Characterization of the reaction layer in U-7wt%Mo/Al diffusion couples

The reaction layer in chemical diffusion couples U-7wt%Mo/Al was investigated using optical and scanning electron microscopy, electron probe microanalysis and X-ray diffraction (XRD) techniques. When the U-7wt%Mo alloy was previously homogenized and the γ(U, Mo) phase was retained, the formation of (U, Mo)Al₃ and (U, Mo)Al₄ was observed at 580 °C. Also a very thin band was detected close to the Al side, the structure of the ternary compound Al₂₀UMo₂ might be assigned to it. When the decomposition of the γ(U, Mo) took place, a drastic change in the diffusion behavior was observed. In this case, XRD indicated the presence of phases with the structures of (U, Mo)Al₃, Al₄₃U₆Mo₄, γ(U, Mo) and α(U) in the reaction layer.     

Investigations on the effect of 100 MeV Ni ions irradiated chloride vapour phase epitaxy (Cl-VPE) grown GaN epilayers

Gallium nitride (GaN) epilayers have been grown by chloride vapour phase epitaxy (Cl-VPE) technique and the grown GaN layers were irradiated with 100 MeV Ni ions at the fluences of 5 × 10¹² and 2 × 10¹³ ions/cm². The pristine and 100 MeV Ni ions irradiated GaN samples were characterized using X-ray diffraction (XRD), UV-visible transmittance spectrum, photoluminescence (PL) and atomic force microscopy (AFM) analysis. XRD results indicate the presence of gallium oxide phases after Ni ion irradiation, increase in the FWHM and decrease in the intensity of the GaN (0 0 0 2) peak with increasing ion fluences. The UV-visible transmittance spectrum and PL measurements show decrease in the band gap value after irradiation. AFM images show the nanocluster formation upon irradiation and the roughness value of GaN increases with increasing ion fluences.     

Microstructural characterization of U-7Mo/Al-Si alloy matrix dispersion fuel plates fabricated at 500 °C

The starting microstructure of a dispersion fuel plate will impact the overall performance of the plate during irradiation. To improve the understanding of the as-fabricated microstructures of U-Mo dispersion fuel plates, particularly the interaction layers that can form between the fuel particles and the matrix, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses have been performed on samples from depleted U-7Mo (U-7Mo) dispersion fuel plates with either Al-2 wt.% Si(Al-2Si) or AA4043 alloy matrix. It was observed that in the thick interaction layers, U(Al, Si)3 and U6Mo4Al43 were present, and in the thin interaction layers, (U, Mo) (Al, Si)3, U(Al, Si)4, U3Si3Al2, U3Si5, and possibly USi-type phases were observed. The U3Si3Al2 phase contained some Mo. Based on the results of this investigation, the time that a dispersion fuel plate is exposed to a relatively high temperature during fabrication will impact the nature of the interaction layers around the fuel particles. Uniformly thin, Si-rich layers will develop around the U-7Mo particles for shorter exposure times, and thicker, Si-depleted layers will develop for the longer exposure times.     

Immobilisation of I by encapsulation in tin by hot-pressing at 200 °C

The volatility of iodine-129 and its soluble nature in anionic form makes it very difficult to incorporate in ceramic or glassy solids for the purpose of long-term immobilisation. Thus encapsulation in a low-melting metal such as tin is an attractive option, and we describe experiments in which we have hot-pressed AgI-bearing alumina beads surrounded by tin powder at 200 °C.     

Characterization of the surface charge of oxide particles of PWR primary water circuits from 5 to 320 °C

The point of zero charge of three typical oxides found as colloids in PWR primary circuits has been measured by mass titration in a large range of temperature: from 5 to 320 °C for magnetite and cobalt ferrite, from 5 to 125 °C for nickel ferrite. Comparisons with zetametry were performed near room temperature. The protonation thermodynamic constants have been calculated. The standard protonation enthalpy at 298 K is −27 ± 5, −31 ± 6 and −32 ± 7 kJ mol⁻¹, for the three oxides respectively. The sign of the surface charge of these colloidal particles in the temperature conditions of the primary circuit indicates that their adhesion onto the materials of the circuit is favored.     

