In the paper, the problem on an interface longitudinal shear crack located between two functionally graded wedge-shaped regions and emerging from their common vertex has been considered. The shear ...modules of the materials are quadratic functions of the polar angle. This kind of functional inhomogeneity made it possible to express all the components of the elastic field through a single harmonic function. Using the Mellin integral transform, the problem was reduced to the Wiener – Hopf scalar equation, for which an exact solution was obtained. The influence of gradients of elastic properties of materials and geometric parameters of the structure on the stress intensity factor was studied.
Currently, there is a lack of computer power to perform high-precision reactor core analysis. In full-scale simulation of nuclear reactor cores using the stochastic Monte Carlo method, there are a ...number of factors that increase the excessive computational load and make calculations difficult. Among them is the large flux attenuation, which can be observed in deep penetration problems. In order to improve the efficiency of Monte Carlo calculations, various reduction techniques are used, which make it possible to reduce the statistical uncertainty of the functional evaluation without increasing the number of simulated histories. This article is devoted to the study and testing of techniques for reducing the variance in the deep penetration problem. A test problem is formulated the solution of which will make it possible to demonstrate the possibility of using various techniques of nonanalog simulation. In order to determine the quantitative efficiency of variance reduction techniques, the FOM characteristic is considered, which is a function of the relative error in a flux estimate and the computational time of the simulation. The article deals with the techniques of nonanalog simulation implemented in the MCU and OpenMC codes. As part of the study, a module of the OpenMC code has been developed which makes it possible to automatically generate weight windows. It is shown that variance reduction techniques increase the calculation efficiency by several times. In particular, the weight window technique in OpenMC increased the efficiency of neutron flux estimation by seven times, while the number of simulated histories remained unchanged. The formulated recommendations can be used in the future for the calculation of full-scale models of cores of innovative nuclear reactors.
The possibility of applying the homotopy (deformation) method to studying the invariance of extremals for a generalized system of equations of relativistic electrodynamics is considered. This ...approach allows to investigate the stability of extremals for the action functional.
We report the observation of the steering of 855 MeV electrons by bent silicon and germanium crystals at the MAinzer MIkrotron. Crystals with 15
μ
m of length, bent along (111) planes, were exploited ...to investigate orientational coherent effects. By using a piezo-actuated mechanical holder, which allowed to remotely change the crystal curvature, it was possible to study the steering capability of planar channeling and volume reflection vs. the curvature radius and the atomic number, Z. For silicon, the channeling efficiency exceeds 35%, a record for negatively charged particles. This was possible due to the realization of a crystal with a thickness of the order of the dechanneling length. On the other hand, for germanium the efficiency is slightly below 10% due to the stronger contribution of multiple scattering for a higher-Z material. Nevertheless this is the first evidence of negative beam steering by planar channeling in a Ge crystal. Having determined for the first time the dechanneling length, one may design a Ge crystal based on such knowledge providing nearly the same channeling efficiency of silicon. The presented results are relevant for crystal-based beam manipulation as well as for the generation of e.m. radiation in bent and periodically bent crystals.
We present the crystalrad simulation code, combining all the features of the crystal simulation code for simulations of charged particles trajectories in a bent crystal and the radcharm++ code for ...calculation of the radiation spectrum. The crystalrad code is based on Monte Carlo simulations of trajectories in the planar and axial electric field either in a straight, bent, or periodically bent crystal taking into account multiple and single Coulomb scattering on nuclei and electrons, nuclear scattering and ionization energy losses. The trajectories simulated are used for calculation of radiation spectra by the Baier-Katkov method. We compare our simulations with experimental data taken at MAMI (MAinzer MIkrotron) as well as give an example for a possible future study with sub-GeV electrons interacting with Si bent crystals.
•The transmutation performance of MAs in the critical SD-TMSR and SMSFR was investigated.•The transmutation ratio of long-lived MAs was calculated using the SERPENT-2 Monte-Carlo code.•The online ...reprocessing and refueling was applied during burnup.•The dynamics of keff, core reactivity, major isotopes inventory, and time evolution of MAs were investigated.•The neutron energy spectrum shift with different MAs loadings was calculated.
