Vol 64, No 1 (2017)

This paper is dedicated to the creation of a facility for the experimental study of a phenomenon of background acoustic emission (AE), which is detected in the main circulation loop (MCL) of WWER power units. The analysis of the operating principle and the design of a primary feed-and-blow down system (FB) deaerator of NPP as the most likely source of continuous acoustic emission is carried out. The experimental facility for the systematic study of a phenomenon of continuous AE is developed. A physical model of a thermal deaerator is designed and constructed. A thermal monitoring system is introduced. An automatic system providing acoustic signal registration in a low frequency (0.03–30 kHz) and high frequency (30–300 kHz) bands and study of its spectral characteristics is designed. Special software for recording and processing of digitized electrical sensor signals is developed. A separate and independent principle of study of the most probable processes responsible for the generation of acoustic emission signals in the deaerator is applied. Trial series of experiments and prechecks of acoustic signals in different modes of the deaerator model are conducted. Compliance of basic technological parameters with operating range of the real deaerator was provided. It is shown that the acoustic signal time-intensity curve has several typical regions. The pilot research showed an impact of various processes that come about during the operation of the deaerator physical model on the intensity of the AE signal. The experimental results suggest that the main sources of generation of the AE signals are the processes of steam condensation, turbulent flow of gas-vapor medium, and water boiling.

When one solves engineering problems related to the cooling of fuel assemblies (FAs) in a spent fuel storage pool (SFSP) and the assessment of nuclear safety of FA storage in an SFSP in the initial event of loss of SFSP cooling, it is essential to determine the coolant density and, consequently, steam volume fractions φ in bundles of fuel elements at a pressure of 0.1–0.5 MPa. Such formulas for calculating φ that remain valid in a wide range of operating parameters and geometric shapes of channels and take the conditions of loss of SFSP cooling into account are currently almost lacking. The results of systematization and analysis of the available formulas for φ are reported in the present study. The calculated values were compared with the experimental data obtained in the process of simulating the conditions of FA cooling in an SFSP in the event of loss of its cooling. Six formulas for calculating the steam volume fraction, which were used in this comparison, were chosen from a total of 11 considered relations. As a result, the formulas producing the most accurate values of φ in the conditions of loss of SFSP cooling were selected. In addition, a relation that allows one to perform more accurate calculations of steam volume fractions in the conditions of loss of SFSP cooling was derived based on the Fedorov formula in the two-group approximation.

Results of experimental determination of the average heat transfer coefficient upon condensation of pure steam α_c and steam from air–steam mixture α_as.m in tubes of a large-scale model of the emergency cooling heat exchanger in the system of passive heat removal through steam generators of AES-2006 project at Leningrad II NPP are presented. The model contained 16 parallel tubes with a diameter of 16 × 2 mm and a length of 2.9 m connected to the upper steam distributing and lower condensate gathering horizontal collectors; the distance between their axes was 2.28 m. The tube segments were vertical, horizontal, or inclined. The internal diameter of the collectors was 40 or 60 mm. The model was placed in the lower part of a tank with a height of 6.5 m and a volume of 5.85 m³ filled with boiling water at atmospheric pressure. The experimental parameters were as follows: pressure range 0.43–7.77 MPa, condensate Reynolds number Re_f = (0.87–9.3) × 10³, and average air volume fraction at the segment with air–steam mixture 0.18–0.85. The studies showed that nonuniformity of static pressure distribution along the steam-distributing collector strongly influences the reduction of α_c value (ejecting effect). The agreement between experimental and calculated according to statutory guidelines values of α_c for vertical tubes is achieved if the dynamic head of the steam flow at the input of the steam-distributing collector does not exceed 1 kPa. Equations for calculation of the diffusion heat transfer coefficient at steam condensation from the air–steam mixture α_as.m on the internal tube surface are proposed. In the considered conditions, air is completely displaced by steam flow from the upper to the lower part of the tubes. The boundary between these regions is characterized by an average reduced steam velocity through this cross section of 1.6 ± 0.4 m/s. Above the boundary cross section, it is recommended to calculate α_c. according to [1].

