Progressive dissolution of molybdenum foils in liquid uranium at 1160°C

Immersion experiments have been performed to investigate the progressive dissolution of 0.3-mm-thick foils of molybdenum metal in liquid uranium at 1160 ° C, for immersion times of 3, 6, 10, and 60 min, and 20 h, in a zarconia crucible. The original foils, as-received and heat-treated at 1160 ° C, and the uranium-reacted foils have been studied microscopically (SEM-EDAX) and the internal morphology has been determined. The flow lines in as-received molybdenum disappear under heat-treatment, while the undistinguishable grains recrystallize upon heating into grains with average size of 20 μm, persisting in samples immersed in liquid uranium. The recrystallization is not uranium-assisted, as uranium does not penetrate into intergranular regions. After incubation time of 3–4 min, outer molybdenum grains dissolve in liquid uranium, thereby reducing the foil thickness progressively. Full dissolution occurs for about 15-min immersion.     

Corrosion of steels with surface treatment and Al-alloying by GESA exposed in lead–bismuth

Corrosion tests were performed for T91, E911 and ODS (oxide dispersion strengthened) with surface treatment and Al-alloying by pulsed electron beam (GESA—GepulsteElektronenStrahlAnlage) in flowing lead bismuth eutectic (LBE) with an oxygen content of 10⁻⁶ wt% at 550 °C for 2000 h. The result was that the surface treatment by GESA led to a faster growing multiphase oxide layer which was very homogenous in thickness. After exposure of specimens to LBE, the average oxide layer at the surface was 14–15 μm thick for ODS, 19–20 μm for E911 and 8–22 μm for T91. No dissolution attack occurred. On the surface of the Al-alloyed specimens, thin protective alumina layers were observed at the places where FeAl was formed by the GESA process, otherwise multiphase oxide layers or corrosion attack were observed.     

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.     

The effect of Fe,Ni and W impurities on uranium diffusion in uranium monocarbide

The self-diffusion of uranium with U-233 as tracer was measured in stoichiometric UC which was doped with Fe, Ni or W impurities. The impurities were added by flash evaporation on the UC and subsequent diffusion into the UC. Uranium diffusion was increased in the doped samples as compared to undoped UC at all temperatures studied (1380 to 2200°C). The increase was most pronounced (more than a factor of 100) at low temperatures. Simultaneously, pronounced grain-boundary penetration was observed at low temperatures, possibly due to eutectic formation at the grain boundaries. The ratio of grain boundary to lattice diffusion coefficients at 1380°C was of the order of 3 × 10⁴. The present data serve to explain some of the scatter of the literature data and correlate well with the known increased rate of sintering of Ni-doped UC.     

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.     

Beta-gamma radiation from leaching resistant glasses containing uranium ions

The β and γ decay of uranium atoms from xUO₃(100 - x)[3B₂O₃ · MO] glass systems, where M=Sr or Pb and 0 ≤ × ≤ 20 mol%, is investigated. The γ decay data are very close to each other, for the same UO₃ contents, in both the systems. The composition dependence of the β decay exhibits a lower slope in the lead borate matrix than in the strontium borate matrix. The ratio between the β activity of samples with the same uranium ion concentrations in the two investigated glass systems is a function of the x values. The results are correlated with the amount of radioactive nuclides and with the structural environments of the radionuclides. The leaching treatment in water at temperatures below 100°C evidenced no aqueous dissolution of glass samples.     

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.     

Fatigue testing of metallurgically-bonded EBR-II superheater tubes

Fatigue crack growth tests were performed on 2¼Cr–1Mo steel specimens machined from ex-service experimental breeder reactor-II (EBR-II) superheater duplex tubes. The tubes had been metallurgically-bonded with a 100 μm thick Ni layer; the specimens incorporated this bond layer. Fatigue crack growth tests were performed at room temperature in air and at 400 °C in air and humid Ar; cracks were grown at varied levels of constant ΔK. In all conditions the presence of the Ni bond layer was found to result in a net retardation of growth as the crack passed through the layer. The mechanism of retardation was identified as a disruption of crack planarity and uniformity after passing through the porous bond layer. Full crack arrest was only observed in a single test performed at near-threshold ΔK level (12 MPa√m) at 400 °C. In this case the crack tip was blunted by oxidation of the base steel at the steel–nickel interface.     

