Physics of Atomic Nuclei最新文献

The article is devoted to the ion-plasma technology being developed to solve the problems of decontamination of irradiated reactor graphite and in-circuit equipment, as well as the problems of decommissioning various types of nuclear reactors. The features of the technical implementation of a device for decontamination and the cooling system of the electrode-collector for deposition of radionuclides to be removed by “shortened” discharge plasma from the surface of intracircular equipment and irradiated graphite are considered. The physical and thermal engineering processes underlying ion-plasma “dry” technology are discussed. The temperature distributions on the electrode-collector and in the cooling stream of the electrode-collector water cooling system are calculated. The operating parameters of the technology for decontamination of irradiated reactor graphite and nuclear power plant metal structures are found: inert gas pressure 0.1–1 atm, current density of a shortened discharge 0.1–1 A/cm², discharge voltage 100–1000 V. It is found that at a power density of a shortened discharge of 1 × 10⁵, 2 × 10⁵, 5 × 10⁵ and 1 × 10⁶ W/m², water cooling flow rate of about 1 m/s is required to cool the electrode-collector.

In this paper, a multinodal model composed different sets of axial nodes determined within the approach of Avery coupled reactors in the axial direction was proposed and implemented in the MATLAB environment for the dynamics of the VVER-1200 nuclear reactor. The number of considered nodes was varied from 2 to 20. To provide a more precise description of dynamic modes of reactor operation, the model was extended by the thermohydraulic Mann’s model, implying that one fuel node is adjacent to two sequential coolant nodes. To model daily maneuvering modes, spatial xenon oscillations were taken into account, and the parameter “axial xenon oscillation index” was introduced. In this paper, a new mathematical multinodal model derived from the model of change in the boric acid concentration in channel geometry was also proposed to reflect the influence of boric acid. This model is coupled to the model of thermohydraulic processes through the mass coolant flow rate. The results of numerical simulation in two experiments with a change in the position of the 12th group of Control and Protection Systems Control Rods (CPS CR) and in the liquid absorbent concentration in the coolant of the primary circuit show that the statistical precision of the proposed model is more than satisfactory as compared to a multifunctional simulator, and the general form of transient processes agrees with physical representations. The submitted work is a contribution to the further development of multipoint models of a nuclear reactor to improve the synthesis of the automatic power controller.

One of the promising projects of the generation IV reactors is water-cooled power reactors with supercritical coolant pressure (VVER-SCP), which is capable of increasing the efficiency of VVER power units by increasing the pressure to 23.5–25 MPa and increasing the coolant temperature to 380–540°C. One of the main problems that will have to be faced when developing the VVER-SCP project is the selection of cladding materials for a fuel element capable of operating at supercritical coolant parameters. To solve this problem, it is necessary to conduct in-reactor tests and post-reactor studies of candidate structural materials for fuel element cladding. For this purpose, it is necessary to develop an irradiation device that could ensure in-reactor tests of candidate structural materials for fuel element cladding under SCP coolant conditions. In the study, thermal hydraulic calculations of the irradiation device design have been carried out using the SolidWorks software package. The results of calculations have shown that this design of the irradiation device will allow for in-reactor testing of VVER-SCP fuel rod layouts at supercritical coolant parameters in the SM-3 research reactor facility.

This report presents a draft of a new detector designed to determine the chemical composition of primary cosmic rays based on the characteristics of the angular distribution of Cherenkov light from EAS. The installation, consisting of several such detectors, will be able to register individual EAS events in the energy range from 1 to 1000 PeV with high angular resolution of up to 0.2°. The proposed detector’s distinctive feature is its simple design and wide viewing angle of above ±30°.

Uranium-gadolinium fuel in a homogeneous design with axial profiling of fuel elements has received practical application. The possibility of heterogeneous use of Gd₂O₃, ZrB₂, Am₂O₃, and other burnable and alloying additives is being investigated. Such additives make it possible to maintain the thermal conductivity of the fuel at the level of conventional oxide fuel. The modifications under study show satisfactory behavior under irradiation at extremely high temperatures and burnup. However, the issues of radiation safety when handling both fresh and spent fuel remain less studied. In this work, a computational assessment of the neutron component of the radiation characteristics of a UO₂ composition with a heterogeneous variant of localization of ^natGd₂O₃ and Am₂O₃ microcapsules has been carried out. This design option does not impair the thermal conductivity of the fuel and has positive effect on the nuclear physical and thermophysical properties of the fuel. Americium has been studied not only as a possible alternative to Gd but also from the perspective of its possible utilization in thermal reactors. The influence of Am on the photon component of radiation characteristics of fresh fuel has been considered. It is concluded that the radiation safety of fresh and irradiated products containing Am should be achieved primarily by solving problems of protection from photon radiation. The research has been carried out to develop procedures and regulations for handling new fuel during its manufacture and after irradiation in reactor. The studies have been carried out using verified calculation codes of the MCNP 6.2 and Nedis 2m programs.

