The release of fission-recoiled xenon from Zr-2.5 wt% Nb alloy

The release of fission-recoiled ¹³³Xe from Zr-2.5 wt% Nb alloy was measured in the temperature range 640–1080 K. In the range 640–880 K, where purely phase exists, a linear relationship between log D versus 1/T is observed and can be represented by the equation: D(640–880 K) = 6.24 × 10⁻⁹exp(−142.7 kJmol/RT)m²/s. The release has been attributed to the non-volume diffusion process.

In the temperature range 930–1080 K where both and β phases coexist, the linearity in the plots of log D versus 1/T is violated.

The present values of the release parameters have been compared with the corresponding values for the release of fission-recoiled ¹³³Xe from Zircaloy-2. Alloying elements seem to have very small effect on the release kinetics. The results have been presented and discussed.     

The kinetics and mechanism of the uranium-water vapour reaction — an evaluation of some published work

The published results of Grimes and Morris on the rate of the uranium-water vapour reaction which were obtained using interferometry have been recalculated using the best values derived from the literature for the complex refractive indices of uranium and uranium dioxide (3.1–3.91 for uranium and 2.2-0.51 for uranium dioxide). The kinetics have been described by Haycock's model and the linear rate constant is given by K₁ = 1.3 × 10⁴P^1/2_H2O exp( − 9.0 kcal/RT )mg U/cm² h, where P_H2O is the water vapour pressure in torr or K₁ = 3.48 × 10⁸r^1/2 exp( −14.1 kcal/RT)mg U/cm² h, where r is the fractional relative humidity, R is the gas constant and T is the absolute temperature.

A mechanism is described which accounts for the observed dependence of the rate of uranium-water vapour reaction on the square root of the water vapour pressure.     

Influence de la pression sur le diagramme de phases Pu-Ga

The phase diagram (P, T) was determined for Pun at % Ga alloys (with n = 2, 4, 6, 8) from 20°C to 700°C in the 0–40 kbar pressure range.

From this work, a three-dimensional (P, T, c%) diagram was deduced. The main emphasis was put on the limits of the δ phase field.     

The thermal conductivity of UO2 vapor

The thermal conductivity, λ of a saturated vapor over UO_1.96 is calculated in the temperature range 3000–6000 K. The calculation shows that the contribution to λ from the transport of reaction enthalpy dominates all other contributions. All possible reactions of the gaseous species UO₃, UO₂, UO, U, O, and O₂ are included in the calculation. We fit the total thermal conductivity to the empirical equation λ = exp(a+ b/T+cT+dT² + eT³), with λ in cal/(cm s K), T in kelvins, a = 268.90, B = − 3.1919 × 10⁵, C = −8.9673 × 10⁻², d = 1.2861 × 10⁻⁵, and E = −6.7917 × 10⁻¹⁰.     

Ion-induced electron emission – monitoring the structure transitions in graphite

The temperature dependence of ion-induced electron emission yield γ under 30 keV Ar⁺ ion impacts at incidence angles θ = 0−80° under dynamically steady-state conditions has been measured for polygranular graphite POCO-AXF-5Q. The fluencies were 10¹⁸–10¹⁹ ion/cm², the temperatures varied from the room temperature (RT) to 400 °C. The RHEED has shown that same diffraction patterns correspond to a high degree of disorder at RT. At high temperature (HT), some patterns have been found similar to those for the initial graphite surfaces. The dependence γ(T) has been found to be non-monotonic and for normal and near normal ion incidence manifests a step-like increase typical for a radiation induced phase transition. At oblique and grazing incidence (θ > 30°), a broad peak was found at T_p = 100 °C. An analysis based on the theory of kinetic ion-induced electron emission connects the behavior of γ(θ,T) to the dependence of both secondary electron path length λ and primary ion ionizing path length R_e on lattice structure that drastically changes due to damage annealing.     

