Computational analysis for prediction of pressure of PWR presurizer under transient conditions

A computer model has been developed for prediction of the pressure in the pressurizer under transient conditions.In the model three separate thermodynamic regions which are not required to be in thermal equilibrium have been considered.The mathematical model derived from the general conservation equations includes all of the important thermal-hydraulics phenomena occurring in the pressurizer,i.e.,stratification of the hot water and incoming cold water,bulk flashing and condensation ,wall condensation,and interfacial heat and mass transfer,etc.The bubble rising and rain-out models are developed to describe bulk flashing and condensation.respectively.To obtain the wall condensation rate,a one-dimensional heat conduction equation is solved by the pivoting method.The presented model will predict the pressure-time behavior of a PWR pressurzer during a variety of transients.The results obtained from the propesed mathematical model are in good agreement with available data on the CHASHMA nuclear power plant‘s pressurizer performance.     

CFD studies on the separation performance of a new combined gas–solid separator used in TMSR-SF

In order to comply with discharge standards, a gas–solid separator is used to remove solid particles from the thorium molten salt reactor-solid fuel(TMSR-SF)system. As a key component, it directly determines system energy efficiency. However, current gas–solid separators,based on activated carbon adsorption technology, result in high pressure drops and increased maintenance costs. In the present study, a new combined gas–solid separator was developed for the TMSR-SF. Based on a simplified computational fluid dynamics(CFD) model, the gas–solid twophase flow and the motion trajectory of solid particles were simulated for this new separator using commercial ANSYS 16.0 software. The flow and separation mechanism for this structure were also been discussed in terms of their velocity effects and pressure field distributions, and then the structure was optimized based on the influence of key structural parameters on pressure and separation efficiency. The results showed that the standard k–e model could be achieved and accurately simulated the new combined separator. In this new combined gas–solid separator, coarse particles are separated in the first stage using rotating centrifugal motion, and then fine particles are filtered in the second stage, giving a separation efficiency of up to 96.11%. The optimum blade inclination angle and numbers were calculated to be 45° and four, respectively. It implicated that the combined separator could be of great significance in a wide variety of applications.     

Simulation of hydrogen distribution and effect of Engineering Safety Features (ESFs) on its mitigation in a WWER-1000 containment

In this study, thermal–hydraulic parameters inside the containment of a WWER-1000/v446 nuclear power plant are simulated in a double-ended cold leg accident for short and long times(by using CONTAIN 2.0 and MELCOR 1.8.6 codes), and the effect of the spray system as an engineering safety feature on parameters mitigation is analyzed with the former code. Along with the development of the accident from design basis accident to beyond design basis accident,the Zircaloy–steam reaction becomes the source of in-vessel hydrogen generation. Hydrogen distribution inside the containment is simulated for a long time(using CONTAIN and MELCOR), and the effect of recombiners on its mitigation is analyzed(using MELCOR). Thermal–hydraulic parameters and hydrogen distribution profiles are presented as the outcome of the investigation. By activating the spray system, the peak points of pressure and temperature occur in the short time and remain below the maximum design values along the accident time. It is also shown that recombiners have a reliable effect on reducing the hydrogen concentration below flame propagation limit in the accident localization area. The parameters predicted by CONTAIN and MELCOR are in good agreement with the final safety analysis report. The noted discrepancies are discussed and explained.     

Gas Breakdown of Radio Frequency Glow Discharges in Helium at near Atmospheric Pressure

A one-dimensional self-consistent fluid model was developed for radio frequency glow discharge in helium at near atmospheric pressure, and was employed to study the gas breakdown characteristics in terms of breakdown voltage. The effective secondary electron emission coefficient and the effective electric field for ions were demonstrated to be important for determining the breakdown voltage of radio frequency glow discharge at near atmospheric pressure. The constant of A was estimated to be 64±4 cm 1 Torr 1 , which was proportional to the first Townsend coefficient and could be employed to evaluate the gas breakdown voltage. The reduction in the breakdown voltage of radio frequency glow discharge with excitation frequency was studied and attributed to the electron trapping effect in the discharge gap.     

