Physics of Atomic Nuclei最新文献

The organization of the plasma–wall interaction remains an urgent problem for long-term operation of a tokamak with an intense thermonuclear fusion reaction. The concept of a lithium cycle and the design of a sectioned divertor for the Demonstration Fusion Neutron Source (DEMO-FNS) tokamak are proposed. The parameters are estimated, and requirements for the components of the lithium cycle are formulated. Technical solutions for the lithium cycle flow rate ≅10 g/s are selected. It is estimated that 0.1-µm liquid lithium layer on the surface of the first wall can protect its solid coating. On the basis of a simple model, it is shown that, at a wall temperature of 200–300°C, a thickness of 0.1 µm can be achieved in ≅1 min. The film can reach quasi-stationary values of 13–15 µm in 3–4 h. Above 340°C, the film does not form because of the increase in the thermal evaporation of lithium. The wall temperature of 700°C of the divertor section with the lithium pool is chosen so that lithium deuteride and lithium tritide do not form in it. They can form in the liquid metal lithium protective layer of the wall at temperatures less than 300°C. In order to significantly reduce the explosion and fire hazard when working with hot liquid lithium, it is proposed to increase the size of the DEMO-FNS divertor section with the lithium pool by 2 to 3 times, which may allow the transition from water to helium coolant.

One of the conditions of safe operation for the experimental tokamak reactor ITER is the possibility of mitigating disruption instability by massive injection of inert gases, in particular, of argon and neon. Here we present the results of assessing the influence of multiplet splitting and line radiation imprisonment during the discharge quenching by intense argon injection in ITER. In this paper, the fine structure of energy levels and the noncoronal collisional-radiative kinetics for the radiating excited state are used. For the radiation of two argon ions, Ar⁺¹⁵ and Ar⁺³, which have spectral lines of high intensity and could be used for plasma diagnostics, it is shown that the optical thickness for the ionic strongest lines has no significant effect on the total power losses of plasma radiation in the considered quenching scenario (massive argon injection in the 15 MA, Q ~ 10 basic scenario in ITER, carried out at the quasi-stationary stage of the discharge, flat-top of the current). The most significant effect appears to be the multiplet splitting of atomic levels, which provides an increase in the radiative losses, e.g., by a factor of ~2 for low-ionized atoms at low temperatures, because the resolution of the fine structure of atomic levels for Δn = 0 transitions leads to a contribution of lower excitation energy than that in the model of multiplet-average radiative transitions.

Collisions of the fast electrons with partially stripped high-Z impurity ions in a tokamak plasma are considered. The Thomas–Fermi model is used in calculation of the form factor which describes the screening of the potential of impurity nuclei. The calculated dependence of the form factor on the transferred momentum of the fast electron at elastic collisions allows accurate evaluation of the differential scattering cross section and transport collision frequency accounting for the relativistic effects. The transport collision frequency for the energetic electrons in the plasma with partially stripped impurity ions is shown to exceed strongly the frequency calculated for the fully ionized plasma with equivalent effective charge. This is apparently the situation occurring in the tokamak plasma disruptions accompanied by generation of runaway electrons. An algorithm to calculate collisional energy loss of the fast electrons is suggested as a generalization of that for electron drag in neutral media. Analysis of the collisional drag of the fast electrons on the partially ionized plasma demonstrates that formal replacement in the collision integral of the electron plasma density with the sum of the free electron density and half of the bound electron density provides sufficiently high, ~10%, accuracy in evaluating the fast electron energy losses. The presented results allow accurate evaluation of collisional effects in the simulation of the fast electron dynamics.

The energy spectra of neutrons in the experimental channel, in the window, and behind the biological shielding of the core of the IGRIK-2 pulse nuclear reactor was measured using the neutron activation method. Approximately 15 neutron activation detectors were employed. The neutron spectrum reconstruction was performed using the method of directed divergence minimization. A comparison of the main integral characteristics of the neutron field with numerical Monte Carlo calculations is presented.

