Horizontal Steam Generators Research Articles

Validation of the STEG Code against Experimental Data on Hydrodynamics of a Horizontal Steam Generator

Validation of the STEG Code against Experimental Data on Hydrodynamics of a Horizontal Steam Generator

Comparison of thermal hydraulic performance between horizontal and vertical steam generators in nuclear power plants

Abstract Steam generators (SG) for Nuclear Power Plants (NPPs) are important large-sized metal consuming equipment of nuclear power installations. Efficiency of steam generator operation determines the overall service life of the whole nuclear facility. Vertical steam generators are used normally in North America, Europe and South East Asia, but horizontal steam generators are currently of great importance to reduce building heights and construction costs that govern the overall cost of new nuclear power plants. The objective of the current study is to measure the performance of nuclear steam generators in NPPs through comparative assessments of vertical and horizontal configurations. For this purpose, the vertical U-tube steam generators of a typical 4-loop Pressurized Water Reactor (PWR) was replaced by a VVER-1000 horizontal steam generators to evaluate the horizontal SG performance, at the same plant conditions and characteristics, in comparison with the vertical SG. The thermal hydraulic system code RELAP5 was used in the current work to perform the required analysis, during steady and transient scenarios.

Investigation on thermohydraulic characteristics of novel superheated steam supply system for low temperature nuclear heating reactor

In a new Chinese low temperature nuclear heating reactor (NHR) demonstration project, a novel superheated steam supply system was designed to meet new requests for the steam produced in the secondary circuit. Different from the previous version of NHR200-II, which used a vertical steam generator to produce saturated steam, this newly designed system features a preheater, a horizontal steam generator, and a superheater for generating superheated steam. Numerical simulation method was used to investigate the feasibility and thermal hydraulic characteristics of this novel superheated steam supply system. The simulation results verify the accuracy and reliability of the system design, showing that the three heat exchangers can operate in coordination under different power levels, and the superheated steam generated in the secondary circuit can meet the users’ requirements. The system also demonstrated a remarkable ability to recover from sudden disturbances within 13.64 % change of the secondary circuit mass flow rate or 2.39 % change of the secondary circuit temperature under full power condition. Besides, the system has a power adjustment ability of ±10 %, and the system can quickly return to the new steady state. RELAP5 simulation results can provide theoretical guidance for the subsequent experimental research of this novel superheated steam supply system.

A thermal-hydraulic and control model for a Pb-Bi micro reactor

Lead-bismuth cooled reactor offers substantial potential in terms of safety, design simplification, proliferation resistance and economic performance. A Pb-Bi micro reactor was studied in this paper, and the primary coolant system models including the horizontal helical-coil once-through steam generator (S/G) model based on four-equation drift-flux, the annular gas tank pressurizer model and the core model, and the control model based on “load following” mode were established. Adopting the fully implicit scheme, Gear algorithm, quasi-Newton method, Steffensen method and first-order Taylor polynomial expansion method were flexibly selected in each module for numerical solution. The steady-state results show that the proposed model can successfully simulate the characteristics of the Pb-Bi micro reactor, and the steady-state calculation results are in good agreement with the design values. The transient results show that the proposed model can successfully simulate the dynamic process under different loads, and can realize the “load following” operation mode.

Dynamic process simulation of a 780 MW combined cycle power plant during shutdown procedure

The share of variable renewables in power generation is increasing due to the push to reduce emissions, and the flexibility of conventional power plants has become a major concern. There are many ways to increase the flexibility of existing power plants and implement a more flexible system for the future, such as a fast start-up procedure and higher load change rates. In this study, a 2D dynamic process simulation model of a reference combined cycle power plant is presented to increase the flexibility of cyclic operation by investigating, for the first time in the literature, the shutdown procedure using APROS software. The 780 MWel Tambak Lorok reference combined cycle power plant consists of the GE 9HA.02 heavy-duty gas turbine and a three-stage horizontal heat recovery steam generator with reheat. Several steps were considered to improve the accuracy of the developed dynamic process simulation model, including varying the steam leakage to the atmosphere to control how much thermal energy remains in the heat recovery steam generator, changing the shape loss coefficients of the tubes to achieve higher or lower recirculation, and decoupling the reheater and the intermediate pressure drum. The developed model is validated with real data from three different combined cycle power plants in different countries with various capacities. The comparison shows that the developed dynamic simulation model can accurately represent the real behaviour of natural convection in the heat recovery steam generator. The main outcome was to provide detailed information on the shutdown procedure of large-scale combined cycle power plants, addressing the aspect of the development of new start-up strategies to reduce the time required for the start-up procedure.

