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[en] Potential-pH diagrams, which present the regions of stability of metallic species with water, are generally known as Pourbaix diagrams. They are especially useful to corrosion scientists because the diagrams indicate the areas of potential and pH in which oxides of the metal are stable and thus the regions in which an oxide corrosion layer can form on the metal, protecting it from corrosion. Potential-pH diagrams are generally available for the metallic elements, even at high temperature (up to about 600 K). But rarely is a pure metal used as a construction material. Stainless steel, which is an alloy of iron, chromium, and nickel plus some trace elements, is often used as a construction material for water systems because of its good corrosion resistance. The oxides in equilibrium with the water-Fe-Cr-Ni sytem are generally mixed metal oxides. In this paper, Pourbaix diagrams for this system are calculated from thermodynamic values at room temperature and at typical LWR (light water reactor) temperature. Diagrams for the ancilliary systems Fe-Cr-water, Fe-Ni-water and Cr-Ni-water are also given. (orig.)
[en] The hydrogen solubility in isotropic graphites ISO 880U and EK 98 has been measured in the temperature range of 700-1000 C at pressures below 2x104 Pa. The solubility data obtained closely obeyed Sieverts' law. The hydrogen solubility and the enthalpy of solution for ISO 880U and EK 98 graphites were compared with those for isotropic graphites IG 110U and POCO AXF-5Q. The hydrogen solubility in a highly oriented pyrolytic graphite PGCCL has also been measured at 1000 C. It was an order of magnitude lower than that in isotropic graphites. Partial thermodynamic functions of hydrogen in isotropic graphites were obtained by a dilute solution model and discussed. (orig.)
[en] The paper is focused on the development and the qualification of the instrumentation suitable for the level and the differential pressure measurements in the experimental facility CIRCE. This large-scale facility is installed at the ENEA Brasimone Centre for studying the fluid-dynamic and operating behavior of ADS reactor plants. This a rather challenging objective since the facility adopts the molten lead bismuth eutectic (LBE) alloy as a coolant and, at present, instrumentation qualified for operating under such conditions is scarce or does not exist. Bubble tubes have been installed in CIRCE to transfer pressure signals from the LBE to differential pressure cells operating with gas at room temperature. The bubble tube is a simple measuring device, but its use in LBE must be carefully assessed. Therefore, preliminary tests of bubble tubes in representative conditions have been carried out in a smaller test section. Experimental tests were performed at several temperatures, with LBE in stagnant conditions. The results obtained in these tests, aiming at checking the performance of the bubble tubes adopted in measuring pressure, differential pressure and level in the CIRCE facility, are discussed here. The obtained information will allow to calibrate the related measuring systems and to verify the accuracy and repeatability of the measurements, as a function of the injected gas flow rate, the tube diameter and the geometry of the tube exit section
[en] The trapping of energetic deuterium codeposited with beryllium, carbon and tungsten has been measured on a silicon collector probe at room temperature. The subsequent release of the trapped deuterium at elevated temperatures was determined by thermal desorption spectroscopy. At room temperature, deuterium codeposits both with carbon and BeO with a ration of 0.41 D-atoms/C-atom and 0.38 D-atoms/BeO, respectively. No codeposition of deuterium with tungsten is observed. The thermal release of codeposited hydrogen from BeO begins at 400 K. All hydrogen is released at temperatures above 800 K. (orig.)
[en] A non-stationary model has been developed to determine the hydrogen diffusivity (D) and Sieverts' constant (Ks) in carbon fibres composites (CFC), from isovolumetric desorption experiments using short loading times. For homogeneous materials such as nickel the model predictions and the experimental results are in good agreement. Assuming the CFC as homogeneous specimen, apparent values of D and K, for two types of CFC (NB11 and N11(SEP)) were obtained. The model was successfully refined in order to account for CFC non-homogeneity. The determinant role of the fibre on the total Ks of hydrogen in CFC and the role of the porosity on the hydrogen D and Ks in matrix is explicitly illustrated. The model capabilities suggest its use as a tool for the design of CFC from the point of view of their hydrogen transport properties. (orig.)
