Effect of Heat-Up Transient Condition on the Thermal Stratification in Nuclear Power Plant Surgeline

2009 ◽  
Author(s):  
Young-Jong Kim ◽  
Maan-Won Kim ◽  
Eunmi Ko ◽  
Jae-Gon Lee ◽  
Byoung Chul Kim
Keyword(s):  
Flow Rate ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Element Model ◽  
Transient Condition ◽  
Analysis Model ◽  
Stratification Effect ◽  
Surge Line ◽  
Temperature And Pressure ◽  
Temperature Rate

During operating transients of the pressurizer, thermal stratification effect may occur especially in the horizontal parts of surge line. Generally, the fatigue usage factor of surge line is comparative high, due to its operating temperature and pressure transients and its thermal stratification loads. Traditional 2-D finite element model (FEM) for thermal stratification analysis has excessive conservativeness. To reduce such an excessive conservativeness, 3-D numerical analysis model for fluid-structure interaction (FSI) problem in the surgeline and some parametric FSI analyses were performed with different heat-up temperature rate and flow rate in the inlet of surgeline during plant heat-up. Based on these FSI analysis results, an efficient condition to reduce the excessive conservativeness in surgeline stratification analysis could be proposed in terms of heat-up rate and flow rate.

Numerical Analyses of Surge Line Piping to Assess Thermal Stratification Phenomenon

2008 ◽  
Author(s):  
Seung-Wan Woo ◽  
Shin-Beom Choi ◽  
Yoon-Suk Chang ◽  
Jae-Boong Choi ◽  
Young-Jin Kim ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Thermal Loading ◽  
Element Model ◽  
Sensitivity Analyses ◽  
Piping System ◽  
Stratification Effect ◽  
Surge Line ◽  
Starting Location

During the last two decades, thermal stratification has been issued as a critical problem in the nuclear power industry. Since the problem caused by this phenomenon also became important in Korea, it is necessary to quantify the thermal stratification effect to ensure the safety of the piping system. In this paper, detailed stress analyses of the surge line, considering the thermal stratification, are conducted. Parametric sensitivity analyses to find out an optimum model were carried out using pipe element models and full 3-D element models. For instance, in case of the pipe element model, the effect of starting location of thermal stratification and boundary condition were investigated. And, in case of the 3-D solid element model, the effect of boundary condition and thermal loading condition were assessed. The stress analysis results showed that the thermal stratification phenomenon significantly affected the integrity of the surge line piping. Also, establishment of insurge and outsurge conditions was derived as one of the further investigations.

The Surge Line Stress Analysis Model Setup With the Consideration of Thermal Stratification

2014 ◽  
Author(s):  
Jianjun Wang ◽  
Zengfang Ge ◽  
Zhongning Sun ◽  
Changqi Yan
Keyword(s):  
Stress Analysis ◽  
Transient Process ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Transient Temperature ◽  
Analysis Model ◽  
Pressurized Water ◽  
Line Model ◽  
Transient Temperature Distribution ◽  
Surge Line

In this paper, we deal with a typical pressurizer surge line in a conventional pressurized water reactor (PWR). This study is performed to develop an understanding of thermal stratification phenomenon, which may occur in the surge line during either normal condition or transient process, in the pressurizer surge line. The pressurizer surge line model of Daya Bay nuclear power plant is used as base analysis model, in which the hot leg is taken into account. The transient temperature distribution required to assess the phenomenon along the pressurizer surge line is obtained through CFD analysis technology using ANSYS FLUENT. The temperature loads are transferred to ANSYS Mechanical for stress evaluation for the heat up transient process. Subsequently, the usage factor is calculated on the basis of ASME Section-III design curve. The possible mitigation scheme for the thermal stratification phenomenon of changing the layout angles is also simulated and analyzed in detail. The results show that the thermal stratification phenomenon will occur both in normal operating condition and in heat up transient process. The circumfluent effect makes the thermal stratification phenomenon exhibit unique profile due to the introduction of the hot leg. The continuous spray mass flow rate may influence both the temperature difference and the occurrence range for the thermal stratification phenomenon. The stress analysis incorporating both temperature load and pressure load is performed for pressurizer surge line model with hot leg for the conservative and complete heat up case.

