Physics of Atomic Nuclei最新文献

The paper presents the neutronic justification of replacement of the burnup gadolinium absorber placed in a small number of fuel elements by erbium placed in all fuel elements of the fuel assembly. A scheme of placement of fuel elements is chosen for the gadolinium absorber that models their real arrangement in fuel assemblies with maximum concentration of gadolinium in fuel elements (8%). In the selected scheme, the center fuel element is symmetrically surrounded by two rows of fuel elements with the total number of fuel elements of 18. When selecting the weight content of erbium in fuel elements, not only is the total compensated reactivity reserve for the campaign taken into account but also intrinsic safety properties such as the density and total temperature coefficients of reactivity of the fuel loading with respect to the coolant, which allows reducing the negative influence of erbium on the burnup of unloaded fuel. In addition, the homogeneous arrangement of erbium in fuel elements leads to a uniform distribution of energy release in comparison with the gadolinium absorber. The comparative analysis of neutronic characteristics of the reactor is carried out for the considered absorbers on unit cells and polycells taking into account simplified burnup models at partial reloads without rearrangements of fuel assemblies. Repetitive structures consisting of three fuel assemblies with different irradiation durations are formed under the condition of application of threefold partial fuel reloading in the core. The results obtained clearly demonstrate that the reactivity coefficients for the erbium absorber have higher values than for the gadolinium variant under the condition of equal compensation of excess reactivity. Taking this factor into account, it is possible to select such a weight content of erbium in fuel elements when losses in burnup will be insignificant.

The dynamics of nonlinear cylindrical Langmuir waves in an isothermal plasma, where ions form a stationary background, has been studied within the framework of hydrodynamic description. The problem has been considered in the electrostatic formulation for two-dimensional geometry. A system of differential equations describing the dynamics of electrons with finite temperature has been obtained using a partial, exact solution for the equations of hydrodynamics. In calculations, a concave temperature profile parabolic over radius associated with an electron density changing only in time has been used. In this model, the influence of initial conditions and thermal effects on the regular dynamics of excited waves and the development of hydrodynamic singularities in the electron beam have been discussed. Estimates that specify the permissible range of plasma parameters, at which either regular wave behavior is realized or the electron wave breaks down, have been obtained. It has been shown that the development of singular behavior due to the intrinsic nonlinearity can be avoided by taking into account the thermal effects and the initial rotation of the electron beam. These results may be useful for establishing the mechanisms of nonequilibrium energy/momentum transfer in plasma media with finite electron and ion temperatures. Estimations specifying the admissible range of plasma parameters have been derived.

The aim of the proposed work is to determine the relationship between the Nuclotron and the NICA collider, as well as to modify the magneto-optical structure of the Nuclotron to create a synchrotron with two functions in one accelerator: a booster of polarized proton and deuteron beams for injection into the collider and an independent synchrotron-storage ring for conducting precision experiments on the study of the EDM of light nuclei and the search for an axion.

This paper presents a comparative analysis of results of computational studies of thermodynamics of austenitic ChS68-ID and ferritic-martensitic EP823-Sh steels during their interaction with carbon and oxygen. Particular attention is paid to the behavior of unbound chromium depending on the content of oxygen and carbon impurities, since it is unbound chromium that is apparently the main protector of intergranular corrosion. According to the results obtained, EP823-Sh ferritic-martensitic steel appears to be significantly less sensitive to the introduction of carbon impurities into fuel compared to ChS68-ID austenitic steel. A possible reason for the relative stabilization of the unbound Cr concentration in the EP823-Sh steel cladding is the redistribution of carbon between chromium and silicon. It was found that the influence of oxygen on the unbound chromium content in the “EP823-Sh steel cladding + fuel” and “EP823-Sh steel cladding + oxygen” systems differs significantly. According to the calculations, owing to the oxidation of chromium silicide in the “EP823-Sh steel cladding + oxygen” system, a lot of unbound Cr is formed, and oxygen combines with silicon. In the “EP823-Sh steel cladding + fuel” system, the oxygen combines with fuel components and Cr is not released in the cladding.

The article presents the results of an analysis and generalization of Russian and foreign experimental programs for the study of the flammability limits in hydrogen-containing mixtures as applied to hydrogen issues at nuclear power plants (NPPs) with VVER during severe accidents. On the basis of the experience of modeling severe accidents for various VVER NPP projects (VVER-1000/1200/TOI), the typical range of values of parameters of hydrogen mixtures in the containment atmosphere is estimated. Recommendations are given for estimating the upper and lower flammability limits for mixtures containing hydrogen and carbon monoxide, including oxygen-lean mixtures. The results of this work are relevant for the assessment of hydrogen hazards at NPPs, including the development, validation, and application of dedicated computer codes.

Uncertainty analysis (UA) is one of the main problems in probabilistic safety analyses (PSAs) of level 2 [1, 2] solved with allowance for the characteristics of the uncertainty of the reliability parameters of the reactor plant components: failures of components and systems, severe accident (SA) events, etc. Many failures of the reactor plant systems depend on the SA scenario. The estimate of such probabilistic indicators of emergency conditions as the probability of dependent failures is impossible without additional calculation estimates. Therefore, PSAs of level 2 are usually accompanied by a series of deterministic supporting calculations with the corresponding UA [3]. In this study, a method for estimating the probability of dependent failures of reactor plant systems has been developed on the basis of recommendations for estimating the uncertainties of the results of calculated safety analyses [3] with allowance for the tasks of PSA of level 2.

The article presents a description of the threaded elements of the ITER blanket and analyzes the nature of the forces acting on the threaded elements under ITER conditions. The Junker test method for verifying self-locking properties is reviewed, and test results are presented for an M24 threaded pair that is part of an electrical connector assembly. The article notes that metric threads exhibit unsatisfactory self-locking properties, as does the EMUGE Self-lock thread, when combined with a low-friction coating at mean stresses in the bolt shank below 35% of the yield strength. However, at mean stresses in the bolt shank reaching 40–50% of the yield strength, no loosening of the threaded pair occurs.

The application of the computational algorithm based on the Stockwell transform for the analysis of experimental data of MHD diagnostics in a tokamak is presented. The capability to apply this method for analyzing the dynamics of multimode tearing instability is demonstrated, in particular, for denoising signals, analyzing the dynamics of components of the initial multicomponent signal, time–frequency analysis of cross-phase correlation of sensor signals, and determining the spatial structure of an individual MHD perturbation component.

The paper studies (1^{+}) excitations in the ({}^{16})O nucleus within the shell model. There are at least three (1^{+}) excitations in the ((p), (gamma)), ((e), (e^{prime})), and ((p), (p^{prime})) reactions at energies of 16.22, 17.14, and 18.79 MeV. To produce such excitations, the valence space of the shell model should minimally contain at least the (0p_{1/2}) and (0d_{5/2}) subshells. The shell model was calculated for this and various other extended valence spaces. Various interaction Hamiltonians were also used. Excitations in nuclei are characterized by spin and current transition densities, which are different for different excited levels. Inelastic electron scattering excites both, but inelastic zero-angle proton scattering excites mainly the spin degrees of freedom. By comparing these two types of level excitation, one can determine the role of the spin and current degrees of freedom in each excitation. Unfortunately, the accuracy of this method is not very high. In this paper, we study the effect of the excitation type (spin or orbital) on the polarization characteristics of inelastically scattered protons, namely, on the spin-flip probability (S_{NN}). The calculated angular dependence of the spin-flip probability on the excitation type is investigated, and its strong dependence on the excitation nature is demonstrated.