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Journal Articles

Measurement of Velocity Field in Five Jets Water Test (FIWAT) for thermal striping in sodium-cooled fast reactor

Aizawa, Kosuke; Kobayashi, Jun; Tanaka, Masaaki; Kurihara, Akikazu; Ishida, Katsuji*; Nagasawa, Kazuyoshi*

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 10 Pages, 2018/11

A conceptual design of an advanced loop type sodium cooled reactor has been carried out in the Japan Atomic Energy Agency (JAEA). Temperature fluctuation is caused by mixing of fluids at different temperature from the control rod channels and the core fuel assemblies, high cycle thermal fatigue may arise on the Core Instrument Plane (CIP) at bottom of the Upper Internal Structure (UIS). In JAEA, 1/3-scaled five jets water tests (FIWAT) have been performed in order to investigate thermal striping phenomena around the CIP. In this study, the velocity field was measured in the mixing area between the jet outlet and the bottom of the structure by using particle image velocimetry (PIV) to compare with the temperature fluctuation characteristics.

Journal Articles

Preliminary calculation on thermal stratification phenomena in the fundamental sodium experiment "SuperCAVNA"

Ezure, Toshiki; Nagasawa, Kazuyoshi*; Tanaka, Masaaki

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 5 Pages, 2018/11

To establish an evaluation method of thermal stratification in sodium-cooled fast reactors (SFRs), a benchmark exercise was performed for a sodium experiment (SuperCAVNA) with a rectangular test section and heated wall. This paper presents a preliminary result using three-dimensional finite differential code AQUA. The influences of mesh size for heat exchange and turbulence model are studied, and the calculation results were also compared to the experimental results in the literature. Then, the calculation results reproduced the thermal stratification in SuperCAVNA experiment. The position and the temperature gradient of the stratified surface also showed good agreement with the experimental result. The applicability of the numerical approach employed in this study for the evaluation of thermal stratification problem in SFRs was confirmed.

Journal Articles

Establishment of numerical estimation method for high cycle thermal fatigue in sodium-cooled fast reactor, 2; Benchmark analysis using planar triple parallel jet sodium test for fundamental validation

Tanaka, Masaaki; Kobayashi, Jun; Nagasawa, Kazuyoshi*

Dai-22-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (USB Flash Drive), 4 Pages, 2017/06

In JAEA, a numerical simulation code named MUGTHES which can deal with conjugate heat transfer between the fluid and the structure parts has been developed for estimation of the thermal fatigue issue. In fundamental validation, the benchmark analysis was considered using the experiment of planar triple parallel jet sodium test (PLAJEST). Three specific experimental conditions at Vr=1, 1.56, and 5.56 were employed for the benchmark analyses according to the knowledge in the literatures. Through the benchmarks, applicability of the large eddy simulation (LES) approach with the standard Smagorinsky model in MUGTHES to simulate thermal striping phenomena was potentially confirmed and issues to be modified in the future works were indicated.

Journal Articles

Fundamental validation of fluid-structure thermal interaction simulation code for thermal striping in sodium-cooled fast reactors with parallel triple jets mixing experiments

Tanaka, Masaaki; Kobayashi, Jun; Nagasawa, Kazuyoshi*

Proceedings of OECD/NEA & IAEA Workshop on Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation (CFD4NRS-6) (Internet), 12 Pages, 2016/09

A numerical simulation code named MUGTHES which can deal with conjugate heat transfer problem between the fluid and the structure parts has been developed in order to predict the thermal response in the structure for estimation of the thermal fatigue issue. To perform fundamental validation of the MUGTHES, the benchmark simulation was considered using the experiment of planar triple parallel jets mixing sodium test (PLAJEST). Since it was known by literatures that three representative flow mixing patterns were shown in accordance with the velocity rate of the side jets to the center jet, three typical experimental conditions in the PLAJEST were employed as boundary conditions for the benchmark. Through the numerical simulations, applicability of the large eddy simulation (LES) approach with the standard Smagorinsky model to simulate thermal striping phenomena was confirmed.