Degradation analysis of horizontal steam generator tube bundles through crack growth due to two-phase flow induced vibration

A correct understanding of vibration-based degradation is crucial from the standpoint of maintenance for Steam Generators (SG) as crucial mechanical equipment in nuclear power plants. This study has established a novel approach to developing a model for investigating tube bundle degradation according to crack growth caused by two-phase Flow-Induced Vibration (FIV). An important step in the approach is to calculate the two-phase flow field parameters between the SG tube bundles in various zones using the porous media model to determine the velocity and vapor volume fraction. Afterward, to determine the vibration properties of the tube bundles, the Fluid-Solid Interaction (FSI) analysis is performed in eighteen thermal-hydraulic zones. Tube bundle degradation based on crack growth using the sixteen most probable initial cracks and within each SG thermal-hydraulic zone is performed to calculate useful lifetime. Large Eddy Simulation (LES) model, Paris law, and Wiener process model are considered to model the turbulent crossflow around the tube bundles, simulation of elliptical crack growth due to the vibration characteristics, and estimation of SG tube bundles degradation, respectively. The analysis shows that the tube deforms most noticeably in the zone with the highest velocity. As a result, cracks propagate more quickly in the tube with a higher height. In all simulations based on different initial crack sizes, it was observed that zone 16 experiences the greatest deformation and, subsequently, the fastest degradation, with a velocity and vapor volume fraction of 0.5 m/s and 0.4, respectively.

Hydrodynamics of vapor-liquid flows in curvilined channels of separation devices of power plants

The main factor that affects the efficiency of the separation process is the lack of contact with the surface of the shutter when moving in the flow of small droplets of wet steam. This process depends on the physical and chemical properties of the wet vapor, the dispersion of the droplets, the parameters of the movement of the two-phase medium, adhesion and edge angle, and the geometry of the channel. Purpose. Determination of the limit modes of operation of separation shutter devices depending on the dispersion and quantity of droplet liquid, flow parameters and geometric characteristics of curved channels. Methodology. The methodology is based on the analysis of the physical model of the movement of a two-phase medium under the action of mass and gravitational forces in a curved horizontal channel. Findings. A mathematical model is presented for determining the trajectory of a liquid droplet in a curvilinear corrugation channel of the louvered package of a separator-superheater. The main conditions of film destruction and dynamic droplet break-up are defined. A method for expanding the range of stable operation of separation devices is proposed. Based on the obtained correlations, the design of the blind package is optimized. Originality. Based on the analysis of the physical model of the movement of a two-phase medium in a curved horizontal channel, a mathematical model was developed and the limit of capture of the dispersed phase was determined. Practical value. The presented results allow optimization of separation devices of boiler drums, horizontal steam generators and steam superheater separators of the II circuit of VVER-1000, fuel preparation systems of GTU.

