Uranium Isotope Exchange between Gaseous UF6 and Solid UF5

A new rate equation is derived for uranium isotope exchange reaction between gaseous UF₆ and solid UF₅ by assuming the total number of UF₅ molecules on the particle surfaces to depend on time. The reaction parameters included in the equation are determined from the experimental results, and are compared with the previous ones. The rate equation given in this work satisfies the related isotopic mass balance, and includes explicitly the terms related to the UF₆ density and the mean size of UF₅ particles, both of which cause an important effect on the reaction. Since the rate equation derived in this work facilitates the simulation of the reaction under various conditions, the long term behavior of a simulated exchange reaction is studied under the condition considered to be close to that in a recovery zone of the MLIS process.     

Anomalous Isotope Fractionation in Uranium Enrichment Process

A benchmark calculation for a deep penetration problem of 14 MeV neutrons through a 3m thick iron slab was carried out by using a vectorized continuous energy Monte Carlo code MVP with the JENDL-3 and ENDF/B-IV cross sections. Reference solutions for neutron spectra and averaged cross sections were obtained at various locations through the iron slab with good statistics owing to a high computation speed of the code. The accuracy of multigroup calculations with the JSSTDL/J3 library was investigated by comparison with the obtained reference solutions.

Both calculations with JENDL-3 and ENDF/B-IV showed a similar attenuation of total fluxes from thermal to 14 MeV through the slab, while differences of one order at the maximum were observed in the calculated fluxes in the resonance energy region. The multigroup calculations with the JSSTDL/J3 295- and 125-group libraries underestimate the streaming effect through the cross section minima above the well-known 24 keV window, which resulted in the underestimation of fluxes above this window by more than two decades at 3 m penetration compared with the continuous energy method. Taking into account the spatial dependence of averaged cross sections, the underestimation was reduced to about one decade. It was found, however, that an accurate prediction of streaming effect is fairly difficult by the multigroup method.     

加速器质谱法测量含铀微粒中铀同位素比的方法研究

准确测定含铀微粒同位素比在核保障中有重要的应用价值。本文采用将含铀微粒溶解并加入高纯Fe粉烘干的方法制样,采用中国原子能科学研究院的HI-13串列加速器质谱测量靶样中的同位素比。通过对CRM铀系列同位素标准样品的分析表明,该方法可测定高于10^-5的²³⁶U/²³⁸U同位素比;对于²³⁵U/²³⁸U同位素比在10^-4～10^-1范围内的含铀微粒,²³⁵U/²³⁸U同位素比相对扩展不确定度均小于10%。     

Uranium Isotope Separation by Cation Exchange Chromatography Using Uranous Sulfate Complexes

A nearly ideal displacement chromatography has been realized with an eluent of MgS0₄ and H₂SO₄ in the study of uranium isotope separation by means of cation exchange chromatography using uranous sulfate complexes. Uranium-235 was enriched at the end of the chromatogram and ²³⁸U was enriched at the front. Two long distance displacement experiments have been carried out, keeping an isotopic plateau region on the chromatogram. Consequently, good accumulation of the isotopic fractionation based on uranous-sulfate complex formation reactions obtained. The separation coefficient ε of this system was estimated to be about 5×10^?5.     

Separation of Uranium Isotope by Plasma Centrifuge

A method of centrifugal separation of isotopes by electromagnetic means is presented. The principle proposed utilizes electromagnetic acceleration by the interaction between an electric current in a slightly ionized gas and an external magnetic field. The analysis shows that an azimuthal flow of 2.6 km/sec can be realized with a magnetic field of 200 gauss and an electric current of 1.5kA. The resulting centrifugal force is large enough to permit realization of a more compact concentration cascade than the conventional mechanical centrifuge.     

An Apparatus for Isotopic Ratio Measurement in UF5 Formed by Infrared Multiphoton Dissociation of UF6 in Molecular Beam

A Separation factor was measured in isotopically selective infrared multiphoton dissociation (IRMPD) of supercooled UF₆ in a supersonic expansion by multiphoton ionization (MPI) and time-of-flight mass spectrometry (TOFMS). A pulsed free-jet nozzle was used to generate a UF₆-molecular beam seeded in Ar (–10^?7 Torr in UF₆ partial pressure). Two-frequency ρ-H₂ Raman laser beams around 16μm were used for the dissociation of UF₆ under collisionless conditions in the molecular beam where the flow velocity for UF₆ is about 500m/s. The ²³⁵U/²³⁸U isotopic ratios in nascent UF₅ photoproducts were determined by selective MPI of UF₅ at 532 nm followed by TOFMS with a mass resolution as high as 1200. A separation factor of about 2 was observed under the experimental conditions chosen for the demonstration of this method.     

Fluorination of Uranium Dioxide by Bromine-Fluorine System

The addition of bromine to fluorine flow makes it possible to fluorinate UO₂ into UF₆even below 200°C, at which temperature fluorination does not proceed with fluorine alone. Presence of bromine corresponding to about 6% of the fluorine concentration is sufficient to induce the fluorination. This effect of bromine is much greater than would be expected from the presence of bromine fluorides in concentrations such as would be produced by direct combination of the fluorine with the added bromine. It appears that the fluorination is enhanced when the mixed gas is held for 3~20 sec before arriving at the sample. The main component of the reactant gas is BrF₃.     

Reduced Partition Function Ratio of Uranyl Ion and Uranium Isotope Effect

Density of 30v/o tri-n-butyl phosphate-n-dodecane solution loaded with uranyl nitrate, nitric acid and water was measured. An empirical density equation was derived from regression analysis of the density data. The equation represents the density values well in a wide range of composition and temperature.     

