scholarly journals Numerical study on thermal-hydraulics of external reactor vessel cooling in high-power reactor using MARS-KS1.5 code: CFD-aided estimation of natural circulation flow rate

2021 ◽  
Author(s):  
Min Seop Song ◽  
Il Woong Park ◽  
Eung Soo Kim ◽  
Yeon-Gun Lee
Keyword(s):  
Flow Rate ◽  
High Power ◽  
Power Reactor ◽  
Numerical Study ◽  
Natural Circulation ◽  
Reactor Vessel ◽  
Thermal Hydraulics ◽  
Circulation Flow ◽  
Circulation Flow Rate

Two-Phase Natural Circulation Cooling Performance Assessment and Safety Analysis for APR1400 Core Catcher System

2014 ◽  
Author(s):  
Ki Won Song ◽  
Shripad T. Revankar ◽  
Hyun Sun Park ◽  
Bo Rhee ◽  
Kwang Soon Ha ◽  
...  
Keyword(s):  
Void Fraction ◽  
Flow Rate ◽  
Natural Circulation ◽  
Scaling Analysis ◽  
Circulation Flow ◽  
Two Phase ◽  
Cooling Performance ◽  
The Core ◽  
Core Catcher ◽  
Circulation Flow Rate

The two-phase natural circulation cooling performance of the APR1400 core catcher system is studied utilizing a drift flux flow model developed via scaling analysis and with an air-water experimental facility. Scaling analysis was carried out to identify key parameters, so that model facility could simulates two-phase natural circulation. In the experimental apparatus, instead of steam, air is injected into the top wall of the test channel to simulate bubble formation and void distribution due to boiling water in the core catcher channel. Measurement of void fraction critical to the heat transfer between the wall and coolant is carried out at certain key position using double-sensor conductivity probes. Results from the model provide expected natural circulation flow rate in the cooling channel of the core catcher system. The observed flow regimes and the data on void fraction are presented. For a given design of the down comer piping entrance condition bubble entrainment was observed that significantly reduced the natural circulation flow rate.

An Experimental Study on Open Natural Circulation Flow Characteristics by Air Injection

2017 ◽  
Author(s):  
Pengjiu Cao ◽  
Xiaxin Cao ◽  
Zhongning Sun ◽  
Ming Ding ◽  
Na Li ◽  
...  
Keyword(s):  
Flow Rate ◽  
Driving Force ◽  
Flow Instability ◽  
Natural Circulation ◽  
Heat Removal ◽  
Air Injection ◽  
Circulation System ◽  
Circulation Flow ◽  
Churn Flow ◽  
Circulation Flow Rate

An open natural circulation system has the characteristics of a simple structure, superior safety performance and strong heat removal capability. However, during long-term operation, the flow instability may occur due to the reduction of the driving force, which will have adverse effects on the heat removal capability and safe operation of the system. Thus, injecting air into the riser is designed in this paper to improve the driving force of the circulation flow, reduce the possibility of flow instability, and increase the heat removal capability. In order to investigate the influence of air injection on the evolution of flow pattern, resistance characteristics and circulation flow rate, the method of visual observation and data analysis is used based on different pore sizes porous media, air injection rate and submergence ratios. The ratio of the driving pressure head to the resistance pressure drop is proposed as the basis for assessing the effect of air injection on the ability of natural circulation. It is found that the driving force of natural circulation increases with the increase of air injection rate, and the circulation flow rate increases obviously when the bubbly flow appears in the riser. However, when the transition from bubbly flow to churn flow appears, the growth of the circulation flow rate slows down because the resistance increases faster than the driving force. Therefore, it can be known that the best performance is obtained when bubbly-churn flow appears in the top of the riser. What’s more, the capacity of lifting water will be reduced and churn flow will appear prematurely when the submergence ratio decreases. This means that in the process of open natural circulation system design, the submergence ratio of the system should be increased as much as possible. Finally, in this paper, it is found that the bubble pump with PS = 0.2 μm has better performance.

