[en] Complete sets of microstructural data have recently become available for two different irradiation times and for pure ternary alloys of austenitic stainless steels. Using these data as input to the classical rate theory of void swelling, swelling rates are computed and compared with the experimental data. Computations are performed for the ranges of physical parameters as suggested by experimental measurements or basic theory. It is found that classical rate theory predicts swelling rates in remarkably good agreement with the data for a limited set of parameter values. For example, dislocation bias factor ratios can be narrowed from the initial range of 1.1-2.0 down to the range of 1.25-1.55. An explanation is provided for the success of classical rate theory in spite of the fact that a significant fraction of interstitials form and migrate as clusters

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[en] Effects of dose rate on microstructural evolution in a simple model austenitic ternary alloy are examined. Annealed specimens are irradiated with fast neutrons at several positions in the core and above core in FFTF/MOTA between 390 deg. C and 435 deg. C in a wide range of doses and dose rates. In Fe-15Cr-16Ni, swelling seems to increase linearly with dose without incubation dose. Cavities are observed even in the specimens irradiated to 0.07 dpa at 1.9x10^-9 dpa/s. Both cavity nucleation and growth are enhanced by low dose rates. These are mainly caused by accelerated formation of dislocation loops at lower dose rates. Low dose rates enhance swelling by shortening incubation dose for the onset of steady-state swelling. In the specimens irradiated at higher dose rates to higher doses, high density of dislocation increases average cavity diameter, however decreases cavity density

[en] Fe-15Cr-16Ni, -0.25Ti, -500appmB, and -0.25Ti-500appmB have been irradiated in FFTF/MOTA over a wide range of dose rate which covers more than two orders difference in magnitude, within the very limited temperature range of 387-444 C. The effects of dose rate and boron addition on swelling are examined. Lower dose rates increase the swelling by shortening the incubation dose for swelling. Addition of boron does not significantly change the swelling nor the dose rate dependence of swelling for both the ternary and Ti-modified alloy. The helium pressure of cavities is found to be much smaller than the surface tension at every irradiation condition including the lowest dose and dose rate, helium generated by boron transmutant does not play any role in cavity formation in this experiment. Cavities form without helium. The difference in cavity morphology by boron addition is most likely caused by formation of borides and by lithium

[en] Model austenitic steels based on Fe-15Cr-16Ni with additions of 0.25Ti, 500 appm B, or 0.25Ti-500 appm B were irradiated in FFTF/MOTA over a wide range of dose rates at ∼400 deg. C. In addition to the effect of dose rate on swelling, it was desired to study the effect of boron addition to produce variations in He/dpa ratio. A strong effect of dose rate was observed, so strong that the relatively small distances separating the boron-free and doped alloys introduced a complication into the experiment. For specimens irradiated within the core, boron addition had no significant effect. For irradiations conducted near or outside the core edge, swelling appeared to be either enhanced or decreased by boron. The variability was a consequence of a strong dose rate effect overwhelming the influence of boron and helium. It is shown that helium exerted little influence relative to other important factors in these alloys

[en] The effect of dose rate on neutron-induced microstructural evolution was experimentally estimated. Solution-annealed austenitic model alloys were irradiated at ≅400 deg. C with fast neutrons at seven different dose rates that vary more than two orders difference in magnitude, and two different doses were achieved at each dose rate. Both cavity nucleation and growth were found to be enhanced at lower dose rate. The net vacancy flux is calculated from the growth rate of cavities that had already nucleated during the first cycle of irradiation and grown during the second cycle. The net vacancy flux was found to be proportional to (dpa/s)^1/2 up to 28.8 dpa and 8.4x10^-7 dpa/s. This implies that mutual recombination dominates point defect annihilation in this experiment, even though point defect sinks such as cavities and dislocations were well developed. Thus, mutual recombination is thought to be the primary origin of the effect of dose rate on microstructural evolution

[en] We have constructed a microprotrusion fabrication system consisting of a differentially pumped ion gun and a seed material supply source, both of which operate under an UHV condition. Using this system, Si (1 0 0) surfaces were bombarded by obliquely incident 3 keV Ar⁺ ions at room temperature with and without a simultaneous supply of Mo atoms. The sputtered surfaces without a Mo supply were flat or characterized by a nano-sized rippled structure, whereas those with simultaneous Mo seeding displayed densely distributed Mo-seeded cones. For a very low seeding rate of ∼7.2 x 10^-2 nm/min, the optimum sputtering rate needed to induce seed cone growth over a sputtered crater was determined to be 4.4 nm/min. The size and number density of cones thus grown at the crater center were estimated to be 65-230 nm in width and ∼3 x 10⁷ mm^-2, respectively. The controlled fabrication of such seed cones may be applicable to the development of electron sources whose basic operational mechanism is field-electron emission

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No abstract available

[en] Since 1988, the Japan Atomic Energy Agency has been developing mixed plutonium-uranium oxide (MOX) fuel fabrication technologies at the Plutonium Fuel Production Facility (PFPF) to provide fuel on a large-scale for the experimental fast reactor JOYO and the prototype fast reactor MONJU and it has been fabricating MOX fuel assemblies for these reactors, too. Low-density pellets were adopted as the MONJU fuel. For the low-density pellet fabrication on a large-scale, various challenges were encountered such as thermal degradation of additives and inhomogeneous dispersion of pore-former in MOX granules. In order to resolve these challenges, countermeasures were considered such as using a new pore-former with a high softening temperature and using an improved granulation method for MOX powder. Also, test using the new pelletizing method (die wall lubrication pelletizing) for low-decontaminated TRU fuel fabrication was carried out at the PFPF. No large pores and no cracks in the obtained sintered pellets were observed. Finally, the standard deviation of pellet density in the test was comparable with that in past fabrications of JOYO pellets. (author)