Thermodynamic properties of nonstoichiometric urania-gadolinia solid solutions in the temperature range 700–1100° C

Partial molar thermodynamic quantities for urania-gadolinia solid solutions of compositions U_1−yGd_yO_2+x, with y values of 0.04 to 0.27, have been obtained using a solid electrolyte galvanic cell technique. The measurements were made for O/M ratios ranging from near stoichiometry to 2.20, and for temperatures ranging from 700 to 1100°C. The results for pure UO_2+x are in accordance with data reported earlier. The oxygen potentials for U_1−yGd_yO_2+x are higher than for pure UO_2+x and increase positively with increasing Gd content or excess oxygen. They can be represented as a function of the mean U valence, except at the stoichiometric composition. Both the partial molar entropy and enthalpy increase negatively with increasing Gd content or excess oxygen.     

An X-ray structural analysis of cesium substitution in the barium hollandite phase of synroc

The X-ray structures of polycrystalline barium hollandite with cesium partially substituting for barium (viz [Ba_xCs_y] [Al_2x+yTi_{8 ? 2x ? y}]O₁₆) have been determined using the Rietveld refinement technique. Electron microprobe results indicate that the level of cesium substitution is constrained by the condition that the total volume occupied per unit cell by the cesium and barium ions remains substantially constant. X-ray refinement revealed that the structural parameters defining the positions of the titanium, aluminium and oxygen ions are not affected greatly by cesium substitution. The only significant change occurs in the parameter z which defines the average Cs/Ba position. This increases with the level of cesium indicating that these ions tend to occupy a more central location with respect to their coordinating oxygen ions. An analysis of the (Cs/Ba)-O bond lengths suggests a limit of structural stability corresponding to 0.25 cesium ions per unit cell.     

Neutron cross-sections of Pu in the energy range 5–20 MeV

The evaluation of neutron cross sections and angular distributions of ²⁴²Pu in the energy range 5–20 MeV was performed using the direct interaction treatment by coupled channel method and the compound nucleus mechanism (statistical model) taking account of pre-equilibrium effects. The calculated cross-sections are in very good agreement with the existing experimental data (total and fission cross-sections). More accurate theoretical data have been obtained by the extension of procedures and parameterizations (previously used only for the main compound nucleus) in the incident neutron energy range where more compound nuclei are involved.     

The creep rupture properties of beta-phase Zircaloy-2 cladding in the region 1000–1500°C

Accurate creep parameters are essential for the prediction and assessment of fuel cladding behaviour under reactor accident conditions. To resolve uncertainties in the limited data available for beta-phase Zircaloy cladding, an extensive programme of isothermal stress rupture tests has been undertaken for Zircaloy-2 tubes in a non-oxidizing environment at temperatures from 1000 to 1500°C. The secondary creep parameters are calculated from an analysis of the strain histories obtained from each test using a novel photo-electronic technique for the continuous monitoring of tube deformation. The resulting creep equation is compared with recent rupture life data for Zircaloy tubes. The analysis also identifies an anomalous primary stage which significantly retards the early stage of deformation for low stress tests at 1200°C and above and which is found to be extremely sensitive to prior annealing. The influence of this primary component on predictions of cladding behaviour is assessed.     

Measurement of (p,p) elastic differential cross-sections for carbon, nitrogen, oxygen, aluminium and silicon in the 500–2500 keV range at 140° and 178° laboratory scattering angles

We measured the (p,p) elastic scattering cross-sections of natural samples of carbon, nitrogen, oxygen, aluminium and silicon at energies ranging between 500 and 2500 keV and at laboratory scattering angles of 178° and 140°. Results are compared with previous literature data and simulations and are presented in graphical form. The measured cross-sections have been used to simulate spectra taken from know samples and have been found appropriate for quantitative calculations.     

The crystal structure of oxides grown on Zr–20Nb alloy

Oxides that were grown on Zr–20Nb in water at 300°C for 3 d, or in air at 400°C for 2 h were characterized by analytical electron microscopy. In both oxides, a similar microstructure was observed and similar electron diffraction patterns and high resolution lattice images were obtained. Analyses of the results showed that the crystal structure of the oxides was identical to that of an incommensurate modulated Nb₂Zr_x−2O_2x+1 phase, with x ≈ 10.     