The total cross section and resonance parameters for the 0.178 eV resonance of Cd

It has been suggested that the capture and scattering cross sections of natural cadmium are not well described by the resonance parameters that are given in the evaluated data files. In particular, doubts on the parameters of the first resonance of ¹¹³Cd at 0.178 eV have been raised. This resonance is of high importance in the interpretation in many integral experiments, such as neutron activation analysis, in which cadmium foils are used to shield from thermal neutrons. A new set of experiments has been designed and performed at the neutron time-of-flight facility GELINA, to determine the total cross section and to extract a set of resonance parameters. The covariance information of the experimental data is propagated and the correlation between the resonance parameters is derived. The obtained parameters are then compared to the data available in the literature. Finally a set of criticality experiments from the international handbook of evaluated critical safety benchmark experiments is used to quantify the influence of the change in the resonance parameters.     

Implantation effects of low energy H and D ions in germanium at −120 °C and room temperature

Germanium was implanted with 5 keV H and D ions at −120 °C or room temperature and thermally annealed in several steps. The samples were analysed at various stages by atomic force microscopy, ion channeling and Raman spectroscopy of Ge-H/D local vibration modes. The results are discussed in comparison with those in the well studied silicon. In general, the evolution of the different types of defects, in germanium at a given temperature, tends to be similar to that of the corresponding defects in silicon at 100-300 °C higher temperature. However, the behaviour of the defects detected by ion channeling (interstitials, lattice distortions) often appears unrelated to the chemical evolution measured by Raman scattering and to the temperature and isotope dependence of blistering.     

Precipitation in AISI 316L(N) during creep tests at 550 and 600 °C up to 10 years

The precipitation behaviour in the gauge lengths and in the heads of initially solution annealed type 316L(N) austenitic stainless steel specimens tested in creep at 550 and 600 °C for periods of up to 85 000 h has been studied using several metallographic techniques. Three phases were detected: M₂₃C₆, Laves, and sigma phase. The volume fraction of the precipitated sigma phase was significantly higher than that of carbides and the Laves phase. M₂₃C₆ carbide precipitation occurred very rapidly and was followed by the sigma and Laves phases formation in the delta ferrite islands. Sigma and Laves phases precipitated at grain boundaries after longer times. Two different mechanisms of sigma phase precipitation have been proposed, one for delta ferrite decomposition and another for grain boundary precipitation. Small quantities of the Laves phase were detected in delta ferrite, at grain boundaries and inside the grains.     

Computer simulation of sputtering at the low index (1 0 0), (1 1 0) and (1 1 1) surfaces of Ni3Al in a STEM

The present study is relevant to the preferential Al sputtering and/or enhancement of the Ni/Al ratio in Ni₃Al observed by the scanning transmission electron microscopy fitted with a field emission gun (FEG STEM). Atomic recoil events at the low index (1 0 0), (1 1 0) and (1 1 1) surfaces of Ni₃Al through elastic collisions between electrons and atoms are simulated using molecular dynamics (MD) methods. The threshold energy for sputtering, E_sp, and adatom creation, E_ad, are determined as a function of recoil direction. Based on the MD determined E_sp, the sputtering cross-sections for Ni and Al atoms in these surfaces are calculated with the previous proposed model. It is found that the sputtering cross-section for Al atoms is about 7-8 times higher than that for Ni, indicating the preferential sputtering of Al in Ni₃Al, in good agreement with experiments. It is also found that the sputtering cross-sections for Ni atoms are almost the same in these three surfaces, suggesting that they are independent of surface orientation. Thus, the sputtering process is almost independent of the surface orientation in Ni₃Al, as it is controlled by the sputtering of Ni atoms with a lower sputtering rate.     

