was distributed uniformly throughout the resin particles, while the unionized one was distributed only on the surface of the resin particle.

Catalytic activity increased with ionized Fe concentration up to 0.5 mmol-Fe/g-dry resin, above which the activity tended to decrease. The X-ray diffraction study attributed this to Fe coagulation in the resin particle. Kinetic models for solid-gas reactions were also applied to the resin oxidation to evaluate catalytic activity quantitatively.     

Comparative study and imaging by PhotoElectroChemical techniques of oxide films thermally grown on zirconium and Zircaloy-4

The oxidation of iron and chromium that are present as impurities in zirconium metal or as alloying elements in Zircaloy-4 was investigated with PhotoElectroChemical techniques (PEC), highlighting the chemical nature, the size and the lateral distribution of Fe and Cr-containing phases in thin zirconia scales formed during the oxidation of pure zirconium and Zircaloy-4 at 470 °C in oxygen. In the case of zirconium, iron and chromium impurities led to the formation of oxides distributed in a homogeneous way in the zirconia scale, while in the case of Zircaloy-4 these elements, present in the form of intermetallic particles in the substrate, led to the formation of localised haematite Fe₂O₃, rhomboedric solid solution (Fe_xCr_1−x)₂O₃ and chromia Cr₂O₃ phases. These phases were accurately studied via the measurement of their respective band-gap (Fe₂O₃: 2.2 eV, (Fe_xCr_1−x)₂O₃: 2.6 eV and Cr₂O₃: 3.0 eV). It is concluded that PEC techniques represent a sensitive and powerful way to locally analyse the various semiconductor phases in the oxide scale at a micron scale.     

Reactivity of hydrogen peroxide towards Fe3O4, Fe2CoO4 and Fe2NiO4

The kinetics of CRUD oxidation by H₂O₂ has been studied using aqueous suspensions of metal oxide powder. Fe₃O₄, Fe₂CoO₄ and Fe₂NiO₄ were used as model compounds for CRUD. In addition, the activation energies for the reaction between H₂O₂ and the three CRUD models were determined. The rate constants at room temperature were determined to 6.6 (±0.4) × 10⁻⁹, 3.4 (±0.4) × 10⁻⁸ and 1.6 × 10⁻¹⁰ m min⁻¹ for Fe₃O₄, Fe₂CoO₄ and Fe₂NiO₄, respectively. The corresponding activation energies are 52 ± 4, 44 ± 5 and 57 ± 7 kJ mol⁻¹, respectively. The mechanism of the reaction is briefly discussed indicating that the final solid product in all three cases is Fe₂O₃. In addition to the experimental studies, the theoretical grounds for kinetics of reactions in particle suspensions are discussed. The theoretical discussion is also used to explain the somewhat unexpected trends in reactivity observed experimentally.     

Adsorption Behavior of Americium on Zeolites

Zeolites are expected to be used in buffer materials as an admixture to bentonite to increase their ion exchange ability. The behavior of ion exchange adsorption of Am³⁺ on various zeolites was examined by batch and column methods. The distribution coefficient of Am³⁺, K_d, increased with equilibrium pH from 1.5 to 4.0. L zeolite and mordenite having large pore size yielded relatively large values of K _d over 10³ at pH 3.0. The K _d for L zeolite was unaffected by the concentration of coexisting cations, i.e. Na⁺ up to 0.1 M, and K⁺, Ca²⁺ and Mg²⁺ less than 0.01 M. The Am³⁺ ion was not detected in the effluent passed through the L zeolite column up to 90 bed volumes, even when the feed solution contained a relatively large amount of Na⁺-0.5 M. Americium ion adsorbed on zeolites could be quantitatively eluted with 0.1 M nitric acid.     

Role of oxidation-reduction processes in the solution of uranium oxides in acid media

The degree of oxidation of the components of the ore material is of decisive importance in the extraction of uranium. Since the solution of uranium is composed of various chemical processes and complicated by the presence of impurities in the ores, it is necessary to study the rules of uranium oxidation and the effect of various compounds which dissolve during the leaching of uranium ores.In the present work we present the results of an investigation of the oxidation and solution of uranouranic oxide in acid media and the effect of ferrous compounds on it. A comparison of the oxidizing power of various oxidants with respect to uranium is given for the first time. It was shown that the oxidation of tetravelent uranium is not determined unequivocally by the normal oxidation-reduction potential. The results obtained show that the reasons for incomplete extraction of uranium by a mixture of nitric and sulfuric acids at low concentrations when considerable amounts of iron ions are present in the solutions are associated with the formation of complexes between Fe²⁺, SO ₄ ^2– , and NO ₃ ^– ions.     