DESIGN CHARACTERISTICS OF THE HORIZONTAL STEAM GENERATOR PGV-1000

The materials of the article consider the design characteristics of horizontal steam generators PGV-1000 for WWER NPPs. The NPP steam generator, in particular the PGV-1000 steam generator, is a specific heat exchange unit. This unit, together with a nuclear reactor and a steam turbine, is one of the main equipment of multi-circuit (double-circuit) steam turbine NPPs. The steam generator produces working steam using heat dissipated from the reactor core by the cooling medium and sent to the heat exchange surface of the steam generator. NPP steam generators, connecting the contours of the coolant and the working substance, equally belong to each of them. The heat-absorbing medium in the steam generator is the working substance (water, steam). PGV-1000 type NPP steam generators with pressurized water reactors produce dry saturated steam. The requirement to maintain high purity of the coolant is due to the heat transfer surfaces of such steam generators made of austenitic stainless steel with electropolished surfaces. WWER reactors do not allow the coolant to boil in the core, so the temperature of the coolant at the outlet of the reactor (at the inlet to the steam generator) is always lower than the saturation temperature corresponding to the water pressure in the coolant circuit. Underheating of the coolant to the saturation temperature (approximately 25 ÷ 30 °С) guarantees the exclusion of vaporization even in the most loaded reactor channels. The design characteristics of modern horizontal steam generators such as PGV-1000 of various modifications provide high technical and economic performance of NPP units with WWER-1000 and high maintainability, which allows to extend the service life of domestic NPPs.

Mathematical model of the horizontal steam generator PGV-1000

The materials of the article consider the design characteristics of horizontal steam generators PGV-1000 for WWER NPPs. The NPP steam generator, in particular the PGV-1000 steam generator, is a specific heat exchange unit. This unit, together with a nuclear reactor and a steam turbine, is one of the main equipment of multi-circuit (double-circuit) steam turbine NPPs. The steam generator produces working steam using heat dissipated from the reactor core by the cooling medium and sent to the heat exchange surface of the steam generator. NPP steam generators, connecting the contours of the coolant and the working substance, equally belong to each of them. The heat-absorbing medium in the steam generator is the working substance (water, steam). PGV-1000 type NPP steam generators with pressurized water reactors produce dry saturated steam. The requirement to maintain high purity of the coolant is due to the heat transfer surfaces of such steam generators made of austenitic stainless steel with electropolished surfaces. The design characteristics of modern horizontal steam generators such as PGV-1000 of various modifications provide high technical and economic performance of NPP units with WWER-1000 and high maintainability, which allows to extend the service life of domestic NPPs.

Numerical investigation on the thermal-hydraulic performance of separated structure steam generator with different tube arrangements

The horizontal steam generator is generally used in nuclear power plant and industry to produce steam. To increase the heat load and reduce the size, a steam drum can be added above the shell. However, it makes the overall flow of water cycle complicated. In this article, the two-phase boiling flow and heat transfer inside tube bundle under the separated structure has been investigated numerically based on the previous experiment. The Drift-Flux model was utilized to solve the equations of heat and mass transfer in the mixture flow. The local pressure drop, void fraction and heat transfer characteristics have been presented and discussed for different arrangements in detail. The analysis results showed that the overall boiling HTC of the tube arrangements of 30°and 60° appear better for this steam generator under the same condition. The boiling heat transfer in both bottom and upper tube bundle was mainly controlled by the nucleate boiling mechanism. However, both heat flux and vapor void fraction were found to affect the heat transfer performance. Beyond this analysis, a new type of heat transfer correlation has been proposed herein to evaluate the local HTC with a good accuracy. These correlations allow better predictions of the boiling heat transfer inside the SS-SG, which provide designers with better reference and guidance.

Two-Phase Flow-Induced Vibration Among the Horizontal Vver-1000 Steam Generator Tubes

Two-Phase Flow-Induced Vibration Among the Horizontal Vver-1000 Steam Generator Tubes

Simulation of the two-phase flow across tube bundle

Experiments on two-phase flow across an in-line tube bundle are analyzed with the STEG code, which has been developed for modeling thermal-hydraulic processes in a horizontal steam generator (SG). An adiabatic, vertical two-phase flows of air-water across horizontal in-line, 5 x 20 rod bundles, with a pitch-to-diameter ratio P/D=1.3 are considered, the mass velocity is varied in the range 27 - 818 kg/m2s. The calculated values of void fraction in the tube bundle are compared with the experimental ones measured by a gamma densitometer. A reasonable agreement between the calculations and the experimental data is obtained.