Flow behaviour of autoclaved, 20% cold worked, Zr-2.5Nb alloy pressure tube material in the temperature range of room temperature to 800 °C

Pressure tube material of Indian Heavy Water Reactors is 20% cold-worked and stress relieved Zr-2.5Nb alloy. Inherent variability in the process parameters during the fabrication stages of pressure tube and also along the length of component have their effect on micro-structural and texture properties of the material, which in turn affect its strength parameters (yield strength and ultimate tensile strength) and flow characteristics. Data of tensile tests carried out in the temperature range from room temperature to 800 °C using the samples taken out from a single pressure tube have been used to develop correlations for characterizing the strength parameters’ variation as a function of axial location along length of the tube and the test temperature. Applicability of Ramberg-Osgood, Holloman and Voce’s correlations for defining the post yield behaviour of the material has been investigated. Effect of strain rate change on the deformation behaviour has also been studied.     

Preliminary operating experiences with the AVR at an average hot-gas temperature of 950°C

The two-loop system with a high temperature reactor, which is operated by the Arbeitsgemeinschaft Versuchsreaktor (AVR) GmbH and which was built by the BBC/Krupp consortium (today HRB), has been in operation for more than seven years. In that time more than 635 × 10⁶ kWhr have been produced and more than 6.5 × 10⁵ spherical fuel elements have been circulated under operation. The fully integrated design, and above all the ceramic gas duct, permit very high gas temperatures although no high alloyed, heat resistant steels were used in the reactor. In February 1974 the average hot-gas temperature at the outlet of the core could thus be increased from its original design value of 850°C to 950°C. Peak temperatures of above 500°C are thereby confined to a small region between the middle of the core and the beginning of the steam generator. Carbon protects the steel structures against high temperatures. Unplanned interruptions and reductions of operation due to the increase of the hot-gas temperature have not occurred so far. Some thermocouples in the hot-gas region failed. All other components functioned satisfactorily and, one year after the increase in the hot-gas temperature, there are no misgivings as to their future functioning. These satis-factory but short operating experiences at 950°C will have to be supplemented in the next few years by experiences over a longer period.     

Statistical model for the random cyclic strain–life relations of 1Cr18Ni9Ti pipe-weld metal under temperature of 240°C

Modeling of random cyclic strain–life (CSL) relations of engineering material should be a basis of strain-based fatigue reliability analysis. A statistical model for the relations of a nuclear engineering material, 1Cr18Ni9Ti stainless steel pipe-weld metal under temperature of 240°C, is presented. In the model, a verified distribution, i.e. lognormal distribution, is used as an appropriate assumed distribution of the material fatigue life data. Based on the Coffin–Manson law, the relations are modeled by mean value- and standard deviation-cyclic curves of the logarithm of fatigue life. Then, fatigue analysis at an arbitrarily given probability can be made conveniently according to the normal distribution function. An approach for estimating the curves and their confidence bounds is developed by a linear regression technique. Different from the existent reliability analysis methods that considered the material constants in the law as independently random variables, present work treats them as dependently random variables from the fit of test data. Availability of the model has been indicated by an analysis of the material test data.     

Use of the α → β quartz transition to monitor the temperature increase produced by a proton microbeam

Ion microbeams induce in certain cases local heating of a sample under investigation, especially in insulators. To obtain experimental values of this temperature increase, we used a quartz sample which presents its own internal thermometer with the α → β transition observed at 573°C. At this temperature, the transition is easily observed from the rapid variation of the bubble size contained in a melted inclusion trapped in the quartz. We measured the temperature increase produced by a 3 MeV proton microbeam. For this purpose, the nuclear microprobe chamber was equipped with a sample heating stage. The decrease of the power injected by the heater element (beam on) required to observe the transition has been interpreted as a local increase of the temperature under microbeam exposure.     

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.     

Effective atomic numbers for photon energy absorption of essential amino acids in the energy range 1 keV to 20 MeV

Effective atomic numbers for photon energy-absorption (Z_PEAeff) of essential amino acids histidine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine have been calculated by a direct method in the energy region of 1 keV to 20 MeV. The Z_PEAeff values have been found to change with energy and composition of the amino acids. The variations of mass energy-absorption coefficient, effective atomic number for photon interaction (Z_PIeff) and Z_PEAeff with energy are shown graphically. Significant differences exist between Z_PIeff and the Z_PEAeff in the energy region of 8-100 keV for histidine and threonine; 6-100 keV for leucine, lysine, tryptophan, phenylalanine and valine; 15-400 keV for methionine. The effect of absorption edge on effective atomic numbers and the possibility of defining two set values of these parameters at the K-absorption edge of high-Z element present in the amino acids are discussed. The reasons for using Z_PEAeff rather than the commonly used Z_PIeff in medical radiation dosimetry for the calculation of absorbed dose in radiation therapy are also discussed.     