Fracture toughness of the hydrogen charged EUROFER 97 RAFM steel at room temperature and 120 °C

The static fracture toughness of EUROFER 97 reduced activation ferritic-martensitic steel was investigated in presence of higher content of hydrogen. The hydrogen effect is shown during fracture toughness testing both of base and weld metals at room temperature and at 120 °C. At the room temperature testing the J_0.2 integral values will decrease depending on hydrogen content in the range of 2-4 wppm. The same hydrogen content of 2 wppm manifests itself by an uneven level of hydrogen embrittlement for base metal and weld metal. This corresponds to a different J_0.2 integral value and a different mechanism of fracture mode. At the hydrogen content of 4 wppm more evident decrease of J_0.2 was observed for both metals. At 120 °C hydrogen decreases J_0.2 integral in base metal at a limited scale only in comparison to weld metal. At room temperature and hydrogen content of about 4 wppm the base metal specimen exhibits inter-granular fracture and trans-granular cleavage on practically the whole crack surface. The weld metal fracture has shown inter-granular and trans-granular mechanism with ductile and dimple rupture.     

Structural recovery of self-irradiated natural and Pu-doped zircon in an acidic solution at 175 °C

We have investigated the aqueous stability of self-irradiated natural and synthetic ²³⁸Pu-doped zircon (4.7 wt% of ²³⁸Pu) in an acidic solution at 175 °C. Both zircon samples have suffered a similar degree of self-irradiation damage, as given by their degree of amorphization. X-ray diffraction measurements revealed that during the hydrothermal treatment only the disordered crystalline remnants recovered in the natural zircon, whereas in the ²³⁸Pu-doped zircon the amorphous phase strongly recrystallized. Such a different alteration behavior of natural and Pu-doped zircon is discussed in terms of two fundamentally different alteration mechanisms. Our results demonstrate that further experimental studies with Pu-doped zircon are required before any reliable prediction about the long-term aqueous stability of an actinide waste form based on zircon can be made.     

Differential cross-sections for nuclear reactions on Al and Si induced by deuterons at low energy (1-2 MeV)

Recent progress in thin film techniques has made possible the fabrication of stable and pollution-free reference standards. Thin Si₃N₄ film (thickness 70 nm) and thin Al foil (150 nm) were selected to measure the differential cross-sections of nuclear reactions induced by deuterons, from 1 to 2 MeV. The absence of oxygen and carbon in the standard, as well as the stoichiometry, were checked prior to measurement by RBS. The differential cross-sections of the ²⁷Al(d,p₀p₁)²⁸Al, ²⁷Al(d,p₂p₃)²⁸Al, ²⁷Al(d,p₅p₆)²⁸Al, ²⁷Al(d,p₉)²⁸Al, ²⁷Al(d,p₁₀)²⁸Al, ²⁷Al(d,p₁₁)²⁸Al, ²⁷Al(d,p₁₂)²⁸Al, ²⁷Al(d,α₀)²⁵Mg and ²⁷Al(d,α₂)²⁵Mg reactions for aluminium and ²⁸Si(d,p₀)²⁹Si- ²⁹Si(d,p₁)³⁰Si, ²⁸Si(d,p₁)²⁹Si- ²⁹Si(d,p₂)³⁰Si, ²⁸Si(d,p₂)²⁹Si, ²⁸Si(d,p₃)²⁹Si, ²⁸Si(d,p₉p₁₀)²⁹Si reactions for silicon were determined for a detector angle of 150°.     

Oxidation kinetics of Zircaloy-4 and Zr-1Nb-1Sn-0.1Fe at temperatures of 700-1200 °C

The oxidation characteristics for the Zircaloy-4 and Zr-1.0Nb-1.0Sn-0.1Fe alloys were investigated in the temperature ranges of 700-1200 °C for 3600 s under steam supply conditions, using a modified thermo-gravimetric analyzer. The oxidation at these temperatures generally complied with the parabolic rate law for the examined duration up to 3600 s. However, the parabolic rate was not obeyed in the temperature ranges of 800-1050 °C. The oxidation kinetics were changed depending on the oxidation temperatures due to the phase transformations of the base metal and its oxide. The oxidation rate exponents of the Zr-1.0Nb-1.0Sn-0.1Fe alloy at all the temperatures were higher than those of Zircaloy-4. Considering the data controlled by the parabolic rates at 700, 1100, 1150, and 1200 °C, the oxidation rate constants were the same slopes as the Baker-Just relationship. The rate transition at 800 °C could have resulted from the phase transformation of the base metal and those at 1000 and 1050 °C could have resulted from the lateral cracks in the oxide due to the ZrO₂ phase transformation from a monoclinic structure to a tetragonal structure.     

