Surface modification of SUS304 stainless steel by atmospheric pressure Ar/N2/O2 plasma

The surface characteristics of SUS304 stainless steel are investigated before and after surface modification by Ar/N₂/O₂ plasma under atmospheric pressure conditions. It was found that plasma treatment of a stainless steel plate has a significant effect on the wettability, contact angle, and free energy of the SUS304 surface. The contact angle and surface free energy were analyzed. The optimal surface modification parameters are a power of 1000 W, a torch-to-sample distance of 80 mm, a treatment time of 300 s, and an oxygen content of 1.5 wt%. Under these processing conditions, a contact angle of just 1.60° was obtained. The surface morphology, surface element composition, and surface roughness of the treated SUS304 specimens were examined using scanning electron microscopy (SEM), and atomic force microscopy (AFM), respectively. The results show that the optimal surface modification conditions lead to the formation of fine, uniformly distributed crystallites in the SUS304 microstructure. Moreover, compared to the untreated surface, the treated surface had a significantly lower carbon content and a more uniform distribution of surface peaks.     

Thermophysical properties of NpO2, AmO2 and CmO2

The information on thermal and mechanical properties of the minor actinide dioxides: NpO₂, AmO₂ and CmO₂, is still very scarce, and a large uncertainty exists because of difficulties related to their fabrication and manipulation. Prognosis based on a set of the sound physical models and the similarity principle can be useful in this situation. Using the combination of the macroscopic and microscopic approaches developed earlier for thermodynamic properties of actinide dioxides, and the Klemmens model for their thermal conductivity, a few relationships bounding the main thermophysical properties of the actinide dioxides were deduced. These relationships were applied for the calculation of the isochoric and isobaric heat capacity, the isobaric thermal expansion coefficient, the isothermal bulk elastic modulus and the thermal conductivity of NpO₂, AmO₂ and CmO₂ in a large temperature range. A rather satisfactory agreement with the available experimental data and recommendations was demonstrated.     

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.     

Formation of U2C3 in the reaction of UC2 with UO2

The formation of U₂C₃ by the reaction of UC₂ with UO₂ has been studied by chemical and X-ray analyses at temperatures between 1400 and 1700 °C in vacuo. The reaction is represented by 7 UC₂ + UO₂ → 4 U₂C₃ + 2 CO.     

Radiotoxicity hazard of U-free PuO2+ZrO2 and PuO2+ThO2 spent fuels in LWR

The radiotoxicity hazard of U-free Rock-like oxide: ROX (PuO₂+ZrO₂) and Thorium oxide: TOX (PuO₂+ThO₂) LWR spent fuels is investigated and radiotoxicity hazard of MOX spent fuel is considered as a reference case. The long-term ingestion radiotoxicity hazard of ROX spent fuel is one third and nearly one fourth of that of TOX and MOX spent fuels, respectively. This is because the discharged Pu and long lived Np in ROX fuel is less than that of TOX and MOX fuels. In TOX fuel, discharged Pu and MA are lower than that of MOX fuel but the long-term radiotoxicity hazard of spent fuel is nearly the same as MOX spent fuel. At the cooling 10⁵ years, the radiotoxicity hazard of TOX spent fuel is approximately ten and three times higher than that of ROX and MOX spent fuels, respectively due to higher toxic contribution of ²²⁹Th in TOX spent fuel.     

Optical properties of UO2 and PuO2

We perform first-principles calculations of electronic structure and optical properties for UO₂ and PuO₂ based on the density functional theory using the generalized gradient approximation (GGA) + U scheme. The main features in orbital-resolved partial density of states for occupied f and p orbitals, unoccupied d orbitals, and related gaps are well reproduced compared to experimental observations. Based on the satisfactory ground-state electronic structure calculations, the dynamical dielectric function and related optical spectra, i.e., the reflectivity, adsorption coefficient, energy-loss, and refractive index spectrum, are obtained. These results are consistent with the available experiments.     