Measurement of the mechanical properties of thermally-shocked zirconia-based simulated inert matrix fuel

The Vickers micro-hardness (H_V) was measured by an indentation technique of simulated ZrO₂-based Inert Matrix Fuel (IMF) material with a composition of Er_0.07Y_0.10Ce_0.15Zr_0.68O_1.915 in two different densities on sintered specimens and specimens thermally shocked with the quenching temperature differences (ΔTs) between 473 and 1673 K and compared with those of simulated MOX, namely, U_0.92Ce_0.08O₂. The H_V values obtained for two IMF materials were found higher, ranging from 6.37 GPa to about 7.84 GPa, depending on ΔT and the sintered density, than those obtained for the simulated MOX which are quasi-constant in the same range of ΔT with a mean value of 6.37 GPa. The fracture toughness (K_IC) was calculated from the measured H_V and the crack length, and it was found to exhibit a slight increase with increasing ΔT, ranging between 1.4 and 2.0 MPa m^1/2, while that of simulated MOX specimen is ranging between 0.8 and 1.1 MPa m^1/2. The thermally shocked specimens were observed with an optical microscope and analyzed in terms of microstructural changes and cracking patterns.     

Thermodynamic studies on Cs4U5O17(s) and Cs2U2O7(s) by emf and calorimetric measurements

The oxygen potentials over the phase field: Cs₄U₅O₁₇(s)+Cs₂U₂O₇(s)+Cs₂U₄O₁₂(s) was determined by measuring the emf values between 1048 and 1206 K using a solid oxide electrolyte galvanic cell. The oxygen potential existing over the phase field for a given temperature can be represented by: Δμ(O₂) (kJ/mol) (±0.5)=−272.0+0.207T (K). The differential thermal analysis showed that Cs₄U₅O₁₇(s) is stable in air up to 1273 K. The molar Gibbs energy formation of Cs₄U₅O₁₇(s) was calculated from the above oxygen potentials and can be given by, Δ_fG⁰ (kJ/mol)±6=−7729+1.681T (K). The enthalpy measurements on Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were carried out from 368.3 to 905 K and 430 to 852 K respectively, using a high temperature Calvet calorimeter. The enthalpy increments, (H⁰_T−H⁰₂₉₈), in J/mol for Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) can be represented by, H⁰_T−H⁰_298.15 (Cs₄U₅O₁₇) kJ/mol±0.9=−188.221+0.518T (K)+0.433×10⁻³T² (K)−2.052×10⁻⁵T³ (K) (368 to 905 K) and H⁰_T−H⁰_298.15 (Cs₂U₂O₇) kJ/mol±0.5=−164.210+0.390T (K)+0.104×10⁻⁴T² (K)+0.140×10⁵(1/T (K)) (411 to 860 K). The thermal properties of Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were derived from the experimental values. The enthalpy of formation of (Cs₄U₅O₁₇, s) at 298.15 K was calculated by the second law method and is: Δ_fH⁰_298.15=−7645.0±4.2 kJ/mol.     

Investigation of in-reactor creep and irradiation growth of zirconium-2.5 wt% niobium channel tubes

We summarize the diametral creep results obtained in the MR reactor of the Kurchatov Institute of Atomic Energy on zirconium-2.5 wt% niobium pressure tubes of the type used in RBMK-1000 power reactors. The experiments that lasted up to 30 000 h cover a temperature range of 270 to 350°C, neutron fluxes between 0.6 and 4.0 ×10¹³ n/cm² · s (E > 1 MeV) and stresses of up to 16 kgf/mm². Diametral strains of up to 4.8% have been measured. In-reactor creep results have been analyzed in terms of thermal and irradiation creep components assuming them to be additive. The thermal creep rate is given by a relationship of the type ε_th = A₁ exp [(A₂ + A _3σt) T] and the irradiation component by ε_rad = A_4σtø(T − A₅), where T = temperature, σ_t = hoop stress, ø = neutron flux and a₁ to A₅ are constants. Irradiation growth experiments carried out at 280° C on specimens machined from pressure tubes showed a non-linear dependence of growth strain on neutron fluence up to neutron fluences of 5 × 10²⁰ n/cm². The significance of these results to the elongation of RBMK reactor pressure tubes is discussed.     