Recommended set of interfacial drag correlations for the two-phase flow under thermal–hydraulic conditions of a horizontal steam generator

A set of interfacial drag correlations is proposed for describing two-phase flows under thermal–hydraulic conditions of a horizontal steam generator (SG). This set of correlations takes into account the peculiarities of the two-phase flow in different regions of the SG. Four characteristic regions are considered: tube bundles, tube-free zones in the SG lower part, zone between the outlet from the tube bundles and the submerged perforated sheet (SPS), and the SG upper part. The flow regime map contains bubbly flow, cap-bubbly flow, churn-turbulent flow and mist flow. A two-group bubbly flow model is used to describe bubbly and cap-bubbly flows in the SG corridors/gaps and in the bubbling layer above the SPS. Churn-turbulent flow occurs at the outlet from the tube bundles. In zones with a high void fraction under the SPS and above the SPS, mist flow occurs as a result of steam escaping from the interface with water droplets being captured and carried up. Some coefficients of the correlations are adjusted on experimental data. The detailed description of the set of interfacial drag correlations is presented in the paper. These correlations are implemented in the STEG-M code, which is validated on the experimental data of the void fraction obtained at two slice models of a horizontal SG (PGV and PGV-1500) and the full-scale WWER-1000 SG. Good agreement between the calculated and experimental data is obtained. The mean absolute deviation of the void fractions is <5.0%.

Numerical analysis of the equalization capability of submerged perforated sheets for wwer-1500 horizontal steam generator

The results of a study on the equalization of a non-uniform steam load using different submerged perforated sheets (SPSs) are presented for a full-scale horizontal WWER-1500 steam generator (SG). The calculations performed with the STEG code are used. A short description of the 3D thermal-hydraulic code STEG is presented. A new model of gravitational separation based on empirical correlations for the size distribution of water droplets and for the modal droplet diameter is implemented in the STEG code. Three variants of the distribution of an SPS perforation degree are analyzed. Various characteristics are compared: the distributions of the superficial velocity on the SPS and evaporation surface, the fractions of the steam flow rate with high velocity in the steam region and the steam moisture at the outlet from the SG. The SPS perforation degrees, which significantly improve the equalization of the non-uniform steam load, are found using the STEG code.

Optimization of the PGV-1000MKO Steam Generator Using Computation Fluid Dynamics

Abstract This paper presents the work carried out in Experimental and design organization OKB “GIDROPRESS” to justify the separation characteristics of VVER-TOI steam generator (SG) using the STAR-CCM+ CFD-code. In the VVER-TOI project, new layout solutions were applied in the reactor plant as part of which the steam removal system from the SG was changed. Namely, in contrast to the VVER-1000 and VVER-1200 where the steam removal was organized through ten nozzles combined into a steam collector, in the VVER-TOI SG the steam removal was arranged through one nozzle located on the cold collector side. This change leads to the formation of a nonuniform velocity field in the separation volume, between the evaporation surface and the distribution perforated plate (DPP), and can lead to the excessive increase of steam humidity. To ensure the steam separation characteristics of a horizontal SG with one steam nozzle, it was proposed to create a nonuniform resistance on the way of steam motion from the evaporation surface into steam nozzle applying a nonuniform degree of the DPP perforation. Two computer models of the SG steam volume with different steam removal schemes (through one and ten nozzles) were developed, a set of studies on verification and validation was carried out and a set of calculations were performed. According to the results of the calculations, the necessity of introducing a nonuniform degree of the DPP perforation was justified. Further, to determine the nonuniform degree of DPP perforation, a set of optimization calculations of the SG steam volume with one steam removal nozzle was performed. The nonuniform degree of DPP perforation of the VVER-TOI SG was selected, which provide steam velocity distribution as close as possible to the SG with ten steam nozzles. To justify the chosen design, sensitivity analysis was also carried out according to the hole diameters tolerance and steam load profile.

