Liquid entrainment through a large-scale inclined branch pipe on a horizontal main pipe

At conventional pressurized water reactors (PWRs), cold water stored in the refueling water tank of emergency core cooling system is injected into the primary coolant system through a safety injection (SI) line, which is connected to each cold leg pipe between the main coolant pump and the reactor vessel during the SI operation, which begins on the receipt of a loss of coolant accident signal. In normal reactor power operation mode, the wall of SI line nozzle maintains at high temperature because it is the junction part connected to the cold leg pipe through which the hot main coolant flows. To prevent and relieve excessive transient thermal stress in the nozzle wall, which may be caused by the direct contact of cold water in the SI operation mode, a thermal sleeve in the shape of thin wall cylinder is set in the nozzle part of each SI line. Recently, mechanical failures that the sleeves are separated from the SI branch pipe and fall into the connected cold leg main pipe occurred in sequence at some typical PWR plants in Korea. To find out the root cause of thermal sleeve breakaway failures, the flow situation in the junction of primary coolant main pipe-SI branch pipe and the vibration modal characteristics of the thermal sleeve are investigated in detail by using both computational fluid dynamics code and structure analysis finite element code. As a result, the transient response in fluid pressure exerting on the local part of thermal sleeve wall surface to the primary coolant flow through the pipe junction area during the normal reactor operation mode shows oscillatory characteristics with the frequencies ranging from 15Hzto18Hz. These frequencies coincide with the lower mode natural frequencies of thermal sleeve, which has a pinned support condition on the outer surface with the circumferential prominence set into the circumferential groove on the inner surface of SI nozzle at the midheight of thermal sleeve. In addition, the variation of pressure on the thermal sleeve surface yields alternating forces and torques in the directions of two rectangular axes perpendicular to the longitudinal axis of cylindrical thermal sleeve, which causes both rolling and pitching motions of the thermal sleeve. Consequently, it is seen that this flow situation surrounding the thermal sleeve during the normal reactor operation can induce resonant vibrations accompanying the shaking motion of the thermal sleeve at the pinned support condition, which finally leads to the failures of thermal sleeve breakaway from the SI nozzle.

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Numerical Estimation of Flow Penetrating Depth Into Stagnant Branch Pipes for Thermal Fatigue Prediction

Volume 3: Design and Analysis ◽

10.1115/pvp2014-28382 ◽

2014 ◽

Author(s):

Yoshihiro Ishikawa ◽

Yukihiko Okuda ◽

Naoto Kasahara

Keyword(s):

Thermal Stress ◽

High Temperature ◽

Temperature Fluctuation ◽

Thermal Stratification ◽

Branch Pipe ◽

Large Temperature ◽

Bend Pipe ◽

Main Pipe ◽

High Temperature Water ◽

Temperature Water

In the nuclear power plants, there are many branch pipes with closed-end which are attached vertically to the main pipe. We consider a situation in which the high temperature water is transported in the main pipe, the branch pipe is filled with stagnant water which has lower temperature than the main flow, and the end of the branch pipe is closed. At the branch connection part, it is known that a cavity flow is induced by the shear force of the boundary layer which separates from the leading edge of the branch pipe along the main pipe wall. In cases where the high temperature water penetrates into the branch pipe, there is a possibility that a steep and large temperature gradient field, called “thermal stratification layer” is formed at the boundary between high and low temperature water in the branch pipe. If the thermal stratification layer is formed in a bend pipe, which is used for connecting the vertical branch pipe and to a horizontal pipe, at the same time, the temperature fluctuation by the thermal stratification layer motion occurs, there may cause the thermal stress in the piping material. Furthermore, keeping the piping material under the thermal stress, there might be a possibility of a crack on the surface of the bend pipe. For this reason, the evaluation of the position where the thermal stratification layer reaches is very important during early piping design process. And, deeply understanding regarding the phenomena, is also important. However, because of the complexities of the phenomena, it is difficult to immediately clarify the whole mechanisms of the thermal stress arising due to the temperature fluctuation by the thermal stratification layer change. The complete prediction method for the position of the thermal stratification layer based on the mechanisms that is able to be applied to any piping system, any temperature and any velocity conditions, is also difficult. Therefore, a practical approach is required. The authors attempt to develop the practical estimation method for the thermal stratification layer position using the three-dimensional Navier-Stokes simulation which was based on the Reynolds-average in order to reduce the computational costs. In this paper, three different configurations of the piping were simulated and the simulation results were compared with the experimental results obtained by the other research group.

