Physics of Atomic Nuclei最新文献

Transition energy crossing at the U-70 proton synchrotron is studied. Motion stability is achieved through the method of transition energy jump at constant betatron tunes. The longitudinal motion is simulated with allowance for higher orders of the momentum compaction factor, along with various impedances and bunch intensities. Experimental data from an accelerator session are presented.

The main features of the frozen and quasi-frozen spin lattice were calculated in the spinor formalism, such as a spin-tune and a direction of the invariant spin axis. As the radial field perturbations play a crucial role in the electric dipole moment (EDM) measurement procedure, the difference of frozen and quasi-frozen spin lattices was investigated in this regard. The possibility of subtraction of a nonlinear term in the spin precession frequency with the change of the injection direction in the quasi-frozen case was investigated. Furthermore, the frequency summation law was derived for the structure of a general form with perturbations in the radial, vertical and longitudinal directions.

Since the modern automatic control theory imposes constraints on the mathematical models of control objects, further development and verification of mathematical models of nuclear power facilities suitable for the synthesis of automatic power control systems is a topical problem. This article deals with a low-order dynamic model with lumped parameters of the Russian-designed pressurized water reactor, as well as with its verification with experimental data from the full-size simulator of the VVER–1200 nuclear reactor in two tests involving the variation of the position of group 12 of CPS CR and the variation of the inlet coolant temperature. This model was created as a MATLAB S-function lv.2 model because of its capability to process any input signals. Within this approach, the equation describing the heating of the coolant is represented as a «two well-stirred tanks in series» model. The article demonstrates the advantage of the given approach over the conventional approach, where the average temperature of the coolant is determined as the arithmetic mean of the inlet and outlet coolant temperatures on the basis of a test with a sudden change in the reactor inlet coolant temperature. In the frequency domain, the authors carry out the stability analysis of the given model in the state-space form with respect to various external perturbations. Conclusions are drawn about the possibility of using the model as a fifth-order control object for the parametric synthesis of a controller for the automatic power control system of a nuclear power facility.

This paper considers and systematizes fuel assembly variants for the WWER-1000 reactor. A fuel assembly of infinite height with six U49G6-type U–Gd fuel rods used in large-capacity WWER-1000 fuel loads is simulated in the Serpent neutronic code. As a result of the calculations, U–Gd fuel rod arrangement with less uneven power density along the fuel assembly is selected, and the effect of the number of U–Gd fuel rods and their arrangement on reactivity is assessed. It is shown that the arrangement of U–Gd fuel rods in the fourth ring is optimal in terms of uneven power density per fuel rod and burnup. The effect of fuel assembly arrangement on the fuel burnup for individual groups of U–Gd fuel rods is considered. An option is proposed for reducing the cost of computing resources by identifying the groups of fuel rods with the greatest differences in power density and burnup. The studied assemblies are compared with the existing U49G6 fuel assembly. A method is proposed for estimating the underproduction of thermal energy in a fuel assembly due to the uneven burnup of fuel rods, while maintaining the maximum burnup for individual fuel rods. Based on the analysis of underproduction, an option is proposed for improving the fuel assembly layout with six U–Gd fuel rods to equalize the power density field and reduce unproductive fuel losses. For this purpose, enrichment in the first, second, and tenth fuel rod rings, counting from the central fuel assembly tube, can be reduced. As a result of such profiling, the burnup of the most burnt fuel rods in the fuel assembly can be reduced to 1.015 of the average burnup.

Some aspects of the use of coatings for various functional purposes on the first wall plasma-facing surface of a thermonuclear reactor are considered. An important characteristic of coatings is adhesive and fatigue strength under cyclic impact of quasi-stationary heat loads, as well as resistance to high pulsed thermal loads. This paper describes thermal cyclic tests with surface thermal load of water-cooled mockups with various coatings on the heat-receiving surface. The B₄C coating, made by atmospheric plasma spraying on a tungsten substrate, demonstrated excellent durability over 1400 thermal cycles at 4.7 MW/m². CVD tungsten coating on a copper substrate demonstrated good results after 1000 thermal cycles at 3.3 MW/m², but after a similar number of cycles at 5 MW/m², cracks were detected on the surface. The stainless steel coating on a copper substrate demonstrated resistance to loads up to 11.9 MW/m², as well as excellent durability over 1000 thermal cycles at 8.2 MW/m².