The work is dedicated to the study of vibration activity of double-span rotor of turbine unit (TU) consisting of a high-pressure rotor and a rotor of medium-low pressure rotor combined with it (HPR—MLPR system) at the lowest critical rotational frequencies at rundown. When using the design model of the system, it was assumed that the rotors were installed on anisotropic elastic-damper supports, tied among themselves by a rigid clutch, and having the initial curvature (nonremovable initial deflection) and the residual unbalances in both spans. Two types of bearings were considered–elliptical and six-shoe segmental bearings. It was believed that the initial deflection during operation or as a result of noncompliance of start-up conditions initially gets only HPR and the axis shape of unloaded HPR is known and it is a flat curve. The resultant curve of nonremovable deflection of the HPR–MLPR system occurring after installing the shafting into the bearings was also considered flat and located in the same plane as the initial deflection of HPR. The cases of additional presence with the rotors of concentrated residual unbalances in the middle of each span are considered. The case of availability with both rotors of the shafting antisymmetric point unbalances on each of the spans was not considered in this work. The values of each of the factors of vibration activity (of the initial deflection of HPR and residual unbalances of both rotors) were chosen to be equal to the maximum permissible established by the active in the practice of TU operation limitations on the maximum values of the initial deflection of thermally unstable rotor and its residual unbalances. The influence of location of residual unbalances in relation to the initial deflection curve of HPR–MLPR system on the total amplitudes of transient vibrations caused by both excitation factors in the reference points of the system at TU rundown was investigated. It was established that, at the unfavorable relations between directions of curvature of the rotors of HPR–MLPR system and their residual unbalances with segmental bearings, touching in the diaphragm seals in the middle of HPR span is possible.

During the bed gasification of solid fuels, the process temperature in the reaction zone is not high enough for reaching the maximum rate of the chemical efficiency factor of the gasification process. In order to increase the chemical efficiency factor, it is necessary to supply extra heat to the reaction zone to increase the reaction temperature. In this article, coal gasification in a chamber with forced fluidized bed is considered and it is proposed to supply extra heat with a circulating flow of an inert particulate heat transfer agent. Circulating inert particulate material is successively heated by coal combustion in a cone chamber with bubbling fluidized bed and in a combustion chamber with a spherical nozzle that inhibits the forced fluidized bed. After that, the heat transfer agent heated to 930–950°C enters first in a gasification chamber with bubbling bed and then in a chamber with forced fluidized bed, where it transfers the physical heat to the air fuel mixture. The experiments conducted with crushed Borodinsky coal and inert particulate heat transfer agent (electrocorundum) showed the temperature rise in a gasification chamber with from 760 to 870°C and the increase in the combustible component (CO) concentration in the gasification products by 5.5%. Based on the kinetic equations of the fuel combustion reactions and the CO₂ reduction to CO and on the thermal balance equations of combustion and gasification chambers, the simulation model for the gas composition and the temperature rate calculated by the height of reaction chambers was developed. The experimental temperature rates and product gas compositions are in good agreement with the simulation results based on the proposed kinetic gasification model.

One of the ways for improving the operational reliability and economy of thermal power station equipment, including combined-cycle equipment, is to decrease the rates of the corrosion of constructional materials and the formation of scales in the water-steam circuit. These processes can be reduced to a minimum via the use of water with a minimum content of admixtures and the correction treatment of a heat-transfer fluid. The International Association for the Properties of Water and Steam (IAPWS), which unites specialists from every country of the world, has developed water and steam quality standards for power station equipment of different types on the basis of theoretical studies and long-term experience in the operation of power plants in 21 countries. Different water chemistry regimes are currently used at conventional and combined-cycle thermal power stations. This paper describes the conditions for the implementation of water chemistry regimes with the use of sodium salts of phosphoric acid and NaOH for the quality correction of boiler water. Water and steam quality standards and some recommendations for their maintenance under different operational conditions are given for each of the considered water chemistry regimes. The standards are designed for the water-steam circuit of conventional and combined-cycle thermal power stations. It is pointed out that the quality control of a heat-transfer fluid must be especially careful at combined-cycle thermal power stations with frequent startups and shutdowns.

Research of a metal of the stop valve case (SVC) of the K-300-23.5 LMZ turbine (steel grade 15Kh1M1FL), destroyed after operation for 331000 hours, is performed. It’s chemical composition and properties are determined as follows: a short-term mechanical tensile stress at 20°C and at elevated temperature, critical temperature, fragility, critical crack opening at elevated temperature, and long-term strength. Furthermore, nature of the microstructure, packing density of carbide particles and their size, and chemical composition of carbide sediment are estimated. A manifestation of metal properties for the main case components by comparison with a forecast of the respective characteristics made for the operating time of 331000 hours is tested. Property-time relationships are built for the forecast using statistical treatment of the test results for the samples cut out from more than 300 parts. Representativeness of the research results is proved: the statistical treatment of their differences are within the range of ±5%. It has been found that, after 150000 hours of operation, only the tensile strength insignificantly depends on the operating time at 20°C, whereas indicators of strength at elevated temperature significantly reduce, depending on the operating time. A brittle-to-ductile transition temperature (BDTT) raises, a critical notch opening changes in a complicated way, a long-term strength reduces. It has been found empirically that the limit of a long-term strength of the SVC metal at 540°C and the operating time of 10⁵ hours is almost 1.6 times less than the required value in the as-delivered state. It is possible to evaluate a service life of the operating valves with the operating time of more than 330000 hours with respect to the long-term strength of the metal taking into account the actual temperature and stress. Guidelines for the control of similar parts are provided.