Synthesis and sintering of Li2SnO3

As one of candidates for solid blanket materials of fusion reactors, lithium stannate Li₂SnO₃ was synthesized by precipitation of a complex, lithium hexahydroxystannate Li₂Sn(OH)₆, and its thermal decomposition. In order to get single-phase precipitates Li₂Sn(OH)₆, aqueous solution SnCl₄ had to be added slowly to LiOH aqueous solution. Decomposition of Li₂Sn(OH)₆ to Li₂SnO₃ proceeded in two steps, abrupt release of about two molecules of water around 200° C and gradual release of remaining water above 260° C. The grains of Li₂SnO₃ obtained at 800° C were porous, consisting of small primary particles of about 0.2 μm size. For the pellets prepared from these porous grains under 20 and 100 MPa, the density saturated to a value of 1.8 and 2.4 g/cm³ within two days at 1000° C, corresponding to the porosity of 64 and 52%, respectively. The porous nature of the original Li₂SnO₃ grains was found to be kept even after 1000° C treatment for a week. For the pellet prepared by ground Li₂SnO₃ under 200 MPa, remarkable sintering was observed at 1000° C; density increased rapidly and became close to theoretical density (7% porosity) after four days. The product Li₂SnO₃ synthesized by the present process has advantages in terms of manufacturing, handling and possibly tritium recovery of the blanket.     

Influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in PWR primary water

The influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in simulated Pressurized Water Reactor (PWR) primary water has been investigated. A-286 microstructure was characterized by transmission electron microscopy for ageing heat treatments at 670 °C and 720 °C for durations ranging from 5 h to 100 h. Spherical γ′ phase with mean diameters ranging from 4.6 to 9.6 nm and densities ranging from 8.5 × 10²² m⁻³ to 2 × 10²³ m⁻³ were measured. Results suggest that both the γ′ phase mean diameter and density quickly saturate with time for ageing heat treatment at 720 °C while the γ′ mean diameter increases significantly up to 100 h for ageing heat treatment at 670 °C. Grain boundary η phase precipitates were systematically observed for ageing heat treatment at 720 °C even for short ageing periods. In contrast, no grain boundary η phase precipitates were observed for ageing heat treatments at 670 °C except after 100 h. Hardening by γ′ precipitation was well described by the dispersed barrier hardening model with a γ′ barrier strength of 0.23. Stress corrosion cracking behaviour of A-286 was investigated by means of constant elongation rate tensile tests at 1.5 × 10⁻⁷ s⁻¹ in simulated PWR primary water at 320 °C and 360 °C. In all cases, initiation was transgranular while propagation was intergranular. Grain boundary η phase precipitates were found to have no significant effect on stress corrosion cracking. In contrast, yield strength and to a lesser extent temperature were found to have significant influences on A-286 susceptibility to stress corrosion cracking.     

Non-equilibrium intragrain concentration redistribution of the alloying elements in austenitic steels under irradiation

Radiation-induced and thermally activated decomposition of austenitic 16Cr15Ni3Mo1Ti, 32Ni, 34Ni steels at high temperature (500–650°C) were examined. High doses (up to 10–200 dpa ) in 16Cr15Ni3Mo1Ti stainless steel with 1.5 MeV Kr ions and 450 keV Fe ions at 550–650°C lead to the appearance of relatively large regions (up to 200–400 nm) of concentration-oscillations with ‘mosaic’ dark–white diffraction contrast in TEM images. The radiation-induced redistribution of alloying elements takes place thanks to inverse Kirkendall effect and, in particular, removal of Cr to cell volume from boundaries of coarse cellular structure. The competing formation of ultrafine subgrains and grains 10–50 nm in size structure in Ti-free steel (16Cr15Ni3Mo) impedes the development of large ingrain segregations. The Mössbauer investigations showed that the 32Ni and 34Ni steels with purposefully produced concentration-oscillations were fully homogenised in that high-temperature region. This fact indicated the absence of the thermal decomposition dome in the Fe–Ni equilibrium diagram.     