Numerical simulation of laser ablation of molybdenum target for laser-induced breakdown spectroscopic application

Laser-induced breakdown spectroscopy has been recognized as a significant tool for element diagnostics in plasma–wall interaction. In this work, a one-dimensional numerical model is developed to simulate the laser ablation processes of a molybdenum(Mo) target in vacuum conditions. The thermal process of the interaction between the ns-pulse laser with wavelength of 1064 nm and the Mo target is described by the heat conduction equation. The plasma plume generation and expansion are described by Euler equations, in which the conservation of mass density, momentum and energy are included. Saha equations are used to describe the local thermal equilibrium of electrons, Mo atoms,Mo~+ and Mo~(2+) Plasma shielding and emission are all considered in this model. The mainly numerical results are divided into three parts, as listed below.Firstly, the rule of the plasma shielding effect varying with laser intensity is demonstrated quantitatively and fitted with the Nelder function. Secondly, the key parameters of plasma plume,such as the number density of species, the propagation velocity and the temperature, are all calculated in this model. The results indicate that the propagation velocity of the plume center increased with time in a general trend, however, one valley value appeared at about 20 ns due to the pressure gradient near the target surface leading to negative plasma velocity. Thirdly, the persistent lines of a Mo atom in the wavelength range from 300 nm to 600 nm are selected and the spectrum is calculated. Moreover, the temporal evolutions of Mo's spectral lines at wavelength of 550.6494 nm,553.3031 nm and 557.0444 nm are given and the results are compared with experimental data in this work.     

Thermal–hydraulic analysis of space nuclear reactor TOPAZ-Ⅱ with modified RELAP5

With the advantages of high reliability, power density, and long life, nuclear power reactors have become a promising option for space power. In this study, the Reactor Excursion and Leak Analysis Program 5(RELAP5), with the implementation of sodium–potassium eutectic alloy(NaK-78) properties and heat transfer correlations, is adopted to analyze the thermal–hydraulic characteristics of the space nuclear reactor TOPAZ-Ⅱ.A RELAP5 model including thermionic fuel elements(TFEs), reactor core, radiator, coolant loop, and volume accumulator is established. The temperature reactivity feedback effects of the fuel, TFE emitter, TFE collector,moderator, and reactivity insertion effects of the control drums and safety drums are considered. To benchmark the integrated TOPAZ-Ⅱ system model, an electrical ground test of the fully integrated TOPAZ-Ⅱ system, the V-71 unit,is simulated and analyzed. The calculated coolant temperature and system pressure are in acceptable agreement with the experimental data for the maximum relative errors of 8 and 10%, respectively. The detailed thermal–hydraulic characteristics of TOPAZ-Ⅱ are then simulated and analyzed at the steady state. The calculation results agree well with the design values. The current work provides a solid foundation for space reactor design and transient analysis in the future.     

Astrophysical constraints on a parametric equation of state for neutron-rich nucleonic matter

Extracting the equation of state(EOS) and symmetry energy of dense neutron-rich matter from astrophysical observations is a long-standing goal of nuclear astrophysics. To facilitate the realization of this goal, the feasibility of using an explicitly isospin-dependent parametric EOS for neutron star matter was investigated recently in [1–3]. In this contribution, in addition to outlining the model framework and summarizing the most important findings from [1–3], we report a few new results regarding constraining parameters characterizing the highdensity behavior of nuclear symmetry energy. In particular,the constraints on the pressure of neutron star matter extracted from combining the X-ray observations of the neutron star radius, the minimum–maximum mass M=2:01 M_⊙, and causality condition agree very well with those extracted from analyzing the tidal deformability data by the LIGO ? Virgo Collaborations. The limitations of using the radius and/or tidal deformability of neutron stars to constrain the high-density nuclear symmetry energy are discussed.     