Journal Articles

Benchmark analysis of thermal striping phenomena in planar triple parallel jets tests for fundamental validation of fluid-structure thermal interaction code for sodium-cooled fast reactor

Tanaka, Masaaki; Nagasawa, Kazuyoshi*

Proceedings of 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16) (USB Flash Drive), p.6650 - 6663, 2015/08

For the fundamental validation of fluid-structure thermal interaction code (MUGTHES), numerical simulations for the planar triple parallel jets tests in WAJECO and PLAJEST have been conducted as the benchmark analysis. In comparison between the numerical results and the provided experimental results, thermal mixing process and large-scale eddy structures generated in the triple jets mixing and the relation between temperature fluctuation generation and large-eddy structures were revealed. And also, the attenuation process of temperature fluctuation from the fluid to the structure was indicated.

Journal Articles

Investigation on thermal striping phenomena in Five Jets Modelled Water Test (FIWAT) simulating Sodium-cooled Fast Reactor

Aizawa, Kosuke; Kobayashi, Jun; Onojima, Takamitsu; Tanaka, Masaaki; Ohno, Shuji; Kamide, Hideki; Nagasawa, Kazuyoshi*

Proceedings of 10th International Topical Meeting on Nuclear Thermal Hydraulics, Operation and Safety (NUTHOS-10) (USB Flash Drive), 13 Pages, 2014/12

Thermal striping phenomenon is one of the most important issues in an advanced loop type sodium cooled reactor JSFR. Temperature fluctuation caused by mixing of fluids at different temperature from the control rod channels and the core fuel assemblies may touch the Core Instrument Plane (CIP) at bottom of the Upper Internal Structure (UIS) and cause high cycle thermal fatigue there. In JAEA, the 1/3-scaled Five Jets Water Test (FIWAT) has been performed in order to investigate thermal striping phenomena around the CIP. In the FIWAT, the test section was simulating a control rod channel, adjacent four fuel subassemblies and a part of the CIP. The flow rate ratio and the absolute velocity of hot jets as the reference experimental condition were equal to that of the JSFR and a third of JSFR, respectively. In the experiment, it was shown that the fluid temperature fluctuation characteristics around the structure depended on the flow rate ratio. The temperature fluctuation which showed sudden decrease and recovery like a spike form was intermittently observed in the fluid near the structure. The amplitude of such spike-like temperature fluctuation in the fluid was much mitigated on the structure surface.

Journal Articles

Study on flow in the subchannels of pin bundle with wrapping wire

Nishimura, Masahiro; Hiyama, Tomoyuki; Kamide, Hideki; Ohshima, Hiroyuki; Nagasawa, Kazuyoshi*; Imai, Yasutomo*

Proceedings of 9th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-9) (CD-ROM), 7 Pages, 2014/11

JAEA Reports

Experimental study on thermal stratification phenomena in compact reactor vessel of sodium cooled fast reactor; Evaluation on stratification interface behavior under natural circulation condition

Hagiwara, Hiroyuki; Kimura, Nobuyuki*; Onojima, Takamitsu; Nagasawa, Kazuyoshi*; Kamide, Hideki; Tanaka, Masaaki

JAEA-Research 2014-014, 178 Pages, 2014/09

JAEA-Research-2014-014.pdf:53.12MB

Thermal stratification in the upper plenum is one of the most important issues of a reactor vessel in sodium cooled fast reactor. The steep temperature gradient across the stratification interface may cause the thermal load against the reactor vessel wall. In this study, the water experiment was carried out using the 1/11 scale upper plenum model of the Japan sodium-cooled fast reactor (JSFR) in order to evaluate the thermal stratification under the natural circulation condition and a direct heat exchanger (DHX) operation condition. The temperature gradient under the natural circulation condition was approximately 1/3 times smaller than that under the forced circulation condition. In the DHX operation case, the steep temperature gradient occurred in the lower region of upper plenum due to the cold fluid from the outlet of DHX.