Thermochemical study of vaporization of LiTiO by a mass spectrometric Knudsen effusion method

The vaporization of Li₄TiO₄ has been studied by a mass spectrometric Knudsen effusion method in the temperature range 1082–1582 K. Identified vapors are Li(g), LiO(g), Li₂O(g) and Li₃O(g). When the vaporization proceeds, the content of Li₂O in the Li₄TiO₄ sample decreases and the condensed phase of the sample changes to β-Li₄TiO₄ plus l-Li₂TiO₃ below 1323 K, to β-Li₄TiO₄ plus h-Li₂TiO₃ in the range 1323–1473 K and to h-Li₂TiO₃ plus liquid above 1473 K. On the basis of the partial pressure data, the enthalpies of formation for β-Li₄TiO₄ from elements and from constituent oxides have been determined to be ΔH_f,298^°(β-Li₄TiO₄,s) = −2247.8 ± 14.3 kJ mol⁻¹ and Δ_fox,298^°(β-Li₄TiO₄, s) = −107.3 ± 14.3 kJ mol⁻¹, respectively.     

Mass spectrometric investigation of the vaporization of li2tio3(s)

The vaporization of Li₂TiO₃(s) has been investigated by the mass spectrometric Knudsen effusion method. Partial pressures of Li(g), LiO(g), Li₂O(g), Li₃O(g) and O₂(g) over Li₂TiO₃(s) have been obtained in the temperature range 1180–1628 K. When the vaporization of Li₂TiO₃(s) proceeds, the content of Li₂O in the Li₂TiO₃(s) sample decreases. The phase of the sample is a disordered Li₂TiO₃ solid solution above 1486 K. The enthalpies of formation and the atomization energies for LiO(g) and Li₃O(g) have been evaluated from the partial pressures to be ΔH^o_f0(LiO, g) = 65.4 ± 17.4 kJ/mol, ΔH^o_f0(Li₃O, g) = − 207.5 ± 56.6 kJ/mol, D^o₀(LiO) = 340.5 ± 17.4 kJ/mol and D^o₀(Li₃O) = 931.6 ± 56.6 kJ/mol, respectively.     

Extraction efficiency of N(T1/2 = 9.96 min) atoms from a graphite target: comparison between off- and on-line obtained results

An off-line release study ¹³N(T1/2 = 9.96 min) produced by proton induced reaction on a graphite target (POCO-graphite EDM3, density = 1.84 g/cm³, grain size /t 3 μm) has been performed. The activation energy for the diffusion process is determined to be 6.15(16)×10⁵ J/mol. With this activation energy, extraction efficiencies for ¹³N are obtained at different temperatures and are compared to on-line measured extraction efficiencies.     

Standard Gibbs energy of formation of Cs2CdI4

The vapor pressures of CdI₂ and Cs₂CdI₄ were measured below and above their melting points, employing the transpiration technique. The standard Gibbs energy of formation Δ_fG° of Cs₂CdI₄, derived from the partial pressure of CdI₂ in the vapor phase above and below the melting point of the compound could be represented by the equations Δ_fG°Cs₂CdI₄ (±6.7) kJ mol⁻¹=−1026.9+0.270 T (643 K≤T≤693 K) and Δ_fG°{Cs₂CdI₄} (±6.6) kJ mol⁻¹=−1001.8+0.233 T (713 K≤T≤749 K) respectively. The enthalpy of fusion of the title compound derived from these equations was found to be 25.1±10.0 kJ mol⁻¹ compared to 36.7 kJ mol⁻¹ reported in the literature from differential scanning calorimetry (DSC). The standard enthalpy of formation Δ_fH°_298.15 for Cs₂CdI₄ evaluated from these measurements was found to be −918.0±11.7 kJ mol⁻¹, in good agreement with the values −920.3±1.4 and −917.7±1.5 kJ mol⁻¹ reported in the literature from two independent calorimetric studies.     