This paper presents a method for analyzing data from cosmic-ray muon detectors, enabling the detection of subtle flux variations that are indistinguishable in the integral muon count rate. The complete mathematical framework of the method is provided. It requires detectors capable of distinguishing muons by their azimuthal arrival angles and, for optimal performance, multiple independent detectors with similar characteristics. A key feature of the proposed approach is that it considers not only the amplitude of the signal (reflecting muon flux variations) but also its direction, which can be correlated with the spatial characteristics of sources of variation, such as atmospheric phenomena. Each step of the method is illustrated using the example of a warm front approaching Moscow, as well as an atmospheric event accompanied by a cloud line. Additionally, the paper presents a visualization of data for the new method that allows a large amount of data to be reduced to a single diagram that can be plotted on satellite images and the observed muon variations to be compared with atmospheric phenomena in situ.

In this paper, one of generalized Vakhnenko–Parkes’ family equations is considered describing the propagation of short-wave disturbances in relaxing media, taking into account the dependence of the wave velocity on the amplitude. A general quadrature solution is obtained for the equation under consideration by reducing it to an ordinary differential equation using the traveling wave variables. Some formal exact solutions of the initial equation are found. The periodic exact solutions are expressed in terms of Jacobi elliptic functions. An explicit solution is also presented, expressed in the terms of a power function of spatial and temporal variables. The obtained exact solutions can be used as the test functions when analyzing the results of a numerical simulation of the processes in the relaxing media described by Vakhnenko–Parkes type equations.

The small-angle neutron scattering (SANS) method was used to study the ordered structure of the pores of the MSM-41 powder coated with a layer of a hydrophobic substance. The studies were carried out on the YuMO spectrometer of the IBR-2 reactor (JINR, Dubna). The process of filling and leakage of a nonwetting liquid (heavy water) from nanosized pores of the material with a change in external pressure was studied. For this purpose, a stand and a high-pressure chamber were designed and manufactured, allowing measurements to be carried out using the SANS method in the pressure range of 1–1000 atm. The results obtained show that this technique allows studying the process of filling pores with a nonwetting liquid in nanoporous materials.

Numerical modeling of the nonstationary radiation transport process in the kinetic model is a very labor-intensive task. The complexity is due to the large dimensionality of the problem and, additionally, for problems of radiant energy transfer, strong nonlinearity. For deterministic approaches based on discretization of the particle flight direction, it is necessary to solve a system of hyperbolic equations of large dimension. Accordingly, it is desirable that the methods used for numerical modeling be economical both in terms of memory use and calculation time and show acceptable results for a wide range of Courant numbers. In the case of radiant transport, the situation is aggravated by the strong nonlinearity of the problem being solved, which leads to a significant change in the properties of the medium at time steps. This imposes increased requirements for monotonicity of the schemes with a change in optical thickness. According to Godunov’s theorem, among two-layer linear schemes in time, there are no monotonic schemes of a higher approximation order. One of the directions of solving this problem is the development of NFC (Nonlinear Flux Correction) schemes of end-to-end counting, in which an increased order of accuracy on smooth solutions and monotonicity are achieved owing to nonlinear correction of flows. The numerical solution is monotonized using a special algorithm in the vicinity of large gradients of the exact solution. The paper provides a brief overview and characteristics of the finite-difference scheme developed and successfully used for many years at RFNC VNIITF to solve radiation transport problems. The Total Variation Diminishing (TVD) technique is used to monotonize the scheme.

The costs of ensuring the protection of modern nuclear engineering installations account for a significant proportion (20–30%) of the total cost of construction. Therefore, optimization of the composition of radiation protection materials is an important direction for minimizing protection costs while maintaining high performance indicators. Natural resources, the deposits of which are located near these facilities, make a significant contribution to reducing the cost of construction of nuclear power facilities. In modern radiation technologies, composite radiation protection materials (RPM) with a matrix of glass, polymers, cement, and other materials play a key role. The inclusion of various fillers in the matrix makes it possible to design the optimal composition of RPM for specific irradiation conditions determined by the isotopic composition of radioactive contamination. Both natural materials and industrial waste can be used as fillers, which helps to solve the problem of their disposal. This article presents the results of computational and experimental studies of samples of natural minerals from the northern part of Vietnam. This research is part of a comprehensive project that has been implemented at the Department of Nuclear Power Plants and Renewable Energy of the Ural Federal University (UrFU) for more than 10 years. The project is aimed at studying the radiation-protective properties of natural minerals and industrial waste in order to assess their potential applicability as part of building materials for the protection of nuclear power plants. To study the calculation of the radiation-protective properties of minerals, the sample density was determined by the Archimedes method using a MH-300A density meter, the chemical composition was determined using X-ray fluorescence analysis in the laboratory of the Egyptian Nuclear Materials Administration (Cairo), and the XCOM database was used. Experimental investigation of the shielding properties of the samples was carried out using the Robotron spectrometric installation. The results of the study of natural materials revealed samples of stones that can be used as a concrete filler in the construction of nuclear power plants and other nuclear power facilities in Vietnam, as well as clay for the manufacture of radiation protection blocks for prefabricated protection.