JAEA Reports

Study on high cycle thermal fatigue in mixing tee; Evaluation of transfer characteristics of temperature fluctuation from fluid to structure

Kimura, Nobuyuki; Kobayashi, Jun; Kameyama, Yuri*; Nagasawa, Kazuyoshi*; Ezure, Toshiki; Ono, Ayako; Kamide, Hideki

JAEA-Research 2014-009, 104 Pages, 2014/07

JAEA-Research-2014-009.pdf:15.23MB
JAEA-Research-2014-009-appendix(CD-ROM).pdf:17.88MB

In this study, water experiments (WATLON) were carried out to clarify the unsteady behavior of heat transfer under wall jet condition in the mixing tee. In experiments, heat transfer coefficients between fluid and wall in the mixing region were obtained from temperature measurements using thermocouples (movable tree type in fluid and embedded type in wall). To clarify the relation between the local velocity and the wall temperature, those were measured simultaneously by the Particle Image Velocimetry (PIV) and the thermocouple measurement, respectively. Sampling time of the velocity by the PIV and the temperature by the thermocouple were synchronized in the measurement. The experimental results showed that the heat transfer coefficient was from 2 - 6 time larger than the reference value predicted by the Dittus-Boelter correlation in straight pipes and was increased as the local velocity near the wall.

JAEA Reports

Study on thermalhydraulics of thermal striping phenomena; Evaluation of transfer characteristics of temperature fluctuation based on conjugated numerical simulation in triple-parallel jet geometry

Kimura, Nobuyuki; Kamide, Hideki; Nagasawa, Kazuyoshi*; Emonot, P.*

JAEA-Research 2012-017, 97 Pages, 2012/07

JAEA-Research-2012-017.pdf:12.12MB

A quantitative evaluation on thermal striping is of importance for reactor safety. In this study, sodium and water experiments of parallel triple jets configuration were performed. For these experiments, numerical simulations were carried out to evaluate the transfer characteristics of temperature fluctuation from fluid to structure. The analysis code, called Trio-U, used in the study has been developed at the CEA in France. In the simulations, the calculated time-averaged temperature distributions in fluid and structure were close to the experimental results in sodium and water. The power spectrum densities of temperature fluctuation in fluid and structure were also in good agreements between the experiments and calculations. Furthermore the calculated decay characteristics of temperature fluctuation from fluid to structure were in good agreements with the experimental results.

Journal Articles

Investigation on velocity distribution around the wrapping wire in an inner subchannel of fuel pin bundle

Nishimura, Masahiro; Sato, Hiroyuki; Kamide, Hideki; Ohshima, Hiroyuki; Nagasawa, Kazuyoshi*; Imai, Yasutomo*

Proceedings of 20th International Conference on Nuclear Engineering and the ASME 2012 Power Conference (ICONE-20 & POWER 2012) (DVD-ROM), 10 Pages, 2012/07

Feature of stream regime in the subchannel existing wrapping wire was visualized in vertical and horizontal plane by the PIV method. And the time averaged velocity field in the horizontal plane was reconstructed from the two vertical plane data in different directions. A detailed simulation code based on FEM was applied to the experimental analysis. The calculated velocity distributions were consistent with the experimental data.

JAEA Reports

Experimental study on thermal stratification in compact reactor vessel of sodium cooled fast reactor; Effects of core outlet velocity and temperature difference during scram

Kimura, Nobuyuki; Hayashi, Kenji; Tobita, Akira; Kamide, Hideki; Nagasawa, Kazuyoshi*

JAEA-Research 2010-065, 191 Pages, 2011/03

JAEA-Research-2010-065.pdf:14.57MB

Thermal stratification water experiments using a 1/10th scale model were carried out for an advanced loop type sodium cooled reactor. Experimental parameters were core outlet velocity, temperature difference during scram, and height of the plug which infill the hole at the dipped plates for setup of a fuel handling machine. It was found that the height and the rising speed of stratification interface depended on the Richardson number. Furthermore the temperature gradient of the stratification interface depended on the Peclet number.

