THERMAL STRATIFICATION IN NUCLEAR REACTOR PIPING SYSTEM

Equipment ◽  
2006 ◽  
Author(s):  
H. C. Rezende ◽  
M. A. Navarro ◽  
A. A. C. dos Santos
Keyword(s):  
Thermal Stratification ◽  
Nuclear Reactor ◽  
Piping System

Fatigue Evaluation for Thermally Stratified DVI Piping

2012 ◽  
Author(s):  
Hwan Ho Lee ◽  
Joon Ho Lee ◽  
Dong Jae Lee ◽  
Seok Hwan Hur ◽  
Il Kwun Nam ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Thermal Stratification ◽  
Nuclear Power ◽  
Heat Removal ◽  
Local Stress ◽  
Piping System ◽  
Hydraulic Analysis ◽  
Fatigue Evaluation ◽  
Core Cooling ◽  
Thermal Hydraulic Analysis

A numerical analysis has been performed to estimate the effect of thermal stratification in the safety injection piping system. The Direct Vessel Injection (DVI) system is used to perform the functions of Emergency Core Cooling and Residual Heat Removal for an APR1400 nuclear power plant (Korea’s Advanced Power Reactor 1400 MW-Class). The thermal stratification is anticipated in the horizontally routed piping between the DVI nozzle of the reactor vessel and the first isolation valve. Non-axisymmetric temperature distribution across the pipe diameter induced by the thermal stratification leads to differential thermal growth of the piping causing the global bending stress and local stress. Thermal hydraulic analysis has been performed to determine the temperature distribution in the DVI piping due to the thermal stratification. Piping stress analysis has also been carried out to evaluate the integrity of the DVI piping using the thermal hydraulic analysis results. This paper provides a methodology for calculating the global bending stresses and local stresses induced by the thermal stratification in the DVI piping and for performing fatigue evaluation based on Subsection NB-3600 of ASME Section III.

scholarly journals A Hydrogen Ignition Mechanism for Explosions in Nuclear Facility Piping Systems

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Robert A. Leishear
Keyword(s):  
Nuclear Power ◽  
Nuclear Reactor ◽  
Nuclear Industry ◽  
Ignition Source ◽  
Piping System ◽  
Nuclear Facilities ◽  
Piping Systems ◽  
Fluid Transients ◽  
Hydrogen Ignition ◽  
Explosion Mechanism

Hydrogen explosions may occur simultaneously with fluid transients' accidents in nuclear facilities, and a theoretical mechanism to relate fluid transients to hydrogen deflagrations and explosions is presented herein. Hydrogen and oxygen generation due to the radiolysis of water is a recognized hazard in piping systems used in the nuclear industry, where the accumulation of hydrogen and oxygen at high points in the piping system is expected, and explosive conditions may occur. Pipe ruptures in nuclear reactor cooling systems were attributed to hydrogen explosions inside pipelines, i.e., Hamaoka, Nuclear Power Station in Japan, and Brunsbuettel in Germany (Fig. 1Fig. 1Hydrogen explosion damage in nuclear facilities Antaki, et al. [9,10–12] (ASME, Task Group on Impulsively Loaded Vessels, 2009, Bob Nickell)). Prior to these accidents, an ignition source for hydrogen was not clearly demonstrated, but these accidents demonstrated that a mechanism was, in fact, available to initiate combustion and explosion. A new theory to identify an ignition source and explosion cause is presented here, and further research is recommended to fully understand this explosion mechanism. In fact, this explosion mechanism may be pertinent to explosions in major nuclear accidents, and a similar explosion mechanism is also possible in oil pipelines during off-shore drilling.

Effect of Thermal Stratification on Full-Cone Spray Performance in Reactor Containment for a Scaled Scenario

2014 ◽  
Author(s):  
Sidharth Paranjape ◽  
Guillaume Mignot ◽  
Domenico Paladino
Keyword(s):  
Thermal Stratification ◽  
Nuclear Reactor ◽  
Initial Conditions ◽  
Fluid Temperature ◽  
Spray Nozzle ◽  
Mass Spectrometers ◽  
Spray System ◽  
Nozzle Configuration ◽  
Paul Scherrer ◽  
Mixing Of Gases

The results of an experimental study on the nuclear reactor containment spray system are presented. Depending on the initial conditions, the spray nozzle configuration and flow rates, the spray may cause higher hydrogen concentration during depressurization due to steam condensation, or it may erode the hydrogen stratification by enhanced mixing. To investigate these phenomena, the tests are performed using a full-cone spray nozzle in PANDA facility at Paul Scherrer Institut, Switzerland. Temporal evolution and spatial distribution of the fluid temperature and the fluid concentrations are measured using thermocouples and mass spectrometers. Two tests are performed with initial vessel wall temperatures of 105°C and 135°C, which create condensing and non-condensing environments respectively. The different initial conditions lead to different density stratifications. The effect of these different density stratification on the flow patterns and mixing of gases in the vessels due to the action of the spray is revealed by these tests.

Assessment of a Piping System Subjected to Thermal Stratification and Thermal Striping

2010 ◽  
Author(s):  
Somnath Chattopadhyay
Keyword(s):  
Thermal Stratification ◽  
Nuclear Power ◽  
Power Plants ◽  
Thermal Stresses ◽  
Temperature Gradients ◽  
Low Flow ◽  
Piping System ◽  
Thermal Transients ◽  
Fatigue Evaluation ◽  
Thermal Striping

Piping systems in nuclear power plants are often designed for pressure and mechanical loadings (including seismic loads) and operating thermal transients. In the last few decades a number of failures have occurred due to thermal stratification caused by the mixing of hot and cold fluids under certain low flow conditions. Such stratified temperature fluid profiles give rise to circumferential metal temperature gradients through the pipe leading to high stresses causing fatigue damage. In this work, thermal stresses due to such temperature gradients have been calculated using a finite element method. The peak stresses calculated by this method has been used for fatigue evaluation. In addition the stresses due to thermal striping associated with stratification have also been independently assessed for high cycle fatigue. The method outlined in this paper is a simplified conservative procedure to obtain stratification stresses.