Mode transition induced by gas pressure in dusty acetylene microdischarges: two-dimensional simulation

Radio-frequency microdischarge in acetylene is investigated by use of a fluid model and an aerosol dynamics model in a cylindrical discharge chamber. In this article, the results at a pressure of 100–500 Torr, a voltage of 80–150 V, and an electrode gap of 400–1000 μm are carefully analyzed and discussed. It is shown that two electron heating modes α and γ appear in the microdischarge, and the pressure-dependent transition from α to γ was accompanied by the abrupt decrease of electron density and electron temperature. The mode transition phenomenon is further confirmed by the variation of the electron temperature axial profiles, the profiles vary continuously from a center high at the pressure of 100 Torr to an edge high at the pressure of500 Torr. Furthermore, in the α mode(100 Torr) the plasma density increases linearly with the increase of electrode gap, but decreases sharply with the increase of electrode gap in the γ mode(100 Torr). The gas pressure and applied voltage effects on the nanoparticle density and degree of nonuniformity are also investigated. It has been shown that the gas pressure greatly influences the axial profiles of nanoparticle density and the values of the degree of nonuniformity, while the values of the plasma parameters(electron density and nanoparticle density) strongly depend on the applied voltage.     

Stress and Thermal Analysis of the In-Vessel Resonant Magnetic Perturbation Coils on the J-TEXT Tokamak

A set of four in-vessel saddle coils was designed to generate a helical field on the J-TEXT tokamak to study the influences of the external perturbation field on plasma. The coils are fed with alternating current up to 10 kA at frequency up to 10 kHz. Due to the special structure, complex thermal environment and limited space in the vacuum chamber, it is very important to make sure that the coils will not be damaged when undergoing the huge electromagnetic forces in the strong toroidal field, and that their temperatures don’t rise too much and destroy the insulation. A 3D finite element model is developed in this paper using the ANSYS code, stresses are analyzed to find the worst condition, and a mounting method is then established. The results of the stress and modal analyses show that the mounting method meets the strength requirements. Finally, a thermal analysis is performed to study the cooling process and the temperature distribution of the coils.     

A non-equilibrium molecular dynamics study of the thermal conductivity of uranium dioxide

The thermal conductivity of uranium dioxide in the temperature range of 300–2400 K was estimated by non-equilibrium molecular dynamics calculation using Fourier law.The Kawamura function was adopted as the interatomic potential function.The calculated thermal conductivities are found to be strongly dependent on the temperature of the simulation cube.The thermal conductivity simulation results are compared with the experiment results and agreed well with the experimental results when the temperature is above 600 K.The thermal conductivities scale effects are found to be existed in uranium dioxide nanometer thin film.The approximate mean free paths of phonons in different temperatures can be examined.     

Condensation heat transfer characteristic in the presence of noncondensable gas on natural convection at high pressure

The steam-gas pressurizer in integrated small reactors experiences very complicated thermal-hydraulic phenomena. Especially, the condensation heat transfer with noncondensable gas under natural convection is an important factor to evaluate the pressurizer behavior. However, few studies have investigated the condensation in the presence of noncondensable gas at high pressure. In this study, therefore, a theoretical model is proposed to estimate the condensation heat transfer at high pressure using the heat and mass transfer analogy. For the high pressure effect, the steam and nitrogen gas tables are used directly to determine the density of the gas mixture and the heat and mass transfer analogy based on mass approach is applied instead of that based on the ideal gas law. A comparison of the results from the proposed model with experimental data obtained from Seoul National University indicates that the condensation heat transfer coefficients increase with increasing system pressure and with decreasing mass fraction of the nitrogen gas. The proposed model is also compared with other conventional correlations proposed in the literature. The proposed model demonstrates the capability to predict the condensation heat transfer coefficients at high pressure better than any other correlation. Finally, the condensate rate is compared to verify the application of the heat and mass transfer analogy at high pressure. The comparison results confirm that the heat and mass transfer analogy can be applied to evaluate the condensation heat and mass transfer at high pressure.     

非凝性气体对汽-气稳压器稳压的影响研究

通过分析相间的传热传质过程以及非凝性气体存在时壁面蒸汽冷凝过程,建立了汽 气稳压器模型,研究了非凝性气体对稳压过程的影响,描述了稳压器的稳压特性,并将模型计算结果与MIT稳压器实验数据进行了对比。结果表明：当不含非凝性气体时,计算精度高,相对偏差在0.8%内,压力峰值为0.647 MPa;当非凝性气体含量从0增至20%时,计算精度相对减小,最高相对偏差为15.4%;压力峰值从0.647 MPa增至1.02 MPa。研究表明非凝性气体对稳压器稳压过程具有重要影响作用,随着非凝性气体的种类和含量的变化,稳压器内稳压过程发生显著变化。     