HfO2 and Ta2O5 as grain growth inhibitors in Eu2O3

Because of the high neutron capture cross section for five consecutive europium isotopes, Eu₂O₃ is of interest as a control material for nuclear reactors. A tendency toward excessive grain growth degrades its mechanical properties. Small amounts of HfO₂ and Ta₂O₅ were added to the Eu₂O₃ in attempts to suppress this grain growth. Three at % substitution of Hf for     

High-temperature specific heat of UO2 ThO2, and A12O3

The high-temperature specific heat of solid UO₂, ThO₂, and Al₂O₃ can be represented by an equation of the form $\text{C}{}_{\mathrm{p(s)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) + dT}{}^3$, (1) where ?_D is the Debye temperature, F(?_D/T) is the Debye function, $\text{d}$ represents contributions of the anharmonic vibrations within the lattice, and $\text{n}$ denotes the number of atoms per molecule. In the liquid the corresponding equation is $\text{C}{}_{\mathrm{p(1)}}\text{= 3}{}_{\mathrm{n}}\text{RF(?}{}_{\mathrm{D}}\text{/T) +}\text{h}\text{T}{}^2$, (2) where h is the anharmonic term. It is shown that for Al₂O₃ and UO₂, where experimental data for the liquid phase are also available, $\text{d}\text{h}$ has the same value, Indicating that both materials behave identically. If we compare the thermodynamic relationship $\text{C}{}_{\mathrm{p}}\text{? C}{}_{\mathrm{v}}\text{= Vα}{}^2\text{KT}$, (3) where V is the volume, $\text{α}$ the volume expansion coefficient, and $\text{K}$ the bulk modulus, with equation (1), It follows that d must be equal to $\text{Vα}{}^2\text{K}\text{T}{}^2$; the value of $\text{Vα}{}^2\text{K}\text{T}{}^2$ is calculated in the temperature region where d was obtained; within experimental error they are equal.     

Kinetics of initial stage of sintering of UO2 and UO2 with Nd2O3 addition

The kinetics of initial stage sintering of UO₂ powder were reinvestigated, using Ar-10% H₂ atmosphere. The effect of the addition of neodynium oxide was studied. The results revealed that surface and grain boundary diffusion mechanisms act simultaneously. The values of activation energies were found to be $\text{48.48 ± 3.51 kcal/mole}$ in the temperature range 870–942°C and $\text{89.88 ± 9.87 kcal/mole}$ in the temperature range of 942–1030°C for UO₂, and $\text{115.61 ± 7.77 kcal/mole}$ in the temperature range 1030–1150°C for UO₂ + Nd₂O₃. An important decrease in the calculated diffusion coefficient occurs by the addition of Nd₂O₃.     

Molecular dynamics simulations of C2, C2H, C2H2, C2H3, C2H4, C2H5, and C2H6 bombardment of diamond (1 1 1) surfaces

The sticking and erosion of C₂H_x molecules (where x=0-6), at 300 and 2100 K onto hydrogenated diamond (1 1 1) surfaces was investigated by means of molecular dynamics simulations. We employed both quantum-mechanical and empirical force models. Generally, the sticking probability is observed to somewhat increase when the radical temperature increases and strongly decrease with increasing number of H atoms in the molecule.     

One-Dimensional Fluid Model of Pulse Modulated Radio-Frequency SiH4 /N2 /O2 Discharge

Driven by pulse modulated radio-frequency source,the behavior of SiH 4 /N 2 /O 2 plasma in capacitively coupled discharge are studied by using a one-dimensional fluid model.Totally,48 different species(electrons,ions,neutrals,radicals and excited species) are involved in this simulation.Time evolution of the particle densities and electron temperature with different duty cycles are obtained,as well as the electronegativity n SiH3 /n e of the main negative ion(SiH3).The results show that,by reducing the duty cycle,higher electron temperature and particle density can be achieved for the same average dissipated power,and the ion energy can also be effectively reduced,which will offer evident improvement in plasma deposition processes compared with the case of continuous wave discharge.     

NHO3氧化去除Np—Pu反萃液中的H2C2O4

研究了用ＮＨＯ３氧化去除ＴＲＰＯ流程反萃Ｎｐ－Ｐｕ的Ｈ２Ｃ２Ｏ４反萃液中Ｈ２Ｃ２Ｏ４的条件。７．５ｍｏｌ．Ｌ＾－１ＨＮＯ３－０．３ｍｏｌ．Ｌ＾－１Ｈ２Ｃ２Ｏ４混合液于９０℃下蒸发１３０ｈ和１００℃下蒸馏回流６ｈ，Ｈ２Ｃ２Ｏ４可完全分解去除；混合液中添加适量催化剂ＭｎＣＯ３，于１００℃下蒸发或蒸馏回流，Ｈ２Ｃ２Ｏ４分解加速，１－１．５ｈ内Ｈ２Ｃ２Ｏ４完全分解。蒸发或蒸馏回流过程中产生的ＨＮＯ２把Ｎｐ     

Role of CaCl2 in the reduction of PuO2

The phase diagram of CaO-CaCl₂ has been determined. Eutectics at CaO (5 mol%) — CaCl₂ (mp 1020K) and CaO (21 mol%) — CaCl₂ (mp 1102K) were found. The congruently melting compound, CaO.4CaCl₂, was supported by X-ray diffraction evidence. The maximum solubility of calcium oxide in calcium chloride at temperatures relevant to the reduction of PuO₂ is about 21 mol% CaO.The ternary liquidus diagram of the CaO-CaCl₂-KCl system has been determined and it was found only a relatively small area of the system is completely molten below 1080K. A maximum solubility of 10 mol% CaO was found in KCl-CaCl₂ at process temperatures. This is in disagreement with published data.     