Gas Chromatographic Measurements of Hydrogen Isotopes Mixture by Using Catalytic Oxidation Type Detector

A new type of gas chromatograph for quantitative measurements of hydrogen isotopes mixture has been developed through the adoption of catalytic oxidation type detector. Experiments using He as the carrier gas were successfully performed for the separation of D₂-HD and H₂-HD-D₂ mixtures. The minimum detection limits were 0.4–0.9 μl-STP for these components. The linear calibration curves were obtained in the range of 10 μl-STP–20 ml-STP. The sensitivities for H₂, HD and D₂ were 843, 774 and 654 (μl-STP)^?1, respectively. The maximum time needed for the analysis was about 16 min.     

Conversion Reactions of Metal Chlorides into Oxides with Boric Acid Applicability to the Vitrification of Molten Salt Wastes Generated in Pyro-reprocessing Process

Conversion reactions of metal chlorides into oxides with boric acid (H₃BO₃) were studied to develop the method for vitrification of radioactive molten salt wastes generated in the pyro- reprocessing process. Mixtures of metal chlorides and H₃BO₃ with appropriate compositions in Pt crucible were heated at 1,000°C for 1h in an electric furnace, followed by rapid cooling to room temperature. The chloride compounds used were LiCl, NaCl, KCl, CsC1, SrCl₂, BaCl₂·2H₂O, and CeC1₃·6H₂O. All chlorides other than CsCl were found to be transformed into oxides (borate glass) in the molar ratios of H₃BO₃/chlorides≧2. Furthermore, four-component systems, i.e., the mixtures of LiCl, KCl, NaCl (or SrCl₂, BaCl₂·2H₂O, CeCl₃·6H₂O), and H₃BO₃ were also examined in a similar manner. The borate glasses were found to be formed in the molar ratio of H₃BO₃/chlorides≧2.     

Effect of Grain Size of AgNO3 Loaded in Porous Material on Adsorption of CH3I

In the development of a new chemical decontamination method which provides a high decontamination effect, less corrosion of base metal, and less radioactive waste generation, we developed a decomposition method for oxalic acid coexisting with hydrazine to decrease the amount of radioactive waste.

Using a catalyst of 0.5 wt% Ru supported by activated carbon grains, we decomposed oxalic acid and hydrazine, simultaneously and efficiently, with a stoichiometric concentration of H₂O₂2. The decomposition ratios were decreased by the deposition of oxides. But even if the simulated reducing agent solution with high concentrations of coexisting Fe and K ions, which negatively effect decomposition ratio, was decomposed, the decomposition ratios of oxalic acid and hydrazine were kept high during decomposition of the amount of reducing agent used in actual chemical decontamination.

Additionally, we examined the deposition ratios of metal ions on the catalyst as metal oxides. These results indicated about 2% of the radioactive species which were removed by the chemical decontamination were deposited on the catalyst column. ⁵⁹Fe and ⁵¹Cr were estimated to be about 90% of the total deposited amount of radioactive species and about 60% of the dose equivalent in the model calculation. But this problem should be easily dealt with by using shielding.     

Detritiation of Glovebox Atmosphere by Using Compact Tritium Removal Equipment

A compact tritium removal equipment (TRE), assembled in a console with casters, has been developed for detritiation of air in a glovebox used for handling of several curies of tritium. The TRE was designed to remove gaseous tritium in the form of T₂, HT and CH₃T through oxidation with precious metal/alumina catalysts followed by adsorption on zeolite pellets.

From the detritiation experiments with hydrogen tritide (HT, 2–20 mCi), the TRE was confirmed to have sufficient performance for the practical use. The tritium concentration in the test gas (total volume –32l; 1%H₂, 5%O₂, 94%N₂) decreased from 0.64 to 6.4 ×10-⁷ Ci.m³ within 155 min when the TRE was operated under the recirculation mode with the flow rate of 200 l-h¹ at the catalyst temperature of 200°C. In addition, the HT-to-HTO fractional conversion was determined at various catalyst temperatures (25–200°C) and flow rates (100–360 lh-¹).     

In-situ Measurement of UO2 2+ Concentration in Molten NaCl-2CsCl by Differential Pulse Voltammetry