Steam oxidation of Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr and Zircaloy-4 at 900-1200 °C

The steam oxidation characteristics for the Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr (HANA-4) and Zircaloy-4 claddings were elucidated at LOCA temperatures of 900-1200 °C by using a modified thermo-gravimetric analyzer. After the oxidation tests, the oxidation behaviors, oxidation rates, surface appearances, and microstructures of the as-received, as-oxidized, and burn-up simulated claddings were evaluated in this study. The high-temperature oxidation resistance of the as-received HANA-4 cladding was superior to that of the Zircaloy-4. The superior oxidation resistance of the HANA-4 cladding could be attributed to the higher Nb and the lower Sn within its cladding. The pre-oxidized layer formed at the low temperatures below 500 °C could retard the oxidation rate at the high temperatures above 900 °C. And the soundness of the pre-oxidized layer formed at a lower temperature could influence the oxidation kinetics and the rate constants during a steam oxidation at LOCA temperatures from 900 to 1200 °C.     

The influence of neutron irradiation in FFTF on the microstructural and microchemical development of Mo-41Re at 470-730 °C

Specimens of Mo-41 wt% Re irradiated in the fast flux test facility (FFTF) experience significant and non-monotonic changes in density that arise first from radiation-induced segregation, leading to non-equilibrium phase separation, and second by progressive transmutation of Re to Os. As a consequence the density of Mo-41Re initially decreases and then increases thereafter. Beginning as a single-phase solid solution of Re and Mo, irradiation of Mo-41 wt% Re over a range of temperatures (470-730 °C) to 28-96 dpa produces a high density of thin platelets of a hexagonal close-packed (hcp) phase identified as a solid solution of Re, Os and possibly a small amount of Mo. These hcp precipitates are thought to form in the alloy matrix as a consequence of strong radiation-induced segregation to Frank loops. Grain boundaries also segregate Re to form the hcp phase, but the precipitates are much bigger and more equiaxed in shape. Although not formed at lower dose, continued irradiation at 730 °C leads to the co-formation of late-forming chi-phase, an equilibrium phase that then competes with the preexisting hcp phase for rhenium.     

Local mechanical properties of Alloy 82/182 dissimilar weld joint between SA508 Gr.1a and F316 SS at RT and 320 °C

The distributions of mechanical and microstructural properties were investigated for the dissimilar metal weld joints between SA508 Gr.1a ferritic steel and F316 austenitic stainless steel with Alloy 82/182 filler metal using small-size tensile specimens. The material properties varied significantly in different zones while those were relatively uniform within each material. In particular, significant gradient of the mechanical properties were observed near the both heat-affected zones (HAZs) of F316 SS and SA508 Gr.1a. Thus, the yield stress (YS) was under-matched with respect to the both HAZs, although, the YS of the weld metal was over-matched with respect to both base metals. The minimum ductility occurred in the HAZ of SA508 Gr.1a at both test temperatures. The plastic instability stress also varied considerably across the weld joints, with minimum values occurring in the SA508 Gr.1a base metal at RT and in the HAZ of F316 SS at 320 °C. The transmission electron micrographs showed that the strengthening in the HAZ of F316 SS was attributed to the strain hardening, induced by a strain mismatch between the weldment and the base metal, which was evidenced by high dislocation density in the HAZ of F316 SS.     

