Physics of Atomic Nuclei最新文献

This article deals with fuzzy and fuzzy PI controllers for the automatic power control system of a linearized mathematical model of the VVER-1200 nuclear reactor. The automatic power control system includes a mathematical model of a step-by-step electromagnetic drive (SED), a model of in-core and ex-core neutron flux sensors, and a refined mathematical model of the group 12 of control and protection system of control rods (CPS CR) obtained by approximating experimental data using the Levenberg–Marquardt algorithm for the nonlinear least squares problem. Based on the state space model, ten transfer function matrices of the nuclear reactor corresponding to a power range of from 10 to 100% of the nominal power were determined, and ten classical PI controllers were designed to ensure stability margins of at least 60° in phase and at least 10 decibels in amplitude for each power level of the plant. Simulation results show a significant advantage of the developed fuzzy controllers both in the steady-state power maintenance mode considering noise in the neutron flux sensor channel and in the load-following mode at different power levels.

Universal features of dynamic failure and turbulence phenomena are considered on the basis of results of research and analyses of published data. The absorbed energy density causing the failure is comparable to the energy parameter of the crystal lattice E, which is fractions of electronvolt per atom in the range of nonequilibrium states t ~ 3 × 10^–6–10^–10 s. Macrofailure, changing the body connectivity, arises when approaching the critical density of the failure center cascade, i.e., percolation cluster, through the cascade of bifurcations. Fully developed turbulence is a chaotic dynamics, which is related to the stochastic instability of the transition through a sequence of period-doubling bifurcations, through intermittency, etc. At present, a strict mathematically grounded theory of dynamic failure phenomena of condensed matters and turbulence theories are absent, which implies the application of scaling relations and phenomenological approaches for their description. On the basis of design-theoretical studies and analysis of published data, it has been shown that phenomena of dynamic metal failure and fully developed turbulence are analogous, meaning that these processes have close values of critical exponents and belong to one universality class.

An analysis is performed of the effectiveness of using spherical gold nanoparticles (AuNPs) with a size of 50 nm in combination with proton irradiation at a dose of 30 Gy (energy of 150 MeV) in order to enhance the cytotoxic effect of binary therapy. The analysis is performed with in vivo experiments using the model invertebrate animal Daphnia magna. The biodistribution of the AuNPs in the animal body is studied, and the biochemical effect of the separate and combined action of AuNPs with irradiation is analyzed. The accumulation of AuNPs in the intestine and the eggs and embryos of the next generation is detected. Analysis of the level of free radicals and malondialdehyde reveals an increase in the cytotoxic effect of irradiation with nanoparticles.

The influence of an ultrafine-grained tungsten structure with an average grain size of 300 nm on the formation of blisters on the surface under high-fluence irradiation by 30-keV He⁺ ions has been studied. Fine-grained tungsten has been used for comparative studies. The microstructure and surface morphology of the samples have been investigated.

The design and characteristics of the detection unit of a gaseous medium spectrometer for measuring gamma rays from inert radioactive gases formed in nuclear power plant reactors and entering the environment as a part of gas-aerosol emissions are described. Gamma rays from inert radioactive gases are detected by one scintillation detector based on a 51 × 51-mm CeBr₃ crystal in two chambers with a volume of 10⁴ and 2 cm³. The energy range of the spectrometer is 0.05–3.0 MeV. Switching of gas inputs and outputs allows both simultaneous and alternate measurements in both chambers, which ensures the calculated dynamic range of measured inert radioactive gas activities from 10³ to 10¹³ Bq/m³ with a relative measurement error of 50% in the nuclide emission lines for time intervals from 1 to 500 s, depending on the activity.

In the PAMELA experiment, precipitation of electrons from the Earth’s radiation belt was detected at moments of recording gamma ray bursts of extraterrestrial origin, leading to a hypothesis about the relationship between these phenomena. This work provides estimates of the number of electrons that have interacted with gamma quanta through the Compton effect and changed their energy and trajectories in the so-called toy model approximation. A formula is obtained for determining the cross section of the interaction between a gamma quantum and a stationary electron, depending on the angle of electron emission and the energy spectrum of the emitted electrons. A narrow peak is observed near the maximum energy in the energy distribution of secondary electrons, which is close to the energy of the initial gamma quantum. An estimate is obtained for the upper limit of the contribution from the considered process to the excess of the electron count rate over the background value recorded in the PAMELA experiment. It is found that the proposed mechanism does not explain the observed effect because the calculated electron count rate is several orders of magnitude lower and can be explained by the small Compton scattering cross section.

The prospect of creation of the accumulator of energy on the basis of nuclear isomer ^186mRe (a half-life of 2 × 10⁵ yr) does actual a question of the choice of conditions of natural rhenium irradiation by reactor neutrons for production of big amounts of the isomer. Calculations of dependence of the isomeric ratio, known in literature, at formation of ¹⁸⁶Re nuclei in ground and isomeric states show insignificant difference in efficiency of production of isomer by thermal neutrons or in active zone of reactor. This conclusion has been confirmed experimentally with an accuracy up to 20% earlier. In the present work, a method of more exact experimental check of results of the isomeric ratio calculation is suggested.

The authors consider a situation where a nuclear power plant operating with a variable daily load schedule receives a signal about the likely start of extreme external influences in the immediate future, forcing the shutdown of the reactor. The plant’s personnel are authorized to establish a regime in which the reactors operate during the period of the threat until it materializes or is canceled. A two-level daily graph is presented of the change in the power of the nuclear reactor. It is assumed a threat warning is received at the beginning of the period, and the reactor power is held constant at a level between day and night regimes for the period of the threat. The problem of finding the optimum level of power is noted and solved. The loss function is calculated as the total economic damage, weighted by the probabilities of the materialization and cancellation of the threat, caused by deviating from the consumption schedule in the event of a false alarm and the downtime in the iodine pit in the event of a real threat. Results show that the effect of optimization grows along with the probability of a threat, so the power regime must be changed to appropriate level a. The effect of optimization is estimated.

This paper is devoted to the actual problems of nuclear energy: deactivation of nuclear power plants (NPPs), hot cells, equipment for isotope separation, and reprocessing of spent nuclear fuel (SNF) to effectively close the nuclear fuel cycle. The authors have proposed the ion-plasma “dry” technology developed to solve these problems. The operating parameters of the ion-plasma technology for deactivation and reprocessing of spent nuclear fuel have been obtained: inert gas pressure of 0.1–1 atm., inert carrier gas flow rate of 1–10 m/s, and current density of 1–5 A/cm² at the operating voltage of 100–1000 V. Using the example of SNF processing, the ranges of partial pressures and deposition temperatures of SNF elements during the process of its separation according to elemental composition have been calculated. Because of the difference in the condensation temperature ranges of each spent fuel element, purification of uranium and plutonium from most fission products of MOX and MNUP spent fuel with a purity of at least 99% has been demonstrated.

The present study explores the application transition energy jump procedure in order to maintain the stability of the beam in the NICA collider. The features of the barrier and harmonic accelerating RF stations and their influence on the dynamics of longitudinal particle motion are described. Study of these features is intended to expand the understanding of the process of transition energy crossing.