In order to assess the applicability of the Differential Pulse Voltammetry technique to the in-situ measurement of UO₂ ²⁺ concentration in the oxide electro-winning process, DPV measurements for UO₂Cl₂ in molten NaCl-2CsCl were studied. DPV measurement of UO₂ ²⁺ in NaCl-2CsCl at 923 K, with a set of optimized parameters (potential sweep rate ?0.1 V/s, pulse cycle 0.1 s, pulse width 10 ms and pulse potential height 50 mV), showed a clear current peak at ?0.9 V vs. Cl₂/Cl^?. This was attributed to the reduction of UO₂ ²⁺ to UO₂ ⁺. The relation between the current peak height and the analytical concentration of the UO₂ ²⁺ showed good proportionality in the concentration region up to 0.06 mol.l ^?1, and the applicability of UO₂ ²⁺ concentration measurement by DPV was confirmed up to 0.4 mol.l ^?1. In order to assess the interference by the coexisting fission product elements to the measurement of UO₂ ²⁺ concentration, DPV measurements of UO₂ ²⁺ concentration in molten NaCl-2CsCl containing PdCl₂, NdCl₃, SmCl₃ and CeCl₃ were also performed. Even before removing Pd, the current peak at ?0.9 V vs. Cl₂/Cl^? by the reduction of UO₂ ²⁺ to UO₂ ⁺ was found to be distinguishable from the reduction currents of Pd²⁺ to Pd at ?0.7 V vs. Cl₂/Cl^?. As a result, the application of DPV measurement technique to the in-situ monitoring of UO₂ ²⁺ concentration in the oxide electro-winning method requires the improvement of the DPV measuring condition or the electrode structure on higher UO₂ ²⁺ concentration condition.     

Reduction of UO2 by H2

The reactivity of H₂ towards UO₂²⁺ has been studied experimentally using a PEEK coated autoclave where the UO₂²⁺ concentration in aqueous solution containing 2 mM carbonate was measured as a function of time at p_H2∼40 bar. The experiments were performed in the temperature interval 74-100 °C. In addition, the suggested catalytic activity of UO₂ on the reduction of UO₂²⁺ by H₂ was investigated. The results clearly show that H₂ is capable of reducing UO₂²⁺ to UO₂ without the presence of a catalyst. The reaction is of first order with respect to UO₂²⁺. The activation energy for the process is 130 ± 24 kJ mol⁻¹ and the rate constant is k_298K=3.6×10⁻⁹ l mol⁻¹ s⁻¹. The activation enthalpy and entropy for the process was determined to 126 kJ mol⁻¹ and 16.5 J mol⁻¹ K⁻¹, respectively. Traces of oxygen were shown to inhibit the reduction process. Hence, the suggested catalytic activity of freshly precipitated UO₂ on the reduction of UO₂²⁺ by H₂ could not be confirmed.     

Simultaneous Adsorption of Cs-137 and I-131 from Water and Milk on “Metal Ferrocyanide-Anion Exchange Resin”

“Metal ferrocyanide-anion exchange resin”, which is made by precipitating the metal ferrocyanide in an anion exchange resin matrix, has been used for selective adsorption of Cs ion in a variety of aqueous solutions.

The “resin” has both properties of metal ferrocyanide and anion exchange resin. Therefore, we tried simultaneous adsorption of radiocesium and radioiodine from water and milk on the “resin”.

Results showed that “metal ferrocyanide-anion exchange resin” such as Cu, Fe and Ni ferrocyanide can be used for a rapid and simple concentration of radiocesium and radioiodine quantitatively from a large volume of sample solutions.

This paper also touches upon the removal of ¹³⁷Cs and ¹³¹I in rain water and milk collected in Japan after the Chernobyl accident.     

Fracture Surface Energy of UO2 and ThO2 Containing Additives

The Hertzian indentation technique is used to study the cracking behavior and to measure the fracture surface energy of UO₂ and ThO₂of high density containing simulated fission products (Nb, Zr). UO₂ + ZrO₂ of 98% density showed permanent “plastic” deformation in addition to Hertzian cone crack formation thus making a quantitative analysis impossible. The Nb₂O₅ containing oxides, in particular ThO₂ + Nb₂O₅, had a more suitable microstructure and showed less or no permanent deformation. The fracture surface energy of ThO₂ + 0.1 ^mYo Nb₂O₅ was γ= (2.6±0.4) Jm-², and thus comparable to that of ThO₂ without additives, (2.5±0.3)Jm-², indicating that the effect of Nb impurities and of excess oxygen introduced together with the Nb⁵⁺ cancel each other.     

Physicochemical study of radiation-grafted LDPE copolymer and its use in metal ions adsorption

Graft copolymerization of (acrylonitrile-co-N-vinylpyrrolidone) AN/NVP binary monomer onto (low density polyethylene) LDPE film was achieved using simultaneous irradiation method. The influence of grafting conditions such as solvent type, comonomer composition and comonomer concentration on the grafting process were investigated. The prepared grafted films were chemically modified into amidoximated form using hydroxyl amine hydrochloride (NH₂OH · HCl). The untreated and amidoximated grafted films were characterized by studying their FT-IR spectroscopy, swelling behavior and mechanical properties. The ability of the amidoximated grafted films to adsorbed metal ions such as Cr³⁺, Ni²⁺, Cd²⁺, Ag⁺ and Pb²⁺ was evaluated. The parameters that might influence the metal ions adsorption capacity of treated grafted LDPE films such as comonomer compositions, the degree of grafting, the feeding metal ions solution concentration and the pH were discussed. The obtained results illustrate that the amidoximated grafted films could be fruitful in the practical field of water treatment.     