Experimental Investigation on Flash Evaporation Related to Pipe Leakage

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Benan Cai ◽  
Qi Zhang ◽  
Yu Weng ◽  
Hongfang Gu ◽  
Haijun Wang
Keyword(s):  
High Temperature ◽  
Thermal Fatigue ◽  
Weber Number ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Power Plants ◽  
Response Speed ◽  
Flash Evaporation ◽  
Main Pipe ◽  
Surge Line

Abstract Pipelines such as the surge line and main pipe are easily subjected to thermal stratification and thermal fatigue as a result of the nonuniform temperature distribution in the nuclear power plants. When the surge line or main pipe subjected to thermal stratification and thermal fatigue keeps operating for long time, the pipe leakage may happen due to the existence of pipeline crack. When the fluids with high temperature and pressure leak in the crack, the water will evaporate quickly, which means this process belongs to spray flash evaporation process. The flash evaporation related to pipe leak was experimentally studied in the paper. The experiment was carried out under high temperature and high pressure with low spray rate. The temperature and relative humidity (T&H) variations over time were monitored in the experiment with installing T&H detectors. The T&H variations at different measurement positions and with different spray rates were analyzed, respectively. In addition, the effect of the dimensionless parameters including the Weber number and Jakob number was also investigated. Results indicated that the response speed increased with the increase of the spray flow rate. Higher Weber number and higher Jakob number led to higher evaporation rate. The slight pipe leakage can be predicted by using the (T&H) in the hazardous areas.

Effect of Thermal Stratification of Coolant in a Vertical Heated Channel

2002 ◽  
Author(s):  
Abolghasem Zare Shahneh
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Thermal Stratification ◽  
Research Reactor ◽  
Rate Versus ◽  
Heated Channel ◽  
Stratification Effect ◽  
Simplifying Assumptions ◽  
Linear Manner

In a vessel type low power research reactor having vertical fuel plates, while circulating pump is switched off, coolant (light water) would flow by natural convection. By using conservation equations, taking into account simplifying assumptions, coolant mass flow rate through the channel can be obtained. Due to the thermal stratification effect, coolant mass flow rate through the channel is shown to decrease. The present study shows that, assuming a linear thermal stratification, the variations of coolant mass flow rate versus stratification parameter behave in a non-linear manner. The aforementioned variations decrease down to 41%.

A New Method to Weaken Thermal Stratification Phenomena in Pipes of Nuclear Power Plant

2013 ◽  
Author(s):  
Shengfei Wang ◽  
Yuxin Pang ◽  
Xiaojing Li ◽  
Dandan Fu ◽  
Yang Li ◽  
...  
Keyword(s):  
Thermal Stratification ◽  
Nuclear Power ◽  
Thermal Stresses ◽  
Heat Pipes ◽  
New Method ◽  
Simple Experiment ◽  
Pressurized Water ◽  
Piping Systems ◽  
Surge Line ◽  
Water Reactors

Thermal stratification phenomena are observed in piping systems of pressurized water reactors, especially in the pressurizer surge line. As a result of the thermal stratification induced thermal stresses, fatigue problems can occur in the pipework. US NRC requirements have also identified flow stratification in surge lines as a phenomenon that must be considered in the design basis of surge lines. In this paper, a new method to reduce thermal stratification is proposed. As we all know, heat pipe is a simple device with no moving parts and can transfer large quantities of heat over fairly large distance. The new method is that using heat pipes to weaken the thermal stratification. In order to validate the new method, a simple experiment and theoretical analysis was taken. The results show that, the temperature difference of thermal stratification with heat pipes is smaller than the stratification without heat pipes. A design scheme was also given at the end of paper.

Fatigue Effect of RCS Branch Line by Thermal Stratification

2003 ◽  
Author(s):  
Hag-Ki Youm ◽  
Kwang-Chu Kim ◽  
Man-Heung Park ◽  
Tea-Eun Jin ◽  
Sun-Ki Lee ◽  
...  
Keyword(s):  
Thermal Stratification ◽  
Nuclear Power ◽  
Power Plants ◽  
Evaluation Methodology ◽  
Element Analysis ◽  
Branch Line ◽  
Reactor Coolant ◽  
Stratification Effect ◽  
Fatigue Evaluation ◽  
Coolant System

Recent events reported at a number of nuclear power plants worldwide have shown that thermal stratification, cycling, and striping in piping can cause excessive thermal stress and fatigue on the piping material. These phenomena are diverse and complicated because of the wide variety of geometry and thermal hydraulic conditions encountered in reactor coolant system. Thermal stratification effect of re-branched lines is not yet considered in the fatigue evaluation. To evaluate the thermal load due to turbulent penetration, this paper presents a fatigue evaluation methodology for a branch line of reactor coolant system with the re-branch line. The locations of fatigue monitoring and supplemented inspections are discussed as a result of fatigue evaluations by Interim Fatigue Management Guideline (ITFMG) and detail finite element analysis. Although the revised CUF was increased less than 50 %, the CUF values for some locations was greater than the ASME Code limits.