Determination of K shell absorption jump factors and jump ratios in the elements between Tm(Z = 69) and Os(Z = 76) by measuring K shell fluorescence parameters

The K shell absorption jump factors and jump ratios have been measured in the elements between Tm (Z = 69) and Os(Z = 76) without having any mass attenuation coefficient at the upper and lower energy branch of the K absorption edge. The jump factors and jump ratios for these elements have been determined by measuring K shell fluorescence parameters such as the total atomic absorption cross-sections, the K_α X-ray production cross-sections, the intensity ratio of the K_β and K_α X-rays and the K shell fluorescence yields. We have performed the measurements for the calculations of these values in attenuation and direct excitation experimental geometry. The K X-ray photons are excited in the target using 123.6 keV gamma-rays from a strong ⁵⁷Co source, and detected with an Ultra-LEGe solid state detector with a resolution 0.15 keV at 5.9 keV. The measured values have been compared with theoretical and others’ experimental values. The results have been plotted versus atomic number.     

Effect of ion irradiation and indentation depth on the kinetics of deformation during micro-indentation of Zr-2.5%Nb pressure tube material at 25 °C

Micro-indentation creep tests were performed at 25 °C on radial-normal samples cut from Zr-2.5Nb CANDU pressure tube material in both the as-fabricated condition and after irradiation with 8.5 MeV Zr⁺ ions. The average indentation stress, and hence the yield stress, was found to increase with decreasing indentation depth and with increasing levels of ion irradiation. The activation energy of the indentation creep rate and hence the, activation energy of the obstacles that limit the rate of dislocation glide, was independent of indentation depth but increased from ΔG₀ = 0.185 to 0.215 μb³ with increasing ion irradiation damage. The magnitude of the activation energy indicates that ion irradiation introduces a new type of obstacle into the microstructure which reduces the low temperature indentation creep rate of Zr-2.5Nb pressure tubes. This is supported by TEM images showing that Zr⁺ ion irradiation produces small, nanometer size, dislocation loops which act as obstacles to dislocation glide and thus influence both the yield stress and the activation energy of the low-temperature thermal creep of Zr-2.5Nb pressure tube material. These findings suggest that neutron irradiation will have similar effect upon yield stress and low-temperature thermal creep as the Zr⁺ ion irradiation since both create similar crystallographic defects in Zr-2.5Nb pressure tubes.     

Cross-section for D(p,p)D elastic scattering from 1.8 to 3.2 MeV at the laboratory angles of 155° and 165°

The D(p,p)D cross-sections for elastic scattering of proton on deuterium over incident proton energy range from 1.8 to 3.2 MeV at both laboratory angles of 155° and 165° were measured. A thin solid state target Ni/TiD_x/Ta/Al used for cross-section measurement was fabricated by firstly depositing layers of Ta, Ti and Ni film on the Al foil substrate of about 7 μm in turn using magnetron sputtering and then deuterating under the deuterium atmosphere. The areal density of metal element in each layer of film was measured with RBS analysis by using a 4.0 MeV ⁴He ion beam, while the areal density of the deuterium absorbed in the Ti film was measured with ERD analysis by using a 6.0 MeV ¹⁶O ion beam. The results show that the cross-sections of p-D scattering under this experimental circumstance were much enhanced over the Rutherford cross-section value. It was found that the enhancement increases linearly as the energy of the incident beam increases. The total uncertainty in the measurements was less than 7.5%.     

Differential cross-section measurements for the C(d, p0)C reaction and applications to surface analysis of materials

This work involves surface analysis by nuclear techniques, which are non-destructive, and computer simulation. The “energy analysis” method for nuclear reaction analysis is used. Energy spectra are computer simulated and compared to experimental data, giving target composition and concentration profile information. Measured values are presented for the differential cross-section of the ¹²C(d, p₀)¹³C reaction in the deuteron energy range 0.81-2.07 MeV for laboratory detection angles of 165° and 135°, using self-supported two-layered targets consisting of high purity thin films of typically 13 μg/cm² natural carbon and 65 μg/cm² gold. The error in the absolute differential cross-section values is generally ∼6%. The method, using these values, is successfully applied to determination of uniform concentration profiles of ¹²C, along considerable depths, for a thick flat target of high purity pyrolitic graphite. It is characterised a thin surface film of carbon on a thick flat quartz target. Uniform concentration profiles of ¹⁶O are also obtained from (d, p) and (d, α) reactions.