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[en] Work accomplished in support of nonweapons programs by LASL Group Q-14 is described. Included are efforts in basic critical measurements, nuclear criticality safety, a plasma core critical assembly, and reactivity coefficient measurements
[en] We consider the superconducting transition in fermionic quantum critical systems. Assuming the validity of Migdal theorem, the gap equation can be written in terms of the retarded pair susceptibility. Instead of the usual BCS form, the pair susceptibility is now subject to scale invariance. The gap and transition temperature is thus of the algebraic form, totally different from the exponential behavior in BCS theory. Consequently, with reasonably small glue strength, we can get very large gap and transition temperature comparable to those discovered in cuprates. The ratio of the gap to retardation gets boosted by increasing retardation. We also find the upper critical field has a different scaling with the critical temperature. With a non-Lorentzian dynamical exponent, the upper critical field is greatly enhanced when approaching the critical point, though the critical temperature only changes modestly, in agreement with recent experiments on heavy fermions.
[en] This article presents an extensive study of the calculations performed in the configuration where the criticality safety is achieved by both controlling the mass of fissile material and the moderation (for example water) of a single unit. This case often occurs when the control of the fissile mass alone is not sufficient to economically or practically operate a process. This method is often used for the fuel fabrication where an important quantity of powder need to be handled but may also be met in other nuclear facilities and transportation. In this context, from a calculation point of view, a homogeneous distribution of the moderation within the fissile material is generally not a penalizing configuration. So a heterogeneous repartition of the moderation is then considered: it currently consists in a given part of the fissile material uniformly moderated by the entire quantity of the moderator, this system being surrounded by the rest of the dry fissile material and eventually another reflector (water, concrete, lead, etc.). This paper will firstly briefly discuss how to calculate safety limits for this kind of configuration, in the past and nowadays, using state-of-the-art algorithms. Then, new results will be presented for this kind of configuration with various enrichments and densities. These calculations show that the penalizing configuration depends on the maximum dry density of the fissile material considered. The new results obtained with high maximum dry densities are more restrictive than those previously presented.
[en] Three-group diffusion theory has been applied to a computation of the 231Pa mass required to sustain a fast-neutron chain reaction. The method was tested by preliminary calculation of several 235U--238U systems and of a single 239Pu--238Pu system. The best agreement between predictions and measurements was found for high-enrichment 235U--238U systems. In the case of 231Pa, where many of the necessary data do not exist, use was made of the characteristics of 237Np as a substitute. The predicted critical radius for 231Pa is 22.67 +- 1.81 cm, and the corresponding critical mass is 750 +- 180 kg
[en] This paper presents the results of an analysis of both published and unpublished critical current data given as a function of both field and temperature. Simple formulas have been obtained for (1) the critical temperature as a function of field that is needed to obtain an estimate of the current sharing temperature and hence temperature margin, (2) the critical current density for constant temperature as a function of field, and (3) the critical current density for constant field as a function of temperature
[en] The preliminary results of development of a new heat transfer correlation for supercritical water flowing in vertical heated tubes have been reported. It has been shown through a comparison with experimental data that the suggested method of allowance for variations of water thermophysical properties near the critical point provides a satisfactory agreement of the predicted and experimental results
[ru]Подведены предварительные итоги исследования, основной целью которого является получение нового уравнения для инженерных расчетов теплоотдачи от поверхности обогреваемых вертикальных труб при движении в них воды сверхкритического давления. Путем сравнения с большим массивом экспериментальных данных показано, что предлагаемый метод учета сильного изменения теплофизических свойств теплоносителя вблизи критической точки обеспечивает удовлетворительное согласование расчетных и экспериментальных результатов
[en] We report our studies on the crystal structures, morphologies, and superconductivity in CeO1-xFxFeAs compounds which were fabricated by solid state reaction. The crystal structures were refined using Rietveld refinement. Superconducting properties such as critical temperature (Tc), critical current density (Jc), and upper critical field (Hc2) were determined using magneto-transport and magnetic measurement over a wide range of temperature below Tc, and in magnetic fields up to 13 T. Jc is 2 x 103 A cm-2 for the x = 0.1 sample. However, the Jc exhibited a weak dependence on magnetic field for B > 1 T and T = 5 and 10 K. A peak effect in the Jc as a function of field was observed at 20 K in the x = 0.1 sample. We estimate Hc2ab of 185 T for CeO0.9F0.1FeAs compound. The broadening of the superconducting transition near Tc with increasing field can be well understood using the thermal activated flux flow model. The pinning potential scales as U0/KB∝B-n with n = 0.2 for B < 3 T and n = 0.71 for B > 3 T in the x = 0.1 sample.