Physics of Atomic Nuclei最新文献

A diagnostic method for material transport (erosion and deposition) in the KTM tokamak vessel has been developed and tested for durations comparable to an experimental campaign. It is based on witness samples mounted in the tiles of the first wall of the tokamak vacuum vessel. It was found that the regions of greatest wall erosion are located near the equatorial plane and on the inner side of the upper dome. Deposition zones were identified on the outer periphery on the lower side of the chamber. Possible effects of conditioning and operational discharges on wall sputtering were considered.

The influence of dispersion strengthening on the temperature dependence of the yield strength of the V–Cr–W–ZrC alloy was investigated in temperature intervals with different tendencies toward a dislocation-free mode of homogeneous deformation associated with BCC → HCP → BCC Bain-type transformations. The role of this deformation mode and of dislocation mechanisms of plastic flow in determining the strength (high-temperature strength) and low-temperature ductility of vanadium alloys is discussed.

One of the key tasks in the framework of creating a prototype plasma rocket thruster based on a quasi-stationary high-current plasma accelerator (QSPA) is the operation of the QSPA in a pulse-periodic mode. The transition from a single-pulse mode, in which the QSPA has been operated until now, to a pulse-periodic mode requires the significant change of a control system. This paper presents the requirements on the control, acquisition and archiving system, which ensures the operation of the QSPA in a pulse-periodic mode. The proposed control system architecture is based on the principles of distributed control and minimal connectivity. Also, the paper describes the testing of a control system key task, namely, the execution a sequence of acquisition and analysis of diagnostic data. Test results demonstrate, that the control system architecture developed using standard hardware is able to ensure the operation of the QSPA in a pulse-periodic mode with a frequency of up to 10 Hz for up to 20 min.

The narrow resonant-like structures were identified in the invariant mass spectra of di-(J/psi) and (J/psi{-}psi(2S)) by three LHC collaborations. These findings point to the possible existence of fully-heavy tetraquarks with a (cbar{c}cbar{c}) configuration. These new exotic resonances require detailed theoretical and experimental investigation. In this review, the latest experimental results and several theoretical approaches towards physics of new states are presented.

A method for accounting for the inhomogeneous density of a material in neutron transport modeling using the Monte Carlo method [1], where the density inhomogeneity is specified in the initial data of the program on the basis of piecewise continuous analytical functions of spatial coordinates, has been considered. This approach is similar to the method of aligned cross sections and is implemented in the KIR calculation code [2, 3] as one of the possibilities. Despite some kinship with the delta-tracking method [4, 5], the presented improved method is a completely independent development. The resulting algorithm for accounting for the continuous material density has been used in conventional zones of the NCG geometric module [6] with tracking of the transitions of particles across the boundary. The algorithm has been tested by calculating test models of VVER reactor cells with a sharp change in coolant density, similar to systems with supercritical coolant parameters, for example, SCWR [7]. In this case, the option of specifying initial data with the continuously changing material density can be applied if it is necessary to any type of problem and systems with any neutron spectrum (thermal, intermediate, and fast).

The substantiation of brittle fracture resistance and probabilistic analysis of NPP equipment and pipeline failure require the calculation of fracture mechanics parameters under multifactorial conditions of normal operation and during emergency processes. New numerical and analytical approaches to calculating stress intensity factors have been developed on the basis of the numerical solution of exact integral equations of two-dimensional elastic problems on cracks, including with analytical consideration of the perturbation of the stress state caused by the proximity of the crack front and the boundary of the body or the interface of materials. A comparison with an exact solution for one problem of fracture mechanics has been performed; the accuracy and efficiency of the proposed approaches for other problems of fracture mechanics modeling calculated cracks near the surface of equipment or pipelines or in the area of the interface between the base metal and the weld deposit have been demonstrated.

The aging of collision cascades with damaging energies of 1–50 keV at temperatures of 300–900 K in BCC metals Fe and V has been simulated by an object kinetic Monte Carlo method. The metals under study are of interest as the basis for low-activation structural steels and alloys for fusion reactors and hybrid fission–fusion systems. The initial spatial distributions of self-point defects surviving after the cascade region cooling (20 ps from the beginning of the cascade development) have been taken from previously obtained molecular dynamics data. The evolution of the system, which includes the processes of diffusion, recombination, clustering, and dissociation of radiation defects, has been surveilled for 5 ns. The temperature and damaging energy dependences of the number of surviving self-point defects after aging and the corresponding size distributions of their clusters have been obtained. During the aging process, cascade efficiency decreases by 12–40% from the initial values, depending on the material, temperature, and damaging energy. The physical mechanisms underlying the observed features of the calculated dependences have been determined.

The paper presents the results of tests of the vertical liquid-metal lithium CPS limiter with external lithium supply during the first two years of its operation. The capillary porous structure (CPS) is made of tungsten “felt” with an average porosity of about 50 μm. The lithium consumption during long-term operation of the limiter was determined and the processes responsible for the lithium consumption were studied. It was shown that the limiter can operate without lithium refilling for at least 500 working discharges. Refilling with lithium allows replenishing the amount of lithium in the limiter to the initial value. It was shown that the main consumption of lithium occurs during the preparation of the tokamak chamber for operating modes during induction heating of the walls and during a glow discharge due to the chemical interaction of residual water vapor with elemental lithium.

This work is aimed at substantiating the conservative approach used in the analysis of an accident at a VVER reactor plant (AES-2006 project) with the ejection of one cluster of absorber elements (AE) from the core. The problem of finding the law of motion of the control and protection system control rod (CPS CR) is solved with its postulated ejection in an accident with a rupture of the drive housing. For this purpose, a mathematical model of CPS CR is used that takes into account the geometric characteristics of AE and the hydrodynamic situation in the core in the event of a leak. An analysis is made of the influence of the law of motion of one CPS CR cluster on the disturbances introduced into the reactor at different initial states of the reactor plant.

Studies of the bremsstrahlung spectrum-weighted average yields of ({}^{187})Os((gamma,p))({}^{186})Re, ({}^{189})Os((gamma,p))({}^{188})Re, and({}^{190})Os((gamma,p))({}^{189})Re were conducted, and experimental values of these yields were obtained for a bremsstrahlung cutoff energy of 23 MeV. The results of simulation within the statistical nuclear model using the TALYS1.96 software code indicate a predominant contribution of nonstatistical mechanisms to the reactions under study. Calculations of the yields of the reactions, semidirect processes taken into account, describe the experimental data satisfactorily.