Micro-PIXE and channeling PIXE analysis of Ag-doped YBa2Cu3O7−δ thin films

Nuclear Microscopy, utilizing a 2 MeV He⁺ beam for channeling Rutherford Backscattering (RBS) and PIXE analysis, was used to characterise Ag-doped YBa₂Cu₃O_7−δ thin films and measure the lateral distribution of the Ag. The samples were prepared by in situ two-beam pulsed laser deposition in order to investigate the effects of such dopings on critical current densities [1 and 2]. Films deposited at temperatures above 650°C form needle-like surface structures with a length of up to 100 μm; these tend to align with in-plane a–b axis. Results for a sample prepared at a substrate temperature of 730°C and a maximum Ag concentration of 5 at.% are discussed. The needle-like structures were found to be rich in Ag and Cu, and the YBa₂Cu₃O_7−δ film contained 0.02 at.% Ag. Broad beam PIXE-channeling results indicate that 19% of the Ag is substitutional.     

Trace elements in sera from patients with renal disease

In hemodialysis (HD) patients, an accumulation of trace elements such as aluminum, copper, silicon and vanadium has been reported. Aluminum-caused encephalopathy and aluminum-related bone diseases are important trace element-related complications. Using particle induced X-ray emission (PIXE) we determined concentrations of aluminum, silicon, copper, zinc, selenium and bromine in sera of 29 patients with HD, 14 nondialysis patients with renal disease (RD) and 27 normal controls. The concentration of serum silicon of the patients with HD was 107.4 ± 61.3 μmol/l, which is markedly higher than that of normal controls (48.3 ± 25.8 μmol/l, p < 0.0001). The serum concentrations of zinc and bromine in patients with HD were 11.9 ± 1.7 and 21.3 ± 3.0 μmol/l, respectively. Both were markedly lower than those of normal controls (15.6 ± 2.6, 69.2 ± 8.3 μmol/l, p < 0.0001). The concentrations of aluminium and bromine in the serum of patients with RD were 171.9 ± 64.3 and 81.9 ± 11.6 μmol/l, which were markedly higher than those of normal controls (p < 0.0001, p < 0.001). No significant differences were observed in the concentration of copper and selenium among three groups.     

Characterisation of ferromagnetic magnetic storage media surfaces by complementary particle induced X-ray analysis and time of flight-energy dispersive elastic recoil detection analysis

Thin (10 nm–1 μm) films of ferromagnetic material constitute an important class of materials that are difficult to analyse by conventional ion beam analytical (IBA) techniques because they are based on the ferromagnetic elements (Co, Fe, Mn, Ni, and Cr). The similar or overlapping isotope masses makes it difficult to separate the elemental signals using time of flight and energy dispersive elastic recoil detection (ToF-E ERD). In this exploratory study we have investigated the use of Particle Induced X-ray Emission (PIXE) measurements to refine the mass dispersive depth profile information from ToF-E ERD. The surfaces of two commercial magnetic media were investigated. One sample was a double density diskette with a coating of ferrite particles in an organic binder. The other sample was a complex C/Co/Cr/Ni–P/Al multilayer structure taken from a standard hard disc. The Lund nuclear microprobe with a 2.55 MeV proton beam was used for PIXE analysis. ToF-ERD measurements were carried out using a 55 MeV ¹²⁷I¹⁰⁺ ion beam incident at 67.5° to the surface normal. The time of flight and kinetic energy of recoils ejected at 45° to the ion beam direction was measured in a detector telescope. The findings demonstrate that by detailed analysis of the PIXE spectra it is possible to remove the ambiguities in mass assignment of the ToF-ERD data associated with the ferromagnetic elements.     