The long-lived Minor Actinides (MAs): 237Np, 241Am, 243Am, 243Cm, 244Cm, and 245Cm are responsible for the effective dose and heat generation after direct disposal in deep geological structures. Thus, long-lived MAs represent a major burden of nuclear power. The long-lived MAs have not yet been utilized as nuclear fuel. Therefore, the transmutation of these MAs is proposed as an alternative to the direct final disposal. In the current work, we analyze and compare the MAs transmutation performance in the critical Single-fluid Double-zone Thorium-based Molten Salt Reactor (SD-TMSR) and Small Molten Salt Fast Reactor (SMSFR). We study the variation of the Keff and core reactivity with different MAs loadings, the neutron spectrum shift, the time evolution of MAs and major nuclides inventories, and the transmutation ratio (TR). The TR of the long-lived MAs is calculated by using the SERPENT-2 Monte-Carlo code. The total neutron flux in the SD-TMSR and SMSFR can reach 4.1 × 1014 and 1.8 × 1015 n.cm−2.s−1, respectively. The results show that the SD-TMSR consumes about 50% of the generated Pu isotopes in the fuel salt, however, the SMSFR consumes about 86.5% of the generated Pu isotopes. During burnup, we apply the online reprocessing and refueling, therefore, the core is maintained critical and the total fuel mass in the core and blanket is almost constant. The results demonstrate that both reactors effectively transmute 237Np, 241Am,243Am, and 243Cm, meanwhile, the SMSFR has a higher TR than the SD-TMSR. The TR of the total MAs reaches 54.84% and 87.97% in the SD-TMSR and SMSFR, respectively.
In the paper, the problem of a semi-infinite antiplane interface crack located between two functionally graded wedge-shaped regions has been considered. The shear modules of the materials’ regions ...are quadratic functions of the polar angle. This kind of functional inhomogeneity made it possible to express all the components of the elastic field through a single harmonic function. Using the Mellin integral transform, the problem was reduced to the Wiener – Hopf scalar equation, for which an exact solution was obtained. The influence of gradients of elastic properties of materials on the stress intensity coefficient at the crack tip and the singularity value at the angular point of the structure was studied.
Thermal-spectrum molten salt reactor (MSR) concepts usually adopt graphite as a neutron moderator. Although graphite as a moderator has many advantages, it also has drawbacks, including a relatively ...short lifespan (it has to be replaced), positive temperature feedback, and loss of impermeability due to expansion. Replacing graphite with heavy water in MSRs can effectively solve the problems introduced by graphite. The SD-HWMSR is a Single-fluid Double-zone Heavy Water-moderated Molten Salt Reactor. Optimization of SD-HWMSR’s fuel channel pitch and radius has been conducted in this work. As a result, the SD-HWMSR with a high breeding ratio (1.07465 ± 0.00060), low initial 233U loading (1.43 t), and negative temperature and void reactivity coefficients is put forward. The SERPENT-2 is used to analyze the neutronics parameters of the reactor design. The current work investigates the change in the multiplication factor, breeding ratio, and the accumulation of significant nuclides in the core. The suitable 232Th and 233U refill rates needed to maintain criticality and enable analysis of the whole core of SD-HMMSR are thoroughly determined in this study. Uranium-233 and thorium-232 both have a maximum refill rate of 3.49 and 3.20 kg/d, respectively. While the average refill rate for 233U and 232Th during the 60 years of operation is 1.90 and 2.35 kg/d, respectively. The net production of 233U rises with time, and by the end of the 60 years, it is around 1.98 t. The doubling time for the SD-HWMSR is 31 years, which is consistent with previous results.
•SD-HWMSR’s fuel channel pitch and radius have been optimized.•The SD-HWMSR with a relatively high breeding ratio has been introduced.•The feed rates of 232Th and 233U have been determined.•Breeding ratio and 233U doubling time have been estimated.•TCR evolution during SD-HWMSR operation has been investigated.
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