[en] Sintering studies of CeO₂ and CeO₂ + 2 wt. % Ga₂O₃ were completed. Firing temperatures studied were 1250-1650 C with 2 to 4 hour firing soak times in air. Powders fabricated by three methods (as-received, attrition-mill and nitrite-derived) were studied. Attrition-milled CeO₂ improved densities as compared with as-received CeO₂. Attrition-milled CeO₂ with 2 wt.% Ga₂O₃ showed decreased densities with increasing temperatures. As-received CeO₂ with 2 wt.% Ga₂O₃ showed a opposite trend, increasing in density with increased firing temperature. Two pellet preparation methods were studied, a one-step-press method and a two-step-press method. The two-step-press method showed greater densities at lower firing temperatures and times as compared with the one-step-press method, however for CeO₂ + 2 wt.% Ga₂O₃, the two methods gave equivalent results at 1650 C, 6 hr. firing conditions

[en] Inconel 600 will undergo stress corrosion cracking (SCC) at grain boundaries when subjected to a high stress and exposed to water without oxygen at high temperature. Very few service failures have occurred but extensive intergranular cracking has also occurred in plants that experienced denting. All of these cracks were from the primary side. The process of denting produced high strains and stresses in the tubing, as well as slow strain rates during deformation. The literature is silent on effects of slow strain rates or cyclic stresses on SCC of Inconel 600 in deaerated, high temperature aqueous media such as pure or primary water. Because of the importance of avoiding primary-to-secondary leaks through the Inconel 600 pressure boundary, a research program was started at BNL in an attempt to improve the qualitative and quantitative understanding of factors influencing SCC in deaerated high temperature aqueous media. These data also predict service performance under given sets of conditions. Preliminary results which indicate that intergranular SCC is produced quite readily in some heats of tubing when exposed at (a) constant deflection, (b) when slightly cold worked and subjected to straining at low rates, (c) when subjected to slow cyclic stress, or (d) when the electrochemical potential of stressed pieces is controlled. Cracking has now been produced in Inconel 600 under conditions that had not been examined and reported before. First trends of temperature dependence of SCC are discussed. Some tentative correlations are made with microstructural variables, although a simple relationship with such structure or prior processing has not been defined. Heating at 700⁰C for about 15 hours improved the SCC resistance dramatically. Future tests will include primary and secondary water ingredients and some impurities

No abstract available

[en] Absolute differential cross sections (DCSs) for elastic electron scattering from water vapor are reported at four incident electron energies between 4 and 50 eV and over scattering angles of 10-180 deg. measured with a crossed beam electron spectrometer. A magnetic angle-changing device based on the suggestion of Read and co-workers has been used to extend the measurements to backward angles (125-180 deg. ). The elastic integral and the momentum transfer cross sections are derived from these elastic DCSs

[en] Currently, there is interest in fissioning weapons-grade plutonium in nuclear reactors, making use of its valuable energy while at the same time reducing certain dangers associated with its potential for nuclear weapons proliferation. In the process of dismantling nuclear weapons, the US intends to convert much of the Pu metal to oxide. This process yields a PuO_2-x powder that potentially can be incorporated into mixed oxide nuclear fuel (MOX), a mixture of PuO₂ and UO₂. This paper describes the process of gallium removal from Ga₂O₃-doped CeO_2-x, a surrogate for weapons-grade PuO_2-x. Gallium is removed from the surrogate feedstock material using thermal techniques. An Ar-6% H₂ gas was used in order to reduce the oxide to gaseous Ga₂O. Experimental results were shown in the temperature range of 600 C to 1,200 C as a function of time and sample geometry. The results to date have shown that CeO_2-x is a very good surrogate for PuO_2-x

[en] The oxidation behavior of titanium-tantalum alloys was investigated with respective concentrations of each element ranging from 0 to 100 wt.%. Alloys were exposed to argon-20% oxygen at 800 to 1400 C. The slowest oxidation rates were observed in alloys with 5--20% Ta. The oxidation kinetics of alloys containing less than approximately 40% Ta were approximately parabolic. Pure Ta exhibited nearly linear kinetics. Alloys containing 50% or more Ta exhibited paralinear kinetics. The activation energies for oxidation ranged between 232 kJ/mole for pure Ti and 119 kJ/mole for pure Ta, with the activation energies of the alloys falling between these values and generally decreasing with increasing Ta content. The activation energies for oxidation of the end members, Ti and Ta, agree well with published values for the activation energies for diffusion of oxygen in α-Ti and Ta. Scale formation in the alloys was found to be complex exhibiting various layers of Ti-, Ta-, and TiTa-oxides. The outermost layer of the oxidized alloys was predominantly rutile (TiO₂). Beneath the TiO₂ grew a variety of other oxides with the Ta content generally increasing with proximity to the metal-oxide interface. It was found that the most oxidation-resistant alloys had compositions falling between Ti-5Ta and Ti-15Ta. Although Ta stabilizes the β-phase of Ti, the kinetics of oxidation appeared to be rate limited by oxygen transport through the oxygen-stabilized α-phase. However, the kinetics are complicated by the formation of a complex oxide, which cracks periodically. Tantalum appears to increase the compositional range of oxygen-stabilized α-phase and reduces both the solubility of oxygen and diffusivity of Ti in the α- and β-phases

[en] A simulator platform for visualization and demonstration of innovative concepts in fast reactor technology is described. The objective is to make more accessible the workings of fast reactor technology innovations and to do so in a human factors environment that uses state-of-the art visualization technologies. In this work the computer codes in use at Argonne National Laboratory (ANL) for the design of fast reactor systems are being integrated to run on this platform. This includes linking reactor systems codes with mechanical structures codes and using advanced graphics to depict the thermo-hydraulic-structure interactions that give rise to an inherently safe response to upsets. It also includes visualization of mechanical systems operation including advanced concepts that make use of robotics for operations, in-service inspection, and maintenance.

No abstract available

[en] Photoluminescence measurements at 4.2 degreeK were used to study the emission behavior and the annealing characteristics in Mg-ion-implanted layers in GaAs. Radiative recombination due to the donor-acceptor pairs and free electrons with holes bound to acceptors involving Mg was observed. The ionization of Mg is esti mated to be 28 +- 2 meV. The donor-acceptor pair band shows a large energy shift with the change of the excitation intensity. Annealing at the temperatures 750--900 degreeC sufficient to optically activate Mg ions implanted and to recover from lattice damages

[en] Photoluminescence emission characteristics from Mg-implanted GaAs are presented for the temperature range T=4.2--293 degreeK. The emission due to recombination of free electrons with holes bound to neutral Mg acceptors is a dominant radiative process in heavily implanted samples at temperatures Tapproximately-less-than210 degreeK. Changes in the emission energies and intensities as a function of temperature lead to the determination of the binding energy of Mg as 28 +- 2 meV. The donor-acceptor pair band involving Mg, which has a large energy shift with the change of excitation intensity, shows the lower-energy shift with an increase of temperature in the range T=4.2--50 degreeK. This is explained by associating deeper donor states than the hydrogenic donors to the donor-acceptor pair band. Depth dependence of the donor-acceptor pair and the free-electrons to the neutral Mg acceptor bands show a deep penetration of Mg acceptors