The microstructure evolution of type 17-4PH stainless steel during long-term aging at 350 °C

The microstructure evolution of 17-4 precipitation hardening (17-4PH) stainless steel during long-term aging at 350 °C was studied mainly by X-ray diffraction and transmission electron microscopy. The results showed that the matrix is lath martensite and the precipitation of nano-metric particles of -Cu phase after the alloy has been subjected to solution and temper treatment. When the alloy is aged at 350 °C to 9 months, some reversed austenite is formed and the -Cu precipitates are coarsening according to ripening process. When the alloy aged from 9 to 12 months, some bulk secondary carbides, M₂₃C₆, are precipitated. With the age time extended to 15 months, an amount of reversed austenite is transformed and the G-phase, a kind of intermetallic compound, precipitation occurs nearby the -Cu precipitates in the matrix at this intermediate temperature.     

Emissivity of zirconium alloys in air in the temperature range 100–400°c

A technique is described for measuring the emissivity of materials in air. This technique was used to determine both the normal total emissivity ($\text{?}{}_{\mathrm{nt}}$) and the total hemispherical emissivity ($\text{?}{}_{\mathrm{ht}}$) of both unoxidized and oxidized samples of Zircaloy-2, Zr/2.5wt.% Nb and other zirconium alloys in the temperature range 100–400°C. Temperature had a negligible effect on the values obtained. However, $\text{?}{}_{\mathrm{nt}}$ values increased from $\text{0.158 ± 0.025}$ for the range of unoxidized zirconium alloys examined to $\text{0.6 ± 0.08}$ for the alloys when they were oxidized to have a $\text{2.0 × 10}{}^{\mathrm{?6}}\text{m}$ thick oxide.     

JR curves of the low alloy steel 20 MnMoNi 5 5 with two different sulphur contents in oxygen-containing high temperature water at 240°C

J_R curves of the low alloy steel 20 MnMoNi 5 5 with two different sulphur contents (0.003 and 0.011 wt.%) were determined at 240°C in oxygen-containing high temperature water as well as in air. The tests were performed by the single-specimen unloading compliance technique at load line displacement rates from 1 × 10⁻⁴ down to 1 × 10⁻⁶ mm s⁻¹ on 20% side-grooved 2T CT specimens in an autoclave testing facility at an oxygen content of 8 ppm and a pressure of 7 MPa under quasi-stagnant flow conditions.In the case of testing in high temperature water, remarkably lower J_R curves than in air at the same load line displacement rate (1 × 10⁻⁴ mm s⁻¹) were obtained. A decrease in the load line displacement rate as well as an increase in the sulphur content of the steel caused a reduction of the J_R curves. At the fastest load line displacement rate a stretch zone could be detected fractographically on the specimens tested in air and in high temperature water and consequently J_i could be determined. When testing in high temperature water, the J_i value of the higher sulphur material type decreases from 45 N mm⁻¹ in air to 3 N mm⁻¹, much more than that of the optimized material type from 51 N mm⁻¹ in air to 20 N mm⁻¹ at 1 × 10⁻⁴ mm s⁻¹.     

Investigation of the impurities and fission products in the AVR coolant gas at an average hot-gas temperature of 950°C

Since 27 February, 1974, the AVR pebble bed reactor has been producing gas at an average temperature of 950°C. Therefore it is possible for the first time to gain experience in high temperature reactor operations and experiments with such a high temperature level. This is of particular interest with regard to efforts using high temperature reactors for production of nuclear process heat. This paper reports briefly on the preparations for a temperature increase and on the first experimental results obtained with a hot-gas temperature of 950°C. Measured data are given on the behaviour of inactive gaseous impurities, on the increase of fission gas activities, and on the increase of concentrations of solid fission products in the helium coolant gas. While the activities of the fission gases showed an insignificant increase in the coolant gas, considerable increase of activity was measured for solid fission products, especially for Ag isotopes. However, activities released from fuel elements are low so that there are no operational or safety problems.     

Growth of amorphous carbon films by carbon atom bombardment in the energy range 10–500 eV

Molecular dynamics (MD) simulations were carried out of the energetic impact of C atoms on amorphous carbon (a-C) substrates in the energy range 10–500 eV. The results show that a densification of the deposited material occurs up to 150 eV energy but with a low sp³ bond content. At 500 eV impact the substrate material shows a significant decrease in density and a porous a-C structure forms.