Journal Articles

Study on thermal striping phenomena in triple-parallel jet; Transfer characteristics of temperature fluctuation in sodium and water based on conjugated numerical simulation

Kimura, Nobuyuki; Kamide, Hideki; Emonot, P.*; Nagasawa, Kazuyoshi*

Proceedings of 7th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Safety (NUTHOS-7) (CD-ROM), 17 Pages, 2008/10

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing between hot and cold fluids causes thermal fatigue in structural components, is of importance for reactor safety. It is necessary for the quantitative evaluation to investigate occurrence and propagate processes of temperature fluctuation, e.g., decay of temperature fluctuation near structures and transfer of temperature fluctuation from fluid to structures. In Japan Atomic Energy Agency, an innovative sodium cooled fast reactor has been designed. The transfer characteristics of temperature fluctuation from fluid to structure in sodium are quite different from that in water. In order to realize the sodium cooled fast reactor, the clarification of the transfer characteristics of temperature fluctuation is of importance for the rational design against the thermal striping phenomena. In this study, sodium and water experiments of parallel triple jets configuration were performed. For these experiments, numerical simulations were carried out to evaluate the transfer characteristics of temperature fluctuation from fluid to structure. The analysis code, called Trio_U, used in the study has been developed at the CEA in France. The large eddy simulation model is incorporated in the code. Furthermore, the code can calculate fluid and structural domains simultaneously. In the simulations, the calculated time-averaged temperature distributions in fluid and structure were close to the experimental results in sodium and water. The power spectrum densities of temperature fluctuation in fluid and structure were also in good agreements between the experiments and calculations. Furthermore the calculated decay characteristics of temperature fluctuation from fluid to structure were in good agreements with the experimental results.

Journal Articles

Study on thermal striping phenomena in triple-parallel jet; Investigation on non-stationary heat transfer characteristics based on numerical simulation

Kimura, Nobuyuki; Kamide, Hideki; Emonot, P.*; Nagasawa, Kazuyoshi*

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-12) (CD-ROM), 14 Pages, 2007/09

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing between hot and cold fluids causes thermal fatigue in structural components, is of importance for reactor safety. In this study, a water experiment of parallel triple jets configuration was performed in order to evaluate temperature fluctuation characteristics in fluid, transfer characteristics of temperature fluctuation from fluid to structure. The power spectrum densities of temperature fluctuation, furthermore, were in good agreements between the experiment and calculation. The calculated results showed that the heat transfer coefficient obtained from the experiment was appropriate and proper. The decay due to the heat transfer at the wall surface was dominant for the decay of temperature fluctuation at the neighborhood of the wall.

JAEA Reports

Study on thermal hydraulics in thermal striping phenomena; Effect of structural materials on transfer of temperature fluctuation from fluid to structure

Kimura, Nobuyuki; Nagasawa, Kazuyoshi*; Miyake, Katsuhiro*; Ogawa, Hiroshi; Kamide, Hideki

JNC-TN9400 2005-037, 82 Pages, 2005/08

JNC-TN9400-2005-037.pdf:6.54MB

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing causes high cycle thermal fatigue in structural components, is of importance for reactor safety. The consideration of decay of temperature fluctuation based on the phenomenological mechanism enables a legitimate design with reactor integrity. In this study, we performed a parallel triple-Jet water experiment along a wall. In this experiment, the material of the wall was changed to acrylic resin, type 316 stainless steel and copper in order to evaluate an effect of thermal properties in wall materials on the transfor characteristics of temperature fluctuation from fluid to structure. The fluid temperature was measured by a movable thermocouple-tree and the structural temperature was measured by thermocouples embedded on the wall surface. The effect of the wall material on the temperature fluctuation in fluid was not observed at the further position from the wall. In the vicinity of the wall, on the other hand, the temperature fluctuation intensity in fluid decreased as the thermal diffusivity of the wall material was large. The temperature fluctuation intensity in structure was small as the thermal diffusivity of the wall material was large. For each wall material, the heat transfer coefficient was obtained from a transfer function between fluid and structure temperature fluctuations. It was seen that the heat transfer coefficient was large as the thermal diffusivity of material was large. In this experiment, furthermore, the dependence of Nusselt number on Reynolds number was dose to the existing correlation in every materials.