Armor materials of the ITER divertor and the first wall will be subjected to intense plasma-thermal impact during reactor operation. One of the prevalent types of metal protective coating erosion is due to displacement of the molten surface layer. In order to obtain solid interpretations of physical processes, development and verification of numerical models are required. The aim of this paper is to outline initial development of the numerical model, which describes the motion of a metal molten layer under the impact of an intense plasma stream. Numerical calculations are based on experimental data obtained at the quasi-stationary high current plasma accelerator QSPA-T. The motion of the molten metal is described by a system of coupled heat transfer and Navier–Stokes equations. In the case of consideration of an external magnetic field, Maxwell’s equations are included in the system. It is assumed that a metal target is exposed to a pulsed plasma stream with specified temporal and spatial distributions of power and pressure. Plasma exposure causes melting and subsequent motion of the surface layer of the material. Thermophysical properties of the metal are considered temperature dependent. Material evaporation from the exposed surface is taken into account in the model. The metal layer displacement was obtained for various values of the plasma stream incident to the surface. It is shown that the melt motion observed in the experiment cannot be explained by the action of the plasma pressure stream gradient alone. The friction force between the near-surface plasma and the molten metal was implemented in the numerical model, whereby a quantitative agreement between the calculation results and experimental data was achieved. In addition, magnetic field conditions were applied in the model. The influence of both the stagnation pressure and power dynamics on the resulting profile of the target surface was studied.

A study of the influence of annealing in the range from 700 to 1600°С on the microstructure features and microhardness values of the V–Cr–W–Zr alloy after thermomechanical treatment was carried out. It was found that, as a result of rolling in the V–Cr–W–Zr alloy, texture fibers α, γ, θ are formed. It has been established that the structural state after thermomechanical treatment is stable up to 800°С. At 900°С, primary recrystallization is activated, which at 1000°С covers the entire volume of the material. Collective recrystallization processes occur in the temperature range of 1100–1400°С. Secondary recrystallization is activated at 1500°С. Under conditions of primary, collective, and secondary recrystallization, against the background of orientational grain growth, the disappearance of the texture components of the θ-fiber is observed. It was established that, in the temperature range of 1500–1600°С, a partial redistribution of W occurs. The influence of the average grain size on the microhardness values of the alloy was analyzed. The main mechanisms of material strengthening are discussed.

The paper reviews the main mechanisms of hydrogen isotope accumulation in fusion devices: the implantation of particles from plasma into plasma-facing components (PFCs), followed by diffusion into the bulk of material, and capture into growing redeposited layers in areas of preferential deposition (co-deposition). The specific features of hydrogen isotope accumulation, depending on the selection of plasma facing material, are considered during the regular application of auxiliary coatings and the utilization of wall components based on liquid metals.

The paper analyzes the well-known vacuum technology method of “drying” vacuum volumes by purging them with “dry” gases, applied to the discharge chambers of tokamaks during their initial preparation phase before plasma experiments. This method competes with the traditional technique of thermal desorption by heating the tokamak chamber under high-vacuum conditions. Using the examples of the TSP and T-11M tokamaks, it is shown that, in the initial phase of preparing the tokamak chamber, before transitioning to plasma methods for wall conditioning, the simple “drying” method, especially when using forced convection of “dry” gases, can have significant advantages over the traditional approach.

The results of investigation of the effect of powerful hydrogen plasma flow created by the 2MK-200 pulsed accelerator on a layer of bismuth 7.5 µm thick previously vacuum-sprayed onto a 30 × 30 × 3 mm tungsten plate are presented. At an energy density of the plasma flow at the level of ≈600 J/cm² with a duration of ≈15 μs, the target with bismuth, owing to the shielding effect, absorbed ≈12 J/cm². On the frontal surface of bismuth, the temperature measured by a spectral pyrometer did not exceed ≈1900 K during the entire exposure to hydrogen plasma. The spectroscopy data of near-surface plasma radiation are presented, according to which the radiation of bismuth plasma in the spectral range ∆λ ≈ 2–20 nm is localized near the surface at a distance of ≤4–6 cm. The rate of bismuth evaporation per exposure at the specified plasma flow parameters was ≈0.5 µm in thickness.