Phase transition temperature in the Zr-rich corner of Zr–Nb–Sn–Fe alloys

The influence of small composition changes on the phase transformation temperature of Zr–1Nb–1Sn–0.2(0.7)Fe alloys was studied in the present work, by electrical resistivity measurements and metallographic techniques. For the alloy with 0.2 at.% Fe we have determined T_↔+β=741°C and T_+β↔β=973°C, and for the 0.7 at.% Fe the transformation temperatures were T_↔+β=712°C and T_+β↔β=961°C. We have verified that the addition of Sn stabilized the β phase.     

Primary creep of UO2 and the effect of amorphous grain boundary phases

Creep experiments were conducted on nearly stoichiometric UO₂ helical springs from 1000 to 1600°C and 2.1 to 80 MPa. Entirely transient behaviour was measured in all experiments with the plastic strain,ε = (Aσ/d^1.5) exp(−Q/RT)t^m, where A is a constant that depends on purity, d is the grain size, σ is the applied stress, Q is the apparent activation energy, t is the time, m is a constant, and the other terms have their usual meaning. At T > 1200°C, Q 100 kcal mol⁻¹, but at T < 1200°C, Q increased dramatically and became strain dependent. The value of m for most experiments was 0.8, but at σ > 48 MPa, m decreased, and for d < 10 μm, it increased. Amorphous or glassy grain boundary phases were observed by transmission electron microscopy in all specimens: specimens containing the largest concentrations of Fe and Si sometimes had anomalously high creep rates. The phases existed as discontinuous, lenticular bodies on grain faces and a continuous network along triple grain junctions. Some instances of precipitation of UO₂ from the phase were observed. At T > 1200°C, glassy phases may accelerate Coble creep by providing short circuit diffusion paths along the grain boundaries or may accelerate superplastic deformation by diffusion along the continuous glassy phase triple line junctions. At low temperatures the glassy phase appears to control grain-boundary sliding.     

Thermodynamic stability of Na2ZrO3 using the solid electrolyte galvanic cell technique

The sodium potential in the test electrode (a) Pt,O₂,Na₂ZrO₃,ZrO₂ was measured by using the emf technique employing Na-β^″-alumina as the solid electrolyte in conjunction with (b) Pt,O₂,Al₂O₃,NaAl₁₁O₁₇, (c) Pt,O₂,Na₂MoO₄,Na₂Mo₂O₇ and (d) Pt,Na₂CO₃,CO₂,O₂ as the reference electrodes over the ranges 880–1045, 700–800 and 850–940 K, respectively. The emf results between electrodes (b) and (c) were utilized for internal consistency checks. From the results on cells formed between (a) and (b) and those on (a) and (c), the standard Gibbs energy of formation, Δ_fG^o (kJ/mol) of Na₂ZrO₃ was determined to be −1699.4+0.3652T (K) valid over the temperature range 700–1045 K. The break in the emf data at 1045 K was corroborated by independent TG/DTA measurements carried out on Na₂ZrO₃ which exhibited an endotherm at 1055 K indicative of a phase transition in Na₂ZrO₃.     

Production, acceleration and use of radioactive ion beams at Louvain-la-Neuve

The production and acceleration of radioactive beams using two cyclotrons coupled by an electron cyclotron resonance ion source is described. Pure beams of ¹³N(T1/2 = 9.96 min) and ¹⁹Ne(T1/2 = 17 s) with an energy around 1 MeV/amu are obtained with intensities larger than 50 ppA. As an example, cross section measurements using a ¹³N beam on hydrogen and deuteron targets are presented. Finally, the ARENAS³ project, a future plan for the production of radioactive beams in Belgium, is described.     

Temperature and dose dependences of nitrogen implantation into aluminium

It has been established that nitrogen implantation into metals can alter their surface properties such as friction, wear, corrosion, etc. Recent studies have shown that nitrogen implantation into aluminium leads to the formation of aluminium nitride which has interesting tribological, electronic and optical properties. For a given implantation energy, the characteristics of the nitrogen profile, e.g. thickness, shape and concentration, depend strongly on the experimental conditions during the implantation. In order to study the influence of the implantation parameters, aluminium samples have been bombarded with ¹⁵N⁺₂ of 100 keV to different doses ((1–20) × 10¹⁷ N⁺/cm²), at several temperatures (25–300° C). Distributions of the implanted species were investigated by nuclear reaction analysis (NRA) and by Rutherford backscattering spectroscopy (RBS). The chemical bonds of aluminium in the matrix were studied by using low-energy electron-induced X-ray spectroscopy (LEEIXS). It is shown that aluminium nitride is formed and that the nitrogen distribution presents a surface peak when the implantation temperature is higher than 200° C.     