Reaction between Uranium Mononitride and Graphite Powders

The carbothermic reaction of UN with graphite in the form of loose powder mixture has been studied in vacuo with the aid of a high-temperature thermobalance in the temperature range of 1,270~1,675°C. The gravimetric measurements were conducted continuously to determine the effect of varying reaction temperature and differences in sample particle size.

The kinetics of the reaction was found to follow the diffusion—controlled kinetic equation for mixed powder, and activation energies of 76.1, 55.1 and 72.7kcal/mol were obtained for samples of (1)—400 mesh UN and—400 mesh natural graphite mixture, (2)—150 +270 mesh UN and—150 +270 mesh natural graphite mixture, and (3)—150 +270 mesh UN and—150 +270 mesh artificial graphite mixture, respectively. X-ray diffraction studies revealed the reaction products of the coarse sample to be composed of two different kinds of UC_xN_1-x solid solutions, one having a x value of 0~0.2, and the other 0.8~0.9. From the above observations, the diffusion of C and/or N atoms through the outer carbon rich UC_xN_1-x layer may be considered to be the rate determining step.     

Hydrogen Isotope Separation by Plasma-Chemical Method

Deuterium transfer (exchange) reaction as shown in HDO+H₂=H₂O+HD was studied as a case similar to the tritium transfer reaction as shown in DTO+D₂=D₂O+DT, the first step in tritium isotope separation of the tritiated heavy water DTO. The transfer reaction was plasma-chemically catalyzed by allowing a gas mixture such as H₂O/D₂, D₂O/H₂, H₂O/HDO/H₂ or H₂O/D₂O/HDO/H₂ to flow through an atmospheric pressure discharge zone formed in a reaction chamber, the inner temperature of which was maintained just above 100°C. The plasma-chemical reactions diagnosed by infrared and emission spectroscopy revealed that the mixture underwent instantaneous deuterium transfer reactions as it passed the zone. The effectiveness of the method was demonstrated by high deuterium transfer rate, high separation factor of the transfer and a possibility of miniaturizing the separation facility.     

Photochemical Reactions of Uranium(VI) in Aqueous Phosphoric Acid Solutions

Photochemical reactions of U(VI) ion with halogen and pseudohalogen anions. I^?, Br^?, Cl^? and NCS^?, were studied in aqueous phosphoric acid solutions under irradiation of nitrogen laser. The formation of U(IV) was observed in the reactions with I^?, Br^? and NCS^?, but not with CI^?. The yield of U(IV) increased in the order Br^?<NCS^?<I^?. This order was the same as the quenching rate constants of the excited U (VI) ion with these anions, but the reverse of their standard redox potentials. These facts are consistent with the electron transfer mechanism between excited U (VI) and these anions. The rates of the formation of U (IV) in the presence of Br^? were measured by the spectrophotometric method. It was found that the rate equation was first order in both U (VI) and Br^?. The results were reasonably interpreted by a series of reaction processes involving U(V) and Br radical. The photo-oxidation of tris(1, 10-phenanthroline)-Fe (II) ion by U (VI) was also studied in the same procedures. Based on the rate law, we proposed a one-electron transfer mechanism involving U(V) as an intermediate.     

Flow in Low Pressure Impactor and Collection Efficiency of Particles

An effect of specimen size on the Charpy impact property was evaluated in the ferritic-martensitic 11Cr-0.5Mo-2W, Nb, V stainless steel (PNC-FMS). The upper shelf energy (USE) is expressed by the power law equation as USE[J]=m(Bb) ⁿ where m is the material constant (m=0.277 in PNC-FMS), B[mm] is the specimen thickness and b[mm] is the ligament size. The normalizing exponent n was empirically derived using the USE of the full size specimen as n=1.38×10^–3USE_full+1.20. The n value varies in the range of 1.2 to 1.7, which is affected by the fracture volume below the notch. The PNC-FMS wrapper takes n=1.42. The ductile-to-brittle transition temperature (DBTT) of PNC-FMS is correlated as DBTT=115(log₁₀ BKt)—158 using an elastic stress concentration factor Kt that represents the effects of notch size, e.g. notch depth, notch root radius and notch angle.     

Intensity and Pressure Effects in CO2 Laser Isotope Separation of Tritium Photolysis of CF3CTCIF with 2-ns Pulses

Albedo-Sn method was developed to predict the angular flux near the coupling boundary in the bootstrap method, using the energy-and-angle dependent double differential albedo boundary condition. In order to verify the applicability of the method to the reactor shielding design, two types of shielding problem have been analyzed. First, the neutron skyshine dose rates measured at the YAYOI reactor in University of Tokyo are predicted within an accuracy of 20%. It is also found that the neutron spectrum in the air-over-ground is much affected by albedo reflection from the ground and is reproduced well by the albedo-Sn method. Second, as for the neutron streaming through a sodium pipe chase-way, the albedo-Sn calculation saves a computer time and gives the results which agree with those by the reference Sn calculation.     

Gaseous Exchange Reaction of Deuterium between Hydrogen and Water on Hydrophobic Catalyst Supporting Platinum

The deuterium exchange reaction between hydrogen and water in the gas phase where the fed hydrogen gas is saturated with water vapor is studied experimentally by use of the proper hydrophobic catalysts supporting platinum. It is found that the activities of those catalysts for this reaction system are very high compared with the other known ones for the systems in which gas and liquid should coexist on catalyst surfaces, and that the apparent catalytic activity becomes larger as the amount of platimun supported on a catalyst particle increases. By analyses of the data the following informations are obtained. The exchange reaction can be expressed by a first order reversible reaction kinetics. The pore diffusion in the catalyst particles has significant effect on the overall reaction mechanisms.