Development of uranium carbide targets for the on-line production of neutron-rich isotopes

A number of on-line and off-line tests have been performed at the IRIS (investigation of radioactive isotopes at synchrocyclotron) facility in order to develop uranium carbide targets with a high density (11 g/cm³) for the on-line production of neutron-rich isotopes by fission of ²³⁸U. A 1 GeV proton beam was used to bombard two kinds of targets held at temperatures in the range of 1900–2100 °C. The first one was a target-ion source assembly slightly modified to withstand 3 months of continuous heating at a temperature of about 2050 °C. The second unit was of a new kind, where ionisation takes place in the target volume itself. A comparison of the on-line isotopic yields before and after heating for 3 months is here reported. The yields and release times of Rb, Cs and In are compared with the ones obtained from a standard reference target, as measured in previous experiments.     

The constitution of the uranium-tin-palladium system

The Pd-rich region of the isothermal section of the ternary U---Sn---Pd system at 1050°C was investigated by metallography, X-ray microanalysis and X-ray diffraction. The fcc -Pd(Sn, U) solid solution dissolves up to 16 at.% Sn and 15 at.% U. The AuCu₃ type phases SnPd₃ and UPd₄ are the end members of a single-phase region. SnPd₂ and UPd₃ are in equilibrium with this solid solution of the composition U_0.68Sn_0.32Pd₃ and with the ternary phase USnPd₂. The Gibbs energies of formation of SnPd₂, SnPd₃ and UPd₄ were used and ideal behaviour of the (Sn, U) Pd_3+x solid solution was assumed to calculate the Gibbs energy of formation of UPd₃ which gives Δ_fG° = −312 kJ/mol at 1050°C. In addition, the annealing experiments in the Pd-rich region of the binary U---Pd system were extended to 950°C which confirm the phase-field distribution established at 1050°C in earlier work.     

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.     

Etude des divers types de transformations structurales caracterisant l'alliage Zr-Nb a 17% poids de niobium

This study was carried out mainly by quenching followed by isothermal annealing or continuous heating. X-ray diffraction, micrography, microhardness and dilatometry during quench were employed. By stepped quenching, it was found that the high-temperature β phase decomposes in different ways —either partial decomposition into _Zr, leading finally to the (_Zr+β_Nb) mixture indicated by the phase-diagram, or a diffusion-transformation into ω', or else a diffusionless transformation into ω. A fast quench breaks down the phase into a complex (β + ω + β″) structure. During isothermal anneals the β″ phase was found to vanish, while either ω' or _Zr was formed according to temperature; meanwhile residual β became enriched in niobium. During continuous heating at rates less than 150°/h, the quench-product, ω, reverts to β; then, above 600°C, is transiently deposited but disappears again above 700°C to yield the equilibrium high-temperature phase, β containing 17 wt % niobium.     

Microbeam RBS on flat panel displays

We have demonstrated the utility of microbeam-Rutherford BackScattering (μ-RBS) in spatially resolved studies of operational plasma effects on the interior surfaces of plasma flat panel displays manufactured by Photonics Imaging. The experiments were performed at the Sandia Nuclear microprobe using a 2.8 MeV He beam with an average beam spot size of less than 8 μm. The interior surface of the top panes of the flat panels is composed of approximately 800 nm of MgO on top of a 2000 nm thick PbO layer. μ-RBS of sample panels operated under varying conditions measured changes in the surface MgO film thickness due to plasma erosion and redeposition as accurately as ± 1.5 nm. The high accuracy in the MgO thickness measurement was achieved by inferring the MgO thickness from the shift of the Pb front edge in the RBS spectrum. An estimate for the thickness accuracy as a function of the acquired statistics is presented. The surface of the flat panels' bottom panes is also comprised of MgO on top of PbO. However, troughs 100 μm wide by 10 μm deep were partially filled with phosphor and cover the entire width of the surface. This leaves only 100 μm long sections of MgO within the trough exposed. Using μ-RBS, we were able to analyze the surface composition of these regions.