Development of nonequilibrium pressurizer model with noncondensable gas

To investigate thermal–hydraulic characteristics of a steam–gas pressurizer in the integral type reactor, the steam–gas pressurizer model based on the two-region nonequilibrium concept was developed and introduced into RETRAN-3D/INT code. The model includes an explicit solution method for the one-dimensional governing equations and the equation of the state solution method to determine the thermal–hydraulic state of the steam–gas pressurizer volume. In addition, the wall condensation model based on the diffusion layer modeling was included to consider the effect of the noncondensable gas. The developed model was verified with the results from the pressurizer insurge experiment conducted at Massachusetts Institute of Technology. From the verification results, it was concluded that the developed steam–gas pressurizer model can sufficiently predict the pressurizer transient and it can be used as a component model of the one-dimensional system code based on the homogeneous equilibrium model.     

PWR pressurizer modeling

A series of experiments have been performed which help to provide fundamental understanding of the phenomena which are important to the analysis of a PWR pressurizer. The transients considered include insurges to a partially-full tank, outsurges, insurges to a tank with hot walls, empty tank insurges, and combined insurges and outsurges. The experiments include the effects of noncondensable gases, and free surface heat transfer. These experiments provide a data base from which recommendations are made for calculating such phenomena, as: (i) stratification of the hot water and incoming cold water, (ii) wall condensation, (iii) flashing, (iv) rainout, (v) suppression of flashing, (vi) wall conduction, (vii) the effect of noncondensable gases on wall heat transfer, and (viii) free surface heat transfer. From these experiments a general model of a PWR pressurizer has been developed. It will predict the pressure-time behavior of a PWR pressurizer during a variety of transients. The model has been benchmarked against the low pressure experiments of this study and a single full scale pressurizer transient experiment. The most significant finding is the pool in the pressurizer remains stratified during an insurge transient so that practically no heat transfer to the cold insurge liquid occurs. Wall heat transfer can be significant for insurge transients, however.     

Numerical Analysis of the PHEBUS Containment Thermal Hydraulics

This paper describes numerical analysis of the PHEBUS FP containment thermal-hydraulics. PHEBUS FP is an international project undertaken with the aim of evaluating the behavior of radioactive fission products released from a LWR pressure vessel into the containment vessel during a hypothetical severe accident. Six integral in-pile tests have been planned and are being carried out at Cadarache, France. The European Union, the United States, Canada, Korea and Japan are participating in this project. From Japan, the Nuclear Power Engineering Corporation and the Japan Atomic Energy Research Institute are collaborating the other parties involved in the project.

Since the behavior of fission products is strongly dependent on the surrounding environmental conditions, accurate prediction of the thermal-hydraulics in the containment vessel is essential to accurately evaluate the behavior. Characteristics of condensation heat transfer in the presence of noncondensable gases play a key role in the PHEBUS thermal-hydraulics, especially under the condition of high noncondensable gas mass fraction. Many models for condensation heat transfer in the presence of noncondensable gases have been proposed. However, these models were not found suitable for PHEBUS analysis, because they were focused on the low noncondensable gas mass fraction condition.

In this study, a single-phase multi-component code, TFLOW-FP has been newly developed to predict thermal-hydraulics in the PHEBUS FP containment. Moreover, a new degradation factor correlation for the condensation heat transfer coefficient due to the presence of noncondensable gases has also been developed and incorporated into the code. This code was applied for analysis of the thermal-hydraulic benchmark tests and the first in-pile test, FPTO. The results show that the code can predict the total pressure, gas temperature distributions, the relative humidity in the containment vessel and steam condensation rate on the surface of condenser rods very well.     

A linearized non steady state model for the pressurizer of the safe integral reactor concept

A linearized model for the pressurizer of the Safe Integral Reactor (SIR) is developed. The mathematical model derived from the general conservation equations includes all the important thermal-hydraulic processes occurring in the pressurizer. These processes are spray condensation, interfacial condensation, vapour rise, condensate fall, and heat tranfer from heaters. Also, the model takes into account some special functional features of the passive spray and the fluidic diodes. The insurge and outsurge events are modelled separately and the pressurizer response to insurge and outsurge flows are compared for the SIR, the H. Robinson, and the Shippingport reactors. It is concluded that the SIR passive spray concept is not as favourable as valved spray in inverting the pressure rise during an insurge flow.     