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Root Cause Analysis of SI Nozzle Thermal Sleeve Breakaway Failures Occurred at PWR Plants

Volume 4: Fluid Structure Interaction, Parts A and B ◽

10.1115/pvp2006-icpvt-11-93497 ◽

2006 ◽

Author(s):

Jong Chull Jo ◽

Myung Jo Jhung ◽

Seon Oh Yu ◽

Hho Jung Kim ◽

Young Gill Yune

Keyword(s):

Branch Pipe ◽

Hot Water ◽

Thin Wall ◽

Reactor Operation ◽

Support Condition ◽

Primary Coolant ◽

Lower Mode ◽

Root Cause ◽

Main Pipe ◽

Flow Situation

Thermal sleeves in the shape of thin wall cylinder seated inside the nozzle part of each safety injection (SI) line at pressurized water reactors (PWRs) have such functions as prevention and relief of potential excessive transient thermal stress in the wall of SI line nozzle part which is initially heated up with hot water flowing in the primary coolant piping system when cold water is injected into the system through the SI nozzles during the SI operation. Recently, mechanical failures that the sleeves are separated from the SI branch pipe and fall into the connected cold leg main pipe occurred in sequence at some typical PWR plants in Korea. To find out the root cause of thermal sleeve breakaway failures, the flow situation in the in the junction of primary coolant main pipe and SI branch pipe and the vibration modal characteristics of the thermal sleeve are investigated in details by using both computational fluid dynamic (CFD) code and structure analysis finite element code. As the results, the transient response in fluid pressure exerting on the local part of thermal sleeve wall surface to the primary coolant flow through the pipe junction area during the normal reactor operation mode shows oscillatory characteristics with the frequencies ranging from 15 to 18, which coincide with the lower mode natural frequencies of thermal sleeve having a pinned support condition on the circumferential prominence on the outer surface of thermal sleeve which is put into the circumferential groove on the inner surface of SI nozzle at the mid-height of thermal sleeve. In addition, the variation of pressure on the thermal sleeve surface yield alternating forces and torques in the directions of two rectangular axes perpendicular to the longitudinal axis of cylindrical thermal sleeve, which causes both rolling and pitching motions of the thermal sleeve. Consequently, it is seen that this flow situation surrounding the thermal sleeve during the normal reactor operation can induce resonant vibrations accompanying the shaking motion of the thermal sleeve at the pinned support condition, which finally leads to the failures of thermal sleeve breakaway from the SI nozzle.

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Verification Test for Hybrid Seismic Experimental Method Using Nonlinear Finite Element Method

Volume 8: Seismic Engineering ◽

10.1115/pvp2005-71228 ◽

2005 ◽

Author(s):

Yoshihiro Dozono ◽

Mayumi Fukuyama ◽

Toshihiko Horiuchi ◽

Takao Konno ◽

Michiya Sakai ◽

...