In the paper, we present a method for validating the KORSAR/GP software package in terms of a mathematical model of nonstationary xenon processes in a VVER reactor that is based on the separation of spatial and temporal variables. The data obtained from various high-power VVER installations in experiments to study the spatial distribution of energy release under nonstationary reactor poisoning conditions caused by the action of various regulators are used. The model is based on the classification of means of affecting reactivity by the type of variable in energy release, which undergoes changes significant for the process as a result of this impact. Nonstationary xenon poisoning processes, which involve control rods of the control and protection systems and water exchange operations with a change in the concentration of boric acid, as well as both of the listed methods, both in the presence of a change in the neutron power of the reactor and when maintaining its constant value, are considered. A machine learning method on the basis of regression analysis making it possible to estimate the error in calculating the parameters of the energy release field under conditions of spatial, temporal, and spatiotemporal feedback of the xenon concentration and regulators is developed. On the basis of the processed experimental data, a training array, which is used for machine learning of this model, is formed. As a result of the developed algorithm, an error estimate for the model of the computing code with allowance for the partial impact of various means of changing the reactivity in a given calculation is made.

In this work, to assess the efficiency of the ANSYS CFX 14.0 code and obtain fluid flow properties, one heat transfer experiment using water as a coolant at supercritical pressures was selected: a 2 × 2 rod bundle with wire spacers along its length. A 3D CFD study of fluid flow and heat transfer at supercritical pressures was conducted for the geometry of the rod bundle, with the key parameter being the temperature of the inner wall of the fuel rod simulator. The influence of turbulence models SST, k–ω, and BSL, as well as various types of computational mesh to ensure the reliability of the assumed wall temperature, was investigated. After the study, the CFD model data was verified against experimental data. It was found that the CFD model was able to qualitatively describe the temperatures of the inner surfaces of the rods as reported in the experiments.

The parameters of the convective filamentary transport in the edge region of the small spherical tokamak MEPhIST-0 are estimated. To describe dynamics of the installation scrape-off-layer plasma, an electromagnetic two-fluid MHD model was employed. The operational parameters of the tokamak and their impact on the characteristics of turbulent plasma transport are discussed. Using the BOUT++ code, dynamics of isolated filaments were simulated under conditions corresponding to the edge region of the tokamak in various discharge scenarios. It is shown that, despite the compactness of the machine, it may be possible to create and study both electrostatic and electromagnetic regimes of anomalous edge plasma transport in the installation.

The problems related to the effect of radiation exposure on the transmission optics used in diagnostic systems of the International Thermonuclear Experimental Reactor (ITER) are considered. These problems are discussed using the example of H-alpha and Visible Spectroscopy (HA&VS) in the equatorial port 11 of the ITER. Using neutron calculations based on the Monte Carlo method, radiation conditions for diagnostic components in the equatorial port, including the port cell area, are determined. A brief review of radiation effects and radiation tests of optical materials is presented. On the basis of the results of these tests and data on the radiation environment, the optical performance of the visible spectroscopy diagnostic components at the end of ITER lifetime is assessed.

Unit 1 of the Novovoronezh NPP-2 operating the first VVER-1200 reactor of the 3+ generation reached a critical state for the first time in May 2016, and the physical start-up of the power unit was carried out. The National Research Center Kurchatov Institute was the scientific supervisor of the start-up of the first-of-a-kind unit with the VVER-1200 reactor at the Novovoronezh NPP-2 and power units of the Belarusian NPP. By now, five VVER-1200 units have been commissioned. The experience gained during the preparation and conduct of physical tests at the first units was used during the start-up of the next ones. Specific features of the preparation and implementation of the program of physical tests at VVER-1200 units, which were developed and implemented by specialists of the National Research Center Kurchatov Institute, are presented.

A primary comprehensive experimental study of the contribution of reactor gamma radiation to the total signal of an SPD with a rhodium emitter was performed. This contribution was assessed by comparing the signals of a rhodium SPD and the same SPD with a palladium emitter, since palladium has similar electron-photonic properties to rhodium, but it lacks the beta decay of neutron activation products, which is the main component of the useful signal of a rhodium SPD. Primary tests comparing the signals of two SPD were carried out at the IR-8 research reactor. To confirm the assumption that the electron-photon properties of rhodium and palladium SPD are similar, special measurements were performed on the GUT200m gamma installation.