JAEA Reports

Study on Thermalhydraulics in Thermal Striping Phenomena; Evaluation on Convective mixing in Sodium and Water based on Sodium/Water Experiments and Quasi-DNS

Kimura, Nobuyuki; Nagasawa, Kazuyoshi*; Miyake, Yasuhiro*; Miyakoshi, Hiroyuki; Kamide, Hideki

JNC-TN9400 2004-064, 216 Pages, 2004/05

JNC-TN9400-2004-064.pdf:27.81MB

Sodium and watrer experiments on thermal striping phenomena were carried out. Triple-parallel jet along a wall was investigated. Further, quasi-DNS was also performed and comparisons between experiments and analyses were carried out. Temperature fluctuation intensity near the wall was larger in water than in sodium. This means that water experiment can predict sodium temperature fluctuation intensity with certain conservative factor.

JAEA Reports

Experimental Study on Thermalhydraulics in Thermal Striping Phenomena; Comparison of Temperature Fluctuations between Sodium and Water

Kimura, Nobuyuki; Miyake, Yasuhiro*; Miyakoshi, Hiroyuki; Nagasawa, Kazuyoshi*; Igarashi, Minoru; Kamide, Hideki

JNC-TN9400 2003-077, 96 Pages, 2003/06

JNC-TN9400-2003-077.pdf:3.96MB

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing causes high cycle thermal fatigue in structural components, is of importance for structural integrity and reactor safety.Thermal conductivity of sodium is approximately 100 times larger than that of water. Thus, temperature fluctuation characteristics will be different between sodium, which is used as a coolant of a fast reactor, and water, which is used in general industries. In this study, a comparison of convective mixing among jets was performed in parallel triple wall jets with the same geometries between sodium and water. The discharged velocity in the sodium experiment was experimental parameter and set at the same velocity and the same Reynolds number in comparison with the water experiment. And also, the velocity ratio among the triple jets was varied to change flow pattern. It was seen that the water jets were mixed in slightly closer region to the nozzle than in sodium jets. As for the power spectrum densities (PSD) of temperature fluctuation, the PSD of sodium was similar to the PSD of water under the same discharged velocity condition. At the neighborhood of the wall, the lower frequency component in the PSD of sodium decreased in comparison with the PSD of water. It was shown that the amplitude and frequency characteristics obtained by rain-flow method, which was important to evaluate structural damage by the thermal fatigue, were identical between sodium and water overall. These experimental results show that water experiment could simulate the frequency and the amplitude in temperature fluctuation characteristics in the sodium cooled reactor.

JAEA Reports

Experimental study on thermal-hydraulic for thermal striping phenomena; Results of temperature and velocity measurement among parallel triple jets

Miyakoshi, Hiroyuki; Nagasawa, Kazuyoshi*; Kimura, Nobuyuki; Miyake, Yasuhiro*; Kamide, Hideki

