[en] Optimal etching parameters were determined on 304 stainless steel and U - 0.1 w/o Cr metallographic samples, by bombardment with argon ions, in a cathodic vacuum etcher

No abstract available

[en] Radiation effects in nuclear fuel elements were studied by fractography. Fuel elements were experimentally irradiated at various doses at the IRR-2. Irradiated, as well as unirradiated fuel elements, were bent till fracture with a bending press. The fractured surfaces were examined by standard replication techniques. The structures reveal the same morphological zones as in standard tensile fractures. The crack origin zone (fibrous zone) appears near the fuel indent. The radial marks zone starts near the origin and covers about 2/3 of the cross-sectional area. The third zone (shear rupture zone) has a bump, sometimes 1 cm high. The crack origin zone is mainly brittle. As the crack propagates in the radial marks zone it becomes more ductile until its entirely ductile at the bump top. Beyond the bump it turns brittle again. (author)

[en] The solidification of Al-U alloys at slow cooling rates was investigated using optical and scanning microscopy. Highly purity uranium (99.9%) and high purity aluminium (99.9%) or 'commercially pure' Al-A5 (Al-1050) alloy containing a maximum of 0.5% wt/o of other alloying elements were used to prepare Al-U alloys in a resistance furnace under controlled atmosphere. The observed eutectic composition for U-(Al-5) was 17±1 wt/o U, while that for U and pure Al was 19±1 wt/o U. These values are significantly different than the value of 13 wt/o U, reported in the literature. The eutectic morphology and its distribution depends on the type of the aluminium used in preparing the alloy. In both cases eutectic colonies were observed. In alloys prepared with pure Al, the eutectic colonies have a diameter less than 0.2 mm, display a lamellar morphology, and are homogenously distributed. In alloys prepared with Al-5, at list 4 different types of eutectic morphologies were observed. Some of the eutectic colonies have diameters as large as 2 to 3 mm. Some interesting nonequilibrium morphological features were observed in the specimen containing hypereutectic compositions. The above results are discussed on the basis of current solidification theories. (authors)

[en] The internal morphology of 0.3-mm-thick foils of tantalum, tantalum 10 w/o tungsten and tungsten is investigated by optical microscopy and a scanning electron microscope capable of microanalysis by EDAX. Comparison is made between foils: as-received, heat-treated at 1300⁰C for 20 hours (for tantalum also for 40 hours), and after reaction and immersion in liquid uranium for 20 hours at 1300⁰C. The heat treatment does not influence the internal morphology (grain size) in tantalum and tantalum - 10 w/o tungsten, and the multilayer structure of these foils following the immersion experiments is solely due to the effect of liquid uranium. This effect depends on prior annealing. In tungsten the heat treatment changes the dominant flow-line character of the foil into a grain structure, and the foil structure following the immersion experiment is due to the combined effect of heat-treatment and uranium penetration. (Author)

[en] Published in summary form only

[en] The diffusion of liquid uranium into solid foils, 0.3 mm thick, was investigated in the temperature range 1160-1350⁰C, for reaction times up to 20 h. The tantalum foils were immersed in liquid uranium contained in zirconia crucibles. Uranium was found to cover the tantalum foils and climb upwards in amounts rising with reaction time and temperature. A scanning electron microscope study with microanalysis by EDAX revealed a multilayer structure. On the tantalum-foil surfaces, exposed to liquid uranium, layers form progressively inwards, under the outer uranium layers, in the following sequence: a uranium-tantalum layer (with a U:Ta ratio between 40:60 and 60:40) forms at 1160 ⁰C and 1185 ⁰C, and disappears completely at 1255 ⁰C; a columnar tantalum layer (containing <1W/O U); an inner uranium layer (at 1210 ⁰C and above); an inner tantalum-grain layer with uranium along grain boundaries (above 1210 ⁰C). The growth of the recrystallized columnar tantalum layer is related to the penetration of uranium as liquid into the solid tantalum foil. Cracks in this layer at 1300 ⁰C and above cause tears and failures in the tantalum. (author)

[en] Immersion experiments have been performed to investigate the progressive dissolution of 0.3-mm-thick foils of molybdenum metal in liquid uranium at 1160⁰C, for immersion times of 3, 6, 10, and 60 min, and 20 h, in a zirconia crucible. The original foils, as-received and heat-treated at 1160⁰C, 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. (orig.)

[en] Short communication

[en] Immersion experiments have been performed to investigate the effect of liquid uranium on 0.3-mm-thick foils of tungsten metal in the temperature range of 1160 to 1350⁰C, for immersion times up to 20 h, in zirconia crucibles. The original and uranium-reacted foils have been studied microscopically (SEM-EDAX) and the internal morphology has been determined. The latter is affected by the heat-treatment and penetration of liquid uranium. The penetration is partial up to 1210⁰C, accompanied by a partial uranium-assisted recrystallization, forming two metallurgically-different regions, which on cooling result in the observed cracks due to inhomogeneous strain. The penetration of liquid uranium is complete at 1255⁰C and above, inducing recrystallization of tungsten grains throughout the foil, with larger, uranium-lined, grains in inner regions, and smaller, progressively-separated, tungsten grains in outer regions (with reduction in foil thickness). (orig.)