Development of Flexible Neutron-Shielding Resin as an Additional Shielding Material

A soft-type neutron-shielding resin has been developed by improving an existing hard-type neutronshielding material using the epoxy-based resin as an additional shielding material. A flexible heat-resistant neutron-shielding material has been developed, which consists of a new polymer-based resin with boron. The neutron shielding performance of the developed flexible heat-resistant resin with the ²⁵²Cf neutron source is almost the same as that of polyethylene. The outgases of H, H₂, NH₄, H₂O, CO, O₂, C₄H₁₀, and CO₂ from the developed resin have been measured at high temperature (up to 250°C) by thermal desorption spectroscopy methods. The soft-type resin and the newly developed heat-resistant resin will be applied to prevent the effects of neutron streaming and to control the movement of a vibrated pipe as the seal material around the plumbing in the future fast reactor and innovative fission reactor.     

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (V)

The difference in electrochemical corrosion potential of stainless steel exposed to high temperature pure water containing hydrogen peroxide (H₂O₂) and oxygen (O₂)is caused by differences in chemical form of oxide films. In order to identify differences in oxide film structures on stainless steel after exposure to H₂O₂ and O₂ environments, characteristics of the oxide films have been examined by multilateral surface analyses, e.g., X-ray diffraction (XRD), Rutherford back scattering spectroscopy (RBS), secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). Preliminary characterization results of oxide films confirmed that the oxide film formed under the H2O2 environment consists mainly of hematite (α-Fe₂O₂), while that under the O₂ environment consists of magnetite (Fe₃O₄). Furthermore oxidation at the very surface of the film is much more enhanced under the H₂O₂ environment than that under the O₂ environment. It was speculated that metal hydroxide plays an important role in oxidation of stainless steel in the presence of H₂O₂. The difference in electric resistance of oxide film causes the difference in anodic polarization properties. It is recommended that several anodic polarization curves for specimens with differently oxidized films should be prepared to calculate ECP based on the Evans diagram.     

Removal of Radioactive Ions from Nuclear Waste Solutions by Electrodialysis

Removal of radioactive ions was studied from low and medium level radioactive waste solutions by electrodialysis using ion exchange membranes. The test solutions contained ¹³⁷Cs⁺, ⁹⁰Sr²⁺, ¹⁰⁶Ru³⁺ or fission products (F.P.) as active ions and NaCl, Na₂SO₄ or Ca(NO₃)₂ as inactive coexisting salts. The decontamination factor of the active ions was in the order: ¹³⁷Cs⁺ (greater than 99%) ⁹⁰Sr²⁺F.P. ¹⁰⁶Ru³⁺. The dialysis time required to attain the saturation was the shortest for monovalent cations K⁺, Cs⁺ and Na⁺, intermediate for divalent cation Sr²⁺, and the longest for trivalent cation Ru³⁺. The ratio of the decontamination factor of an active ion ηA to the desalination factor of an inactive ion A₊ was nearly equal to unity for ²⁴Na, ⁴²K, ¹³⁷Cs and ^S),Sr. On the other hand, the apparent selective permeability of an active ion (A⁺) against Na⁺ ion, T_A+ was higher than unity for all the active ions tested, and was in the order of ¹³⁷>Cs⁹⁰Sr>⁴²>K²⁴Na, where T^A _Na+ is defined by the ratio of γA to γ_Na+ with γA being the ratio of dilution of A in the diluate and γ_Na+ being that of Na⁺ in the same diluate. The decontamination factor of the active ions did not depend significantly on the species and concentrations of the coexistent salts or on the concentration of the active ions.     

Hydrous Titanium Oxide Ion Exchanger, (I)

Abstract

Synthesis of hydrous titanium oxide ion exchanger was tried from three systems: (a) TiCl₄-NaOH-H₂O, (b) ATS (ammonium titanyl sulphate monohydrate)-NaOH-H₂O and (c) TiCl₄-NH₄OH-H₂O. The first method gave the best results under the conditions covered in the present work.

It was found that repeated washing and aging of the hydrous titanium oxide precipitate were indispensable in order to obtain reproducible results, and that this operation further obviated the need of precisely adjusting the conditions for mixing the reagents.

Both the yield of exchanger and the ion exchange capacity of the resulting product increase with concentration of the reagents. A cation exchange capacity of about 3 meq·Na⁺/g could be obtained, which is considerably higher than any corresponding value reported in literature. The value decreased with increasing drying temperature. Irrespectively of the conditions of synthesis, the chemical composition was TiO₂·(2.0–2.2) H₂O, and the impurities contained in the product were found to be less than 0.1%. The exchanger produced is in granular form suitable for use in column operation. It is fairly stable in alkaline solution, and also in mineral acid solutions of <0.1 n concentration.