Applying second law of thermodynamic for optimization of horizontal steam generator

One of the essential components in a pressurized water reactor is the steam generator (SG) that has an important role in efficiency of nuclear power plants. In the present work, a horizontal steam generator (HSG) was investigated based on entropy generation as a consequence of second law of thermodynamic. The thermal hydraulic operation parameters were calculated by considering a single-phase model for the primary loop related to the tube and two-phase model for the secondary loop related to steam generator shell. Then, the effect of each parameter against different constraints such as length-to-diameter ratio, mass flow rate, tube diameter, and inlet temperature on the generated entropy was investigated. To validate the physical equations and the framework used in this model, the results of the developed code are compared with the research articles related to enthalpy generation. The results showed that a significant increase in length-to-diameter ratio and tube diameter resulted in a decrease in entropy generation number (EGN). Therefore, it is concluded that decreasing the entropy generation enhances the performance of steam generators as well as their economic efficiency.

Investigation of the equalization capability of submerged perforated sheets forWWER-1500 horizontal steam generator

Non-uniform heat transfer occurs at the steam generator secondary side, thus inducing a non-uniform steam generation and a non-uniform steam flow rate along the evaporation surface. In order to equalize the steam flow rate, submerged perforated sheet is installed in the horizontal SGs An analysis of the equalization of the non-uniform steam load in the WWER-1500 horizontal steam generator is performed using the STEG calculation code. Variant calculations of various options for the perforation of sheets allowed us to determine the design of submerged perforated sheet, which very well equalizes the initially non-uniform steam load.

Analysis of experimental data on the hydrodynamics in a horizontal steam generator using the STEG code

The new model of interfacial drag is proposed and implemented in the STEG code based on the 3D two-fluid model is presented. Experimental data obtained at the PGV test facility is used for validation of the modified STEG code. The PGV test facility comprises a model of the horizontal steam generator used for Russian type water-water energetic reactors. A quantitative comparison with experimental values of void fractions has been performed. It can be argued that the results generally indicate the relatively good predictive ability of the modified STEG code.

Fuzzy logic algorithms for classification and parameterization of eddy-current signals

Safety of nuclear power plants operation depends on steam generator safe operation. Russian nuclear power plants with water-water energetic reactors WWER-440 and WWER-1000 use horizontal type steam generators which are cylindrical objects of 3 m diameter and 12 - 15 m length. Steam goes through steam generator tube sheets in the bottom from hot end and passes its energy through heat-exchanger tube system and become colder on the other tube sheet. Reactors WWER-440 have more than 5,000 tubes in one steam generator and reactors WWER-1000 have already 11,000 tubes in one steam generator. Each block of WWER-440 reactor has 6 steam generators, and each block of WWER-1000 reactor has 4 steam generators. A thin-walled steam generator tube can be a threat of nuclear fallout in case of high pressure in primary coolant loop. To be an effective barrier these tubes should be free from corrosion, thinning and cracks.

Optimizing the Design of the Steam-Receiving Perforated Sheet Used in the PGV-1000MKO Steam Generator

The VVER-TOI reactor plant has for the first time been furnished with a new layout of steam generators in the NPP reactor building, according to which the steam produced in the steam generator is removed from it through one steam nozzle. The shift for using one steam-offtake nozzle results in that a nonuniform steam velocity field is produced in the separation volume between the evaporation surface and steam-receiving perforated sheets (SRPSs), which is caused by steam motion along the path with the lowest friction, and this can entail excessive carryover of moisture from the steam generator (SG). To obtain the necessary moisture-separation performance of a horizontal steam generator equipped with one steam nozzle, it is necessary to set up a uniform field of the steam velocity vector’s vertical component in the separation volume with limiting the pressure loss in the SG steam path down to the design value. Therefore, it is proposed to arrange nonuniform flow friction along the steam motion path from the evaporation surface to the steam line by using a variable SRPS perforation ratio. In this study, a set of optimization numerical analyses of the SRPS design for the PGV-1000MKO steam generator performed using the CFD methods was carried out for determining the perforation ratio. In carrying out the optimization numerical analyzes, the performance characteristics of the steam-receiving device equipped with one steam nozzle located in the steam generator’s upper part and consisting of more than 50 perforated sheets had to be made maximally close to the performance characteristics of the steam-receiving device equipped with ten steam nozzles. By using an elaborated computer model, a set of optimization numerical analyses of the SRPS design was carried out, and an optimized design version of the steam-receiving device with a variable perforation ratio for the PGV-1000MKO steam generator has been obtained.