The Influence of the Wall Stored Energy on the Natural-Circulation Mode in the Core Make-Up Tank Test Facility

2016 ◽  
Author(s):  
Mingzhang Zhu ◽  
Huajian Chang ◽  
Han Wang ◽  
Xi Xu ◽  
Yang Shi
Keyword(s):  
Flow Rate ◽  
Thermal Stratification ◽  
Turning Point ◽  
Natural Circulation ◽  
Test Facility ◽  
Circulation Flow ◽  
Stored Energy ◽  
The Core ◽  
Circulation Mode ◽  
Circulation Flow Rate

Scaled down thermal-hydraulic test facility is widely used in the nuclear reactor safety analysis. The wall stored energy is one of the common problem in a scaled down test facility, which will cause distortions in the simulation of the transients or local phenomena. For the natural-circulation mode in the Core Makeup Tank (CMT), the cold wall will work as heat sink and absorb heat from the heated water, and then has an influence in energy balance on the simulation of the prototype phenomena with scaled down test facility. In order to study the influence of the wall stored energy on the natural-circulation mode in the CMT test facility, this paper established the CMT test facility model with RELAP5/MOD 3.4, and studied the influence caused by the wall stored energy distortion. The simulation results show that the natural-circulation process in the CMT test facility can be divided into two stages: 1. Before the thermal stratification reaches the outlet, the natural-circulation flow rate decreases gradually. 2. Once the thermal stratification reaches the outlet, the natural-circulation flow rate has an apparent turning point and decreases faster. That is because the heated water reaches the outlet and fills the discharge line quickly, which reduces the density difference between the hot leg and cold leg, thus causing the natural-circulation flow rate decrease faster. Besides, before the turning point, the wall stored energy basically has no influence on the natural-circulation process, and the influence can be neglected in the design of test facility. However, after the turning point, the wall stored energy distortion results in a slower descent speed of natural-circulation flow rate, which is not conservative. Therefore, we can conclude that the scaled down CMT test facility can only simulate the prototype properly and conduct the natural-circulation simulation experiment before the thermal stratification reaches the exit, while afterwards, the simulation of the test facility won’t be accurate and conservative.

Study on improvement for the prediction accuracy of natural circulation flow rate by investigating void fraction correlation

2021 ◽  
Vol 380 ◽  
pp. 111293
Author(s):  
Shunsuke Yoshimura ◽  
Takuma Yamaguchi ◽  
Keisuke Ino ◽  
Masahiro Furuya ◽  
Shinichi Morooka
Keyword(s):  
Void Fraction ◽  
Flow Rate ◽  
Prediction Accuracy ◽  
Natural Circulation ◽  
Circulation Flow ◽  
Circulation Flow Rate

Analysis of Flow Instabilities in Two-Phase Natural Circulation

2009 ◽  
Author(s):  
Geping Wu
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Rate ◽  
Natural Circulation ◽  
Flow Instabilities ◽  
High Heat Flux ◽  
Circulation Flow ◽  
Two Phase ◽  
Drift Flux Model ◽  
Circulation Flow Rate

Safety concerns of nuclear reactors have attracted the attention of researchers on flow instabilities in natural circulation boiling loops. In this theoretical study, a drift flux model which solves the conservation equations of mass, momentum and energy applicable to boiling two-phase natural circulation systems is adopted. The influence of two-phase flow parameters such as drift velocity and void distribution parameter on the loop flow rate is weak. The model is used to analysis the effects of heat flux and inlet subcooling on steady circulation flow rate. High circulation flow rate is accompanied by high heat flux and low inlet subcooling. According to the region and number of meeting points which connects the resistance pressure drop curve and the driving pressure drop curve, flow excursion and density-wave instability sometimes may occur. Further, investigations are carried out to study the effect of heat flux and system pressure on the instabilities region in natural circulation.

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