Sevastopol National University of Nuclear Energy and Industry

The practical implementation of automated systems for management of primary-to-secondary leakage is a crucial issue for operational safety improvement at Ukrainian nuclear power plants. In this case, one of the main indicators of the primary-to-secondary leakage is the activity concentration increasing in the main steam lines of the affected steam generator. The detailed analysis of the geometrical features, arrangement of the main steam lines of the steam generator in VVER-1000 and radiation detectors allow identifying the crosstalk effect and its influence on the correct determination of the affected steam generator. The paper describes the main components of the developed models in the detection region in MCNP6.2 software. For the correctness of the comparative analysis, the distance between two adjacent main steam lines of the steam generators remains constant in all models. The radiation detectors have been modelled in the regular location and adjacent to the main steam lines of the steam generator. The registration efficiencies of ionizing radiation from 16N by the sensitive elements of the detectors such as BDMG-04-02, SGLM-201-1 and GIM-204 have been assessed. BDMG-04-02, SGLM-201-1 and GIM-204 responses, depending on the activity concentration of 16N in the detection area and considering the nonproportionality features of the devices, have been estimated. The presence of crosstalk effects has been confirmed. The significant influence of the paralyzing and non-paralyzing dead time on the reliable determination of the activity concentration and correct identification of the affected steam generator have been emphasized. The obtained results can be used as initial data for justification of system setpoints for launching the automated algorithm to manage the primary-to-secondary leakage accident without operator’ actions and fulfill its improvement.

This paper reports on improvement of the technological conditions for nano-heteroepitaxial structures (NHES) growth with Ge quantum dots (QDs) by liquid phase epitaxial (LPE) method applying impulse cooling on the substrate (ICS) The physical and mathematic modeling of the processes of growth and the analysis of the thermodynamic status has been carried out to optimize the construction of the thermal unit, the located in it graphite cassette and of the thermal conditions. For the analysis the Solid Works Flow Simulation program is applied, which has a satisfactory accuracy of calculations of heat-transfer simulation. The analysis has revealed shortcomings in the construction of the equipment. Having in mind these results the equipment is reconstructed and new different elements of the thermal block are installed. Good agreement of the experimental and calculated temperature distribution in the process of NHES with Ge QDs growing is obtained. The grown Ge QDs have improved structure with homogeneous distribution and size and depth of the Quantum Wells. The experiments carried out show good reproducibility of the growing process confirming the correctness of the mathematic modeling.

In this study, the behavior of vibration of sandwich cylindrical shells covered by functionally graded coatings and resting on the Pasternak elastic foundation considering combined influences of shear stresses and rotary inertia are examined. It is assumed that the effective material properties of functionally graded coatings changes exponentially in thickness direction. The modified Donnell type equations of motion of functionally graded and homogeneous sandwich cylindrical shells on the Pasternak elastic foundation are deduced using the first-order shear deformation theory. Basic equations are reduced to an algebraic equation of the sixth order and numerically solving this algebraic equation gives the dimensionless fundamental frequency. The expressions for the dimensionless fundamental frequencies of functionally graded and ceramic coated sandwich cylindrical shells with and without taking into account the effects of Pasternak elastic foundation and shear stresses obtained in a special case. Calculations, the influences of an elastic foundation, compositional profiles of coatings, shear stresses, rotary inertia, and sandwich shell geometry parameters on the nondimensional fundamental frequency are described. The results are verified by comparing the obtained values with those in the existing literature.