JNC-TN9410 2003-003, 0 Pages, 2003/03

JNC-TN9410-2003-003.pdf:5.25MB

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing among jets causes thermal fatigue in structural components, is of importance for structural integrity and also reactor safety. The reasonable and safety design could be approved by taking account of decay of temperature fluctuation in fluid, during heat transfer from fluid to structure surface and thermal onduction in the structure. In this study, water experiment was performed for vertical and parallel triple jets along wall, those are cold jet in the center and hot jets on both sides. The local temperature and velocity were measured by movable thermocouples and particle image velocimetry(PIV). The both hot jets flowed leaning to the cold jet. The lean of the jets increased as the jets approached the wall. So the convective mixing region among the jets was shifted upstream near the wall. Temperature fluctuation intensity was dependent of the distance from the wall. Under isovelocity condition, prominent frequency component was observed in the power spectrum density of the temperature fluctuation at the furthest position from the wall. The power at the prominent component decreased as the jets approached the wall. Under non-isovelocity condition, on the other hand, the power spectrum density of temperature fluctuation was independent of the distance from the wall. Comparison of the second moment between of velocity PIV and laser Doppler velocimetry showed that the PIV system had high measurment accuracy. Under non-isovelocity condition, the normal components in the second-order moments of fluctuation were smaller than those under isovelocity condition. Normal components in the second-order moments in turbulence was dependent of the distance from the wall."

JAEA Reports

Study on thermalhydraulics in thermal striping phenomena; Experimental analysis of sodium parallel triple-jet DNS

Kimura, Nobuyuki; Nagasawa, Kazuyoshi*; Miyakoshi, Hiroyuki; Miyake, Yasuhiro*; Igarashi, Minoru; Kamide, Hideki

JNC-TN9400 2003-003, 66 Pages, 2002/10

JNC-TN9400-2003-003.pdf:3.61MB

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing causes high cycle thermal fatigue in structural components, is of importance for reactor safety. The reasonable and safety design could be approved by taking account of decay of temperature fluctuation in fluid, during heat transfer from fluid to structural surface and thermal conduction in the structure. Temperature fluctuation characteristics due to convective mixing will be influenced by the velocity/temperature boundary layers near the structure. In this study, an experimental analysis was performed using DNS in order to separate influence of heat capacity of the structure and to evaluate an attenuation due to the boundary layer near the wall surface for a sodium experiment of parallel triple jets configuration. In the experiment, a cold jet on center and hot jets on both sides flowed vertically and along the wall, and the discharged velocities of triple jets were O.5m/s equally. The calculated temperature field was in good agreement with the experimental result at further position from the wall surface, including the power spectrum density of the temperature fluctuation. On the other hand, at near position from the wall surface, calculated temperature fluctuation intensity was not attenuated whereas the experimental intensity was decreased. This means that the intensity of temperature fluctuation is not decreased by the boundary layer. Thermal interaction between fluid and the wall will decrease the temperature fluctuation intensity in the fluid near the wall. The effect of wall friction on second moments of turbulence was evaluated.

JAEA Reports

Experimental study on thermal striping phenomena; Evaluation on transfer characteristics of temperature fluctuation from fluid to structure

Kimura, Nobuyuki; Miyake, Yasuhiro*; ; Nagasawa, Kazuyoshi*; ; Kamide, Hideki

JNC-TN9400 2002-059, 70 Pages, 2002/09

JNC-TN9400-2002-059.pdf:2.98MB

A quantitative evaluation on thermal striping, in which temperature fluctuation due to convective mixing causes high cycle thermal fatigue in structural components, is of importance for reactor safety. The reasonable and safety design could be approved by taking account of decay of temperature fluctuation in fluid, heat transfer from fluid to structural surface and thermal conduction into structure. In this study, a sodium experiment of parallel triple jets configuration was performed in order to evaluate transfer characteristics of temperature fluctuation from fluid to structure. As for the experimental geometry, a cold jet at the center and hot jets in both sides flowed vertically along a wall. The temperature fluctuation is transferred from fluid to the wall in the wall jet geometry. In addition, double jets experiment was carried out. The experimental parameters were discharged velocities of the jets. The temperature fluctuation intensity decreased as the frequency of temperature fluctuation increased where temperature fluctuation was transferred from fluid to structure. The time-delay of transfer of temperature fluctuation from fluid to structure decreased as the discharged velocity increased. The non-stationary heat transfer characteristics from fluid to structure could be described by using a time-constant heat transfer coefficient. The heat transfer coefficient was proportional to Peclet number to the power of 0.8 and independent of the flow pattern in which the ratio of discharged velocities of the jets was varied.

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