Contribution of uranium diffusion on creep behavior of uranium dicarbide

Compressive creep tests of uranium dicarbide (UC₂) have been conducted. The general equation best describing the creep rate over the temperature range 1200–1400°C and over the stress range 2000–15000 psi is represented by the sum of two exponential terms ge =A(σ/E)^0.9 exp(−39.6 ± 1.0/RT) + B(σ/E)^4.5 exp(−120.6 ± 1.7/RT), where pre-exponential factors are A(σ/E)^0.9 = 12.3/h at low stress region (3000 psi) and B(σ/E)^4.5 = 3.17 × 10¹³/h at high stress region (9000 psi), and the activation energy is given in kcal/mol. Each term of this experimental equation indicates that important processes occurring during the steady state creep are grain-boundary diffusion of the Coble model at low stress region and the Weertman dislocation climb model at high stress region. Both mechanisms are related to migration of uranium vacancies.     

Threshold oxygen levels in sodium necessary for the formation of NaCrO2 in sodium-steel systems

A knowledge of the threshold oxygen level in liquid sodium necessary for the formation of NaCrO₂ in sodium-steel systems is useful in the operation of fast breeder reactors. There is considerable discrepancy in the data reported in the literature. In order to resolve this, the problem was approached from two sides. Direct measurement of oxygen potential in the Na(l)-Cr(s)-NaCrO₂(s) phase field using the galvanic cell In, In₂O₃/YDT/Na, Cr, NaCrO₂ yielded: _o2 = −800847 + 147.85 T J/mol O₂ (657–825 K). Knudsen cell-mass spectrometric measurements were carried out in the phase field NaCrO₂(s)-Cr₂O₃(s)-Cr(s) to obtain the Gibbs energy of formation of NaCrO₂ as: ΔG^o_f,T(NaCrO₂) = −870773 + 193.171 T J/mol (825–1025 K). The threshold oxygen levels deduced from G^o_f,T (NaCrO₂) data were an order of magnitude lower than the directly measured values. The difference between the two sets of data as well as differing experimental observations from operating liquid sodium systems are explained on the basis of the influence of dissolved carbon.     

Extraction behavior of Ga(III) and Pd(II) with 2-methyl-8-quinolinol derivatives into supercritical fluid CO2

The extraction behavior of gallium(III) and palladium(II) with 2-methyl-8-quinolinol (HMQ), 2-methyl-5-hexyloxymethyl-8-quinolinol (HMO₆Q) and 5-hexyloxymethyl-8-quinolinol (HO₆Q) from an acidic solution into supercritical fluid (SF) CO₂ were investigated. Furthermore, the pH of an acidic solution contacting with SF CO₂ was spectrophotometrically measured, and the distribution constants of HMO₆Q between SF CO₂ and water were also determined at I = 0.1 M (H, Na)NO₃, 45°C, and 8.6 – 20.4 MPa. Above pH 3, the pH of the aqueous phase in contact with SF CO₂ was levelled to about 3. On the other hand, below pH 3, the pH change is negligibly small. The distribution constant (K_{D,SF CO2} of HMO₆Q between SF CO₂ and water at 20.4 MPa was about one tenth of the K_D for heptane - water system, indicating that the solubility of HMO₆Q in SF CO₂ is remarkably smaller compared with that in heptane. The Ga(III)-HMO₆Q and Ga(III)-HO₆Q complex extracted into SF CO₂ were assigned to be Ga(OH)(MO₆Q)₂ and Ga(O₆Q)₃, respectively. Palladium(II) was extracted with HMQ as Pd(MQ)₂ from a weakly acidic solution. Even in the presence of HMQ, the Pd(II)-HMQ complex extracted from the higher HCl concentration should be H₂PdCl₄.