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.

Use of bimetallic welds in nuclear reactors: Associated problems and structural integrity assessment issues

2006 ◽  
Vol 220 (8) ◽  
pp. 1121-1133 ◽  
Author(s):  
R Chhibber ◽  
N Arora ◽  
S R Gupta ◽  
B K Dutta
Keyword(s):  
Heat Transport ◽  
Nuclear Reactor ◽  
Structural Integrity ◽  
Nuclear Reactors ◽  
Human Life ◽  
Structural Safety ◽  
Piping System ◽  
Clear Understanding ◽  
Safety Issues ◽  
Integrity Assessment

The bimetallic welds (BMWs) play a critical and indispensable role in the primary heat transport piping system of nuclear reactors. The primary heat transport system in itself is the critical part of a nuclear reactor. Any failure of this system can lead to grave consequences, not only speaking of huge monetary losses resulting from non-utilization of the reactor setup, but also immensely valuable and irreparable loss of human life. The present paper is an effort towards identifying and understanding the problems affecting the BMWs and is as well an attempt to highlight the current issues in the structural integrity assessment of structures having these welds. The basic aim of this work is to provide a clear understanding of the current structural safety issues and their importance in underpinning the use of BMWs in modern nuclear reactors.

Temperature Measurements of Thermal Stratification and Turbulent Mixing in Nuclear Systems With a Single Heated Jet

2016 ◽  
Author(s):  
Lane B. Carasik ◽  
Saya Lee ◽  
Arturo A. Cabral ◽  
Yassin A. Hassan
Keyword(s):  
Turbulent Mixing ◽  
Thermal Stratification ◽  
Nuclear Reactor ◽  
Temperature Data ◽  
Data Sets ◽  
Spent Fuel ◽  
Entire Volume ◽  
University Of Tennessee ◽  
Loss Of Coolant Accident ◽  
Nuclear Systems

Large volumes or enclosures are utilized in nuclear systems such as the sodium fast reactor (SFR) upper plenum, spent fuel pools, and containment structures seen in common nuclear reactor designs. These volumes may be quiescent or turbulent the injection of a hotter or cooler jet of fluid. This can lead to turbulent mixing of the entire volume or thermal stratification of a hotter layer of fluid. Due to the large thermal gradients experienced by the structures due to a stratified volume, the structures can experience degradation which can lead to severe consequences such as a loss of coolant accident. In order to prevent or mitigate these consequences, computational fluid dynamics (CFD) codes can be utilized to predict the occurrence of turbulent mixing and thermal stratification. This data can be used in conjunction with structural analysis codes to determine the severity of phenomena occurrence on structures. Unfortunately, the validity of CFD codes to predict this type of behavior is limited due to the lack of experimental data to validate the predicted behavior. In response, the twin jet water facility (TJWF) created by the University of Tennessee was repurposed to create data sets of temperature using thermocouples and particle image velocimetry (PIV) for this effort. The temperature data collected using the thermocouples is similar to previous experiments conducted within an older version of the facility with a different geometric configuration. The most recently collected data was created by conducting several runs of each each set of experiment conditions and ensemble averaged. This was done to confirm the observed behavior is due to the physical processes and not due to noise or random happenstance. The spectral frequency responses of the temperature data were determined to observe frequencies or spectral behavior corresponding to turbulent mixing and stratification. The temperature and frequencies are reported to compare the experiments to simulations being conducted in conjunction with this study.

A Complete Piping Analysis With Thermal Stratification Loads

2002 ◽  
Author(s):  
Milton Dong ◽  
Hong Ming Lee ◽  
Chii Chern
Keyword(s):  
Computer Program ◽  
Fatigue Damage ◽  
Thermal Stratification ◽  
Nuclear Regulatory Commission ◽  
Piping System ◽  
Analysis Program ◽  
Cyclic Stresses ◽  
Class 1 ◽  
Cumulative Fatigue Damage ◽  
Regulatory Commission

The U. S. Nuclear Regulatory Commission (USNRC) had issued Bulletins 88-08, 88-11, 89-90, and 93-38 to address the concerns and problems due to thermal stratification loading during the life span of normal plant operation. The thermal stratification condition typically will cause pipe to bow in on a long horizontal segment. These conditions have not been commonly considered in piping design. However, the additional thermal cyclic stresses and loads due to these conditions could lead to the fatigue damage of the piping components and the failures of pipe supports. Analyzing the effects of thermal stratification loads can be very cumbersome if it is not a built-in functionality of the analysis program. Thus in response to the recent increase in such cases we have incorporated this feature in our piping stress computer program. A stress engineer can now define the thermal stratification conditions easily and the program will compute the pipe stresses and pipe support loads automatically as one of the load cases. The program then combines the thermal stratification load cases with other load cases as required in accordance with the load histogram to determine the cumulative fatigue damage of the piping system. The thermal cyclic stresses are evaluated in accordance with the design rules of Nuclear Class 1 piping components provided in NB-3650 of ASME section III Code. This paper presents the method, modeling and validation for implementing the functionality of analyzing thermal stratification loads in a computer program, as well as an application on an actual piping system as an illustration.

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