[en] Kinetics of the oxygen-to-metal ratio change in (U0.8Pu0.2)O2-x and (U0.7Pu0.3)O2-x was evaluated in the temperature range of 1523-1623 K using a thermo-gravimetric technique. The oxygen chemical diffusion coefficients were decided as a function of temperature from the kinetics of the reduction process under a hypo-stoichiometric composition. The diffusion coefficient of (U0.7Pu0.3)O2-x was smaller than that of (U0.8Pu0.2)O2-x. No strong dependence was observed for the diffusion coefficient on the O/M variation of samples.
[en] The thermodynamic activities of Fe in the U-Fe system for xFe = 0.05 to 0.90 in the 1440 K to 1850 K temperature range, and of Ga in the U-Ga system for xGa = 0.05 to 0.28 between 1100 and 1670 K are investigated by the multiple Knudsen cell-mass spectrometric method. The integration of the Gibbs-Duhem equation then yields the uranium activity. These systems are found to exhibit negative deviations from the ideal behavior. Polynominal fits of the relative partial molar excess Gibbs energy referred to liquid elements versus composition and temperature are deduced (in J mol-1), Δanti GxsFe/(1 - xFe)2 = ( - 187 200 + 92.646T) + (203 834 - 184.437T)(1 - xFe) + ( - 15 614 + 75.289T)(1 - xFe)2, Δanti GxsGa/(1 - xGa)2 = ( - 284 769 + 133.390T) + (242 863 - 110.390T)(1 - xGa), and compared to previous ones. We have measured the Gibbs energies of formation of the following intermetallic compounds: UFe2 (ΔG0f = - 52.8 ± 3.4 kJ mol-1 at 1501 K), U6Fe (ΔG0f = -31 ± 6 kJ mol-1 at 998 K) and U2Ga3 (ΔG0f = 111.9 ± 3.9 kJ mol-1 at 1250 K). Our values for UFe2 and U6Fe are in good agreement with previous data. Concerning the U-Ga system, our measurements suggest a large solubility of gallium in uranium. (orig.)
[en] In-situ strain neutron diffraction measurements were conducted at temperature on specimens coming from a clock-rolled α-uranium plate, and Elasto-Plastic Self-Consistent (EPSC) modeling was employed to interpret the findings. The modeling revealed that the active slip systems exhibit a thermally activated response, while deformation twinning remains athermal over the temperature ranges explored (25–150 °C). The modeling also allowed assessment of the effects of thermal residual stresses on the mechanical response during compression. These results are consistent with those from a prior study of room-temperature deformation, indicating that the thermal residual stresses strongly influence the internal strain evolution of grain families, as monitored with neutron diffraction, even though accounting for these residual stresses has little effect on the macroscopic flow curve, except in the elasto-plastic transition.
[en] Reaction diffusion in the zirconium-iron system has been investigated in the temperature range 973 to 1213 K using diffusion couples of pure zirconium and pure iron. Electron microprobe analysis and metallographic techniques have been employed to investigate the formation of compounds in the diffusion zone. The Boltzmann-Matano-Heumann method and Wagner's method have been used to evaluate the interdiffusion coefficients. The temperature dependence of this diffusion coefficient has been established. The activation energy for interdiffusion in FeZr3 compound is found to be 120.0 kJ/mol. The formation of compounds and their stability in the diffusion zone have been discussed on the basis of existing thermodynamic and other physical properties. (orig.)
[en] The mechanical properties of a lead-bismuth alloy were studied by compression testing at different temperatures between 20 and 112 deg. C with strain rates from 10-3 to 10-6/s. The results indicate that the yield strength depends strongly on both temperature and strain rate. The yield stress is linearly proportional to the logarithms of strain rate at constant temperature. The yield stress can be fit with a second order polynomial of temperature at constant strain rate. With these fittings the yield stress can be fairly estimated for any temperature and strain rate in the present temperature and strain rate ranges