AP1000自动降压系统误开启事故仿真分析

针对AP1000的具体结构和运行特点,采用FORTRAN程序设计语言,开发了AP1000瞬态热工水力计算程序RETAC。利用RETAC对AP1000自动降压系统(ADS)误开启事故进行仿真分析,得到稳压器压力、堆芯归一化热功率、堆芯归一化流量、堆芯平均温度、燃料中心最高温度和最小偏离核态沸腾比（MDNBR）等主要系统参数的响应特性。分析结果表明,在稳压器低压停堆保护的作用下,燃料中心最高温度和MDNBR未超出规定限值,满足安全准则要求。并将计算结果与美国西屋公司AP1000分析软件LOFTRAN的计算结果进行对比,对比趋势符合良好,证明了RETAC建模和自动降压系统临界流模型计算的合理性。     

Forced convection condensation in the presence of noncondensable gas in a horizontal tube; experimental and theoretical study

To have a better understanding on forced convection condensation with noncondensable gas inside a horizontal tube, an experimental research and theoretical investigation were conducted under annular and wavy flow. The effects of noncondensable gas mass concentration, mixture gases velocity, pressure and inner wall sub-cooling on the condensation heat transfer have been analyzed. The results indicate that the local heat transfer coefficient increases with the increase of the mixture inlet velocity and pressure while decreases with the increase of the noncondensable mass fraction and wall sub-cooling. Based on the above conclusions, an empirical correlation for predicting the local heat transfer coefficient was proposed which showed a good agreement with the experimental data with an error of ±20%. Furthermore, a theoretical model using the heat and mass transfer (HMT) analogy method was developed including the suction effect. The heat transfer capacity for the film, gaseous boundary and convective heat transfer of the bulk gases were compared along the tube. Besides, the axial distribution of the bulk gases and liquid–gas interface temperatures inside the tube were analyzed. The present theoretical model fits better with the experimental data compared with Lee's and Caruso's models for stratified flow.     

Assessment of TAPINS code for application to thermal-hydraulic analysis of an integral reactor,REX-10

The thermal-hydraulic analysis program for integral reactor system (TAPINS) is a thermal-hydraulic system code developed by Seoul National University for transient analysis of an integral reactor, REX-10. Specialized for a fully passive integral pressurized water reactor, TAPINS adopts a one-dimensional four-equation drift-flux model for two-phase flows. It also consists of component models for the core, the helical-coil steam generator, and the steam-gas pressurizer. This paper presents the developmental assessment of TAPINS to validate its applicability to the thermal-hydraulic analysis of REX-10. Assessment problems are determined by taking into account thermal-hydraulic phenomena expected during design basis accidents of REX-10, including the loss-of-feedwater accident and the small-break loss-of-coolant accident. To confirm the predictive capability of TAPINS for these phenomena, the TAPINS model is validated against four sets of separate effects problems, including the pressurizer insurge test, the subcooled boiling experiment, the critical flow test, and the Edwards pipe problem. In addition, the calculation results of TAPINS are compared with the experimental data obtained from a series of integral effects tests using a scaled apparatus of REX-10. From the validation results, it is demonstrated that TAPINS can provide the reasonable prediction on the thermal-hydraulic responses of REX-10 during the transient and accident conditions.     

基于支持向量回归的稳压器水位信号重构研究

稳压器水位是船用压水堆非常重要的监测参数，是操纵员判断堆运行瞬变的重要依据。然而，稳压器却时常出现假水位、超量程水位及水位测量丢失的问题。为此，根据稳压器水位参数与反应堆进出口平均温度、稳压器压力与温度、主回路系统的冷却剂装量、充排水流量等热工水力参数的耦合关系，提出一种基于支持向量回归的稳压器水位信号重构方法。模拟试验分析表明，该方法能快速、准确、有效地重构出正常运行工况下的稳压器水位信号。