Effect of Ag and Li ion irradiation on superconducting Tl2Ca2Ba2Cu3O10 single crystals

The effect of irradiation by 50 MeV Li³⁺ and 200 MeV Ag¹⁵⁺ ions on single crystals of Tl₂Ca₂Ba₂Cu₃O₁₀ (Tl2223) superconductor has been investigated at different fluences. Isothermal magnetization hysteresis loops have been recorded at different temperatures using a SQUID magnetometer and the effect of irradiation on the critical current density, irreversible field, second magnetization peak and pinning force has been studied. Irradiation by 200 MeV Ag¹⁵⁺ ions resulted in increased hysteresis and irreversibility field while no change in second magnetization peak position and critical temperature was observed. A broadening in the hysteresis loop before the second magnetization peak was also observed for the crystals irradiated by Li³⁺ ions. Annealing of irradiated crystals at 500 °C resulted in reduction of point defects created by Li³⁺ ions.     

The creep of UO2 fuel doped with Nb2O5

The creep of UO₂ containing small additions of Nb₂O₅ has been investigated in the stress range 0.5–90 MN/m² at temperatures between 1422 and 1573 K. The functional dependence of the creep rate of five dopant concentrations up to 0.8 mol% Nb₂O₅ has been examined and it was established that in all the materials the secondary creep rate could be represented by the equation /.εkT = Aσⁿexp(?Q/RT), where /.ε is the steady state creep rate per hour, Q the activation energy and A and n are constants for each material. It was observed that Nb₂O₅ additions can cause a dramatic increase in the steady state creep rate as long as the niobium ion is maintained in the Nb⁵⁺ valence state. Material containing 0.4 mol% Nb₂O₅ creeps three orders of magnitude faster than the pure material.Analysis of the results in terms of grain size compensated viscosity suggest that, like “pure” UO₂, the creep rate of Nb₂O₅ doped fuel is diffusion-controlled and proportional to the reciprocal square of the grain size. A model is developed which suggests that the increase in creep rate results from suppression of the U⁵⁺ ion concentration by the addition of Mb⁵⁺ ions, which modifies the crystal defect structure and hence the uranium ion diffusion coefficient.     

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.     

Characterization and densification studies on ThO2-UO2 pellets derived from ThO2 and U3O8 powders

ThO₂ containing around 2-3% ²³³UO₂ is the proposed fuel for the forthcoming Indian Advanced Heavy Water Reactor (AHWR). This fuel is prepared by powder metallurgy technique using ThO₂ and U₃O₈ powders as the starting material. The densification behaviour of the fuel was evaluated using a high temperature dilatometer in four different atmospheres Ar, Ar-8%H₂, CO₂ and air. Air was found to be the best medium for sintering among them. For Ar and Ar-8%H₂ atmospheres, the former gave a slightly higher densification. Thermogravimetric studies carried out on ThO₂-2%U₃O₈ granules in air showed a continuous decrease in weight up to 1500 °C. The effectiveness of U₃O₈ in enhancing the sintering of ThO₂ has been established.     

Phasengleichgewichte in den systemen UO2-UO2,67-ThO2 und UO2 + x-NPO2

Solid-state chemical investigations have established that in the compositional range UO₂-UO_2.67-ThO₃ of the U-Th-O ternary system, the following single-phase domains exist: U₃O₈, which does not dissolve any ThO₂ in the solid state; an ordered M₄O₉ phase on the section between U₄O₉ and U₂Th₂O₉, below ≈ 1150 °C; and a phase with fluorite structure which occupies a large part of the system and which at 1250 °C is bounded by the compositions UO₂-UO_2.25 (U_0.43, ThO_0.57)O_0.25-ThO₃. The maximum O/M ratio of the “fluorite” phase is O:(U + Th) = 2.25. The highest oxidation valency of uranium is 5.30; this value falls as more thorium oxide is incorporated in the (U.Th)O_{2 + x} “fluorite” phase.