Keyword(s):

Finite Element ◽

Numerical Model ◽

Experimental Method ◽

Large Scale ◽

Branch Pipe ◽

Nonlinear Finite Element ◽

Shaking Table ◽

Piping System ◽

Analysis Tool ◽

Seismic Testing

An improved substructure hybrid seismic experimental method has been developed. This method consists of numerical computations using a general-purpose nonlinear finite element analysis tool and a pseudo-dynamic vibration test. Therefore, it enables seismic testing of large-scale structures that cannot be loaded onto a shaking table. The method also visualizes both data measured by sensors placed on the specimen and the results of the numerical analysis, and it helps us to understand the behavior of an entire structure consisting of a specimen and a numerical model. We performed verification tests for a piping system, in which we used a numerical model including supports, valves, and a branch pipe, and a specimen including two elbows. As results of tests, we conclude that the developed system has enough accuracy to be used as a seismic testing method.

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Study on Characteristics of Wall Temperature Fluctuation at a Mixing Tee With an Upstream Elbow

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2018-84182 ◽

2018 ◽

Author(s):

Koji Miyoshi ◽

Akira Nakamura

Keyword(s):

Wall Temperature ◽

Temperature Fluctuation ◽

Hot Spot ◽

Branch Pipe ◽

Circumferential Direction ◽

Wall Jet ◽

Main Pipe ◽

Inner Surface ◽

Fluctuation Range ◽

Dominant Frequencies

The characteristics of wall temperature fluctuation at the mixing tee with an upstream elbow were investigated and compared to those of the case without the elbow. The elbow of 90 degrees was installed in the inlet of the horizontal main pipe. The inlet flow velocities in the main and branch pipes were set to about 1.0 m/s and 0.7 m/s, respectively, to produce a wall jet pattern where the jet from the branch pipe was bent by the main pipe flow and made to flow along the pipe wall. A total of 148 thermocouples were installed near the pipe inner surface to measure the temperature distribution in the mixing tee. The upstream elbow decreased the temperature fluctuation intensity and the temperature fluctuation range at the inner surface. On the other hand, the distribution profiles and the dominant frequencies of temperature fluctuations were similar. The temperature fluctuation was also caused by the movement of a hot spot in the circumferential direction for both cases with and without the upstream elbow. The reduction of the movement of the hot spot in the circumferential direction decreased the temperature fluctuation for the case with the upstream elbow.

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Numerical Simulation on Internal Flows of Reducing Cross

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.945-949.980 ◽

2014 ◽

Vol 945-949 ◽

pp. 980-986

Author(s):

Jian Ping Yuan ◽

Wen Ting Sun ◽

Yin Luo ◽

Bang Lun Zhou

Keyword(s):

Numerical Simulation ◽

Flow Rate ◽

Branch Pipe ◽

Three Dimensional ◽

Uniform Flow ◽

Hydraulic Loss ◽

Steady Flows ◽

Internal Flows ◽

Inlet Velocity ◽

Main Pipe

In order to study the internal flows and hydraulic loss of reducing cross, numerical simulation was carried out on a horizontally installed reducing cross. Three schemes of pipe diameters were studied. The time-averaged N-S equations of three-dimensional steady flows in the reducing pipe were calculated by CFX 14.5 based on the standard - two equation turbulence model together with standard wall function. The results show that the higher the inlet velocity, the hydraulic loss become larger when the split ratios are same for the reducing cross. With the uniform inlet velocities the higher the inlet velocity, the quicker the increasing rate of the hydraulic loss in main pipe, as well as the branch pipe. The integral change rules of hydraulic loss are similar with the condition of uniform flow rate inflow when the flow patterns at inlet are uniform. But with the same spilt ratio, the hydraulic loss of uniform velocity inflow is markedly less than that of uniform flow rate inflow in both main pipe and branch pipe. The bigger the differences of the diameters between the main pipe and the branch pipe, the larger the hydraulic loss of the branch pipe.