Thermal Stratification Analysis and Fatigue Evaluation for Pressurizer Surge Line in Nuclear Power Plant

2017 ◽  
Author(s):  
Xiao Xu ◽  
Pan Liu ◽  
Guihe Zhang ◽  
Dasheng Wang ◽  
Ting Jin
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Influence Factors ◽  
One Dimension ◽  
Three Dimension ◽  
Penetration Length ◽  
Surge Line ◽  
Fatigue Evaluation

Thermal stratification of pressurizer surge line in nuclear power plant induced by the stratification of fluid results in additional stresses (system-dependent and system-independent stresses). These additional stresses are related to the thermal stratification distribution, such as temperature difference, stratification location, stratification length and boundary layer slope and thickness. This thermal stratification distribution is effected by several parameters such as turbulent penetration length and surge line slope. These influence factors are studied with numerical method. For the additional stresses, this study theoretically establishes the solution of the system-dependent stresses according to the thermal stratification distribution assumption. With the system-dependent and system-independent stresses, a complex three-dimension problem is simplified into a one-dimension. Using this effective one-dimension method, fatigue evaluation can be fast processed and accurate improved in engineering analyses.

Experimental Investigation Into Thermal Stratification by Direct Condensation in a Scaled Suppression Pool of Fukushima Daiichi Nuclear Power Plant

2014 ◽  
Author(s):  
Byeongnam Jo ◽  
Shinji Takahashi ◽  
Daehun Song ◽  
Wataru Sagawa ◽  
Nejdet Erkan ◽  
...  
Keyword(s):  
Power Plant ◽  
Nuclear Power Plant ◽  
Flow Rate ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Experimental Results ◽  
Steam Condensation ◽  
Wide Range ◽  
Fukushima Daiichi ◽  
Suppression Pool

Experimental and numerical studies into thermal stratification by direct steam condensation in a torus type suppression pool were carried out to investigate the reactor core isolation cooling in the accidents of Fukushima Daiichi nuclear power plants. The suppression pool was manufactured to be a 1/22 scaled model of a Fukushima Daiichi nuclear power plant. Two different types of spargers were employed to simulate different units of the plants. In a sparger, 132 holes were uniformly drilled on the side of a pipe. However, the other sparger injected steam to the bottom. Flow rate was varied in a wide range to examine the effect on thermal stratification in the suppression pool. The experimental results showed that the sparger type influenced formation of thermal stratification. Moreover, steam flow rate strongly affected the onset time of thermal stratification, and the disappearance of the thermal stratification was affected by subcooling temperature. Computer simulation using a commercial software was conducted and the results show similar temperature profiles to the experimental results. Steam condensation was visualized in a vicinity of the spargers using high speed camera.

Stress and Fatigue Analysis of Pressurizer Surge Line under Thermal Stratification

2019 ◽  
Vol 795 ◽  
pp. 268-275
Author(s):  
Peng Tang ◽  
Zhi Wei Liu ◽  
Hong Wei Qiao ◽  
Peng Zhou Li
Keyword(s):  
Temperature Distribution ◽  
Temperature Difference ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Power Plants ◽  
Load Condition ◽  
Maximum Temperature ◽  
Large Temperature ◽  
Maximum Temperature Difference ◽  
Surge Line

Pressurizer surge line is one of the key equipments of nuclear power plants. The thermal stratification due to the intersection of hot and cold fluids inside the pressurizer surge line may affect the safe operation of nuclear power plant. In order to investigate the stress distribution and fatigue characteristics of surge line subjected to long-term thermal stratified loadings, a mechanical model of the surge line was established. And then, according to different temperature distribution assumptions, thermal stress analysis and fatigue assessment were conducted. The results show that the maximum stress appears under the load condition with maximum temperature difference, and finer temperature distribution can obtain more accurate stress and displacement results. The maximum value of fatigue cumulative coefficient appears at the junction of straight pipe and elbow with large temperature difference.

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