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Thermal Fatigue Analysis at a Mixing Tee by a Fluid-Structural Simulation

ASME 2011 Pressure Vessels and Piping Conference: Volume 1 ◽

10.1115/pvp2011-57585 ◽

2011 ◽

Cited By ~ 1

Author(s):

Masayuki Kamaya ◽

Yoichi Utanohara ◽

Akira Nakamura

Keyword(s):

Thermal Stress ◽

Fatigue Damage ◽

Cold Water ◽

Axial Stress ◽

Branch Pipe ◽

Three Dimensional ◽

Dynamics Simulation ◽

Cold Spot ◽

Current Case ◽

Main Pipe

In this study, the thermal stress at a mixing tee was calculated by the finite element method using temperature transients obtained by a fluid dynamics simulation. The simulation target was an experiment for a mixing tee, in which cold water flowed into the main pipe from a branch pipe. The cold water flowed along the main pipe wall and caused a cold spot, at which the membrane stress was relatively large. Based on the evaluated thermal stress, the magnitude of the fatigue damage was assessed according to the linear damage accumulation rule and the rain-flow procedure. Precise distributions of the thermal stress and fatigue damage could be identified. Relatively large axial stress occurred downstream from the branch pipe due to the cold spot. The position of the cold spot changed slowly in the circumferential direction, and this was the main cause of the fatigue damage. In the thermal stress analysis for fatigue damage assessment, it was concluded that the detailed three-dimensional structural analysis was not required. Namely, for the current case, a one-dimensional simplified analysis could be used for evaluating the fatigue damage without adopting the stress enhancement factor Kt quoted in the JSME guideline.

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Onset condition of gas and liquid entrainment at an inclined branch pipe on a horizontal header

Nuclear Engineering and Design ◽

10.1016/j.nucengdes.2007.01.002 ◽

2007 ◽

Vol 237 (10) ◽

pp. 1046-1054 ◽

Cited By ~ 15

Author(s):

Jae Young Lee ◽

Soo Hyun Hwang ◽

Manwoong Kim ◽

Goon Cherl Park

Keyword(s):

Branch Pipe ◽

Liquid Entrainment ◽

Onset Condition

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Numerical Simulations of Thermal-Mixing in T-Junction Piping System Using Large Eddy Simulation Approach

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D ◽

10.1115/ajk2011-18009 ◽

2011 ◽

Cited By ~ 1

Author(s):

Masaaki Tanaka ◽

Satoshi Murakami ◽

Yasuhiro Miyake ◽

Hiroyuki Ohshima

Keyword(s):

Numerical Simulations ◽

Large Scale ◽

Branch Pipe ◽

Three Dimensional ◽

Piping System ◽

Thermal Mixing ◽

Eddy Simulation ◽

Large Eddy ◽

Thermal Striping ◽

High Cycle Thermal Fatigue

Thermal striping phenomenon caused by mixing of fluids at different temperatures is one of the most important issues in design of fast breeder reactors (FBRs), because it may cause high-cycle thermal fatigue in structure. Authors have been developed a numerical simulation code MUGTHES to investigate thermal striping phenomena in FBRs and to give transient data of temperature in the fluid and the structure for an evaluation method of the high-cycle thermal fatigue problem. MUGTHES employs the boundary fitted coordinate (BFC) system and deals with three-dimensional transient thermal-hydraulic problems by using the large eddy simulation (LES) approach and artificial wall conditions derived by a wall function law. In this paper, numerical simulations of MUGTHES in T-junction piping system appear. Boundary conditions for the simulations are chosen from an existing water experiment in JAEA, named as WATLON experiment. The wall jet condition in which the branch pipe jet flows away touching main pipe wall on the branch pipe side and the impinging jet condition in which the branch pipe jet impinges on the wall surface on the opposite side of the branch pipe are selected, because significant temperature fluctuation may be induced on the wall surfaces by the branch pipe jet behavior. Numerical results by MUGTHES are validated by comparisons with measured velocity and temperature profiles. Three dimensional large-scale eddies are identified behind of the branch pipe jet in the wall jet case and in front of the branch pipe jet in the impinging jet case, respectively. Through these numerical simulations in the T-pipe, generation mechanism of temperature fluctuation in thermal mixing process is revealed in the relation with the large-scale eddy motion.

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